Influences of some extrinsic and intrinsic factors on reproduction by big brown bats (Eptesicus fuscus) in southeastern Alberta

I found that both extrinsic and intrinsic factors influenced the energetics of reproduction of big brown bats (Eptesicus fuscus) in southeastern Alberta. During a two year study of two maternity colonies in Medicine Hat, cooler ambient temperatures during the early portion of the reproductive period in 1990 as compared to 1991 were associated with fewer females breeding, later parturition and fledging dates, depressed growth rates of young, and an indication of lower offspring survival over their first winter. Age, body size and body condition of breeding females were correlated with the sex ratio and size of litters produced. Small, young, light females were likely to be non-reproductive, especially during the cool year. Older females were likely to produce litters biased towards males. Juvenile mortality rates and season length are probably the key factors influencing the reproductive strategy of western populations of fuscus.