Outcomes of decades long installation of nest boxes for arboreal mammals in southern Australia

Nest boxes are commonly installed to support hollow‐using species where the abundance of hollow‐bearing trees is deficient. Recent studies have provided equivocal evidence about the effectiveness of nest box projects and have highlighted significant management costs associated with some projects. We document the functionality of 303 nest boxes installed across five different community‐led projects in southern Australia for periods of 10–25 years. As expected, we found that nest boxes lost functionality over time. However, 60% remained functional to support the Brush‐tailed Phascogale (Phascogale tapoatafa) and the Sugar Glider (Petaurus breviceps) after almost 20 years. Years installed, method of nest box attachment and tree species influenced whether boxes remained functional. Nest box construction material changed over time so could not be assessed specifically. When inspected in a single year, the Brush‐tailed Phascogale occupied 9% of functional boxes and another 48% contained their nests. The Sugar Glider occupied 15% of functional boxes and another 22% contained their nests. These values suggest the nest box installations were highly effective for these species, although more detailed study is needed to understand what contribution these installations have made to support the local populations. Maintenance of most nest boxes occurred twice a year in the first five years after installation, but many received no maintenance for periods of three years, and some 10–15 years, before our census. Our findings suggest that infrequent maintenance by community groups can sustain nest box projects over periods of several decades. Research into employing nest boxes as a management tool in Australia is still in its infancy. Further studies are needed to resolve factors that limit their effectiveness.     

Nest box contentions: Are nest boxes used by the species they target?

Nest boxes have grown in popularity as a habitat management tool in Australia during the last decade. This management use remains contentious because some studies suggest nest boxes are ineffective. There are three recent contentions: (i) nest boxes mostly benefit common species, (ii) exotic species may be dominant users of nest boxes, and (iii) species of conservation concern use nest boxes infrequently. We address these contentions using data from 1865 nest boxes involving eight nest box designs. These nest boxes were installed predominantly <200 m from a road in association with highway duplication and re‐alignment across 16 projects in New South Wales. The Common Brushtail Possum (Trichosurus vulpecula) is the species of most relevance to contention 1. It used 9% of boxes overall including 26% of ‘possum’ designated boxes. The most frequent nest box users were small petaurid gliders (mostly Sugar Gliders, Petaurus breviceps) which used 63% of ‘small glider’ designated boxes. This nest box and another suited to the Sugar Glider comprised 40% of all boxes installed, so it is not surprising that this species might be a common user. Exotic species were uncommon users of the nest boxes enabling contention 2 to be rejected. Active hives of Feral Honeybees (Apis mellifera) occupied just 1% of boxes, and another 1% of boxes were used by introduced rodents and birds. The Squirrel Glider (Petaurus norfolcensis) is the species most relevant to contention 3. It was seen in 80 boxes across 11 projects, representing 7% of the three types most frequently used. These observations are not consistent with the third contention. Nest boxes can provide many important insights about the requirements and interactions of hollow‐dependent fauna. However, they are not intended as an alternative to retaining hollow‐bearing trees.     

Do nest boxes in restored woodlands promote the conservation of hollow‐dependent fauna?

Vegetation restoration is considered as an important strategy for reversing biodiversity decline in agricultural areas. However, revegetated areas often lack key vegetation attributes like large old hollow‐bearing trees. As these trees take a long time to develop, artificial cavities such as nest boxes are sometimes provided to address lag effects. We conducted a 3‐year experiment using 150 nest boxes with 4 designs to quantify patterns of occupancy within 16 replanted areas and 14 patches of remnant old‐growth eucalypt woodland. We quantified patterns of occupancy of nest boxes in physically connected versus isolated remnants and plantings, and multiple covariate effects on nest box occupancy at the nest box, tree, patch, and landscape levels. Our analyses revealed a lower probability of nest box occupancy within remnants (vs. plantings) for 2 of the 6 response variables examined: any species and the Feral Honeybee. Nest boxes in connected remnants and plantings were more likely to be occupied than those in isolated plantings and remnants by any mammal and the Common Brushtail Possum. Nest boxes in restored woodlands are used by some hollow‐dependent fauna but principally already common species and not taxa of conservation concern. Nest boxes were also used by pest species. A key management consideration must be to create connected habitat to facilitate colonization of nest boxes by mammals. Approximately 15% of the cavity‐dependent vertebrates within the study area used next boxes, possibly because the diverse requirements of the array of other species were not met by the range of nest boxes deployed.     

Predation and infanticide influence ideal free choice by a parrot occupying heterogeneous tropical habitats

The ideal free distribution (IFD) predicts that organisms will disperse to sites that maximize their fitness based on availability of resources. Habitat heterogeneity underlies resource variation and influences spatial variation in demography and the distribution of populations. We relate nest site productivity at multiple scales measured over a decade to habitat quality in a box-nesting population of Forpus passerinus (green-rumped parrotlets) in Venezuela to examine critical IFD assumptions. Variation in reproductive success at the local population and neighborhood scales had a much larger influence on productivity (fledglings per nest box per year) than nest site or female identity. Habitat features were reliable cues of nest site quality. Nest sites with less vegetative cover produced greater numbers of fledglings than sites with more cover. However, there was also a competitive cost to nesting in high-quality, low-vegetative cover nest boxes, as these sites experienced the most infanticide events. In the lowland local population, water depth and cover surrounding nest sites were related with F. passerinus productivity. Low vegetative cover and deeper water were associated with lower predation rates, suggesting that predation could be a primary factor driving habitat selection patterns. Parrotlets also demonstrated directional dispersal. Pairs that changed nest sites were more likely to disperse from poor-quality nest sites to high-quality nest sites rather than vice versa, and juveniles were more likely to disperse to, or remain in, the more productive of the two local populations. Parrotlets exhibited three characteristics fundamental to the IFD: habitat heterogeneity within and between local populations, reliable habitat cues to productivity, and active dispersal to sites of higher fitness.     

Comparative nest habitat characteristics of sympatric White‐tailed Haliaeetus albicilla and Golden Eagles Aquila chrysaetos in western Scotland

Capsule Golden and White‐tailed Eagles selected different habitats for nesting.

Aim To investigate differences in nesting habitat used by sympatrically breeding eagles in western Scotland, following reintroduction of White‐tailed Eagles from 1975 onwards.

Methods Nest‐site locations from national surveys in 2003–05 were entered into a geographical information system (GIS) in order to measure a set of geographic parameters for each nest site. Binary logistic regression with backwards deletion of non‐significant terms was used to derive minimum adequate models at two spatial scales of the likelihood of an eagle nest belonging to one species or the other. We compared changes in occupancy between 1992 and 2003 of Golden Eagle territories inside and outside a GIS model of potential White‐tailed Eagle habitat and according to proximity to White‐tailed Eagle nests.

Results White‐tailed Eagles nested at lower altitudes than Golden Eagles, in more wooded habitats with more open water close by, tending to nest in trees where these were present. There were 3359 km² of potential White‐tailed Eagle nesting habitat within 25 km of existing White‐tailed Eagle nests, containing 54 Golden Eagle territory centres, but we found no difference in change of occupancy for Golden Eagle territories close to White‐tailed Eagles compared with those further away.

Conclusion White‐tailed and Golden Eagles appear to partition nesting habitat in the west of Scotland by altitude. This corresponds with behaviour in western Norway and with the situation described in historical accounts of nest‐sites in western Scotland prior to extinction of White‐tailed Eagles. It is also consistent with recent studies showing little overlap in breeding season diet of Golden and White‐tailed Eagles in western Scotland, and likely partitioning of foraging habitat by altitude. We conclude that the likelihood of competitive exclusion is less than previously suggested.     

Natural cavity restoration as an alternative to nest box supplementation

Nest box supplementation is widely used to increase nest‐site availability for cavity nesting animals but the analysis of its effects on individuals breeding in natural cavities is often neglected. This study offers a novel restoration technique to revert abandonment of natural breeding sites by a secondary cavity avian bird, the European roller (Coracias garrulus), and other ecologically similar species. We found that, after a program of nest box supplementation with ensuing monitoring, rollers gradually abandon nesting in natural and seminatural cavities in favor of nest boxes because the latter are of higher quality. We examine whether reducing the entrance size of natural and seminatural cavities improves their suitability for rollers. A 6‐year program reduced the diameter of the entrance of sandstone cavities and cavities in bridges. This led to a high occupancy (59%) of manipulated nest‐sites. Manipulated sites were most frequently occupied by rollers and little owls (Athene noctua) (31 and 18% of sites, respectively). Manipulation did not affect clutch size or fledgling success. We suggest that nest‐site diversity and nesting in natural cavities should be preserved to reduce nest box dependence. Our study illustrates the value of nest boxes when used alongside restoration of natural breeding sites and provides insights for the management of natural cavities.     

Limited use of bat boxes in a rural landscape: implications for offsetting the clearing of hollow‐bearing trees

Bat boxes frequently form part of hollow‐bearing tree offsets; however, their effectiveness is poorly documented. We investigated the effectiveness of a bat box program designed to partially offset tree hollow loss from clearing for a coal mine. During the first year of monitoring, we detected bats in 5% of 1,308 box checks. Only 3 of 13 local tree cavity‐roosting bat species/species groups used boxes and occupancy was not strongly associated with modeled box and site attributes. In the second year, we tested two hypotheses that may explain the relatively low box use: (1) solar exposure of boxes was inadequate for heterothermic bats and (2) available box designs were of low suitability. Relocating boxes to increase solar exposure did not increase use, or enhance the temperature profiles of relocated boxes. Introduction of a new box design led to 11 times higher use compared with existing designs for Nyctophilus spp. (long‐eared bat). Overall, our data suggest that the bat box program was ineffective due to few bat species using boxes, infrequent box use by three species, and rarity of maternity roosting. The knowledge gap of species‐specific box designs and roosting ecology limits the effectiveness of boxes to offset cleared hollow‐bearing trees. Lack of knowledge and the widespread use of bat boxes to offset lost tree hollows highlights the need to (1) rigorously protect hollow‐bearing trees and (2) advance our understanding of species‐specific roost ecology, box design preferences and mechanical hollow creation into trees, before artificial hollows can be considered a meaningful offset measure.     

Specific nest box designs can improve habitat restoration for cavity‐dependent arboreal mammals

Tree‐cavity‐dependent wildlife faces future shortages of cavities due to a decline in the abundance of large, old trees in many parts of the world. Nest boxes are proposed as a tool to restore habitat value but evidence of their effectiveness for arboreal mammals remains equivocal. This may arise from a poor understanding of design preferences. We conducted investigations in two landscapes in eastern Australia to determine whether species show a preference for specific designs. We observed a preference by some mammal species for particular designs (33–78% occupied/used), suggesting that design refinement can improve the frequency with which nest boxes are used. Although feral species may out‐compete target species for nest boxes, we did not observe this. We recorded feral honeybees (Apis mellifera) in 6–9% of nest boxes but they did not remain, and many occupied boxes were later used by mammals. The introduced common myna bird (Acridotheres tristis) was prevalent in one landscape, but competition for nest boxes was localized. For nest boxes to be an effective habitat restoration tool, they must be able to be occupied over long periods of time. We investigated this for the squirrel glider (Petaurus norfolcensis), an arboreal marsupial threatened through part of its geographic range. Squirrel gliders occupied and bred within nest boxes (100% used) at two locations continuously over a 10‐year period with minimal nest box maintenance. Individuals occupied boxes for up to 7 years. This confirms that targeted nest box programs can be an effective restoration tool for cavity‐dependent arboreal mammals.     

Latitudinal trends in within-year reoccupation of nest boxes and their implications

Multiple brooding can substantially increase the annual reproductive output of birds, and the propensity for multiple brooding can vary geographically. Thus, studies attempting to understand the evolution of geographic variation in nesting success need to account for variation in re‐nesting potential. However, direct assessment of rates of multiple brooding requires individually recognizable breeding adults, which are not generally available. We explore the possibility of comparing relative indices of multiple broodedness across a latitudinal gradient from studies of un‐banded birds locally restricted to nest boxes. We analyzed nest box reoccupation by a multiple‐brooding species, the eastern bluebird Sialia sialis, reported by volunteers in a citizen‐participation project (1998–2002) in which nest boxes were monitored throughout much of the breeding range of the bluebirds. We found nest boxes in the southern portion of the bluebird range (30° latitude) had, on average 17–33% higher likelihood of repeated egg‐laying, brooding, and successful fledging events than boxes in the north (48° latitude). Latitudinal variation in the reoccupation of nest boxes may indicate that either (1) the number of broods per female varies with latitude, (2) female breeding dispersal/site fidelity varies with latitude, (3) the density, distribution, and/or availability of suitable nest sites varies with latitude, or (4) observer bias varies with latitude. Various lines of evidence suggest that nest re‐occupancy is a useful index of latitudinal variation in re‐nesting. During the time‐frame of second attempts, first‐time box occupancy was as likely as second occupancy and approximately 45% more likely in the south than north, suggesting that, despite considerable breeding dispersal, observed trends in box reoccupation conservatively reflect latitudinal trends in the number of nest attempts/broods per female. Furthermore, despite a compressed nesting cycle in the north (shorter incubation and re‐nesting interval), the shorter duration of the breeding season in the north restricted the potential number of broods. Studies of banded birds are necessary to confirm the behavior underlying the latitudinal trends in box reoccupation.     

Nest boxes for Cape Parrots Poicephalus robustus in the Hogsback area,Eastern Cape,South Africa

Breeding propensity of tree-cavity nesting bird species are often limited by a shortage of natural nesting sites. Artificial nests can be used to provide alternative nest sites. Cape Parrots Poicephalus robustus are nationally endangered and nest in existing tree-cavities in high-altitude fragmented Afromontane forests in South Africa, assumed to be in short supply due to historic and current logging practices. To increase nest site availability, 179 wooden bird boxes and 28 bee boxes (to ‘pull’ bees) were erected during 2011–2012 in Hogsback, Eastern Cape. In 2016, no bird boxes were occupied by Cape Parrots. A total of 43% were used by other species, 51% were unused and 6% could not be inspected due to tree instability and inaccessibility. Two bird boxes were inspected by two pairs of Cape Parrots, but were never occupied. Occupancy of boxes by birds was not associated with nest, tree or habitat characteristics. However, occupancy of boxes by bees was associated with habitat type and tree species. Future conservation efforts will include locating natural Cape Parrot nesting sites and reforestation efforts to ensure the long-term availability of natural nesting sites.     

The value of 'bat boxes' for attracting hollow-dependent fauna to farm forestry plantations in southeast Queensland

Summary Small artificial nest/roost boxes, originally designed for microbats, were deployed in three farm forest plantations and at one native forest site in southeast Queensland in order to assess their use by vertebrates and their contribution toward enhancing biodiversity in plantation forests through the provision of habitat. Two sites were located in a relatively 'intact' forest landscape (SF 351 and Strano) and two sites in a more 'fragmented' or 'variegated' landscape (Askham and Thomas). Twenty-four boxes were placed at each site over an area covering approximately 1.2–1.8 ha. Each site was checked from five (SF 351) to nine (Askham) times between April 1996 and November 2000. The artificial nest/roost boxes were attractive to a range of small fauna that included Feathertail Gliders ( Acrobates pygmaeus ), Sugar Gliders ( Petaurus breviceps ), Squirrel Gliders ( Petaurus norfolcensis ) and the Yellow-footed Marsupial Mouse ( Antechinus flavipes ), all of which constructed nests inside boxes. Gould's Long-eared Bats ( Nyctophilus gouldi ) used boxes primarily as roosts and maternity sites. In general, fewer animals were recorded in boxes at the two sites located within a relatively 'intact' landscape, while the highest numbers of animals were recorded in boxes in two farm forest plantations within 'variegated' landscapes. The availability of alternative natural hollows and landscape factors appear to be important determinants of the extent to which boxes are occupied. The present study indicates that the biodiversity of farm forests can be enhanced through simple habitat manipulation utilizing artificial roosting or nesting boxes.
Key words Antechinus, biodiversity, farm forestry, glider, marsupial, microbat, nest box, roost.     

Nest sites as limiting resources for cavity‐nesting birds in mature forest ecosystems: a review of the evidence

ABSTRACT Assumptions that populations of cavity‐nesting birds are limited by access to nest sites have largely been based on anecdotal reports or correlative data. Nest‐box‐addition experiments or tree‐cavity‐blocking experiments are potentially rigorous ways to investigate how densities of breeding birds are affected by access to nest cavities. Experimental evidence indicates that natural tree holes are limited in human‐altered landscapes, but the possibility that cavity nests are limited in old growth (unmanaged) forests is less clear. I reviewed 31 nest‐cavity‐removal or addition experiments conducted with 20 species of cavity‐nesting birds in mature forests. Of these 31 experiments conducted with a variety of different species of birds, only 19% reported statistically significant changes in breeding densities. However, none of these studies included data about the reproductive history of individuals colonizing the boxes (i.e., whether birds using the boxes would have otherwise been floaters or that birds excluded from blocked cavities on the plots did not simply move elsewhere), so they provided no strong evidence that the number of breeding pairs was limited by availability of nest sites at the population scale. Although some studies indicate that nest sites are limited at local (plot) scales in old growth forests, there is still little empirical evidence for nest‐site limitation at the population‐ and landscape‐level in mature, unmanaged forests. I review the challenges in designing and interpreting box‐addition experiments and highlight the main gaps in knowledge that should be targeted in the future.     

Selection of nest sites by a hole-nesting duck, the Goldeneye Bucephala clangula

Nest site preferences were examined for a population of Goldeneye Ducks breeding in nest boxes in Värmland, central Sweden. Some nest boxes were occupied more often than others even if females returning to the same nest box were excluded from the analysis. Nest boxes located higher up trees were occupied more often than those close to the ground and some spatial 'cluster groups' of boxes were occupied more often than others. Otherwise nest site prefernces were not related to any measured physical attributes of the boxes. Prefernces for nest boxes seemed to be based mainly on a tendency for females to select those that had been occupied by other females in the preceding year, especially if they had bred successfully. As a result of this, the occupancy of nest boxes was not random over years but rather progressed in a series of runs; a period of consecutive years in which a box was occupied was followed by a period of years in which it was empty.
There were reproductive consequences for these prefernces in that females occupying preferred boxes were less likely to lose their clutch to a predator. These females also bred earlier in the year and produced larger clutches and broods than females breeding in other boxes.     

Fragmentation in eucalypt woodlands promotes nest‐tree occupancy by a despotic species,the noisy miner (Manorina melanocephala)

The effects of habitat fragmentation as a threat to biodiversity are well known; decreased connectivity can potentially influence population processes and dynamics, resulting in smaller, isolated populations that may not function optimally. However, fragmentation may also increase the amount of edge or ecotone habitat available to open country species, benefiting their populations and enabling them to dominate remnant habitats. Noisy miners (Manorina melanocephala) are one such species, occupying eastern‐Australian eucalypt woodlands. They are considered a ‘despotic’ species, in that their presence negatively impacts woodland avifauna biodiversity due to their aggressive exclusion of other taxa from occupied areas. Despite this well‐known impact, little information exists on the patterns of nest‐tree occupancy by noisy miners within eucalypt woodlands. In the current study, we explored the patterns of nest‐tree occupancy by noisy miners across two successive years, aiming to identify preferences for breeding areas relative to vegetation structure. Our results show that both habitat fragmentation and the characteristics of individual eucalypt trees in an area influenced nest‐tree occupancy. Noisy miners constructed nests in trees near the edge of woodland patches more often than expected. Moreover, the nest tree chosen was a eucalypt that was significantly smaller than randomly selected trees from the surrounding area. The results highlight the importance of habitat management measures that may reduce the suitability of woodland patches as nesting sites for this species, in order to mitigate the severe effects of this despotic edge specialist.     

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.     

Multi‐season occupancy models identify biotic and abiotic factors influencing a recovering Arctic Peregrine Falcon Falco peregrinus tundrius population

Critical information for evaluating the effectiveness of management strategies for species of concern include distinguishing seldom occupied (or low‐quality) habitat from habitat that is frequently occupied and thus contributes substantially to population trends. Using multi‐season models that account for imperfect detection and a long‐term (1981–2002) dataset on migratory Arctic Peregrine Falcons Falco peregrinus tundrius nesting along the Colville River, Alaska, we quantified the effects of previous year's productivity (i.e. site quality), amount of prey habitat, topography, climate, competition and year on occupancy dynamics across two spatial scales (nest‐sites, cliffs) during recovery of the population. Initial occupancy probability was positively correlated with area of surrounding prey habitat and height of nest‐sites above the Colville River. Colonization probability was positively correlated with nest height and negatively correlated with date of snowmelt. Local extinction probability was negatively correlated with productivity, area of prey habitat and nest height. Colonization and local extinction probabilities were also positively and negatively correlated, respectively, with year. Our results suggest that nest‐sites (or cliffs) along the Colville River do not need equal protection measures. Nest‐sites and cliffs with historically higher productivity were occupied most frequently and had lower probability of local extinction. These sites were on cliffs high above the river drainage, surrounded by adequate prey habitat and with southerly aspects associated with early snowmelt and warmer microclimates in spring. Protecting these sites is likely to encourage continued occupancy by Arctic Peregrine Falcons along the Colville River and other similar areas. Our findings also illustrate the importance of evaluating fitness parameters along with climate and habitat features when analysing occupancy dynamics, particularly with a long‐term dataset spanning a range of annual climate variation.     

Experimental test of nest-site limitation in mature mixed forests of central British Columbia,Canada

Nest-site availability limits cavity-using populations in many harvested forests; however, little is known about the extent of nest-site limitation in mature forests with a full complement of excavator species and intact processes of cavity creation and loss. To examine the role of nest-site availability in limiting cavity-using populations in mature mixed conifer forests in central British Columbia, Canada, we conducted an 11-year before-after control-impact experiment in which we increased nest-site availability via nest box addition. Our 7 sites (3 treatments, 4 controls) had low cavity densities (<2/ha) prior to treatment and cavity occupation rates were also low (<10%/yr), which is a relationship often cited in the literature as evidence of non-limitation in cavity-nesting populations. Following nest box addition at our treatment sites, which tripled the availability of cavities, total density of bird and mammal nests more than tripled. Density of mountain chickadee (Poecile gambeli) nests increased 9-fold on treatment sites and returned to pre-treatment levels following box removal, suggesting that chickadee populations were limited by cavity availability at our study sites. Density of red squirrel (Tamiasciurus hudsonicus) and northern flying squirrel (Glaucomys sabrinus) nests and roosts also increased significantly at treatment sites following box addition and declined following box removal. We noted little change in chickadee or squirrel nest density at control sites monitored concurrently. Squirrels preferred large-sized over small-sized boxes, and significantly enlarged the entrance areas of small boxes by chewing, suggesting that there may have been a shortage of suitable nest and roost sites for them in our study area. We contend that low cavity occupancy rates may not accurately reflect nest-site availability for cavity nesters in mature forests, and that cavity size may influence the true availability of cavities on the landscape. © 2011 The Wildlife Society.     

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

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

千岛湖栖息地片段化对大山雀营巢资源利用的影响

为了解栖息地片段化对次级洞巢鸟营巢资源利用的影响, 我们于2008年2-8月, 在千岛湖地区选取21个岛屿, 采用悬挂人工巢箱方法进行大山雀(Parus major)招引实验。通过测定岛屿面积、岛屿隔离度、捕食者活动率、人工巢箱周围植被盖度和人工巢箱巢向等5种参数, 分析大山雀人工巢箱利用与上述参数间的关系。实验期间, 共悬挂443个人工巢箱, 其中有72个(16.3%)被大山雀利用。大山雀倾向于选择捕食者活动率低、植被盖度低、巢口向东或向南的人工巢箱; 岛屿面积和隔离度对大山雀利用人工巢箱不存在显著的直接影响, 但岛屿面积可通过影响捕食者的活动率, 对大山雀利用人工巢箱产生间接影响。因此, 我们认为在栖息地片段化后, 应更多关注对洞巢鸟营巢资源利用有直接影响的栖息地特征因素, 以及片段化效应的间接影响。     

Experimental analysis of retreat‐site selection by thick‐tailed geckos Nephrurus milii

Abstract Although animals use habitats non‐randomly in the wild, complex correlations among environmental features mean that proximate influences on habitat selection can be identified only by experimental manipulation of potential cues. Thick‐tailed geckos Nephrurus milii are large lizards that are widely distributed through southern Australia. These nocturnally active animals typically spend daylight hours under surface rocks. We presented captive geckos with alternative retreat‐sites (rock crevices) differing in attributes potentially relevant to habitat selection. The lizards showed strong preference for shelter‐sites that enhanced thermoregulation (warm rather than cool) and that reduced the animal's vulnerability to predators (narrow crevices with small openings and not containing the scent of a predatory snake). Horizontal rather than sloping crevices were also preferred. Overall crevice size and thickness of the overlying rock did not influence retreat‐site selection in the laboratory, but could be important in the field because of their influence on thermal regimes under rocks. The present study supports the idea that nocturnal reptiles base their selection of diurnal shelters on multiple aspects related to the fitness consequences of occupancy of alternative available retreat‐sites.