Spatiotemporal Patterns of Avian Species Richness Across Climatic Regions

Abstract

This study highlights the spatial, seasonal, and climatic variations in bird species richness across Türkiye, a country with rich avian richness situated at the intersection of major migratory routes. Bird species richness was calculated for each province. Differences between regions, Köppen–Geiger climate classes, and seasons were analyzed using the Kruskal–Wallis method. Non-parametric analysis of longitudinal data in factorial experiments was also employed to determine seasonal differences within regions and climate classes. The results revealed significant spatial variations in species richness, particularly between temperate and cold climate regions. While seasonal differences were generally less pronounced, they were critical for both migratory and resident bird species. Wetlands, coastal areas, and transitional habitats were identified as biodiversity hotspots for both resident and migratory birds. This study underscores the need to integrate regional, climatic, and seasonal variations into ecosystem-based management plans. Protecting critical habitats, enhancing connectivity through ecological corridors, and adopting adaptive conservation strategies are essential for sustaining Türkiye’s rich avian diversity. These results provide valuable insights for conservation planning and emphasize the importance of addressing spatial and seasonal dynamics to ensure long-term biodiversity preservation.

1. Introduction

Studies have shown that the distribution of species in natural ecosystems is not random. These studies indicate that topographic, climatic, and edaphic factors significantly influence species distributions [1,2,3,4,5,6,7]. Additionally, factors such as predator–prey relationships and the presence of migratory pathways can also dramatically affect species distributions. These factors often vary by region and over time, making spatial and seasonal changes in species distributions inevitable.

Understanding the interactions between biotic and abiotic factors at both the individual and species richness levels requires the evaluation of complex interrelationships. Considering Earth’s ecological, historical, and evolutionary processes, the intricate interactions between species and their environment can be seen as an expected outcome [8]. This is particularly evident as changing climatic conditions force species to adapt to their environments, resulting in spatial and temporal variations in species distributions. For instance, climate change is altering bird species’ behaviors, genetics, phenology (such as breeding and migration timing), abundances, and distributions. As climate conditions shift, many species can relocate to higher altitudes and latitudes. These impacts present significant challenges for the conservation of Important Bird and Biodiversity Areas (IBAs). Some species identified as critical in an IBA may no longer survive in the area if conditions become unsuitable, while others may colonize these habitats. Consequently, IBAs have the potential to remain pivotal in conserving birds and other biodiversity under climate change. However, achieving this will require a much more dynamic approach to site management objectives [9,10,11,12]. Therefore, studies conducted in areas with diverse topographic and climatic characteristics are considered essential and of increasing importance.

Türkiye is a country rich in geographical diversity, encompassing three distinct phytogeographical regions: the Mediterranean, Euro-Siberian, and Irano-Turanian zones. Within these regions, topography varies on both macro- and microscales. This topographic variability, combined with the influence of the seas surrounding Türkiye on three sides, results in a highly heterogeneous climatic distribution along its coastal zones. This environmental heterogeneity is considered the primary reason for the spatial and temporal variations in Türkiye’s bird species richness [13,14].

The scientific literature on birds is extensive. On average, 1217 papers were published on bird conservation every year from 2010–2021, compared to 892, 609 and 341 for mammal, insect, and amphibian conservation, respectively. A “Web of Science” keyword search reveals that, from 2010–2020, over 75,000 articles were published in academic journals with the word “bird” in the title or abstract—an increase of more than 70% since the previous decade [15,16,17,18,19,20,21]. Among these studies, those that determine the habitat preferences of bird species and relate them to climatic factors are of great importance. The findings from such research play a key role in developing ecologically based planning aimed at ensuring the sustainability of bird species, as they provide critical evidence on how habitat preferences interact with climatic factors. Such insights are essential for identifying priority areas for conservation, designing effective habitat management strategies, and ensuring that migratory routes and breeding grounds remain viable under changing environmental conditions [22,23,24]. A recent review of the scientific literature, largely focused on Europe and North America, shows that 24% of the 570 bird species studied globally have already been negatively affected by climate change to date, while only 13% have responded positively. For half of those studied, the impact remains uncertain [25,26].

A recent review of the scientific literature largely limited to Europe and North America shows that 24% of the 570 bird species studied globally have already been negatively affected by climate change to date, while only 13% have responded positively. For half of those studied, the impact remains uncertain [25,26].

Birds, with their global distribution and ecological diversity, are highly sensitive to environmental change and can act as early indicators of ecological threats. Many species are already responding to climate change by shifting their distributions or altering the timing of key life-cycle events such as migration [21,27].

Bird migration occurs as an instinctive response to survival and the search for new habitats when the topographic and climatic factors in their living areas are altered, either naturally or artificially [28,29]. During migration, birds often follow the same routes every year [30]. However, there is still no definitive evidence explaining how they navigate these routes. Although various theories exist, none have been conclusively proven to date. Bird migrations can occur in large flocks forming massive groups, in smaller groups, or even individually [31]. Extreme conditions such as heavy snow, rain, hailstorms, extreme temperatures, and the resulting droughts are among the primary threats to birds. Snow, in particular, is one of the most significant climatic factors causing many bird species to either migrate or perish during winter. Similarly, drought is another critical climatic factor that affects migratory birds. The drying up of water sources, especially along long migration routes, leads to many birds dying or altering their migratory paths. For instance, drought along the Pacific Flyway, a key migratory route used by millions of birds annually, poses a severe threat to both breeding and migratory bird populations in the region. The reduction in water resources in their habitats forces more birds into smaller areas, increasing competition and stress. Additionally, this process is reported to contribute to the rise of infectious diseases [32].

As evident from the information provided, environmental factors such as topography and climate, along with migratory routes, are key parameters influencing the distribution of bird species [33,34]. A review of studies in this field reveals that early research primarily focused on fauna identification [35]. However, over time, factors such as shifts in ecological paradigms, advancements in statistical approaches, and technological developments have broadened the perspective of these studies [36].

In Türkiye, ornithological research has a history of more than a century. Early efforts in the 1920s by Turkish biologist Ali Wahby and subsequent work by foreign and local scholars laid the foundation for documenting the country’s avifauna [37]. From the mid-20th century onwards, systematic studies expanded with contributions from Prof. Curt Kosswig, Dr. Saadet Ergene, and later Max Kasparek, whose publications and the first national inventory of Important Bird and Biodiversity Areas (IBAs) marked significant milestones [38,39,40]. These pioneering efforts provided the baseline knowledge that underpins modern ornithological research and conservation planning in Türkiye, where IBAs now play a central role in safeguarding avian diversity [41,42].

Between 1998 and 2003, three major bird surveys were conducted across large regions of Türkiye, marking the first time that breeding bird data were collected using standardized methodologies. These surveys focused on the Konya Basin [43], Mediterranean forests [44], and southeastern Anatolia [45]. Studies after the 2000s began to emphasize the use of quantitative approaches [15,46]. Factors such as the increasingly dramatic impacts of climate change, the publication of climate scenarios by the Intergovernmental Panel on Climate Change (IPCC), and advancements in both computer technologies and machine learning methods facilitated the rapid integration of statistical and model-based approaches into studies on bird species [47,48,49,50,51]. In the context of the global drive for sustainability, the integration of quantitative approaches has become increasingly critical for addressing complex biodiversity challenges. As ecosystems face mounting pressures from climate change and habitat loss, quantitative methodologies enable the identification of patterns and processes that inform sustainable conservation strategies [52]. In Türkiye, where diverse ecological regions support rich avian biodiversity, these approaches are essential for linking spatial and temporal variations in species richness to actionable, evidence-based management practices [53,54,55,56,57,58,59]. Hence, in the present study, a quantitative process was employed to identify the spatial and temporal variations in bird species richness across Türkiye. The primary aim of this study was to investigate the spatial, seasonal, and climatic variations in bird species richness across Türkiye, a key region located at the intersection of major migratory flyways. We hypothesized that bird species richness would show significant variation among provinces, reflecting differences in climate, topography, and habitat diversity, and that both seasonal dynamics and climatic conditions would play critical roles in shaping these patterns.

Contributions provided by eBird users are being utilized to facilitate a more comprehensive understanding of spatial and temporal variations in bird abundance, as well as long-term population trends [60,61,62,63], particularly for species that are not adequately represented in traditional avian monitoring efforts [64]. Although discrepancies in sampling density across submitted eBird checklists can be accounted for during data analysis [60,61,63,64], certain aspects of shifts in spatiotemporal preferences or species presence may not be fully reflected or captured within the eBird dataset [65]. In this study, datasets consistently adhered to throughout the analysis are presented, and the significance of ensuring the recording of remaining datasets through intercontinental collaboration is emphasized.

2. Materials and Methods

• Study area

Türkiye is a country that straddles both Europe and Asia, lying at a key geographical intersection that has made it a place of strategic importance. Located between latitudes 36° N and 42° N and longitudes 26° E and 45° E, the country covers a vast and diverse landmass of approximately 8 million hectares [66]. Its terrain is remarkably varied, ranging from coastal plains in the west to rugged mountains in the east. The northern regions are dominated by the Pontic Mountains, which run parallel to the Black Sea, while the Taurus Mountains line the southern coast, adjacent to the Mediterranean. In central Türkiye, the Anatolian Plateau extends across a semiarid landscape at an average elevation of 1000 m. To the east, the terrain becomes more mountainous, culminating in Mount Ağrı, which at 5137 m is the country’s highest peak [67].

Türkiye is composed of 81 provinces across seven geographical regions: Mediterranean (MDR), Eastern Anatolia (EAR), Aegean (AR), Southeastern Anatolia (SAR), Central Anatolia (CAR), Black Sea (BSR), and Marmara (MR). In these regions, climate reflects the country’s geographical diversity, with notable variation from one region to another. The Aegean and Mediterranean coasts experience a typical Mediterranean climate, characterized by hot, dry summers and mild, rainy winters [68]. In contrast, the Black Sea coast has a humid subtropical climate with consistent rainfall throughout the year [69]. Inland, the Anatolian Plateau is defined by a continental climate with hot, dry summers and cold winters marked by sharp temperature fluctuations [70]. The elevated regions in the east endure harsher winters, with heavy snowfall due to their altitude [71].

In addition to this climatic diversity, Türkiye spans three major phytogeographical regions that further shape its avifauna. The Euro-Siberian region primarily covers the Black Sea Region (BSR) and parts of the Marmara Region (MR), supporting extensive deciduous and coniferous forests. The Mediterranean Region encompasses the Aegean (AR) and Mediterranean (MDR) coasts, dominated by maquis shrublands, evergreen forests, and olive groves. The Irano-Turanian region extends across much of Central Anatolia (CAR), Eastern Anatolia (EAR), and Southeastern Anatolia (SAR), where steppe vegetation and drought-adapted shrubs predominate. This overlap of multiple phytogeographical regions, together with the country’s topographic diversity, creates highly varied habitats that support remarkable avian diversity.

• Avifauna and Migration Routes of Türkiye

Situated at the crossroads of Europe, Asia, and Africa, Türkiye lies on two major global bird migration routes and hosts exceptional avian diversity. According to recent Trakuş data, more than 500 bird species have been recorded in the country, with the majority listed on the IUCN Red List [72,73,74]. Key migratory corridors such as the Bosphorus, the Dardanelles, and Iskenderun Bay support massive seasonal movements, including the largest raptor migration in the western Palearctic [31,75]. These ecological and geographical features formed the basis for our analysis of spatial, climatic, and seasonal variations in avian species richness across Türkiye.

• Data collection

Bird species data for Türkiye presented in Trakuş and eBird databases were used in the study. Trakuş is a scientific database that has documented bird species observed, photographed, or recorded in Türkiye since 2007, based on the species list recognized by the International Ornithologists’ Committee (Category A: Species that have been observed in their natural state at least once after 1950. Species that are migratory birds and therefore likely to be observed coincidentally, species that are observed, photographed, and confirmed in the future will be added to this category) [67]. One of the best known and widely used community science platforms is eBird, a semistructured effort launched in 2002 by the Cornell Lab of Ornithology, which allows birdwatchers anywhere in the world to record their bird observations. Trakuş data indicate that by 2023 a total of 461 species had been documented, with 505 species potentially occurring in Türkiye [74]. The number of birdwatchers has also increased markedly, from an estimated 200 in 2010 to over 8.700 registered contributors by 2025 [76,77]. As of 2025, Türkiye ranks 33rd globally in bird observations, with more than 179.000 observation records. The provinces with the highest number of observations were Istanbul (36.122) and Ankara (12.790), illustrating a doubling of observation effort in the past two years [78,79].

Rapidly expanding community science datasets are increasingly being utilized to address gaps in the understanding of long-term regional avifaunal dynamics [80]. In this study, eBird records submitted by observers in Türkiye were employed to conduct a comprehensive temporal and spatial assessment of the status of migratory bird species observed during the summer and winter months from 2007 to 2024.

Using records from Trakuş covering 501 bird species, only species present in summer and winter were identified on a provincial basis and organized into tables in MS Excel [74,81]. Resident species, or those nesting and remaining in the same region year-round in Türkiye, were excluded from the scope. Trakuş and eBird provide data on a common platform. Trakuş members’ observations are integrated into eBird and become part of birdwatching data worldwide. The eBird platform is a global birdwatching network and provides an important resource for scientific research, conservation projects, and biodiversity monitoring. Trakuş’s collaboration with eBird makes the data of birdwatchers in Türkiye more accessible internationally and increases the contribution of these data to scientific studies.

• Mapping of bird species richness

In this study, eBird data submitted by watchers in Türkiye were used to assess the province preference of the country’s birds according to seasons. First, the distribution of eBird checklists submitted was mapped across the country to identify areas of the country where previously undersampled migratory birds occur, both temporally and spatially. Next, presence–absence analyses were conducted to model the population trends of most birds in Türkiye for species considered migratory by eBird and to determine which species have been most abundant in which regions over the last 28 years. Finally, an overview of the challenges and solutions for both working with and improving the quality of eBird data is presented, and an approach and workflow for analyzing nationwide eBird data is presented that could be applied by other researchers to other countries and regions anywhere in the world. The need to integrate into a transparent system for researchers, fully compatible with the EBBA2 database, in order to be able to produce more comprehensive data analyses is emphasized.

In the present study, we determined the species richness using bird observation data collected from Türkiye’s 81 provinces during both the summer and winter seasons. Subsequently, we mapped species richness values for both seasons using ArcGis Pro software (https://www.esri.com/en-us/arcgis/products/arcgis-pro/overview accessed on 4 August 2025). To enable an objective comparison between the summer and winter maps, the species richness values in the legends of both maps were grouped based on threshold values identified through the Jenks natural breaks classification method. The Jenks natural breaks classification method, widely used in cartography and geographic information systems (GISs), identifies natural thresholds in data by minimizing variance within classes and maximizing variance between classes [82,83]. For this analysis, we run the “getJenksBreaks” function from the “BAMMtools” package in R [84]. Using this function, the species richness values for the summer season were first classified into five groups based on the calculated thresholds, and the map was categorized accordingly. The same threshold values were then applied to the winter species richness data, resulting in two final species richness maps for the summer and winter seasons. These maps highlighted the seasonal variations in species richness across Türkiye.

• Köppen–Geiger Climate Classification

We utilized the Köppen–Geiger climate classification, one of the most widely applied and globally recognized systems, due to its ability to integrate both temperature and precipitation patterns into ecologically meaningful climate categories. This approach enabled us to illustrate regional climatic differences in a standardized manner and to directly assess their influence on spatial and seasonal variations in avian species richness across Türkiye. Originally introduced by Köppen in 1900 and refined by Geiger in 1961, this classification remains a cornerstone in ecological and biogeographical research [85,86] (Supplementary Document S1).

There are various studies that present Köppen–Geiger climate classification maps for Türkiye using different datasets [87,88,89]. In this study, we used the Köppen–Geiger climate classification map produced by Taşoğlu et al. (2024), which was generated using monthly average temperature and monthly total precipitation data with a resolution of 30 arc seconds (~1 km), downloaded from the Chelsa database [89].

The climate type corresponding to each province was identified based on the map of Türkiye’s major Köppen–Geiger climate types presented as Supplementary Document S2.

• Statistical analysis

To determine the appropriate method for assessing whether the differences in bird species richness across seasons, regions, and Köppen–Geiger climate classes were statistically significant, the Kolmogorov–Smirnov normality test [90,91,92] was applied to assess whether the data were parametric or non-parametric. Since the analysis showed that the assumption of normality was not met, a logarithmic transformation was applied to the data. However, even after this transformation, the normality assumption was still not satisfied. Hence, we used the non-parametric Kruskal–Wallis test [93] to examine the differences between groups. The Kruskal–Wallis test was first used to identify differences between seasons, followed by an analysis of the differences across regions and climate classes. To determine which groups contributed to these differences, Dunn’s test, a non-parametric post hoc analysis often used after the Kruskal–Wallis test, was employed [94]. The Kruskal–Wallis and Dunn tests were performed using the “ggpubr” [95] and “dunn.test” [96] packages in R, respectively. Then, the “non-parametric analysis of longitudinal data in factorial experiments” method was employed using the “nparLD” package in R [97] to reveal whether there were significant differences both between regions and climate classes according to seasons. This approach focuses on non-parametric methods for the analysis of repeated measures, longitudinal data, and factorial experiments, with the key advantage of performing statistical analysis without relying on traditional parametric assumptions such as normal distribution and homogeneity of variance [98]. Accordingly, Wald test results, a parameter of the mentioned method, were used to determine whether the species richness of regions and climate classes showed significant seasonal differences.

3. Results

Studies on the populations or population densities of bird species in Türkiye are almost non-existent. Research conducted between 2014 and 2017 determined that 313 bird species breed regularly in Türkiye. Additionally, three new species, whose breeding records have been monitored, were added to the list of regularly breeding species in Türkiye. However, it was found that three significant species no longer breed in Türkiye, as their breeding populations have disappeared in recent years. On the other hand, some species experiencing population declines across Europe, such as Streptopelia turtur, Alauda arvensis, Lanius collurio, and Emberiza hortulana, maintain healthy populations in Türkiye [72].

In the present study, resident species (those that breed in Türkiye and remain in the same area year-round) were excluded. Supplementary Document S3 (compiled by the authors based on the dataset) provides information on summer migratory bird species, which come to Türkiye to breed and spend the winter in other countries, as well as winter migratory bird species, which come to Türkiye solely to overwinter.

This study utilized data from 42 bird species across 81 provinces in Türkiye. During the summer, Apus pallidus and Clamator glandarius were the most widespread species, each observed in 44 provinces, while the province of Şanlıurfa recorded the highest species richness, with 17 species. In winter, Mareca penelope was the most frequently observed species, present in 42 provinces, and the province of Istanbul had the highest species richness during this season, with 21 species. On an annual basis, the province of Istanbul also recorded the highest species richness, with data for 26 species.

When seasonal data were evaluated, a total of 20 species were recorded during the summer and 22 species during the winter. The species richness across provinces for summer, winter, and the entire year is summarized in

Table 1. The minimum, average, and maximum bird species richness values for the summer, winter, and the entire year (compiled by authors based on species richness values).

	Species Richness
	Minimum	Mean	Maximum
Summer	1	4.14	17
Winter	1	6.43	21
Year	1	8.76	26

.

The summer and winter species richness for each province was visualized on maps using ArcGis Pro. Prior to mapping, natural threshold values for the summer period were determined using the Jenks natural breaks classification method to allow for an objective comparison. These thresholds were identified as 2, 4, 7, 11, and 17. The species richness values for both the summer and winter periods were visualized on the maps according to this classification (Figure 1 and Figure 2).

Figure 1 and Figure 2 illustrate the seasonal variations in bird species richness across Türkiye. Figure 1 represents species richness during the summer season, while Figure 2 focuses on the winter season. Noticeable differences can be observed, particularly in regions like the Southeastern Anatolia Region and the Black Sea Region, where richness levels vary significantly between seasons. These seasonal dynamics highlight the influence of climate and habitat availability on bird diversity, emphasizing the need for region-specific conservation strategies.

The Kolmogorov–Smirnov normality test results indicated a rejection of the normality assumption (p < 0.05), meaning the data did not follow a normal distribution. A logarithmic transformation was then applied, and the normality test was repeated. However, as the normality assumption still could not be satisfied (p < 0.05), the Kruskal–Wallis test, a non-parametric method, was chosen to determine differences between groups.

The Kruskal–Wallis test was first applied to compare species richness between the summer and winter seasons. The analysis revealed no statistically significant difference (chi-squared = 0.89989, p = 0.3428) between them (Figure 3).

Although no statistically significant difference was found in bird species richness between seasons, Figure 1 and Figure 2 clearly show notable differences in species richness across Türkiye’s geographical regions. When these differences were statistically evaluated using the Kruskal–Wallis test, a significant difference (chi-squared = 21.326, p = 0.001603) was found (Figure 4).

Dunn’s test was conducted to determine the source of differences between regions, revealing statistically significant differences between the Mediterranean and Eastern Anatolia Regions (MDR-EAR), the Eastern Anatolia and Marmara Regions (EAR-MR), and the Central Anatolia and Marmara Regions (CAR-MR) (

Table 2. Dunn test results for regions (compiled by authors based on species richness values of seasons and regions).

Regions	Z	p
MDR-EAR	3.328	0.009 *
MDR-AR	1.215	1
EAR-AR	−1.940	0.549
MDR-SAR	1.483	1
EAR-SAR	−1.635	1
AR-SAR	0.268	1
MDR-CAR	2.686	0.076
EAR-CAR	−0.660	1
AR-CAR	1.334	1
SAR-CAR	1.036	1
MDR-BSR	1.742	0.857
EAR-BSR	−2.051	0.423
AR-BSR	0.312	1
SAR-BSR	−0.003	1
CAR-BSR	−1.283	1
MDR-MR	−0.102	1
EAR-MR	−3.791	0.002 *
AR-MR	−1.410	1
SAR-MR	−1.698	0.939
CAR-MR	−3.063	0.023 *
BSR-MR	−2.058	0.416

* Statistically relevant ones (p < 0.05) are indicated in bold.

).

The Kruskal–Wallis test for bird species richness of Köppen–Geiger climate classes also revealed significant differences (chi-squared = 18.31, p = 0.0004) (Figure 5).

The results of Dunn’s test for climate classifications showed a significant difference (p < 0.05) only between the Cold (C) and Temperate (T) climate classes (

Table 3. Dunn test results for Köppen–Geiger climate classes (compiled by authors based on species richness values of climate classes).

Köppen–Geiger Climate Classes	Z	p
AT-C	1.567	0.351
AT-T	−2.173	0.089
C-T	−3.988	0.000 *
AT-CT	0.162	1
C-CT	−1.353	0.529
T-CT	2.253	0.073

* Statistically relevant ones (p < 0.05) are indicated in bold.

).

Finally, to determine whether the regions and climate classifications showed seasonal differences, the non-parametric analysis of longitudinal data in factorial experiments was applied. The Wald test results from this analysis (

Table 4. Results of Wald tests (compiled by authors based on seasonal and regional species richness values).

Results for Regions
	Statistic	p
Group (regions)	28.975	0.000
Time (seasons)	10.135	0.001
Group: Time	167.089	0.000 *
Results for Climate Classes
	Statistic	p
Group (Köppen–Geiger Climate Classes)	26.966	0.000
Time (seasons)	3.99	0.046
Group: Time	12.578	0.005 *

* Statistically relevant ones (p < 0.05) are indicated in bold.

) revealed significant seasonal differences for both regions and climate classifications (p < 0.05).

The Wald statistic results in Table 4 indicated significant seasonal differences (p < 0.05) for both regions and climate classifications.

4. Discussion

This study thoroughly examined the seasonal variations in bird species richness across Türkiye’s geographical regions and their relationships with Köppen–Geiger climate classes and environmental factors. The findings revealed that, while there were no significant overall differences in species richness between summer and winter seasons, notable differences were observed between regions and climate classifications. These results are consistent with findings from similar studies. For instance, a study by Parish et al. (1994) supports this conclusion, as they found seasonal differences in bird species richness in their research conducted in two different areas of eastern England [99]. Another study with similar findings was conducted by Hurlbert and Haskell (2003), where the results identified seasonal variations in bird species richness in relation to the normalized difference vegetation index (NDVI) [100]. Okçu (1999) also reported that NDVI varies across regions and seasons in Türkiye [101]. The results of these studies align with the seasonal patterns we observed in both regions and climate classifications in our research.

On the other hand, significant topographical and climatic variations exist among regions, where climatic differences largely stem from topographical diversity, or more specifically, topographical heterogeneity. Elevation and latitudinal gradients emerge as the primary topographical parameters influencing species distribution. Numerous studies highlight the potential effects of elevation differences on bird species richness [8]. In understanding patterns of species richness, the species–area relationship and the latitudinal gradient have been well-documented and widely debated, as explored in foundational works by Brown and Gibson (1983), Brown (1988), and Begon et al. (1990) [3,5,7]. While the latitudinal species richness gradient is now thought to be reasonably well understood [102,103], species richness along elevational gradients remains less explored. Nevertheless, many researchers propose that an inverse relationship between species richness and elevation could be as widespread as the latitudinal gradient [5,7,104,105,106,107]. This perspective largely arises from repeated citation of selected studies on tropical avifauna, particularly Terborgh’s (1977) research in the Peruvian Andes, which initially appeared to show a monotonic decline in species richness with increased elevation [108]. However, Terborgh himself noted that, with standardized sampling efforts, the species richness curve displayed a hump-shaped rather than monotonic pattern, suggesting a more nuanced relationship between elevation and species richness [109].

The results of our study can be indirectly related to various other parameters. One of the most important of these parameters is bird migration routes. Türkiye is located at the crossroads of two major migration routes, the East Africa–West Asia flyway and the Black Sea–Mediterranean flyway, making it a vital passage and stopover site for millions of birds [38,110]. These migration routes are particularly critical for bird movements during the spring and autumn months [111]. Narrow straits such as the Bosphorus, the Dardanelles, and the Gulf of Iskenderun create a natural “bottleneck” effect for migratory birds, causing large flocks to congregate at specific points [112]. These types of narrow passageways allow birds to conserve energy over long distances, contributing to the concentration of species richness in these areas [113,114]. The high bird diversity observed throughout the year in provinces along these straits, such as Istanbul, is a reflection of this phenomenon [115].

Habitat diversity is another critical factor that supports bird species richness [116,117]. Türkiye spans a vast geography with diverse ecosystem types, and this diversity facilitates access to various habitats for birds [118,119]. The presence of different habitat types, such as forests, agricultural areas, open spaces, wetlands, and mountainous regions, plays an essential role in meeting the shelter, feeding, and breeding needs of bird species [120,121,122,123,124]. For instance, the coexistence of both forested areas and agricultural lands in the Marmara Region can be seen as a factor enhancing species diversity [125,126]. Similarly, the maquis shrublands and coastal forests in the Mediterranean and Aegean Regions serve as key stopover sites where migratory birds rest and replenish their energy [38,127]. While these ecological and habitat-related factors strongly influence avian richness, the comparability of richness estimates across regions and seasons also depends on the methods used to standardize data. Rarefaction extrapolation curves are often suggested for such purposes, as they account for unequal sampling effort. However, the application of rarefaction was not feasible in this study. This is because rarefaction requires abundance, frequency, or coverage data, whereas our dataset was based on presence–absence records at the provincial level. Dependent rarefaction could have resulted in substantial information loss, and independent approaches [128] also require abundance data that were not available. Moreover, applying rarefaction in this context would have limited our ability to use Dunn’s test to examine both seasonal and regional differences simultaneously. Nevertheless, rarefaction remains a valuable tool for enhancing comparability in biodiversity studies, and we recommend its consideration in future research where appropriate abundance data are available.

The presence of wetlands is also of great importance for bird species richness [129,130,131]. Lakes, rivers, deltas, and marshes located in various regions of Türkiye provide essential feeding, resting, and energy-storing opportunities for migratory birds [132]. For example, significant wetlands such as Lake Manyas [133], Lake Tuz [134], the Göksu Delta [135], and Sultan Marshes [136] are frequently visited by birds during migration. These wetlands play a critical ecological role in ensuring the continuity of migration routes and enhancing the survival chances of bird species. The study’s findings support the observation that regions with such wetlands exhibit higher bird species richness.

Coastal provinces near the sea are another significant factor for bird species richness. The Mediterranean, Aegean, and Black Sea coastlines provide key landing and departure points, particularly for birds migrating over the sea. In these coastal regions, the influence of moisture from the sea and the higher plant diversity create rich habitats for birds. The forests and humid climate along the Black Sea coast offer ideal environments for meeting the shelter and feeding needs of birds during migration. This is one of the primary reasons for the high species richness observed in the Black Sea Region [137,138]. Hence, to sustain the ecological integrity of coastal habitats, which are vital for migratory birds, it is crucial to adopt conservation strategies that address both current and future challenges posed by climate change and human activities. The rich biodiversity along the Mediterranean, Aegean, and Black Sea coastlines is not only shaped by plant diversity and climatic conditions but also relies heavily on the preservation of interconnected habitats like wetlands and coastal forests. Integrating these habitats into sustainable land-use planning will ensure their resilience while safeguarding critical migratory pathways. This approach becomes particularly important in regions like the Black Sea, where climatic factors and habitat diversity converge to support high avian richness.

The impact of climate classes on bird species distribution is also among the key findings of this study. The differences between Temperate (T) and Cold (C) climate regions highlight the crucial role of climatic factors in shaping bird diversity [139]. Temperate climates provide more favorable temperatures and abundant food resources, supporting greater species diversity, whereas colder climates may limit this diversity. This underscores the importance of anticipating the potential impacts of climate change and adapting conservation strategies to suit varying climate conditions.

It would also be good to have a brief discussion about the dataset used for the results obtained. Türkiye was a partner in the national atlas contributing to EBBA2, which was created to contribute country based data sources (the second European Breeding Bird Atlas (EBBA2) project was carried out by the EBCC network of partner organizations located in 48 countries, including the whole of eastern Europe). WWF Türkiye undertook the project management. In the atlas, which was created with the contribution of the Ministry of Agriculture and Forestry, Nature Conservation and National Parks, and the intensive efforts of academics working on the subject, research and field observations carried out from 2014–2017 were reported and EBBA2 data were created. With these resources, WWF Living Planet Report 2024 output was also created. In addition, the Trakuş database, which provides summer and winter sightings of migratory birds, was created by utilizing this bird atlas. Therefore, the dataset from Trakuş was also checked and criticized for the data in the EBBA2 source [140]. i. While these datasets provided a robust foundation for our analyses, it should be noted that our study relied on species richness data rather than abundance or frequency measures. This choice was made to minimize potential biases that often arise in large-scale citizen science datasets, where observer effort and reporting intensity vary considerably. Although abundance data could offer additional ecological insights, their integration without standardized sampling protocols may in fact amplify bias. Dependent rarefaction approaches, for instance, risk substantial information loss, while independent methods such as those proposed by Sanders (1968) also require individual-level abundance data that were unavailable in this context [128]. For these reasons, directly observed species richness at the provincial scale was deemed the most reliable measure for this study. Nevertheless, we recognize this as a limitation and suggest that future research integrate standardized abundance or frequency data, when available, to refine our understanding of avian diversity across Türkiye.

5. Conclusions

This study emphasizes the need for strategic measures to conserve and sustainably manage bird species in Türkiye. Expanding existing protected areas and establishing new protection statuses are crucial for safeguarding bird migration routes. In particular, the conservation of critical habitats, such as wetlands, straits, and coastal zones—essential during migration—can be achieved by restricting development and agricultural activities in these areas. Forestry policies should be designed to prevent the degradation of natural forest structures, and suitable habitats should be created for bird species with forest rehabilitations. In other words, sustainable forestry practices and approaches that focus on preserving natural vegetation must be adopted.

Agricultural and forestry activities should be planned in a way that maintains ecological balance to ensure the sustainability of habitats. Promoting agroecological methods in agricultural areas will not only increase productivity but also support biodiversity. Similarly, adopting principles of sustainable forest management will help make forest ecosystems more resilient to climate change. Future adaptation strategies must be developed with the effects of climate change in mind. These strategies should include flexible, locally tailored measures to protect bird species that are sensitive to climate change.

More integrated approaches to biodiversity conservation should be adopted, and ecosystem-based management practices must be developed. For instance, creating ecological corridors to strengthen connections between protected areas can enable birds to move safely between habitats. These recommendations provide a scientific foundation for informed and effective decisions aimed at conserving Türkiye’s bird diversity and ecosystem health.

Finally, every country in the world should create a workflow that combines data from every continent with a cross-project approach in order to be more global with the data they obtain through projects and research. Since bird species are continentally migratory species, regular reporting will increase the accuracy of scientific results.