Unused Habitat Research Articles

Comparative exploratory movements of two terrestrial isopods (suborder: Oniscidea), in response to humidity and availability of food

Abstract Unfavourable conditions within familiar environments may prompt organisms to make forays into other habitats, at least temporarily. This behaviour is in turn linked to key demographic processes such as immigration, emigration, and eventually, metapopulation dynamics. How such movements are triggered by environmental conditions (much less their interaction effects) has rarely been experimentally tested. To address this, we examined how environmental conditions (3 levels of food and 3 levels of humidity) within a microcosm affect the movements of two species of isopods (Armadillidium vulgare and Porcellio scaber) out of their familiar habitat. We used web-camera checkpoints to record the movements of individually marked animals as they conducted forays along corridors that lead to new, unused habitats. Thirty-six trials were run in total for each species, with each trial involving 16 animals (8 ♂♂, 8 ♀♀). Relatively unfavourable conditions of low humidity, low food levels, and their interaction prompted changes to all the foray metrics we measured. However, different levels of mobility and tolerance to desiccation between the two species also appeared linked to the degree of responses, e.g., Porcellio demonstrated a greater tendency to depart from familiar habitat under low humidity, possibly due to their superior mobility and greater susceptibility to desiccation. This study improves our understanding of how different environmental conditions act in concert to affect the exploratory movements away from familiar habitat, and how these responses differ even for closely-related species.

Land sharing is essential for snow leopard conservation

Conserving large carnivores in an increasingly crowded planet raises difficult challenges. A recurring debate is whether large carnivores can be conserved in human used landscapes (land sharing) or whether they require specially designated areas (land sparing). Here we show that 40% of the 170 protected areas in the global range of the snow leopard (Panthera uncia) are smaller than the home range of a single adult male and only 4–13% are large enough for a 90% probability of containing 15 or more adult females. We used data from 16 snow leopards equipped with GPS collars in the Tost Mountains of South Gobi, Mongolia, to calculate home range size and overlap using three different estimators: minimum convex polygons (MCP), kernel utility distributions (Kernel), and local convex hulls (LoCoH). Local convex hull home ranges were smaller and included lower proportions of unused habitats compared to home ranges based on minimum convex polygons and Kernels. Intra-sexual home range overlap was low, especially for adult males, suggesting that snow leopards are territorial. Mean home range size based on the LoCoH estimates was 207km2±63 SD for adult males and 124km2±41 SD for adult females. Our estimates were 6–44 times larger than earlier estimates based on VHF technology when comparing similar estimators, i.e. MCP. Our study illustrates that protected areas alone will not be able to conserve predators with large home ranges and conservationists and managers should not restrict their efforts to land sparing.

Nesting habitat requirements of two species of North African woodpeckers in native oak forest

Capsule Nests of Levaillant's Woodpecker Picus vaillantii and Great Spotted Woodpecker Dendrocopos major were associated with higher densities of snags and downed wood than foraging locations.Aims To quantify the nesting requirements of two sympatric woodpecker species in Tunisian oak forests.Methods We compared habitat structure around nests and foraging locations for both woodpecker species using logistic regression. We examined evidence for preferences in nesting substrates using resource selection indices. Then, we used discriminant function analysis to identify variables separating nesting, foraging, and unused habitat of each species.Results The probability of presence of nests of both species was significantly related to densities of downed wood and snags. Nests of Levaillant's Woodpecker were located in areas with slightly higher snag densities. Habitat structure differed between nesting and foraging locations of Great Spotted, but not Levaillant's WoodpeckerConclusion Both Levaillant's and Great Spotted Woodpecker showed high requirements for large-diameter trees and snags, which provide substrates for both nesting and foraging. Nesting habitat requirements may not always be higher than those associated with foraging, but the fact that they were for the Great Spotted Woodpecker calls for caution when planning for woodpecker conservation.

Altitudinal occurrence of non-native plant species (neophytes) and their habitat affinity to anthropogenic biotopes in conditions of South-Western Slovakia

Abstract Many ecological studies showed that species density (the number of species per unit area) in nonnative organism groups of the mountain areas decreases with increasing altitude. The aim of the paper is to determine the variability in the incidence of non-native plant species (neophytes) associated with the change in altitude and links of the invading taxons to reference habitat types, as well as their links to three ecologically very similar, however in natural conditions, different areas. In general, the most invaded habitats are those which are highly influenced by human activities. Firstly, data collection was conducted through field mapping of build-up areas in South-western Slovakia. Subsequently, with the assistance of ordination methods, we evaluated the level of association of invasive neophytes according to the set objectives. We found that altitude was an important factor determining variability of invasive neophytes’ occurrence. Total amount of habitats with invasive neophytes’ occurrence showed a linear increase along the altitudinal gradient. Many invasive neophytes adapted to abandoned habitats of upland territory were also able to grow along roads, and vice versa, abandoned and unused habitats of lowland areas created conditions for many typical invasive neophytes occurring along roads and habitats of gardens and yards. Railways of lowland areas provided habitats and means of spread of invasive woody neophytes. Gardens and yards were important sources of alien neophytes in all observed territories. Invasive neophyte Aster novi-belgii can be described as a very variable species tolerant to a wide range of factors limiting the spread of species along the elevation gradient.

Phytochemistry predicts habitat selection by an avian herbivore at multiple spatial scales

Animal habitat selection is a process that functions at multiple, hierarchically. structured spatial scales. Thus multi-scale analyses should be the basis for inferences about factors driving the habitat selection process. Vertebrate herbivores forage selectively on the basis of phytochemistry, but few studies have investigated the influence of selective foraging (i.e., fine-scale habitat selection) on habitat selection at larger scales. We tested the hypothesis that phytochemistry is integral to the habitat selection process for vertebrate herbivores. We predicted that habitats selected at three spatial scales would be characterized by higher nutrient concentrations and lower concentrations of plant secondary metabolites (PSMs) than unused habitats. We used the Greater Sage-Grouse (Centrocercus urophasianus), an avian herbivore with a seasonally specialized diet of sagebrush, to test our hypothesis. Sage-Grouse selected a habitat type (black sagebrush, Artemisia nova) with lower PSM concentrations than the alternative (Wyoming big sagebrush, A. tridentata wyomingensis). Within black sagebrush habitat, Sage-Grouse selected patches and individual plants within those patches that were higher in nutrient concentrations and lower in PSM concentrations than those not used. Our results provide the first evidence for multi-scale habitat selection by an avian herbivore on the basis of phytochemistry, and they suggest that phytochemistry may be a fundamental driver of habitat selection for vertebrate herbivores.

Propensity score methods for assessing habitat selection with telemetry data

Summary Wildlife studies to determine preferred habitat often involve sampling used sites and making comparisons with unused background sites. We apply these data to a somewhat different purpose, which is to assess the spatial distribution of important habitat variables relative to spotted owl nest sites. It is necessary to compare habitat characteristics of used and unused sites to understand habitat preferences. However, ecological literature provides little guidance for selection of appropriate background sites necessary for such an analysis. We apply propensity score matching to telemetry gathered samples of spotted owl habitat for the purpose of weighting the selected background sites. This helps to ensure that important covariates have similar distributions in the used and unused habitat samples. We propose a two-stage process where propensity score matching of used and unused sites results in weights that are applied in the second stage modelling process. The objective is to quantify how wildlife responses to important variables change with distance from a nest, den site or other central location. The expectation is that this will strengthen guidance to managers who wish to protect or to improve wildlife habitat on their forest land. Example applications using spotted owl telemetry data demonstrate how to apply the methods and show the potential to elucidate habitat characteristics.

Subpopulation range estimation for conservation planning: a case study of the critically endangered Cross River gorilla

Measuring and characterizing the area utilized by a population or species is essential for assessment of conservation status and for effective allocation of habitat to ensure population persistence. Yet population-level range delineation is complicated by the variety of available techniques coupled with a lack of empirical methods to compare the relative value of these techniques. This study assesses the effect of model choice on resulting subpopulation range estimation for the critically endangered and patchily distributed Cross River gorilla, and evaluates the conservation conclusions that can be drawn from each model. Models considered range from basic traditional approaches (e.g. minimum convex polygon) to newer home range techniques such as local convex hull (LoCoH). Overlap analysis comparing sub-sampled to complete data sets are used to evaluate the robustness of various modeling techniques to data limitations. Likelihood cross validation criterion is employed to compare core range model performance. Results suggest that differing LoCoH models produce similar range estimates, are robust to data requirements, provide a good fit for core habitat estimation, and are best able to detect unused habitat within the subpopulation range. LoCoH methods may thus be useful for studies into habitat selection and factors limiting endangered species distributions. However, LoCoH models tend to over-fit data, and kernel methods may provide similar information about animal space use while supporting protection of larger swaths of critical habitat. Subpopulation range analyses for conservation/management planning should therefore explore multiple modeling techniques, and employ both qualitative and quantitative assessments to select the best models to inform decision making for species of conservation concern.

Fine‐scale group structure and demography of African savanna elephants recolonizing lands outside protected areas

AbstractAim Dispersal is a critical component of animal ecology that is poorly understood for most species. In particular, savanna elephants (Loxodonta africana) have been studied for decades in national parks across Africa, but little is known about their dispersal into new or unused habitats or their population dynamics in human‐dominated landscapes. We capitalized on a natural dispersal event of savanna elephants recolonizing communal land in southern Kenya to document their demographic characteristics and genetic relationships.Location Rift Valley province of Kenya.Methods We collected faecal samples and used genetic methods to identify individuals, estimate the sex ratio and evaluate the patterns of relatedness within the female groups and male aggregations. We also measured dung bolus circumference to assign age classes to individuals and estimate the age structure.Results We identified 112 individuals with a sex ratio not different from one (1.32:1.00). The age structure was skewed towards younger elephants (71%), suggesting the potential for rapid growth from reproduction. We detected significantly higher kinship levels within female groups (R = 0.124 ± 0.023), suggesting that family groups colonized the site, but found little support for higher‐order genetic relationships among female groups. Males detected together were unrelated (R = 0.003 ± 0.030).Main conclusions Our results suggest that highly social mammals, such as savanna elephants, disperse into unoccupied habitat as family groups and that a young demographic structure and a large number of males might be expected in establishing populations. These findings highlight the potential value of indirect, non‐invasive methods for assessing elephant herd and demographic characteristics when direct observations are difficult.

Habitat Use of Nesting and Brood-rearing King Rails in the Illinois and Upper Mississippi River Valleys

Most studies of King Rail (Rallus elegans) have investigated habitat use during the nesting season, while few comparisons have been made between the nesting and brood-rearing seasons. King Rails were located during the nesting season in Missouri using repeated surveys with call playback, and systematic searches for broods were conducted during the brood-rearing season. King Rail adults were located at twelve points in 2006 and 14 points in 2007, and five King Rail broods were located in each year. Water depth was measured and dominant cover type determined for randomly sampled 5-m plots within used and unused habitats. Logistic regression models were fitted to the data and top models were selected from the candidate set using AICc. Nesting adults occurred more often in areas dominated by short (≤1 m) emergent vegetation ( = 0.77 ± 0.27) and deeper water ( = 0.05 ± 0.02). Broods occurred more often in areas dominated by short emergent vegetation ( = 1.19 ± 0.37) and shallow water ( = -0.17 ± 0.06), and avoided areas dominated by tall (>1 m) emergent vegetation ( =-1.15 ± 0.45). A modified catch-curve analysis was used to estimate chick daily survival rates during selected 7-day periods for each year. Daily survival rate ranged from 0.92 ± 0.008 in late June 2007 to 0.96 ± 0.005 in late July 2006. Management plans for King Rails should include the different habitat types needed during the nesting and brood-rearing stages.

Habitat Selection by Prairie Dogs in a Disturbed Landscape at the Edge of Their Geographic Range

ABSTRACT Although habitat attributes of black‐tailed prairie dog (Cynomys ludovicianus) colonies have been described for central and northern portions of the species' geographic range, little is known about these associations at the southern edge of this species' distribution. Because high‐quality habitats are expected to be scarcer at the edge of the species' geographic range, different patterns of habitat selection might emerge in these populations. We analyzed habitat selection by black‐tailed prairie dogs in a human‐disturbed mosaic of desert grasslands and shrublands in northwestern Chihuahua, Mexico. We contrasted 151 used and 133 unused habitat units producing 11 case‐control logistic regression models to explain site occupancy by prairie dogs with different combinations of environmental variables. Prairie dogs from Chihuahua occupy sites similar in most respects to sites in more northern regions, although these prairie dogs appear to be more tolerant of increased shrub density and reduced herbage cover. We found that site occupancy was best modeled by positive effects of soil moisture level, cover of forbs, cover of unpalatable vegetation, cover of bare ground, and amount of prairie‐dog colony area within 1 km and by the inverse of altitude, shrub density, herbage height, and amount of hostile habitat within 1 km. The 2 most significant variables were herbage height and shrub density, which might reflect the prominent role that visibility plays in habitat selection by prairie dogs. In contrast, we found weak evidence that human features have significant impacts on site occupancy by prairie dogs. Our results support the prediction that environmental conditions of sites used by prairie dogs in edge regions partially differ from those observed in more northern latitudes. We suggest that reserve managers focus conservation efforts on areas with short vegetation, low density of shrubs, and high herbage cover, conditions that could be promoted by controlled burns, herbage mowing, and mechanical removal of shrubs.

Stochasticity as an alternative to deterministic explanations for patterns of habitat use by birds

Stochasticity is rarely explicitly investigated as a determinant of patterns of habitat use, even though evidence of its influence would undermine support for deterministic models of habitat selection. To assess the role of stochasticity in generating patterns in habitat use, we compared observed patterns of year‐to‐year variation in habitat use of 20 bird species over five years with patterns randomly generated from null models with different biological constraints (i.e., abundance, territoriality, exclusion of unused habitat, site fidelity, and habitat preference). We were able to recreate patterns of variability in spatial distributions with one or more null models for 18 species, suggesting an important role of stochasticity. Although year‐to‐year variability could be modeled as a purely stochastic process for only four species, null models in which random variability was constrained by the influences of vegetation or site fidelity collectively matched the observed patterns of variability of all 18 species. Support for these two models suggested that factors that increase the likelihood of returning to a previously used area and thus limit the spatial extent of random territory placement can generate patterns similar to those we observed. Greater support for models with preference constraints (i.e., models that included bird–vegetation associations) over models with avoidance constraints (i.e., models that excluded areas that were never occupied) indicated that preference was the primary mode of habitat selection. Stochastic patterns in habitat use may have resulted from a weak relationship between habitat selection and habitat quality, influence of non‐vegetation habitat features (e.g., climatic fluctuations), nonequilibrium conditions, and a greater influence of stochastic variation at small spatial and temporal scales. Alternatively, responses to environmental cues may have been deterministic, but in summation, these responses may have created variability in spatial distribution patterns that was indistinguishable from random variation. In such cases, we suggest that it may be easier to model variation in habitat use as a random process rather than using deterministic models that account for a multitude of environmental factors influencing habitat selection of birds. Regardless, stochasticity may play a larger role in generating patterns of habitat use than is often considered, and it deserves wider attention.

Optimizing the use of decoy plots for blackbird control in commercial sunflower

In 2004, USDA's Wildlife Services began to cost share 8-ha Wildlife Conservation Sunflower Plots (WCSP) with sunflower growers to lure migrating blackbirds away from commercial sunflower fields. During late summer and fall of 2004 and 2005, blackbirds used sunflower more than other crops, especially WCSP placed near blackbird roosts. Blackbird density in WCSP and commercial sunflower was negatively associated with nearby habitat types (<2.4 km) that provided alternative foraging locations, including hectares of sunflower, wheat, and fallow lands. Blackbird density was positively associated with shelterbelts, wetlands, and unused habitats, such as soybean fields. Blackbird damage was lower in commercial sunflower fields closely associated with WCSP (≤2.4 km) than commercial sunflower fields >10 km from WCSP. Across both years, birds removed an average of 435 kg/ha and 49 kg/ha of sunflower seed in WCSP and commercial sunflower fields, respectively. Additionally, in 2005, blackbirds removed 181 kg/ha of seed in commercial sunflower >10 km from WCSP (reference fields). WCSP had a cost-benefit ratio of 3.4:1; however, in reference sunflower fields, birds removed 3.2 times more sunflower seed than in commercial sunflower fields near WCSP. Our data suggest that producers should consider planting cost-shared WCSP as part of an integrated pest management strategy to reduce blackbird damage to commercial sunflower.

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 ...

Does life‐history variability in salmonids affect habitat use by juveniles? A comparison among streams open and closed to anadromy

1. Migratory and resident forms of salmonids coexist in many river systems. Although such coexistence is widespread, little is known about its ecological basis and no studies have compared the habitat use of premigratory juveniles and residents. 2. We employed a comparative approach to explore the differential habitat use of juvenile anadromous and resident brook trout. This required the investigation of habitat use in streams closed to anadromy, containing only resident brook trout Salvelinus fontinalis ('resident-only' streams) and streams open to anadromy, containing coexisting Atlantic salmon Salmo salar and anadromous and resident brook trout ('migrant-resident' streams). 3. We demonstrate that fast habitats (riffles) are occupied more frequently in streams with migratory brook trout relative to riffle habitats of streams with only resident brook trout. In contrast, occupation of slow current velocities (pools) was observed in both migrant-resident and resident-only streams as both stream types contain resident brook trout. The net effect is a wider distribution of occupied habitats (pool and riffles) in migrant-resident streams relative to resident-only streams, resulting in few, if any, unused habitats. 4. These results are consistent with previously reported bioenergetic, morphological and stable isotope differences observed between anadromous and resident brook trout. 5. Our findings suggest that a link exists between juvenile habitat use, metabolic costs and life-history strategies.

Assessment of the potential for negative interaction between re-introduced elk (Cervus elaphus) and resident white-tailed deer (Odocoileus virginianus) in their wintering areas in Ontario, Canada

Attempts have been made to reintroduce elk (Cervus elaphus) in Ontario, Canada, since the early 1900's. These efforts are on-going and current plans are to establish viable elk populations in 6 pre-selected restoration sites in Ontario. Significant populations of white-tailed deer (Odocoileus virginianus) exist in close proximity to some of the proposed restoration sites. Therefore a decision was made to assess the potential impact of restoring elk in white-tailed deer wintering areas in Ontario, prior to the release of elk. The primary concerns regarding white-tailed deer/elk competition are transmission of the meningeal worm (Parelaphostrongylus tenuis) from white-tailed deer to elk and the winter carrying capacity of habitat where the restoration is to occur. A review of existing data revealed that significant winter concentrations of white-tailed deer do exist in the vicinity of the Haliburton Highlands elk release site in southern Ontario. However, that proposed release site is at least 10 km from white-tailed deer wintering areas and restrictive winters occur infrequently in that area. A review of the literature, as well as interviews with Provincial and State biologists and elk managers revealed that although there was anecdotal evidence of competition between elk and white-tailed deer in a few jurisdictions, there was neither quantitative nor qualitative data to support or refute those claims. However, as snow depths increase and elk switch to browse dominated diets, there is potential for white-tailed deer/elk competition for resources if sharing the same winter range, especially during severe winters. The chances that elk and white-tailed deer will share the same winter range will depend on where the released elk decide to settle for the winter, which may be influenced by availability of unused winter habitat and the quality of the available habitat. Therefore, elk will not be released directly into traditional white-tailed deer wintering areas in Ontario. A comprehensive research and monitoring program will be mandatory for future elk releases in Ontario.

Modelling nesting habitat as a conservation tool for the Eurasian black vulture ( Aegypius monachus) in Dadia Nature Reserve, northeastern Greece

The Eurasian black vulture ( Aegypius monachus) is a globally endangered species, vulnerable in Europe and endangered in Greece. We modelled its nesting preferences in Dadia reserve, northeastern Greece using logistic models at multi-scale level combined by Bayesian statistics. Compared with the random sites, the vultures nested at trees with greater diameter (DBH), lower height, and lower total number of trees around the nest tree, steeper slopes and greater distance from forest roads. Our results indicate that conservation and management guidelines for black vultures must aim: (1) to preserve old, isolated mature trees in the reserve, (2) to maintain the zones of strict protection as vulture sanctuary, including most of the suitable nesting habitat, (3) to protect the apparently suitable but still unused habitat in the rest of the reserve from disturbance and logging, (4) to monitor any changes in habitats and use our models to evaluate and predict their effect on vulture nesting in the reserve.

Bwindi Impenetrable National Park, Uganda: gorilla census 1997

AbstractBwindi Impenetrable National Park in south-west Uganda supports a population of gorillas that has become the primary gorilla population for tourism following the genocide in Rwanda. Previous estimates made in the early 1990s indicated that the population numbered around 300 individuals. The census reported here was the first in Bwindi to use the method successfully developed in the Virungas, which utilizes a complete sweep across the park within a short period of time by a large number of teams working simultaneously. We estimated the population to be 292 individuals; to the best of our understanding – based on previous estimates – the population, therefore, appears to be stable. Most gorillas were found within the centre of the southern section of the park. It appears that there are some areas of unused habitat and, therefore, room for the population to grow. We found no clear relationship between gorilla distribution and human presence, but some forms of disturbance were more frequent and close to the edge of the park and may contribute to the gorillas' avoidance of these areas. The effects of human disturbance, including tourism, on the gorillas and other wildlife should be investigated in more detail and monitored over time. This is particularly important in multiple-use zones which have been established around the edges of the park for bee-keeping, collection of nontimber forest products, and tourism.

Predicting broad-scale occurrences of vertebrates in patchy landscapes

Spatially explicit landscape-scale models that predict species distributions, where patches of habitat are shown as having potential to be occupied or unoccupied, are increasingly common. To successfully use such data, one should understand how these predicted distributions are created and how their relative accuracies are assessed. Geographic ranges, defined upon observations (e.g., atlases), literature review, and expert review, are a primary data layer. A map of land cover is created, often from interpretation of satellite imagery or other remotely-sensed data. Species/habitat associations are defined based upon a literature review and expert review, describing associations for habitats derived from the cover map. Included as ancillary associations are how species relate to physical features, where appropriate, such as elevation and hydrography. The three layers of information (range, land cover, and associations) are merged, often using raster-based algebraic statements that exclude unused habitats or patches outside the range of a species. The accuracy of predictions for a suite of species is typically assessed with surveys by comparing the species predicted to occur in an area to the species observed. Omission (i.e., present in species lists but not predicted) and commission (i.e., predicted but not present in lists) errors are reported. Errors may be due to many sources. For example, ranges of species change, cover types may be misidentified, species/habitat associations may be incorrect or change, or species may be rare and unlikely to be seen in surveys and judged in-error even though the species may be present. An example is given of an appropriate use of broad-scale species predicted distributions, in which patterns and threats to Maine terrestrial vertebrate diversity are summarized.

Why is the coral-reef fish Valenciennea strigata (Gobiidae) monogamous?

Parental-investment theory predicts that monogamy should be rare, and empirical evidence supports this prediction. Monogamy has generally been explained by either (1) a need for biparental care, or (2) a uniform distribution of limiting resources. By contrast, monogamy has evolved in several coral-reef fishes without biparental care, and many coral-reef fishes may not be limited by resources. Monogamy in these fishes might be explained by either (3) a low population density that favors mate fidelity, or (4) an abundance of resources that allows all males to breed and thus lowers the cost-benefit ratio for females that mate guard. We tested predictions of these hypotheses in the coral-reef fish, Valenciennea strigata, except that (1) biparental care had previously been rejected. We found no evidence of resource limitation (2a): food densities within territories did not differ from the density of food in unused habitat adjacent to territories; potential nest sites also existed in this unused habitat. Similarly, (2b) if resources limit the population, territory defense might require the coordinated efforts of a pair; however, widowed fish maintained their territories and (3) remated rapidly. Finally, (4) all males maintained a nest, both sexes enforced monogamy by mate guarding, and females benefited from guarding a high-quality (large) mate. Females mated to large males fed more than when they paired with small males. The results support the hypothesis that abundant and uniformly distributed resources can lead to monogamy by lowering the cost of guarding a mate when mate guarding provides benefits.

Habitat Selection by Immature Spanish Imperial Eagles During the Dispersal Period

The Spanish imperial eagle Aquila adalberti is the most endangered bird of prey in Europe, with less than 150 pairs remaining alive, and it is one of the most endangered species in the world. The densest Spanish imperial eagle population is located in the Donana National Park, south-western Spain and is made up of 15-16 breeding pairs. Since 1973, a variety of management techniques have been implemented to increase productivity in the breeding population. Despite this, eagles have not colonized the surrounding area. Studies were carried out to provide a quantitative description of the habitats selected by immature Spanish imperial eagles during their dispersal period. The exact locations of the 23 temporary settling areas were determined by radio-tracking from the ground and periodic checks by light aircraft. To evaluate available but unused habitats, coordinates of the same number of random points were generated and compared to actual locations. The results indicated that young eagles select areas with pasture or cultivated farmland covered by scattered Quercus spp. trees (Oak savanna) and avoid irrigated fields and paved roads. The ecological data provided by this study can be used to predict those areas where changing land use would have the greatest, and least effects on dispersing eagles and, in consequence, on the stability of the breeding population. Management recommendations for those areas include modification of power lines to avoid electrocution during the dispersal phase, presumption against construction of new power lines or roads, presumption against any increase in tree plantations, and financial incentives to maintain existing management regimes in preferred areas, i.e. non-irrigated fields, pastures and cultivated farmland with a scattered distribution of Quercus spp. and Olea spp.