Variation in Physiological Stress between Bridge- and Cave-Roosting Brazilian Free-Tailed Bats

Abstract

Since the late 1980s, Brazilian free-tailed bats (Tadarida brasiliensis) have increasingly used bridges as roosts in the southern United States. We examined differences in blood cortisol levels, body condition, and parasite load, as measures of physiological stress in bats roosting in bridges and bats roosting in caves. We collected data during three periods, coinciding with female phases of reproduction. For all measures, bats were captured during the nightly emergence from the roost and immediately sampled. Cortisol levels were significantly higher during pregnancy and lactation and in individuals with lower body-condition scores (length of forearm to mass ratio) and significantly higher in bats roosting in caves than in those roosting in bridges. Thus, we concluded that individuals of this species that roost in bridges are not chronically stressed and seem to be unaffected by human activities present at bridges. This is a rare documented instance where a human-dominated environment does not appear to be adversely affecting the physiological health of a free-ranging animal.

Birth size and postnatal growth in cave‐ and bridge‐roosting Brazilian free‐tailed bats

“…Results from our study indicate that some bridges may make suitable roosts, at least in the short term and may be better for raising young bat pups. Although, we were only able to assess reproductive success at one roost of each type, we have found consistent roost‐type patterns in other measures (immune function and stress hormone levels) and we suggest that ecological variation in health measures may be influenced by predictable differences in roost environment (Allen, 2009; Allen et al , 2009). However, the long‐term effects of roosting in man‐made structures on overall population health and sustainability is currently unknown.…”

Variability in Seroprevalence of Rabies Virus Neutralizing Antibodies and Associated Factors in a Colorado Population of Big Brown Bats (Eptesicus fuscus)

“…Prolonged drought may mimic chronic stress, which can impair IgG production and other aspects of immune function in laboratory mice [77], [78]. Chronic stress also can elevate baseline cortisol in mammals, and in other species of bats baseline cortisol increases during seasonal food scarcity and periods of poor body condition [79], [80]. Although cortisol effects on immunity can be complex, chronic elevation of cortisol can be immunosuppressive [81], [82]; restricted energy availability also has negative effects on immune function [83].…”

Ecology of Zoonotic Infectious Diseases in Bats: Current Knowledge and Future Directions

“…Specifically, cave colonies in this system are known to harbour up to a million individual bats (Betke et al., 2008), mostly reproductively active females, leading to a short window of time where population size doubles following parturition, and contact rates between adult and newborn bats are elevated during early lactation. Individual‐ and roost‐level variation in physiological stress was also demonstrated in this system (Allen et al., 2011), although direct impacts of stress on susceptibility or immune response of bats to RABV or other pathogen infections have not been well characterized to date (but see Smith, 1981).…”