The uptake of artificial roosts by long-tailed bats (Chalinolobus tuberculatus) in Hamilton City

Abstract

Globally, short to medium-term mitigation for the loss of bat roosting habitat has largely favoured the implementation of artificial roosts. However, their implementation has somewhat outpaced research, resulting in highly generalised guidelines concerning installation, maintenance, and reported suitability. Large-scale infrastructure and urban development projects in New Zealand are increasingly occurring in recognised long-tailed bat (Chalinolobus tuberculatus) habitat. In 2019, to provide mitigation for the Southern Links Roading Project, 80 artificial roosts were installed in urban parks within Hamilton City. To better understand the uptake and suitability of artificial roosts for long-tailed bats. Research objectives included determination of artificial roost uptake and identification of specific areas of occupation or seasonal differences in occupation. In addition, seasonal acoustic bat surveys and mammalian predator surveys were conducted in ten locations within the vicinity of artificial roosts to determine their potential influence on roost uptake. Habitat surveys and geospatial analyses were also undertaken to understand what factors are important for artificial roost occupation, and if those factors can be used to reliably predict the probability of occupation. Twenty-four (31%) of the 76 monitored artificial roosts were observed as occupied by long-tailed bats. Occupation was largely infrequent, with no clear seasonal difference, or specific areas of occupation. Two triple-chambered boxes installed in 2012 in Sandford Park-A were the exception, with the number of roosting bats notably increasing over the summer maternity season. Areas with comparatively high bat activity (>50 bat passes/night) corresponded with a greater percentage of occupied artificial roosts. The prevalence of mammalian predators in urban parks connected to the Mangakotukuku Gully, was comparatively high with 50% of the chew track cards damaged by rats and possums each month, and at least one possum pass was recorded by camera traps per survey night. However, predator prevalence appeared to have little influence on artificial roost uptake due to the anti-predator bands on trees. General linear modelling indicated positive probability of roost occupation with increasing distance to stand edge, high canopy cover, and increasing terrain slope. This indicated that Hamilton City long-tailed bats prefer sheltered artificial roosts, installed further from the stand edge within landscape features such as gullies. The logistic model also identified that distance to stand edge was the only variable that could be used to reliably predict roost occupation. Positive probability of roost occupation with an increasing number of chambers indicated that bats prefer multichambered roosts that facilitate clustering, and the provision of a range of microclimatic conditions within the roost. Negative probability of roost occupation as distance to occupied roosts increased indicated that bats may prefer to roost in clusters of artificial roosts. Future artificial roost installation in Hamilton City should situate roosts in sheltered locations, ideally nearby natural or already occupied artificial roosts to facilitate discovery and uptake. Prior to installation, bat activity should be monitored so box installation can prioritise areas with high activity. Anti-predator band maintenance should also occur at least every 6-months to ensure bands have not detached, which may place roosting bats at risk of predation.