Eurasian Sparrowhawk Accipiter Nisus Research Articles

Mortality rates in the national bird ringing programme of Denmark and the Faroe Islands

ABSTRACT Capsule Mortality varies across capture methods but remains overall low. Aims To investigate mortality associated with ringing operations in Denmark and the Faroe Islands, including the effects of species and capture methods. Methods We analyzed data for mortality rates of birds arising from ringing operations in Denmark and the Faroe Islands over a 20-year period. The data included a variety of capture methods and altogether the reports involve 1.8 million individuals. Results The overall mortality rate during ringing operations was 0.16%. The dominant form of capture, mist-netting, had a mortality rate of 0.21%, comparable to similar published studies. Capture methods with higher mortality rates were generally used in research aimed at informing management decisions. Predation was directly responsible for most deaths, with the Eurasian Sparrowhawk Accipiter nisus being the most common predator of birds captured in nets. Migrating passerines occurring in large numbers at bird observatories contributed most to the mortality rates in Denmark, with young birds on their first autumn migration being especially prevalent. Conclusions Overall, our study confirms that bird ringing remains an acceptable method of data collection and highlights the variation in mortality among species and methods. The results should be used to inform working practices to minimize any associated mortality, as far as possible.

Geographical variation in nest defense among cinereous tit populations in China.

Behavioral divergence among populations is common across taxonomic groups, still we know very little about anti-predator behaviors. Animal exposure to predation risk is variable in different ecological contexts. In addition, reproduction value of animals in different geographical regions usually varies. In this study, we tested whether cinereous tits Parus cinereus in different populations exhibited nest defense behaviors similar to those of nest or adult predators and whether their nest defense behaviors showed geographical variation. By using field dummy experiments, we observed tits' nest defense behavior in nest predator common chipmunk Tamias sibiricus and red squirrel Sciurus vulgaris, adult predator Eurasian sparrowhawk Accipiter nisus and nonthreatening species Oriental turtle dove Streptopelia orientalis in the ZJ (44° N), DZ (31° N), and DLS (18° N) populations, respectively. The response scores varied significantly across the 4 dummies in ZJ-tits and DLS-tits but did not in DZ-tits. When facing the chipmunk, ZJ-tits showed the highest response score and DZ-tits showed the lowest response score. When facing the squirrel, ZJ-tits showed a higher response score than tits in the other 2 populations. However, tits among the 3 populations responded similarly to a sparrowhawk or dove with slight response behaviors. In addition, response scores to nest predators were positively correlated with brood size across the 3 populations, but no trend was found for sparrowhawks or doves. Our results indicated that the nest defense behaviors of cinereous tits have evolved in response to large-scale geographical variation in ecological contexts and reproduction value.

JENIS BURUNG PEMANGSA DI RESORT TEGALLEGA TAMAN NASIONAL GUNUNG GEDE PANGRANGO

The presence of birds of prey at the ecosystems in Gunung Gede Pangrango National Park (TNGGP) is very important as the top predator that helps stabilizing the pyramid or food chain. This study purpose to examine the diversity of raptors at Tegallega Resort in TNGGP. Fieldwork had been conducted from June 2021 to Maret 2022 and Oktober 2022 at this resort. Data collection used 1 km line transect where the point counts applied. Three line transects with 1 km in between distance were visited 11 times during the field data collection. The result shows that Tegallega Resort has five raptor species: crested serpent-eagle Spilornis cheela, changeable hawk-eagle Nisaetus limnaeetus, javan hawk-eagle N. bartelsi, Eurasian sparrowhawk Accipiter nisus, and barn owl Tyto alba. The eagles and hawk are protected by Indonesian regulations, while the owl is least concern species according to IUCN Redlist. When found the eagles flies in circles (soaring) with a sound when the weather is sunny and hot.

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.

To get sick or not to get sick\u2014Trichomonas infections in two Accipiter species from Germany

Trichomonosis caused by the flagellate Trichomonas gallinae is one of the most important avian diseases worldwide. The parasite is localised in the oesophageal area of its host and mainly infects pigeon and dove species. During the last decade, a host expansion to passerine birds occurred, making the disease a potential threat for passerine predators as naïve host species. Here, we investigated the effect of the parasite on two Accipiter species in Germany which show a comparable lifestyle but differ in prey choice, the Northern goshawk (Accipiter gentilis) mainly hunting pigeons and the Eurasian sparrowhawk (Accipiter nisus) mainly feeding on passerines. We genetically identified the parasite strains using the Fe-Hydrogenase gene as marker locus and compared the incidence of parasite presence and clinical signs of trichomonosis between nestlings of the two Accipiter species. In total, we identified 14 strains, with nine strains unknown so far. There was a higher strain diversity and prevalence of Trichomonas spp. in goshawks than sparrowhawks (42.4% vs. 21.2%) whereas sparrowhawks when being infected more often displayed clinical signs of trichomonosis than goshawks (37.1% vs. 6.1%). Even though sparrowhawks were mainly infected with the finch epidemic strain and genetic data indicated some variation between isolates, no correlation with virulence could be detected. All in all, goshawks seem to be better adapted to Trichomonas infections, whereas to sparrowhawks, this is a novel disease with more severe manifestations, from individual morbidity to a higher risk of population decline caused by trichomonosis.

Sex and age differences in the diet of the Eurasian Sparrowhawk (Accipiter nisus) using web‐sourced photographs: exploring the feasibility of a new citizen science approach

Diet differences between the sexes and ages have often been recorded for bird species. Many raptor species show extreme sexual size dimorphism, with females often considerably larger than the males and these differences may be reflected in their diets. Diet studies in raptors most frequently focus on analysing prey remains or pellets collected at nest‐sites. These methods are subsequently limited to breeding birds in the breeding season and are also restricted by their inability to distinguish prey items between the sexes. The use of web‐sourced photographs to examine raptor diet has the potential to overcome some limitations of more traditional methods used to assess diet. We used this approach for the Eurasian Sparrowhawk Accipiter nisus in the United Kingdom, exploring diet between the sexes and ages throughout the entire year. In total, we obtained 843 web‐sourced photographs of Sparrowhawks with their prey items. There were 12 key prey items that had a frequency ≥ 10 in the Sparrowhawk diet: Common Wood Pigeon Columba palumbus, Common Starling Sturnus vulgaris, Eurasian Collared Dove Streptopelia decaocto, Rock Dove Columba livia, Common Blackbird Turdus merula, House Sparrow Passer domesticus, unidentified ‘small’ and ‘medium’ birds, European Goldfinch Carduelis carduelis, European Greenfinch Chloris chloris, Eurasian Blue Tit Cyanistes caeruleus and Stock Dove Columba oenas. Several prey species were more often seen in the diet of one sex or age group. Overall, average prey weights of adult females were two and a half times heavier than for adult males and one and a half times heavier for juvenile females. However, this method may be slightly biased towards larger prey items, which should be considered in future studies. Despite this limitation, our method enabled dietary differences between the sexes and ages of this highly sexual size dimorphic raptor species to be explored throughout the year.

Killing of raptors on grouse moors: evidence and effects

Owing to the intensity of game management in Britain, managers of grouse moors have illegally killed raptors to increase the numbers of Red Grouse Lagopus l. scotica available for shooting. This paper summarizes evidence for the recent scale of illegal raptor killing on grouse moors and its effects on populations. It provides insights into how raptors themselves respond demographically to different levels of killing. Over Britain as a whole, most raptors have increased and expanded considerably since the 1970s, in response to reduced killing and nest destruction, and the diminished impacts of organo‐chlorine pesticides; however, in recent decades the populations of some species have declined on and around grouse moors. This is widely evident in Hen Harrier Circus cyaneus, Peregrine Falcon Falco peregrinus and Golden Eagle Aquila chrysaetos populations and in more restricted areas also in Northern Goshawk Accipiter gentilis and Red Kite Milvus milvus populations, in all of which illegal killing has been sufficient to affect numbers over wider areas. The evidence consists mainly of: (1) greater disappearance of nesting pairs, lower breeding densities or reduced occupancy of apparently suitable traditional territories on grouse moors compared with other areas; (2) reduced nest success compared with other areas; (3) reduced adult survival compared with other areas; (4) reduced age of first breeding, reflecting the removal of adults from nesting territories and their replacement by birds in immature plumage; (5) greater levels of disappearance of satellite‐tracked birds on grouse moors than elsewhere; and (6) the finding of poisoned baits and traps, and shot or poisoned carcasses of raptors. Not all these types of evidence are available for every species, and other types of evidence are available for some. The Common Buzzard Buteo buteo is currently the most numerous raptor in Britain and also seems to be killed in the greatest numbers. Other raptor species, including Merlin Falco columbarius, Common Kestrel Falco tinnunculus and Eurasian Sparrowhawk Accipiter nisus which nest on or near grouse moors, have little or no significant impact on grouse and are killed less often or not at all. In the absence of illegal killing, some raptor species breed as well or better on grouse moors than in other habitats. Merlins, in particular, seem to thrive on grouse moors, benefiting from the management involved (including predator control). Other aspects of illegal raptor killing are discussed, including suggestions for ways in which it might be reduced.

Warblers perform less nest defense behavior and alarm calls to human intruders: A result of habituation

Human disturbance is caused by the anthropogenic activities in the environment. While human threat to wildlife is considered to be complex (nonlethal recreations and lethal hunting activities). To date, there has been few studies that focus on nest defense behavior of animals to human disturbance. In this study, we tested whether the behavioral response of Oriental reed warblers Acrocephalus orientalis against a human intruder are similar to other nest intruders. We used dummies of common cuckoo Cuculus canorus (the parasite), Eurasian sparrowhawk Accipiter nisus (the predator), Oriental turtle dove Streptopelia orientalis (the neutral control), also a human intruder to induce the nest defense behaviors and alarm calls of Oriental reed warblers. Our results showed that Oriental reed warblers performed less intense nest defense behavior and uttered the least number of calls and shortest duration of calls to a human intruder than those to other nest intruders, suggesting that human pose a low threat level to warblers. Warblers produced different number and duration of alarm calls against the cuckoos, sparrowhawks and doves, even though they performed similar behavioral responses to the three types of avian intruder, indicating that they could distinguish the three types of avian intruders. The present study provided experimental evidence for the different behavioral responses between human disturbance and other types of intruders and suggested that the less intense behavioral response to human disturbance may be the result of habituation.

Assessing factors associated with changes in the numbers of birds visiting gardens in winter: Are predators partly to blame?

The factors governing the recent declines observed in many songbirds have received much research interest, in particular whether increases of avian predators have had a negative effect on any of their prey species. In addition, further discussion has centered on whether or not the choice of model formulation has an effect on model inference. The study goal was to evaluate changes in the number of 10 songbird species in relation to a suite of environmental covariates, testing for any evidence in support of a predator effect using multiple model formulations to check for consistency in the results. We compare two different approaches to the analysis of long‐term garden bird monitoring data. The first approach models change in the prey species between 1970 and 2005 as a function of environmental covariates, including the abundance of an avian predator, while the second uses a change–change approach. Significant negative relationships were found between Eurasian Sparrowhawk Accipiter nisus and three of the 10 species analyzed, namely house Sparrow Passer domesticus, starling Sturnus vulgaris, and blue tit Cyanistes caeruleus. The results were consistent under both modeling approaches. It is not clear if this is a direct negative impact on the overall populations of these species or a behavioral response of the prey species to avoid feeding stations frequented by Sparrowhawks (which may in turn have population consequences, by reducing available resources). The species showing evidence of negative effects of Sparrowhawks were three of the four species most at risk to Sparrowhawk predation according to their prevalence in the predator's diet. The associations could be causal in nature, although in practical terms the reduction in the rate of change in numbers visiting gardens accredited to Sparrowhawks is relatively small, and so unlikely to be the main driver of observed population declines.

Heterospecific alarm-call recognition in two warbler hosts of common cuckoos

Species facing similar selection pressures should recognize heterospecific alarm signals. However, no study has so far examined heterospecific alarm-call recognition in response to parasitism by cuckoos. In this study, we tested whether two sympatric host species of the common cuckoo Cuculus canorus, Oriental reed warbler Acrocephalus orientalis (ORW, main host), and black-browed reed warbler Acrocephalus bistrigiceps (BRW, rare host), could recognize each other’s alarm calls in response to cuckoos. Dummies of common cuckoo (parasite) and Eurasian sparrowhawk Accipiter nisus (predator) were used to induce and record alarm calls of the two warbler species, respectively. In the conspecific alarm-call playback experiments, ORW responded more strongly to cuckoo alarm calls than to sparrowhawk alarm calls, while BRW responded less strongly to cuckoo alarm calls than to sparrowhawk alarm calls. In the heterospecific alarm-call playback experiments, both ORW and BRW responded less strongly to cuckoo alarm calls than sparrowhawk alarm calls. BRW seemed to learn the association between parasite-related alarm calls of the ORW and the cuckoo by observing the process of ORW attacking cuckoos. In contrast, alarm calls of BRW to cuckoos were rarely recorded in most cases. BRW with low parasite pressure still developed recognition of heterospecific parasite-related alarm call. Unintended receivers in the same community should recognize heterospecific alarm calls precisely to extract valuable information.

The paradox of nest reuse: early breeding benefits reproduction, but nest reuse increases nest predation risk

Many animals build new nests every breeding season instead of saving time by reusing old ones. One hypothesis is that nest reuse leads to increased predation risk if predators memorize nest locations and revisit these sites. Here we examine patterns in the prevalence of facultative nest reuse. Further, we relate nest reuse and timing of breeding to nest predation risk, clutch size and nestling survival. We analyse 1570 breeding attempts of the Eurasian sparrowhawk (Accipiter nisus) from Denmark (1977–1997) and from two sites in Norway (1985–2017). The probability of reuse varied between study areas, increased in replacement clutches, and was lower in adults compared to 1-year-old breeders. Pairs reusing nests laid their first egg on average 2.6 ± 1.0 SE days later than those building new nests, suggesting they are compensating for an already late breeding schedule. Indeed, reuse increased nest predation risk, but we discovered no other productive effects of reuse. In non-predated nests, late breeders had both smaller clutches and lower nestling survival. We propose that nest predation is a contributing driver to the behaviour of building a new nest each year, whereas nest reuse is a strategy to compensate for delayed onset of breeding, mainly used by inexperienced males.

Autumn Passage of Soaring Birds over Dobrogea (Romania): A Migration Corridor in Southeast Europe

The Dobrogea region in southeastern Romania, which is part of the Eurasian-East African Flyway, is listed as one of the important migration corridors for soaring birds on the western coast of the Black Sea. However, our knowledge regarding migration intensity, phenology and geographical patterns of soaring birds over the area is poor. To determine the migration intensity and phenology of soaring birds, we recorded the autumn migration in the Măcin Mountains (northern Dobrogea) from mid-August to the end of October between 2002–2007. To describe the geographical patterns of migration at a regional scale, we recorded migration intensity in the second half of September in 2010 and 2011, simultaneously from 15 and 13 counting points, respectively, covering the entire region of Dobrogea. In the Măcin Mountains we recorded a mean number (±SD) of 11,297 ± 2333.5 (CV = 20.7%) migrating raptors per year, and of 21,367 ± 10,949.3 (51.2%) and 455.6 ± 43.6 (9.6%) migrating White Storks Ciconia ciconia and Black Storks Ciconia nigra, respectively. Migration phenology parameters varied across raptor and non-raptor species. Migration occurred over a broad front, covering all of Dobrogea. However, migration intensity was more pronounced in the western, central and eastern parts of the region, and was less intensive in the northern central areas. Overall, we recorded 30 migrating raptor species and three non-raptor species. The most abundant raptors were Common Buzzard Buteo buteo, European Honey Buzzard Pernis apivorus, Lesser Spotted Eagle Clanga pomarina, Eurasian Sparrowhawk Accipiter nisus and Western Marsh Harrier Circus aeruginosus. The three non-raptor species were White Stork, Black Stork and Great White Pelican Pelecanus onocrotalus. Our study provides the first general overview of the autumn passage of soaring birds over Dobrogea, highlighting the importance of this area as part of a global migration network.

Diet of Eurasian Sparrowhawks in a Northwest Iberian Hedgerow Habitat throughout the Year

Abstract Little is known about Eurasian Sparrowhawk Accipiter nisus feeding habits outside the breeding season in its wide geographical range. The present study concerns the autumn-winter and spring-summer diet of this raptor species in Northwest Spain in a hedgerow habitat. A total of 23 avian prey species were recorded, only six of which occurred in both periods of the year. However, Eurasian Sparrowhawks fed mainly on medium-sized birds that often forage on the ground at some distance from shrubs and trees, mostly the Song Thrush Turdus philomelos and the Common Blackbird Turdus merula, both species together accounting for approximately half of the prey in any season of the year. The contribution of larger birds, i.e., pigeons, was considerable in terms of ingested biomass. In spring-summer, the mean body weight of avian prey was over 15 g less than in autumn-winter.

Predator discrimination and anti-predator behaviour by wintering parids: an experimental study

Even though birds’ perceptions of risk are biased towards starvation avoidance in winter, recognition of the level of threat of a predator is an important precondition. To investigate the ability of three tit species (Blue Cyanistes caeruleus , Great Parus major and Willow Tits Poecile montanus ) to recognise dangerous and harmless objects, I studied their mobbing reaction and the latency of the tits to return to the feeder after being exposed to life like models of Eurasian Sparrowhawk Accipiter nisus , Siberian Jay Perisoreus infaustus and Three-toed Woodpecker Picoides tridactylus , birds similar in size (about 30 cm) but differing widely from each other in feeding. The mobbing level was higher and the latency time of each of the tit species were significantly longer after presenting the Sparrowhawk than the Siberian Jay, whereas the woodpecker aroused no specific reaction. The tits apparently recognised the individual predator species and made decisions on their perceptions of the threat level.

Breeding success and productivity of urban and rural Eurasian sparrowhawks Accipiter nisus in Scotland

ABSTRACTThe conversion of rural habitat into built-up areas often affects animal species negatively. However, some generalist bird species and raptors relying on avian prey have colonised urban environments. Surprisingly, no study has compared the breeding biology of urban and rural populations of a very common old-world raptor, the Eurasian sparrowhawk (Accipiter nisus). Here, we compare the territory occupancy rate, breeding success and productivity (i.e., the number of fledglings) over four years (2009–2012) of an urban and a rural sparrowhawk population in Scotland. Our results showed that urban sparrowhawk territories were occupied significantly more frequently (mean % years occupied ± se: 66.8 ± 5.9%) than rural territories (42.8 ± 4.7%). Clutch size, brood size and the number of fledglings produced did not differ between the populations. However, the breeding success was significantly higher in the urban (annual mean ± se: 97.2 ± 2.3% nests successful) than in the rural population (80.5 ± 6.6%) because of a higher nest desertion rate at the egg and chick stages in the rural population. Our study suggests that warm weather in July may have more negative effects on rural sparrowhawks compared to urban sparrowhawks. The mechanism behind the difference is unknown and requires further work.

Alarm call‐based discrimination between common cuckoo and Eurasian sparrowhawk in a Chinese population of great tits

AbstractMorphological resemblance of the common cuckoo Cuculus canorus to the Eurasian sparrowhawk Accipiter nisus has been regarded as an example of predator mimicry. Common hosts could distinguish parasites as the result of coevolution, while rare hosts or non‐hosts may mistake cuckoos for hawks because rare hosts or non‐hosts behave similarly when faced with these two species. Birds usually produce alarm calls in addition to showing behavioral responses when in danger. However, previous studies of identification by rare hosts or non‐hosts of sparrowhawks usually lacked experimental evidence of alarm calls. Great tits Parus major, a rare cuckoo host, perform similar behaviors and usually produce alarm calls in response to sparrowhawks and common cuckoos. Here, we tested whether great tits could distinguish common cuckoo from sparrowhawk based on analysis of their alarm calls and the effects of playback of alarm calls on conspecific behavior. Previous studies showed that great tits have a complex communication system that conveys information about predators, and they could perform different kinds of response behavior to different alarm calls. If great tits have not made the ability to distinguish between common cuckoo and sparrowhawk, then their acoustic responses to these two species and their response behaviors in playback experiments should be similar. Specimens of a common cuckoo (parasite), a sparrowhawk (predator) and an Oriental turtle dove Streptopelia orientalis (harmless control) were used to elicit and subsequently record the response behavior and alarm calls of great tits. There was no significant difference in behavioral response among great tits when exposed to the dummy of cuckoo, sparrowhawk and dove. In contrast, they differed significantly in alarm calls. Great tits produced more notes per call that contained increasing D‐type and decreasing I‐type notes when responding to sparrowhawk as compared to cuckoo or dove. In playback experiments, we found that great tits responded more strongly to great tit hawk than to great tit cuckoo or great tit dove alarm calls. Our study suggests that great tits are able to distinguish sparrowhawks from common cuckoos and convey relevant information in alarm calls by adjusting the number and combinations of notes of a single call type.

Habitat and weather requirements of diurnal raptors wintering in river valleys

AbstractThe winter raptor community was studied in river valleys of North Eastern Poland during the winters of 2000- 2010. Via transect counts method we showed the potential drivers of raptor abundance, and co-occurrence patterns. We analysed the influence of weather and habitat factors along on the single species abundance and diversity of the raptor assemblage. We found that higher temperatures corresponded with higher occurrence of the common buzzard Buteo buteo, rough-legged buzzard Buteo lagopus, Eurasian sparrowhawk Accipiter nisus, hen harrier Circus cyaneus and lower of the common kestrel Falco tinnunculus. When considering the effect of each habitat variable on the whole raptor assemblage, the relative proportion of urban areas to pasture had the most distinct effect on species abundance and diversity. Most of species were found to be less abundant in areas with a high proportion of urban areas, while some, like the Eurasian sparrowhawk and the northern goshawk Accipiter gentilis, occurred more often on such areas. We observed that the difference in the number of these species could be explained mainly by the different habitat requirements due to individual food preferences and flexibility of migration strategies

Trichomonosis in Eurasian sparrowhawks in the Czech Republic.

Pigeon, doves and songbirds are hosts of the parasite Trichomonas gallinae (Rivolta, 1878), which causes avian trichomonosis. Raptors are infected when they digest infected prey. A high percentage of the diet of Eurasian sparrowhawk Accipiter nisus (Linnaeus) is comprised of birds. During the breeding season 2012 and 2013, we clinically tested 298 nestling Eurasian sparrowhawks from urban and rural areas of the Czech Republic for the presence of trichomonads. Sparrowhawk nestlings in the urban area were more infected (32.9%) than in the rural area (12.2%) in 2012 (χ(2) = 6.184, P = 0.045). The number of infected nestlings dropped in the urban area (5.4%) and remained similar in the rural area (16.6%) in 2013. Sequences of ITS region and SSU rDNA confirmed that the isolates from infected sparrowhawk nestlings belonged to Trichomonas gallinae.

Advantage of specialism: reproductive output is related to prey choice in a small raptor.

Predatory species' usage of different prey types is affected by both prey availability and selectivity. The diet during the breeding season may affect the reproductive success of individual pairs. We studied the prey use of a small reversed size-dimorphic raptor, the Eurasian sparrowhawk Accipiter nisus, with respect to prey weight on two organizational levels. Using 13 years of data from southern Norway, we related reproductive output of individual breeding events to prey size taken. Further, we assessed the regional variation in prey usage between five Fennoscandian populations. This was done by fitting optimum-type functions to the prey species' numbers or relative predation risks. Pairs that successfully completed the season with more fledglings displayed less variation in prey size, suggesting a possible adaptive benefit of diet specialism, or possibly a correlative effect due to higher prey availability or lower female hunting effort. This finding contrasts with earlier raptor studies, which have suggested benefits of dietary (and hence nutritional) diversity. Indeed, our results might be limited to nutritionally substitutable prey items. We also found a tendency suggesting that older females raised more fledglings than 1-year-old females. In the population-level analysis, we found that optimum-type functions with constant width and spatially variable average best described the relationship between relative predation risk and log weight. This can reflect local conditions, such as prey availability. Our findings and new methodological tools could apply to a broader spectrum of predators. They also highlight the role of viewing usage or choice of prey at several spatial scales.

Intensity of Melanin-Based Color and Risk of Predation in the Barn SwallowHirundo rustica

Predators are supposed to exert strong selection pressures on their prey, especially when phenotypic traits such as secondary sexual characters promote mating success at the expense of costs in terms of natural selection. Signaling theory predicts that individuals of superior phenotypic quality will enjoy an advantage in term of mating success, but also in term of natural selection, if such individuals are in prime condition both before and after development of exaggerated secondary sexual characters. We tested this prediction in the Barn Swallow Hirundo rustica being preyed upon by the Eurasian Sparrowhawk Accipiter nisus, using extensive samples of feathers from prey and non-prey. We measured tail length and coloration of outermost tail feathers in the black area of the proximal and distal part of tail feathers, but also the white spot of the tail feathers. Prey had significantly less dark distal, but not proximal parts of their tails, while there was no difference in coloration of the white spot between prey and non-prey. Prey had significantly paler tail feathers than non-prey, especially among long-tailed individuals. These results suggest that Barn Swallows with long tails that fail to deposit large amounts of melanin in their tail feathers run an elevated risk of predation.