The use of culverts in road networks as roost sites to maintain landscape connectivity for a trawling bat: a case study of the large-footed myotis (Myotis macropus) in Australia

The use of culverts in road networks as roost sites to maintain landscape connectivity for a trawling bat: a case study of the large-footed myotis (Myotis macropus) in Australia

Vanessa Gorecki1, Ramona Maggini1, Boyd Tarlinton1, Caroline Hauxwell1, Stuart Parsons1

1 School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Australia

Corresponding author: vanessagorecki@gmail.com
Presentation: Pitch
Program topic: 1. Innovative Solutions for Linear Infrastructure Impact Assessment, Mitigation and Monitoring. d. Molecular road ecology/landscape genetics
Keywords: Culvert, myotis, roost, microhabitat, connectivity
Anthropogenic environments can fragment habitats and introduce barriers to movement between populations, and this can have a profound effect on the population structure and viability of wildlife populations. The large-footed myotis (Myotis macropus) is a trawling bat with a specialisation for foraging directly over water surfaces and movement across landscapes is restricted to riparian corridors. This species has adapted to roosting and breeding in concrete culverts under roads. However, little is known about the roost selection of these artificial sites and how much gene flow occurs between individuals roosting in an urban environment. We investigated M. macropus roost selection at two spatial scales and population structure in a large subtropical city in eastern Australia. We surveyed 365 concrete culverts, identified 23 roosts and collected wing tissue samples from 72 bats.
Using generalized additive models, we found the distribution of M. macropus roosts in concrete culverts can be predicted at a landscape level using the variables stream order, channel width and waterway density, and culvert height. Bats preferred culverts >1.2 m in height, and a preference for box culverts was detected although pipe culverts were also occupied. Predictive modelling identified that culvert roosts were a limited resource with only 5.5% of culverts identified as potential roosts.

We examined roost selection at the roost scale by comparing roost culverts to available culverts. Roost culverts differed significantly from available culverts and the primary difference was the availability of microhabitat (lift holes and crevices). Roost culverts had lift holes that had greater cavity dimensions than available culverts and crevices were only found at roost culverts. Culverts containing microhabitat were a limited resource in this urban landscape.
We used single nucleotide polymorphisms and the mitochondrial cytochrome b gene to study gene flow. We found evidence of female philopatry with related females within roosts. Gene flow was moderate between peri-urban roosts and restricted between urban roosts. Moderate levels of relatedness between peri-urban roosts indicates M. macropus roosting in culverts are part of a larger, outward breeding population with greater availability of roost sites. Comparatively, the urban roosts in our study had more related pairs than the peri-urban roosts, indicating reduced gene flow in urban culvert roosts. This finding reflects the limited availability of urban culvert roosts in our study.
This study found that culvert roosts were limited at two spatial scales and that gene flow was restricted between urban culvert roosts. These findings suggest that disturbance to, or removal of, a culvert containing a roost has the potential to be a significant impact to an urban population of M. macropus. Disturbance impacts are not equal across culvert roosts, and the impact of disturbance can be partially alleviated by increasing the number of culverts available for roosting. Road networks provide an opportunity to provide permanent roost sites for M. macropus. Additional culvert roost sites can be created by providing microhabitat in existing culverts by simply leaving lift holes unsealed, and this would increase the availability of urban culvert roosts. Increasing the amount of potential roost habitat available will maintain landscape and genetic connectivity and contribute to the viability of urban M. macropus populations.