Evidence of Late-Summer Mating Readiness and Early Sexual Maturation in Migratory Tree-Roosting Bats Found Dead at Wind Turbines

Abstract

Understanding animal mating systems is an important component of their conservation, yet the precise mating times for many species of bats are unknown. The aim of this study was to better understand the details and timing of reproductive events in species of bats that die most frequently at wind turbines in North America, because such information can help inform conservation strategies. We examined the reproductive anatomy of hoary bats (Lasiurus cinereus), eastern red bats (L. borealis), and silver-haired bats (Lasionycteris noctivagans) found dead beneath industrial-scale wind turbines to learn more about when they mate. We evaluated 103 L. cinereus, 18 L. borealis, and 47 Ln. noctivagans from wind energy facilities in the United States and Canada. Histological analysis revealed that most male L. cinereus and L. borealis, as well as over half the Ln. noctivagans examined had sperm in the caudae epididymides by late August, indicating readiness to mate. Testes regression in male hoary bats coincided with enlargement of seminal vesicles and apparent growth of keratinized spines on the glans penis. Seasonality of these processes also suggests that mating could occur during August in L. cinereus. Spermatozoa were found in the uterus of an adult female hoary bat collected in September, but not in any other females. Ovaries of all females sampled had growing secondary or tertiary follicles, indicating sexual maturity even in first-year females. Lasiurus cinereus, L. borealis, and Ln. noctivagans are the only North American temperate bats in which most first-year young of both sexes are known to sexually mature in their first autumn. Our findings provide the first detailed information published on the seasonal timing of mating readiness in these species most affected by wind turbines.

Behavior of bats at wind turbines

“…Similarities in the social behaviors of tree bats in North America and Europe led to speculation that bats might use the tallest trees in landscapes as flocking or gathering places (35). Tree bats tend to begin mating during the time when most mortality is documented at turbines (36), and bats seeking mates at trees may be drawn toward turbines (37) and other tall structures (31). We observed pairs of bats in 3% of our observations, and in about half of those cases they appeared to be following or chasing each other.…”

Continental‐scale, seasonal movements of a heterothermic migratory tree bat

“…Previous authors have noted the disappearance of adult male hoary bats from certain western areas during late summer (e.g., Findley et al 1975), and our findings suggest that adult male hoary bats embark on migratory journeys similar to those made by adult females, but perhaps delay movement into areas farther east until females have weaned their young in late summer and are approaching sexual receptivity. Mating occurs in hoary bats during late summer through winter, with females delaying pregnancy until the following spring (Druecker 1972, Koehler and Barclay 2000, Cryan et al 2012a). If some adult male hoary bats indeed delay their longest migration movements until mating begins, it would represent a potentially unique migration strategy driven more by reproduction than food availability and/or favorable environmental conditions.…”

Correlative 3D‐imaging of Pipistrellus penis micromorphology: Validating quantitative microCT images with undecalcified serial ground section histomorphology

“…The thick preputium might effect coital locking, as proposed for Myotis lucifugus by Wimsatt and Kallen (). Contrary to findings in some other bat species (Vamburkar, ; Ryan, ; Crichton and Krutzsch, ; Armstrong, ; Cryan et al, ), we did not find penile spines on the penes of the species studied.…”