Cowichan Bats Mini-Symposium
As a follow-up to CERCA's Bat Symposium in June, reported on by Steve Nazar on our website, a "Mini-Symposium" was implemented on July 6 at the Providence Farm with focus on CERCA's bat monitoring project which has entered its third year. Due to time constraints at the June Symposium, three of the scheduled speakers (all three Directors of the CERCA Board) were unable to present the results of CERCA's bat monitoring project. Since the three missed presentations deal exclusively with CERCA's bat work which is of great interest to the Cowichan Valley residents and all former and current active participants in the project there appeared to be a need for this "Mini-Symposium". Last year's presentation to the Cowichan Stewardship Round Table by Parker Jefferson in particular triggered a lot of interest in bats amongst Valley residents. So far more than 35 CERCA members and members from associated groups have been recording bats with our Echometers in the Cowichan Valley. Strategic locations covering all major habitat types were chosen for monitoring bats.
The Mini-Symposium held on an evening in the middle of the week attracted over 30 persons interested to hear what the presenters had to say. It started with a presentation by CERCA's Co-Chair Bill Heath who reported on how CERCA got involved with this exciting project which has become highly popular. This was followed by a very comprehensive and detailed PowerPoint presentation by Bernie Juurlink focusing on the voices of bats, species identification by the gadgets used, and the meaning of bat talk/communication. In the final presentation, Cliff Stainsby discussed the results of our monitoring efforts based on his elaborate statistical analysis of recordings from different locations/habitats from May to late October. If you are interested in details check out the three PowerPoint Presentations published on our new Website.
The very enlightening presentations resulted in a lively discussion on many aspects of bat biology, behavior, their ecological and economic importance, and more, but also on bats being the carriers of viral diseases. Although many questions could be answered by the biologists in the audience and the presenters, many more remained unanswered showing that there is still a lot to learn about these fascinating species. Meanwhile, I found some interesting scientific papers on topics touched upon in the discussions without satisfactory answers. One was the question about the "home" ranges of bats. This is the spatial area needed to meet all bat habitat requirements during their 7 months of activity period following hibernation. In their paper on "home range of bats" (see Abstract below) I found the findings on the importance of water for bats of special interest, but also the influence of temperature on home range size.
(If you missed the symposium, please click the bolded links above to download the PowerPoint presentations of each presenter — Bill, Bernie & Cliff)
Seasonal variation in home range size of evening bats (Nycticeius humeralis) in an urban environment
Ellen M Hall, Victoria J Bennett
Journal of Mammalogy, Volume 102, Issue 6, December 2021, Pages 1497–1506, https://doi.org/10.1093/jmammal/gyab106
Published: 13 October 2021
Abstract
Despite the negative impacts of urbanization on bats, green spaces in urban environments, such as parks, cemeteries, and golf courses, have the potential to provide resources necessary for these animals. Water resources in these areas include natural or semi-natural ponds, streams, and drainage ditches. Such water resources, however, are frequently ephemeral when subject to prolonged periods of high temperatures and low precipitation. We hypothesized that home ranges of evening bats (Nycticeius humeralis) would increase in size or shift from urban green spaces into surrounding neighborhoods to access alternative resources, such as residential swimming pools, when water resources in green spaces are scarce. To explore whether seasonal variations in bat home ranges occurred, we radio-tracked resident evening bats in a local park system during their summer activity period 2017–2019 in Fort Worth, Texas, USA. We used Local Convex Hulls created by associating point locations with their nearest neighbor to estimate home range size, location, and the percentage area that fell within the surrounding neighborhood. We compared these variables to temperature and precipitation using various regression models. We successfully tracked 30 bats over the 3-year period and found a positive correlation between home range size and temperature. Home range sizes increased 6-fold when temperatures exceeded 30°C. Our study indicates the importance of urban neighborhoods surrounding green spaces in providing alternative resources, such as water, for bats. If managed appropriately, these urban areas have the potential to act as oases for bat populations.
Recently, our Board member Bernhard Juurlink published an article in the Shawnigan Paper "Focus" which provides more interesting facts on bats, very worthwhile reading:
The Cowichan Estuary Restoration and Conservation Association (CERCA) has been carrying out acoustic monitoring to determine which species of bats are present in the Cowichan Valley since 2021. A number of members of the SBS have participated in these surveys. Officially there are 15 species of bats residing in British Columbia and another three species considered to be occasional visitors. The following nine species are considered to be present on Vancouver and the Gulf Islands: Townsend’s Big-eared bat, Hoary bat, Silver-haired bat, Big Brown bat, Yuma myotis, California myotis, Long-legged myotis, Little brown bat, Long-eared myotis and the occasional visitor, Mexican Free-tailed bat. The acoustic monitoring by CERCA also suggests that the Eastern Red bat is present on Vancouver Island.
BC bats all use echolocation to visualize their environment and prey in the dark. Fossil records show that this ability to use sound to ‘see’ was already present in bats 50 million years ago. All BC bats are insectivores. Bats, which have an undeservedly bad reputation, carry out a number of environmentally important roles and are considered beneficial to humans because they eat many insects harmful to trees and to agricultural crops as well as eat mosquitos and gnats. In summer, many of our bats roost in snags, under bark or on branches of trees while others roost in caves, mines, rock crevices or under bridges. In the winter, the Eastern Red bat, the Hoary bat and the Mexican Free-tailed bat are thought to migrate south while others seek buildings, caves, mines and rock crevices as their hibernaculae.
BC bats are small, ranging in size from 5 grams (Little Brown bat) to 17 grams (Big Brown bat). They have an extremely long potential lifespan for their size, with some individuals living for 30 to 40 years, depending upon species; however, because of predation and other factors, most live for 10 to 20 years. Bats have a low reproductive rate with most mature female bats only having one offspring per year. Pups mature in about 80 days but experience a high mortality (up to 50%) during their first winter, likely because they have not stored enough fat to last the winter. Once they survive their first winter, mortality rates are low.
There are a number dangers facing bats. Cats appear to be major predators of bats. In a recent study of killed and injured bats brought to Animal Health Centre in Abbotsford, BC, 24% were due to cat predation. Wind turbines can be significant killers of bats; however, with the use of acoustic monitoring to detect bats, there are a number of ways to decrease bat mortality due to turbines. A major concern is the white nose disease, caused by a fungus introduced into eastern North America around 2006 from Europe or Asia. This fungus causes ulceration of the skin and increases the bat’s metabolism resulting in depletion of fat stores before hibernation is over. This fungus has now been detected in BC, although, to date, no white nose disease has been observed in our bats. There is some preliminary evidence that bacteria associated with bat hibernaculae in BC may have anti-white nose fungus activity.
But bats should be appreciated for being such wonderful forms of life, forming 20% of all mammalian species. They are the only mammals that have true flight. Did you know that baby bats babble and their mothers respond with the bat equivalent of baby talk.
In his concluding remarks Goetz Schuerholz highlighted CERCA's two-pronged approach to its bat project, one aiming at increasing the scientific knowledge base, the other focusing on raising public awareness of the ecological and economic importance of bats and showing them in the light they deserve instead of being looked at with un-founded fear.
Goetz Schuerholz
CERCA Chair
