"Refugia From White-Nose Syndrome: Ecology and Behavior of Northern Myo" by Samantha Hoff

Date of Award

1-1-2023

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Biological Sciences

Content Description

1 online resource (xii, 131 pages) : illustrations (some color)

Dissertation/Thesis Chair

Ing-Nang Wang

Committee Members

Wendy C Turner, Jeff T Foster, Daniel Bogan

Keywords

fall behavior, island populations, myotis septentrionalis, northern myotis, occupancy, White-nose syndrome, Northern long-eared myotis

Subject Categories

Ecology and Evolutionary Biology

Abstract

Recent increases in anthropogenic environmental change have been directly linked to the global loss of biodiversity and are a primary driver of disease emergence in wildlife populations. Infectious diseases interact with other threats to cause population declines and changes in community composition, potentially resulting in local or global extinctions. Yet, outcomes are variable across the landscape, leading some host populations to persist at low numbers. One of the biggest challenges in conserving species threatened by disease is determining whether persisting populations can remain viable into the future once they have been driven to low abundance. White-nose syndrome (WNS) is one of the most devastating disease outbreaks in wildlife populations to emerge over the last century, affecting multiple species and causing mass mortality. Northern myotis (Myotis septentrionalis) have experienced the most severe effects of this disease with population declines of up to 99% throughout much of their range, leading to their listing as endangered under the Endangered Species Act. Remnant populations of northern myotis have been discovered in habitat refugia of coastal regions in the United States (U.S.), however it is unknown what mechanisms are promoting persistence and whether these populations will be able to sustain the species long-term. I investigated the ecology and behavior of northern myotis populations on three islands in the northeastern Atlantic Coastal Plain of the U.S.: Long Island, New York, Martha’s Vineyard, Massachusetts, and Nantucket, Massachusetts, to understand patterns underlying their survival despite this disease and to fill knowledge gaps about their ecology to inform conservation efforts. My study addressed the following three objectives: 1) determine the land-use and abiotic factors affecting the species distribution, 2) characterize seasonal roost differences and assess fall activity and winter hibernation behavior, and 3) evaluate the role that host behavior and environmental conditions play in shaping disease dynamics of WNS on the islands in comparison to mainland populations. To establish the distribution of northern myotis on the islands, I conducted a large-scale summer acoustic survey to collect presence/absence data. These data were incorporated into multi-scale occupancy models to estimate the nightly detection probability on each island and occupancy at two spatial scales: landscape and local, with abiotic factors and land cover variables included in models to determine their influence on detection or occupancy. To assess seasonal roost differences and fall activity patterns, I captured and radio-tracked individuals to document roost characteristics and compared these data with previously described summer roosts. Individuals were tracked through the life of the transmitter to measure movements between roosts and ultimately locate local hibernacula. I also captured bats during spring and compared seasonal patterns in infection intensity of Pseudogymnoascus destructans (Pd), the fungal pathogen causing WNS. Infection data on the islands was compared with previously collected data of northern myotis winter colonies in the Midwest U.S. Additionally, I measured the microclimate of coastal hibernacula to compare with NY mainland hibernacula that had some of the highest winter colony counts of northern myotis pre-WNS. To determine the hibernation duration on the islands, I collected acoustic data from September – May and assessed seasonal changes in activity. Estimates of occupancy and detection probability suggest wide-spread presence of northern myotis across the island study areas. Detection rates on the islands were higher than those reported from previous occupancy studies conducted elsewhere in the species range, suggesting that range contraction is occurring and persisting populations are potentially isolated in the extremities. I found strong support for a relationship between local occupancy and the amount of forest on Martha’s Vineyard, and a negative relationship between development and local occupancy on Long Island, while none of the broad land cover variables explained the variation in occupancy at the landscape scale. Tree roosts used by northern myotis differed between summer and fall, and although roosting in anthropogenic structures (primarily associated with human dwellings, e.g. under trim boards on houses, garages, barns, or other structures such as telephone poles and bat houses) was documented in both seasons, it was greater during fall and increased as the season progressed. Activity on the landscape occurred until late November, with males active later into the season than females. We tracked bats to local hibernacula in subterranean anthropogenic structures, the majority of which were crawlspaces underneath houses. Based on seasonal activity patterns, the hibernation period is up to a month and a half shorter on the islands compared to the mainland and is interspersed with periods of winter activity. Coastal hibernacula microclimates were within the range of temperature and humidity that supports growth of P. destructans, although island hibernacula were more variable than mainland hibernacula. Pathogen transmission appears lower on the islands, both across seasons and over time since P. destructans arrival. Mainland populations of northern myotis are rapidly extirpated from hibernacula within three years of pathogen arrival and show no signs of resistance or tolerance, factors predicted to lead to extinction. Survival on the islands appears to be supported by a combination of factors that are expected to reduce disease transmission, severity, and mortality, including a network of local hibernacula with low bat densities, a shorter hibernation period, and mid-winter foraging opportunities. Nonetheless, individual survival may not equate to long-term population viability, and more information regarding the fitness and reproductive success of these populations is needed to understand the ability and potential for these populations to stabilize and potentially serve as source populations to support the species in the long-term.

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