The diet of the Sea Eagle Haliaeetus albicilla and Golden Eagle Aquila chrysaetos in western Scotland

The diets of Sea Eagles Haliaeetus albicilla and Golden Eagles Aquila chrysaetos living sympatrically in western Scotland were studied using pellets and prey remains collected at roosts and nest sites throughout the year. Both species showed changes in diet between winter and summer, and there were differences between species in both seasons. As a rule, Sea Eagles took proportionately more seabirds, waterfowl (ducks and waders) and fish, whilst Golden Eagles took proportionately more rabbits and hares. Sea Eagles had a broader diet than Golden Eagles but a measure of dietary overlap based on taxonomic composition indicated an overlap of more than 90% between the two species.     

Temporal changes in prey composition and biomass delivery to African Crowned Eagle nestlings in urban areas of KwaZulu-Natal,South Africa

Globally urban areas are expanding rapidly and this usually has negative effects on biodiversity. Despite this, some species manage to persist in urban areas, as is the case with African Crowned Eagles Stephanoaetus coronatus in KwaZulu-Natal, South Africa. As relatively little is known about African Crowned Eagle nestling diet, especially about how it changes with nestling age, we investigated this with nest camera-traps. We analysed temporal changes in prey composition and biomass delivery during the nestling stage. We also recorded which adults provisioned and attended the nest. The main prey fed to nestlings were Rock Hyrax Procavia capensis and Hadeda Ibis Bostrychia hagedash. Adult males did most of the food provisioning, especially at the start of the nestling period. We found a decrease in total prey number and biomass with nestling age. This may be caused by changing requirements of nestlings. Furthermore, delivering fewer prey at later nestling stages may be a facilitating mechanism to enhance fledging of the nestling. Although the total number of prey brought to the nest decreased, we found an increase in numbers of Vervet Monkey Chlorocebus pygerythrus in the diet with nestling age. This indicated an increase in larger prey being delivered to the nests as the nestling aged. We suggest that this could be caused by increased participation in hunting by the larger female as her nest attendance time decreased as the nestling aged. We conclude with emphasising the importance of protecting the Durban Metropolitan Open Space System (D’MOSS) zones for the persistence of this Near Threatened raptor species, and populations of its prey in urban areas for its breeding success.     

Ecological and environmental correlates of territory occupancy and breeding performance of migratory Golden Eagles Aquila chrysaetos in interior Alaska

Understanding relationships between environmental conditions and reproductive parameters is important when interpreting variation in animal population size. The northwestern North American population of Golden Eagles Aquila chrysaetos canadensis initiates courtship and nesting in early spring when prey diversity is low and weather conditions are severe. Snowshoe Hare Lepus americanus and Willow Ptarmigan Lagopus lagopus, the primary prey of Golden Eagles early in their nesting season in interior Alaska, both exhibit cyclical fluctuations in abundance, providing the opportunity to investigate such relationships. We used Bayesian hierarchical models to explore variation in territory occupancy, nesting rates, nesting success and productivity of Golden Eagles from 1988 to 2010 in Denali National Park and Preserve, Alaska, in relation to annual and site‐specific parameters including prey abundance, weather conditions, elevation and human activity. We also investigated the long‐term fluctuations of breeding performance over the course of the study. The abundance of Hares influenced both the number of Eagles that laid eggs and the number of Eagles that produced fledglings. The conditions on the breeding ground did not explain observed declines in nesting rates and fledgling production, suggesting that other factors such as change in the age structure of the population, increased intraspecific competition or deterioration of migration and wintering habitat are driving the long‐term trends of these parameters.     

Activity patterns of parent Great Tits Parus major feeding their young during rainfall

The influence of rainfall on the foraging patterns of Great Tit Parus major parents while feeding chicks at the nest was investigated using automated nest monitoring with electronic balances and photography. Great Tit females significantly reduced their visit rate to the nest during all rain intensities, while male feeding frequency did not significantly change. The female response was probably due to increased brooding requirements of young since the reduction in visit rate was most apparent at early nestling stages. At this time the chicks are incapable of thermoregulation and females significantly increased their nestbox occupancy time during rain. There was no indication that parents were compensating for periods of female inactivity during rainfall: there was no significant increase in visit rate following rainfall and no significant increase in prey size delivered to the nest during periods of rain. An analysis of data from six consecutive years revealed that the proportion of wet hours within the first week of the nestling period significantly influenced fledging weight in this species.     

Breeding behaviour and time-activity budgets of Bonelli’s Eagles Aquila fasciata: marked sexual differences in parental activities

ABSTRACT

Capsule: Differences in parental investment between sexes and stage of the breeding period were found in Bonelli’s Eagles Aquila fasciata.

Aims: To describe the sexual differences in parental behaviour of Bonelli’s Eagles and to assess the sex-specific pattern of variation in parental investment in relation to the breeding period.

Methods: Between 2006 and 2016, we monitored the parental behaviour of 11 pairs of Bonelli’s Eagles during the incubation and chick-rearing periods in southeastern Spain. Observations were made using 20–60× telescopes from points overlooking the territory at a distance of about 500–800?m from the nest.

Results: Our results reveal a marked division in parental duties in Bonelli’s Eagles. Females invested more effort in incubation, nest attendance, chick feeding and nest-building, while males contributed more to food provisioning. Nest attendance and feeding by females decreased with time, and both parents adjusted their provisioning effort in relation to nestling age. Most changeovers took place during the middle of the day, when male provisioning rates and temperatures reach their maximum.

Conclusion: Intersexual differences are discussed in the context of the prey capture difficulty hypothesis, which proposes that intra-pair prey differences, due to large sexual size dimorphism, should be particularly advantageous among raptors that pursue agile prey.     

Prey of White-throated Hawks (Buteo albigula) in the southern temperate forest of Argentina

ABSTRACT.   We examined the diet of White-throated Hawks ( Buteo albigula ) during the incubation and nestling periods in the southern temperate forest of Argentina. Pellets ( N = 74) and prey remains ( N = 59) were collected at 10 nests from 1998 to 2003, and preys delivered to two nests were monitored during the 2001–2002 breeding seasons. White-throated Hawks fed on small mammals, birds, lizards, and insects. The three methods of identifying prey (pellets, prey remains, and direct observation) produced different results. All types of prey except large birds were detected in pellets, and arthropods may have been over-represented in pellets due to secondary consumption. No remains of either arthropods or reptiles were identified among prey remains collected at nest sites and, during nest observations, we were unable to identify many of the prey items delivered by adults. Our results indicate that accurate determination of the diet of White-throated Hawks requires more than one method of identifying prey.     

Predation risk of eggs and nestlings relative to nest‐site characteristics of the Bull‐headed Shrike Lanius bucephalus

Appropriate nest‐site selection is one of the most important ways to minimize loss of reproductive investment due to predation. We determined the environmental characteristics associated with nest predation during the incubation and nestling periods of arboreal nesting Bull‐headed Shrikes on the oceanic Minami‐Daito Island where the predator community has low species diversity and includes only three introduced mammals: Ship Rat Rattus rattus, Japanese Weasel Mustela itatsi and Feral Cat Felis catus. Egg predation declined with increasing grassland cover around nests, whereas nestling predation declined with increasing nest concealment and nest height. Our results suggest that effective nest‐site characteristics for avoiding nest predation differ during the incubation and nestling periods and are dependent on the predator species and their search strategies, at least in habitats with low predator species diversity.     

Nocturnal nest predation: a potential obstacle to recovery of a Florida Scrub-Jay population

ABSTRACT.   Population declines among birds are often linked to habitat change and associated increases in nest predation rates. In species of conservation concern identifying nest predators is an important first step in developing management strategies to mitigate low nesting success caused by depredation. Because predator composition varies geographically and with landscape factors habitat restoration may need to be tailored to reduce locally important predators. We used miniature video cameras to identify nest predators in a population of Florida Scrub-Jays ( Aphelocoma coerulescens ) significant to conservation. At 22 nests we observed 25 predation events; 22 (88%) of these events were nocturnal. Yellow rat snakes ( Elaphe obsoleta ) had the highest daily predation rate and accounted for 76% of egg and nestling losses. Florida Scrub-Jays are vulnerable to nocturnal nest predation because their vigilance behavior is ineffective against nocturnal predators, breeders cannot defend against nocturnal predators, and brooding females are at risk of being killed by nocturnal predators. If current habitat restoration efforts do not reduce numbers of yellow rat snakes and improve scrub-jay nesting success, management actions to reduce populations of nocturnal snakes may need to be considered.     

The diurnal Afro-alpine raptor community of the Ethiopian Bale Highlands

Clouet, M, Barrau, C & Gar, J-L. 2000. The diurnal Afro-alpine raptor community of the Ethiopian Bale Highlands. Ostrich 71(3&4): 380-384. The diurnal raptor community of the Afro-alpine level of the Bale Highlands (i.e. 3500-4000 m a.s.l.) Ethiopia was observed during eight expeditions spread over five consecutive years. Among the 25 species recorded, nine are residents, including three which nest at lower altitudes. Small mammal hunters are the most numeraus species, including a unique assemblage of various Aquila species, among which the Golden Eogle Aquila chrysaetos is the outstanding feature. Population densities are high for Golden Eagle and Verreaux's Eagle, Aquila verreauxii, Tawny and Steppe Eagles, Aquila rapox and A. niplensis, Augur Buzzard, Buteo augur and Lanner Falcon, Falco biarmicus. This is related to the abundance of prey, mainly hyraxes, hares and rodents. For the largest species, the start of breeding coincides with the onset of the dry season (Navember). The period with the largest number of young raptors on the nest (February-March) corresponds to the peak in the prey papulation. Migrants and Palaearctic winter visitors are present at the same time and use the same faad resources as the breeders. The main factors isolating closely related species are diet for the Golden and Verreaux's Eagles and the period of habitat use for the Tawny and Steppe Eagles.     

Bill harnesses on nestling Tufted Puffins influence adult provisioning behavior

ABSTRACT.   For burrow-nesting seabirds, investigators have examined nestling diet by attaching harnesses to the bills of nestlings to intercept food delivered by the parent. To determine whether this method provides an unbiased estimate of nestling diet, we evaluated its effect on the provisioning behavior of Tufted Puffins ( Fratercula cirrhata ) nesting on Triangle Island, British Columbia. Adults delivering food to nestlings with bill harnesses always hesitated before entering a burrow with food, increasing their susceptibility to kleptoparasitism by gulls, and did not always leave the food intended for the nestling. These responses by adult puffins could lead to underestimates of energy intake rates of nestlings and unreliable comparisons with other species if prey left by adults in nest burrows were the only source of data. We also compared estimates of the species, number, and size of prey delivered by adult puffins as determined by direct observation from blinds to samples of prey collected directly from nest burrows and found that the two sampling techniques produced similar results. However, identifying rare prey species and gathering precise information about prey length, mass, and condition require collection of prey, and we recommend using a combination of techniques to obtain the most reliable estimates of nestling diet.     

Comparative nest habitat characteristics of sympatric White‐tailed Haliaeetus albicilla and Golden Eagles Aquila chrysaetos in western Scotland

Capsule Golden and White‐tailed Eagles selected different habitats for nesting.

Aim To investigate differences in nesting habitat used by sympatrically breeding eagles in western Scotland, following reintroduction of White‐tailed Eagles from 1975 onwards.

Methods Nest‐site locations from national surveys in 2003–05 were entered into a geographical information system (GIS) in order to measure a set of geographic parameters for each nest site. Binary logistic regression with backwards deletion of non‐significant terms was used to derive minimum adequate models at two spatial scales of the likelihood of an eagle nest belonging to one species or the other. We compared changes in occupancy between 1992 and 2003 of Golden Eagle territories inside and outside a GIS model of potential White‐tailed Eagle habitat and according to proximity to White‐tailed Eagle nests.

Results White‐tailed Eagles nested at lower altitudes than Golden Eagles, in more wooded habitats with more open water close by, tending to nest in trees where these were present. There were 3359 km² of potential White‐tailed Eagle nesting habitat within 25 km of existing White‐tailed Eagle nests, containing 54 Golden Eagle territory centres, but we found no difference in change of occupancy for Golden Eagle territories close to White‐tailed Eagles compared with those further away.

Conclusion White‐tailed and Golden Eagles appear to partition nesting habitat in the west of Scotland by altitude. This corresponds with behaviour in western Norway and with the situation described in historical accounts of nest‐sites in western Scotland prior to extinction of White‐tailed Eagles. It is also consistent with recent studies showing little overlap in breeding season diet of Golden and White‐tailed Eagles in western Scotland, and likely partitioning of foraging habitat by altitude. We conclude that the likelihood of competitive exclusion is less than previously suggested.     

Diet of Montagu's Harrier Circus pygargus in central Spain: analysis of temporal and geographic variation

The diet of Montagu's Harrier Circus pygargus was studied for 4 years near Madrid, Spain, with the use of pellets and prey remains collected during the breeding season. The diet of the study birds included a wide variety of prey categories, the most important one by weight being lagomorphs (mainly Hares Lepus granatensis ). The diet varied seasonally, with Hares predominating early in the breeding season, while birds increased in importance later. The shift was partly a result of variation in availability (with fledgling birds being more abundant late in the season), but statistical analysis suggested that lagomorphs and then birds were actively chosen in the prelaying and nestling periods, respectively. Montagu's Harrier seemed to be an opportunistic species, hunting a wider range of prey types in more southern latitudes, but specialized in each region in the prey species that was most profitable. This was the only study on Montagu's Harriers to date which found lagomorphs to be the most important part of the diet throughout the season.     

First nest descriptions,nesting biology and food habits for Bernier's Vanga,Oriolia bernieri,in Madagascar

Four nests of the rare and endemic Bernier's Vanga, Oriolia bernieri, were discovered; one in 1997, one in 1998, and two in 1999 on the Masoala Peninsula, northeastern Madagascar. At the 1998 nest, the female made 189 visits with 186 deliveries of nesting material during 34.6 h of observation. The female spent 9.2% (194.2 min) of the observation time building the nest while an immature male delivered nest material six times and spent 3.2 min at the nest placing the material. Nesting material included: 67.2% (125) decomposed root material, 24.7% (46) palm fibres, 6.5% (12) dry leaves, 1.1% (2) moss, and 0.5% (1) white plant dawn. In 41.0 h of observation during the incubation period the female incubated for 53% (21.7 h) of the time, the adult male for 32.3% (13.2 h), the immature male for 4.3% (1.8 h), and the nest was unattended for 10.4% (4.3 h). This breeding attempt foiled on day 13 of incubation when a Madagascar Harrier-Hawk, Polyboroides radiatus, ate the egg(s). At one of the 1999 nests, the incubation and nestling periods were 17 days each. Three young fledged during the middle of November. Of the 82 identified prey items recorded during the nestling period, 91% were invertebrates and 9% vertebrates. Spiders, crickets, cockroaches, and geckos represented the most numerous prey taken, totaling 77% of the identified prey.     

Live blind snakes (Leptotyphlops dulcis) in eastern screech owl (Otus asio) nests: a novel commensalism

Summary Eastern screech owls bring live blind snakes to their nestlings, whereas all other prey are delivered dead. Some of the snakes are eaten but most live in nest debris, where they eat soft-bodied insect larvae from the decomposer community in fecal matter, pellets, and uneaten prey. Consumption of larvae may reduce larval parasitism on owl nestlings or larval competition with nestlings for food stored in the nest, because nestlings with live-in blind snakes grow faster and experience lower mortality than same-season broods lacking snakes. We propose a commensalistic association in which the screech owl benefits reproductively and the live-in blind snake is not affected.     

Community reorganization revealed by exploring shifts in the diet of an apex predator,the Golden Eagle Aquila chrysaetos,with stable isotopes and prey remains

Golden Eagles Aquila chrysaetos colonized the northern California Channel Islands, an archipelago located off the coast of southern California, USA, in the early 1990s, owing in part to the presence of Feral Pigs Sus scrofa. Eagles preyed on piglets and on the endemic Island Fox Urocyon littoralis, driving three endemic subspecies of the Island Fox (U. l. santacruzae, U. l. santarosae and U. l. littoralis) toward extirpation. Using stable isotopes (δ¹³C and δ¹⁵N) measured from feathers and blood of Golden Eagles and from meat and bone of their prey, along with the proportion of prey consumed estimated from nest excavations as informative priors, we show that shifts in Eagle isotopic signatures tracked community reorganization: when pigs and foxes were abundant, Eagles consumed them in higher proportions than other prey; when foxes became scarce owing to Eagle predation, Eagle diet shifted toward pigs, but also diversified to include Common Ravens Corvus corax and seabirds (Larus spp. and Phalacrocorax spp.); and finally, after pigs were eradicated and 35 Golden Eagles had been captured and removed from Santa Cruz Island, a lone remaining pair of Eagles reversed their diet to include more foxes. Our findings reveal that shifts in stable isotope signatures from tissues of an apex predator can be used as a general proxy to monitor changes in the prey community; however, if sample sizes are small, informative priors are both essential and overwhelmingly influential, and changes in abundance of preferred prey may mask or fail to reveal changes in less preferred prey. Given that apex predators are at the top of trophic hierarchies, that they are often important drivers of community structure and that they sample prey continuously from their community, isotopic signatures of their tissues may be useful for monitoring community change.     

Snake predation on North American bird nests: culprits,patterns and future directions

Predation is the leading cause of nest failure for most birds. Thus, for ornithologists interested in the causes and consequences of variation in nest success, knowing the identity and understanding the behavior of dominant nest predators is likely to be important. Video documentation of nests has shown that snakes are frequent predators. Here we reviewed 53 North American studies that used nest cameras and used these data to identify broad patterns in snake predation. Snakes accounted for 26% (range: 0–90%) of recorded predation events, with values exceeding 35% in a third of studies. Snakes were more frequent nest predators at lower latitudes and less frequent in forested habitat relative to other nest predators. Although 12 species of snakes have been identified as nest predators, ratsnakes Elaphe obsoleta, corn snakes E. guttata and fox snakes E. vulpina were the most frequent, accounting for > 70% of all recorded nest predation events by snakes and have been documented preying on nests in 30–65% of studies conducted within their geographic ranges. Endotherm‐specialist snakes (Elaphe and Pituophis genera) were more likely to depredate nests in forests and the canopy relative to other snakes, due to their affinity for edge habitat. Predation by only ratsnakes and corn snakes was predominantly nocturnal and only ratsnakes were more likely to prey on nests during the nestling stage. Snakes were not identified to species in over 30% of predation events, underlining the need for more complete reporting of results. A review of research to date suggests the best approach to investigating factors that bring snakes and nests into contact involves combining nesting studies with radio tracking of locally important snake nest predators.     

Understanding avian nest predation: why ornithologists should study snakes

Despite the overriding importance of nest predation for most birds, our understanding of the relationship between birds and their nest predators has been developed largely without reliable information on the identity of the predators. Miniature video cameras placed at nests are changing that situation and in six of eight recent studies of New World passerine birds, snakes were the most important nest predators. Several areas of research stand to gain important insights from understanding more about the snakes that prey on birds' nests. Birds nesting in fragmented habitats often experience increased nest predation. Snakes could be attracted to habitat edges because they are thermally superior habitats, coincidentally increasing predation, or snakes could be attracted directly by greater prey abundance in edges. Birds might reduce predation risk from snakes by nesting in locations inaccessible to snakes or in locations that are thermally inhospitable to snakes, although potentially at some cost to themselves or their young. Nesting birds should also modify their behavior to reduce exposure to visually orienting snakes. Ornithologists incorporating snakes into their ecological or conservation research need to be aware of practical considerations, including sampling difficulties and logistical challenges associated with quantifying snake habitat use.     

Snake activity affects seasonal variation in nest predation risk for birds

Variation in predator behavior has been proposed, but not tested, as a mechanism producing seasonal declines in avian nest success. We test this hypothesis by documenting seasonal activity of Texas ratsnakes Elaphe obsoleta and nest failure of endangered black-capped vireos Vireo atricapilla and golden-cheeked warblers Dendroica chrysoparia on which the snakes prey. Nest survival analysis was based on 880 vireo and 228 warbler nests and 3,060 snake locations from 62 radio-tracked snakes. Although nest success varied with snake activity for both birds, specific patterns differed substantially. Vireo daily nest survival was negatively correlated with snake activity over the three-year study, despite substantial variation among years in weather, and the fact that these birds are almost certainly a minor prey species of the ratsnakes. Warblers exhibited less clear-cut seasonal variation in nest success, and the association between nest success and snake activity was less pronounced than for vireos. Increased activity at warmer temperatures explained some of the seasonal change in snake movements, although mating may have accounted for a mid-season peak in activity. These results indicate that variation in predator behavior can be associated with and potentially cause seasonal changes in nest success, but also that these relationships are species specific even within the same community and may depend on aspects of the nesting ecology of the prey such as nest site selection.     

18S rRNA metabarcoding diet analysis of a predatory fish community across seasonal changes in prey availability

Predator–prey relationships are important ecological interactions, affecting biotic community composition and energy flow through a system, and are of interest to ecologists and managers. Morphological diet analysis has been the primary method used to quantify the diets of predators, but emerging molecular techniques using genetic data can provide more accurate estimates of relative diet composition. This study used sequences from the 18S V9 rRNA barcoding region to identify prey items in the gastrointestinal (GI) tracts of predatory fishes. Predator GI samples were taken from the Black River, Cheboygan Co., MI, USA (n = 367 samples, 12 predator species) during periods of high prey availability, including the larval stage of regionally threatened lake sturgeon (Acipenser fulvescens Rafinesque 1817) in late May/early June of 2015 and of relatively lower prey availability in early July of 2015. DNA was extracted and sequenced from 355 samples (96.7%), and prey DNA was identified in 286 of the 355 samples (80.6%). Prey were grouped into 33 ecologically significant taxonomic groups based on the lowest taxonomic level sequences that could be identified using sequences available on GenBank. Changes in the makeup of diet composition, dietary overlap, and predator preference were analyzed comparing the periods of high and low prey abundance. Some predator species exhibited significant seasonal changes in diet composition. Dietary overlap was slightly but significantly higher during the period of high prey abundance; however, there was little change in predator preference. This suggests that change in prey availability was the driving factor in changing predator diet composition and dietary overlap. This study demonstrates the utility of molecular diet analysis and how temporal variability in community composition adds complexity to predator–prey interactions.     

Biases in Studying the Diet of the Bearded Vulture

Abstract: We compared methods of assessing the diet of the bearded vulture (Gypaetus barbatus) during the nestling period in the Pyrenees, northeast Spain. We determined diet from direct observations of food items delivered to the nest, recent prey remains present in the nest, remains collected in the nests after fledging, and remains collected in the ossuaries (bone-breaking sites). Data suggest that direct observation (food items delivered and recent prey remains present in the nest) is the only valid method of assessing the bearded vulture's diet accurately. Remains overestimated the presence of large mammals, such as cows (Bos taurus) and horses (Equus caballus), Suidae, and birds; delivered samples contained a higher proportion of small mammals, medium-sized mammals, micromammals, and reptiles. Ossuaries also differed from delivered samples because remains collected there overestimated large and medium-sized mammals. Concerning the skeletal parts, ossuaries, compared to all other methods, underestimated extremities and overestimated long bones, such as femur, humeri and tibiae, scapulae, vertebrae, and skulls. Remains samples, which overestimated scapulae, also differed from delivered and present samples. Our results suggest that bearded vultures favor extremities of prey (78% of the mammal remains, which make up 95% of the diet). The prevalence of small carcasses (almost 17%) suggests that vultures select small animals for food for the young. Because food quality may influence breeding success, future conservation projects based on the selective provision of food to breeding pairs should add to food stations meat remains and small carcasses consistent with our assessment of the birds’ dietary needs.