In this contribution to Dr. Brock Fenton's Festschrift, we briefly reflect on Dr. Fenton's seminal works examining bat swarming behaviour in Ontario and use these reflections as a launch pad to conduct a global review on autumn swarming in bats, and underlying hypotheses to explain this behaviour. Our review frames the swarming period as a time of critical transitions, during which bats must balance multiple life history trade-offs, and we consider how various intrinsic and extrinsic factors may contribute to inter- and intraspecific differences in autumn behaviour. We discuss the transition away from summer residency, including maternity colony breakup, day roosting, and migration during autumn. We review key life history elements of swarming, including mating behaviours and associated reproductive condition, genetic exchange during swarming, and variation among sexes, ages, and species. Finally, we discuss the behaviours and physiological states of bats transitioning from the swarming period to hibernation. Throughout, we identify common patterns and also exceptions. Over 50 years of research has yielded many insights into autumn swarming, but knowledge gaps remain. Future research focus on a greater diversity of species will reveal general principles underlying the transition from summer active season, through the swarming period, and into winter hibernation.

We investigated the migratory movements of silver-haired bats (Lasionycteris noctivagans) across the eastern extent of the species’ range. We conducted stable hydrogen isotope analysis of fur samples (δ²H_fur) from museum specimens collected across latitudes and at all times of the year. We first used these data to estimate the timing of fur replacement and to develop a model associating δ²H_fur with that of local precipitation (δ²H_precip) at the location where fur replacement occurred. We then used this model to 1) identify individuals that had migrated across latitudes, and 2) investigate the presence of continental-scale patterns in the estimated distance traveled. Bats were at their location of fur replacement between 20 June and 26 August, and there was a strong linear relationship between δ²H_fur and δ²H_precip in bats collected during this time. There was substantial variation in the migratory movements of this species. Twenty-four of 38 females and 14 of 30 males showed isotopic evidence of leaving the area where fur replacement occurred (i.e., migrating across latitudes), whereas the remaining bats were either sedentary or moved at a small spatial scale. Males appeared to migrate consistently, regardless of latitude of origin, whereas there was a partial leapfrog pattern in migratory movements of females. To our knowledge, this is the first evidence of leapfrog migration in bats.

Mortality of migratory bat species at wind energy facilities is a well-documented phenomenon, and mitigation and management are partially constrained by the current limited knowledge of bat migratory movements. Analyses of biochemical signatures in bat tissues (“intrinsic markers”) can provide information about the migratory origins of individual bats. Many tissue samples for intrinsic marker analysis may be collected from living and dead bats, including carcasses collected at wind energy facilities. In this paper, we review the full suite of available intrinsic marker analysis techniques that may be used to study bat migration, with the goal of summarizing the current literature and highlighting knowledge gaps and opportunities. We discuss applications of the stable isotopes of hydrogen, oxygen, nitrogen, carbon, sulfur; radiogenic strontium isotopes; trace elements and contaminants; and the combination of these markers with each other and with other extrinsic markers. We further discuss the tissue types that may be analyzed for each and provide a synthesis of the generalized workflow required to link bats to origins using intrinsic markers. While stable hydrogen isotope techniques have clearly been the leading approach to infer migratory bat movement patterns across the landscape, here we emphasize a variety of lesser used intrinsic markers (i.e., strontium, trace elements, contaminants) that may address new study areas or answer novel research questions.

Emerging infectious diseases can have substantial impacts on wildlife health, but also provide an opportunity to understand how populations respond to novel selective pressures. White-nose syndrome (WNS) has decimated some populations of bats in eastern North America, but impacts vary among species. We counted bats in 11 hibernacula in Ontario, Canada, before and after WNS arrived, and compared the relative abundance of 5 bat species captured pre-WNS (1966–1968 and 2007–2009) and post-WNS (2017–2019) during swarming at one of these hibernacula. Counts of hibernating bats declined by 87%–100% after WNS arrived. However, we observed a recent, gradual increase in bat counts in the two largest, monitored hibernacula. During swarming, little brown bat ( Myotis lucifugus (Le Conte, 1831)) was the most frequently captured bat in all sampling periods. Capture frequency of northern long-eared bat ( Myotis septentrionalis (Trouessart, 1897)) declined precipitously after WNS arrived, while eastern small-footed bat ( Myotis leibii (Audubon and Bachman, 1842) represented a higher proportion of bat captures in 2017–2019 compared to other sampling periods. Our data suggest potential adaptation of some bat populations to WNS, but also highlight the importance of protecting bats and their habitat during the active season to facilitate population recovery.

Photo-point monitoring through repeat photography allows assessment of long-term ecosystem changes, and photos may be collected using citizen science methods. Such efforts can generate large photo collections, but are susceptible to varying participation and data quality. To date, there have been few assessments of the success of citizen science projects using repeat photography methods in meeting their objectives. We report on the success of the PhotoMon Project, a photo-point monitoring program at Pinery Provincial Park, Canada, at meeting its primary goals of affordably collecting seasonal reference photographs of significant ecosystems within the park, while providing a stewardship opportunity for park visitors. We investigated how the quantity of submitted photos varied over time (quantity), and how closely those photos matched the suite of criteria of the PhotoMon Project (quality). Photo submissions occurred year-round and at all sites, although a low proportion of park visitors participated in the program. Photo quantity varied among sites and seasonally, reaching a low during the winter, but with proportional participation in the project lowest in summer. Photo quality was consistent year-round, with most photos meeting most program criteria. Common issues with photo quality included photo lighting and orientation. We conclude that the program met its scientific goal of compiling seasonal reference photos, but that comparatively few park visitors engage in the program. We suggest changes to increase visitor motivation to participate, but recognize that these may compromise the program’s current affordability and ease of management.