Variation in size at birth and post-natal growth in the insectivorous bat Pipistrellus subflavus (Chiroptera: Vespertilionidae)

Abstract

We describe the size and developmental state at birth, examine factors which in¯uence intra-and inter-year variation in post-natal growth, and derive age-predictive equations and logistic growth parameters for the eastern pipistrelle bat, Pipistrellus sub¯avus. Ambient and roost temperature and insect abundance were lowest, and precipitation highest, before and during the post-natal growth period in 1982, as compared to 1981. We found no sex differences in the size of pups at birth or in post-natal growth rates in a given year; however, body mass and length of forearm of neonates differed signi®cantly between years, being smaller in 1982 than in 1981. During the ®rst two weeks of post-natal growth in both years, the body mass and length of forearm of pups increased linearly at mean rates of 0.15 g.day 71 and 1.12 mm.day 71 , respectively. Post-natal growth rates for length of forearm and body mass were the same during the early linear phase of growth, but the intercept for body mass was less and growth trajectories were more variable in 1982. Length of forearm was the least variable and thus most reliable character for estimating age of P. sub¯avus pups during the ®rst 14 days of post-natal growth. When length of forearm was used in combination with mean changes in the length of the fourth metacarpal-phalangeal epiphyseal gap, we derived reliable ageestimation equations ranging from 1 to 45 days. Litter size averaged 1.96 and 1.93 at birth, but this was reduced to one by the time pups became volant. At birth, litter mass represented 44, and 54% of the postpartum mass of females in 1981 and 1982, respectively. This maternal effort during pregnancy is among the highest reported for bats. At weaning, the body mass of pups approached 80% of adult post-partum body mass, and the length of forearm exceeded 90% of adult female size. Our results suggest that size at birth and post-natal growth are in¯uenced by ambient and roost temperature, rainfall, and the quantity of insects available to pregnant and lactating females. Thus, energetic constraints on both mothers and pups can lead to inter-year and inter-individual differences in maternal effort and post-natal growth of pups.

Day roost selection in female Bechstein's bats (Myotis bechsteinii): a field experiment to determine the influence of roost temperature

“…After the first young were born (4 July), they subsequently favoured sunny over shaded, and black over white boxes. This change in roost preference is in agreement with the hypothesis that female bats should favour warm roosts during lactation and avoid torpor to accelerate the growth of their young (Tuttle 1976;Kunz 1982;Speakman and Racey 1987;Hamilton and Barcley 1994;Grenevitch et al 1995;Hoying and Kunz 1998). At this time of the year, the reproductive status of the bats influenced roost selection.…”

“…We thought that pregnant females would select warm roosts to stay homeothermic and accelerate embryonic development. Although this generally seems to be a good strategy for female bats during gestation, it is possible only if the food supply is high enough to support rapid embryonic growth (Racey 1973;Speakman and Racey 1987;Hoying and Kunz 1998). In spring 1996, the weather, and as a consequence the food supply, was obviously so bad that female bats had difficulties sustaining pregnancy.…”

“…Among the 43 occupied boxes, the females generally preferred warm roosts, independently of their reproductive status. These somewhat contradictory results probably reflect temporary differences in the energetic needs of reproductive and non-reproductive females (see also Hoying and Kunz 1998;McLean and Speakman 1999). While mothers benefit from fast development of their young in warm roosts, non-reproductive bats might be better off becoming torpid in colder roosts during periods of low food availability, thereby saving energy.…”

“…Bell et al 1986). For example, juvenile growth is dependent on roost temperature both during gestation and lactation (Racey 1973;Tuttle 1976;Racey and Swift 1981;Hoying and Kunz 1998). Unlike many other small mammals, such as rodents (Eisenberg 1983), bats are generally not able to build their refuges themselves.…”

Free-Ranging Little Brown Myotis (Myotis lucifugus) Heal from Wing Damage Associated with White-Nose Syndrome

“…A trade-off between reproduction and immune function has been shown in a number of vertebrate taxa, including small mammals (French et al 2007(French et al , 2009). If limited energy resources are allocated to repair wing tissue, then bats will face increased risks to survival and reproduction during the early weeks of the active season, a trade-off that would be exacerbated by low ambient temperatures (increasing thermoregulatory costs) and reduced insect availability during the spring in New England (Hoying and Kunz 1998).…”