Structure and heterogeneity of habitat determine diet of predators despite prey abundance:Similar response in Long-eared,Short-eared Owls and Common Kestrels

According to one of the theses of optimal foraging theory,main prey species abundance in the hunting area is the main factor determining the diet and habitat choices of birds of prey.However other factors can also be important.The habitat structure influences the predators’diets as well.In this study we examined the influence of habitat structure on diet compositions of three species of birds:Long-eared Owl(Asio otus),Short-eared Owl(A.flammeus)and Common Kestrel(Falco tinnunculus).The study was carried out from 2007 to 2019 in a 48 km2area of the Crane’s Homeland Reserve,Moscow Region,Russia.The habitat structures of model species’hunting territories(ratio of different types of landscape elements)were classified in module"Semi-Automatic Classification Plugin"based on the QGIS.A boosted regression tree analysis identified that the share of the main prey species in the diet is primarily determined by the landscape structure of hunting territories.The largest share of Common Vole(Microtus arvalis)in birds’diet was determined by the shrubs area(15%of hunting area),the meadow area(75%),the habitat heterogeneity(70%)and the arable land area(5%).The same predictors determined the largest share of Root Vole(Microtus oeconomus):the shrubs area 25%,the meadow area 70%,and the arable land area 3%.The annual mean abundance of prey species did not determine their importance in the diet of birds of prey.Thus,the main prey abundance in the hunting area is not a determining factor for the formation of diet composition of birds of prey.

Myological variation in the hindlimb of three raptorial birds in relation to foraging behavior

Raptors share a common predatory lifestyle,but are different in food preferences and hunting behavior.The grip force and talons’grasping capabilities are fundamentally crucial for subduing and killing their prey to feed,but the abilities and differences to generate force are less known.In this study,the entire pelvic muscles were dissected with the muscle mass and fibre length measured and physiological cross-sectional area counted in the Common Kestrel(Falco tinnunculus),Eurasian Sparrowhawk(Accipiter nisus),and Long-eared Owl(Asio otus).Statistical tests were performed to explore the possible differences in architectural parameters among species.These species were same in distributing the greatest proportion of muscle mass to the shank region and the digital flexor functional group,allocating more than 60%muscle mass in relation to total single leg muscle mass to the same seven individual muscles including flexor digitorum longus(FDL),flexor hallucis longus(FHL),and tibialis cranialis(TC)which are three major muscles responsible for talon closure.Interspecies differentiations were most present in the shank and tarsus instead of other regions of the leg,which might reflect their difference in hunting mode and foot use.Greater force-generation capacity of FHL and some anatomical features suggest that digits 1and 2 work together as an efficiently vise-like set,playing more critical role than digits 3–4 in foraging of diurnal raptors but to a different degree.In accordance with zygodactyl foot morphology,each digit of the Long-eared Owl plays a subequal role when hunting,evidenced by anatomical and architectural features.Because of its unique insertion to the base of the pygostyle,the striking numerical difference in the development of M.caudofemoralis was possibly related to raptors’flight behavior and feeding ecology.Concluded from anatomical and architectural aspects,the similarities and differences of the hindlimb musculature were correlated to common predatory lifestyle and different foraging behaviors in three raptor species.These results illustrated the underlying myological basis for the functional capacities of the leg muscles and may provide additional information useful in further biomechanical investigation and computer simulation.

Home range variability and philopatry in Cinereous vultures(Aegypius monachus)breeding in Iberia

Large scavengers are strongly dependent on environmental conditions and carrion distribution and abundance,so season and breeding-related factors may influence the spatial ecology of species such as the Cinereous Vulture(Aegypius monachus),the largest European raptor.Iberia holds one of the biggest populations worldwide,but some aspects of the spatial ecology of the species in this region remain unknown.In this study,17 adult Cinereous Vultures were GPS-tracked in order to study their spatial ecology during the adult phase.The average monthly home ranges(95%Kernel Density Estimation,KDE)and core areas(50%KDE)were 6543±19,935 km^(2)and 1174±4004 km^(2),respectively.The average monthly home range fidelity ranged between 50 and 73%.Differences in movement-related variables between the seasonal periods(incubation,chick-rearing and non-breeding)were found.During the chick-rearing period,the monthly accumulated distance was higher than during the other periods:3316±1108(chick-rearing)vs.1621±622(incubation)vs.1726±1159 km per month(nonbreeding).Additionally,large home range sizes were more frequent during the chick-rearing period.There are two likely causes for these seasonal differences.Firstly,chick-rearing entails a higher energetic expenditure by the parental individuals in foraging activities,so larger movements and foraging areas are expected during this period.Secondly,the flight is favoured during spring and summer due to environmental conditions.Matching chick-rearing and warm months is a great evolutionary advantage for soaring-gliding raptors,as it allows them to cover larger areas with low energy expenditure.Furthermore,six individuals tagged as nestlings highlight the philopatric behaviour of the species:vultures settle their breeding areas 54±51 km from their natal nest(range=9–138 km).

Delayed juvenile behavioral development and prolonged dependence are adaptations to desert life in the grey falcon

Rapid learning in the young of most endothermic animals can be expected to be favored by natural selection because early independence reduces the period of vulnerability.Cases of comparatively slow juvenile development continue,therefore,to attract scientific attention.In most species of birds,including raptors,the young depend on their parents for some time after fledging for the provisioning of food and for protection while they learn to become nutritionally and otherwise independent.Among raptors,post-fledging dependence periods that exceed 6 months are exclusive to the largest species and these have reproductive cycles that exceed 12 months.By contrast,young of the medium-sized grey falcon Falco hypoleucos have been reported in close company with their parents up to 12 months after fledging,that is,at a time when the adults are expected to breed again.We investigated the occurrence and characteristics of prolonged adult–juvenile association relative to other falcons and similar-sized raptors.We found that the behavioral development of grey falcon young is extremely delayed,and that they even depend nutritionally on their parents for up to 12 months after fledging.We suggest that these 2 distinctive features are,ultimately,adaptations of the grey falcon to its extreme environment,Australia’s arid and semi-arid zone,one of the hottest environments in the world.