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

Abstract

As the human population continues to expand, increased encroachment on natural landscapes and wildlife habitats is expected. Organisms able to acclimate to human-altered environments should have a selective advantage over those unable to do so. Over the past two decades, bats have increasingly begun to roost and raise offspring in spaces beneath pre-cast concrete bridges. Few studies have examined the health or fitness of individuals living in these anthropogenic sites. In the present study, we examined birth size and postnatal growth, as surrogates of reproductive success, in Brazilian free-tailed bat pups born at a natural and a human-made roost. Based on putative stress-related conditions (noise from vehicular traffic, chemical pollutants and a modified social environment) present at bridges, we predicted that bats at these sites would have reduced reproductive success. Contrary to our prediction, pups born at a bridge site were on average heavier and larger at birth and grew faster than those born at a cave site. Also, both birth size and growth rates of pups differ between years. We attribute observed differences to a combination of roost-related conditions (i.e. roost temperature and proximity to foraging areas), climate and maternal effects with larger mothers raising larger pups. Thus, some bridge roosts, at least in the short term, are suitable, and in some cases may provide better conditions, for raising young bat pups than cave roosts.

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

“…Thus, the traditional interpretation that high baseline cortisol levels signify stress may be appropriate in this species. Results from our other studies (Allen et al 2009, 2010) are consistent with the conclusion that bats that roost in bridges are not chronically stressed.…”

“…Allen et al (2010) found that McNeil Bridge had higher roost temperatures than Davis Blowout Cave. But it is unknown whether this pattern is consistent across other bridges and caves.…”

“…Keeley and Tuttle (1999) suggest bridges provide important roosts for Brazilian free‐tailed bats, whose abundances may be declining (Betke et al 2008). To the best of our knowledge, however, prior to our work no one has evaluated the relative health and fitness of bats roosting in bridges relative to those roosting in natural caves (Allen et al 2009; Allen et al 2010; Turmelle et al 2010).…”

Bat colony size reduction coincides with clear-fell harvest operations and high rates of roost loss in plantation forest

“…Bats save energy either by choosing roosts close to profitable foraging grounds (Boland et al 2009;Encarnação et al 2005) or that buffer ambient temperature allowing them to either use torpor or maintain the high temperatures required for fetal growth and milk production (Hamilton and Barclay 1994;Hood et al 2002;Racey and Swift 1981;Russo et al 2004;Speakman and Thomas 2003;Wilde et al 1999). An inability to maximize energetic savings can affect fetal and post-natal growth rates (Allen et al 2010;Sedgeley 2001), and impact on the survival of adults and juveniles, their reproductive fitness and the long-term viability of the population (O'Donnell 2002;O'Donnell and Sedgeley 2006;Sedgeley 2001;Sedgeley and O'Donnell 2004).…”

Postnatal development of morphological features and vocalization in the pomona leaf-nosed bat Hipposideros pomona

“…Thus, age estimation of young bats should be based on length of forearm and the length of the total epiphyseal gap, which is consistent with other studies (Hood et al 2002;Sharifi 2004a;Kunz et al 2009). However, on the other hand, postnatal growth rates in bats are influenced by climate, food supply, roost temperature, latitude, maternal factors, colony size, and anthropogenic factors (Allen et al 2009;Kunz et al 2009), which might limit the application of growth equations to their general areas of origin. Thus, as suggested by , we encourage researchers to compare the changes in different years and to generate geographically specific equations whenever possible.…”