Measured Habitat Characteristics Research Articles

Winter food selection and exploratory behavior vary with natal territory characteristics in wild great tits

Differences in habitat characteristics experienced during rearing associate with variation in a range of behavioral phenotypes such as exploratory behavior, foraging behavior and food selection. The habitat-dependent selection hypothesis predicts that animals develop behavioral characteristics fitted to their rearing environment. Yet, little is known about how habitat characteristics during rearing shape how animals face winter conditions and adjust their winter foraging behavior. The aim of this study was to explore how fine-scale rearing habitat characteristics associate with exploratory behavior, food selection, and foraging performance during winter. For this, we measured habitat characteristics during the breeding season in territories of wild great tits (Parus major) and tested first-year juvenile birds that fledged from these territories for exploratory and foraging behavior at feeders during winter. We found evidence that faster explorers were raised in territories with lower quality habitat characteristics. In addition, fast exploring fledglings visited the feeders significantly more (total visits). Moreover, the rearing environment, via caterpillar availability and tree species composition, determined diet selection during winter in first-year birds. These results show support for the habitat-dependent selection hypothesis, since exploratory behavior as well as food selection during winter associate with habitat features of the rearing territories during development. This pattern can be caused either by the kinds of natural foods prevalent during rearing at these sites or because of intrinsic individual differences. Further experiments are needed to disentangle these two.Significance statementIndividuals vary in how they behaviorally adapt foraging and food selection strategies to the environmental conditions. A number of studies have shown that animals develop behavioral characteristics fitted to their rearing environment. However, how habitat characteristics during rearing shape the foraging strategy that animals use to face winter conditions is still unknown. We studied these links in yearling great tits using automated feeders that recorded their visits during winter. Fledglings with a higher exploratory score were born in territories with lower quality habitat characteristics and visited the feeders more. Furthermore, we found an association between caterpillar availability and tree species composition in the rearing territory of juveniles and their subsequent food selection in winter. Our study indicates that certain environmental conditions might favor the development of particular behaviors in birds and that early nutrition could shape food choice later in life.

Habitat Characteristics Supporting Bird Species Richness in Mid-Field Woodlots

Farmland biodiversity has undergone drastic declines due to agricultural intensification during the last decades. To prevent further biodiversity loss, the maintenance and restoration of non-productive habitats is essential. Woodlots, small patches of woody vegetation in agricultural landscapes, are one such habitat that are currently subsidized by the European Union’s Common Agricultural Policy (EU’s CAP). For effective implementation, however, it is necessary to assess what habitat characteristics are the most beneficial for biodiversity. Our study performs such an assessment using birds as model organisms. Specifically, we related characteristics of various woodlots to (I) the species richness of all birds, and (II) the species richness of both forest and farmland birds–groups with different ecological requirements. For this purpose, we counted birds (27 farmland and 26 forest species) and measured habitat characteristics (describing vegetation structure, diversity and nativeness) and spatial characteristics (area, shape and isolation) in 82 mid-field woodlots (0.76–1.25 ha, average 0.46 ha) in the Czech Republic (Central Europe). After accounting for the effects of spatial characteristics, overall bird species richness increased with vegetation height and woody plant species richness. In addition, richness showed a non-linear decrease with the cover of an invasive tree, the Black Locust Robinia pseudoaccacia. Interestingly, forest bird species richness was related to the same habitat characteristics as the overall bird species richness. By contrast, farmland bird species richness was positively related to the diversity of woodlot microhabitats, which reflects mainly enrichment by non-forest sites such as grassland or sparse shrubs. Our results indicate that the ecological performance of habitat characteristics (and not only the woodlot area) is important for the restoration of bird diversity in woodlots, and as such should be taken into consideration by the EU’s CAP subsidy system. Moreover, if woodlot management aims to maximize the overall bird diversity—a common practice in biodiversity conservation—our results show that current practices may favor widespread forest bird species, but not the farmland birds that are more threatened in Europe. To manage the woodlot habitat for farmland birds, we suggest that microhabitat heterogeneity should be maximized.

Five-Year Monitoring of a Desert Burrow-Dwelling Spider Following an Environmental Disaster Indicates Long-Term Impacts.

Simple SummaryDeserts are characterized by unpredictable precipitation, extreme temperatures, and plants and animals that are specialized to live in these habitats. Consequently, desert organisms often recover slowly, if at all, from human-induced environmental disasters. We studied the effects of two nearby oil spills from a broken pipeline, one that occurred in 1975 and another recent one in 2014, on a burrow-dwelling spider in the extreme desert of the ‘Arava valley (Israel). We compared the abundance of spider burrows in plots contaminated by the oil with nearby unaffected plots over a 4-year period. The abundance was significantly lower in plots with oil-contaminated soil, both in the recent (2014) oil spill area and in the area affected by the 1975 spill. In the laboratory, we found that when offered oil-contaminated versus clean desert soil substrates, spiders chose the clean soil substrate. We conclude that the populations of this burrow-dwelling spider were affected negatively by the oil spills and, furthermore, showed long-lasting impacts from a 40-year-old spill. We propose that burrow-dwelling spiders can be used as effective bioindicators of persistent soil pollution in desert habitats.Deserts are characterized by unpredictable precipitation and extreme temperatures. Their fauna and flora are sensitive to anthropogenic environmental changes, and often recover slowly from environmental disasters. The effects of oil spills on the biota of desert regions, however, have scarcely been studied. We predicted that terrestrial invertebrates suffer long-term negative effects from an oil spill, due to their close association with the substrate. Thus, we investigated the effects of two oil spills that occurred in 1975 and 2014 in the hyper-arid ‘Arava desert (Israel), on a spider that constructs silk-lined nests in burrows in compact, sandy soil in this extreme desert habitat. The spider, Sahastata aravaensis sp. nov. (Filistatidae), is described herein. We assessed spider burrow abundance in plots located in oil-contaminated and nearby uncontaminated clean soil (control) areas over five consecutive years and measured habitat characteristics in these plots. In the laboratory, we determined the preference of individuals for clean vs. oil-contaminated soil as a resting substrate. Finally, as this species was previously undescribed, we added a new species description. The abundance of Sahastata was significantly lower in oil-contaminated plots, and this was the case in the 40-year-old oil spill (1975) as well as in the recent one (2014). In laboratory tests, spiders showed a significant preference for the clean soil substrate over the oil-contaminated substrate. In the field, soil crust hardness and vegetation density did not differ significantly between oil-contaminated and control plots, but these measures were highly variable. The burrows were significantly clustered, suggesting that the young disperse only short distances. In the laboratory adult spiders did not dig burrows, perhaps indicating that adults remain permanently in their natal burrows and that in the field they may use vacant burrows. We conclude that Sahastata populations were affected negatively by the oil spills and these effects were long-lasting. We propose that by monitoring their spatial distribution, burrow-dwelling spiders such as Sahastata can be used as effective bioindicators of soil pollution in desert habitats.

Urbanization is associated to a loss of phylogenetic diversity of birds in a medium size city on the Andes of Colombia, South America

ABSTRACT Accelerated rates of urbanization negatively impact natural habitats and biodiversity. Studies of the effects of urbanization on fauna have emphasized taxonomic diversity, but this does not necessarily reflect effects on the evolutionary history of assemblages. Here, we study how urbanization influences phylogenetic diversity (PD) of bird assemblages in a small–medium city in the Central Andes of Colombia. Between 2016 and 2017, we performed bird surveys in 76 urban cells and 23 rural cells around the city. Then, we measured habitat characteristics (e.g. anthropogenic noise level, impervious and forested area) in sampled cells. PD of birds was between 1.37–1.42 MY higher in the rural than in the urban habitat. Within the urban habitat, the PD of birds reduces as impervious area and noise levels increase, while in the urban cells with most forested areas reach the highest PD values. Most of these differences and relationships disappear when we performed similar analysis controlling for differences in species richness. A low turnover of PD between assemblages of birds recorded inside Armenia and its less urbanized surroundings suggest green areas in the study area could mitigate the effects of urbanization in native fauna, and ameliorate connectivity between urban cells.

Small owls in relation to habitat structure: occurrence of Tropical Screech-owl (Megascops choliba) and Ferruginous Pygmyowl (Glaucidium brasilianum) in the mountain forests of central Argentina

Owls are top predators poorly studied in the Neotropics. Their occurrences can be affected by forest structure and landscape features. We report Tropical Screech-Owl (Megascops choliba) and Ferruginous Pygmy-Owl (Glaucidium brasilianum) detections in relation to habitat characteristics in central Argentina. During the spring of 2019, we surveyed 250 ha of mountain forest, measured habitat characteristics in presences/absences sites, and estimated owls’ densities. M. choliba (0.16 individuals/ha) was positively associated with snag whereas G. brasilianum (0.05 individuals/ha) was positively associated with proportions of small trees. Our results suggest that these habitat characteristics might be important covariates when studying these two species.

Headwaters Fed by Subterranean Ice: Potential Climate Refugia for Mountain Stream Communities?

Near-term extirpations of macroinvertebrates are predicted for mountain streams worldwide as a warming climate drives the recession of high-elevation ice and snow. However, hydrological sources likely vary in their resistance to climate change, and thus streams fed by more resistant sources could persist as climate refugia for imperiled biota. In 2015–2016, we measured habitat characteristics and quantified macroinvertebrate community structure along 6 alpine streams in the Teton Range, Wyoming, USA. Strong differences in habitat characteristics (e.g., temperature, bed stability, conductivity) confirmed 3 major stream sources: surface glaciers, perennial snowfields, and subterranean ice. Subterranean ice-fed streams—termed “icy seeps”—appear common in the Teton Range and elsewhere, yet are globally understudied. Midges in the family Chironomidae dominated our study sites, representing 78.6% of all specimens sampled, with nematodes, caddisflies (Neothremma), and mayflies (Epeorus) also common. At the community scale, glacier- and snowmelt-fed streams differed significantly in multivariate space, with icy-seep communities intermediate between them, incorporating components of both assemblages. Because the thermal environment of subterranean ice, including rock glaciers, is decoupled from large-scale climatic conditions, we predict that icy seeps will remain intact longer than streams fed by surface ice and snow. Furthermore, our results suggest that icy seeps are suitable habitat for many macroinvertebrates occupying streams fed by vulnerable hydrological sources. Thus, icy seeps may act as key climate refugia for mountain stream biodiversity, an idea in need of further investigation.

An experimental test of information use by wood ducks (Aix sponsa): external habitat cues, not social visual cues, influence initial nest site selection

Birds may use a variety of cues to select a nest site, including external information on habitat structure and nest site characteristics, or they may rely instead on social information obtained directly or indirectly from the actions of conspecifics. We used an experimental manipulation to determine the extent to which a California population of the wood duck (Aix sponsa) used social information gleaned from visual cues inside nest boxes that might indicate the quality or occupancy of that site. Over two nesting seasons, we manipulated the contents of newly installed boxes to simulate one of three states: (1) presence of wood duck eggs, indicating current use of a nest site; (2) presence of down and shell membranes, indicating a previously successful nest; and (3) control nests with fresh shavings indicating an unused box. In addition, we measured habitat characteristics of the area surrounding each box to assess the use of external, non-social information about each nest site. We found no evidence that females laid eggs preferentially, or that conspecific brood parasitism was more likely to occur, in any of the treatments. In contrast, nest site use and reproductive traits of wood ducks did vary with vegetation cover, and orientation and distance of the box from water. Our results suggest that personal information, not social information, influences initial nest site selection decisions when females are unfamiliar with a site. Social cues likely become increasingly important once nest sites develop their own history, and a population becomes well established. In selecting a nest site, birds may use many types of information, including habitat characteristics, their own previous breeding experience, or social cues inadvertently provided by other individuals of the same or different species. We examined information use in a Californian population of wood ducks by experimentally manipulating the visual cues within nest boxes and found that females did not use internal box cues to direct their nesting behaviors, appearing to rely on key habitat characteristics instead. These results contrast with previous studies of this system, suggesting that females may change the cues they use depending on their prior experience with a particular area. In the nest site selection literature, there appears to be a divergence between research on passerines versus waterfowl, and we advocate unifying these perspectives.

Nest site selection by Loggerhead Shrike (Lanius ludovicianus) in a fragmented landscape

Understanding which factors influence nest site selection can lead to more effective species conservation. The Loggerhead Shrike (Lanius ludovicianus) has experienced severe declines since the 1940s and could potentially benefit from fine-scale management for nesting habitat, especially where fragmentation impedes conservation at the landscape scale. We examined how habitat characteristics at the nest tree and territory core scales influenced nest site selection by Loggerhead Shrikes in the coastal plain of South Carolina. We found 41 Loggerhead Shrike nests and measured habitat characteristics at the nest site and at available sites to model selection factors at the tree and territory core scales. Loggerhead Shrikes selected for low heterogeneity of vegetation density, high heterogeneity of vegetation height, and lower shrub and tree densities at the territory core scale. Loggerhead Shrikes also preferred nest trees with larger diameters at breast height. Overall, Loggerhead Shrikes appeared to select for nest site characteristics that enhanced foraging ease and success, and limited predation risk. We suggest that landowners in the southeastern coastal plain increase grassy habitat on their property and retain large trees in suitable nesting locations to increase optimal nesting habitat for Loggerhead Shrikes.

Influence of prescribed fire and forest structure on woodland salamander abundance in the central Appalachians, USA

Prescribed fire is used in the central Appalachians to promote and maintain mixed-oak and pine forests, create open forest conditions, improve habitat for wildlife, and to reduce the risk of impact of higher intensity wildfires on human development. Few studies have investigated responses of terrestrial salamander populations to habitat management using fire, and estimated responses have been neutral, negative, and positive depending on geography, species, and fire-severity. We examined woodland salamander (genus Plethodon) population responses to habitat management using prescribed fire on Shenandoah Mountain in the George Washington National Forest in West Virginia and Virginia, USA. We focused on responses of the Cow Knob Salamander (P. punctatus), a talus specialist and species of high conservation concern, but also examined responses of the Eastern Red-Backed Salamander (P. cinereus), a widespread habitat generalist. Three burn units were subjected to two low-severity burns and one unit was burned five times with ca. 40% tree mortality. Using a combination of nighttime visual encounter surveys and coverboard surveys, we compared terrestrial salamander abundance and body condition in unburned and burned areas. We also measured habitat characteristics at sampling sites to determine if prescribed burn histories were correlated with habitat conditions important to woodland salamanders. Mean abundance for P. punctatus was lower at sites that were burned, but there was not a strong burn effect for P. cinereus. Abundance of both species was positively correlated with canopy cover. Mean and median body condition index (BCI) score was higher for P. punctatus and lower for P. cinereus on the West Virginia side of Shenandoah Mountain, and lower in burned areas for both species. However, the most parsimonious BCI models did not contain the burn predictor. Management using prescribed fire altered microhabitat conditions that are important for woodland salamanders, such as canopy cover, leaf litter depth, and vegetation groundcover. Our study suggests that woodland salamanders in the central Appalachians can persist in forests managed using prescribed fire, but also indicates that prescribed fire can result in reduced habitat quality for some woodland salamander species.

Characterization of Pallid Sturgeon ( Scaphirhynchus albus ) Spawning Habitat in the Lower Missouri River

Acipenseriformes (sturgeons and paddlefish) globally have declined throughout their range due to river fragmentation, habitat loss, overfishing, and degradation of water quality. In North America, pallid sturgeon (Scaphirhynchus albus) populations have experienced poor to no recruitment, or substantial levels of hybridization with the closely related shovelnose sturgeon (S. platorynchus). The Lower Missouri River is the only portion of the species’ range where successful reproduction and recruitment of genetically pure pallid sturgeon have been documented. This paper documents spawning habitat and behavior on the Lower Missouri River, which comprises over 1,300 km of unfragmented river habitat. The objective of this study was to determine spawning locations and describe habitat characteristics and environmental conditions (depth, water velocity, substrate, discharge, temperature, and turbidity) on the Lower Missouri River. We measured habitat characteristics for spawning events of ten telemetry-tagged female pallid sturgeon from 2008–2013 that occurred in discrete reaches distributed over hundreds of kilometers. These results show pallid sturgeon select deep and fast areas in or near the navigation channel along outside revetted banks for spawning. These habitats are deeper and faster than nearby river habitats within the surrounding river reach. Spawning patches have a mean depth of 6.6 m and a mean depth-averaged water-column velocity of 1.4 m per second. Substrates in spawning patches consist of coarse bank revetment, gravel, sand, and bedrock. Results indicate habitat used by pallid sturgeon for spawning is more common and widespread in the present-day channelized Lower Missouri River relative to the sparse and disperse coarse substrates available prior to channelization. Understanding the spawning habitats currently utilized on the Lower Missouri River and if they are functioning properly is important for improving habitat remediation measures aimed at increasing reproductive success. Recovery efforts for pallid sturgeon on the Missouri River, if successful, can provide guidance to sturgeon recovery on other river systems; particularly large, regulated, and channelized rivers.

Disentangling effects of invasive species and habitat while accounting for observer error in a long‐term amphibian study

AbstractThe invasive American bullfrog (Lithobates catesbeianus) and a variety of non‐native sport fish commonly co‐occur in lowland lentic habitats of the western United States. Both invasive taxa are implicated in declines of native amphibians in this region, but few long‐term studies of communities exist. Further, field studies of invasive–native interactions are complicated by confounding habitat modifications and observation errors. We surveyed amphibians and measured habitat characteristics for 12 yr across 38 wetland sites within the Willamette Valley, Oregon, USA. We assessed the influence of invasive species, habitat, and their interactions on the distributions of five native amphibian species using a multispecies dynamic occupancy model that accounted for false‐negative and false‐positive detections. In general, habitat characteristics—such as within‐pond vegetation cover, surrounding forest, and drought severity—were important for local persistence of native species when bullfrogs co‐occurred. We also found evidence of a cumulative negative effect of bullfrogs and non‐native fish (families Centrarchidae and Ictaluridae) on northern red‐legged frog (Rana aurora) local persistence that was mediated by the dominance of invasive reed canarygrass (Phalaris arundinacea). Non‐native fish and bullfrogs had variable effects on native amphibian species, but neither invasive taxon appears to be causing declines in occupied sites within our study area. Moreover, species relationships with habitat differed when invaders were present, indicating that certain habitats may increase persistence of native amphibians in the invaded landscape.

Overlap and selection of dust-bathing sites among three sympatric montane galliform species

ABSTRACT Niche theory predicts that, to avoid interspecific competitive exclusion, ecologically similar bird species in sympatry should reduce habitat use overlap, especially when shared resources are limiting in an environment. Dust-bathing sites represent a distinctive behavior-specific habitat, differing from other habitats as they are used for short durations and infrequently. However, we have little understanding of selection, potential interspecific overlap, and partitioning of dust-bathing sites among sympatric species. In this study, we examined overlap and selection of dust-bathing sites of 3 sympatric montane galliform species on the Qinghai-Tibet Plateau: Blood Pheasant (Ithaginis cruentus), Szechenyi's Partridge (Tetraophasis szechenyii), and White Eared-Pheasant (Crossoptilon crossoptilon). We identified dust-bathing scrapes and measured habitat characteristics of dust-bathing sites along 10 transects established in Gexigou National Nature Reserve, Sichuan Province, China, from April to Augus...

Habitat drives dispersal and survival of translocated juvenile desert tortoises

Summary In spite of growing reliance on translocations in wildlife conservation, translocation efficacy remains inconsistent. One factor that can contribute to failed translocations is releasing animals into poor‐quality or otherwise inadequate habitat. Here, we used a targeted approach to test the relationship of habitat features to post‐translocation dispersal and survival of juvenile Mojave desert tortoises Gopherus agassizii. We selected three habitat characteristics – rodent burrows, substrate texture (prevalence and size of rocks) and washes (ephemeral river beds) – that are tied to desert tortoise ecology. At the point of release, we documented rodent burrow abundance, substrate texture and wash presence and analysed their relationship to the maximum dispersal. We also documented the relative use by each individual for each habitat characteristic and analysed their relationships with survival and fatal encounters with a predator in the first year after release. In general, the presence of refugia or other areas that enabled animals to avoid detection, such as burrows and substrate, decreased the overall mortality as well as predator‐mediated mortality. The presence of washes and substrate that enhanced the tortoises’ ability to avoid detection also associated with the reduced dispersal away from the release site. These results indicate an important role for all three measured habitat characteristics in driving dispersal, survival or fatal encounters with a predator in the first year after translocation. Synthesis and applications. Resource managers using translocations as a conservation tool should prioritize acquiring data linking habitat to fitness. In particular, for species that depend on avoiding detection, refuges such as burrows and habitat that improved concealment had notable ability to improve the survival and dispersal. Our study on juvenile Mojave desert tortoises showed that refuge availability or the distributions of habitat appropriate for concealment are important considerations for identifying translocation sites for species highly dependent on crypsis, camouflage or other forms of habitat matching.

Density, Abundance, and Habitat Associations of the Inland Swamp Sparrow (Melospiza georgiana georgiana) in Iowa

Wetlands continue to decline throughout North America and the Prairie Pothole Region, thus emphasizing the importance of understanding population trends and habitat associations of wetland species to ensure effective conservation and habitat management of those species. We estimated density and abundance and evaluated habitat associations of the Inland Swamp Sparrow (Melospiza georgiana georgiana) in Iowa. We conducted standardized distance sampling surveys for Swamp Sparrows and measured habitat characteristics at 307 wetlands in two regions of Iowa in 2009 and 2010. We used Program Distance to model detection probability and estimate region-specific breeding densities of Swamp Sparrows at Iowa wetlands. We then extrapolated density estimates to the total area of wetlands in each region to obtain estimates of breeding abundance. We correlated Swamp Sparrow counts to nine habitat variables using Poisson regression in Program R. Swamp Sparrow counts were positively correlated with percent cover of cattail (Typha spp.) and water depth (cm) and negatively correlated with percent cover of woody vegetation, vegetation size (m), and wetland size (ha). We estimated breeding densities of Swamp Sparrows to be 1.488 birds/ha (95% CI 5 1.308 � 1.692) in region 1 (Des Moines Lobe landform) and 0.041 birds/ha (95% CI 5 0.006 � 0.275) in region 2 (remainder of the state). Our results, in comparison to those of other studies, indicate that Swamp Sparrows associate with a variety of wetland characteristics depending upon what is available. Swamp Sparrows are relatively uncommon breeders in Iowa, and our work confirms that most occur in the Des Moines Lobe landform in north-central and northwestern Iowa. Biologists and land managers should incorporate our findings on this species' habitat associations into management activities to ensure that Swamp Sparrow populations persist into the future. Received 5 January 2015. Accepted 30 April 2015.

Short-term effects of irregular shelterwood cutting on yellow birch regeneration and habitat use by snowshoe hare

Irregular shelterwood cutting has been recently prescribed to improve the regeneration of semi-tolerant species such as yellow birch (Betula alleghaniensis B.), while also maintaining the complexity of natural mixed forests. However, its effects on forest dynamics are poorly known. In this study, we document the short-term effects of three irregular shelterwood cutting patterns on the establishment and composition of regeneration as well as on its use by snowshoe hare (Lepus americanus E.). Specifically, we compared uniform, gap, and strip cutting patterns with soil preparation, relative to uncut controls. We counted seedlings, browse, and hare pellets, and measured habitat characteristics after two growing seasons in micro-plots delimited in each of the shelterwood cutting patterns. The mixture of soil and humus resulting from scarification promoted yellow birch establishment. Yellow birch seedlings in gaps were more abundant than in controls, but their abundance was comparable to other irregular shelterwood patterns. All irregular shelterwood patterns promoted competition mainly by pin cherry (Prunus pensylvanica L.f.), beaked hazel (Corylus cornuta M.), and mountain maple (Acer spicatum Lam.). Snowshoe hare browse on yellow birch was low for all irregular shelterwood patterns. Moose browse pressure was higher than that from hare. We found no short-term impact of the snowshoe hare on yellow birch seedling establishment and survival. Snowshoe hare pellet counts suggested a preference for gaps. This result could be explained by increased food and protective cover from higher seedling and shrub densities in gaps than in other treatments. In the short-term, up to three years post-treatment, irregular shelterwood cutting helps to promote yellow birch regeneration, a semi-tolerant species, while maintaining habitat for snowshoe hare.

Roost Habitat of Mexican Spotted Owls (Strix occidentalis lucida) in the Canyonlands of Utah

ABSTRACT In large portions of their geographic range, Mexican Spotted Owls (Strix occidentalis lucida) roost in forest-dominated environments, but in some areas the owls use relatively arid rocky canyonlands. We measured habitat characteristics at 133 male roosts (n = 20 males) during 1992–95, and 56 female roosts (n = 13 females) during 1994–95 in canyon environments of southern Utah. Across all years, 44% of Mexican Spotted Owls’ roosts were located in small stands of mixed-conifer forest, 30% in desert scrub vegetation, 16% in pinyon-juniper woodlands, and 10% of roosts were in riparian habitat. Roost sites were located in canyons composed of cliff-forming geologic formations. The width of canyons measured at roosts averaged 68.6 m (8.2 SE), and ranged from 1–500 m. The mean height of cliffs at roost sites was 77 m (10.9 SE) and ranged from 6–411 m. Roosts were located at caves and ledges (46% of all roosts) or in various tree species (54%). Roost height above ground averaged 9.5 m overall (1.1 SE), wi...

Structure of tree vegetation may reduce costs of territory defence in Eurasian Nuthatch Sitta europaea

Capsule In pastured old oak woodland, breeding pairs of Eurasian Nuthatch selected territories with significantly higher densities of trees and cavities.Aims To define territorial borders that exist within a nuthatch population and to compare densities of trees and cavities between used and non-used parts of their available habitat in order to determine habitat preferences.Methods The number and location of territories was estimated by mapping the individual positions of colour-ringed birds. We measured habitat characteristics in regular sampling grid (number of trees and number of cavities per 50 × 50 m) during three successive seasons and modelled probability of occurrence of nuthatch territories in the area.Results Breeding pairs were observed to defend territories of median size between 1.46 and 2.93 ha. These sizes correspond well to high-quality habitat territories for this species. We found that pairs tended to occupy territories with higher densities of trees and cavities. Based on generalized linear mixed-effects model estimates, we found that in pastured oak woodland habitat with density of 60 trees per ha, the estimated probability of occurrence (with 95% confidence interval) of a nuthatch territory was about 96% (83−99). For cavity density, the probability of territory occurrence was about 74% (52−89) at the level of 60 cavities per ha.Conclusion We suggest that higher tree and cavity densities reduce territory defence costs in the species because birds may use less energy during foraging, predation avoidance and competition for a nest hole.

Fire severity has mixed benefits to breeding bird species in the southern Appalachians

Fire is frequently applied as a management tool on both public and private lands. However, in some ecosystems there is little information about bird species’ responses to these fire programs. In 2004 we measured habitat characteristics and conducted point counts in 12 burned sites and four unburned sites in the Chattahoochee National Forest of northern Georgia. Burns were categorized by severity (low, medium, or high) and time since fire (1–2 or 3–6 years). The basal area of snags, shrub stem density and percent canopy cover were similar among all treatments except high severity. Otherwise, fire severity had limited impacts on measured habitat characteristics. Following fires the densities of early-succession species such as eastern towhee ( Pipilo erythropthalmus) and indigo bunting ( Passerina cyanea) were greatest in areas of higher fire severity. A ground-nesting species (ovenbird [ Seiurus aurocapilla]) was less abundant in burned sites and the density of a shrub nesting species, the hooded warbler ( Setophaga citrine) was greatest in areas that received low severity fires. Scarlet tanager ( Piranga olivacea), tufted titmouse ( Baeolophus bicolor), red-eyed vireo ( Vireo olivaceus), black-throated green warbler ( Setophaga virens), and black-and-white warbler ( Mniotilta varia) had similar densities among all burn severities and showed no relationships with time since fire. Low and medium severity fires provided few benefits for most bird species. When conditions allow for their application, severe fires may be considered as a useful and historically appropriate management tool for some high-priority bird species in the southern Appalachian Mountains.

Importance of environmental and spatial gradients on patterns and consequences of resource selection

Strategies to conserve rare species require identifying resources that function as important habitat elements and that promote high demographic performance. Assessing the relative importance of resources, however, can be confounded by natural variation in resource availability and by the hierarchical spatial structure in which resources are organized. Because availability and relative importance of resources often vary across environmental and spatial gradients, we used gradients together with resource selection functions and variance decomposition to assess the relative importance of resources to nest site selection and reproductive performance of Ferruginous Pygmy-Owls (Glaucidium brasilianum). We measured habitat characteristics of 106 nests and paired available sites at five spatial scales across a 220-km gradient of precipitation and vegetation in northwest Mexico, in a region adjacent to the southwestern United States where pygmy-owls have declined to near extinction. Resources explained 76-85% of variation in nest site selection and 21-31% of variation in reproductive performance across all spatial scales combined. Although we found evidence of resource selection at each scale, the magnitude of selection and influence of resources on reproductive performance were greatest where availability of selected resources were low and where temperature extremes and predation risk likely increased the relative importance of these resources. At larger scales, geographic changes in resource use corresponded with changes in availability, whereas at smaller scales, resource use varied little despite changes in availability, suggesting higher specificity and importance of resources at smaller scales. At the smallest scale, owls selected nest cavities with smaller entrances, larger volume, greater height, and orientations that produced cooler microclimates in the hottest regions of the study area; these choices promoted higher reproductive performance. Cavity resources explained more variation in selection and reproductive performance than resources at larger scales, highlighting their importance as conservation targets. High correlation of resource characteristics among spatial scales, however, indicated that selection of resources at small scales depended on characteristics of resources at larger scales. Assessing how resource selection changes in response to underlying variation in resource availability can help prioritize resources most important for conservation and management.

Ambush site selection and ontogenetic shifts in foraging strategy in a semi‐aquatic pit viper, the Eastern cottonmouth

AbstractAlthough habitat selection has been studied in a variety of snake taxa, little is known about habitat selection in aquatic snake species. Additionally, due to their small size and secretive nature, juvenile snakes are seldom included in habitat selection studies. The Eastern cottonmouth Agkistrodon piscivorus is a semi‐aquatic pit viper known to use ambush, sit‐and‐wait foraging strategies. Ambush hunters are likely to select habitats that increase opportunity for successful prey capture while minimizing predation risk and maintaining appropriate thermal and hydric conditions. We characterized the foraging strategy and microhabitat use of cottonmouths at Ellenton Bay, an isolated Carolina bay freshwater wetland on the Savannah River Site in SC, USA. We measured habitat characteristics of 55 ambush sites used by 51 individual cottonmouths located during nighttime visual surveys, as well as 225 randomly selected sites within our search area. Cottonmouths exhibited an ontogenetic shift in foraging strategy with juveniles using predominately ambush foraging around the edge of the wetland while adults were most often encountered actively moving within the wetland. Principal components analysis revealed that juveniles selected foraging microhabitats that were different from random and consisted of mud substrate with sparse vegetation, whereas adults occupied a greater variety of microhabitats that did not differ from random. Concomitantly, free‐ranging cottonmouths exhibited ontogenetic shifts in diet: juveniles consumed mostly salamanders, while adults ate a greater variety of prey including other snakes and birds. Our results highlight the importance of understanding how ontogenetic changes in coloration, diet and predation risk influence foraging strategy and microhabitat selection in snakes.