Previous Article in Journal
Wintering Red Kites in Central Spain: Macrohabitat Selection and Population Density Estimate
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Birds
Volume 6
Issue 4
10.3390/birds6040055
birds-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Close Relatives, Different Niches: Urban Ecology of Two Range-Expanding Thrushes Recently Meeting in the Argentinian Pampas

by
Miriam Soledad Vazquez
1,2,*,
Alberto L. Scorolli
1 and
Sergio M. Zalba
1,2
1
GEKKO—Conservation and Management Study Group, Department of Biology, Biochemistry, and Pharmacy, National University of the South, San Juan, 670 Bahía Blanca, Buenos Aires B8000, Argentina
2
Consejo Nacional de Investigaciones Científicas y Técnicas—CONICET, Buenos Aires C1425, Argentina
*
Author to whom correspondence should be addressed.
Birds 2025, 6(4), 55; https://doi.org/10.3390/birds6040055
Submission received: 18 August 2025 / Revised: 14 October 2025 / Accepted: 15 October 2025 / Published: 17 October 2025
Browse Figures
Versions Notes

Abstract

Simple Summary

Urban growth alters natural habitats, yet some native birds adapt and expand their ranges by using cities. We studied two thrush species that recently colonized two Argentine cities and found that, despite being closely related, they exploit different urban resources. One species (Austral Thrush) was mainly associated with open ground and grassy areas, while the other (Rufous-bellied Thrush) relied more on trees and shrubs and avoided highly built environments. This divergence in habitat use reduces competition and allows both species to coexist in urban landscapes. Our results show that the diversity of habitats within cities plays an important role in helping different bird species coexist. Understanding how native birds adapt to urban environments can guide city planning to support biodiversity and maintain healthy bird communities in growing urban areas.

Abstract

Urbanization reshapes bird communities by filtering species according to their ecological traits, often reducing richness, altering relative abundances, and favoring a subset of functionally tolerant species that dominate urban assemblages. Some native taxa are able to inhabit cities, even using them as stepping stones for range expansion. We examined urban habitat use, microhabitat selection, and potential niche partitioning between two range-expanding thrushes (Austral Thrush [Turdus falcklandii] and Rufous-bellied Thrush [Turdus rufiventris]) in two urban settlements in the Pampas region, Argentina. Using 131 transects across green areas and urbanized zones, we related abundance patterns to habitat features at the transect scale and evaluated microhabitat selection at the individual level. Austral Thrush abundance increased with herbaceous cover, tree cover, and even concrete surfaces, suggesting a relatively high tolerance to fragmented green spaces within dense urban matrices. In contrast, Rufous-bellied Thrush showed a positive association with tree cover, avoided tall buildings, and reached higher abundance in the smaller city, consistent with its recent arrival in the region and preference for less intensively urbanized environments. Microhabitat data revealed marked vertical stratification: Austral Thrush foraged almost exclusively at ground level on grassy or bare substrates, while Rufous-bellied Thrush used trees, shrubs, and vines more frequently. These differences reflect fine-scale resource partitioning that may contribute to reducing niche overlap and favor the coexistence of both species in recently colonized urban areas, while recognizing that such dynamics occur within broader bird assemblages where multiple species interact and compete for space and resources. Our findings highlight that even closely related species can respond divergently to urban structure, and that maintaining structural and substrate heterogeneity within cities may help support native bird diversity.

1. Introduction

Rapid urbanization is one of the most drastic land use changes worldwide [1], often leading to declines in biodiversity by filtering out disturbance-intolerant species and favoring generalists capable of thriving in human-altered environments [2]. While many wild species are displaced by urbanization, cities, especially urban green spaces—including parks, gardens, and remnant vegetation—can sustain surprisingly high levels of biodiversity by providing refuges for species that tolerate or adapt to urban conditions [3,4]. Thus, human settlements may act as opportunities as well as challenges for native avifauna [5]. Beyond filtering species according to their traits, urbanization alters access to key resources. It can reduce natural foraging and nesting substrates, while simultaneously providing new anthropogenic sources of food and artificial nesting structures [6,7,8,9]. At the same time, the presence of domestic animals, altered predator communities, and high human activity can generate new types of disturbances [10,11]. Moreover, cities bring together species that did not previously coexist, reshaping competitive dynamics and leading to novel assemblages [12,13]. Such new associations can modify interspecific competition, facilitate hybridization events [14], or alter pathogen transmission dynamics [15], with consequences for both native and urban-adapted species [16].
Bird species that persist in cities often exhibit diverse responses to urbanization depending on their ecological traits and behavioral flexibility—including dietary plasticity, tolerance to human disturbance, and innovative foraging strategies—which allow them to adjust to rapidly changing and heterogeneous urban conditions [17,18]. After colonizing urban habitats, some of these species may subsequently increase in abundance over time within cities, leading to growing populations that consolidate their presence in urban bird communities [19], while others go even further, successfully exploiting the urban habitats to expand beyond their historical ranges [20,21]. These responses underscore the importance of understanding how urban environments shape resource use and ecological interactions.
The colonization of novel environments by species actively expanding their geographic ranges introduces new dynamics in community assemblages, including increased competition, potential facilitative interactions, and even the displacement of resident taxa, particularly when newcomers overlap spatially and ecologically with resident species [22]. Ecological theory predicts that for morphologically and ecologically similar species to coexist with low competition, niche segregation whether spatial, temporal, or trophic is necessary [23,24]. Therefore, the theoretical prediction for the scenario of secondary contact between species would be the occurrence of such resource partitioning. However, the interaction mechanisms and niche-partitioning strategies that operate among closely related species that have only recently become sympatric in urban environments remains poorly understood (but see [19]). In urban environments, niche partitioning can arise through both broad-scale habitat characteristics (e.g., ornamental vegetation, tree-lined streets, lawns, or artificial structures used for foraging and nesting) [25,26,27] and fine-scale microhabitat features (e.g., preferences for specific substrates, vertical space, or specific plant species cover) [28,29]. Habitat selection is a hierarchical process that integrates these multiple spatial scales [30,31,32], shaping the environmental conditions and resources that determine the occurrence and persistence of bird species in cities [33]. Understanding these differences is essential to identify the traits and strategies—such as habitat use, microhabitat selection, and niche partitioning—that allow some species to persist and thrive in anthropogenic environments, especially as urbanization intensifies.
To fully capture these patterns, it is essential to consider the spatial scale at which birds perceive and interact with the environment. In urban ecosystems, habitat selection occurs across a hierarchy of spatial scales, from the broader extent of entire cities, to intermediate levels such as neighborhoods or urban parks, and down to fine-scale patches and microhabitat features that directly influence foraging and nesting opportunities [34,35,36,37]. In this study, we adopt a multi-scale approach to examine patterns of urban habitat and microhabitat use, and to assess whether and how niche partitioning occurs between two native thrushes (Austral Thrush [Turdus falcklandii] and Rufous-bellied Thrush [Turdus rufiventris]) that have recently expanded their ranges and overlap spatially in urban environments of the Pampas region in Argentina [38]. These two species are particularly suitable for testing hypotheses of resource partitioning because they are closely related congeners with broadly similar ecological requirements, yet they have only recently come into contact in this region, creating opportunities for potential competition. By addressing these questions, we seek to contribute to the understanding of the mechanisms that underlie the persistence and coexistence of native birds recently established in urban areas of the biome. We propose that coexistence between Austral Thrush and Rufous-bellied Thrush in the studied urban areas is facilitated by fine-scale niche partitioning. Based on this hypothesis, we predicted that (i) both species would differ in their patterns of habitat and microhabitat use within cities, and (ii) such differences would be consistent with resource segregation that may reduce potential competition and facilitate their co-existence in urban environments. We compared their abundance across two cities with contrasting urban characteristics (Bahía Blanca and Coronel Pringles), assessed habitat use across transects differing in urbanization intensity, and evaluated whether microhabitat-level differences reflect emerging niche partitioning. Our findings extend recent research on Turdus range expansion [39,40], offering new insights into how expanding species respond to novel urban environments and how ecological dynamics operate under conditions of recent sympatry in human-altered landscapes.

2. Materials and Methods

2.1. Study Area

The study was conducted in two cities in the southwest of Buenos Aires province, Argentina: Bahía Blanca and Coronel Pringles, both included in the Pampas ecoregion, characterized by a temperate subhumid climate with hot summers and cool winters, and an average annual precipitation ranging from 600 to 800 mm [41]. Natural vegetation in this region is dominated by grasslands with scattered shrubs and riparian woodlands, although much of the original cover has been replaced by agriculture, livestock, and urban development [42]. Bahía Blanca is a coastal city, approximately 600 km southwest of Buenos Aires. With a population of ca. 337,000 according to the 2022 national census, it ranks among the most populous cities in the province and functions as a regional hub of commerce, education and industry. In contrast, Coronel Pringles is a smaller inland city situated about 120 km northeast of Bahía Blanca, near the Ventania mountains. It has lower building density, with a population of ca. 24,500 as of the 2022 census, and is surrounded by extensive agricultural lands and remnants of natural vegetation, giving it a landscape context that contrasts with the more densely urbanized Bahía Blanca. Despite their geographical proximity and their location more or less on the same latitude and at similar heights above sea level, differences in the size of both cities may result in disparities in microclimates [43], and habitat availability and quality.
Both cities also differ in urban form, green-space configuration, and landscape context. Bahía Blanca is a large, heterogeneous city with a predominantly continuous built matrix interspersed with squares, tree-lined avenues and the major urban parks, as well as highly built-up areas and industrial zones. Particularly in peripheral, residential neighborhoods there is an extensive street-tree yielding dense vegetation cover. In contrast, Coronel Pringles has a compact, grid-like urban core where green areas are concentrated in central squares and along boulevards, and the surrounding landscape is dominated by agricultural fields. Although it lacks extensive urban parks, peri-urban elements such as recreational trails, rural properties, sports fields, and tree lines at the agricultural interface create a mosaic of vegetated patches.

2.2. Sampling Design

We deployed strip transects of a 100 m line, with a belt width of 20 m on each side, within which all individuals of the focal species were recorded, following the protocol proposed by standard bird census techniques [44]. Transects were allocated using a stratified design to reflect variation in habitat availability. In each city, we established transects in both green areas (squares, parks, tree-lined boulevards) and urbanized areas (residential and peripheral neighborhoods). In the case of Coronel Pringles, this represented the entire town, while in Bahía Blanca, these environments were distributed mostly in the periphery, and sampling in the downtown area was avoided. In Bahía Blanca, we excluded the downtown core from sampling because it is almost completely built-up, with minimal vegetation and extremely high pedestrian and vehicle disturbance, conditions that prevent collecting reliable data on the patterns of habitat use by the focal thrushes. We acknowledge, however, that this exclusion may have limited our ability to fully capture the entire urban gradient, potentially biasing comparisons between the two cities. For each transect we recorded maximum building height and visually estimated mean percentage cover of: trees (>5 m tall), shrubs (1–5 m), grass and herbs (<1 m), bare soil, and concrete. The latter included all artificial surfaces such as buildings, paved roads, sidewalks, and other constructed elements. In this procedure, the transect as a whole was considered as 100%, and the relative cover of each category was estimated as the proportion of this total occupied by that surface type. Cover was estimated in 10% intervals, based on visual inspection by the same observer (MSV).
In Bahía Blanca, 37 transects were surveyed, including 28 in urbanized areas (i.e., inhabited residential neighborhoods) and 9 in green spaces. In Coronel Pringles, 94 transects were established, 68 in urbanized areas and 26 in green spaces. This imbalance in sampling effort between cities was considered in the analyses, but we acknowledge that it may nonetheless limit the direct comparability of results. A detailed map of the distribution of all sampled transects in both cities is available in Figure 1. Sampling took place from 2022 to 2024, covering two breeding seasons (spring-summer) and two non-breeding seasons (autumn-winter). Within each transect we recorded the presence or absence of the target species (Austral Thrush and Rufous-bellied Thrush). All bird surveys were conducted between dawn and 10:00 a.m., when avian activity is highest. A maximum of 15 min was spent in each transect, during which all individuals of the focal species were recorded. To minimize variability in detectability, sampling was not carried out on days with rain or strong winds. We counted the number of individuals and recorded the substrate on which each bird was detected (ground, shrub, tree, building), along with its height above ground. Additionally, for each detection, we estimated the shrub and tree cover within a 1.5 m radius centered on the individual.

2.3. Data Analysis

We used boxplots and Wilcoxon rank-sum tests to compare the assessed habitat features between the transects in Bahía Blanca and Coronel Pringles. The mean numbers of Austral Thrush and Rufous-bellied Thrush per transect were calculated for each city and season (breeding and non-breeding). To enable fair comparisons between cities and seasons despite unequal numbers of transects, we standardized descriptive statistics by sampling effort. We calculated weighted mean abundance as the total number of individuals divided by the number of distinct transects, and derived standard errors using the number of transects as the sampling denominator. Mean abundance of each species was compared between season and city with Wilcoxon rank-sum tests.
To evaluate the environmental predictors of abundance, we fitted generalized linear mixed models (GLMMs) with a Poisson error distribution and log link function, running separate models for Austral Thrush and Rufous-bellied Thrush with the number of individuals per transect as the response variable. Predictor variables included season (breeding or non-breeding), city (Bahía Blanca or Coronel Pringles), and six standardized continuous habitat variables measured at the transect level: tree cover, shrub cover, herbaceous cover, bare soil, concrete cover, and the maximum height of buildings. Transect identity was included as a random factor to account for repeated sampling and spatial autocorrelation. We considered “city” as a fixed effect, given the limited number of levels (n = 2), and acknowledge that inference about city-level differences should therefore be interpreted with caution. We used transect identity as a random intercept, treating each transect as an independent sampling unit and thus accounting for among-transect variation and the differing number of transects across cities.
Prior to modeling, we examined multicollinearity among predictors using variance inflation factors (VIF < 5) and pairwise correlations, and did not include highly correlated variables in the same model. Model selection was performed using the dredge function from the MuMIn package [45], which compares all possible subsets of the full model based on the corrected Akaike Information Criterion (AICc). When the top-ranked model had a dominant weight (>0.8), it was selected for inference; otherwise, we applied model averaging across all models with ΔAICc < 2 to obtain averaged parameter estimates, standard errors, and confidence intervals. Plots are shown for the top-ranked model, which provides a clear visualization of predictor effects, whereas inference in the text is based on model-averaged coefficients. For the top-ranked model, we inspected the significance and direction of effects of the retained variables. We assessed model fit by calculating a dispersion statistic based on Pearson residuals. Dispersion values near 1 were used as indicators of adequate model fit without overdispersion. We generated marginal effect plots showing predicted values for each species and significant predictor, and used coefficient plots to visualize the relative effect sizes and associated confidence intervals. Model fit was also assessed using marginal and conditional R2 values and residual diagnostics with DHARMa package.
Height above ground and substrate type used by each individual detected were summarized using histograms, density plots, and bar charts, weighted by the number of individuals per detection event. Substrate use proportions were compared between species using combined bar plots with color gradients reflecting the number of observations. To assess habitat selection, we considered only transects where each species was detected. For each individual, we compared the percentage of tree and shrub cover within a 1.5 m radius of its location to the corresponding values for the entire transect where it was observed. Differences between use and availability were assessed using kernel density plots and two-sample Kolmogorov–Smirnov tests. We also calculated mean and median values for each variable and reported their differences as a descriptive measure of selection.
All analyses and visualizations were performed in R (version 4.4.2, Vienna, Austria), using the packages lme4 [46], ggplot2 [47] and dplyr [48].

3. Results

Habitat structure of the sampled environments differed markedly between Bahía Blanca and Coronel Pringles (Figure 2). Bahía Blanca exhibited significantly higher values of tree cover, shrub cover, and concrete cover, indicating a landscape combining more vertical vegetation and built structures, whereas Coronel Pringles showed greater values of bare soil (p < 0.05; Figure 2). Mean abundance per transect differed across seasons and cities for both Turdus species (Figure 3). Austral Thrush was consistently more abundant in Bahía Blanca than in Coronel Pringles during both breeding and non-breeding seasons (p < 0.001; Figure 3). In Bahía Blanca, mean abundance per transect was 1.43 individuals (95% CI: 1.01–1.85) in the breeding season and 2.35 (95% CI: 1.45–3.25) in the non-breeding season, whereas in Coronel Pringles abundances were much lower, with 0.29 (95% CI: 0.18–0.40) and 0.28 (95% CI: 0.10–0.45), respectively (Figure 3). Within each city, estimates overlapped across seasons, indicating little seasonal variation. In contrast, Rufous-bellied Thrush showed higher abundance in Coronel Pringles, where mean abundance was 0.56 (95% CI: 0.40–0.73) in the breeding season and 0.36 (95% CI: 0.19–0.54) in the non-breeding season. In Bahía Blanca, abundances were lower, with 0.16 (95% CI: 0.06–0.27) in the breeding season and no individuals recorded in the non-breeding season (Figure 3).
For Austral Thrush, the top-ranked model had a weight of 0.38, with several other models showing comparable support (weights 0.05–0.21). Therefore, we applied model averaging across all models with ΔAICc < 2. Model-averaged coefficients indicated that herbaceous cover (IRR = 3.58, 95% CI: 1.58–8.07, p = 0.002), tree cover (IRR = 2.40, 95% CI: 1.24–4.67, p = 0.01), and concrete cover (IRR = 3.09, 95% CI: 1.23–7.78, p = 0.017) all had significant positive effects on abundance (Figure 4A). In contrast, the species was markedly less abundant in Coronel Pringles compared to Bahía Blanca (IRR = 0.13, 95% CI: 0.04–0.43, p < 0.001; Figure 4A), and abundance was slightly higher during the non-breeding season than the breeding season (IRR = 1.42, 95% CI: 1.06–2.39, p = 0.018; Figure 4A). Shrub cover and maximum building height showed no significant effects. To visualize effect sizes, we present incidence rate ratio plots based on the top-ranked model (Figure 5). The incidence rate ratio plot indicates that the likelihood of encountering Austral Thrush increased about threefold in areas with higher herb or concrete cover and more than doubled in areas with greater tree cover, whereas abundance was about 90% lower in Coronel Pringles than in Bahía Blanca and moderately higher during the non-breeding season.
Model evaluation of top-ranked model indicated an adequate fit and its results were consistent with the model-averaged coefficients. The best-fitting GLMM showed no evidence of overdispersion (dispersion statistic = 0.04, p = 0.34), no deviation from uniformity of residuals (Kolmogorov–Smirnov test: D = 0.053, p = 0.12), and no signs of zero inflation (ratioObsSim = 1.03, p = 0.26). Outlier frequency was low (0.4% of observations; p = 0.27). Marginal and conditional R2 values were moderately high (R2m = 0.47; R2c = 0.89), indicating that the model explained a substantial proportion of the variance while accounting for random effects.
For Rufous-bellied Thrush, the top-ranked model had a weight of 0.22, with several other models showing similar support (weights 0.13–0.21). Therefore, no single model was dominant, and we applied model averaging across all models with ΔAICc < 2. Model-averaged coefficients indicated that tree cover had a strong positive effect on abundance (IRR = 3.08, 95% CI: 1.39–6.38, p = 0.003; Figure 4B), while maximum building height showed a significant negative effect (IRR = 0.27, 95% CI: 0.07–0.88, p = 0.03; Figure 4B). Abundance was also strongly influenced by city and season, being significantly higher in Coronel Pringles than in Bahía Blanca (IRR = 12.6, 95% CI: 2.2–69.2, p = 0.004; Figure 4B), and higher during the breeding than the non-breeding season (IRR = 0.58, 95% CI: 0.38–0.89, p = 0.013; Figure 4B). Shrub cover had no significant effects. To visualize effect sizes, we present incidence rate ratio plots based on the top-ranked model (Figure 5). These plots show that the likelihood of encountering Rufous-bellied Thrush was on average markedly higher in Coronel Pringles than in Bahía Blanca; however, the wide confidence interval (2.2–69.2) highlights substantial uncertainty, and results should therefore be interpreted with caution. In addition, the species was more than three times more likely to occur in areas with greater tree cover, while abundance was reduced about 75% in areas with taller buildings and by nearly 40% during the non-breeding season (Figure 5), reinforcing the species’ preference for greener and less urbanized areas, particularly during the reproductive period.
Model evaluation confirmed that the GLMM adequately described the data, and its results were consistent with the model-averaged coefficients. The top-ranked model showed no evidence of overdispersion (dispersion statistic = 0.28), uniformity of residuals was not violated (Kolmogorov–Smirnov test: D = 0.027, p = 0.86), and no signs of zero inflation were detected (ratioObsSim = 1.01, p = 0.78). Outliers were rare (0.4% of cases; p = 0.27). Marginal and conditional R2 values were high (R2m = 0.57; R2c = 0.98), indicating that the model explained a substantial proportion of variance both through fixed effects and random structure.
Both species exhibited distinct patterns of microhabitat use in terms of height (χ2 = 42.7, p < 0.001) and substrate selection (Figure 6). Austral Thrush was most frequently observed on the ground, with most detections on grass (46% of observations) or bare soil (22%). A smaller proportion of individuals used anthropic structures (12%), and very few (less than 20%) were recorded perching on trees or shrubs (Figure 6). In contrast, Rufous-bellied Thrush was recorded predominantly on woody vegetation (43%), followed by grass (33%) and bare soil (11%). This species frequently used trees, such as Populus and Salix species, and was also recorded using Hedera helix, a vine not used by Austral Thrush (Figure 6B). These contrasting patterns highlight the Austral Thrush’s specialization in ground-level foraging versus the Rufous-bellied Thrush’s greater use of arboreal and mid-story habitats.
Patterns of microhabitat selection differed between the two species (Table 1; Figure 7). Austral Thrush showed a marked avoidance of shrub and tree cover, evidenced by the density plots, where the distribution of used values was significantly skewed toward lower cover values compared to availability (KS test, p < 0.05; Figure 7). On average, used shrub cover was 36% lower and tree cover 55% lower than availability (Table 1). In contrast, Rufous-bellied Thrush used shrub-covered areas more than expected based on availability (KS test, p < 0.05; Figure 7), with mean shrub cover at used sites exceeding availability by 32% (Table 1). For tree cover, use was lower than availability (a 23% difference in the mean; Figure 7), suggesting a moderate avoidance (Figure 7).

4. Discussion

Our results indicated that Austral Thrush is more tolerant of built-up areas and often uses open ground with low woody cover, whereas Rufous-bellied Thrush is associated with greener spaces, showing higher use of trees, shrubs and vines and avoidance of tall infrastructure. Vertical space use also diverged between the species, with Rufous-bellied Thrush exploiting a wider range of strata than Austral Thrush. At the landscape scale, abundance patterns further reflected contrasting responses to urban structure, with Austral Thrush more frequently observed in areas with higher concrete cover, while Rufous-bellied Thrush was more abundant in less urbanized sites. Collectively, these findings suggest that urban areas can sustain fine-scale ecological segregation between species that have only recently come into contact, highlighting the role of urban heterogeneity in shaping species coexistence.
These results are consistent with our original predictions. First, we expected that the two thrushes would differ in their patterns of habitat and microhabitat use, which was supported by both landscape-level models and microhabitat selection analyses. Second, we predicted that such differences would reflect resource segregation that could reduce potential competition and facilitate coexistence. Our findings also confirm this prediction, showing that niche partitioning operates at multiple scales and may be an important mechanism enabling the persistence of both species in urban environments of the Pampas.
The two studied cities were different in terms of degree of urbanization and urban vegetation structure and composition. We acknowledge that we did not directly measure habitat quality or connectivity, which are central to interpreting these differences, and therefore treat our explanations as hypotheses requiring further testing. Sites sampled in Bahía Blanca, with its denser built infrastructure interspersed with tree- and shrub-rich neighborhoods and green spaces, offered a mosaic of vegetated patches embedded in a highly urbanized matrix. In contrast, vegetation in Coronel Pringles was more restricted to specific green areas and periurban zones, with higher bare soil cover and fewer vegetated residential blocks. Such contrasts in habitat composition and spatial arrangement are known to influence habitat quality and connectivity, two key factors shaping bird assemblages in cities [49,50]. In our system, these differences may help explain why Austral Thrush was observed in more concrete-rich areas while Rufous-bellied Thrush was more abundant in greener and less urbanized sites. We acknowledge that we did not directly measure habitat quality or connectivity, and therefore interpret these contrasts as hypotheses that warrant further testing. Nonetheless, linking these landscape differences with the divergent habitat associations of the two thrushes highlights the role of urban form in shaping species-specific strategies and coexistence dynamics.
Both thrush species exhibited marked seasonal and spatial variation in abundance, with contrasting trends between cities. Austral Thrush was consistently more abundant in Bahía Blanca across both seasons, while Rufous-bellied Thrush reached higher numbers in Coronel Pringles and showed only a moderate seasonal increase in Bahía Blanca during the breeding period. These differences likely reflect a combination of ecological preferences and species-specific adjustments to urban environments. Differences in colonization history may also contribute to these patterns. Austral Thrush has been present in the southern Pampas biome for approximately five decades, with populations established in urban and peri-urban areas, suggesting a more advanced stage of urban integration. In contrast, Rufous-bellied Thrush is a more recent colonizer in the region, that in the last two decades become a more frequently observed species and currently expanding southward from northern Argentina [38,39]. Its earlier establishment in Coronel Pringles, located northeast of Bahía Blanca and closer to its expansion front, could have favored its higher abundance and more stable presence there. In Bahía Blanca, where the presence of Rufous-bellied Thrush seems to be more recent, the observed seasonal variation might indicate incomplete year-round establishment or exploratory movements during the breeding season [40]. These alternative explanations remain hypotheses that should be tested through future studies integrating demographic and movement data. Seasonal variation in Rufous-bellied Thrush abundance in Bahía Blanca may alternatively reflect temporary fluctuations in habitat use, reproductive cycles, or resource tracking, as reported in other Turdus species [51]. More broadly, these dynamics align with patterns observed in other range-expanding species, where abundance can vary depending on the stage of colonization and local habitat suitability [52,53].
At the transect scale, Austral Thrush showed positive associations with herbaceous vegetation, tree cover, and concrete surfaces. The link with herbaceous cover is consistent with its ground-foraging behavior in grassy patches where ground invertebrates and fallen fruits are abundant [54]. The positive association with tree cover, in turn, supports the species’ dependence on trees and shrubs for shelter and nesting [55]. The relationship with concrete cover is more difficult to interpret, as it may partly reflect the higher abundance of the species in Bahía Blanca, where built infrastructure is interspersed with vegetated neighborhoods and urban parks. Rather than indicating a preference for concrete per se, this pattern likely suggests tolerance of more urbanized environments when sufficient green space is present. Similar adaptability has been documented in Chile, where the species frequently nests in anthropogenic environments such as urban gardens and introduced vegetation [56]. Such behavioral flexibility may facilitate persistence of urban birds in cities with contrasting levels of urbanization [57], although further work is needed to disentangle habitat preference from city-level effects.
In contrast, Rufous-bellied Thrush abundance was positively associated with tree cover and showed a negative relationship with building height, suggesting a preference for greener and less densely built environments. These patterns are consistent with studies showing that tree-rich environments can buffer urban stressors and provide urban birds with critical resources for nesting, foraging and shelter [36,58]. Although the effect of shrub cover was only marginally significant, its positive trend suggests that intermediate vegetation layers may also contribute to habitat suitability. The decline in abundance with increasing building height may reflect an apparent avoidance of highly urbanized cores, but this effect could also be mediated by correlated factors such as reduced vegetation or higher disturbance levels in taller built-up areas. This contrasts with the more tolerant Austral Thrush, which showed a positive association with herbaceous and even concrete cover, suggesting species-specific thresholds of urban tolerance. The higher abundance of Rufous-bellied Thrush in Coronel Pringles may point to an interaction between urban form and colonization history, but we stress that this remains a hypothesis rather than a demonstrated mechanism.
Both thrush species exhibited marked divergence in microhabitat preference, particularly in relation to vertical distribution and substrate use. Originally allopatric, these species have expanded their ranges and now coexist in sympatry in a growing range, including the studied cities, where fine-scale ecological segregation likely reduces the potential for direct competition. Despite their close phylogenetic relatedness and broadly similar ecological requirements, our results reveal contrasting microhabitat strategies in urban contexts. Austral Thrush was observed almost exclusively on the ground, predominantly using grassy substrates and bare soil, and showed strong avoidance of shrub and tree cover, suggesting a preference for open, low-structure environments. This behavior is consistent with its known diet of invertebrates and fallen fruits [54,59], and aligns with its positive association with herbaceous cover at the transect level. In contrast, Rufous-bellied Thrush used a wider variety of substrates, often perching and foraging above ground on trees, shrubs, and even vines like Hedera helix, reflecting greater vertical flexibility and preference for structurally complex vegetation [60,61,62]. This divergence in microhabitat use was further reinforced by the species’ selection patterns: while Austral Thrush tended to avoid woody cover, Rufous-bellied Thrush used shrub and tree layers more than expected based on availability, suggesting reliance on this stratum for foraging or refuge. Interestingly, this pattern contrasts with observations from the species’ historical range in Brazil, where it is frequently recorded foraging on the ground, pointing to behavioral plasticity and a possible context-dependent adjustment in vertical niche use when in sympatry with Austral Thrush. Such context-dependent responses resemble patterns reported for other closely related species that differ in their tolerance to urbanization [24,63], highlighting that microhabitat divergence between congeners may emerge from a combination of ecological specialization, behavioral flexibility, and urban habitat structure.
These interspecific differences may contribute to coexistence, although competition was not directly tested in this study and should therefore be considered a hypothesis rather than a demonstrated mechanism. Similar cases in Brazilian thrush assemblages show that subtle differences in fruit use and fine-scale habitat partitioning can facilitate coexistence despite broad dietary overlap [64]. Although the specific resources differ between systems—fruit exploitation in Brazil versus microhabitat use in our study—both examples illustrate that ecological divergence can reduce niche overlap and allow closely related species to persist in sympatry. Seasonal segregation, as noted for other synanthropic thrushes [51], may further promote coexistence by reducing temporal overlap, but in our system this remains speculative, as direct evidence of seasonal niche partitioning was not collected. In our system, this ecological divergence appears to support stable coexistence in recently colonized urban areas, underscoring the role of microhabitat specialization in community assembly during range expansion.
Both studied thrushes are currently undergoing range shifts in South America [39], and their ability to exploit urban habitats likely facilitates their expansion. The strong association of Rufous-bellied Thrush with tree and shrub cover suggests that urban greening could promote its establishment, especially in recently colonized cities like Bahía Blanca, in a landscape context of open natural grasslands and agriculture. At the same time, our results show that woody vegetation alone is not sufficient to explain the presence of these species, since other substrates such as bare soil and herbaceous cover play key roles in supporting Austral Thrush. This highlights the contribution of habitat heterogeneity to support native bird assemblages, as noted in other urban systems [27]. The contrasting habitat associations and fine-scale microhabitat segregation observed between Austral Thrush and Rufous-bellied Thrush illustrate how structural heterogeneity within cities can shape distinct ecological strategies, which may reduce the potential for competitive overlap. We hypothesize that such habitat mosaics could also provide complementary resources across different life stages and seasons, although this was not directly tested here. From an applied perspective, maintaining and enhancing vegetation cover, vertical structure, and substrate diversity can help urban planning foster more diverse bird communities and counteract biotic homogenization.
While our study provides novel insights into the coexistence of two native thrushes in urban environments, some limitations should be acknowledged. Transect allocation was uneven between the two cities; however, our analyses incorporated city as a fixed factor and included transect identity as a random effect, which accounted for repeated sampling and differences in sampling effort. Nevertheless, this imbalance may still constrain direct comparisons, and results should therefore be interpreted with caution. In addition, the downtown area of Bahía Blanca was excluded due to its highly built-up character and minimal vegetation, whereas in Coronel Pringles we surveyed the entire urban extent, which may affect comparability. Vegetation and surface cover were visually estimated in broad intervals by a single observer, ensuring consistency but limiting accuracy at fine scales. We also did not explicitly account for detection probability, nor did we collect microclimatic data that could have refined the environmental context. Finally, our focus on two cities within the same ecoregion and on two focal species limits the generalization of our conclusions. Despite these caveats, the standardized protocols and multi-scale approach provide a robust basis for our analyses and highlight how range-expanding species partition resources in urban environments.

5. Conclusions

Our study provides an integrative perspective on how two closely phylogeneticallyrelated thrushes, Turdus falcklandii and Turdus rufiventris, partition space and resources in recently colonized urban environments of the southern Pampas, Argentina. Despite their shared ecological requirements, both species exhibited consistent differences in abundance, habitat use, and microhabitat preferences. Turdus falcklandii showed greater tolerance to built-up areas and open, low-structure environments, whereas Turdus rufiventris was more frequent on greener spaces with higher tree and shrub cover. These contrasting associations indicate fine-scale habitat segregation that likely reduces competitive overlap and facilitates coexistence in urban settings. Our findings highlight the role of urban heterogeneity in promoting species concurrency and suggest that the capacity to exploit distinct habitat components may contribute to the species coexistence. By linking behavioral flexibility with habitat structure, this study advances our understanding of how urban areas can sustain native biodiversity under ongoing environmental change.

Author Contributions

Conceptualization, M.S.V., A.L.S. and S.M.Z.; Methodology, M.S.V., A.L.S. and S.M.Z.; Formal Analysis, M.S.V.; Data Curation, M.S.V.; Writing—Original Draft Preparation, M.S.V.; Writing—Review and Editing, M.S.V., A.L.S. and S.M.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by a fellowship to MSV from the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Argentina.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The original data presented in the study are openly available in FigShare at https://figshare.com/articles/dataset/Turdus_habitat/29941043, DOI 10.6084/m9.figshare.29941043.

Acknowledgments

This research was supported by National Council for Scientific and Technical Research (CONICET) and National University of the South (UNS).

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Grimm, N.B.; Faeth, S.H.; Golubiewski, N.E.; Redman, C.L.; Wu, J.; Bai, X.; Briggs, J.M. Global Change and the Ecology of Cities. Science 2008, 319, 756–760. [Google Scholar] [CrossRef] [PubMed]
  2. Sol, D.; Trisos, C.; Múrria, C.; Jeliazkov, A.; González-Lagos, C.; Pigot, A.L.; Ricotta, C.; Swan, C.M.; Tobias, J.A.; Pavoine, S. The Worldwide Impact of Urbanisation on Avian Functional Diversity. Ecol. Lett. 2020, 23, 962–972. [Google Scholar] [CrossRef] [PubMed]
  3. Aronson, M.F.; Lepczyk, C.A.; Evans, K.L.; Goddard, M.A.; Lerman, S.B.; MacIvor, J.S.; Nilon, C.H.; Vargo, T. Biodiversity in the City: Key Challenges for Urban Green Space Management. Front. Ecol. Environ. 2017, 15, 189–196. [Google Scholar] [CrossRef]
  4. Spotswood, E.N.; Beller, E.E.; Grossinger, R.; Grenier, J.L.; Heller, N.E.; Aronson, M.F. The Biological Deserts Fallacy: Cities in Their Landscapes Contribute More than We Think to Regional Biodiversity. BioScience 2021, 71, 148–160. [Google Scholar] [CrossRef]
  5. Lera, D.N.; Cozzani, N.; Camina, J.L.; Tella, J.L.; Zalba, S. Urban Parrots in Southern South America: Challenges and Opportunities. Birds 2024, 5, 752–773. [Google Scholar] [CrossRef]
  6. Sinkovics, C.; Seress, G.; Pipoly, I.; Vincze, E.; Liker, A. Great Tits Feed Their Nestlings with More but Smaller Prey Items and Fewer Caterpillars in Cities than in Forests. Sci. Rep. 2021, 11, 24161. [Google Scholar] [CrossRef]
  7. Höhn, D.; Masello, J.F.; Kümmel, M.N.; Griep, S.; Goesmann, A.; Quillfeldt, P. Nestling Diet of Two Sympatric Insectivorous Passerines in Different Habitats—A Metabarcoding Study. Birds 2024, 5, 67–89. [Google Scholar] [CrossRef]
  8. Seress, G.; Sándor, K.; Bókony, V.; Bukor, B.; Hubai, K.; Liker, A. Radio-Tracking Urban Breeding Birds: The Importance of Native Vegetation. Ecol. Appl. 2025, 35, e3095. [Google Scholar]
  9. James Reynolds, S.; Ibáñez-Álamo, J.D.; Sumasgutner, P.; Mainwaring, M.C. Urbanisation and Nest Building in Birds: A Review of Threats and Opportunities. J. Ornithol. 2019, 160, 841–860. [Google Scholar] [CrossRef]
  10. Sol, D.; Griffin, A.S.; Bartomeus, I.; Boyce, H. Exploring or Avoiding Novel Food Resources? The Novelty Conflict in an Invasive Bird. PLoS ONE 2011, 6, e19535. [Google Scholar]
  11. Ramellini, S.; Lapadula, S.; Bonomelli, L.; Sciandra, D.; Falaschi, M. Effects of Human Disturbance on Detectability of Non-Breeding Birds in Urban Green Areas. Glob. Ecol. Conserv. 2024, 51, e02873. [Google Scholar] [CrossRef]
  12. Gorosito, C.A.; Cueto, V.R. Do Small Cities Affect Bird Assemblages? An Evaluation from Patagonia. Urban Ecosyst. 2020, 23, 289–300. [Google Scholar] [CrossRef]
  13. Muñoz, A.-R.; Delgado, D.; Ortega, P.; Ortega, J.; Sepúlveda, A.; Barón, P.; Bratek, E.; Elorriaga, J.; Malia, C.; Owen, R.; et al. Bridging Continents: The Expansion and Establishment of the House Bunting (Emberiza sahari) from North Africa to Europe. Birds 2025, 6, 29. [Google Scholar] [CrossRef]
  14. Figarski, T.; Kajtoch, Ł. Hybrids and Mixed Pairs of Syrian and Great-Spotted Woodpeckers in Urban Populations. J. Ornithol. 2018, 159, 311–314. [Google Scholar] [CrossRef]
  15. Vaschalde, P.J.; Barolin, J.; Monje, L.D.; Flores, F.S. Established Populations of Ixodes silvanus (Acari: Ixodidae) in the Chaco Serrano, Argentina. Exp. Appl. Acarol. 2025, 94, 12. [Google Scholar] [CrossRef]
  16. Martin, P.R.; Bonier, F. Species Interactions Limit the Occurrence of Urban-Adapted Birds in Cities. Proc. Natl. Acad. Sci. USA 2018, 115, E11495–E11504. [Google Scholar] [CrossRef]
  17. Abou Zeid, F.; Morelli, F.; Ibáñez-Álamo, J.D.; Díaz, M.; Reif, J.; Jokimäki, J.; Suhonen, J.; Kaisanlahti-Jokimäki, M.-L.; Markó, G.; Bussière, R.; et al. Spatial Overlap and Habitat Selection of Corvid Species in European Cities. Animals 2023, 13, 1192. [Google Scholar] [CrossRef]
  18. Liordos, V.; Jokimäki, J.; Kaisanlahti-Jokimäki, M.-L.; Valsamidis, E.; Kontsiotis, V.J. Niche Analysis and Conservation of Bird Species Using Urban Core Areas. Sustainability 2021, 13, 6327. [Google Scholar] [CrossRef]
  19. Leveau, L.M. Long-Term Directional Changes in Urban Bird Communities of Mar Del Plata City, Argentina. Front. Ecol. Evol. 2024, 12, 1457476. [Google Scholar] [CrossRef]
  20. Greig, E.I.; Wood, E.M.; Bonter, D.N. Winter Range Expansion of a Hummingbird Is Associated with Urbanization and Supplementary Feeding. Proc. R. Soc. B Biol. Sci. 2017, 284, 20170256. [Google Scholar] [CrossRef]
  21. Le Louarn, M.; Clergeau, P.; Strubbe, D.; Deschamps-Cottin, M. Dynamic Species Distribution Models Reveal Spatiotemporal Habitat Shifts in Native Range-Expanding versus Non-Native Invasive Birds in an Urban Area. J. Avian Biol. 2018, 49, jav-01527. [Google Scholar] [CrossRef]
  22. Ortega-Álvarez, R.; Berrones Benitez, E.; Medina Mena, I.; Zúñiga-Vega, J.J. Assessing the Effects of Habitat Characteristics and Co-Occurrence with Closely Related Species on Occupancy of Resident ‘Wood-Warblers’ in a Neotropical Working Landscape. Ibis 2020, 162, 1262–1278. [Google Scholar] [CrossRef]
  23. Schoener, T.W. Resource Partitioning in Ecological Communities: Research on How Similar Species Divide Resources Helps Reveal the Natural Regulation of Species Diversity. Science 1974, 185, 27–39. [Google Scholar] [CrossRef] [PubMed]
  24. Jokimäki, J.; Suhonen, J.; Kaisanlahti-Jokimäki, M.-L. Differential Long-Term Population Responses of Two Closely Related Human-Associated Sparrow Species with Respect to Urbanization. Birds 2021, 2, 230–249. [Google Scholar] [CrossRef]
  25. Curzel, F.E.; Bellocq, M.I.; Leveau, L.M. Local and Landscape Features of Wooded Streets Influenced Bird Taxonomic and Functional Diversity. Urban For. Urban Green. 2021, 66, 127369. [Google Scholar] [CrossRef]
  26. Douini, I.; Squalli, W.; Mansouri, I.; Mounir, M.; Benka, E.-M.; Dakki, M.; Hammada, S. Diversity and Abundance of Breeding Birds, Habitat, and Nesting Substrate Selection in Urban Areas: A Relevant Case from the Southern Slope of the Mediterranean. Int. J. Zool. 2023, 2023, 8554860. [Google Scholar] [CrossRef]
  27. Leveau, L.M. Microhabitat Selection by Ground-Foraging Birds in Urban Parks. Animals 2025, 15, 1155. [Google Scholar] [CrossRef]
  28. Sotayo, F.; Isah, A. Habitat Utilization and Niche Partitioning in Starling Birds at Federal University Dutse, Nigeria. Dutse J. Pure Appl. Sci. 2024, 10, 176–183. [Google Scholar] [CrossRef]
  29. Berlusconi, A.; Gobbi, M.; Martinoli, A.; Alba, R.; Assandri, G.; Bona, F.; Buzzetti, F.M.; Battisti, C.D.; Morelli, C.; Scridel, D.; et al. Foraging Niche Partitioning within a Recently Established Guild of Falcons. Ibis 2025, 167, 734–749. [Google Scholar] [CrossRef]
  30. Hildén, O. Habitat selection in birds: A review. Ann. Zool. Fenn. 1965, 2, 53–75. [Google Scholar]
  31. Cody, M.L. Habitat Selection in Birds: The Roles of Vegetation Structure, Competitors, and Productivity. BioScience 1981, 31, 107–113. [Google Scholar] [CrossRef]
  32. Cody, M.L. Habitat Selection in Birds; Elsevier: Amsterdam, The Netherlands, 1987. [Google Scholar]
  33. Amissah, C.; Iwajomo, S.B.; Abraham, J.; Deikumah, J.P. Urban Lawn Vegetation Structure Impact Arthropod Abundance and Cattle Egret Foraging Success. Sci. Afr. 2024, 24, e02137. [Google Scholar] [CrossRef]
  34. Hostetler, M.; Holling, C. Detecting the Scales at Which Birds Respond to Structure in Urban Landscapes. Urban Ecosyst. 2000, 4, 25–54. [Google Scholar] [CrossRef]
  35. Hostetler, M. The Importance of Multi-Scale Analyses in Avian Habitat Selection Studies in Urban Environments. In Avian Ecology and Conservation in an Urbanizing World; Springer: Boston, MA, USA, 2001; pp. 139–154. [Google Scholar]
  36. Callaghan, C.T.; Major, R.E.; Lyons, M.B.; Martin, J.M.; Kingsford, R.T. The Effects of Local and Landscape Habitat Attributes on Bird Diversity in Urban Greenspaces. Ecosphere 2018, 9, e02347. [Google Scholar] [CrossRef]
  37. Melo, M.A.; Piratelli, A.J. Increase in Size and Shrub Cover Improves Bird Functional Diversity in Neotropical Urban Green Spaces. Austral Ecol. 2023, 48, 440–460. [Google Scholar] [CrossRef]
  38. Vazquez, M.S.; Scorolli, A.L.; Zalba, S.M. Range Expansion of Native Thrushes in South America. Ornithol. Res. 2024, 32, 255–265. [Google Scholar] [CrossRef]
  39. Vazquez, M.S.; La Sala, L.F.; Scorolli, A.L.; Caruso, N.C.; Zalba, S.M. Pushing the Boundaries: Actual and Potential Distribution of Thrushes Expanding Their Ranges in South America. Sci. Rep. 2024, 14, 17587. [Google Scholar] [CrossRef]
  40. Vazquez, M.S.; Ripa, R.; Scorolli, A.; Zalba, S. Seasonal Dynamics of Range Expansion in South American Thrushes. Mov. Ecol. 2025, 13, 7. [Google Scholar] [CrossRef]
  41. Aliaga, V.S.; Ferrelli, F.; Piccolo, M.C. Regionalization of Climate over the Argentine Pampas. Int. J. Climatol. 2017, 37, 1237–1247. [Google Scholar] [CrossRef]
  42. Pratolongo, P.D.; Fiori, S.M. The Bahía Blanca Estuary in a Regional Context; Ecology and Biodiversity; Springer: Berlin/Heidelberg, Germany, 2021; pp. 1–16. [Google Scholar]
  43. Fernández, M.E.; Lopez, M.; Gentili, J.O. The Influence of Urban Morphology and Meteorological Factors on Vertical Thermohygrometric Distributions in a Mid-Sized Latin American City. Environ. Process. 2025, 12, 5. [Google Scholar] [CrossRef]
  44. Bibby, C.J.; Burgess Neil, D.; Hill David, A.; Mustoe Simon, H. Bird Census Techniques; Academic Press: London, UK, 2000. [Google Scholar]
  45. Bartoń, K. MuMIn: Multi-Model Inference, R Package Version 1.48.11. 2025. Available online: http://cran.r-project.org/package=MuMIn (accessed on 17 August 2025).
  46. Bates, D.; Mächler, M.; Bolker, B.; Walker, S. Fitting Linear Mixed-Effects Models Using Lme4. J. Stat. Softw. 2015, 67, 1–48. [Google Scholar] [CrossRef]
  47. Wickham, H. Ggplot2: Elegant Graphics for Data Analysis; Springer: New York, NY, USA, 2016; ISBN 978-3-319-24277-4. [Google Scholar]
  48. Wickham, H.; François, R.; Henry, L.; Müller, K.; Vaughan, D. Dplyr: A Grammar of Data Manipulation, Version 1.1.4. 2025. Available online: https://CRAN.R-project.org/package=dplyr (accessed on 17 August 2025).
  49. Hughes, A.C.; Orr, M.C.; Lei, F.; Yang, Q.; Qiao, H. Understanding Drivers of Global Urban Bird Diversity. Glob. Environ. Change 2022, 76, 102588. [Google Scholar] [CrossRef]
  50. Buenaño-Mariño, C.d.P.; Sabán, J.; Barba, E.; García-Esparza, J.A. Urban Form Shapes Bird Niches: Insights from the European Green Capital 2024. Biodivers. Conserv. 2025, 34, 1857–1879. [Google Scholar] [CrossRef]
  51. Vogel, H.F.; Zawadzki, C.H.; Metri, R. Occurrence of Thrushes in an Urban Fragment of Araucaria Forest in Southern Brazil. Biota Neotrop. 2012, 12, 242–247. [Google Scholar] [CrossRef]
  52. Di Cecco, G.J.; Hurlbert, A.H. Multiple Dimensions of Niche Specialization Explain Changes in Species’ Range Area, Occupancy, and Population Size. Front. Ecol. Evol. 2022, 10, 921480. [Google Scholar] [CrossRef]
  53. Warmer, F.E.; van Vliet, W.A.; van Hooft, P.; Hof, A.R. The Role of Intrinsic Factors in Explaining Range Shifts of European Breeding Birds: A Meta-Analysis. Ecol. Evol. 2025, 15, e71308. [Google Scholar] [CrossRef]
  54. Orellana, J.I.; Smith-Ramírez, C.; Rau, J.R.; Sade, S.; Gantz, A.; Valdivia, C.E. Phenological Synchrony between the Austral Thrush Turdus falcklandii (Passeriformes: Turdidae) and Its Food Resources within Forests and Prairies in Southern Chile. Rev. Chil. De Hist. Nat. 2014, 87, 11. [Google Scholar] [CrossRef]
  55. Benito, J.F.; Escobar, M.A.; Villaseñor, N.R. Conservación En La Ciudad: ¿Cómo Influye La Estructura Del Hábitat Sobre La Abundancia de Especies de Aves En Una Metrópoli Latinoamericana? Gayana 2019, 83, 114–125. [Google Scholar] [CrossRef]
  56. Marín, M. Biología Reproductiva e Historia Natural Del Zorzal (Turdus falcklandii) En Chile Central. Boletín Mus. Nac. De Hist. Nat. 2015, 64, 121–132. [Google Scholar]
  57. Callaghan, C.T.; Major, R.E.; Wilshire, J.H.; Martin, J.M.; Kingsford, R.T.; Cornwell, W.K. Generalists Are the Most Urban-Tolerant of Birds: A Phylogenetically Controlled Analysis of Ecological and Life History Traits Using a Novel Continuous Measure of Bird Responses to Urbanization. Oikos 2019, 128, 845–858. [Google Scholar] [CrossRef]
  58. Wood, E.M.; Esaian, S. The Importance of Street Trees to Urban Avifauna. Ecol. Appl. 2020, 30, e02149. [Google Scholar] [CrossRef]
  59. Gasperin, G.; Aurélio Pizo, M. Frugivory and Habitat Use by Thrushes (Turdus spp.) in a Suburban Area in South Brazil. Urban Ecosyst. 2009, 12, 425–436. [Google Scholar] [CrossRef]
  60. Pruscini, F.; Morelli, F.; Sisti, D.; Rocchi, M.B.L.; Santolini, R. Role of Ivy in Determining the Attractiveness of the Blackbird Turdus merula Territory. Avocetta 2014, 38, 83–87. [Google Scholar]
  61. Montaldo, N.H. Dispersión Por Aves y Éxito Reproductivo de Dos Especies de Ligustrum (Oleaceae) En Un Relicto de Selva Subtropical En La Argentina. Rev. Chil. De Hist. Nat. 1993, 66, 75–85. [Google Scholar]
  62. Scheibler, D.R. De Melo-Junior Frugivory by Birds on Two Exotic Ligustrum Species (Oleaceae) in Brazil. Ararajuba 2003, 11, 89–91. [Google Scholar]
  63. Ribeiro Soares, P.K.; Rechetelo, J.; Vogel, H.F.; Macedo Mestre, L.A. Habitat Features Predicting the Abundance of Thrushes (Turdus spp.) in Urban and Forested Restinga Sites in Paraná, Brazil. Nativa 2024, 12, 124–132. [Google Scholar] [CrossRef]
  64. Bosenbecker, C.; Bugoni, L. Trophic Niche Similarities of Sympatric Turdus Thrushes Determined by Fecal Contents, Stable Isotopes, and Bipartite Network Approaches. Ecol. Evol. 2020, 10, 9073–9084. [Google Scholar] [CrossRef]
Birds 06 00055 g001
Figure 1. Sampling sites in the cities of Bahía Blanca (yellow diamond) and Coronel Pringles (yellow triangle), Buenos Aires, Argentina. (A) shows a map of Argentina showing the location of the study region and the two focal cities. A detailed map of the sampling area in Coronel Pringles and Bahia Blanca can be seen in (B,C), respectively. The color of each point represents species presence recorded during transect surveys: blue points indicate no detection of Turdus species, green points indicate the presence of Rufous-bellied Thrush (Turdus rufiventris) only, orange points correspond to transects where only Austral Thrush (Turdus falcklandii) was recorded, and violet points represent locations where both species were detected.
Figure 1. Sampling sites in the cities of Bahía Blanca (yellow diamond) and Coronel Pringles (yellow triangle), Buenos Aires, Argentina. (A) shows a map of Argentina showing the location of the study region and the two focal cities. A detailed map of the sampling area in Coronel Pringles and Bahia Blanca can be seen in (B,C), respectively. The color of each point represents species presence recorded during transect surveys: blue points indicate no detection of Turdus species, green points indicate the presence of Rufous-bellied Thrush (Turdus rufiventris) only, orange points correspond to transects where only Austral Thrush (Turdus falcklandii) was recorded, and violet points represent locations where both species were detected.
Birds 06 00055 g001
Birds 06 00055 g002
Figure 2. Habitat variables recorded at Bahía Blanca (orange) and Coronel Pringles (blue), Buenos Aires province, Argentina. Variables include percentage cover of bare soli (A), concrete (B), herbs (C), shrubs (E), and trees (F), and maximum building height (D). Boxes represent the interquartile range, with the median indicated by a horizontal line. Points beyond this range are shown as outliers. Asterisks indicate statistically significant differences between cities based on Wilcoxon rank-sum tests: p < 0.01 (**), p < 0.001 (***).
Figure 2. Habitat variables recorded at Bahía Blanca (orange) and Coronel Pringles (blue), Buenos Aires province, Argentina. Variables include percentage cover of bare soli (A), concrete (B), herbs (C), shrubs (E), and trees (F), and maximum building height (D). Boxes represent the interquartile range, with the median indicated by a horizontal line. Points beyond this range are shown as outliers. Asterisks indicate statistically significant differences between cities based on Wilcoxon rank-sum tests: p < 0.01 (**), p < 0.001 (***).
Birds 06 00055 g002
Birds 06 00055 g003
Figure 3. Mean abundance (± standard error) of Austral Thrush (Turdus falcklandii) and Rufous-bellied Thrush (Turdus rufiventris) during the breeding and non-breeding seasons in transects at Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina. Asterisks indicate statistically significant differences between cities within the same season as calculated by Wilcoxon rank-sum tests: p < 0.05 (*), p < 0.001 (***). Different letters (A, B) indicate significant differences between seasons within the same city (p  <  0.05).
Figure 3. Mean abundance (± standard error) of Austral Thrush (Turdus falcklandii) and Rufous-bellied Thrush (Turdus rufiventris) during the breeding and non-breeding seasons in transects at Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina. Asterisks indicate statistically significant differences between cities within the same season as calculated by Wilcoxon rank-sum tests: p < 0.05 (*), p < 0.001 (***). Different letters (A, B) indicate significant differences between seasons within the same city (p  <  0.05).
Birds 06 00055 g003
Birds 06 00055 g004
Figure 4. Predicted abundance of Austral Thrush (Turdus falcklandii) (A) and Rufous-bellied Thrush (Turdus rufiventris) (B) in Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina, across predictors retained in the best-fitting Poisson model. Top row: effects of significant continuous predictors showing the relationship between expected abundance and percentage cover of trees, concrete, and herbs and grasses, and maximum height of building (m). Shaded ribbons represent 95% confidence intervals. Bottom row: predicted abundance across seasons (left) and cities (right), based on the model, and represented by boxplots displaying the median and the interquartile range. Vertical error bars also denote 95% confidence intervals. Number of asterisks indicate the strength of statistical significance: p < 0.05 (*), p < 0.01 (**), p < 0.001 (***).
Figure 4. Predicted abundance of Austral Thrush (Turdus falcklandii) (A) and Rufous-bellied Thrush (Turdus rufiventris) (B) in Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina, across predictors retained in the best-fitting Poisson model. Top row: effects of significant continuous predictors showing the relationship between expected abundance and percentage cover of trees, concrete, and herbs and grasses, and maximum height of building (m). Shaded ribbons represent 95% confidence intervals. Bottom row: predicted abundance across seasons (left) and cities (right), based on the model, and represented by boxplots displaying the median and the interquartile range. Vertical error bars also denote 95% confidence intervals. Number of asterisks indicate the strength of statistical significance: p < 0.05 (*), p < 0.01 (**), p < 0.001 (***).
Birds 06 00055 g004
Birds 06 00055 g005
Figure 5. Incidence rate ratios (IRRs) and 95% confidence intervals for predictors retained in the final Poisson model explaining the abundance of Austral Thrush (Turdus falcklandii) and Rufous-bellied Thrush (Turdus rufiventris) in Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina. An IRR greater than 1 indicates a positive association with abundance, while values below 1 indicate a negative effect. The IRR = 1 represents a null effect. Values are based on the top-ranked GLMM. While inference in the main text is based on model-averaged coefficients (ΔAICc < 2), the top model is shown here for clarity of presentation. Number of asterisks indicate the strength of statistical significance: p < 0.05 (*), p < 0.01 (**), p < 0.001 (***).
Figure 5. Incidence rate ratios (IRRs) and 95% confidence intervals for predictors retained in the final Poisson model explaining the abundance of Austral Thrush (Turdus falcklandii) and Rufous-bellied Thrush (Turdus rufiventris) in Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina. An IRR greater than 1 indicates a positive association with abundance, while values below 1 indicate a negative effect. The IRR = 1 represents a null effect. Values are based on the top-ranked GLMM. While inference in the main text is based on model-averaged coefficients (ΔAICc < 2), the top model is shown here for clarity of presentation. Number of asterisks indicate the strength of statistical significance: p < 0.05 (*), p < 0.01 (**), p < 0.001 (***).
Birds 06 00055 g005
Birds 06 00055 g006
Figure 6. Microhabitat use by Austral Thrush (Turdus falcklandii) (A) and Rufous-bellied Thrush (Turdus rufiventris) (B) in Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina. For each species, the left side of the panel shows the percentage of different substrate types (e.g., ground, shrub, tree, anthropogenic structures) use, with bar color intensity indicating the number of individuals. The right side shows the vertical distribution of observations, with bars lengths representing the number of individuals detected at different heights above ground, and the overlaid density curve illustrating the kernel density estimation.
Figure 6. Microhabitat use by Austral Thrush (Turdus falcklandii) (A) and Rufous-bellied Thrush (Turdus rufiventris) (B) in Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina. For each species, the left side of the panel shows the percentage of different substrate types (e.g., ground, shrub, tree, anthropogenic structures) use, with bar color intensity indicating the number of individuals. The right side shows the vertical distribution of observations, with bars lengths representing the number of individuals detected at different heights above ground, and the overlaid density curve illustrating the kernel density estimation.
Birds 06 00055 g006
Birds 06 00055 g007
Figure 7. Percentage cover of trees and shrubs at transects where Austral Thrush (Turdus falcklandii) and Rufous-bellied Thrush (Turdus rufiventris) were recorded in Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina. The curves represent kernel density estimates of the distribution of vegetation cover values. Orange areas represent habitat availability at the transect level, and blue areas in 1.5 m surrounding individual bird observations. Asterisks indicate significant differences between availability and use based on Kolmogorov–Smirnov tests. Number of asterisks indicate the strength of statistical significance: p < 0.05 (*), p < 0.01 (**), p < 0.001 (***).
Figure 7. Percentage cover of trees and shrubs at transects where Austral Thrush (Turdus falcklandii) and Rufous-bellied Thrush (Turdus rufiventris) were recorded in Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina. The curves represent kernel density estimates of the distribution of vegetation cover values. Orange areas represent habitat availability at the transect level, and blue areas in 1.5 m surrounding individual bird observations. Asterisks indicate significant differences between availability and use based on Kolmogorov–Smirnov tests. Number of asterisks indicate the strength of statistical significance: p < 0.05 (*), p < 0.01 (**), p < 0.001 (***).
Birds 06 00055 g007
Table 1. Summary of shrub and tree cover at transects in urban environments at Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina, where Austral Thrush (Turdus falcklandii) and Rufous-bellied Thrush (Turdus rufiventris) were present. For each species and variable, mean and median values of vegetation cover are shown separately for habitat availability (measured at the transect level) and habitat use (measured at the individual level, within a 1.5 m radius). The last two columns indicate the difference between use and availability (mean and median, respectively). Negative values indicate selection for lower-than-available cover (avoidance), while positive values suggest higher-than-available cover use (preference). Values close to zero indicate use proportional to availability. Statistics for availability were calculated from unique transects with species presence (n = 38 for Austral Thrush; n = 25 for Rufous-bellied Thrush). Habitat use was based on individual observations (n = 120 for Austral Thrush; n = 76 for Rufous-bellied Thrush).
Table 1. Summary of shrub and tree cover at transects in urban environments at Bahía Blanca and Coronel Pringles, Buenos Aires province, Argentina, where Austral Thrush (Turdus falcklandii) and Rufous-bellied Thrush (Turdus rufiventris) were present. For each species and variable, mean and median values of vegetation cover are shown separately for habitat availability (measured at the transect level) and habitat use (measured at the individual level, within a 1.5 m radius). The last two columns indicate the difference between use and availability (mean and median, respectively). Negative values indicate selection for lower-than-available cover (avoidance), while positive values suggest higher-than-available cover use (preference). Values close to zero indicate use proportional to availability. Statistics for availability were calculated from unique transects with species presence (n = 38 for Austral Thrush; n = 25 for Rufous-bellied Thrush). Habitat use was based on individual observations (n = 120 for Austral Thrush; n = 76 for Rufous-bellied Thrush).
SpeciesVariableMean AvailabilityMean UseMedian AvailabilityMedian UseDif. MeanDif. Median
Turdus falcklandiiShrub cover26.6217.08200−9.54−20
Tree cover49.7222.505010−27.22−40
Turdus rufiventrisShrub cover18.4824.471020610
Tree cover54.1341.585040−12.55−10
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Vazquez, M.S.; Scorolli, A.L.; Zalba, S.M. Close Relatives, Different Niches: Urban Ecology of Two Range-Expanding Thrushes Recently Meeting in the Argentinian Pampas. Birds 2025, 6, 55. https://doi.org/10.3390/birds6040055

AMA Style

Vazquez MS, Scorolli AL, Zalba SM. Close Relatives, Different Niches: Urban Ecology of Two Range-Expanding Thrushes Recently Meeting in the Argentinian Pampas. Birds. 2025; 6(4):55. https://doi.org/10.3390/birds6040055

Chicago/Turabian Style

Vazquez, Miriam Soledad, Alberto L. Scorolli, and Sergio M. Zalba. 2025. "Close Relatives, Different Niches: Urban Ecology of Two Range-Expanding Thrushes Recently Meeting in the Argentinian Pampas" Birds 6, no. 4: 55. https://doi.org/10.3390/birds6040055

APA Style

Vazquez, M. S., Scorolli, A. L., & Zalba, S. M. (2025). Close Relatives, Different Niches: Urban Ecology of Two Range-Expanding Thrushes Recently Meeting in the Argentinian Pampas. Birds, 6(4), 55. https://doi.org/10.3390/birds6040055

Article Metrics

Back to TopTop