Effects of Habitat on Competition Between Kit Foxes and Coyotes

Abstract: San Joaquin kit foxes (Vulpes macrotis mutica) are an endangered species with a narrow geographic range whose natural populations are limited by predation by coyotes (Canis latrans). In the warm, arid grassland and shrubland habitats where kit foxes occur, coyotes are more cover dependent than kit foxes, creating the possibility of habitat segregation. Effects of habitat variation on coyote and kit fox competition are unknown. We assessed exploitation and interference competition between coyotes and kit foxes in grassland and shrubland habitats to determine if such competition varies among habitats. With respect to exploitation competition, we evaluated habitat and spatial partitioning, diet, prey abundance, and survival for kit foxes and coyotes at the Lokern Natural Area in central California, USA, from January 2003 through June 2004. Kit foxes partitioned habitat, space, and diet with coyotes. Coyotes primarily used shrubland habitats whereas kit foxes selectively used burned grasslands. Kit foxes and coyotes had high dietary overlap with regards to items used, but proportional use of items differed between the 2 species. Kit foxes selected for Heermann's kangaroo rats (Dipodomys heermanni), which were closely tied to shrub habitats. With respect to interference competition, predation was the primary source of mortality for kit foxes, and survival of individual kit foxes was inversely related to proportion of shrub habitat within their home ranges. Our results suggest that a heterogeneous landscape may benefit kit foxes by providing habitat patches where predation risk may be lower.     

Cropland edge,forest succession,and landscape affect shrubland bird nest predation

The effects of habitat edges on nest survival of shrubland birds, many of which have experienced significant declines in the eastern United States, have not been thoroughly studied. In 2007 and 2008, we collected data on nests of 5 shrubland passerine species in 12 early successional forest patches in North Carolina, USA. We used model selection methods to assess the effect of distance to cropland and mature forest edge on nest predation rates and additionally accounted for temporal trends, nest stage, vegetation structure, and landscape context. For nests of all species combined, nest predation decreased with increasing distance to cropland edge, by nearly 50% at 250 m from the cropland edge. Nest predation of all species combined also was higher in patches with taller saplings and less understory vegetation, especially in the second year of our study when trees were 4–6 m tall. Predation of field sparrow (Spizella pusilla) nests was lower in landscapes with higher agricultural landcover. Nest predation risk for shrubland birds appears to be greater near agricultural edges than mature forest edges, and natural forest succession may drive patterns of local extirpation of shrubland birds in early successional forest patches. Thus, we suggest that habitat patches managed for shrubland bird populations should be considerably large or wide (>250 m) when adjacent to crop fields and maintained in structurally diverse early seral stages. © 2011 The Wildlife Society.     

Plant species diversity and polyploidy in islands of natural vegetation isolated in extensive cultivated lands

Natural polyploidy is often related to a longer life span, vegetative reproduction and higher competitive ability. In this paper, we test the possibility that these characteristics may favour the survival of polyploid taxa under conditions of long-term habitat fragmentation. In islands of natural vegetation isolated in extensive vineyards located in the South of France and in a large neighbouring area of natural vegetation, plant species richness and the relative abundance of polyploid taxa were assessed according to island size, isolation and vegetation structure. High species richness was observed, with numerous species restricted to the islands, suggesting that these may constitute refugia. However, species richness was not related to island size or to degree of isolation except for the flora of the woody areas. A very positive effect of area fragmentation on plant richness was observed, which is probably attributable to relatively low species overlap among the islands. Particularly high species richness was observed in open areas, provided that these were not extensively colonized by shrubs which seem to be responsible for local extinction of many annual taxa. Polyploids, which comprised mostly perennial herbs and woody species, were predominant in all the islands and in the large reference area. In open habitats invaded by shrubby species, a higher relative frequency of polyploids was observed in islands than in the reference area. Moreover, polyploid taxa were present in a larger number of islands than the diploid taxa, which were often restricted to a single island, suggesting that, after a long period of isolation, the polyploids may still have a lower probability of extinction. Evidence was obtained from vegetation structure analysis that diploid and polyploid annual herbs were restricted to open habitats and were both eliminated by shrubby species. Conversely, the diploid perennial herbs were also significantly affected by shrub colonization whereas the polyploids were mostly present in shrubby areas. This suggests that the higher competitive ability of polyploid perennial herbs may constitute a critical factor responsible for their wider distribution over the islands. We report the implications of our findings on conservation strategies, more particularly for a Mediterranean flora.     

Assessing the response of open-habitat bird species to landscape changes in Mediterranean mosaics

In Mediterranean landscapes, wildfires and land abandonment lead to major landscape modifications primarily by favouring the presence of open, shrub-like habitats. At present, we know very little of how these changes affect patterns of species occurrence at the landscape scale. In this work, we analyse the impact of these landscape changes on the occurrence patterns of eight open-habitat species by using presence/absence data collected in the Catalan Breeding Bird Atlas (NE Spain). We compared the species occurrence patterns along habitat gradients for three different landscape settings: a semi-permanent farmland–forest landscape (i.e. with variable proportions of farmland and forests) and two landscape settings which mimic those favoured by land abandonment and fire: farmland–shrubland landscapes and mosaic landscapes (i.e. variable proportions of farmland and forest coexisting with a shrubby matrix). In the forest–farmland landscape, we found a dominant negative effect of adjacent forest on species occurrence rates. This overall effect mostly disappeared in farmland–shrubland landscapes composed by two habitats with more similar vegetation structure. In mosaic landscapes, the general negative effect of forest habitats also appeared to be partially compensated by the presence of a shrubby matrix. Our results suggest that landscape gradients induced by fire and to some degree also land abandonment, mainly favouring availability of shrublands may potentially enhance the resilience of threatened open-habitat species at the landscape scale by increasing the range of potential habitats used. The analysis of species-occurrence patterns along predefined habitat gradients appears as a useful tool to predict potential species responses to land use change.     

Spatial patterns of granivorous ant nest abundance and nest site selection in agricultural landscapes of Central Spain

Summary Patterns of abundance and site selection of granivorous ant nests were investigated in extensive cereal croplands of Central Spain. Nest densities and distributions were measured in two consecutive summers (1988 and 1989), together with habitat physiognomy and seed availability. Nest site selection patterns were analysed at two spatial scales (landscape and microhabitat) with respect to habitat physiognomy. Results indicate a very constant and predictable pattern of both nest abundance and nest site selection. Granivorous ant nests were most abundant in shrublands, and shrubby microsites were selected for nest placement. Croplands, and microsites with high covers of bare ground and litter, were avoided. These patterns were consistent between years despite a 1.7-fold increase in shrubland nest densities, that was attributed to the exceptionally dry winter between nest censuses. I suggest that winter survivorship of ant nests in the unploughed landscape units, and periodic ploughing in croplands, may be the main factors constraining granivorous ant densities in the landscape studied.     

Territory quality, survival and reproductive success in southern emu-wrens Stipiturus malachurus

Multi-factor analyses of territory quality in relation to fitness components of adults are rare, especially in non-migratory species. I studied the influence of multiple attributes of territory quality (habitat type and the abundance of food and predators) on the reproductive success and survival of a threatened Australian passerine, the southern emu-wren Stipiturus malachurus . The abundance of frequently-selected prey types (lepidoptera, diptera, hemiptera and larvae) varied significantly across territories according to habitat type. Reproductive success (number of offspring fledged) was highest in territories containing a greater proportion of tall shrubland, which had the highest insect abundance of any habitat. Closed heathland and sedge/rushland also had high food abundance compared to other habitat types, but higher fledging success occurred only within closed heathland, possibly because predator density was lower in this habitat type. High snake density was associated with reduced adult survival during the breeding season and a lower probability of nest success. In sedge/rushland, any benefits of prey abundance may therefore be offset by a high density of predators. Emu-wren age and size were unrelated to breeding output of pairs, suggesting that ecological factors may swamp effects of individual quality on emu-wren fitness components. Preservation of tall shrubland and closed heathland habitats appear to be of key conservation priority for emu-wrens.     

Characteristics of Golden‐winged Warbler territories in plant communities associated with regenerating forest and abandoned agricultural fields

In the Appalachian portion of their breeding range, Golden‐winged Warblers (Vermivora chrysoptera) nest in shrubland and regenerating forest communities created and maintained by disturbance. Because populations of Golden‐winged Warblers have exhibited precipitous declines in population throughout their Appalachian breeding range, management activities that create or maintain early successional habitat are a priority for many natural resource agencies and their conservation partners. Within these early successional habitats, however, additional information is still needed concerning the relative importance of different vegetation features in selection of breeding territories by Golden‐winged Warblers. Our objective, therefore, was to use logistic regression to estimate the probability of territory‐level occupancy by Golden‐winged Warblers in north‐central Pennsylvania at two sites, each with its own early successional community, based on vegetation characteristics. Our communities were composed of shrublands and regenerating forest sites resulting from two disturbances: agriculture and forest fire. Despite differences in vegetation structure, portions of both study areas (regenerating forest and old field) supported territorial Golden‐winged Warblers. Probability of territory occupancy by Golden‐winged Warblers increased with percent blackberry (Rubus) cover in the regenerating forest community, and decreased as basal area and distance to microedge increased (i.e., as vegetation patchiness decreased) in both communities. These habitat features have also been found to influence other aspects of Golden‐winged Warbler breeding ecology such as nest‐site selection, pairing success, and territory abundance. Vegetation features influencing Golden‐winged Warbler territory establishment can differ among shrubland and regenerating forest communities, and management decisions and outcomes may be affected by these differences. Our study provides a starting point for a more comprehensive hypothesis‐driven occupancy survey to investigate features of the territories of Golden‐winged Warblers across a broader geographic range and in different vegetation communities.     

Fine-Scale Habitat Selection by Breeding White-Tailed Ptarmigan in Colorado

Species distributions are influenced by climate and topography in alpine ecosystems, yet resource selection studies of alpine species are uncommon. Basic characteristics of habitats used by alpine-endemic white-tailed ptarmigan (Lagopus leucura) have been described to explain foraging behavior, morphology, and survival in many alpine regions; however, there is a lack of information about fine-scale habitat selection for nesting and brood-rearing, particularly in the southern extent of the species’ range. Few studies have tested whether nest and brood-site selection by white-tailed ptarmigan are influenced by fine-scale components such as vegetation and arthropod communities. We assessed these fine-scale habitat characteristics analyzing paired use-available resource selection for nest (n = 61) and brood (n = 54) sites. We used conditional logistic regression for data collected in 2 alpine areas along the Front Range of Colorado, USA, during 2014 and 2015. We evaluated resource selection at larger (patch) and finer (nest site) scales. Nest-site selection at the patch scale was best predicted by cover (%) of forage forbs, rock and gravel, and shrubs. Forage forb cover explained more variation in our top nest model at the patch scale when compared to models with specific vegetation species. Females placed their nests along elevational gradients but more so at lower elevations and selected for less graminoid cover at the nest-site scale. Brood habitat selection at the patch level was influenced by cover (%) of rock and gravel and proximity to shrubs (m). Analysis of a subset of our brood data (n = 34) revealed females selected brood habitat that contained high arthropod abundance (e.g., Cicadellidae) over high vegetation cover, likely as a response to meet dietary requirements of chicks. Our results demonstrate how and where white-tailed ptarmigan are currently selecting these different breeding sites in Colorado's alpine, giving us insight into consequences this alpine-endemic bird may face if their breeding habitat is altered. © 2019 The Wildlife Society.     

Nest Predation Deviates from Nest Predator Abundance in an Ecologically Trapped Bird

In human-modified environments, ecological traps may result from a preference for low-quality habitat where survival or reproductive success is lower than in high-quality habitat. It has often been shown that low reproductive success for birds in preferred habitat types was due to higher nest predator abundance. However, between-habitat differences in nest predation may only weakly correlate with differences in nest predator abundance. An ecological trap is at work in a farmland bird (Lanius collurio) that recently expanded its breeding habitat into open areas in plantation forests. This passerine bird shows a strong preference for forest habitat, but it has a higher nest success in farmland. We tested whether higher abundance of nest predators in the preferred habitat or, alternatively, a decoupling of nest predator abundance and nest predation explained this observed pattern of maladaptive habitat selection. More than 90% of brood failures were attributed to nest predation. Nest predator abundance was more than 50% higher in farmland, but nest predation was 17% higher in forest. Differences between nest predation on actual shrike nests and on artificial nests suggested that parent shrikes may facilitate nest disclosure for predators in forest more than they do in farmland. The level of caution by parent shrikes when visiting their nest during a simulated nest predator intrusion was the same in the two habitats, but nest concealment was considerably lower in forest, which contributes to explaining the higher nest predation in this habitat. We conclude that a decoupling of nest predator abundance and nest predation may create ecological traps in human-modified environments.     

Effects of vegetation, corridor width and regional land use on early successional birds on powerline corridors

Powerline rights-of-way (ROWs) often provide habitat for early successional bird species that have suffered long-term population declines in eastern North America. To determine how the abundance of shrubland birds varies with habitat within ROW corridors and with land use patterns surrounding corridors, we ran Poisson regression models on data from 93 plots on ROWs and compared regression coefficients. We also determined nest success rates on a 1-km stretch of ROW. Seven species of shrubland birds were common in powerline corridors. However, the nest success rates for prairie warbler (Dendroica discolor) and field sparrow (Spizella pusilla) were <21%, which is too low to compensate for estimated annual mortality. Some shrubland bird species were more abundant on narrower ROWs or at sites with lower vegetation or particular types of vegetation, indicating that vegetation management could be refined to favor species of high conservation priority. Also, several species were more abundant in ROWs traversing unfragmented forest than those near residential areas or farmland, indicating that corridors in heavily forested regions may provide better habitat for these species. In the area where we monitored nests, brood parasitism by brown-headed cowbirds (Molothrus ater) occurred more frequently close to a residential area. Although ROWs support dense populations of shrubland birds, those in more heavily developed landscapes may constitute sink habitat. ROWs in extensive forests may contribute more to sustaining populations of early successional birds, and thus may be the best targets for habitat management.     

Symbiotic nesting of birds with formidable animals: a review with applications to biodiversity conservation

Increased predation and parasitism of bird nests has become a major problem in many biological communities altered by human activities, often causing declines in bird populations. To help solve this threat to biodiversity, I propose restoring the abundance of symbiotic nest-protecting animals in habitats where birds face an increased risk from predators and parasites, so that birds there can increase their chances of reproductive success by nesting close to these protectors. The re-establishment of such protective nesting associations to increase avian reproductive success differs from other proposed solutions to this problem in that it involves point defense of bird nests themselves. Rather than diminishing the number of nest predators and brood parasites in the whole habitat or community, as proposed with other approaches, the presence, activity and success of these enemies are reduced only within the microhabitat defended by the protector. The animal protecting the nest need not be larger in size than the predators or brood parasites, and is often many times smaller. In addition, it need not be from a higher trophic position, and in many cases comes from the same or a lower trophic level. Research suggests that an informed and careful use of nest protecting animals by wildlife managers can help reverse or prevent the decline of many bird populations, especially when used in combination with other approaches such as restoration of top predator populations and habitats. Although wildlife biologists have long recognized the important role that plants play in concealing and protecting bird nests from enemies, and regularly recommend manipulation of vegetation to enhance nest survival, they have generally ignored the important role that formidable animals play in protecting bird nests, and failed to incorporate animal protectors into management strategies. Because of this neglect, a host of new studies and experiments are urgently needed to provide managers with the critical information needed to use protective nesting associations effectively in integrated strategies to preserve avian biodiversity.     

Do Birds Alter Levels of Parental Investment Based on Nest‐Site Habitat Features?

Many habitats have undergone rapid changes over the past century as a result of anthropogenic activities. Organisms can respond to changes in their environment in many ways, including how much they invest in a given reproductive bout. Optimality theory and life history theory together have provided a framework for understanding how individuals make decisions about the risks and rewards of investing high levels of resources into their offspring within the context of current vs. future reproduction. Shrubland birds in the United States often breed in habitat that has been impacted by humans to varying degrees and provide an ideal system for examining whether organisms alter their levels of parental investment based on the habitat around the nest site. In this study, we assessed levels of nest‐defense behavior during a simulated nest predation event in four shrubland birds: American robins (Turdus migratorius), gray catbirds (Dumetella carolinensis), brown thrashers (Toxostoma rufum), and northern cardinals (Cardinalis cardinalis). We found that thrashers and catbirds exhibited significantly higher levels of nest defense compared to robins and cardinals and that birds with larger broods acted more aggressively in defending them. We also found that thrashers acted less aggressively as the proportion of shrubland around the nest increased and as the proportion of developed land around the nest decreased and that cardinals acted less aggressively as the proportion of developed land around the nest increased. These patterns suggest that nest‐defense behavior can covary with features of the landscape surrounding the nest, but that the factors shaping that behavior can differ by species.     

Nest‐site selection and demography of Wilson's Plovers on a North Carolina barrier island

Despite concerns about their population status, information about the habitat preferences, population size, and vital statistics of Wilson's Plovers (Charadrius wilsonia) is currently lacking. We compared habitat characteristics of nest sites and unused sites and examined factors affecting nest success on a barrier island in North Carolina in 2010 and 2011. We monitored 83 nests with cameras and added heart‐rate monitors in artificial eggs to 36 of these nests for a concurrent study of the effects of jet overflights; predator exclosures were placed around 17 of the nests with cameras. Wilson's Plovers used interdune areas, flats, and isolated dunelets on flats more than expected based on availability, and nests were located closer to dense vegetation than unused sites. Nests in interdune areas had higher daily survival rates than nests on flats, but distance to dense vegetation did not affect nest survival. Nests without cameras, heart‐rate monitors, or exclosures had a 35% predicted probability of hatching at least one egg. Exclosed nests had higher daily survival rates than nests without exclosures, but daily survival rates were lower for nests with cameras or heart‐rate monitors and for nests initiated later in the season. Daily survival rates also declined as nests aged. The predicted probability of fledging was 74%, resulting in a reproductive output of 0.78 fledglings/pair. Apparent annual adult survival was 77%, and the apparent annual survival rate for birds banded as chicks was 42%. Additional research is needed throughout the range of Wilson's Plovers to determine if populations are stable or decreasing, and to predict the productivity rates needed to maintain current populations. However, our results suggest that in our study area, predator removal and protection of sparsely vegetated overwash habitats will likely have the greatest impact on reproductive output.     

Nest placement and nesting success in two finch species colonizing a recently established plantation in an arid region

This study examines variations in nest placement and its effects on nesting success in the Desert Finch (Rhodospiza obsoleta) and the Linnet (Carduelis cannabina) which coexist in a recently established plantation (novel habitat) in a desert region in Jordan. A comparison with other habitats (old plantation in the desert and native, Mediterranean-type, habitat of the Linnet) showed that each species displayed similarity in nest placement patterns across habitats. Nest concealment predicted nesting outcome in the Linnet, whereas nest height predicted nesting outcome in the Desert Finch. Daily survival rates were significantly higher in Desert Finch nests compared to the Linnet's, perhaps because Desert Finches placed nests higher in the novel habitat, which lacked aerial nest predators. In accordance with predation theories of life history evolution, we provide evidence that variation in nest placement among the two species in a novel habitat resulted from previous exposure to different predation risks.     

The role of territory settlement,individual quality,and nesting initiation on productivity of Bell's vireos Vireo bellii bellii

Variation in habitat quality among territories within a heterogeneous patch should influence reproductive success of territory owners. Further, territory settlement order following an ideal despotic distribution (IDD) should predict the fitness of occupants if territory selection is adaptive. We recorded settlement order and monitored nests in territories occupied by individually marked Bell's vireos Vireo bellii bellii across a range of shrubland habitats in central Missouri, USA. We used an information theoretic approach to evaluate multiple hypotheses regarding the relationship between territory settlement order and seasonal territory productivity (productivity), which we define as the number of young fledged from all nest attempts in a territory. Territory settlement order and arrival date were not analogous and later arriving males displaced early settlers in 13 of 49 territories. Settlement order and lay date together were the best predictors of a territory's productivity; productivity decreased 2.08 young from earliest to latest settlement rank and lay date. Males that defended the same territory in successive years occupied territories with earlier settlement dates, but we found little evidence that age or prior ownership influenced productivity. Territory selection by male Bell's vireos was adaptive because males preferred to settle in territories that had high seasonal offspring production, but even though settlement rank was linked to territory quality, high productivity was only realized on high quality territory when also linked to early nest initiation date. While settlement rank was related to territory quality, obtaining a high quality territory had to be combined with early nest initiation to maximize productivity. We found support for the IDD hypothesis because the highest quality territories, (i.e. most productive), were settled earlier. Research that identifies high quality habitat by linking individual fitness with habitat characteristics may elucidate the importance of habitat quality, individual experience and temporal factors to productivity of Bell's vireos.     

Postlogging Succession and Habitat Usage of Shrubland Birds

ABSTRACT In the first decades after logging, the vegetation structure of harvested areas changes rapidly due to succession. For shrubland birds, many of which specialize on regeneration of specific ages, the changing vegetation structure makes determining how much habitat is available for individual species difficult. We conducted a meta-analysis to determine how populations of shrubland birds in the eastern United States and Canada respond to succession in the first 20 years after timber harvest. Based on those results, we used the area under the abundance-time regression curves to estimate the proportion of regenerating forest actually used by each bird species. Of the 28 species for which we had sufficient data, 14 showed significant changes in abundance over time. For 6 species, abundance was highest immediately after logging and decreased thereafter. Abundances of 7 other species were initially low, peaked roughly 10 years after harvest, and declined thereafter. Based on these results, shrubland birds would be expected to occupy a mean of just 53% (SD = 17%) of regenerating forests up to 20 years old. Thus, current estimates of habitat availability for shrubland birds may be too high by a factor of 2. Our findings also suggest that managed openings should be maintained on longer rotations than are currently used, providing habitat for birds that prefer older regeneration.     

Genetic monogamy in blue-headed vireos and a comparison with a sympatric vireo with extrapair paternity

Based on the breeding synchrony hypothesis, we predicted, intwo congeners that nest in simiilar habitat but differ in nestingsynchrony, that blue-headed vireos (Vireo solitarius) wouldhave fewer extrapair fertilizations (EPFs) thaii red-eyed vireos(V. olivaceus EPFs were rare in blue-headed vireos (1/37 nestlings),but common in red-eyed vireos (11/19 nestlings). We studiedthe behavior of blue-headed vireos to determine what factorscould promote genetic monogamy. We found no evidence that malesmate guarded to prevent extrapair copulations from occurring.Males did not follow fertile mates closely when mates left thenest (14–25% of female departures) and, during the egg-layingperiod, males were often alone on the nest (22.3 mm/h). Femaleblue-headed vireos, but not red-eyed vireos, obtain direct benefitsfrom social mates such as nest building and incubation (49.1%of the total), and they assess male quality long before becomingfertile. Female blue-headed vireos spent more time incubatingwhen their mates had low incubation effort. Furthermore, maleincubation effort was positively correlated with nest survivalduring incubation. We discuss the evolution of genetic monogamyand sex role convergence in blue-headed vireos in relation toasynchronous breeding.     

Multiscale Nest-Site Selection by Black-Capped Vireos

Abstract: We used an information-theoretic approach to investigate nest-site selection by black-capped vireos (Vireo atricapilla) at the landscape and habitat-patch scales on Fort Hood Military Reservation in central Texas, USA, during 2003 and 2004. We used a use-availability sampling design and logistic regression to compare woody cover characteristics at nests to random points in the landscape to determine habitat selection at the landscape scale. At the habitat-patch scale, we used matched case-control logistic regression to compare habitat measures at nests and random non-nest points to evaluate support for hypotheses concerning the influence of woody cover, nest-patch, and nest-site characteristics on black-capped vireo nest-site selection. At the landscape scale, we found strong support (Akaike wt [w_j] = 1.0) for a model with a cubic effect of percent woody cover and woody cover edge density. Sites with the greatest predicted probabilities of use had woody cover values between 30% and 60% and increasing amounts of edge. We found strong support (w_i = 0.93) for the global model at the habitat-patch scale that included characteristics of the nest site, nest patch, and woody cover within 25 m. Based on odds ratios and confidence limits, percent woody cover, cover below 2 m, cover type, and substrate height had the greatest effect on nest-site selection. The predicted probability a site was selected for a nest site increased with foliage cover below 2 m, taller substrates, deciduous cover, and decreased at high levels of percent woody cover (especially >80%). Texas red oak (Quercus buckleyi) was the most used nest substrate (100 of 358 nests), followed by shin oak (Q. sinuata var. breviloba; 86 of 358 nests) and Ashe juniper (Juniperus ashei; 44 of 358 nests). Black-capped vireos used Texas red oak and shin oak in greater proportion to their availability, whereas Ashe juniper was used less in proportion to its availability, suggesting vireos avoided this species. We suggest that managers promote dense deciduous cover for nesting habitat and maximize edge-to-area ratios to maintain spatial and structural heterogeneity.     

Adaptive habitat preferences in the Tawny Owl Strix aluco

Capsule: Tawny Owls Strix aluco occupying nest boxes preferred habitats which were positively associated with the probability of nesting success.

Aims: We aimed to determine whether or not: (1) Tawny Owls showed habitat preferences when occupying nest boxes; (2) nesting performance was related to the habitats around occupied nest boxes and (3) habitat availability had changed around available and occupied nest boxes between 1995–2004 and 2005–14.

Methods: Tawny Owls were studied using nest boxes erected in a commercial forest. During nest boxes checks (724 cases), data on occupancy and nesting performance (88 cases) were recorded, and habitat within a 0.4?km radius around nest boxes was analysed.

Results: Tawny Owls had preferences for clearings within forests, mature forests and grasslands but avoided young forests. We found a positive relationship between nesting success and abundance of clearings within the forest, and a negative relationship between nesting success and abundance of young forests. A change in habitat preferences over the two decades was evident, but habitat availabilities remained similar.

Conclusions: Findings indicate adaptive habitat selection in Tawny Owls because preferred habitats were associated with higher fitness and this type of habitat became more frequently selected over time.     

Habitat selection and web plasticity by the orb spider Argiope keyserlingi (Argiopidae): Do they compromise foraging success for predator avoidance?

Abstract Orb web spiders face a dilemma: forage in open habitats and risk predation or forage in closed habitats to minimize risk but at reduced foraging profitability. We tested whether Argiope keyserlingi opts for safer habitats at the expense of foraging success by (i) determining habitat selection indices in open and closed habitats; (ii) marking and releasing individual juvenile, subadult and adults over two 4‐week periods to determine if life‐history stage influences habitat selection; and (iii) determining the biotic and abiotic environmental parameters that relate to A. keyserlingi abundance. We found that A. keyserlingi selected closed habitats. Sedge and anthropogenic structures were selected and trees were avoided. Juveniles were never found in open habitats, most likely because of high postdispersal mortality. Subadults and adults may shift from closed to open habitats while juveniles never shifted habitat. Foliage density, plant height, potential prey abundance, and mantid and bird abundance were correlated with A. keyserlingi abundance, with only bird abundance explaining habitat selection. We measured web capture area, spiral distance (distance between spiral threads) and the number of decoration arms (0, 1, 2, 3 or 4) in the field and did laboratory experiments to test the influence of (i) space and vegetation; (ii) prey abundance; and (iii) web damage, on web architecture. Argiope keyserlingi webs exhibited geometric plasticity by having larger prey capture areas and spiral distances in open habitats. Decoration design did not differ between habitats however. Variation in space availability, air temperature, prey abundance and web damage explained the variations in web architecture. Potential prey size and diversity differed between habitats but prey abundance did not. As large prey may be important for spider survivorship, foraging success appears to be compromised by occupying closed habitats.