Surface reflectance drives nest box temperature profiles and thermal suitability for target wildlife

Creating wildlife habitat using artificial structures: a review of their efficacy and potential use in solar farms

The biodiversity crisis is exacerbated by a growing human population modifying nearly three-quarters of the Earth's land surface area for anthropogenic uses. Habitat loss and modification represent the largest threat to biodiversity and finding ways to offset species decline has been a significant undertaking for conservation. Landscape planning and conservation strategies can enhance habitat suitability for biodiversity in human-modified landscapes. Artificial habitat structures such as artificial reefs, nest boxes, chainsaw hollows, artificial burrows, and artificial hibernacula have all been successfully implemented to improve species survival in human-modified and fragmented landscapes. As the global shift towards renewable energy sources continues to rise, the development of photovoltaic systems is growing exponentially. Large-scale renewable projects, such as photovoltaic solar farms have large space requirements and thus have the potential to displace local wildlife. We discuss the feasibility of 'conservoltaic systems' - photovoltaic systems that incorporate elements tailored specifically to enhance wildlife habitat suitability and species conservation. Artificial habitat structures can potentially lessen the impacts of industrial development (e.g., photovoltaic solar farms) through strategic landscape planning and an understanding of local biodiversity requirements to facilitate recolonization.

Improving the science and practice of using artificial roosts for bats

Worldwide, artificial bat roosts (e.g., bat boxes, bark mimics, bat condos) are routinely deployed for conservation, mitigation, and community engagement. However, scant attention has been paid to developing best practices for the use of artificial roosts as conservation tools. Although bats readily occupy artificial roosts, occupancy and abundance data are misleading indicators of habitat quality. Lacking information on bat behavior, health, and fitness in artificial roosts, their conservation efficacy cannot be adequately validated. We considered the proximal and ultimate factors, such as evolutionarily reliable cues, that may prompt bats to preferentially use and show fidelity to suboptimal artificial roosts even when high-quality alternatives are available. Possible negative health and fitness consequences for artificial roost inhabitants include exposure to unstable and extreme microclimates in poorly designed roosts, and vulnerability to larger numbers of ectoparasites in longer lasting artificial roosts that house larger bat colonies than in natural roosts. Bats using artificial roosts may have lower survival rates if predators have easy access to roosts placed in conspicuous locations. Bats may be lured into occupying low-quality habitats if attractive artificial roosts are deployed on polluted urban and agricultural landscapes. To advance the science behind artificial bat roosts, we present testable research hypotheses and suggestions to improve the quality of artificial roosts for bats and decrease risks to occupants. Because continued loss of natural roosts may increase reliance on alternatives, such as artificial roosts, it is imperative that this conservation practice be improved.

Is bedding material a more effective thermal insulator than trap cover for small mammal trapping? A field experiment

Live trapping is a key technique for conducting ecological studies on small mammals. All-metal live traps are popular in monitoring schemes owing to their tested performance, lightweight design (aluminium) and foldability. However, capture represents a stressful situation for small mammals, particularly during cold seasons, when individuals are susceptible to cold weather starvation resulting from low temperature and insufficient food to maintain body temperature. Metal live traps provide limited protection against cold temperatures, and it is often recommended to use covers to buffer external temperature fluctuations and prevent entry of moisture. Here, we compared the insulative performance of a PVC cover designed for Sherman traps and of bedding material, using data loggers to record temperature and humidity inside traps. We conducted different experiments simulating field conditions (traps at night with a heat source inside) and different treatments (cover, bedding material) to test the thermal insulation capacity of three models of widely used commercial traps: Longworth, Sherman, and Heslinga. Our findings indicated that Longworth and Sherman traps were better insulated against ambient air temperature fluctuations than Heslinga traps (+2.0 °C warmer on average). Bedding material was paramount in reducing relative humidity and increasing thermal insulation capacity of traps (+3.1 °C), an effect that was strengthened when a PVC cover was additionally used (+4.2 °C). The covered traps prevented the direct entrance of rain and dew (reducing damp bedding), provided camouflage (reducing thefts), and improved thermal and humidity conditions of traps (potentially increasing survival of captive small mammals). Our results suggest that using covers and bedding materials can improve thermal and humidity conditions within live traps, thus reducing the metabolic costs of thermoregulation and increasing survival chances for trapped small mammals during cold seasons.

What makes a house a home? Nest box use by West European hedgehogs (Erinaceus europaeus) is influenced by nest box placement, resource provisioning and site-based factors

Artificial refuges provided by householders and/or conservation practitioners potentially represent one mechanism for mitigating declines in the availability of natural nest sites used for resting, breeding and hibernating in urban areas. The effectiveness of such refuges for different species is, however, not always known. In this study, we conducted a questionnaire survey of UK householders to identify factors associated with the use of ground-level nest boxes for West European hedgehogs (Erinaceus europaeus), a species of conservation concern. Overall, the percentage of boxes used at least once varied with season and type of use: summer day nesting (35.5-81.3%), breeding (7.2-28.2%), winter day nesting (20.1-66.5%) and hibernation (21.7-58.6%). The length of time the box had been deployed, the availability of artificial food and front garden to back garden access significantly increased the likelihood that a nest box had been used for all four nesting types, whereas other factors related to placement within the garden (e.g., in a sheltered location, on hardstanding such as paving, distance from the house) and resource provisioning (bedding) affected only some nesting behaviours. The factors most strongly associated with nest box use were the provisioning of food and bedding. These data suggest, therefore, that householders can adopt simple practices to increase the likelihood of their nest box being used. However, one significant limitation evident within these data is that, for welfare reasons, householders do not routinely monitor whether their box has been used. Consequently, future studies need to adopt strategies which enable householders to monitor their boxes continuously. Ultimately, such studies should compare the survival rates and reproductive success of hedgehogs within artificial refuges versus more natural nest sites, and whether these are affected by, for example, the impact of nest box design and placement on predation risk and internal microclimate.

Evaluating bat boxes: design and placement alter bioenergetic costs and overheating risk

Bat box microclimates vary spatially and temporally in temperature suitability. This heterogeneity subjects roosting bats to a variety of thermoregulatory challenges (e.g. heat and cold stress). Understanding how different bat box designs, landscape placements, weather and bat use affect temperature suitability and energy expenditure is critical to promote safe and beneficial artificial roosting habitat for species of conservation concern. From April to September 2019, we systematically deployed 480 temperature dataloggers among 40 rocket box style bat boxes of 5 designs and regularly monitored bat abundance. We used bioenergetic models to assess energy costs for endothermic and heterothermic bats and modelled the overheating risk for each box as a function of design, placement, bat abundance and weather. For endothermic bats, predicted daily energy expenditure was lower for solar-exposed placements, large group sizes and a box design with enhanced thermal mass. For heterothermic bats, shaded landscape placements were the most energetically beneficial and bat box design was not important, because all designs generally offered microclimates suitable for torpor use at some position within the box. Overheating risk was highest for solar-exposed landscape placements and for designs lacking modifications to buffer temperature, and with increasing bat abundance, increasing ambient temperature and slower wind speeds. The external water jacket design, with the greatest thermal mass, concomitantly decreased overheating risk and endothermic energy expenditure. By assessing bat box suitability from two physiological perspectives, we provide a robust method to assess the conservation value of bat box design and placement strategies. We recommend future studies examine how changing thermal mass and conductance can be used to diminish overheating risk while also enhancing the effects of social thermoregulation for bat box users.

Insulated nest boxes provide thermal refuges for wildlife in urban bushland during summer heatwaves

In urban bushland, the installation of nest boxes is widely used to compensate for the loss of natural tree hollows. However, current nest box designs may not provide thermal refuges for wildlife during summer heatwaves, particularly if internal temperatures exceed the upper critical temperatures of wildlife. We investigated whether the addition of roofing insulation to nest boxes deployed for sugar gliders (Petaurus breviceps) and squirrel gliders (Petaurus norfolcensis) in urban bushland would reduce internal nest box temperatures during summer heatwaves. We measured temperatures of 44 insulated and 47 uninsulated nest boxes during one of the hottest summers on record (2018–2019) in the Lake Macquarie region of NSW, Australia, a period during which several prolonged heatwaves occurred. Over the 90-day study, maximum temperatures were, on average, 3.1°C lower in insulated boxes than in uninsulated boxes. The addition of insulation significantly lowered nest box temperatures regardless of aspect (north or south facing) or day of measurement. Temperatures exceeded the upper critical temperature (35.1°C) of gliders more frequently in uninsulated nest boxes (28% of days) than in insulated nest boxes (8% days). Although the addition of insulation to nest boxes lowered their internal temperatures, during heatwaves spanning 23 days, nest box temperatures exceeded the upper critical temperatures of gliders on 58% and 23% of days in uninsulated and insulated nest boxes respectively. These findings underscore the importance of retaining natural hollows in urban bushland to provide thermally suitable refuges for wildlife during extreme heat events.

Artificial refuges for wildlife conservation: what is the state of the science?

Artificial refuges are human-made structures that aim to create safe places for animals to breed, hibernate, or take shelter in lieu of natural refuges. Artificial refuges are used across the globe to mitigate the impacts of a variety of threats on wildlife, such as habitat loss and degradation. However, there is little understanding of the science underpinning artificial refuges, and what comprises best practice for artificial refuge design and implementation for wildlife conservation. We address this gap by undertaking a systematic review of the current state of artificial refuge research for the conservation of wildlife. We identified 224 studies of artificial refuges being implemented in the field to conserve wildlife species. The current literature on artificial refuges is dominated by studies of arboreal species, primarily birds and bats. Threatening processes addressed by artificial refuges were biological resource use (26%), invasive or problematic species (20%), and agriculture (15%), yet few studies examined artificial refuges specifically for threatened (Vulnerable, Endangered, or Critically Endangered) species (7%). Studies often reported the characteristics of artificial refuges (i.e. refuge size, construction materials; 87%) and surrounding vegetation (35%), but fewer studies measured the thermal properties of artificial refuges (18%), predator activity (17%), or food availability (3%). Almost all studies measured occupancy of the artificial refuges by target species (98%), and over half measured breeding activity (54%), whereas fewer included more detailed measures of fitness, such as breeding productivity (34%) or animal body condition (4%). Evaluating the benefits and impacts of artificial refuges requires sound experimental design, but only 39% of studies compared artificial refuges to experimental controls, and only 10% of studies used a before-after-control-impact (BACI) design. As a consequence, few studies of artificial refuges can determine their overall effect on individuals or populations. We outline a series of key steps in the design, implementation, and monitoring of artificial refuges that are required to avoid perverse outcomes and maximise the chances of achieving conservation objectives. This review highlights a clear need for increased rigour in studies of artificial refuges if they are to play an important role in wildlife conservation.

Feasibility Analyses of Real-Time Detection of Wildlife Using UAV-Derived Thermal and RGB Images

Wildlife monitoring is carried out for diverse reasons, and monitoring methods have gradually advanced through technological development. Direct field investigations have been replaced by remote monitoring methods, and unmanned aerial vehicles (UAVs) have recently become the most important tool for wildlife monitoring. Many previous studies on detecting wild animals have used RGB images acquired from UAVs, with most of the analyses depending on machine learning–deep learning (ML–DL) methods. These methods provide relatively accurate results, and when thermal sensors are used as a supplement, even more accurate detection results can be obtained through complementation with RGB images. However, because most previous analyses were based on ML–DL methods, a lot of time was required to generate training data and train detection models. This drawback makes ML–DL methods unsuitable for real-time detection in the field. To compensate for the disadvantages of the previous methods, this paper proposes a real-time animal detection method that generates a total of six applicable input images depending on the context and uses them for detection. The proposed method is based on the Sobel edge algorithm, which is simple but can detect edges quickly based on change values. The method can detect animals in a single image without training data. The fastest detection time per image was 0.033 s, and all frames of a thermal video could be analyzed. Furthermore, because of the synchronization of the properties of the thermal and RGB images, the performance of the method was above average in comparison with previous studies. With target images acquired at heights below 100 m, the maximum detection precision and detection recall of the most accurate input image were 0.804 and 0.699, respectively. However, the low resolution of the thermal sensor and its shooting height limitation were hindrances to wildlife detection. The aim of future research will be to develop a detection method that can improve these shortcomings.

Using mounting, orientation, and design to improve bat box thermodynamics in a northern temperate environment

Wildlife managers design artificial structures, such as bird houses and bat boxes, to provide alternative nesting and roosting sites that aid wildlife conservation. However, artificial structures for wildlife may not be equally efficient at all sites due to varying climate or habitat characteristics influencing thermal properties. For example, bat boxes are a popular measure employed to provide compensatory or supplementary roost sites for bats and educate the public. Yet, bat boxes are often thermally unstable or too cold to fulfill reproductive females needs in northern temperate environments. To help improve the thermodynamics of bat boxes, we tested the effect of (1) three mountings, (2) four orientations, and (3) twelve bat box designs on the internal temperature of bat boxes. We recorded temperatures in bat boxes across a climate gradient at seven sites in Quebec, Canada. Bat boxes mounted on buildings had warmer microclimates at night than those on poles and those facing east warmed sooner in the morning than those facing west or south. Our best new model based on passive solar architecture (Ncube PH1) increased the time in the optimal temperature range (22–40 °C) of targeted species by up to 13% compared to the most commonly used model (Classic 4-chamber) when mounted on a building with an east orientation (other designs presented in the Supplementary Information). Based on bioenergetic models, we estimated that bats saved up to 8% of their daily energy using the Ncube PH1 compared to the Classic 4-chamber when mounted on a building with an east orientation. We demonstrate that the use of energy-saving concepts from architecture can improve the thermal performance of bat boxes and potentially other wildlife structures as well.

Tolerance to high temperature by arboreal mammals using nest boxes in southern Australia

Nest boxes are used to manage populations of tree-cavity dependent birds and mammals. Concerns have been raised that due to their poor insulative properties nest boxes may cause heat stress and occasionally death during summers of extreme maximum temperatures. Our study investigated whether this nest box heat stress hypothesis applies to two small cavity-dependent mammals (brush-tailed phascogales and sugar gliders). Focusing on days when ambient temperature reached ≥40 °C, we recorded: i) temperatures within occupied nest boxes, ii) temperatures within nearby unoccupied tree cavities, iii) the duration of temperatures of ≥40 °C within nest boxes, iv) whether direct mortality was observed, and v) the relative abundance of these species in nest boxes before and after a very hot summer. When ambient temperature reached ≥40 °C, nest boxes were equivalent to ambient or 1-2 °C cooler, whereas tree cavities were 3-7 °C cooler than ambient. Exposure in nest boxes to temperatures of ≥40 °C lasted an average of 2-8 h. We observed no mortality over 65 records of phascogales and 31 records of gliders in nest boxes on days when ambient reached ≥40 °C. No decline in abundance was recorded after a summer with 11 days of temperatures ≥40 °C, with each species subsequently occupying >40 nest boxes. Our observations suggest these species are tolerant of the high temperatures that occurred. Nonetheless, provision of nest boxes designed to minimise summer heating is recommended.

Breeding birds actively modify the initial microclimate of occupied tree cavities

The microclimate of cavities used by endothermic animals may depend on dynamic relationships between a cavity's physical properties and the heating activity of cavity users, but the rudiments of these relationships are unclear. I compared the temperature and relative humidity of active tree cavities that were occupied by nesting marsh tits Poecile palustris with the conditions in vacant tree cavities previously used for breeding by this species. I tested how presence of active nests modified initial cavity microclimate, and if this modification changed with nest progression or cavity insulation. In 2013-2014, mean daily internal-ambient temperature differences averaged 1.5-4.1 °C higher and relative humidity 8-10% lower, in active cavities relative to vacant sites, with greatest differences in the late nestling period. Compared to vacant cavities and relative to respective ambient values, the greatest daily minimum temperature increase was in active cavities located in the thinnest trees, which insulated least efficiently. As daily minimum temperatures were elevated to a similar level relative to outside within all active cavities, birds appeared to compensate for heat loss from cavities by warming the air within in a homeostatic manner. Similar to vacant cavities, the differences between daily maximum internal and ambient temperatures decreased with tree girth in active cavities, indicating that daily temperature maxima were systematically moderated in the thickest trees. The study demonstrates the modifying effect of birds' breeding activity on tree-cavity microclimate and highlights the role of a cavity's thermal properties in reducing the energy expenditure and risk of overheating for cavity users.

Variation in Summer and Winter Microclimate in Multi-Chambered Bat Boxes in Eastern Australia: Potential Eco-Physiological Implications for Bats

Bat boxes are commonly used as a conservation tool. Detailed knowledge on the influence of box elements on microclimate is lacking, despite eco-physiological implications for bats. Summer and winter box temperature and relative humidity patterns were studied in narrow multi-chambered plywood and wood-cement boxes in eastern Australia. Box exteriors were black or white and plywood boxes comprised vents. Relative humidity was higher in white boxes than black boxes and box colour, construction material, chamber sequence and vents influenced temperatures. Maximum box temperature differences between designs varied by up to 9.0 °C in summer and 8.5 °C in winter. The black plywood box consistently recorded the warmest temperatures. This design comprised a temperature gradient between chambers and within the front chamber (influenced by vent). During the 32-day summer sampling period, the front chamber rarely recorded temperatures over 40.0 °C (postulated upper thermal tolerance limit of bats), while the third and fourth chamber never reached this threshold. At the study site, the tested black boxes are considered most thermally suitable for bats during average summer conditions. However, during temperature extremes black boxes likely become too hot. Wood-cement, a durable material not previously tested in Australia should be considered as an alternative construction material.