PREY OF GIANT EAGLE OWLS IN THE DE HOOP NATURE RESERVE,CAPE PROVINCE,AND SOME OBSERVATIONS ON HUNTING STRATEGY

Avery, G., Robertson, A. S., Palmer, N.G. & Prins, A. J. 1985. Prey of Giant Eagle Owls in the De Hoop Nature Reserve, Cape Province, and some observations on hunting strategy. Ostrich 56: 117–122.

Prey remains of Giant Eagle Owls Bubo lacteus in the De Hoop Nature Reserve were analysed in terms of numerical composition and mass. Thirteen species of bird contributed 57,8 % of the mass, six species of mammal 41,4 %, four species of invertebrate less than 0,4 % and one species of amphibian 0;4% Black-headed Heron Ardea melanocephala was the most common bird representing 14,8 % of the mass. Accipitridae (buzzards and harriers) and Tytonidae (owls represented 10,1 % of the mass. Leporidae (hares) were the most common mammals represented 10,7% of the mass. A single bone of an adult Grysbok Raphicerus melanoris represented 20,1% of the mass and was almost certanly taken as carrion. Similarities with diet data from other areas are apparent. The Giant Eagle Owl is omnivorous, its diet being determined bayrhabitat and local abundance. Comparison with the diet of Cape Eagle Owl Bubo capensis confirms that separation of habitats, with associated differences in the accessibility and availability of prey, explains the differences in prey taken by these species.     

乌鲁木齐市区越冬期长耳鸮的食性分析

2009～2011年间,利用食团分析法对乌鲁木齐市越冬长耳鸮(Asio otus)的食性进行分析。3年累计收集长耳鸮食团683份,辨认出1 132只猎物。分析结果表明,长耳鸮在冬季共捕食小型哺乳类6种,鸟类2种。小家鼠(Mus musculus)是最常见的食物,占总捕食量的53.45%。小型哺乳类是长耳鸮的主要食物,它在食物组成中出现的总频率为88.16%,以生物量计,小型哺乳类占食物构成的95.13%。长耳鸮的食物组成年度间差异显著,与当地猎物资源多样性和可获得性密切相关,表明长耳鸮可能采用机会主义者的捕食策略。     

Extirpation of alternative prey during a small rodent crash

Summary We document two episodes, in different years, of Barn Owls (Tyto alba) preying on a winter population of Burrowing Owls (Athene cunicularia) on a southern California island. The predation in each case followed a marked shift in the diet of the Barn Owls, due to the cyclic decline of their normal small mammal prey. Heavy predation in the first year resulted in the extirpation of the Burrowing Owls on the island. Such heavy predation on alternative prey species is commonly reported in cyclic predator-prey systems, however this is the first documented case of extirpation of the alternative prey. Complete elimination of any prey species by terrestrial predators is, in fact, very rare.     

Cyclic population changes in three mouse species in the same woodland

Summary In two forest areas of West Berlin the population-changes in three mouse species have been investigated over 28 years (1952–1979). Significant changes in absolute density have been established for the Short-Tailed Vole (Microtus agrestis) at 5-year intervals, for the Common Vole (Microtus arvalis) at 4-year intervals, and for the Yellow-Necked Field Mouse (Apodemus flavicollis) at 3-year intervals. The investigations were based on a total of 43,535 small vertebrates, 90% of which had been found in the pellets of breeding Tawny Owls. The remaining 10% belonged to pellets collected in the territories of breeding Long-Eared Owls. It is assumed that, for those prey animals whose percentage in the total prey of a predator is fairly high, the percentage proportionally approximates the real fluctuations in their (absolute) density.     

What determines prey selection in owls? Roles of prey traits,prey class,environmental variables,and taxonomic specialization

Ecological theory suggests that prey size should increase with predator size, but this trend may be masked by other factors affecting prey selection, such as environmental constraints or specific prey preferences of predator species. Owls are an ideal case study for exploring how predator body size affects prey selection in the presence of other factors due to the ease of analyzing their diets from owl pellets and their widespread distributions, allowing interspecific comparisons between variable habitats. Here, we analyze various dimensions of prey resource selection among owls, including prey size, taxonomy (i.e., whether or not particular taxa are favored regardless of their size), and prey traits (movement type, social structure, activity pattern, and diet). We collected pellets of five sympatric owl species (Athene noctua, Tyto alba, Asio otus, Strix aluco, and Bubo bubo) from 78 sites across the Mediterranean Levant. Prey intake was compared between sites, with various environmental variables and owl species as predictors of abundance. Despite significant environmental impacts on prey intake, some key patterns emerge among owl species studied. Owls select prey by predator body size: Larger owls tend to feed on wider ranges of prey sizes, leading to higher means. In addition, guild members show both specialization and generalism in terms of prey taxa, sometimes in contrast with the expectations of the predator–prey body size hypothesis. Our results suggest that while predator body size is an important factor in prey selection, taxon specialization by predator species also has considerable impact.     

Incidental nest predation in freshwater turtles: inter- and intraspecific differences in vulnerability are explained by relative crypsis

There has long been interest in the influence of predators on prey populations, although most predator–prey studies have focused on prey species that are targets of directed predator searching. Conversely, few have addressed depredation that occurs after incidental encounters with predators. We tested two predictions stemming from the hypothesis that nest predation on two sympatric freshwater turtle species whose nests are differentially prone to opportunistic detection—painted turtles (Chrysemys picta) and snapping turtles (Chelydra serpentina)—is incidental: (1) predation rates should be density independent, and (2) individual predators should not alter their foraging behavior after encountering nests. After monitoring nest survival and predator behavior following nest depredation over 2 years, we confirmed that predation by raccoons (Procyon lotor), the primary nest predators in our study area, matched both predictions. Furthermore, cryptic C. picta nests were victimized with lower frequency than more detectable C. serpentina nests, and nests of both species were more vulnerable in human-modified areas where opportunistic nest discovery is facilitated. Despite apparently being incidental, predation on nests of both species was intensive (57% for painted turtles, 84% for snapping turtles), and most depredations occurred within 1 day of nest establishment. By implication, predation need not be directed to affect prey demography, and factors influencing prey crypsis are drivers of the impact of incidental predation on prey. Our results also imply that efforts to conserve imperiled turtle populations in human-modified landscapes should include restoration of undisturbed conditions that are less likely to expose nests to incidental predators.     

Environmental factors affecting patterns of distribution and co‐occurrence of two competing raptor species

Habitat selection is a complex process, that is affected by several factors, including habitat characteristics, environmental conditions, and both intra‐ and interspecific interactions. We analysed habitat preferences of two top avian predators, Peregrine Falcon Falco peregrinus, a medium‐sized diurnal raptor, and Eagle Owl Bubo bubo, a large nocturnal raptor. These two species are known to compete for preferred nest‐sites, and proximity to cliffs with Eagle Owls may reduce Peregrine breeding output through predation of young Falcons. We investigated the environmental factors affecting occurrence and coexistence of the two species and the potential role of habitat suitability in favouring co‐occurrence in 3519 km² of the central pre‐Alps of Italy, where the two species breed on cliffs and sometimes co‐occur on the same cliff. Peregrines settled on long, steep and favourably orientated cliffs in woodland landscapes close to urban areas. Eagle Owls settled on topographically similar cliffs, but in lower rainfall areas compared with cliffs occupied by Peregrines and cliffs unoccupied by either species. Sites where the two species co‐occurred were characterized by more horizontally extended cliffs compared with sites of exclusive occurrence of each species. An analysis of relative habitat suitability revealed that sites where the two species co‐occurred had the highest predicted probability of occupancy for both species, suggesting that those sites should be regarded as high‐quality sites. Breeding productivity of Eagle Owls was negatively affected by the co‐occurrence of Peregrines, whereas the effect of Eagle Owl proximity on Peregrine productivity varied according to cliff suitability for the Peregrines. Habitat selection had fitness consequences for Eagle Owls because breeding productivity increased with cliff length. Environmental conditions, particularly climatic factors, could allow the widespread coexistence of these competing raptors at the landscape scale, whereas at the local scale co‐occurrence could take place only on larger cliffs. These were preferred sites for both species, presumably because breeding at such sites offsets the costs of settling close to the competitor species.     

Predation of Svalbard reindeer by polar bears

Polar bears (Ursus maritimus) are believed to be obligate predators on marine mammals, and particularly, on two species of seals. This paper reports on observations of polar bears preying (n=7) and scavenging (n=6) on Svalbard reindeer (Rangifer tarandus platyrhyncus). Similar to their closest evolutionary ancestor, the brown bear (U. arctos), polar bears are opportunistic and will prey on ungulates. Reindeer are likely of minor importance to the foraging ecology of polar bears in Svalbard, but the observations suggest behavioural plasticity in response to a novel prey item. Accepted: 26 March 2000     

FIRST ANNUAL REPORT ON THE RHODESIAN ORNITHOLOGICAL SOCIETY'S NEST RECORD SCHEME FOR THE YEAR ENDED 30 JUNE, 1956

MENDELSOHN, J. M. 1989. Habitat preferences, population size, food and breeding of six owl species in the Springbok Flats, South Africa. Ostrich 60:183-190.

Information on the habitat preferences, population size, food and breeding of Barn, Grass, Whitefaced, Marsh, Pearlspotted and Spotted Eagle Owls was obtained in a 6900-ha area in the Springbok Flats, South Africa. Seventy-two per cent of the area consisted of cultivated fields not usually used by owls. Hunting, roosting and nesting requirements were largely met in 1930 ha of verges, farmyards and patches of wood land ant grassland, here was an estimated total population of 303 owls in the area, giving an overall density of 22,7 ho/owl for the whole area or 6.4 ha/owl for those areas used by owls. These high densities were attributed to an abundance of Mastomys natalensis, the most important prey item for all except Pearlspotted Owls. Rates of predation on M. natalensis varied in relation to their population density, as indicated by rodent trapping results. Marsh Owls ate more insects in summer than at other times. Barn and Marsh Owls usuall laid in March-April and August-September, while other species started breeding in July-October. de timing of breeding of some owls may be related to changes in rates of recruitment of juvenile M. natalensis. Most Marsh Owl nests were placed on the southwestern sides of grass clumps or shrubs.     

Wildflower areas within revitalized agricultural matrices boost small mammal populations but not breeding Barn Owls

Agro-ecosystems have recently experienced dramatic losses of biodiversity due to more intensive production methods. In order to increase species diversity, agri-environment schemes provide subsidies to farmers who devote a fraction of their land to ecological compensation areas (ECAs). Several studies have shown that invertebrate biodiversity is actually higher in ECAs than in nearby intensively cultivated farmland. It remains poorly understood, however, to what extent ECAs also favour vertebrates, such as small mammals and their predators, which would contribute to restoring functional food chains within revitalised agricultural matrices. We studied small mammal populations among eight habitat types—including wildflower areas, a specific ECA in Switzerland—and habitat selection (radiotracking) by the Barn Owl Tyto alba, one of their principal predators. Our prediction was that habitats with higher abundances of small mammals would be more visited by foraging Barn Owls during the period of chicks’ provisioning. Small mammal abundance tended to be higher in wildflower areas than in any other habitat type. Barn Owls, however, preferred to forage in cereal fields and grassland. They avoided all types of crops other than cereals, as well as wildflower areas, which suggests that they do not select their hunting habitat primarily with respect to prey density. Instead of prey abundance, prey accessibility may play a more crucial role: wildflower areas have a dense vegetation cover, which may impede access to prey for foraging owls. The exploitation of wildflower areas by the owls might be enhanced by creating open foraging corridors within or around wildflower areas. Wildflower areas managed in that way might contribute to restore functional links in food webs within agro-ecosystems.     

Winter diet and lead poisoning risk of Greater Spotted Eagles Clanga clanga in southeast Spain

ABSTRACT

Capsule: Diet analysis revealed high lead exposure for Greater Spotted Eagles Clanga clanga wintering in southeast Spain.

Aims: To describe the diet composition of the endangered Greater Spotted Eagle in a wintering area located in southeast Spain, and determine lead ammunition exposure through analysis of regurgitated pellets and prey remains.

Methods: Between 2008 and 2018, a total of 26 pellets, 29 prey remains and 10 direct predation observations were collected in El Hondo Natural Park, Spain. All the pellets and 10 prey remains were analysed with X-ray in order to detect metal from ammunition.

Results: Greater Spotted Eagles fed mainly on birds, with 18 different species accounting for 73.1% of prey items and 66.1% of biomass consumed. The most frequent species identified were Common Moorhen Gallinula chloropus (23.1%), rats Rattus spp. (15.4%) and Common Teal Anas crecca (8.9%). Ammunition was detected in 42.3% of regurgitated pellets and in 40.0% of prey remains analysed. Of those containing ammunition, lead shot was found in 63.9% of pellets and 25.0% of prey remains.

Conclusion: High lead shot presence in pellets and prey remains of wintering Greater Spotted Eagles in southeast Spain warns of a high risk of lead poisoning. Factors such as feeding behaviour, the large space–time overlap between the raptor presence and the waterbird hunting season and non-compliance with the ban on the use of lead ammunition are likely contributing to high lead exposure.     

Hunting behaviour in West African forest leopards

The leopard (Panthera pardus) is a major predator of mammals within the rainforest ecosystem of West Africa. Most of the available information on leopard hunting behaviour comes from studies conducted in open savannah habitats, while little is known about forest leopards. Our radio‐tracking data and scat analysis show that forest leopards differ in various ways from the savannah populations. Forest leopards are diurnal and crepuscular hunters who follow the activity pattern of their prey species. They exhibit seasonal differences in activity patterns, and they develop highly individualized prey preferences. These findings challenge the widespread notion of leopards as opportunistic nocturnal predators.     

南充高坪机场短耳鸮越冬期的食性分析和习性观察

2006年3～5月,收集南充高坪机场草地和周围松林越冬期短耳鸮(Asio flammeus)的食团,进行食性分析。在805个完整食团和一些零碎的食团中,小型兽类是短耳食物组成的主要成分,占98.4%,其中四川短尾(Anourosorex squamipes)所占比例最高,为97.2%。通过调查短耳鸮的食团在南充高坪机场草地里的分布情况,分析短耳v在机场草地的栖息地选择,发现短耳鸮并没有选择草高和密集的区域作为栖息场所,而高20cm左右的白茅(Imperata cylindrical)丛是短耳最喜欢栖息的场所。     

Food partitioning between breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in southern Brazil.

I examined the diet of breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in an agrarian area of southern Brazil by analyzing regurgitated prey remains. The objective was to evaluate how these raptors, which differ markedly in their hunting activity periods (owls are nocturnal and kites diurnal), share their mammalian food component. 2,087 prey consumed by Barn Owls and 1,276 by White-tailed Kites were identified. They presented a high overlap of food-niches (Piankas index was 0.98). Based on the daily activity period of their main small mammal prey, a lower overlap would be expected. The crepuscular/nocturnal Mus musculus was the main prey for the diet of breeding Barn Owls (81%) and White-tailed Kites (63%). This small exotic rodent provided 63% of the small mammal biomass ingested by owls and 44% by kites. Larger native small mammals were also considered important for the diet of kites, mainly because of their biomass contribution. Although these raptors differ markedly in their hunting activity periods, Barn Owls and White-tailed Kites are very similar predators in southern Brazil, overlapping their diets.     

Numerical and functional response of predators to a long-term decline in mammalian prey at a semi-arid Neotropical site

Summary Occurrence and diet of ten carnivorous predators (four falconiforms, four owls, and two foxes), and population levels of their mammalian prey, were monitored over 45 months at a semi-arid site in north-central Chile. Early in this period, small mammals irrupted and then declined markedly to a density 7% of that at peak. All four falconiforms (Buteo polyosoma, Falco sparverius, Geranoaetus melanoleucus, Parabuteo unicinctus) and one owl (Tyto alba) responded numerically to the decline in mammalian prey by virtually abandoning the study site. The three other owls (Athene cunicularia, Bubo virginianus, Glaucidium nanum) and the two foxes (Pseudalopex culpaeus and P. griseus) remained. With few exceptions, throughout the study predators maintained species-specific preferences among small mammal species regardless of the absolute and proportional abundance of these prev. At no time did the two prey species most responsible for the irruption (the rodents Phyllotis darwini and Akodon olivaceus) occur in predators' diets out of proportion to their estimated relative abundance in the field. Predators were clearly unable to prevent the irruption from occurring. Given the absence of a clear functional response to the most irruptive species, predators seemed unlikely to have been responsible for the observed crash. At present, however, predators may be prolonging the crash and delaying the return of small-mammal populations to typical densities.     

The role of the southern water vole Arvicola sapidus in the diet of predators: a review

相似文献   

Both novelty and conspicuousness influence selection by mammalian predators on the colour pattern of Plethodon cinereus (Urodela: Plethodontidae)

Predators influence the evolution of colour pattern in prey species, yet how these selective forces might differ among predators is rarely considered. In particular, prey colour patterns that indicate unpalatability to some predator species may not carry the same signal for other predators. We test several hypotheses of selection on patterning between mammal predators and the polymorphic salamander Plethodon cinereus, which, under an avian visual system appears as a mimic of the toxic newt Notophthalmus viridescens. We fit each hypothesis against field observations of mammalian attacks on salamander clay replicas. We then develop a novel analytical procedure that enables the combination of multiple non‐exclusive models in a likelihood framework. We find that mammals do not follow any single hypothesis proposed, including the hypothesis of mimicry. Instead, mammals in this system use visual cues while foraging to avoid unfamiliar, novel prey and attack conspicuous prey. We propose that mammals may help to maintain colour pattern polymorphism within populations of P. cinereus by avoiding novel, unfamiliar colour morphs. Additionally, selective pressures from multiple predators and variation in predator communities among sites may contribute to the maintenance of colour polymorphism within and among localities in this salamander species.     

Mortality of an apex predator,the eagle owl bubo bubo,in Israel 2007–2021

Anthropogenic structures and installations in wild areas are known to directly and indirectly affect wildlife populations, especially apex predators such as Eagle Owls (Bubo bubo). To understand the situation at the national level we analyzed data collected by the Scientific Data Department of the Israel Nature and Parks Authority and the wildlife hospital at the Safari in Ramat Gan. We analyzed a total of 189 dead Eagle Owls during fifteen years, 2007–2021; 39.7% were electrocuted, 29.2% roadkill, 12.7% flew into fences/barbed wire, 3.8% drowned, and 14.9% died from other causes. The largest mortality of the Eagle Owls was detected in agricultural (34.92 %) and urban areas (31.74%). Also, the pylons identified as lethal should be prioritized and modified with appropriate insulators. Only a sincere effort on the part of the authorities will the continued electrocution of eagle owls and other avian wildlife be truncated.     

Foraging behavior of an estuarine predator, the blue crab Callinectes sapidus in a patchy environment

To define general principles of predator‐prey dynamics in an estuarine subtidal environment, we manipulated predator density (the blue crab, Callinectes sapidus) and prey (the clam, Macoma balthica) patch distribution in large field enclosures in the Rhode River subestuary of the central Chesapeake Bay. The primary objectives were to determine whether predators forage in a way that maximizes prey consumption and to assess how their foraging success is affected by density of conspecifics. We developed a novel ultrasonic telemetry system to observe behavior of individual predators with unprecedented detail. Behavior of predators was more indicative of optimal than of opportunistic foraging. Predators appeared responsive to the overall quality of prey in their habitat. Rather than remaining on a prey patch until depletion, predators appeared to vary their patch use with quality of the surrounding environment. When multiple (two) prey patches were available, residence time of predators on a prey patch was shorter than when only a single prey patch was available. Predators seemed to move among the prey patches fairly regularly, dividing their foraging time between the patches and consuming prey from each of them at a similar rate. That predators more than doubled their consumption of prey when we doubled the number of prey (by adding the second patch) is consistent with optimizing behaviors ‐ rather than with an opportunistic increase in prey consumption brought about simply by the addition of more prey. Predators at high density, however, appeared to interfere with each other's foraging success, reflected by their lower rates of prey consumption. Blue crabs appear to forage more successfully (and their prey to experience higher mortality) in prey patches located within 15–20 meters of neighboring patch, than in isolated patches. Our results are likely to apply, at least qualitatively, to other crustacean‐bivalve interactions, including those of commercial interest; their quantitative applicability will depend on the mobility of other predators and the scale of patchiness they perceive.     

Dietary shifts,niche relationships and reproductive output of coexisting Kestrels and Long-eared Owls

Summary Food samples of breeding Kestrels (Falco tinnunculus) and Long-eared Owls (Asio otus) were collected in the peak and low phase of their preferred prey (Microtus voles) in western Finland. Diets of pairs that bred as neighbours (1 km) with interspecifics were compared with those of non-neighbours. In both species, neighbouring pairs fed less on Microtus voles and more on alternative prey than did non-neighbours. Competition theory predicts that diet overlap should be lower during prey shortage and that diet similarity should be especially reduced in neighbouring pairs. Observations were consistent with expectations: diet similarity was lower in the low vole years and neighbouring pairs showed less diet overlap that non-neighbours. Differences in habitat composition and prey availability at the sample sites should not confuse the results. In addition to the high diet similarity, hunting habitats and nest sites of the species overlapped almost completely; they only showed clear temporal segregation in hunting. Probably because of food competition, the neighbouring pairs of both species produced significantly fewer young than the non-neighbours. These results contrast with the view that the diet composition and dietary shift of rodent-feeding predatory birds can be interpreted in terms of simple opportunistic foraging. In the breeding season, interspecific competition for food seems to be an important factor that affects the niches of these species, especially in northern areas, where the seasonal low phase of voles in spring and the number of alternative prey are lower than in more southern areas.