Den Trees Research Articles

Raccoon Use of Den Trees and Plant Associations in Western Mesophytic Forests: Tree Attributes and Availability or Landscape Heterogeneity?

We monitored 15 radio-collared raccoons (Procyon lotor) on Davies Island in March 1987 - May 1988 to determine the extent to which individual tree attributes or spatial configuration of plant associations (habitat types) across the landscape influenced den use. Of 1091 verified den sites, 428 were in tree cavities. Raccoon occurrence among 4 cover types differed from that expected based on the total area of each across the island and varied across all seasons for all habitat types except Cedar Wood. Preference varied among age and sex groups and across seasons with some groups showing opposite selection for the same cover type in different seasons. Species and diameter-class distributions of selected den trees differed from a random sample of trees across the landscape. Species composition of trees with cavities also differed from the species composition across the study area. American beech (Fagus grandifolia—relative abundance 8.7%) was over-represented in the sample of trees with cavities (29.4%) and trees selected as dens (65%); diameter at breast height (dbh) of beech den trees averaged 80.0 cm, whereas all beech trees averaged 71.2 cm. For all species combined, mean dbh of den trees was 78.4 cm as compared to trees with cavities (67.6 cm), or all trees (50.4 cm). The relative availability of large, cavity-prone tree species was related to previous logging practices.

Longevity and reuse of black bear dens in managed forests of coastal British Columbia

AbstractWe evaluated longevity and reuse of denning structures by American black bears (Ursus americanus) in coastal temperate rainforests of British Columbia from 1992 to 2010 to assess potential impacts of forest management on these critical habitat features over time. We identified 67 dens during a 4‐yr intensive radio‐telemetry study (1992–1995): 40 dens of 21 radio‐collared black bears and 27 dens found incidentally. Dens occurred in or beneath large diameter trees or wooden structures derived from trees (i.e., logs, root boles, and stumps;${\bar {x}}$ = 143 cm diameter, SD = 49 cm). Longevity of dens varied by type, tree species that formed the den, and forest management that occurred at or near the den. Twenty‐four of 28 dens of radio‐collared bears that were monitored were still usable in 2010, whereas only 5 of 14 dens found incidentally were still usable in 2010. We assessed reuse of bear dens 3 times following initial identification: during the radio‐telemetry study, again in 2000, and finally in 2010. Radio‐collared bears reused dens from previous years on 7 of 25 potential occasions during the course of the radio‐telemetry study. Upon assessment in 2000 and 2010, 17 of 24 (71%) available dens first used by radio‐collared bears were reused at least once between 1993 and 2010. The high rate of reuse may indicate low availability of den structures in our study area. Because black bears in coastal British Columbia only used trees or structures derived from trees for winter dens and forest harvesting reduces the supply of these necessary structures, conservation and recruitment of suitable den trees is necessary if maintaining black bear populations is a management goal in these areas. © 2011 The Wildlife Society.

Spatial Organization of Northern Flying Squirrels,Glaucomys sabrinus: Territoriality in Females?

We determined home-range overlap among northern flying squirrels (Glaucomys sabrinus) to assess their spatial organization. We found extensive home-range overlap among females, and though this overlap could reflect social behavior, we found no evidence of attraction among females, with only one instance of den sharing. Instead, our results suggest that females share foraging areas but may be territorial in portions of the home range, especially around den trees and during young-rearing. Home-range overlap could also result from, the extrinsic effect of forest fragmentation due to timber harvest, which might impede dispersal and force squirrels to cluster on remaining fragments of suitable habitat.

Den trees, hollow-bearing trees and nest boxes: management of squirrel glider (Petaurus norfolcensis) nest sites in tropical Australian woodland

The squirrel glider (Petaurus norfolcensis) is an arboreal marsupial potentially impacted throughout its geographic range by the loss of hollow-bearing trees. We investigated the use of den trees and the availability of hollow-bearing trees near Mackay in the tropical north of the squirrel glider range where information was deficient. Mean den tree size (41.1 ± 2.9 cm (s.e.), diameter at breast height (dbh)) was significantly larger than that of available trees (27.5 ± 0.9 cm). Dead trees (stags) comprised 52% of 27 dens but comprised only 12% of available trees. This likely reflects the greater frequency of hollows in dead trees compared with other trees. Surveys found that 59% of 720 available trees contained hollows. A much lower percentage of trees in the 10–30-cm dbh size class were hollow-bearing (22%) compared with trees >30 cm (77%), and we view these smaller trees as those providing future den trees. Their density varied from 17 to 95 ha–1 among sites, which suggests that most sites have an adequate supply of future hollows. We installed 56 nest boxes to determine use by squirrel gliders. Only 20% were used after 3 years, but use was not influenced by the availability of tree hollows. Tree hollow availability appears adequate for the squirrel glider in these tropical woodlands but further studies are needed to understand the dynamic processes that govern this resource.

A Multiscale Assessment of Den Selection by Black Bears in Louisiana

ABSTRACT Understanding den selection for the federally threatened Louisiana black bear (Ursus americanus luteolus) will assist managers in effectively managing bear populations and the landscapes they inhabit. We assessed den selection of 72 female Louisiana black bears at multiple spatial scales in northern and central Louisiana, USA. We used 230 den‐years to examine den type preference, microhabitat characteristics of dens, and effects of landscape characteristics on den selection. We also evaluated reuse of tree dens and their availability across several study areas. Bears selected tree dens more frequently (65%) than ground dens. Most (55%) ground dens were associated with standing or downed trees, and most tree dens were in baldcypress (Taxodium distichum; 86%) or surrounded by water (80%). Selection of ground dens was positively associated with landscape metrics related to presence of water, whereas selection of tree dens was positively associated with proximity to edge and greater proportions of swamp and areas containing water. Reuse of tree dens averaged 15% (range = 0–20%) across study areas and our estimates of tree‐den availability indicated that tree dens were not a limiting resource for Louisiana black bears in the northern or central portions of Louisiana. Although Louisiana black bears demonstrated plasticity in den selection, we recommend managers use forest management practices that conserve appropriate tree dens and create ground‐denning opportunities, because both would promote the recovery of Louisiana black bear populations.

Maternal Response to Conspecific Visits at Natal Dens in Raccoons (Procyon lotor)

The response of postparturient females to conspecifics at the natal den can provide insights into intraspecific dynamics, particularly the risk of infanticide. In solitary species, the risk of infanticide may be high and mothers are expected to secure dependent young in dens and tolerate little, if any visitation by males. We monitored 10 male raccoons (Procyon lotor) and 11 females from pregnancy through lactation that were equipped with proximity detecting collars during the neonate rearing period (Apr.–Jul.). Natal den trees were identified and proximity detectors were also attached to these trees to document the mother's movements and visitation by conspecifics. A total of 21 den trees (1–8 dens/mother) were used, yielding 337 den-nights of data. Besides those of the mother, 284 visits (0–2.9 visits/night) were recorded and dens were visited by three to 10 individuals. Time spent away from the den by the mother increased with litter age (F = 45.36, P < 0.001, R2 = 0.19). Females who moved their litters from the primary natal den tended to receive more (t = −1.99, P = 0.08, df = 8) male visits/night before their move, than females that stayed in the primary natal den. Males also visited natal den trees more often (t = 2.26, P = 0.05, df = 7) when a natal family was occupying the den tree than once the family had stopped using the den tree. We were unable to examine den trees that were abandoned by their mothers, but our data suggested that female raccoons are intolerant of adult males at natal dens while raising their litters. This may be a response to the risk of male-driven infanticide.

The use of den trees by the squirrel glider (Petaurus norfolcensis) in temperate Australian woodlands

Effective conservation relies on understanding the biology of particular species and how they use key resources. For many arboreal mammals, tree hollows are a key den site. We examined the use of tree hollows by the squirrel glider (Petaurus norfolcensis) in south-eastern Australia. Over a five-month study, individual squirrel gliders used multiple hollow trees (average = 7) as den sites. Den sites were often adjacent to areas where nocturnal activities took place. The average distance between den sites used by individual gliders on successive days was 218 m. Dens were often shared by an adult pair and a juvenile. Den trees were disproportionably used, with gliders showing preference for 1–2 primary den trees often located on steep slopes. Our findings have implications for the number and spatial arrangement of den trees needed to promote the conservation of populations of the squirrel glider, particularly where land is used for agriculture and livestock grazing.

Characteristics of Porcupine, &lt;em&gt;Erethizon dorsatum&lt;/em&gt;, Winter Den-sites in Living Trees in Wisconsin

Although Porcupines (Erethizon dorsatum) denned in a variety of structures in Sandhill Wildlife Area, Wood County, Wisconsin, hollow living trees predominated (67 percent). Diameter at breast height of den trees was significantly greater than that of trees in the surrounding forest, and den openings in living hollow trees were nearly twice the circumference of Porcupines. Porcupines probably do not prefer certain tree species over others; rather, they select species more prone to heart rot with cavities large enough to house a Porcupine.

The characteristics of den trees used by the squirrel glider (Petaurus norfolcensis) in temperate Australian woodlands

Being able to recognise critical habitat features such as nesting and denning sites is essential for wildlife conservation. It is particularly true for the den trees of species threatened by habitat loss, such as the squirrel glider (Petaurus norfolcensis). Measurements of 146 den trees of the squirrel glider were made in fragmented woodlands of the South-west Slopes of New South Wales and data compared with random trees to quantify the key characteristics of den sites. The likelihood of use as a den tree increased with increasing numbers of visible tree hollows and tree size. Dieback was also a positive indicator of den use. However, when visible hollows within a tree are abundant, dieback-free trees were preferred. Measures of den tree context such as basal area, the number of neighbouring large trees and distance to the next nearest tree, were also found to be important determinants of the likelihood of usage. The above variables were combined into a multiple regression model. The squirrel glider favoured particular Eucalyptus species and some broader eucalypt groups. We believe such variations were most likely due to interspecific differences in hollow development and dieback among the various groups, rather than bark type, a factor previously cited as an important determinant of den tree usage. The ‘best’ model had high negative predictive power, suggesting it would be useful for identifying (1) trees that could be felled without a loss of this critical habitat resource (e.g. at development sites) and (2) areas unsuitable for potential squirrel glider relocation or habitat enhancement. Squirrel gliders show preference for a combination of tree and tree context features in selecting den trees. Understanding these features will help managers enhance and protect denning resources for this species.

The characteristics of squirrel glider (Petaurus norfolcensis) den trees in subtropical Australia

Effective management of tree-hollow-dependent wildlife requires a sound knowledge of the characteristics of the trees used for shelter or breeding. We used radio-tracking to identify the den trees of squirrel gliders (Petaurus norfolcensis) in south-east Queensland (Qld) and north-east New South Wales (NSW). Squirrel gliders used dead trees as well as 13 species of living tree for dens across the two locations. Dead trees accounted for a large percentage of dens (54% of 48 dens in Qld, and 50% of 18 dens in NSW) despite comprising only 3–10% of the forest (trees &gt;20 cm diameter at breast height (dbh)) at each location. This preference is largely due to dead trees being more likely to contain hollows, accounting for 26–44% of available hollow-bearing trees. Mean den tree size (dbh) was 48.9 ± 2.4 cm in Qld and 62.8 ± 5.6 cm in NSW. Den entrance height averaged 6.8 ± 1.2 m in Qld and 11.9 ± 1.3 m in NSW. Fissures in the trunk and holes in branches were the most common of six hollow types used. At one location branch end hollows were ignored relative to their availability. Den entrances varied in size (2.5–12 cm wide) but most were ≤5 cm in diameter. Entrance size of hollows appears to be the hollow attribute of most importance to squirrel gliders. Monitoring of these den trees over several years revealed the collapse of three dead den trees at each location, which is equivalent to an annual loss of 3% of den trees. Further research is needed to determine whether this will lead to a future shortage of den trees.

Use of Winter Dens by Porcupines, &lt;em&gt;Erethizon dorsatum&lt;/em&gt;, in Wisconsin

Porcupine (Erethizon dorsatum) dens were monitored in Sandhill Wildlife Area in central Wisconsin between 1996-1997 and 2002-2003 to determine whether they displayed fidelity. Fidelity declined between years, with a higher proportion of Porcupines displaying fidelity to a specific den within a single winter than between winters. Yearlings displayed higher fidelity to den sites than adults. Fidelity was stronger among Porcupines occupying rock vs. tree dens. Familiarity with home spaces and onset of snowfall and snowfall depth also probably influence selection of dens.

Factors Predicting Den Use by Maternal Giant Pandas

ABSTRACT We studied the denning ecology of giant pandas (Ailuropoda melanoleuca) in the Foping Nature Reserve, China. We identified 17 used and 21 unused cavities of appropriate size to accommodate denning and measured several variables potentially affecting the suitability of these cavities for panda denning. Principal component analysis, combined with traditional univariate tests, indicated that maternal females preferred deeper cavities with a high interior‐to‐entrance ratio for height and width, suggesting a preference for narrow entrances and roomy chambers. Microhabitat features, including slope and distance to water, were also useful in predicting den use by maternal females. We believe that the availability of suitable dens may limit population size, especially in areas where tree dens have been eliminated by logging of old growth forests. Conservation managers in giant panda reserves can use our data to determine the number of suitable panda dens that are in an area, estimate whether there are enough for the adult female population to use as birthing dens, and—if needed—construct suitable artificial dens to increase the rate of reproduction.

Home range and habitat use of a low-density population of greater gliders, Petauroides volans (Pseudocheiridae: Marsupialia), in a hollow-limiting environment

Greater gliders, Petauroides volans, were radio-tracked within a large tract of forest in the dry inland of southern Queensland. This forest has been commercially logged for timber for more than 100 years. Home-range estimates ranged from 1.4 ha (female) to 19.3 ha (male). Minimum convex polygon (MCP) estimates were larger for males (average, 11.5 ha) than females (average, 3.3 ha) and combined (6.8 ha, sexes pooled) were larger than estimates from other Australian populations. Gliders were located foraging in myrtaceous tree species only, using mostly Eucalyptus moluccana, E. fibrosa and Corymbia citriodora. E. moluccana was used for foraging more frequently than would be expected on the basis of its availability in the forest. E. fibrosa and C. citriodora were used in proportion to their availability in the forest. Gliders were not seen foraging in non-myrtaceous species or myrtaceous trees &lt;20 cm diameter at breast height (dbh), preferring trees in 30–70-cm dbh classes and as ‘mature’ and ‘over-mature’ classified according to growth-stage characteristics. Den tree species included the same species used for foraging as well as dead trees (16% of den trees). E. fibrosa and E. tereticornis were preferred significantly more than expected by their availability in the forest. Non-myrtaceous species were not used as live den trees. Large (dbh &gt;50 cm) and old living trees (in deteriorating and senescent condition: ‘late mature’ and ‘over-mature’ categories) were primarily used as den trees. Individual gliders utilised 4–20 den trees. Females utilised more den trees per unit area of home range (3.8 den trees ha–1, maximum) than males (0.9 den trees ha–1, maximum). Fewer den trees were used per unit area of home range than by gliders at a coastal location with approximately the same latitude. The density of live stems containing hollows suitable as dens is currently lower than 1 tree ha–1 in some parts of the study forest. Gliders were two and half times less likely to be observed during standardised spotlighting surveys in the study area than elsewhere in southern Queensland. It is likely that low availability of den trees is contributing to large home ranges and the apparent low population density observed in this study.

Monogamy in an Australian arboreal marsupial, the yellow-bellied glider (Petaurus australis)

Several Australian arboreal marsupials have been reported to show variation in mating system across populations, but most previous studies have not included genetic analyses to confirm the observations. Our aim was to test the hypothesis that monogamy was the predominant mating system in a population of yellow-bellied gliders (Petaurus australis) in south-western Victoria, using a combination of behavioural observations and molecular genetic analyses. Home-range overlap, cohesiveness of pairs, rates of den site co-occupancy and location of den trees within the home ranges of 13 adult gliders were determined via radio-tracking. A monogamous social system predominated, demonstrated by extensive home-range overlap between cohabiting adult males and females (40–100%) and little home-range overlap between adjacent territories (&lt;14%). Males spent ~55% of their active time within 25 m of their female partners and 55–85% of their sleeping time in dens with their female partner. The parentage of all juveniles spotlighted within the 400-ha study area was analysed using five microsatellite DNA markers. Of 37 individuals genotyped, eight of 13 juveniles were assigned both social parents as true parents with ≥80% confidence. These results suggest that social and genetic monogamy predominated in this population of yellow-bellied gliders.

Home range and den characteristics of the brush-tailed rabbit-rat (Conilurus penicillatus) in the monsoonal tropics of the Northern Territory, Australia

Radio-telemetry was used to investigate the home range and den characteristics of the brush-tailed rabbit-rat (Conilurus penicillatus) from three sites in the monsoonal tropics of the Northern Territory, Australia. Radio-tracking was conducted in a series of discontinuous 4–17-day sessions, over a 2-year period. The home ranges of 61 C. penicillatus were estimated using the minimum convex polygon (MCP) and fixed kernel (K95% and K50%) methods. There were no significant differences in home-range size among the three sites or between wet and dry seasons, which suggests that vegetation structure, floristics and season play relatively little role in movements of C. penicillatus. The mean home-range size was 0.79 ± 0.09 ha (MCP estimate) to 0.97 ± 0.12 ha (K95% estimate). The home ranges of males were larger than those of females (mean MCP estimates of 1.07 ± 0.15 and 0.45 ± 0.06 ha respectively). C. penicillatus denned primarily in fallen logs and in hollows of eucalypts and bloodwoods (Corymbia spp.). Rough-barked trees appeared to be preferred. The diameter at breast height (DBH) of den trees varied significantly between the three sites, being greatest at site C1 (34.5 ± 2.4 cm) and least at site C2 (26.1 ± 1.0 cm). Den trees had larger DBH than randomly selected trees at each site. The diameter at the mid-point (DMP) of both den and randomly selected logs were not significantly different between sites. Many individuals used more than one den site per tracking session. The small home ranges of C. penicillatus and its reliance on hollows in trees and logs suggest that this species is very vulnerable to local extinction following long-term annual and destructive fire regimes and land clearing, even in comparatively small patches.

Using ecological studies to understand the conservation needs of the squirrel glider in Brisbane?s urban forest-remnants.

This paper provides an overview of our current ecological research on squirrel gliders (Petaurus norfolcensis) living in forest-remnants within an urban matrix in south-east Queensland. We have conducted population censuses and behavioural observations primarily in one 60-ha remnant. The number of tagged gliders (minimum number known alive) in this remnant varied from 75 in 2002 when flowering trees were abundant, to 33 the following year when flowering was poor. Poor flowering led to a delay in breeding and a decline in the probability of glider survival. Feeding observations on gliders in the year of abundant flowering revealed that almost 50% of the diet was comprised of nectar and pollen derived from 10 tree species. A more detailed focus on flowering and its influence on population dynamics at several sites would be of considerable value in understanding the population ecology of this species. We assessed the viability of the subpopulations of P. norfolcensis distributed across the various remnants to allow identification of management actions that may improve viability. Viability analyses under various scenarios suggest that our focal metapopulation will have a high likelihood of extinction within the next 100 years. Predictions of population viability are sensitive to changes in life history parameter estimates. Thus, current field-work has been directed by the need for more precise empirical values. The remnants containing our metapopulation need to be functionally linked to larger nearby remnants to enable glider dispersal among sites. We need a better understanding of glider dispersal behaviour and how permeable the urban matrix might be for P. norfolcensis. Arterial roads and freeways sever connections between many remnants, requiring novel approaches to corridor provision. Future research should examine how habitat quality of the remnants changes over time due to tree die-back and wind-throw. We are investigating the potential role of nest boxes to facilitate glider dispersal and to supplement the availability of den trees. The findings of our studies should contribute to a greater understanding of the general conservation requirements of P. norfolcensis.

Assessing American black bear habitat in the Mobile–Tensaw Delta of southwestern Alabama

American black bears (Ursus americanus) have been extirpated from all but a few areas in southwestern Alabama, and the remaining habitat is being rapidly lost to development. Remnant bear populations exist near extensive (>125,000 ha) bottomland hardwood forests in the Mobile–Tensaw Delta (MTD), but those bottomland areas are rarely used by bears. Reintroduction of black bears to the MTD may improve viability of the remaining bear populations in southwestern Alabama. To evaluate the suitability of this area for bears, we compared habitat conditions at the MTD with similar alluvial habitats at White River National Wildlife Refuge (White River NWR), where bears are numerous. We measured overstory, midstory, and understory vegetation in the MTD and on the North and South management units at White River NWR. We used principal components analysis and principal variable selection to identify 9 variables associated with 5 principal components (hard mast, soft mast, cavity tree availability, large tree availability, and total basal area) that best explained variation among study areas. Differences among the study areas were associated with hard mast, soft mast, and cavity tree availability (P ≤ 0.001). Hard and soft mast production in the MTD was lower than at White River NWR, but we believe it was adequate. However, suitable den trees, which may be a critical habitat component given the duration and severity of winter flooding, appeared to be lacking in the MTD.

Den Characteristics of Black Bears in Southwestern Virginia

Abstract Proper den sites are crucial to the reproduction of female black bears (Ursus americanus). We monitored 31 bears for 39 bear winters in the Southern Appalachians with 95% of the bears confirmed to have denned. Bears denned in trees (41%), rock cavities (32%), excavations (14%), snags (8%), and ground nests (5%). Chestnut oak (Quercus prinus; n = 9), red oak (Q. rubra; n = 8), and tulip-poplar (Liriodendron tulipifera; n = 1) were used as tree dens. Habitat characteristics did not differ between ground dens and tree dens; however, older bears used ground dens more frequently than tree dens (Z = −2.484, P = 0.013). We documented one instance of den reuse. Our results provide managers with more accurate information about black bear dens.

Patch use by the greater glider (Petauroides volans) in a fragmented forest ecosystem. II. Characteristics of den trees and preliminary data on den-use patterns

This paper presents the results of a study of the use of den trees by the greater glider (Petauroides volans) in five patches of remnant eucalypt forest embedded within an extensive radiata pine (Pinus radiata) plantation near Tumut in south-eastern Australia. Radio-tracking was used to identify 171 den trees occupied by 40 animals over 948 animal-tracking days between September 1997 and September 1998. All radio-tracked P. volans used multiple den trees. Males used significantly more den trees than females and a greater proportion of these were used for single visits. Males also used fewer new den trees over the study period in the smaller patches, although they still used more than females. In the larger patches, males and females used similar numbers of den trees. Commonly used den trees tended to be situated in (or close to) core areas of an individual’s home range. Den tree sharing, either concurrently or independently, was predominantly between adult males and females, or between adults and their young. Trees most likely to be used by more than one individual had the same characteristics as trees that had the highest probability of use per se – that is, they were of large ‘average size’.

Modifying Forest Management for Biodiversity

Modifying Forest Management for Biodiversity