Hunting Habitat Research Articles

Habitat alteration enables hybridisation between Lesser Spotted and Greater Spotted Eagles in north-east Poland

SummaryWetlands in the Biebrza Valley, north-east Poland, are inhabited by two closely related Aquila species: the more numerous Lesser Spotted Eagle A. pomarina prefers human-transformed landscapes, whereas the very rare Greater Spotted Eagle A. clanga is associated with natural marshy landscapes. At least since the last decade of the 20th century, these two species have been known to hybridise in the broad zone of their sympatric occurrence in Europe. The aim of the present study was to compare habitat preferences of both spotted eagle species in order to detect which environmental factors could increase the probability of hybridisation. We analysed nesting and hunting habitats for 148 breeding territories (61 of A. pomarina, 56 of A. clanga and 31 of mixed pairs). As expected, the presence of breeding Greater Spotted Eagles was associated with non-transformed marshy landscapes, whereas Lesser Spotted Eagles clearly preferred human-transformed areas. We hypothesised that mixed pairs should occur in intermediate habitat, confirming this assumption by analysing several variables: distance to human settlements, distance to open areas, and proportion of wetlands, shrublands, grasslands, agricultural mosaic and arable land. Results of this study suggest that some landscape changes can enable two species with different habitat requirements to inhabit the same area and hybridise. This scenario has potential conservation implications for the rarer species, Greater Spotted Eagle, which has narrower habitat preferences.

Echolocation intensity and directionality of perching and flying fringe-lipped bats, Trachops cirrhosus (Phyllostomidae)

The Neotropical frog-eating bat, Trachops cirrhosus, primarily hunts stationary prey, either by gleaning on the wing, or in a sit-and-wait mode hanging from a perch. It listens passively for prey-generated sounds, but uses echolocation in all stages of the hunt. Like other bats in the family Phyllostomidae, T. cirrhosus has a conspicuous nose leaf, hypothesized to direct and focus echolocation calls emitted from the nostrils. T. cirrhosus is highly flexible in its cognitive abilities and its use of sensory strategies for prey detection. Additionally, T. cirrhosus has been observed to echolocate both with closed and open mouth. We hypothesize that its flexibility extends to echolocation call design. We investigated the effect of hunting mode, perching or flying, as well as the effect of mouth opening, on the acoustic parameters and directionality of the echolocation call. We used a multi-microphone array, a high-speed video camera, and a microphone-diode-video system to directly visualize the echolocation sound beam synchronized with the bat's behavior. We found that T. cirrhosus emits a highly directional sound beam with half amplitude angle (HAM) of 12–18° and DI (directionality index) of ~17 dB, among the most directional bat sonar beams measured to date. The directionality was high both when flying and when perching. The emitted intensity was low, around 88 dB SPL at 10 cm from the mouth, when hanging, but higher, around 100 dB SPL at 10 cm, when flying or just before take-off. Our data suggests that the limited search volume of T. cirrhosus sonar beam defined by the high directionality and the rather low intensity of its echolocation calls is adapted to the highly cluttered hunting habitat and to the perch hunting mode.

A new species of small owl of the genusAegolius(Aves: Strigidae) from Quaternary deposits on Bermuda

Fossil remains of a small owl found in eight separate localities on Bermuda ranging in age from the end of the last interglacial period (Marine Isotope Stage 5a, ca. 80,000 years ago) and up into the Holocene are described here as a new species, Aegolius gradyi, the only representative of its genus known from a remote oceanic island. This differed from its probable North American ancestor, A. acadicus, in its more robust hindlimb elements, smaller head, and a possible tendency for smaller wing elements. Its colonization was probably made possible by the unique conditions of suitable habitat for hunting, roosting, and nesting afforded by Bermuda, including the presence of woodpeckers (Picidae) that would have excavated nest sites suitable for the owls in the endemic palm trees (Sabal bermudana). From accounts dating to the early 1600s, the species appears likely to have persisted into the historic period.

High Trophic Similarity in the Sympatric North European Trawling Bat Species Myotis daubentonii and Myotis dasycneme

Most European bat species are insectivorous and share foraging areas to some extent. Where similar species rely on similar resources in the same foraging habitat, they are likely to interact. This study addresses the trophic niche of the Northern European trawling bat species Myotis dasycneme (Boie, 1825) and Myotis daubentonii (Kuhl, 1817), occurring in the same habitat, and possible interactions or differences within their dietary behaviour. Dietary data of both species were analysed to draw conclusions on their ecology, possible dietary overlap, hints for coexistence mechanisms and community structure. In this study, M. dasycneme and M. daubentonii fed mainly on Chironomidae (M. dasycneme: 44.4%; M. daubentonii: 32.8%) and Trichoptera (M. dasycneme: 20.4%; M. daubentonii: 22.2%), showing a high trophic niche overlap and similar niche breadth. Nevertheless, there were differences in the diet of the two species concerning the predation of chironomids. Differences also occur regarding the prey types, referring to the terrestrial or aquatic life-cycle of prey groups. This could be evidence for different foraging habitats and a spatial segregation of both species. High resource abundance is also likely to allow the coexistence of both species within the same hunting habitat.

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.

Goshawk breeding densities in relation to mature forest in southeastern Norway

Forest harvesting practices have been assumed to be the main reason for the decrease in Goshawk Accipiter gentilis populations in Fennoscandia during the late 1900s, by reducing prey density, especially grouse and Red Squirrel ( Sciurus vulgaris), and preferred hunting habitats (mature forest). In Norway, the highest breeding densities are now found in areas with a high proportion of farmland and urban areas where corvids and pigeons are important prey. To assess the importance of mature forest for Goshawk populations in southeastern Norway, we compared breeding densities from 20 municipalities with different percentages of farmland and mature forest. In multiple regression models, regional breeding densities were positively related to both the percentage of mature forest, and the percentage of farmland and urban areas. We conclude that the recommendation of establishing buffer zones around nest sites will not be sufficient to maintain Goshawk populations if the proportion of mature forest is reduced at a landscape level.

Male-biased predation of western green lizards by Eurasian kestrels

Selective predation can be an important force driving the evolution of organisms. In particular, sex-biased predation is expected to have implications for sexual selection, sex allocation and population dynamics. In this study, we analysed sex differences in the predation of the western green lizard (Lacerta bilineata) by the Eurasian kestrel (Falco tinnunculus) during the reproductive season. In addition, we investigated whether the rate of predation differed during the 8-year study period and among the three habitats studied. We collected lizard remains from nest boxes of kestrels. Freshly killed lizards were sexed by visual inspection, whilst the sex of head remains was assigned by analysing the cephalic scale morphology using geometric morphometrics. Our results show that the risk of being predated by a kestrel in our population was overall about 3.55 times higher for males than for females. To our knowledge this is the first study showing a male-biased predation in a lizard species. The selective predation of males was consistent between years over the 8-year study period (1999-2006) and also consistent between the three types of kestrel hunting habitat. Overall predation rates on lizards differed between habitats, depending on the year. We propose that the observed sex-biased predation is mainly due to sex differences in lizard behaviour.

LANDSCAPE FEATURES OF RED-TAILED HAWK NESTING HABITAT IN AN URBAN/SUBURBAN ENVIRONMENT

ABSTRACT We described urban/suburban Red-tailed Hawk (Buteo jamaicensis) nesting habitat and compared nesting habitat to unused habitat based on presence and absence of Red-tailed Hawks. We developed a landscape-scale logistic model of nesting habitat occupancy, then applied it to other locations to determine whether unoccupied patches of Red-tailed Hawk nesting habitat existed in urban locations. Red-tailed Hawk nesting habitat in urban/suburban Milwaukee usually included large areas of grassland and other herbaceous cover types. Urban/suburban Red-tailed Hawk nesting habitat was comprised of more than three times as much grasslands and woodlands, and had greater land-cover diversity and patch richness than unused habitat. Characteristics of unused habitat indicated that Red-tailed Hawks avoided areas of heaviest urbanization, perhaps because of insufficient hunting habitat. The logistic regression model developed from our data demonstrated that suitable, unoccupied nesting habitat existed in this urban ...

Tunnels as a possibility to connect bat habitats

Fragmentation of the landscape is one of the greatest problems for animals which use large home ranges and/or different habitats within a landscape. Even in the case of undisturbed hunting habitats and roosts, disconnection of flight paths could lead to a decline in the populations of bats. Tunnels connecting both sides of a barrier, allowing exchange, can be used to minimise the impact of e.g. motorways. Results of studies in different parts of Germany and anecdotal observations in other parts of Germany demonstrate the use of tunnels for nine species of bats. Data are analysed with respect to different types of tunnels. Although our data do not allow quantitative analysis, observations suggest smaller bats like Myotis nattereri, and M. daubentonii can use relatively low and narrow tunnels, whereas the larger M. myotis, was only observed using larger tunnels. The results support the role of tunnels as effective for the conservation of the connectivity of landscapes.

Electrocution alters the distribution and density of a top predator, the eagle owl Bubo bubo

Summary Electrocution has frequently been suggested as a cause of territory abandonment and eventual population decline of threatened species, but this has been rarely tested. We investigated the impact of electrocution in two eagle owl Bubo bubo populations located in the Italian Alps and Apennines and subject to different levels of electrocution risk (i.e. low and high risk). The eagle owl is one of the species most affected by electrocution, to the point of causing local conservation and economic concern. In a review of 25 studies, electrocution was frequently cited as the major cause of death and has progressively increased in the last three decades, independently from other causes of mortality. The impact of electrocution was tested by (i) comparing estimates of electrocution risk between currently occupied owl territories and infrequently occupied or abandoned territories; (ii) collecting information on the spatiotemporal frequency of electrocution incidents; (iii) measuring density, breeding success and post‐fledging survival for populations and territories subject to different electrocution risk. In the low‐risk population electrocution casualties varied spatiotemporally, peaking in the period of immature dispersal and at pylons that were good hunting perches. Furthermore, eagle owls over‐selected low‐altitude habitats, which forced them into close contact with power lines. However, nest‐site selection was independent of electrocution risk, although territories that were not occupied every year were nearer to power lines than stable territories. In contrast, in the high‐risk population, territories near to power lines, most of them at low altitude, were progressively abandoned during a 10‐year period, leading to a steeply declining, scattered, low‐density and increasingly high‐altitude population. Although there was no effect on long‐term breeding success, the presence of pylons within 200 m of the nest increased the likelihood of partial or complete brood loss in the post‐fledging period. We estimated that 17% of the fledged young were lost to electrocution. At the population level, density was negatively related to electrocution risk in eight Alpine study areas. However, comparison between the two regions suggested that electrocution impact may interact with other factors, such as resource availability. Synthesis and applications. Our results show how subtle anthropogenic disturbance may affect population breeding performance and quickly alter the gradient of environmental quality for an endangered bird, leading to potential population limitation. Conservation guidelines should prioritize the insulation of those pylons most likely to cause casualties (e.g. in good hunting habitat and close to nests), ensuring that all new lines are raptor safe.

Cheetah Acinonyx jubatus feeding ecology in the Kruger National Park and a comparison across African savanna habitats: is the cheetah only a successful hunter on open grassland plains?

The literature on cheetah Acinonyx jubatus ecology is dominated by studies on the Serengeti Plains (SNP) in East Africa. Because of this and the cheetah's hunting strategy it is generally considered to be a predator that prefers open grassland plains. However, cheetahs also inhabit a range of bush, scrub and woodland habitats. A field study using direct observations of radio‐collared individuals in the woodland savanna habitat of the Kruger National Park (KNP), South Africa, and a literature review of studies across savanna habitats examined cheetah predation, hunting behaviour and habitat use in relation to prey composition, cover availability and kleptoparasitism. The cheetah's main prey is medium‐sized herbivores, with a bias towards male prey. The group size and sex of the hunting cheetah may influence the results of prey selection studies as male coalitions tend to take larger prey than females. Cheetahs initiated more hunts and had a higher success rate in the open woodland savanna of the KNP compared to other available habitats with thicker bush, and in other wooded savanna areas they also prefer more open habitat for hunting. Although they appear to have shorter chase distances in more wooded habitats, hunting success appears to be slightly higher in open grassland habitat. Woody vegetation appears to obstruct the cheetah's high‐speed hunting strategy, thereby lowering hunting success. However, cheetahs use cover for stalking prey and open habitats with bordering woodlands, or patches of cover are considered preferred cheetah habitats. In these habitats, cheetahs can stalk closer to their prey using available cover, but also successfully pursue their prey into available open spaces. Across African savanna ecosystems, cheetahs appear to be kleptoparasitised less in more wooded habitats. Therefore they may also prefer these habitats because they provide greater concealment from kleptoparasites. Our study suggests that the cheetah is more adaptable to habitat variability than is often thought and is not only a successful hunter on open grassland plains.

Analysis of nest occupancy and nest reproduction in two sympatric raptors: common buzzard Buteo buteo and goshawk Accipiter gentilis

Nest site selection can have important fitness consequences in birds. I analysed the habitat characteristics of 392 nests of two sympatric raptor species (common buzzard Buteo buteo and goshawk Accipiter gentilis) in Germany and their relation to nest occupation rate and nest reproductive success. For common buzzard, multivariate models explained only small proportions of the variance in nest occupation rate and nest reproductive success (13–19%). Important variables related to nest occupation rate were human disturbances, intra‐ and interspecific neighbour density, the amount of forested area and nest tree crown cover. Variables related to nest site reproductive success also included human disturbance, intra‐ and interspecific neighbour density and nest tree crown cover as well as nest distance to the nearest forest edge. In contrast, models for the goshawk explained a much higher proportion of the variation in nest occupation rate and nest reproductive success (41–43%). Important variables related to nest occupation rate were the remoteness of the nest site and direct human disturbance. Variables related to nest site reproductive success were remoteness of the nest site and good hunting habitat. Goshawks seem to be more sensitive to human disturbance than buzzards. A multiple discriminant analysis showed that nest site characteristics substantially overlapped between the species and there is a good evidence that competition for optimal nest sites occurs. Thus, buzzards might be constrained by the dominant goshawk in their nest site selection.

Prey Use in two Sympatric Species of the Digger wasp Genus Bembecinus (Hymenoptera: Apoidea: Sphecidae)

Prey use and prey spectrum in the sympatric digger wasps Bembecinus hungaricus (Frivaldzky 1876) and B tridens (Fabricius 1781) was investigated by field studies in north eastern Austria. Both species hunted for adult leafhoppers, mainly of the family Cicadellidae. Both wasp species prey upon leafhoppers of the same body size. Comparison of prey taxa demonstrated little overlap in prey utilization. Significant differences in the choice of prey species resulted from different hunting habitats: B hungaricus shows a preference for arboricolous leafhopper species, while B tridens mainly provisioned with praticolous taxa. No significant sexual bias of prey was observed.

EFFECTS OF PREDATION ON COMMUNITY ASSEMBLY AND SPATIAL DISPERSION OF BREEDING FOREST BIRDS

In a landscape context, nesting avian predators cause variation in predation risk with respect to the distance to their nests, which may have both direct (predation) and indirect (predation risk) effects on the prey community. We studied the community assembly and spatial distribution of a breeding forest bird community in a structurally complex forest landscape surrounding forest-hunting Sparrowhawk (Accipiter nisus) nests. Birds were cen- sused on transect arrays within 1-ha study plots divided into four subplots. We determined whether the distribution of species within study plots was clumped, random, or uniform. Because predation risk is higher nearer a hawk's nest than farther away, we predicted that species would show a more clumped distribution within study plots near the Sparrowhawks' nests than farther away. We also expected densities and community patterns to vary with respect to predation risk. The results suggest that predation and/or its risk has a complex and local effect on the prey community. The predation risk negatively affected the number of species and densities of birds only in the first year (1996) of study. The relationship between the density of large birds (?20 g, preferred prey) and predation risk was also negative in 1996, but not in 1997, whereas the density of small birds (<20 g) was not affected by predation risk in either year. There was no relationship between predation risk and clumping for all species together. When we analyzed separately plots that contained large and small birds or large birds alone, however, increasing predation risk positively affected the index of dispersion, but only in thicket (one of the forest types), which is probably the preferred hunting habitat for Sparrowhawk. These results are well in line with studies made on predator-prey interactions in farmlands. In those studies, however, the effects of predators on prey communities were much stronger and extended farther in the landscape from the nest of predators than in this forest study. A possible reason for this difference is higher habitat structural complexity in forests, which may mitigate the effect of predators.

Effects of Predation on Community Assembly and Spatial Dispersion of Breeding Forest Birds

In a landscape context, nesting avian predators cause variation in predation risk with respect to the distance to their nests, which may have both direct (predation) and indirect (predation risk) effects on the prey community. We studied the community assembly and spatial distribution of a breeding forest bird community in a structurally complex forest landscape surrounding forest-hunting Sparrowhawk (Accipiter nisus) nests. Birds were censused on transect arrays within 1-ha study plots divided into four subplots. We determined whether the distribution of species within study plots was clumped, random, or uniform. Because predation risk is higher nearer a hawk's nest than farther away, we predicted that species would show a more clumped distribution within study plots near the Sparrowhawks' nests than farther away. We also expected densities and community patterns to vary with respect to predation risk. The results suggest that predation and/or its risk has a complex and local effect on the prey community. The predation risk negatively affected the number of species and densities of birds only in the first year (1996) of study. The relationship between the density of large birds (≥20 g, preferred prey) and predation risk was also negative in 1996, but not in 1997, whereas the density of small birds (<20 g) was not affected by predation risk in either year. There was no relationship between predation risk and clumping for all species together. When we analyzed separately plots that contained large and small birds or large birds alone, however, increasing predation risk positively affected the index of dispersion, but only in thicket (one of the forest types), which is probably the preferred hunting habitat for Sparrowhawk. These results are well in line with studies made on predator–prey interactions in farmlands. In those studies, however, the effects of predators on prey communities were much stronger and extended farther in the landscape from the nest of predators than in this forest study. A possible reason for this difference is higher habitat structural complexity in forests, which may mitigate the effect of predators.

Detecting Publication Bias in Meta-analyses: A Case Study of Fluctuating Asymmetry and Sexual Selection.

Those familiar with human nature and the publication process acknowledge that biases due to selective reporting of results are likely widespread in all fields of academic inquiry that depend on tools of statistical inference (e.g., see Begg and Berlin 1988; Iyengar and Greenhouse 1988; and the extensive discussion following each). However, although qualitative and quantitative methods exist for assessing the prevalence of selective reporting, and selective reporting has been studied in the medical and social sciences (Begg 1994, and references therein), the issue has received little attention in recent meta-analyses of ecological and evolutionary patterns. Clearly, “if publication bias is present, and if it operates in the same direction for all studies (as is likely), then [meta-analysis] is likely not only to produce biased summary estimates but also to produce estimates which are apparently precise and accurate leading to conclusions which may not only be wrong but appear convincing” (Begg and Berlin 1988, p. 437). To biologists unacquainted with the formal study of publication patterns, the terms “selective reporting” (statistical significance of an outcome influences its likelihood of being reported or published) and “publication bias” (the inflation of average effect size due to selective reporting) may imply a conscious intent to deceive, but this

Clear‐cut areas and breeding success of Tengmalm's owls Aegolius funereus

The effect of mature forest fragmentation on breeding success of vole‐eating Tengmalm's owls Aegolius funereus was studied in western Finland during 1981–1995. The owl pairs produced more fledglings in territories with high (&gt;30%) proportions of clear‐cut and plantation areas than in territories with low (&lt;30%) proportions of such areas. Territory occupancy, clutch size, laying date, and parental characteristics such as wing length, body mass and age were not associated with the proportion of clearcut areas within territories. Snap‐trapping data from the ‘increase’ vole year 1994 revealed that the Microtus vole density tended to be higher in large clear‐cuttings than in small ones. The increasing amount of sapling and clear‐cut areas in coniferous forests during the last three decades has created suitable grass habitats for Microtus voles, and simultaneously new hunting habitats for Tengmalm's owls. Therefore, forest fragmentation due to clear‐cuttings may benefit Tengmalm's owls at the present scale. However, nest‐boxes should be erected and old groves should be protected, because forest harvesting apparently reduces the number of suitable natural cavities for owls in the long run.

The hunting habitats of Goshawks Accipiter gentilis in boreal forests of central Sweden

Radio‐tracking was used to study the habitat utilization of hunting GoshawksAccipiter gentilisin central Swedish boreal forest. Data were collected during September‐June, in 1977–1981. There was no major difference between autumn, winter or spring in any aspect of habitat preference, despite seasonal differences in prey composition. Despite the strong reversed sexual size‐dimorphism, no habitat segregation between the sexes was found. It is argued that this is due to the lack of prey segregation between the sexes. Goshawks showed a strong preference for mature forest, which was chosen twice as often as would be expected from its prevalence in the environment, whereas the younger successional stages of the forest were under‐used. Goshawks preferred large habitat patches, and showed no major preference with respect to tree species composition of the forest. Kills made by radio‐tagged Goshawks showed the same habitat‐ and patch‐size distribution as did Goshawk locations in general. It is argued that the profitability of different hunting habitats, and thus habitat preferences, is not only determined by prey density in the habitats, but also by other habitat features influencing the Goshawk's ability to hunt there. Winter home‐ranges averaged 5700 ha, considerably larger than Goshawk ranges recorded in areas with richer prey supply.