Browsing by Author "True, Michael C."

Now showing 1 - 7 of 7
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    Fall migration, oceanic movement, and site residency patterns of eastern red bats (Lasiurus borealis) on the mid-Atlantic Coast
    True, Michael C.; Gorman, Katherine M.; Taylor, Hila; Reynolds, Richard J.; Ford, W. Mark (2023-06-14)
    Along the mid-Atlantic coast of the United States, eastern red bats (Lasiurus borealis) are present during fall mating and migration, though little is currently known about most aspects of bat migration. To reveal migration patterns, and understand drivers of over-water flight, we captured and radio-tagged 115 eastern red bats using novel technology, and subsequently tracked and described their movements throughout the region. We compared over-water flight movements to randomly generated patterns using a use-availability framework, and subsequently used a generalized linear mixed effects model to assess the relationship of over-water flight to atmospheric variables. We used hidden Markov models to assess daily activity patterns and site residency. Most bats with long-distance movements traveled in a southwesterly direction, however path vectors were often oriented interior toward the continental landmass rather than along the coastline. We observed that some bats transited wide sections of the Chesapeake and Delaware bays, confirming their ability to travel across large water bodies. This over-water flight typically occurred in the early hours of the night and during favorable flying conditions. If flight over large water bodies is a proxy for over-ocean flight, then collision risk at offshore wind turbines – a major source of migratory bat fatalities – may be linked nightly to warm temperatures that occur early in the fall season. Risk, then, may be somewhat predictable and manageable with mitigation options linking wind-energy operation to weather conditions and seasonality.
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    Fire, land cover, and temperature drivers of bat activity in winter
    Jorge, Marcelo H.; Sweeten, Sara E.; True, Michael C.; Freeze, Samuel R.; Cherry, Michael J.; Garrison, Elina P.; Taylor, Hila; Gorman, Katherine M.; Ford, W. Mark (2021-06-16)
    Background Understanding the effects of disturbance events, land cover, and weather on wildlife activity is fundamental to wildlife management. Currently, in North America, bats are of high conservation concern due to white-nose syndrome and wind-energy development impact, but the role of fire as a potential additional stressor has received less focus. Although limited, the vast majority of research on bats and fire in the southeastern United States has been conducted during the growing season, thereby creating data gaps for bats in the region relative to overwintering conditions, particularly for non-hibernating species. The longleaf pine (Pinus palustris Mill.) ecosystem is an archetypal fire-mediated ecosystem that has been the focus of landscape-level restoration in the Southeast. Although historically fires predominately occurred during the growing season in these systems, dormant-season fire is more widely utilized for easier application and control as a means of habitat management in the region. To assess the impacts of fire and environmental factors on bat activity on Camp Blanding Joint Training Center (CB) in northern Florida, USA, we deployed 34 acoustic detectors across CB and recorded data from 26 February to 3 April 2019, and from 10 December 2019 to 14 January 2020. Results We identified eight bat species native to the region as present at CB. Bat activity was related to the proximity of mesic habitats as well as the presence of pine or deciduous forest types, depending on species morphology (i.e., body size, wing-loading, and echolocation call frequency). Activity for all bat species was influenced positively by either time since fire or mean fire return interval. Conclusion Overall, our results suggested that fire use provides a diverse landscape pattern at CB that maintains mesic, deciduous habitat within the larger pine forest matrix, thereby supporting the diverse bat community at CB during the dormant season and early spring.
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    Forecasting the distribution of a range-expanding bat reveals future response to climate change and habitat
    True, Michael C.; Perry, Roger W.; Ford, W. Mark (2021-06)
    Many terrestrial vertebrate species are exhibiting geographic distribution changes including poleward range limit shifts in response to increases in regional temperature. Bats are a highly mobile taxa capable of rapid responses to changes in abiotic or biotic conditions. In North America, recent extralimital records of the non-hibernating Lasiurus seminolus (Seminole bat) have been attributed to climate change, however such attributions remain speculative and potentially subject to sampling bias in the form of increased recent sampling efforts at latitudes north of the historical range. We used historical occurrence records and simple environmental variables within a Maxent modeling framework to model the historical distribution of suitable areas for this species. We transferred the model using near current environmental conditions and measured the ability of the model to capture the apparent expansion in distribution using recent extralimital occurrence records. Our model transferred well over time concluding that the distribution expansion may be largely attributed to increasing minimum temperatures. We used the model to forecast the expansion in distribution of suitable areas at three 20-year intervals and various climate change scenarios and provide extrapolation risk maps for each scenario. Although increasing temperatures may increase potentially occupiable areas, the species is associated with forests and often roosts in pines (Pinus spp.). This suitable habitat is more limited to the northwest of the species' range, which may constrain the future species expansion despite favorable temperatures. We demonstrated this effect by mapping limiting factors through future climate change scenarios. We discovered a broad shift of effects that constrained the distribution from minimum temperature to an abundance metric of evergreen cover type as time and climate change intensity increased. Although uncertainties exist, we predict further expansion of the Seminole bat widely over the next 60 years across the eastern United States where suitable habitat and climate conditions converge. Our results appear consistent with other bat species showing similar range extensions and in turn provide further evidence that bats may serve as bioindicators of global change.
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    Monitoring and Modeling Tree Bat (Genera: Lasiurus, Lasionycteris) Occurrence Using Acoustics on Structures off the Mid-Atlantic Coast—Implications for Offshore Wind Development
    True, Michael C.; Reynolds, Richard J.; Ford, W. Mark (MDPI, 2021-11-04)
    In eastern North America, “tree bats” (Genera: Lasiurus and Lasionycteris) are highly susceptible to collisions with wind energy turbines and are known to fly offshore during migration. This raises concern about ongoing expansion of offshore wind-energy development off the Atlantic Coast. Season, atmospheric conditions, and site-level characteristics such as local habitat (e.g., forest coverage) have been shown to influence wind turbine collision rates by bats onshore, and therefore may be related to risk offshore. Therefore, to assess the factors affecting coastal presence of bats, we continuously gathered tree bat occurrence data using stationary acoustic recorders on five structures (four lighthouses on barrier islands and one light tower offshore) off the coast of Virginia, USA, across all seasons, 2012–2019. We used generalized additive models to describe tree bat occurrence on a nightly basis. We found that sites either indicated maternity or migratory seasonal occurrence patterns associated with local roosting resources, i.e., presence of trees. Across all sites, nightly occurrence was negatively related to wind speed and positively related to temperature and visibility. Using predictive performance metrics, we concluded that our model was highly predictive for the Virginia coast. Our findings were consistent with other studies—tree bat occurrence probability and presumed mortality risk to offshore wind-energy collisions is highest on low wind speed nights, high temperature and visibility nights, and during spring and fall. The high predictive model performance we observed provides a basis for which managers, using a similar monitoring and modeling regime, could develop an effective curtailment-based mitigation strategy.
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    North American Tree Bat (Genera: Lasiurus, Lasionycteris) Migration on the Mid-Atlantic Coast—Implications and Discussion for Current and Future Offshore Wind Development
    True, Michael C. (Virginia Tech, 2022-01-18)
    In eastern North America, "tree bats" (Genera: Lasiurus and Lasionycteris) are highly susceptible to collisions with wind energy turbines and are known to fly offshore during migration. This raises concern about ongoing expansion of offshore wind-energy development off the Atlantic Coast. Season, atmospheric conditions, and site-level characteristics such as local habitat features (e.g., forest coverage) have been shown to influence wind turbine collision rates by bats onshore, and similar features may be related to risk offshore. In response to rapidly developing offshore wind energy development, I assessed the factors affecting coastal and offshore presence of tree bats. I continuously gathered tree bat nightly occurrence data using stationary acoustic recorders on five structures (four lighthouses on barrier islands and one light tower offshore) off the coast of Virginia, USA, across all seasons, 2012–2019. I used generalized additive models to describe nightly tree bat occurrence in relation to multiple factors. I found that sites either indicated maternity or migratory patterns in their seasonal occurrence pattern that were associated with local roosting resources (i.e., presence of forest). Across all sites, nightly occurrence was negatively related to wind speed and positively related to temperature and visibility. Using predictive performance metrics, I concluded that the model was highly predictive for the Virginia coast. My findings were consistent with other studies—tree bat occurrence probability and presumed mortality risk to offshore wind-energy collisions is highest on nights with low wind speed, high temperature and visibility during spring and fall. The high predictive model performance I observed provides a basis for which managers, using a similar monitoring and modeling regime, could develop an effective curtailment-based mitigation strategy. Although information at fixed points is helpful for managing specific sites, large questions remain on certain aspects of tree bat migration, in part because direct evidence (i.e., tracking of individuals) has been difficult to obtain so far. For instance, patterns in fall behavior such as the timing of migration events, the existence of migratory pathways, consistencies in the direction of travel, the drivers of over-water flight, and the activity states of residents (or bats in stopover) remain unstudied in the mid-Atlantic. The recently established Motus Wildlife Tracking System, an array of ground-based receiver stations, provides a new technique to track individual bats via the ability to detect course-scale movement paths of attached very high frequency radio-tags. To reveal patterns in migration, and to understand drivers of over-water flight, I captured and radio-tagged 115 eastern red bats (Lasiurus borealis) and subsequently tracked their movements. For the bats with evidence of large movements, most traveled in a southwesterly direction whereby paths were often oriented interior toward the continental landmass rather than being oriented along the coastline. This observation challenges earlier held beliefs that bats closely follow linear landscape features, such as the coast, when migrating. I documented bats traveling across wide sections of the Chesapeake and Delaware bays confirming the species' ability to travel across large water bodies. This behavior typically occurred in the early hours of the night and during favorable flying conditions such as low wind speeds, warm temperatures, and/or during sudden increases in temperature associated with the passage of cold fronts. For bats engaging in site residency through the fall, the proportion of night-hours in which bats were in a resting state (and possibly torpor), increased with colder temperatures and the progression of the fall season. My study demonstrated that bats may be at risk to offshore wind turbine collisions off the mid-Atlantic, but that this risk might be minimal if most bats are migrating toward the interior landscape rather than following the coast. Nonetheless, if flight over large water bodies such as Chesapeake and Delaware bays is a viable proxy for over-ocean flight, then collision risk at offshore wind turbines may be somewhat linked to atmospheric, seasonal timing, or other effects, and therefore some level of predictable and manageable with mitigations options such as smart curtailment.
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    Unique Land Cover Classification to Assess Day-Roost Habitat Selection of Northern Long-Eared Bats on the Coastal Plain of North Carolina, USA
    De La Cruz, Jesse L.; True, Michael C.; Taylor, Hila; Brown, Dorothy C.; Ford, W. Mark (2022-05-19)
    Reproductively successful and over-wintering populations of the endangered northern longeared bat (Myotis septentrionalis) have recently been discovered on the Coastal Plain of North Carolina. Empirical data on resource selection within the region is limited, likely hindering management of these coastal forests. Our objectives were to determine roosting home range size, selection of day-roost tree species, second- and third-order roosting habitat selection, and to quantify the overall availability of resources in the surrounding landscape. We found core and peripheral roosting home range estimates were large, yet similar to observations from other areas of contiguous forests. Prior to juvenile volancy, female northern long-eared bats appear to select red maple (Acer rubrum), water ash (Fraxinus caroliniana), and loblolly pine (Pinus taeda) as day-roosts, but then use sweetgum (Liquidambar styraciflua), swamp bay (Persea palustris), and water tupelo (Nyssa aquatica) after juvenile volancy. At the second-order spatial scale, roosting home ranges were associated with woody wetlands farther from anthropogenic development and open water. However, within the third-order scale, northern long-eared bats were associated with undeveloped woody wetlands and upland forests, areas containing shorter trees and occurring proximal to open water. Peripheral and core areas were predicted to comprise approximately 20% of the local landscape. Our results show that complex and large tracts of woody wetlands juxtaposed with upland forests in this part of the Coastal Plain may be important for northern long-eared bats locally, results largely consistent with species management efforts in eastern North America.
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    Winter roost selection of Lasiurine tree bats in a pyric landscape
    Jorge, Marcelo H.; Ford, W. Mark; Sweeten, Sara E.; Freeze, Samuel R.; True, Michael C.; St Germain, Michael J.; Taylor, Hila; Gorman, Katherine M.; Garrison, Elina P.; Cherry, Michael J. (2021-02-09)
    Day-roost selection by Lasiurine tree bats during winter and their response to dormant season fires is unknown in the southeastern United States where dormant season burning is widely applied. Although fires historically were predominantly growing season, they now occur in the dormant season in this part of the Coastal Plain to support a myriad of stewardship activities, including habitat management for game species. To examine the response of bats to landscape condition and the application of prescribed fire, in the winter of 2019, we mist-netted and affixed radio-transmitters to 16 Lasiurine bats, primarily Seminole bats (Lasiurus seminolus) at Camp Blanding Joint Training Center in northern Florida. We then located day-roost sites to describe roost attributes. For five Seminole bats, one eastern red bat (Lasiurus borealis), and one hoary bat (Lasiurus cinereus), we applied prescribed burns in the roost area to observe bat response in real-time. Generally, Seminole bats selected day-roosts in mesic forest stands with high mean fire return intervals. At the roost tree scale, Seminole day-roosts tended to be larger, taller and in higher canopy dominance classes than surrounding trees. Seminole bats roosted in longleaf (Pinus palustris), slash (Pinus elliotii) and loblolly pine (Pinus taeda) more than expected based on availability, whereas sweetbay (Magnolia virginiana), water oak (Quercus nigra) and turkey oak (Quercus laevis), were roosted in less than expected based on availability. Of the seven roosts subjected to prescribed burns, only one male Seminole bat and one male eastern red bat evacuated during or immediately following burning. In both cases, these bats had day-roosted at heights lower than the majority of other day-roosts observed during our study. Our results suggest Seminole bats choose winter day-roosts that both maximize solar exposure and minimize risks associated with fire. Nonetheless, because selected day-roosts largely were fire-dependent or tolerant tree species, application of fire does need to periodically occur to promote recruitment and retention of suitable roost sites.