Tree Hollows Research Articles

Diurnal and Sex Ratio Flight Activity of Rare Cavity-Dweller Eucnemis capucina Ahrens, 1812 (Coleoptera: Eucnemidae) in Lowland Deciduous Forest: Case Study from Czech Republic

The cavity-dwelling saproxylic beetles are very poorly studied because of their hidden way of life, and they are threatened by forest management. Eucnemis capucina is a rare and sporadic species in all of its distribution area. This species is associated with old hollow trees, which may be why it is on the red lists of many European countries; however, this association could be an indicator of diverse forest structure. We monitored diurnal and seasonal flight activity with intercept flight traps installed on massive ash trees during three seasons. The observed peak of seasonal activity was in May and June. Contrasting most eucnemids, E. capucina is clearly a daytime species, with flight activity between 8:00 and 20:00 and peaking at 14:20. The peak of flight activity is the same for both sexes, but males are more active at the beginning and end of the flight period compared to females. An unequal sex ratio 1.91:1 (F:M) of captured individuals was recorded. The increasing body size of females affected the number of eggs in the body of adult females. The average potential fecundity of a female was 54 eggs, 10 eggs per 1 mm of female body length. The eggs themselves were oval in shape and only the length of the eggs correlated to the body size of the females; the width did not change with body size and did not correlate with egg length, either. We also confirmed that even a single hollow tree can host high numbers or whole populations of rare species and, thus, have a high conservation value. Our study may help better understand the biology of cavity-dwelling beetles and their active life.

Evaluating modelled wildlife corridors for the movement of multiple arboreal species in a fragmented landscape

ContextIn highly fragmented landscapes, arboreal mammals are limited by their ability to move and disperse between core habitats. Connectivity modelling for multiple species allows scientists to identify the most efficient movement and/or dispersal pathway(s) to prioritise for conservation efforts.ObjectivesIn this study, we evaluated the most cost-effective corridor pathway for eight species of arboreal mammals, with particular emphasis on an endangered population of greater gliders (Petauroides volans).MethodsWe use species distribution modelling and circuit theory to calculate connectivity in the landscape for each species. An all-species corridor was then modelled using a least cost path analysis. The final corridor was evaluated for all species through ground-truthing accessible segments.ResultsWe identified that some segments of the corridor had low suitability for highly specialised species, and those with tree hollow requirements for denning. The all-species corridor also utilised an artificial crossing structure over a highway, and monitoring of this rope bridge found only two species (sugar gliders; Petaurus breviceps and ringtail possums; Pseudocheirus peregrinus) used the structure on occasion. Thus, the modelled corridor pathway was not suitable for all species, rather it was found to be more suitable for generalist species such as sugar gliders, ringtail possums, brown antechinus; Antechinus stuartii and brushtail possums; Trichosurus vulpecula.ConclusionsOur study exemplifies the importance of ground-truthing in connectivity conservation studies to ensure conservation outcomes are realised. Furthermore, we provide detailed recommendations for relevant conservation managers, to improve the usage of these existing habitat corridors by arboreal species.

Evaluation of the Occurrence of Hollows in Trees in Managed Forest in the Eastern Brazilian Amazon

Abstract This study proposed to generate information related to the abundance and the structural characteristics of hollows at the tree and species levels in an area of managed forest in the Amazon. A database was used that was composed of 29,899 trees from thirty-eight species that were inventoried, harvested, and measured in ten annual production units that were managed between 2008 and 2017 in the Tapajós National Forest, state of Pará, Brazil. The data was tabulated and reported in absolute and percentage values. Contingency tables were created to identify patterns of occurrence of hollows in commercial stems. A total of 24% of the harvested trees had hollows in at least one section of the commercial stem, and species had different propensities for hollow occurrence. It was found that the larger the tree diameter the greater the possibility for occurrence of hollows, and these hollows were proportionally larger. Most of the hollows in harvested trees were small. Patterns of occurrence in commercial stem hollows were observed, and these were dependent on tree species and size. Most trees had hollows distributed along the entire stem or only at the base of the stem. Study Implications: The presence of hollows in managed native forest trees in the Amazon depends on the species, and trees with larger diameters have a greater probability of having hollows. Furthermore, trees with larger diameters have hollows that have larger diameters, lengths, and volumes. Commercial trees have different patterns of hollows along the stem, and these patterns are dependent on tree species and size. The results of this study will contribute to management of trees with hollows in the Amazon Forest as well as to serve as a base for future studies related to this theme.

Thermal Profiles of Chainsaw Hollows and Natural Hollows during Extreme Heat Events.

Loss of hollow-bearing trees threatens many hollow-dependent wildlife. To mitigate this process, artificial chainsaw-carved hollows (CHs) are often created in dead trees, yet little is known about their thermal profiles. We measured temperatures inside 13 natural hollows (8 live and 5 dead trees) and 45 CHs (5 live and 40 dead trees) in the central west of NSW, Australia, over the course of 2 summers. Maximum temperatures and daily temperature ranges within natural hollows and artificial hollows were similar in 2017-2018. Hollow temperatures were lower in thicker-walled hollows than in thinner-walled hollows. During the January 2019 heatwave, temperatures inside CHs in dead trees exceeded 4-35 °C higher than the upper limit of the thermal neutral zone of sugar gliders-for 6.2 consecutive days (range 0-9 days). CHs in dead trees provided little buffering from thermal extremes; when air temperatures peaked at 44.6 °C, CHs in dead trees were on average 2.4 °C cooler than ambient (range: 5.5 °C cooler to 1.0 °C hotter than ambient). These results show that CHs created in dead trees may not provide suitable thermal conditions for hollow-dependent marsupials during summer heatwaves. Retention of large live trees, coupled with revegetation, is crucial for conserving hollow-dependent fauna in agricultural landscapes.

Elephant rewilding affects landscape openness and fauna habitat across a 92-year period.

Trophic rewilding aims to promote biodiverse self-sustaining ecosystems through the restoration of ecologically important taxa and the trophic interactions and cascades they propagate. How rewilding effects manifest across broad temporal scales will determine ecosystem states; however, our understanding of post-rewilding dynamics across longer time periods is limited. Here we show that the restoration of a megaherbivore, the African savannah elephant (Loxodonta africana), promotes landscape openness (i.e., various measures of vegetation composition/complexity) and modifies fauna habitat and that these effects continue to manifest up to 92 years after reintroduction. We conducted a space-for-time floristic survey and assessment of 17 habitat attributes (e.g., floristic diversity and cover, ground wood, tree hollows) across five comparable nature reserves in South African savannah, where elephants were reintroduced between 1927 and 2003, finding that elephant reintroduction time was positively correlated with landscape openness and some habitat attributes (e.g., large-sized tree hollows) but negatively associated with others (e.g., large-sized coarse woody debris). We then indexed elephant site occurrence between 2006 and 2018 using telemetry data and found positive associations between site occurrence and woody plant densities. Taken alongside the longer-term space-for-time survey, this suggests that elephants are attracted to dense vegetation in the short term and that this behavior increases landscape openness in the long term. Our results suggest that trophic rewilding with elephants helps promote a semi-open ecosystem structure of high importance for African biodiversity. More generally, our results suggest that megafauna restoration represents a promising tool to curb Earth's recent ecological losses and highlights the importance of considering long-term ecological responses when designing and managing rewilding projects.

Effects of the temperature on activity patterns and torpor in Saccolaimus saccolaimus in Bangladesh with notes on its morphometrics and roosting behaviour

Saccolaimus saccolaimus is one of the six Emballonurid bats and the only species from the genus Saccolaimus that occurs in South and Southeast Asia. This species utilizes tree hollows, damaged palm trees, and occasionally artificial structures as roosts. We recorded a total of 22 bats from 10 colonies located at two dormitories in Jahangirnagar University (JU) in a sub-urban setting in central Bangladesh. The number of bats per colony varied between 1-9 individuals, with an average of four bats per colony. We found that the colonies of S. saccolaimus emerged from roosting sites when the temperature was 22.5°C or higher. The highest bat activity was recorded in September (79.66 mins) when the air temperature was 27.66°C, and the lowest was in January (47.01 mins) when the air temperature was 17.46°C. We observed variations in bat activity in different months, and bat activity was strongly correlated (R-square = 0.52) with air temperature. The most extended torpor period for the colonies was recorded for 27 days. The mean weight for male S. saccolaimus in JU was 41.66 ± 0.29 (41.46-42) g, whereas for females was 45.32 ± 3.08 (43.14- 47.5) g. Although some variation was observed in the morphological measurements, the morphometric analysis indicated no significant differences between specimens from Bangladesh and the neighbouring countries. Further research is needed to understand various ecological aspects of S. saccolaimus in Bangladesh. Therefore, to do so, the existing colonies on JU campus should be extensively monitored.

Selection of Nest Material and Summer Nest Location by the Hazel Dormouse (Muscardinus avellanarius) in the Bidstrup Forests, Denmark.

Hazel dormice (Muscardinus avellanarius) construct summer nests for resting and breeding. The nests are built directly in the vegetation, in tree hollows, or in nest boxes. The availability of nest materials and vegetation coverage may affect the likelihood of finding hazel dormice at a location. The aim of the study is: (1) To investigate the preferences of hazel dormice for nesting materials today compared to four decades ago. (2) To investigate hazel dormice preferences for vegetation coverage at nest sites. In total, 148 hazel dormouse summer nests from the Bidstrup forests in Zealand (Denmark), were analysed. Of these, 82 were collected in the period A: 1980-1985 and 66 were collected in B: 2019-2020. In total 26 different nest materials were found. Beech was the major nest material in both periods, and Jacob's selectivity index indicates that beech is selected for as nesting material and that hazel dormice may travel to collect beech leaves. Nests from period A contained more beech (W = 1521, p < 0.05) and less oak (W = 1304, p < 0.01) compared to nests from period B. Vegetation analysis showed that coverage of shrubs higher than 2 m above ground (W = 1.5, p = 0.07) may be of great importance for hazel dormice.

3D Printed Percutaneous Transhepatic Cholangiography and Drainage (PTCD) Simulator for Interventional Radiology.

Learning how to perform percutaneous transhepatic bile duct drainage (PTCD) is challenging for interventional radiology (IR) trainees. Therefore, simulators are crucial for IR training and are being increasingly demanded in the evolving healthcare environment of value-based care. To facilitate interventional training, we tried to evaluate our newly developed liver phantom for further use in IR training. We developed a liver phantom with a flexible hollow biliary tree, hydrogel-based liver parenchyma, plastic ribs, and silicone skin. The phantom was evaluated by 20 radiology residents from two hospitals. After an introduction, all participants tried to obtain biliary access by fluoroscopic guidance within 25min. Puncture time, fluoroscopy time, and kerma area product were measured. After 7days, the participants repeated the procedure on an altered and more difficult model. Additionally, a survey was handed out to every participant (20 residents, 5 experts, and 5 IR fellows) to evaluate the phantom in terms of accuracy and haptic feedback, as well as general questions regarding simulation. The residents performed significantly faster and were more self-confident on Day 7 than on Day 1, significantly decreasing puncture time, fluoroscopy time, and kerma area product (p ≤ 0.0001). The participants were very satisfied with their simulation experience and would trust themselves more in real-life scenarios. We were able to develop a phantom with high anatomical accuracy for fluoroscopy and ultrasound-guided interventions. The phantom successfully helped residents learn and improve their PTCD performance.

Influence of nest box design on internal microclimate: Comparisons of plastic prototypes

AbstractHollow‐dependent fauna are declining worldwide, due primarily to the widespread clearing of hollow‐bearing trees. Artificial cavities such as timber and plywood boxes are commonly used to increase hollow availability, yet there is increasing evidence that they are poor facsimiles of natural cavities, characterized by lower insulative properties and a shorter field life. We evaluated whether plastic materials could create a nest box with a stable thermal profile that more closely resembles the complex shapes and textures of natural tree hollows while containing fewer mechanical joins that represent potential failure points when installed. We developed three sets of prototype nest boxes comprising various combinations of plastic density (10%, 25% and 50%), insulation (single vs. double wall with or without sawdust between them), nesting chamber (with or without timber inserts) and bedding (with or without decomposed heartwood) and compared their thermal performance in a temperature‐controlled laboratory to compare internal temperature and relative humidity. We found double‐walled plastic nest box with an internal timber‐lined chamber was best able to buffer ambient temperature fluctuations, consistently recording internal temperatures of 6+°C below maximum ambient temperature, maintaining high levels of relative humidity (76%–92%) when furnished with decomposed timber heartwood. This design also performed better during a simulated hot day; internal temperatures exhibiting twice the lag time of single‐walled designs, noting that plastic density had little influence on internal conditions. While the recruitment and protection of hollow‐bearing trees must be a priority, this work shows significant potential in improving the design and functionality of artificial hollows that are critical to the conservation of hollow‐dependent species.

Nesting sites of cavity nesting honey bees (Apis spp.) in natural ecosystems of Kerala, India

Natural colonies of cavity nesting honey bees are important for the conservation of bees. This study was aimed to determine the nesting habitat, nesting sites, nest height, and nest characteristics of naturally occurring cavity nesting honey bees in Kerala. The results showed that primary forests, disturbed or agricultural land as well as undisturbed lands were found to be the nesting habits of cavity nesting bees in Kerala. Among the nesting sites, tree hollows were the prevalent nesting sites of cavity nesting bees in Kerala wherein, the predominant tree species was Tectona grandis. The nest height of honey bee colonies from ground level varied from 0 cm to 600 cm and the number of combs in a colony varied from five to twelve. No significant differences were observed in the nest height and number of combs in the honey bee colonies in hill and plain regions of Kerala. Biserial correlation analysis revealed that in the plain regions, the proportion of parallel arrangement of combs to the direction of nest entrance was high (0.83) whereas in hilly regions the proportion of comb arrangement at right angles to the nest entrance was high (0.88).

Seven urgent actions to prevent the extinction of the critically endangered Leadbeater’s possum (Gymnobelideus leadbeateri)

The conservation status of Leadbeater’s possum (Gymnobelideus leadbeateri) was upgraded to ‘Critically Endangered’ in 2015 following major impacts on populations and habitat arising from the ‘Black Saturday’ bushfires of 2009. This conservation listing was subsequently reviewed and retained in 2019. Despite this recognition of significant extinction risk, major gaps exist in the conservation strategy being applied, including the absence of a current recovery plan or meaningful recovery targets. The cumulative impacts and legacies on forest condition and hollow-bearing tree abundance from logging and bushfire pose the most significant threats to the species, and several studies indicate that the current reserve system is inadequate to protect viable populations. Seven high-level actions are recommended that should be implemented with urgency to prevent the extinction of this iconic, flagship species amidst increasing threats from climate change. Most significantly, this includes the rapid phase-out of logging within the species’ range as the highest priority action. Other urgent measures include re-formation of a recovery team to coordinate action implementation, provision of nest boxes and chainsaw hollows to increase den site availability, intensive population management and habitat restoration for the lowland population that now contains fewer than 40 individuals, and translocations to expand the area of occupancy in response to increasing risks from bushfire and climate change.

Further dietary samples for Eastern Barn Owls Tyto javanica near Tamworth, New South Wales, revealed by habitat clearance

The diet of the Eastern Barn Owl Tyto javanica was investigated by examination of two samples of pellets (n = 11 and 39), pellet debris and prey remains from: (1) an occupied nest with fledgling in May 2009, and (2) an Owl’s winter roost in August 2009 near Tamworth in the grain belt of New South Wales. The breeding diet consisted, by number, of 91% mammals (90% rodents, including 87% House Mice Mus musculus) and 9% common farmland birds (n = 116 food items). The winter diet consisted of 99% House Mice and 1% bird (n = 188 food items). The fledgling Owl was killed when it failed to flush from its nest hollow as the tree was being felled, during approved clearing of the now Critically Endangered White Box–Yellow Box–Blakely’s Red Gum Grassy Woodland and Derived Native Grassland. Given the dependence of the Barn Owl on House Mice, and the ongoing clearing of hollow trees, we note the potential for (a) secondary poisoning of owls by rodenticides, especially during plagues of the invasive House Mouse in the grain belt, and (b) the Barn Owl’s long-term decline in abundance in New South Wales.

Characteristics of stingless bees (Hymenoptera: Apidae: Meliponini) from Universitas Andalas Limau manis campus complex and its implication in pollination and ecotourism

Stingless bees, of the tribe Meliponini, subfamily Meliponinae and family Apidae, have been renowned as honey-producing bees and pollinators. An inventory survey on stingless bees was conducted at Universitas Andalas campus complex (UACC) between 2019-2022 with the aim of documenting their morphological characteristics and nesting behavior that are important for developing meliponiculture. It used direct observation and specimen collection at nest entrances, along with plant species identification from around the nests. A total of nine (37 % of stingless bee species known in Sumatra), of four genera, were recorded at different nesting spots within UACC. Five species were under genus Tetragonula, two of genus Lepidotrigona, and one each for genera Tetrigona and Heterotrigona. Tetragonula fuscobalteata was the smallest species found in this study, reaching 3.2 mm body length and less than 3.5 mm wing length. On the other hand, Tetrigona apicalis was the biggest species, measuring 7 mm body length and more than 7.2 mm wing length. Tetragonula consists of members with small bodies and inhabit either anthropogenic areas or natural habitats such as tree hollows, fences, wall crevices or other forms of cavity. Thirty-one plant families were recorded as potential resources around the stingless bee colonies. These families are dominated by Fabacease, Asteraceae, Moraceae, Euphorbiaceae and Verbenaceae. There might be differences in capacity to provide nectar, pollen, resin or gum among plant families; however, the diversity of plant species in the community should be complementary in providing resources for stingless bee colony. The nine stingless bee species recorded in this study possess an array of potential for meliponiculture and aesthetic purposes. Anthropogenic-tolerant species can be possibly reared and aesthetically integrated with decorative aspects of human settlement. The knowledge on existing stingless bee species, along with their biological aspects become crucial in initiating meliponiculture system within the University boundaries, with possible venture can be extended into ecotourism where people come and enjoy the beekeeping within this scenic University environment. Key words: Stingless bees, Taxonomy, Morphological, Meliponiculture, Pollinator, Ecotourism, Campus

Quantifying the direct fire threat to a critically endangered arboreal marsupial using biophysical, mechanistic modelling

AbstractHistorically unprecedented areas of forest habitat have been impacted by fire, as climate change and other anthropogenic disturbances drive increases in fire burned area and severity. Although 88% of Australia's [threatened] land mammals are threatened by inappropriate fire regimes, calculations of animal mortality resulting from specific events have been impeded by knowledge gaps relating to both the direct (first‐order) and long‐term (second‐order) effects of fire on different species. This study addresses the need for a quantified, mechanistic understanding of first‐order effects, presenting an extension of the Fire Research and Modelling Environment (FRaME) to allow prediction of species‐specific mortality. FRaME is demonstrated and tested here by replicating an incident in which a prescribed burn caused 77% mortality of a population of the critically endangered ngwayir (Pseudocheirus occidentalis, Pseudocheiridae). FRaME correctly predicted heavy mortality (62–79%) arising from partial and full‐thickness burns and asphyxiation due to burns in the respiratory tract. Mortality varied with animal fire‐avoidance strategies (p < 0.001) and the thickness of tree hollow walls (r = −0.95, p < 0.001). Although management guidelines specified low intensity fire, mortality had no significant relationship with Byram intensity and larger flames due to ‘torching’ were most frequent when fire spread was slowest. FRaME modelling predicted that individuals would be impacted by temperatures exceeding 500°C for several minutes. Fire management that is premised on discredited notions of fire behaviour and overly simple models can lead to catastrophic management outcomes such as those documented here. FRaME addresses this need by providing a platform to account for heterogeneous fire behaviour as well as animal behaviour and habitat quality, calculating fire risk to fauna and guiding management that maximizes safe habitat.

Smallest Iberian songbirds at risk from lethal heat in warming world

According to the World Meteorological Organization, temperatures in Europe are increasing at more than twice the global average. And in 2022, the mercury rocketed as a summer-long heatwave engulfed the continent – hitting an all-time high in Pinhão, Portugal, of 47°C – triggering wildfires as rivers ran dry and the European maize harvest crashed. ‘The Mediterranean Basin… [has] experienced a 1.5°C increase in mean annual surface temperatures since pre-industrial values’, says Julián Cabello-Vergel, from the University of Badajoz, Spain, adding that the smallest warm-blooded (endothermic) creatures are some of the most susceptible to these dramatic climate shifts. ‘Small songbirds are especially vulnerable to heatwaves due to their diurnal habitats, small body sizes with large area to volume ratios and high metabolic rates’, says Cabello-Vergel. To remain cool, many small songbirds pant like dogs; however, this strategy is costly, consuming energy and scarce water, placing the birds at risk during extreme heat. So just how vulnerable are the songbirds of Spain?Cabello-Vergel, José Abad-Gómez, Núria Playà-Montmany and Auxiliadora Villegas, with support from Erick González-Medina, Jose Masero and Jorge Gutiérrez, all from University of Badajoz, headed out into the surrounding countryside to catch birds from a range of habitats, including open landscapes and dense riverside woods. ‘We captured birds by setting up nets’, Cabello-Vergel explains. Eventually, the team transported the eight species, including house sparrows (Passer domesticus), crested larks (Galerida cristata) and goldfinches (Carduelis carduelis), back to the lab. There, they calculated the amount of energy each bird used as the temperature rose to 40°C by measuring their oxygen consumption, as well as body temperature and the amount of water they exhaled, before raising the temperature in 2°C blocks above 40°C until each bird began to struggle in the heat, at which point the team released the animal back to its home.After analysing the responses of the songbirds to the increasing heat, it was clear that they were not well prepared for extreme temperatures. Although desert songbirds can withstand temperatures ranging from 46 to 54°C, the highest temperatures that the Mediterranean songbirds could cope with peaked between 40 and 46°C, placing the Mediterranean residents at risk from extreme heatwaves, such as the one they endured in 2022. In addition, the songbirds had to work physically harder at the higher temperatures to keep cool, increasing their resting metabolic rate by 40% at the highest temperatures, as well as losing significantly more water as they panted harder to maintain a safe body temperature during the laboratory-simulated heatwave. By comparing the birds’ cooling efficiencies, the team realised that the crested lark – the largest species that the team caught – was the only bird that was able to keep itself cool when the air temperature exceeded its body temperature, and Cabello-Vergel adds, ‘Because small songbirds lose water at higher rates, they dehydrate faster than larger ones, resulting in greater risk of death during extremely hot days’.But what does this mean for Mediterranean songbirds facing warmer summers and more extreme heatwaves? ‘Although the studied species are not currently experiencing lethal dehydration risks, they all are experiencing several summer days in which their thermoregulatory capacities are challenged’, says Cabello-Vergel, which suggests that the long-term future for the Iberian Peninsula's smallest songsters is bleak. However, the team recommends that conservation managers prioritise the protection of wooded areas and cool riverbanks, where vulnerable songbirds could retreat to, seeking shade and protection in bushes and tree hollows on the most searing days.

Microclimate in hollow trees and how it affects an inhabiting beetle species,Osmoderma eremita

AbstractStudies of species' responses to microclimatic conditions have increased our understanding of their habitat requirements and possible responses to climate warming. However, little is known about the role of microclimate for insects inhabiting hollow trees.We explored the relationship between tree characteristics and microclimate, and analysed how the microclimate in tree‐hollows affects the occurrence and body size of an endangered beetle species,Osmoderma eremita.We placed temperature data‐loggers in wood mould (= loose material in tree‐hollows) and surveyedO. eremitain 47 hollows in oak pastures in south‐eastern Sweden. We found that tree characteristics previously known to be associated with occurrence of beetle species confined to tree‐hollows (larger diameters, more wood mould, entrances higher up, and not directed upwards) tend to decrease moisture and moisture variation, while their effects on temperature and temperature fluctuations differ during different seasons. This indicates that microclimatic conditions are important for beetles in hollow trees, and many specialised species seem to avoid conditions that are too moist.O. eremitaoccurred more frequently in trees with a warmer and more stable microclimate, while adult body size decreased with a warmer microclimate. A positive effect of a warmer microclimate was expected, since the study was done near the northern margin of the species' range.O. eremitais confined to living in hollow trees, which may be due to the microclimate there being more stable in comparison to both the ambient climate and the microclimate in standing and downed dead wood.

The effect of logging on fission-fusion behaviour of tree-dwelling bats explored by an agent-based model

Logging is one of the greatest threats to global biodiversity, while forests are one of the most important habitats for bats. Bats that roost in tree cavities require a large number of potential roosts due to their frequent roost switching. However, the density of tree cavities and hollows sufficient to sustain large populations of bat species in forests is unknown. The fission-fusion dynamics of bat groups in forest environment is associated with ritualised dawn swarming behaviour at potential tree cavities that serves to exchange information in a non-centralised decision-making process. We used a computer model based on the swarm algorithm, SkyBat, that resembles this complex process and aimed to determine how population size changes over time when cavity trees are removed from roosting territory of the local population of Leisler's bats (Nyctalus leisleri), which inhabit a forest habitat in Central Europe. Simulations revealed that social bonds between bats, maintained by frequent switching among groups, play an important role in this highly dynamic system. When strong social contact was not considered, reducing the original number of trees with cavities (20 cavities × ha−1) to 50% was still acceptable to bats, but further interventions and/or increased demand for social contact would have led to local extinction of the species. Results suggest that potential bat roosts in mature forest stands should be preserved as much as possible and that non-intensive logging and management can be beneficial to tree-dwelling bats.

Bat Use of Hollows in California's Old-Growth Redwood Forests: From DNA to Ecology.

The loss of roosting resources, either through disturbance or removal, negatively affects bats. Identifying sensitive species and determining roost requirements are critical components in conserving their habitat. Cavity-roosting bats on the North Coast of California are known to use hollows in large redwood trees. In this study, we examined the factors determining the use of basal tree hollows by different bat species at eight redwood forest sites in Del Norte, Humboldt, and Mendocino Counties, California. Bat guano was collected from 179 basal hollow roosts from 2017 to 2018, and guano mass was used as an index of roosting activity. Nine bat species and one species group were identified by analysis of DNA in guano. We made a total of 253 identifications from 83 hollows into the 10 species categories. The most prevalent species were Myotis californicus (California myotis; 28.5% of all identifications), the Myotis evotis-Myotis thysanodes group (17.4%), Corynorhinus townsendii (17.0%), and Myotis volans (15.0%). We evaluated the extent to which habitat variables at the scales of the hollow, vicinity, and site influenced the level of roost use. The correlations between guano mass and habitat variables were examined using generalized additive mixed models. At the hollow scale, guano mass increased with ceiling height above the opening. At the vicinity scale, guano mass increased with less cover of small trees. At the site scale, there was no association between guano mass and distance to foraging areas, elevation, or the number of nearby hollows. These tree hollow roost preferences can inform land managers when planning the management and conservation of redwood forests.

Den supplementation for black bears in coastal British Columbia

American black bears (Ursus americanus) require suitable den sites that provide security and cover to successfully survive the winter denning period. On Vancouver Island, British Columbia, Canada, black bears prefer to use cavities associated with large-diameter hollow trees or structures derived from trees (i.e., cavities in or under logs, root boles and stumps) as den sites. Extensive harvesting of coastal forests has reduced the availability of natural den structures such that their supply may affect population sustainability. I attempted to develop new methods to address the declining supply of denning opportunities by creating and testing new den structures constructed in trees, stumps and from plastic. Between 2014–2021, I created or deployed and monitored 17 potential den structures in 2 study areas that were believed to have low den supply. I documented up to 51 visits by bears at each structure; every one of the video-monitored structures was investigated at least 5 times. None of the plastic artificial den structures were used by bears, but an enhanced natural structure was used as a den over 4 consecutive winters. My work indicates that bears will find and investigate all natural or artificial denning structures in their environment, but artificial structures do not appear to be a viable method to mitigate losses of dens caused by forest harvesting.

Sex specificity of dispersal behaviour and flight morphology varies among tree hollow beetle species

BackgroundFlight performance and dispersal behaviour can differ between sexes, resulting in sex-biased dispersal. The primary sex ratio of populations may also explain dispersal bias between sexes, as this bias may evolve with the primary sex ratio to reduce intrasexual competition. Although dispersal bias between sexes is relevant to population dynamics, there are few studies on sex-biased dispersal in insects. We studied the flight performance and dispersal behaviour of seven saproxylic beetle species associated with tree hollows from a sex perspective. We also analysed the possible coevolution of flight performance with the primary sex ratio.MethodsWing loading and wing aspect ratio were used as measures of the flight performance of species and sexes. Dispersal behaviour was explored by analysing the frequency of each sex in interception traps versus the primary sex ratio obtained by tree hollow emergence traps using contingency tables and posthoc standardized residuals. A more active flight behaviour was expected for the sex with higher capture frequency in the interception traps. To explore the causes of flight performance bias between sexes, we searched for possible correlations between wing loading or wing aspect ratio and primary sex ratio using Pearson’s correlation coefficient.ResultsWing loading and wing aspect ratio differed between species and sexes, with flight performance being higher in males than in females for four of the seven species analysed. Dispersal behaviour and flight performance matched in the case of Elater ferrugineus; males showed higher flight performance and were the most collected sex in the interception traps (more active flyers). In contrast, the higher flight activity of Cetonia carthami aurataeformis females was not correlated with a higher flight performance than that of males. Moreover, we found that a bias in the primary sex ratio towards females is often correlated with a decrease in female flight performance.ConclusionsWe stress that flight performance and dispersal behaviour of sexes do not always go hand in hand. Moreover, the relationship between the sex ratio and flight performance bias between sexes is not driven by competition within the most abundant sex. The inclusion of a sex perspective in insect dispersal studies would be useful to detect dispersal bias between sexes and its causes and would allow for further analysis of its effects on population dynamics.