Eurasian Kestrel Falco Tinnunculus Research Articles

Fine-Scale Spatial Variation in Eurasian Kestrel Falco tinnunculus Diet in Southern England Revealed from Indirect Prey Sampling and Direct Stable Usotope Analysis

Fine-Scale Spatial Variation in Eurasian Kestrel Falco tinnunculus Diet in Southern England Revealed from Indirect Prey Sampling and Direct Stable Usotope Analysis

The benefits of being smaller: Consistent pattern for climate-induced range shift and morphological difference of three falconiforme species

Climate exerts a dominant control over the distribution of species. Generally, species migrate to higher elevations to track thermal niches, but variations in morphological traits can result in trait-specific responses to climate change. Here we attempted to explore how three sympatrically distributed raptor species (the Upland Buzzard Buteo hemilasius, UB; the Common Kestrel, also called Eurasian ​Kestrel Falco tinnunculus, EK; and the Saker Falcon Falco cherrug, SF) would respond to climate change over time, and whether their responses would bias by different morphology. We tested the alternative hypotheses for Allen's rule for UB, EK, and SF in Qinghai Province, China, by modeling their current and future habitat suitability and confirming whether a consistent pattern exists between climate-induced range shifts and morphological differences among species. The extent of the projected distribution range within protected areas was also calculated for each species. We identified the future downward elevation shift for all the species, but with the notable northeastward shifting of the suitable climate space for UB and SF. Climate change would induce range contraction in the future, and the most acute influence is always the result of the pessimistic SSP585 scenario. No obvious pattern in climate-induced range shift was found for EK, for whom the morphological traits were significantly smaller all the time. More seriously, the ratios of highly suitable habitats being protected for our three raptor species were almost at a deficient level (below 1%). This study firstly tested the alternative hypothesis of Allen's rule among raptors in Qinghai Province unprecedently, confirmed the morphological basis for different responses to changing climate across species, and demonstrated the protection deficiency under the current protected area design. We advocate more related studies in the future to verify our findings across more taxa.

Competition between the black‐winged kite and Eurasian kestrel led to population turnover at a subtropical sympatric site

Population expansion of the black‐winged kite Elanus caeruleus has been a global trend in recent decades. Since first recorded in Taiwan in 2001, they rapidly occupied plains areas of this subtropical island which has led to interspecific competition with the wintering Eurasian kestrel Falco tinnunculus. In this study, we analyzed historical surveys to estimate the population trends of both species in Taiwan. We then used Pianka's index to quantify the degree of niche overlap based on diet composition and foraging peaks. Finally, we designed an experiment to test the aggressiveness of the two raptors when facing conspecific or heterospecific intruders. Airport avifauna survey (2002–2017) data from eight different airports and eBird data (2000–2019) from 21 hotspot grids both showed population turnover between the two raptors, with a decline in the wintering Eurasian kestrel and an expansion of the black‐winged kite. Rodents were the largest share of prey for both species, indicating that the two raptors have a high degree of niche overlap (an overlap index of 0.74 by prey frequency, 0.97 by prey biomass and 0.89 by foraging time). The black‐winged kite exhibited higher boldness and aggressiveness toward intruders, with its aggressiveness toward kestrel specimens (2.9 ± 2.4 strikes) significantly higher than that toward kite specimens (1.1 ± 1.8 strikes). Attacks by the black‐winged kite may have prompted the Eurasian kestrel to choose other wintering grounds. As a result, the number of wintering kestrels decreased, leading to opposing population trends of the two species.

A Survey of Sex Ratios of Raptors at a Rescue Center in China

ABSTRACT The sex ratio is an important concept in estimating population demography, and such data could contribute to both theoretical research and conservation. Although numerous studies have analyzed the sex ratios of raptors in the wild, few studies have focused on the sex ratios of raptors in wildlife rehabilitation facilities. Here, we report the results of polymerase chain reaction (PCR)-based sex identification of raptors brought to the Beijing Raptor Rescue Center in 2018–2020. This rescue center is located in eastern China, on a major migratory route for raptors in East Asia. We identified the sex of 646 individuals (belonging to 29 species) using two sets of primers, and analyzed the sex ratios of five species with a sample size >30 individuals. Generally, the sex ratios differed among species: the sex ratio of Eurasian Kestrels (Falco tinnunculus) was skewed toward males (P = 0.006), while the sex ratio of Eurasian Sparrowhawks (Accipiter nisus) was skewed toward females (P = 0.024). The sex ratio of Long-eared Owls (Asio otus) tended to be female-biased (P = 0.058). There was no significant bias of sex ratio in Oriental Scops-Owls (Otus sunia) or Amur Falcons (Falco amurensis). We discussed several possible reasons that could drive the biased sex ratios of raptors brought into rehabilitation centers. Our findings could be helpful for future studies on sex identification of raptors and conservation efforts.

Shifting Breeding Phenology in Eurasian Kestrels Falco tinnunculus: Effects of Weather and Urbanization

Human-induced climate change and the destruction of natural habitats are two of the main threats to biodiversity worldwide. Animals can use local weather conditions as environmental cues for optimal breeding conditions, but climate change can cause severe phenological mismatches. Migratory species that have a shorter time period for their settlement decision, or species that breed in heavily transformed habitats, might be specifically sensitive to such change. Here, we analyzed the arrival and egg-laying dates of Eurasian kestrels (Falco tinnunculus) in Vienna (415 km2), Austria, gathered by academic and citizen scientists between 2010 and 2018. To identify critical time windows in which weather variables affect phenology, we used a sliding window approach and considered the degree of urbanization as an additional predictor to unravel habitat-dependent relationships. Furthermore, we assessed the relationship between arrival and egg-laying (i.e., the length of the time gap in-between). We found that arrival dates were not influenced by urbanization, and that egg-laying started earlier in drier weather conditions prior to arrival, and earlier in more natural areas than in the urban center. The time gap between arrival and egg-laying was slightly shorter in breeding pairs that arrived later at their nest sites. Our results might indicate a strategy to mitigate later arrival by relatively earlier egg-laying through reducing the length of the courtship period. Such a behavioral adaptation could avoid negative effects of a later onset of breeding on their reproductive success, which is known from previous studies in our urban population.

Landscape homogenization due to agricultural intensification disrupts the relationship between reproductive success and main prey abundance in an avian predator

BackgroundSelecting high-quality habitat and the optimal time to reproduce can increase individual fitness and is a strong evolutionary factor shaping animal populations. However, few studies have investigated the interplay between land cover heterogeneity, limitation in food resources, individual quality and spatial variation in fitness parameters. Here, we explore how individuals of different quality respond to possible mismatches between a cue for prey availability (land cover heterogeneity) and the actual fluctuating prey abundance.ResultsWe analyse timing of breeding and reproductive success in a migratory population of Eurasian kestrels (Falco tinnunculus) breeding in nest-boxes, over a full three-year abundance cycle of main prey (voles), and consider several components of individual quality, including body condition, blood parasite infection, and genetic diversity (n = 448 adults) that act on different time scales. Older individuals, and kestrel parents in higher body condition started egg-laying earlier than younger birds and those in lower body condition. Additionally, egg-laying was initiated earlier during the increase and decrease phases (2011 and 2012) than during the low phase of the vole cycle (2013). Nestling survival (ratio of eggs that fledged successfully) was higher in early nests and in heterogeneous landscapes (i.e., mosaic of different habitat types), which was evident during the increase and decrease phases of the vole cycle, but not during the low vole year.ConclusionsWe found a strong positive effect of landscape heterogeneity on nestling survival, but only when voles were relatively abundant, whereas a difference in the timing of breeding related to territory landscape heterogeneity was not evident. Therefore, landscape heterogeneity appeared as the main driver of high reproductive performance under favourable food conditions. Our results show that landscape homogenization linked to agricultural intensification disrupts the expected positive effect of vole abundance on reproductive success of kestrels.

Video Evidence of Siblicide and Cannibalism, Movement of Nestlings by Adults, and Interactions with Predators in Nesting Hen Harriers

During a nest-camera study of Hen Harriers (Circus cyaneus), we recorded siblicide, cannibalism, movement of nestlings by adult birds, and interactions with predators. We deployed cameras at 13 nests across three study areas in Ireland between 2008 and 2010. At a nest with two well-developed nestlings (approximately 25–30 d old), the older nestling killed its sibling and fed on it. This was the first documented case of siblicide in this species, to our knowledge. Recordings also revealed three other events of cannibalism in which one of the nestlings in a brood died from unknown causes and was then eaten by its siblings (n = 1), by the adult male (n = 1), or was used by the adult female to feed the remaining nestlings (n = 1). At two nests, recordings showed the adult female picking up and moving nestlings that were outside the nest cup. In addition, cameras recorded two instances of full brood predation by red fox (Vulpes vulpes) and an attack on a nest by a female Eurasian Kestrel (Falco tinnunculus) that had no apparent consequences for the nestlings or the female Hen Harrier. The behaviors reported here, which are difficult to observe directly, may have important consequences for our understanding of productivity and population dynamics of Hen Harriers.

Breeding Diet of Eurasian KestrelsFalco tinnunculuson the Oceanic Island of Tenerife

The diet of Eurasian Kestrels Falco tinnunculus during the breeding season is well documented in continental populations, but not in their island-dwelling counterparts. The subspecies F. tinnunculus canariensis is a habitat-generalist on the oceanic island of Tenerife, one of its southernmost breeding sites in the Western Palaearctic. We analysed trophic diversity and diet in its main five habitat-types by identifying 5284 prey items in regurgitated pellets from nest sites and roosting sites collected during two consecutive breeding seasons. Secondly, we analysed 2585 prey remains collected from nest sites during 19 breeding seasons. In terms of numbers, insects (mainly Orthoptera and Coleoptera) predominated in pellets: 71% in chicks and 89% in adults, with variation in taxa according to habitat. This reflects opportunistic predation of insects, with grasshoppers being the staple diet in subalpine scrub (above 2000 m a.s.l). The endemic Gallot's Lizard Gallotia galloti provided the greatest biomass in pellets (58% in chicks, 55% in adults) and comprised the most abundant source of prey remains found at nest sites (92% in terms of numbers). Chick diet showed broader trophic diversity than adults. We found high overlap in diet composition between habitats in Tenerife (71% chicks; 66% adults). Kestrels inhabiting anthropogenic environments and northern scrub showed broader trophic diversity; those inhabiting subalpine scrub showed the lowest values. Kestrels inhabiting different habitats in Tenerife showed broad trophic diversity which suggests opportunistic and flexible foraging strategies, as expected of a generalist species. Regardless of habitat, trophic diversity showed high overlap in adult diet composition not only between the Canary Islands (87%), but also between insular and continental reference populations, especially the Iberian Peninsula (81%). Thus, the generalist habits of the Eurasian Kestrel seem to predominate over any expected ecological adaptations associated with island populations.

Density‐dependent increase in superpredation linked to food limitation in a recovering population of northern goshawks Accipiter gentilis

A better understanding of the mechanisms driving superpredation, the killing of smaller mesopredators by larger apex predators, is important because of the crucial role superpredation can play in structuring communities and because it often involves species of conservation concern. Here we document how the extent of superpredation has changed over time, and assessed the impact of such temporal variation on local mesopredator populations using 40 yr of dietary data collected from a recovering population of northern goshawks Accipiter gentilis, an archetypical avian superpredator. We then assessed which mechanisms were driving variation in superpredation, e.g. was it opportunistic, a response to food becoming limited (due to declines in preferred prey) or to reduce competition. Raptors comprised 8% of goshawk diet on average in years when goshawk abundance was high, which is higher than reported elsewhere. Additionally, there was a per capita increase in superpredation as goshawks recovered, with the proportion of goshawk diet comprising raptors increasing from 2 to 8% as the number of goshawk home‐ranges increased from ≤ 14 to ≥ 25. This increase in superpredation coincided with a population decline in the most commonly killed mesopredator, the Eurasian kestrel Falco tinnunculus, which may represent the reversal of the ‘mesopredator release’ process (i.e. mesopredator suppression) which occurred after goshawks and other large raptors declined or were extirpated. Food limitation was the most likely driver of superpredation in this system given: 1) the substantial decline of two main prey groups in goshawk diet, the increase in diet diversity and decrease in goshawk reproductive success are all consistent with the goshawk population becoming food‐limited; 2) it's unlikely to be purely opportunistic as the increase in superpredation did not reflect changes in the availability of mesopredator species; and 3) the majority of mesopredators killed by goshawks do not compete with goshawks for food or nest sites.

Raptors as legitimate secondary dispersers of weed seeds

Although raptors are not usually seen as seed dispersers, we demonstrate their important ecological role as legitimate seed dispersers of weeds. On the oceanic island of Fuerteventura in the Canary Islands, up to 11 000 weed seeds from a total of 39 and 62 different plant species, respectively, were found in 300 and 319 pellets, respectively, of two native predatory birds, the Common Buzzard Buteo buteo and the Eurasian Kestrel Falco tinnunculus, which consumed European Rabbits Oryctolagus cuniculus and Barbary Ground Squirrels Atlantoxerus getulus, both invasive mammals that carried these seeds in their guts. Four and seven weed species appeared with a frequency of occurrence greater than 10% in the pellets of Kestrels and Buzzards, respectively. Despite the time interval between pellet collection and germination experiments, almost 10% of planted seeds germinated, even after passing through two digestive processes, one inside the mammal and another inside the raptor. Our study encourages a change of perspective in this regard, as raptors may be involved in complex interactive dispersal processes on a wider geographical scale.

Mechanisms and reproductive consequences of breeding dispersal in a specialist predator under temporally varying food conditions

Individual variation in breeding dispersal has extensive ecological and evolutionary consequences, but the factors driving individual dispersal behaviour and their fitness consequences remain poorly understood. Our data on dispersal events of a rodent‐specialist predator, the Eurasian kestrel Falco tinnunculus, over 20 years in western Finland offers a unique opportunity to explore the mechanisms underlying breeding dispersal behaviour and its reproductive consequences in a wild bird population. Sex, age, body condition and previous breeding success affected breeding dispersal. Dispersal distances were longer in females than in males as well as longer in yearlings than in older individuals. Body condition was positively correlated to breeding dispersal distances, particularly for females. The lowest dispersal distances were recorded for intermediate brood sizes in the year preceding dispersal. Our results highlight sex‐ and environment‐specific consequences of breeding dispersal on reproductive performance. During increase phases of the three‐year vole cycles, males dispersing further had lower reproductive performance after dispersal, whereas in females, long breeding dispersal distances were associated with increased breeding success under all environmental conditions. These results suggest benefits associated to breeding dispersal in females, potentially related to large spatio‐temporal variation in main food abundance and intensity of intra‐specific competition. Breeding dispersal of males was costly during increasing food abundance, indicating the potential fitness benefits of environmental familiarity in this migratory species. Overall, our results indicate that both individual traits and environmental factors interact to shape breeding dispersal strategies in wide‐ranging predator populations under fluctuating food conditions.

Reproductive performance of Eurasian Kestrel Falco tinnunculus in an agricultural landscape with a mosaic of land uses

There are serious concerns about the environmental and ecological degradation caused by modern agriculture and its impact on animal populations. There is therefore a need to assess the reproductive performance of free‐living animals in agricultural landscapes. We undertook a 4‐year study on the reproductive biology of Eurasian Kestrel Falco tinnunculus in the Parma district of Italy. Kestrels breeding in areas of intensive agriculture delayed egg‐laying and their offspring were in poorer condition compared with those breeding in areas of temporary or permanent grasslands. However, egg volume and fledging success were similar among sites. The availability of temporary and permanent grasslands may limit the negative impacts of intensive agriculture on the breeding activity of Kestrels.

The response of Eurasian kestrel Falco tinnunculus to falconry at Deblin Military Airfield, East Poland

Birds, including kestrels, constitute a serious impediment to air traffic and are considered pests when they disrupt aviation operations. This study investigated the behaviour of kestrels at Deblin Military Airfield (eastern Poland) in response to bird strike risk management by means of falconry. Trained raptors changed the behaviour of kestrels. During the period when trained raptors worked at the airfield, kestrels were less often found there compared to the control period. During falconry sessions, kestrels perched less often compared to the control period. Kestrels also hovered less during falconry sessions compared to the control period. Falconry reduced the risk of bird strikes at the airfield and also changed the composition of kestrels' diets.

Size-biased allocation of prey from male to offspring via female: family conflicts, prey selection, and evolution of sexual size dimorphism in raptors

In birds with bi-parental care, the provisioning link between prey capture and delivery to dependent offspring is regarded as often symmetric between the mates. However, in raptors, the larger female usually broods and feeds the nestlings, while the smaller male provides food for the family, assisted by the female in the latter part of the nestling period, if at all. Prey items are relatively large and often impossible for nestlings to handle without extended maternal assistance. We video-recorded prey delivery and handling in nests of a raptor with a wide diet, the Eurasian kestrel Falco tinnunculus, and simultaneously observed prey transfer from male to female outside the nest. The male selectively allocated larger items, in particular birds and larger mammals, to the female for further processing and feeding of nestlings, and smaller items, in particular lizards and smaller mammals, directly to the nestlings for unassisted feeding. Hence, from the video, the female appeared to have captured larger prey than the male, while in reality no difference existed. The female's size-biased interception of the male's prey provisioning line would maximize the male's foraging time, and maximize the female's control of the allocation of food between her own need and that of the offspring. The male would maximize his control of food allocation by capturing smaller prey. This conflict would select for larger dominant females and smaller energy-efficient males, and induce stronger selection the longer the female depends on the male for self-feeding, as a proportion of the offspring dependence period.

Breeding dispersal of Eurasian kestrels Falco tinnunculus under temporally fluctuating food abundance

Costs and benefits of dispersal can vary in space and time, depending on environmental factors and individual state. Plastic, condition-dependent dispersal strategies, in which individuals rely on external cues such as food abundance to adjust their dispersal distances, are therefore expected to evolve in temporally fluctuating environments. We examined factors affecting breeding dispersal distances in Eurasian kestrels Falco tinnunculus subsisting on multi-annually and cyclically fluctuating voles as their main food. We attempted to avoid traditional bias in dispersal studies by having large study areas and by taking detection probabilities into account. We observed 320 dispersal events of male and 215 events of female kestrels from our study areas in western Finland during 24 yr. After correcting for distance-specific detection probability, the estimates of mean dispersal distances increased two-fold being still clearly higher for females than males. Vole abundance in the spring of settlement was more important in determining average dispersal distances than vole abundance in the previous autumn. At the population level (cross-sectional model), both males and females dispersed longer distances when the spring abundance of their main food (voles) was low compared to when it was abundant, as predicted by the food depletion hypothesis. At the individual level (longitudinal model), only females responded to the food situation by dispersing more when food abundance was low in the spring of settlement. Females also dispersed longer when vole abundance in the previous autumn had been high. Individual males did not respond to vole abundance, which implies that the population level response in males might have been caused by long-distance dispersers, which breed in the study area only in good vole years. Our results show that the dispersal distances of kestrels at northern latitudes depend both on individual properties (gender, age, and possibly individual tendency to disperse) and environmental conditions (temporal variation in main food abundance).

Delivery of Common Lizards (Zootoca (Lacerta) vivipara) to nests of Eurasian Kestrels (Falco tinnunculus) determined by solar height and ambient temperature

Recent development in video monitoring has allowed collecting of data on prey deliveries at raptor nests, and this offers an opportunity to relate prey selection to short-term changes in environmental factors on a scale of hours. Whereas raptors may specialize on ectothermic prey at southern latitudes, only some generalist raptors may include such prey in their diet at northern latitudes. In particular, at northern latitudes the activity pattern of ectothermic reptiles is strongly dependent on the prevailing weather conditions. To test whether this dependence affects the exposure of reptiles to raptors, we used video recording of prey deliveries at nests of the Eurasian Kestrel ( Falco tinnunculus L., 1758) at 61°N in Norway, where the Common Lizard ( Zootoca ( Lacerta ) vivipara (Jacquin, 1787)) is the only lizard available to kestrels. The probability that a prey item delivered at a kestrel nest was a lizard increased towards midday and also increased independently with increasing ambient temperature, which on average, was 20.2 °C when lizards were delivered compared with 15.7 °C when other types of prey were delivered. Thus, the delivery of lizards by kestrels in our study may be regarded as a functional response, where the abundance of lizards is determined by solar height and ambient temperature.

Informative content of melanin‐based plumage colour in adult Eurasian kestrels

Covariation between melanin‐based colorations and other phenotypic attributes has been rarely measured simultaneously in males and females. Such covariations and mechanisms mediating them have crucial importance determining the signalling function of these coloured ornaments in the two sexes. We examined the role of four melanin‐based coloured plumage patches as indicators of quality in both males and females of the sexually dimorphic and dichromatic Eurasian kestrel Falco tinnunculus. Previous kestrel studies have focused on the size of melanin plumage patches in either males or females as indicators of individual quality. Here, we used spectrophotometric measurements of three plumage patches and the size of another plumage patch to investigate the information content of multiple plumage colour traits in male and female kestrels. We found that females with bright plumage in the head and with high UV chroma in black parts of the rump showed good body condition and innate immunity. In addition, laying date was significantly explained by the intensity of the brown in the head of females. Meanwhile, in males we only found that individuals with greyer rumps showed better innate immunity. Altogether, our results indicate that, irrespective of the mechanism promoting covariation between coloration and individual quality, melanin‐based coloration can inform on individual quality in adult kestrels.

Development of the adrenocortical response to stress in Eurasian kestrel nestlings: Defence ability, age, brood hierarchy and condition

The developmental hypothesis proposes that the adrenocortical response to stress during postnatal development in birds should not develop when the benefits of elevated corticosterone do not outweigh the deleterious effects on growth and development. We tested three predictions developed from this hypothesis in free-living, semi-altricial Eurasian kestrel Falco tinnunculus nestlings. We measured baseline and handling-induced corticosterone levels and the binding capacity of corticosteroid binding globulins CBG on day 10 and 21 of age and related these to age, the development of the defence behaviour, hatching asynchrony and fat stores (a measure of body condition). First, the adrenocortical response to handling (total plasma corticosterone) increased with age and thus during the time when nestlings developed the ability to defend themselves, but free corticosterone did not, because of a concomitant increase of CBG with age. Second, nestlings with adequate fat stores mounted a stronger adrenocortical stress response to an acute stressor, while nestlings with low fat stores avoided additional energy expenses. While baseline corticosterone levels were negatively related to fat stores, increase in corticosterone to handling was positively related. Third, both baseline corticosterone levels and the adrenocortical response to handling were not related to hatching order, but predominantly determined by body condition. The pattern of decreasing corticosterone levels with hatching order found in the lab seems to be neutralized by opposite effects of varying body condition on corticosterone levels in free-living birds. We argue that the postnatal adrenocortical response to stress is adaptively modulated by both variations in the release of corticosterone and in CBG, which is particularly important because elevated corticosterone may adversely affect the phenotype.

Impact of Weather on Breeding Success of the Eurasian KestrelFalco tinnunculusin a Semi-Arid Island Habitat

In semi-arid ecosystems, rainfall and temperature induce changes in the food chain and affect breeding conditions of raptors. We examined the influence of rainfall and temperature on the breeding success of the Eurasian Kestrel Falco tinnunculus inhabiting xerophytic scrub on Tenerife Island, Canary Archipelago. Reproductive performance was recorded during five years, and food availability (arthropods, lizards, mice and birds) was monitored monthly during a wet and a dry breeding season. We found that increased rainfall in the previous autumn was associated with an earlier laying date and a more prolonged breeding season. Mean clutch size showed a positive correlation with rainfall in the month prior to laying. Hatching and fledgling success did not vary significantly between a wet and a dry year. Temperature did not influence breeding parameters. Despite the advanced laying date and larger clutch size observed, high prey availability during egg formation in the wet year did not result in higher overall breeding success. Stable between-year number of fledglings coincided with stable prey availability during the nestling or fledgling periods. Food conditions in the dry year were more stable and attuned to harsh weather conditions regardless of rainfall during the previous autumn and pre-breeding period.

Retracted:MHC diversity and differential exposure to pathogens in kestrels (Aves:Falconidae)

Pathogen diversity is thought to drive major histocompatibility complex (MHC) polymorphism given that host's immune repertories are dependent on antigen recognition capabilities. Here, we surveyed an extensive community of pathogens (n = 35 taxa) and MHC diversity in mainland versus island subspecies of the Eurasian kestrel Falco tinnunculus and in a sympatric mainland population of the phylogenetically related lesser kestrel Falco naumanni. Insular subspecies are commonly exposed to impoverished pathogen communities whilst different species' ecologies and contrasting life-history traits may lead to different levels of pathogen exposure. Although specific host traits may explain differential particular infections, overall pathogen diversity, richness and prevalence were higher in the truly cosmopolitan, euriphagous and long-distance disperser Eurasian kestrel than in the estenophagous, steppe-specialist, philopatric but long-distance migratory lesser kestrel. Accordingly, the continental population of Eurasian kestrels displayed a higher number (64 vs. 49) as well as more divergent alleles at both MHC class I and class II loci. Detailed analyses of amino acid diversity revealed that significant differences between both species were exclusive to those functionally important codons comprising the antigen binding sites. The lowest pathogen burdens and the smallest but still quite divergent set of MHC alleles (n = 16) were found in island Eurasian kestrels, where the rates of allele fixation at MHC loci seem to have occurred faster than at neutral markers. The results presented in this study would therefore support the role of pathogen diversity and abundance in shaping patterns of genetic variation at evolutionary relevant MHC genes.