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.

Mejoras en la ciencia y práctica del uso de perchas artificiales para murciélagos Resumen Las perchas artificiales para murciélagos (cajas, imitaciones de corteza, condominios) se usan en todo el mundo para la conservación, mitigación y participación de la comunidad. Sin embargo, se ha prestado poca atención al desarrollo de las mejores prácticas en cuanto al uso de perchas artificiales como herramientas de conservación. Aunque los murciélagos ocupan fácilmente las perchas artificiales, los datos de su abundancia y ocupación son indicadores engañosos de la calidad del hábitat. La falta de información sobre el comportamiento, salud y adaptabilidad de los murciélagos en las perchas artificiales causa que no pueda validarse adecuadamente la eficiencia de conservación de las perchas. Consideramos los factores proximales y finales, como las pautas de confianza evolutiva, que pueden llevar a los murciélagos a usar con preferencia y mostrar fidelidad a las perchas artificiales subóptimas cuando existen alternativas de gran calidad. Las posibles consecuencias negativas para la salud y adaptabilidad de los habitantes de los nidos artificiales incluyen la exposición a microclimas inestables y extremos en perchas mal diseñadas y la vulnerabilidad a un mayor número de ectoparásitos en perchas artificiales de mayor duración que albergan colonias mayores a las perchas naturales. Los murciélagos que usan perchas artificiales pueden tener tasas menores de supervivencia si los depredadores tienen acceso fácil a las perchas colocadas en ubicaciones conspicuas. Puede que los murciélagos terminen ocupando hábitats de baja calidad si se construyen perchas artificiales atractivas sobre terrenos agrícolas y urbanos contaminados. Presentamos hipótesis comprobables de investigación y sugerencias para mejorar la calidad de las perchas artificiales y reducir los riesgos para sus habitantes y así avanzar la ciencia detrás de las perchas artificiales para murciélagos. Ya que la pérdida continua de perchas naturales puede incrementar la dependencia de alternativas, como las perchas artificiales, es imprescindible que se mejore esta práctica de conservación.

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.