New York: Two recent scientific studies under a project led by the Wildlife Conservation Society (WCS) have revealed new insights on where and when bats hibernate across their range, and subsequently predict continued extreme levels of mortality from white-nose syndrome.
White-nose syndrome has already killed more than 90 per cent of some hibernating bat species east of the Mississippi.
The disease is the result of a fungus that grows on a bat and damages tissues during hibernation. The fungus grows well in near-freezing and humid environments that bats use for hibernation, with the name ‘white-nose’ describing the appearance of fungal growth on infected bats.
It usually kills susceptible bats before they emerge in the spring; and it’s thought that hibernation duration is a factor that influences who survives. The fungal infection also changes bat behaviors so that bat survival partially depends on having enough fat to survive winter, as well as the energetic cost of hibernating with the disease.
Using updated models of hibernation duration, or when bats hibernate, and relationships between body mass and body fat, researchers at Massey University were able to spatially estimate the energetic cost of hibernation with and without white-nose syndrome.
The study, published in Ecology and Evolution, focused on the white-nose susceptible little brown bat (Myotis lucifugus), which ranges across most of North America, and found that the energetic cost of hibernating with white-nose syndrome is substantial.
In support of prior findings, the researchers concluded little brown populations not yet been impacted will fair no better than populations first infected in the East, which were decimated.
The study’s lead author, Reed Hranac, now a Data Analyst at the Colorado Department of Public Health and Environment and the study’s lead author, said: “Originally we hoped that colder temperatures in the northern part of the range or warmer temperatures in the southern part of the range would slow the disease process and allow bats there to survive. Unfortunately the energetics suggest little brown bats are going to suffer across their range.”
This news increases the importance of understanding the conservation needs of susceptible bat species, such as where species hibernate in the winter. Surprisingly, species level knowledge of where and when bats hibernate has received a little attention.
A separate study, published in the Journal of Biogeography, conducted by Conservation Science Partners, took a hybrid approach to answering this question. Instead of estimating winter distributions of five bat species using landcover and climate features alone, the researchers added in a spatial layer estimating winter survival based on energetics.
Not surprisingly the contribution of factors like land cover, winter survival, topography, and subterranean features were significant, but the relative influence of these factors varied by species.
The importance of winter survival based on energetics in predicting winter distributions indicates that mechanistic energetic models of hibernation are improving and valuable. Moreover, it is promising that there are data rich landscape features that correlate with winter species distributions, as opposed to just subterranean features that are typically very data poor.
Sarah Olson, WCS Health Program co-author and project Principle Investigator, said: “Our unique approach to mapping winter distribution highlights the utility of blending mechanistic energetic models of survivorship with more traditional correlative approaches to map species distribution.
“Survivorship was retained as an important predictor of winter occurrence in all five species studied, showing that physiology can enhance our understanding a species’ environmental niche.”
Improving knowledge of what influences where and when bats hibernate contributes to addressing multiple threats like white-nose syndrome as well as habitat loss and climate change.
Bats are critical to ecosystem health, keeping insects populations, including agricultural pests in check.