Birds

7 pages, 398 KB

Open AccessBrief Report

Evidence of Intraspecific Brood Parasitism and Abnormal Egg-Laying Behavior in the Lesser Kestrel (Falco naumanni)

by Adiv Gal, Malamati A. Papakosta, Christos G. Vlachos, Dimitrios D. Bakaloudis, Vassilis Goutner and Reuven Yosef

Birds 2026, 7(1), 1; https://doi.org/10.3390/birds7010001 (registering DOI) - 25 Dec 2025

Abstract

Intraspecific brood parasitism (IBP), where one female lays eggs in another’s nest, is considered rare in raptors, including typically monogamous and solitary or semi-colonial falcons. The Lesser Kestrel (Falco naumanni) is a colonial falcon with a usual clutch size of one [...] Read more.

Intraspecific brood parasitism (IBP), where one female lays eggs in another’s nest, is considered rare in raptors, including typically monogamous and solitary or semi-colonial falcons. The Lesser Kestrel (Falco naumanni) is a colonial falcon with a usual clutch size of one to five eggs, yet two independent cases of anomalously large clutches consistent with suspected IBP are described from long-term studies in Greece and Israel. In central Greece (Armenio; 39°29′ N, 22°41′ E), a nest box colony monitored since 1998 produced a clutch of eight unhatched eggs in 2017; egg volumes formed two statistically distinct groups (V₁ = 850.74 ± 27.72 vs. V₂ = 926.78 ± 18.87 mm³; t = 4.146, p = 0.006), suggestive of contributions from two females. In Israel (Alona District; 32°35′ N, 35°05′ E), a nest under an asbestos roof contained a mixed clutch of eight eggs laid over two seasons (2003–2004), with four new eggs added to four unhatched eggs from the previous year; only one egg hatched and the chick was subsequently predated by a Little Owl (Athene noctua). Given the species’ typical clutch size and the occurrence of double clutches, these cases are interpreted as rare instances of parasitic egg-laying. Their extreme rarity—only one event over more than 20 years of monitoring ~120 pairs annually in Greece—underscores how uncommon IBP appears to be in Lesser Kestrels and how easily such events may be overlooked without intensive, long-term monitoring. The results emphasize the need to combine detailed field observations with molecular parentage analyses, quantify IBP frequency, and clarify the ecological and evolutionary relevance of alternative reproductive strategies in this and other colonial raptors. Full article

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13 pages, 654 KB

Open AccessArticle

Singing Behavior and Availability of Golden-Cheeked Warblers

by Jennifer L. Reidy

Birds 2025, 6(4), 66; https://doi.org/10.3390/birds6040066 - 18 Dec 2025

Abstract

Incomplete detection during auditory point counts includes the component that individuals are present but silent (“availability”). If the probability of being ‘available’ is less than one and is not random with respect to time or space, population estimates that fail to address availability [...] Read more.

Incomplete detection during auditory point counts includes the component that individuals are present but silent (“availability”). If the probability of being ‘available’ is less than one and is not random with respect to time or space, population estimates that fail to address availability will be biased. I recorded minute-by-minute singing of 60 male Golden-cheeked Warblers (Setophaga chrysoparia) in 2010–2011 (133 surveys; 6517 min) to estimate availability, evaluate predictors, and provide survey guidance. The per-minute availability was 0.45 (95% confidence intervals [CI]: 0.37–0.54). The availability was higher for unpaired versus paired males (0.82 [0.64–0.92] versus 0.30 [0.20–0.42]) and when ≥1 conspecific was singing (0.61 [0.46–0.75] vs. 0.54 [0.39–0.68]). Availability declined across both day of year and hour of day. Aggregating to common survey lengths, the probability of ≥ 1 song per bin increased with duration but showed the same temporal declines: 3 min = 0.61 (0.52–0.70), 5 min = 0.72 (0.63–0.79), and 10 min = 0.83 (0.74–0.90). Temperature had a modest positive effect, clearest at the 10 min bins. Interaction terms among day, hour, and temperature were unsupported (all likelihood ratio tests p > 0.10). These findings indicate that availability is <1 and varies predictably with day and time, implying that point count protocols should standardize survey windows or model availability explicitly. Full article

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8 pages, 2239 KB

Open AccessEditorial

Ornithological Publishing: The First Five Years of Birds

by Jukka Jokimäki

Birds 2025, 6(4), 65; https://doi.org/10.3390/birds6040065 - 17 Dec 2025

Abstract

Birds was founded on September 2020 [...] Full article

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10 pages, 2168 KB

Open AccessCommunication

Behavioural Responses of Captive Large-billed Crows to Owl Decoys with Different Motion Patterns

by Momoyo Fujioka, Maki Yamamoto and Masaki Shirai

Birds 2025, 6(4), 64; https://doi.org/10.3390/birds6040064 - 9 Dec 2025

Abstract

Corvids exhibit avoidance behaviour when foraging in the presence of potentially risky stimuli, yet it remains unclear how stimulus characteristics influence the strength of such responses. In this paper, we present wild-caught Large-billed Crows (Corvus macrorhynchos) with five conditions: no visual [...] Read more.

Corvids exhibit avoidance behaviour when foraging in the presence of potentially risky stimuli, yet it remains unclear how stimulus characteristics influence the strength of such responses. In this paper, we present wild-caught Large-billed Crows (Corvus macrorhynchos) with five conditions: no visual stimulus, a cardboard box (non-biological, stationary), an immobile owl decoy (biological, stationary), a continuous-motion owl decoy (biological, moving), and a sensor-activated-motion owl decoy (biological, moving, and sudden). Avoidance was quantified using feeding latency, landing frequency, total time spent in the feeding area, and food consumption. Compared with the condition with no visual stimulus, the presence of any visual stimulus elicited increased latency, indicating that crows detect and respond to objects near food. Among the four objects, the sensor-activated-motion owl decoy produced stronger avoidance responses of the crows than the non-biological and stationary object (cardboard box). This indicates that they evaluate not only the presence of an object but also its motion characteristics and/or perceived biological cues when adjusting their foraging behaviour. Although sample size and individual variation impose limitations, these findings suggest that both the presence of visual stimuli and/or the complexity of their appearance play key roles in shaping avoidance behaviour in corvids. Full article

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11 pages, 1015 KB

Open AccessArticle

Beneath the Feathers: Hidden Burden of Serratospiculum and Other Endoparasites in Falcons Raised in Captivity in Serbia

by Dajana Davitkov, Tamara Ilic, Milan Vidakovic, Sofija Solaja, Vladimir Nesic and Nemanja M. Jovanovic

Birds 2025, 6(4), 63; https://doi.org/10.3390/birds6040063 - 4 Dec 2025

Abstract

Parasitic infections represent an important health challenge in falcons (Falconidae), where they may negatively influence survival, reproduction, and performance. This study is the first investigation in Serbia assessing the prevalence and diversity of endoparasites in captive falcons, with special emphasis on Serratospiculum spp. [...] Read more.

Parasitic infections represent an important health challenge in falcons (Falconidae), where they may negatively influence survival, reproduction, and performance. This study is the first investigation in Serbia assessing the prevalence and diversity of endoparasites in captive falcons, with special emphasis on Serratospiculum spp. A total of 145 live birds (hybrid falcon, Falco peregrinus, F. cherrug, F. rusticolus) and 1 dead individual were examined. Diagnostic procedures included necropsy, coprological analysis, and molecular detection. Endoparasites were confirmed in 55.2% of fecal samples. The most frequent were Caryospora spp. (41.4%), followed by Porrocaecum spp. (18.6%), Capillaria spp. (3.4%), and Serratospiculum spp. (2.8%). Statistically significant differences were observed between sexes, locations, and preventive health management. Falcons kept under preventive measures showed a markedly lower prevalence compared with those lacking such care. These findings highlight the persistent occurrence of endoparasites in Serbian falcons and underscore the importance of preventive programs. Regular deworming, strict hygiene, and vector control represent essential strategies for minimizing infections, particularly of Serratospiculum spp., which poses a serious respiratory health threat. Full article

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14 pages, 594 KB

Open AccessArticle

Touchdown Rate and Success in Vole Hunting by Wintering Hen Harriers (Circus cyaneus): Roles of Intrinsic and Extrinsic Factors

by Remo Probst and Renate Probst

Birds 2025, 6(4), 62; https://doi.org/10.3390/birds6040062 - 21 Nov 2025

Abstract

Raptors wintering in temperate regions face strong energetic constraints due to low temperatures and limited prey availability. Understanding how intrinsic traits and environmental conditions shape hunting performance helps to clarify the mechanisms underlying winter foraging efficiency. We studied wintering Hen Harriers (Circus [...] Read more.

Raptors wintering in temperate regions face strong energetic constraints due to low temperatures and limited prey availability. Understanding how intrinsic traits and environmental conditions shape hunting performance helps to clarify the mechanisms underlying winter foraging efficiency. We studied wintering Hen Harriers (Circus cyaneus) in Austria over five consecutive winters (2020/21–2024/25) to quantify touchdown attempt rate and outcome in relation to sex, age, territorial status, and weather. Using generalized linear mixed models, we analyzed 1829 recorded touchdowns with individual identity as a random effect. Territorial females showed slightly higher attempt rates than males, whereas non-territorial females exhibited a tendency toward lower touchdown success. Adult males achieved the highest per-attempt efficiency, but age alone had no significant effect. Touchdown outcomes improved under cloud cover and declined with wind speed, while temperature showed no influence. Attempt rate was unaffected by any environmental variable. These results demonstrate that both intrinsic and extrinsic factors jointly determine winter foraging performance: males, with their smaller body size and agility, can persist even in vole-poor habitats by compensating through efficient flight and prey capture; territorial females benefit from stable access to vole-rich patches; and non-territorial females remain constrained by competition and limited access to prey. The findings highlight the need to maintain open farmland and vole-rich habitat to support diverse overwintering strategies. Full article

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14 pages, 823 KB

Open AccessArticle

Density-Dependent and Predator-Specific Nest Defense Strategies in Colonially Breeding Saunders’s Gulls

by Seon-Ju Lee, Bo-Yeon Hwang and Jongmin Yoon

Birds 2025, 6(4), 61; https://doi.org/10.3390/birds6040061 - 11 Nov 2025

Abstract

Nest defense is a key component of avian reproductive success, yet its intensity and expression often depend on ecological and social contexts. We investigated the nest defense behaviors of Saunders’s Gulls (Saundersilarus saundersi) breeding in Incheon Bay of South Korea in [...] Read more.

Nest defense is a key component of avian reproductive success, yet its intensity and expression often depend on ecological and social contexts. We investigated the nest defense behaviors of Saunders’s Gulls (Saundersilarus saundersi) breeding in Incheon Bay of South Korea in 2022 in relation to nest density and perceived threats. Using decoy presentations of three heterospecifics, Oriental Magpie (Pica serica; diurnal avian nest predator), common raccoon dog (Nyctereutes procyonoides; nocturnal mammalian nest predator), and Little Tern (Sternula albifrons; neutral co-nester), we quantified latency to respond, bombing attack rate, and the number of mobbing individuals at high- and low-density nesting sites within a breeding colony. Mixed models revealed that latency to respond and attack rates varied strongly with stimulus type, with diurnal predator magpies eliciting the fastest and most intense responses, followed by nocturnal predator raccoon dogs and co-nester terns. Nest density influenced the number of mobbing individuals, which was significantly greater at high-density sites. Principal Component Analysis reduced the three behavioral metrics into a composite score, which correlated negatively with latency and positively with bombing attack rate and mobbing intensity. This score varied with both nest density and stimulus type. Our findings demonstrate that Saunders’s Gulls adjust their nest defense strategies according to both the social context and predator type, highlighting the importance of density-dependent collective nest defense in colonial breeders. Full article

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16 pages, 5435 KB

Open AccessArticle

Passive Acoustic Monitoring Provides Insights into Avian Use of Energycane Cropping Systems in Southern Florida

by Leroy J. Walston, Jules F. Cacho, Ricardo A. Lesmes-Vesga, Hardev Sandhu, Colleen R. Zumpf, Bradford Kasberg, Jeremy Feinstein and Maria Cristina Negri

Birds 2025, 6(4), 60; https://doi.org/10.3390/birds6040060 - 10 Nov 2025

Abstract

Birds are important indicators of ecosystem health and provide a range of benefits to society. It is important, therefore, to understand the impacts of agricultural land use changes on bird populations. The cultivation of energycane (EC)—a sugarcane hybrid—for biofuel production represents one form [...] Read more.

Birds are important indicators of ecosystem health and provide a range of benefits to society. It is important, therefore, to understand the impacts of agricultural land use changes on bird populations. The cultivation of energycane (EC)—a sugarcane hybrid—for biofuel production represents one form of agricultural land use change in southern Florida. We used passive acoustic monitoring (PAM) to examine bird community use of experimental EC fields and other agricultural land uses at two study sites in southern Florida. We deployed 16 acoustic recorders in different study plots and used the automatic species identifier BirdNET to identify 40 focal bird species. We found seasonal differences in daily avian species diversity and richness between EC experimental plots and reference agricultural fields (corn fields, orchards, pastureland), and between time periods (pre-planting, post-planting). Daily avian species diversity and richness were lower in the EC experimental plots during Fall and Winter months when plants reached maximum height (>400 cm in some areas). Despite seasonal differences in daily measures of species diversity and richness, we found no differences in cumulative species richness, suggesting that there may be little overall (season-long) effects of EC production. These findings could provide insight to avian seasonal habitat preferences and underscore the potential limitations of PAM in areas experiencing dynamic vegetation changes. More research is needed to better understand if utilization of EC cropping systems results in positive or negative effects on avian populations (e.g., foraging habitat quality, predator–prey dynamics, nest success). Full article

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Graphical abstract

15 pages, 10415 KB

Open AccessArticle

Genetic Identity of the Red-legged Partridge (Alectoris rufa, Phasianidae) from the Island of Madeira

by Monica Guerrini, Hans-Martin Berg, Sylke Frahnert, Manuel Biscoito and Filippo Barbanera

Birds 2025, 6(4), 59; https://doi.org/10.3390/birds6040059 - 5 Nov 2025

Abstract

The Red-legged Partridge (Alectoris rufa, Phasianidae) is a non-migrant gamebird endemic to southwestern Europe that was introduced into Mediterranean and Atlantic islands in historical times. This is the case for Madeira, Portugal, where a population morphologically assigned to A. r. hispanica [...] Read more.

The Red-legged Partridge (Alectoris rufa, Phasianidae) is a non-migrant gamebird endemic to southwestern Europe that was introduced into Mediterranean and Atlantic islands in historical times. This is the case for Madeira, Portugal, where a population morphologically assigned to A. r. hispanica has been present since the XV century. We assessed its genetic identity using 2248 (Cytochrome-b, Cyt-b + Control Region, CR) and 297 bp-long (CR) mitochondrial DNA sequences obtained from modern and archival (1900–1964, including Caccabis rufa maderensis syntypes) partridges, respectively. These sequences were compared against an already published dataset covering the entire Iberian A. rufa range. We found that all the haplotypes of modern birds from Madeira were private to this island. The putative subspecies was confirmed, and northern Portugal with northwestern Spain turned out to host the closest mainland populations. This result was in line with the origin of the first human settlers of Madeira from, among other historical provinces, Douro Litoral and Minho, the latter neighboring Galicia. Despite relatively recent A. rufa importations from continental Europe, we did not find any significant change over time in the haplotypic pattern of Madeiran partridges as well as any evidence for maternal introgression from species such as the congeneric Chukar Partridge (A. chukar). Studies relying on genome-wide markers and including the only captive-bred population of Madeira are needed to gain more comprehensive information for the management of the local A. rufa. Full article

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Graphical abstract

26 pages, 1556 KB

Open AccessArticle

Reintroduction of Indian Grey Hornbills in Gir, India: Insights into Ranging, Habitat Use, Nesting and Behavioural Patterns

by Mohan Ram, Devesh Gadhavi, Aradhana Sahu, Nityanand Srivastava, Tahir Ali Rather, Tanisha Dagur, Vidhi Modi, Lahar Jhala, Yashpal Zala and Dushyantsinh Jhala

Birds 2025, 6(4), 58; https://doi.org/10.3390/birds6040058 - 24 Oct 2025

Abstract

Reintroduction efforts of wildlife species seek to re-establish self-sustaining populations of targeted species within their historical ranges. Our study focuses on the Indian Grey Hornbill, which faced local extinction in the Gir National Park and Sanctuary, Gujarat, India. The last recorded direct sighting [...] Read more.

Reintroduction efforts of wildlife species seek to re-establish self-sustaining populations of targeted species within their historical ranges. Our study focuses on the Indian Grey Hornbill, which faced local extinction in the Gir National Park and Sanctuary, Gujarat, India. The last recorded direct sighting of the Indian Grey Hornbill in the study area dates back to the 1930s. Its presence gradually declined, leading to its eventual extinction in the region between 1950 and 1960. Since the declaration of Gir Forest as a sanctuary in 1965 and subsequently as a national park in 1975, habitat conditions have significantly improved. This positive trend created an opportunity for the reintroduction of the hornbills to establish a self-sustaining population. The reintroduction was conducted in two phases. During the first phase, twenty-eight birds were captured from known hornbill ranges within Gujarat, and five of them were equipped with PTT/GSM satellite transmitters. And in the second phase, twelve birds were captured, and six of them were fitted with PTTs to study their ranging patterns, habitat associations, and potential breeding activities. During the establishment or initial phase of reintroduction, the birds exhibited exploratory behaviour, resulting in larger home ranges (mean ± Standard Deviation, SD) (60.87 ± 68.51 km²), which gradually reduced to smaller home ranges (5.73 ± 10.50 km²) during later stages. Similarly, the daily and monthly distances travelled by the birds were significantly greater in the initial phase than in the later one. Nest site selection correlated significantly with girth at breast height (GBH) and tall trees. Our study provides essential information for hornbill reintroduction in the Gir landscape, aiding future conservation efforts for Indian Grey Hornbills. Full article

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14 pages, 1271 KB

Open AccessArticle

AI-Assisted Binoculars Improve Learning in Novice Birders

by Christoph Randler and Florian Dechant

Birds 2025, 6(4), 57; https://doi.org/10.3390/birds6040057 - 24 Oct 2025

Abstract

AI tools like Passive Acoustic Monitoring (PAM) and apps like iNaturalist and Merlin are increasingly used in bird monitoring and species identification. The purpose of this study was to assess whether AI-assisted binoculars improve bird species knowledge, particularly in novice birders, and to [...] Read more.

AI tools like Passive Acoustic Monitoring (PAM) and apps like iNaturalist and Merlin are increasingly used in bird monitoring and species identification. The purpose of this study was to assess whether AI-assisted binoculars improve bird species knowledge, particularly in novice birders, and to examine users’ motivation and experience. This study focuses on the learning impact of users, not data quality or accuracy of the device itself. Participants were recruited via social media, mostly novices (10 women, 9 men, 1 diverse). Four experimental groups (A–D, with N = 5 participants each) were designated. Participants used AI-supported binoculars to identify 10 bird species and the same binoculars with AI function switched off to identify another 10 bird species based on two sets of different species (counterbalanced to avoid order effects). This allowed a between-group as well as a within-subject comparison. We used a pre-test/post-test design for learning. Significant knowledge gains occurred only when using AI binoculars (Wilcoxon tests, p = 0.008). Pooled data across the intervention groups showed strong learning effects for AI-assisted users (Z = −3.736, p = 0.001). No significant learning occurred under control conditions. As a conclusion, AI-assisted binoculars significantly enhance bird identification learning in novices, but as a cautionary note, the study needs to be extended to live birds and in longitudinal settings. Full article

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24 pages, 2368 KB

Open AccessArticle

Trends in Landcover Suitability for Sandhill Cranes Wintering in the Central Valley of California

by Gary L. Ivey, Andrew J. Caven, Dorn M. Moore and Sara K. Gomez-Maier

Birds 2025, 6(4), 56; https://doi.org/10.3390/birds6040056 - 24 Oct 2025

Abstract

The Central Valley of California provides critical wintering habitat for Sandhill Cranes (Antigone canadensis), which rely on wetlands, grasslands, and grain crops to meet their energetic needs. However, temporary row crops that support Sandhill Cranes and other wintering birds are ostensibly [...] Read more.

The Central Valley of California provides critical wintering habitat for Sandhill Cranes (Antigone canadensis), which rely on wetlands, grasslands, and grain crops to meet their energetic needs. However, temporary row crops that support Sandhill Cranes and other wintering birds are ostensibly being replaced by permanent woody crops, which offer little value for wetland and grassland-dependent species. To better understand how landcover changes may be affecting habitat availability for these wintering cranes, we analyzed landcover trends within priority crane wintering areas from 2008 to 2023. We employed a mixed-methods approach that allowed us to describe both linear and non-linear trends over time and across regions. Our findings indicate a significant decrease in landcover types suitable as crane habitat over the 16-year period (

τ

= −0.90, p < 0.001), with an average annual decline of approximately −1.15 ± 0.21% (B± 95% CI). The best-fit trendline showed that habitat suitability in priority wintering areas decreased from over 81% in 2008 to under 65% in 2023. Specifically, grasslands, rice fields, and alfalfa acreage declined across priority wintering areas, while woody landcover—including orchards, vineyards, and riparian forest breaks—increased significantly (

τ

= 0.88, p < 0.001; B = 1.14 ± 0.20%). These landscape-level changes may constrain the regional carrying capacity for Sandhill Cranes and reduce their overall resilience. Full article

(This article belongs to the Special Issue Resilience of Birds in Changing Environments)

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19 pages, 3671 KB

Open AccessArticle

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

by Miriam Soledad Vazquez, Alberto L. Scorolli and Sergio M. Zalba

Birds 2025, 6(4), 55; https://doi.org/10.3390/birds6040055 - 17 Oct 2025

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 [...] Read more.

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. Full article

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13 pages, 656 KB

Open AccessArticle

Wintering Red Kites in Central Spain: Macrohabitat Selection and Population Density Estimate

by Alan Omar Bermúdez-Cavero, Edgar Bernat-Ponce, José Antonio Gil-Delgado and Andrés López-Peinado

Birds 2025, 6(4), 54; https://doi.org/10.3390/birds6040054 - 13 Oct 2025

Abstract

The Red Kite (Milvus milvus), a Western Palearctic raptor, experienced a severe population decline across its range during the 19th and 20th centuries, nearly disappearing as a breeding species in Spain. Although conservation and reintroduction efforts have facilitated recovery, information on [...] Read more.

The Red Kite (Milvus milvus), a Western Palearctic raptor, experienced a severe population decline across its range during the 19th and 20th centuries, nearly disappearing as a breeding species in Spain. Although conservation and reintroduction efforts have facilitated recovery, information on its wintering ecology remains limited. We evaluated the population size and habitat selection of wintering Red Kites in and around the La Mancha Húmeda Biosphere Reserve (MHBR), Central Spain, and assessed whether survey route type affected detectability. Surveys comprised 325 vehicle-based line transects along paved roads and dirt tracks during the winters of 2021–2022 and 2022–2023, and the 2022 breeding season. Detection rates and density did not differ between route types. Across 212 winter transects, we recorded 124 individuals, with none detected during 113 breeding season transects. Density estimates were consistent across winters (1.3–1.4 individuals/km²), yielding a population estimate of approximately 1430 individuals. Habitat analysis indicated clear selection for open agricultural mosaics dominated by fallow land and vineyards, while rugged terrain was avoided. These results identify MHBR as an important wintering area. Yet, super-intensive agriculture is a poor habitat due to its uniformity. Enhancing heterogeneous open landscapes, including farmland, is essential for Red Kite colonization and expansion. Full article

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8 pages, 518 KB

Open AccessArticle

Hissing Predicts Lower Tonic Immobility and Higher Nest Success in Female Great Tits (Parus major)

by Tatjana Krama, Ronalds Krams, Didzis Elferts, Colton B. Adams, Dina Cirule and Indrikis A. Krams

Birds 2025, 6(4), 53; https://doi.org/10.3390/birds6040053 - 13 Oct 2025

Abstract

Antipredator behavior can vary consistently among individuals, yet links between proactive nest defense and passive fear strategies are rarely quantified in the wild. We tested whether hissing, a conspicuous, snake-like display at the nest, predicts tonic immobility (TI) and breeding success in female [...] Read more.

Antipredator behavior can vary consistently among individuals, yet links between proactive nest defense and passive fear strategies are rarely quantified in the wild. We tested whether hissing, a conspicuous, snake-like display at the nest, predicts tonic immobility (TI) and breeding success in female Great Tits (Parus major). In pine forests in southeastern Latvia (2023–2024), we presented a taxidermic Great Spotted Woodpecker (Dendrocopos major) at nest-box entrances during incubation and scored whether females hissed and how many calls they produced. The same females were later assayed for TI by brief supine restraint when nestlings were 3–4 days old. Of 141 incubating females, 105 (74.5%) hissed. TI duration differed sharply between groups: non-hissing females showed significantly longer TI than hissing females. Nest failure was significantly lower in hissing than non-hissing female nests. These results reveal a strong negative association between proactive defense and passive fearfulness, and they show that hissing can translate into higher reproductive success in a Woodpecker-dominated predator environment. We conclude that defense strategies covary within individuals along a personality axis and that predator community composition may shape selection on these strategies. Full article

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22 pages, 2609 KB

Open AccessReview

A Review of Coronaviruses in Wild Birds and Opportunities for Future Research on Migratory Waterfowl

by Allison A. Vestal-Laborde, Rebecca C. Christofferson, Kevin M. Ringelman and Ashley M. Long

Birds 2025, 6(4), 52; https://doi.org/10.3390/birds6040052 - 1 Oct 2025

Abstract

Coronaviruses (CoVs) were first described in poultry in the early 1930s and formally recognized as pathogens of both animal and human populations in the late 1960s. They are now considered among the most abundant viral families in the world. Though their distribution and [...] Read more.

Coronaviruses (CoVs) were first described in poultry in the early 1930s and formally recognized as pathogens of both animal and human populations in the late 1960s. They are now considered among the most abundant viral families in the world. Though their distribution and diversity remain understudied in wild animals, representatives from 13 orders of wild birds worldwide have tested positive for CoVs of the gamma and delta genera over the last 25 years. Many of these wild bird species are in the orders Charadriiformes (shorebirds and their relatives) and Anseriformes (waterfowl including ducks, geese, and swans). Waterfowl are particularly concerning as potential reservoirs for CoVs because they are globally distributed; often congregate in large, mixed-species flocks; and may exist in close proximity to humans and domesticated animals. This review describes the history and current knowledge of CoVs in birds, provides an updated list of global detections of CoVs in 124 species of wild birds as reported in the peer-reviewed literature since 2000, and highlights topics for future research that would help elucidate the role of waterfowl in CoV transmission. Our review reiterates the need for continuous surveillance to detect and monitor CoVs across all bird species and for standardization in data reporting and analysis of both negative and positive results. Such information is critical to understand the potential role of free-ranging birds in the maintenance, evolution, and transmission of the virus. Further, we believe that research on the potential impacts of coronavirus infections and coinfections on avian demographics, especially reproduction in waterfowl, is warranted given known consequences in domestic poultry. Full article

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22 pages, 1979 KB

Open AccessArticle

Bayesian Structure Learning Reveals Disconnected Correlation Patterns Between Morphometric Traits and Blood Biomarkers in White Stork Nestlings

by Alma Mikuška, Sabina Alić, Ivona Levak, Jorge Bernal-Alviz, Mirna Velki, Rocco Nekić, Sandra Ečimović and Dora Bjedov

Birds 2025, 6(4), 51; https://doi.org/10.3390/birds6040051 - 28 Sep 2025

Cited by 1

Abstract

Environmental stressors, particularly agricultural pesticides, can influence both growth and physiology in developing birds, yet the relationship between morphometric condition indices and biochemical biomarkers remains poorly understood. We investigated body mass, beak length, tarsus length, and body condition index (BCI) alongside plasma and [...] Read more.

Environmental stressors, particularly agricultural pesticides, can influence both growth and physiology in developing birds, yet the relationship between morphometric condition indices and biochemical biomarkers remains poorly understood. We investigated body mass, beak length, tarsus length, and body condition index (BCI) alongside plasma and S9 biomarkers, including the activities of acetylcholinesterase (AChE), carboxylesterase (CES), and glutathione S-transferase (GST), as well as the levels of glutathione (GSH) and reactive oxygen species (ROS) in nestling White Storks (Ciconia ciconia) from Croatia. Bayesian undirected graphical model (BUGM) inferred a disconnected correlation structure composed of two communities, with a strong beak length–GSH association. Biomarkers further exhibited plasma-specific affinity: plasma markers reflected short-term adjustments, whereas S9 enzymes represented distinct metabolic pathways. Overall, morphometry and physiological status showed only limited integration, restricted mainly to plasma biomarkers, and residual body condition index did not serve as a reliable proxy for physiological stress. We conclude that integrated monitoring approaches, combining morphometric and biochemical profiling, provide a more nuanced assessment of nestling condition and strengthen the use of White Storks as sentinels of agroecosystem health. Full article

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17 pages, 3708 KB

Open AccessArticle

Bird Survival in Wind Farms by Monte-Carlo Simulation Modelling Based on Wide-Ranging Flight Tracking Data of Multiple Birds During Different Seasons

by Nikolay Yordanov, Heinz Nabielek, Kiril Bedev and Pavel Zehtindjiev

Birds 2025, 6(3), 50; https://doi.org/10.3390/birds6030050 - 22 Sep 2025

Abstract

Wind energy development is a key component in the transition to sustainable clean energy. Collision probability depends on turbine dimensions and species-specific behaviour, and understanding these relationships is essential for effective Environmental Impact Assessment (EIA). We applied a simulation approach based on flight-height [...] Read more.

Wind energy development is a key component in the transition to sustainable clean energy. Collision probability depends on turbine dimensions and species-specific behaviour, and understanding these relationships is essential for effective Environmental Impact Assessment (EIA). We applied a simulation approach based on flight-height distributions of a medium-sized diurnal raptor, the Common Buzzard (Buteo buteo). Long-term Global Positioning System (GPS) tracking data from an area with over 200 operating wind turbines in Northeastern Bulgaria were combined with Monte Carlo simulations of the Band collision risk model, and the predictions were validated against 18 years of systematic carcass searches under 114 turbines. Importantly, collision probability of the Common Buzzard was season-dependent, being greater during breeding and wintering, when flights occurred at lower altitudes, and lower during migration, when birds flew higher. Both the simulations and the field data supported an overall relatively low collision probability, indicating a high avoidance rate in this species. These findings suggest that wind energy planning should account for seasonal variation in flight behaviour and community composition, while long-term monitoring remains essential to ensure that cumulative impacts are adequately assessed. Full article

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14 pages, 590 KB

Open AccessArticle

Infrequent Cooperative Breeding in a Short-Lived Migratory Songbird, the Wilson’s Warbler

by William Gilbert

Birds 2025, 6(3), 49; https://doi.org/10.3390/birds6030049 - 18 Sep 2025

Abstract

Cooperative breeding, or helping behavior, has long been recognized in birds. An ignored dichotomy, however, separates the helping found in many individuals of some long-lived, sedentary species from the helping occasionally found in the territories of isolated breeding pairs of some short-lived, long-distance [...] Read more.

Cooperative breeding, or helping behavior, has long been recognized in birds. An ignored dichotomy, however, separates the helping found in many individuals of some long-lived, sedentary species from the helping occasionally found in the territories of isolated breeding pairs of some short-lived, long-distance migrant species. Both types of helping are called “cooperative breeding” in the literature. However, recognizing a dichotomy of “frequent” versus “infrequent” cooperative breeding would help justify the study of infrequent helping as a distinct discipline. Cooperative breeding in Wilson’s Warblers is infrequent, and among the unique behaviors found during this study were (1) solicitations by helper males, which aborted host male attacks and apparently initiated territorial acceptance, (2) an absence of sexual aggression between helper males and fertile host females, (3) attacks by helper males on intruding males during host female nest building, (4) helper males singing with impunity when host males were absent from territories, but being attacked when host males were present, and (5) a single male simultaneously serving as a helper in four adjacent host territories. Infrequent helping has essentially been ignored in studies and summaries of cooperative breeding. However, recognizing and studying infrequent helping as a distinct behavioral process could reveal interactions between helping and population ecology. Thus, infrequent cooperative breeding detected in a breeding population could reveal territorial saturation and could indicate that the population is likely ecologically healthy. Full article

(This article belongs to the Special Issue Unveiling the Breeding Biology and Life History Evolution in Birds)

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