The diet of migrant Red Kites Milvus milvus during a Water Vole Arvicola terrestris outbreak in eastern France and the associated risk of secondary poisoning by the rodenticide bromadiolone

Poisoning by pesticides is considered one of the primary threats to the Red Kite Milvus milvus. We studied the diet of this raptor in an area of eastern France where the rodenticide bromadiolone is widely used to control Water Vole Arvicola terrestris outbreaks. A high degree of specialization for Water Voles was noted, as their remains were identified in all 119 pellets collected in autumn 2008, whereas other small rodent species and insects occurred in 27 and 9% of pellets, respectively. We estimated that Water Voles constituted 94% of the total biomass ingested by Red Kites under these conditions. Based on these data, the risk of secondary poisoning due to feeding on poisoned voles was assessed. Acute exposure on a single day was not considered a risk for Kites, but exposure to poisoned voles over 1 week represented the maximal risk for the Red Kite; the calculated dose of bromadiolone ingested by a Red Kite was 137 times higher than the toxicological benchmark for birds. A field survey in the studied area detected four dead Red Kites and one moribund bird in autumn 2008 but did not confirm that the cause of death was bromadiolone poisoning. We suggest that professional monitoring is needed to assess the impact of rodenticides on Red Kites in areas where voles are controlled.     

Wind conditions facilitate the seasonal water‐crossing behaviour of Oriental Honey‐buzzards Pernis ptilorhynchus over the East China Sea

Migratory raptors rarely fly over stretches of water larger than 25 km, although different species undertake water crossings of varying lengths, depending mainly on their wing morphology. Oriental Honey‐buzzards fly c. 680 km over the East China Sea in autumn from breeding areas in Japan to wintering areas in Southeast Asia, but avoid this long water crossing in spring. We investigated the effects of weather on this exceptional migratory behaviour and its seasonality through a maximum entropy niche modelling approach. We used data collected through satellite tracking of 31 adult birds as presence points and a set of variables related to wind, precipitation and convective condition as environmental predictors. Results of modelling showed very different, almost non‐overlapping, areas suitable for migration over the East China Sea region in autumn and spring. Suitable migration routes in autumn mostly occurred over the sea, whereas suitable areas for spring migration mostly occurred over land, suggesting that circumnavigating the East China Sea is preferable in spring. At the regional scale, wind conditions facilitate water‐crossing behaviour of Oriental Honey‐buzzards in autumn, but not in spring. Specifically, suitable tailwinds over the sea enable water‐crossing in autumn, whereas in spring, wind support and convective conditions are best over land. Our modelling did not suggest any importance of convective conditions for autumn migration. However, we expect that at smaller temporal scales, convective conditions would be a considerable facilitator of the water‐crossing behaviour in this species.     

Avian and Bat Fatality Rates at Old-Generation and Repowered Wind Turbines in California

ABSTRACT Wind turbines in the Altamont Pass Wind Resource Area (APWRA), California, USA, have caused annual fatalities of thousands of raptors and other birds. Alameda County implemented an Avian Protection Program requiring mitigation measures and eventual repowering to modern wind turbines, all intended to reduce raptor fatality rates 50% from levels estimated for 1998–2003. Two years into the 3-year program, we compared estimates of fatality rates between 1998–2003 and 2005–2007 and between a repowered wind project (Diablo Winds) and the APWRA's old-generation wind turbines. The APWRA-wide fatality rates increased significantly for multiple bird species, including 85% for all raptors and 51% for all birds. Fatality rates caused by the Diablo Winds repowering project were not lower than replaced turbines, but they were 54% and 66% lower for raptors and all birds, respectively, than those of concurrently operating old-generation turbines in 2005–2007. Because new-generation turbines can generate nearly 3 times the energy per megawatt of rated capacity compared to the APWRA's old turbines, repowering the APWRA could reduce mean annual fatality rates by 54% for raptors and 65% for all birds, while more than doubling annual wind-energy generation. Alternatively, the nameplate capacity of a repowered APWRA could be restricted to 209 megawatts to meet current energy generation (about 700 gigawatt-hr), thereby reducing mean annual fatalities by 83% for raptors and 87% for all birds. In lieu of repowering, bird fatalities could be reduced by enforcing operating permits and environmental laws and by the County requiring implementation of the Alameda County Scientific Review Committee's recommendations.     

Narrow sea crossings present major obstacles to migrating Griffon Vultures Gyps fulvus

The flight behaviour of Griffon Vultures Gyps fulvus was studied at a major migration bottleneck, the Strait of Gibraltar in southernmost Spain, during the autumns of 2004 to 2007. The 14‐km‐wide sea channel significantly impeded the southern migration of the species into Africa, with many birds attempting repeated passage for weeks before crossing, and others not crossing at all and overwintering in Southern Spain. Water‐crossing attempts were restricted to times between 11:00 and 14:00 h on days with light or variable winds, or on days with strong winds from the north or west. No crossing attempts were made on days with strong winds from the south or east. Vultures attempted to cross the Strait in large flocks and never attempted to do so alone. Although 29% of the birds soared during crossing attempts, at least until they flew beyond visible range of approximately 4 km, most engaged in considerable flapping flight when attempting to cross. Overall, birds flying over water flapped more than 10 times as frequently as those flying over land prior to crossing attempts. Vultures did not flap continuously, but intermittently in brief bouts of flapping interspersed with periods of gliding or soaring flight. The number of flaps per bout over water was significantly greater than the number of flaps per bout over land. Vultures flying over water that flapped at rates of 20 flaps or more per minute typically aborted attempted crossings and returned to Spain in intermittent flapping and gliding flight. There are numerous reports of Vultures falling into the Strait and drowning while attempting to cross, as well as reports of returning Vultures collapsing on the beach having reached Spain in spring ( Barrios Partida 2006 ). Our observations indicate that passage of Griffon Vultures at the Strait of Gibraltar is limited by the species’ over‐water flapping‐flight abilities, including its inability to flap continuously for even short periods of time. We suggest that even relatively short sea crossings represent significant obstacles to migrating Vultures and discuss the implications of this limitation on the distribution and abundance of the species.     

Evolution of prey holding behaviour and large male body size in Ninox owls (Strigidae)

The hawk owl genus Ninox is unique among raptorial birds in that it includes three species in which males are substantially larger than females. This is a reversal of the normal pattern observed in both diurnal and nocturnal raptorial birds in which females are larger. Interestingly, these three Ninox species also are both the largest of the 22 species in the genus and the only species that exhibit the striking behaviour of ‘prey holding’ in which large (> 600 g) mammalian or avian prey is captured at night and held with body parts intact, and draped below a roost for the entire day without being consumed. Because explanations of the evolution of large male size suggest that it results from competition among males, the adaptive significance of prey holding was studied in a wild population of powerful owl Ninox strenua. Prey holding is largely confined to breeding males and its occurrence varies significantly across the breeding cycle, being most frequent during incubation and brooding. The study did not clearly resolve whether prey holding is a form of food storage or territorial display; however, both functions can select for large male body size and therefore play a significant role in the evolution of nonreversed size dimorphism. Although female‐only incubation and brooding is typical of Ninox owls and other owl species, prey holding appears to occur only in the large Ninox species because of the unique combination of large body size, large prey size, separate sex roles, and obligate cavity nesting. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 284–292.     

Preen oil chemical composition encodes individuality,seasonal variation and kinship in black kites Milvus migrans

Evidence that bird odour can encode social information that can be used in chemical communication is growing, but is restricted to a few taxonomic groups. Among birds, diurnal raptors (i.e. birds from the Accipitriformes and Falconiformes order) have always been considered as mainly relying on their visual abilities. Although they seem to have a functional sense of smell, whether their odour can convey social information has yet to be determined. Combining gas‐chromatography‐mass‐spectrometry (GCMS) and microsatellite data, we tested whether chemical compounds from preen gland secretions can encode sex, age, individuality, seasonal differences and genetic relatedness in the gregarious accipitriform black kite Milvus migrans. While no differences in preen oil composition were found between age classes, an individual signature was detected. While a seasonal variation was found in both sexes, compounds differ between sexes in the non‐breeding season. Finally, a significant correlation between chemical proximity and genetic proximity was detected in male–male dyads and male–female dyads but not in female–female dyads. Our study provides the first evidence in raptors that preen secretion can convey information that may potentially be used in individual recognition, reproductive synchronization and inbreeding avoidance, and suggests that raptors may rely upon their olfactory abilities more than previously thought. This study opens promising avenues for further studies in raptor chemical communication.     

Comparative breeding performance of Marsh Harriers Circus aeruginosus along a gradient of land‐use intensification and implications for population management

Assessing variation in breeding performance in relation to habitat characteristics may provide insights into predicting the consequences of land‐use change on species ecology and population dynamics. We compared four Marsh Harrier Circus aeruginosus populations subject to similar environmental conditions, but which differed in habitat composition, ranging from natural habitats to intensively cultivated areas. Using a 6‐year dataset, we characterized breeding habitat and diet in these four study sites, and analysed breeding performance in relation to this gradient of land‐use intensification. There was minimal variation in breeding performance between study years but consistent variation between study sites. Unexpectedly, Marsh Harriers breeding in intensively cultivated habitats had higher reproductive success than those breeding in more natural habitats, which, however, hosted higher breeding densities, so overall net population productivity (fledglings per unit area) was similar across sites. This resulted from combined effects of density‐dependence and different predation rates between study sites. The colonization of intensive farmland habitats may not necessarily impact negatively on population sustainability when breeding success and population density are traded against each other. However, our findings should not mask longer‐term conservation issues for populations breeding in these intensively managed areas, and further studies should assess potential long‐term negative effects of occupancy of human‐altered habitat.     

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.     

Turnover and post‐bottleneck genetic structure in a recovering population of Peregrine Falcons Falco peregrinus

Dispersal is a process that increases genetic diversity and genetic connectivity of populations. We studied the turnover rate of breeding adults and genetic population structure to estimate dispersal in Peregrine Falcons in Finland. We used relatedness estimates among Finnish Peregrine Falcons over a 5‐year period, genotyping over 500 nestlings with 10 microsatellite loci to reveal the rate of turnover. Our results reveal a high turnover rate (21.7%) that does not seem to be correlated with the breeding success of the previous year. The extent of population genetic structure and diversity, and possible signs of the population crash during the 1970s, was assessed with a reduced dataset, excluding relatives. We found genetic diversity to be similar to previously studied falcon populations (expected heterozygosity of 0.581) and no population genetic structuring among our sampled populations. We did not find a genetic imprint of the past population bottleneck that the Finnish Peregrine population experienced. We conclude that high dispersal rates are likely to have contributed to maintaining genetic diversity across the landscape, by mixing individuals within the species’ distribution in Finland and thus preventing genetic structuring and negative effects associated with the population decline in the 1970s.