Feeding Ecology of a Temperate Insectivorous Bat (Myotis Velifer)

Abstract

The feeding behavior and ecology of the cave bat, Myotis velifer, in south—central Kansas are investigated. Emergence behavior and foraging patterns varied according to sex, age, reproductive condition, season, and colony size. Females had one synchronous period of departure in late states of pregnancy. Two feeding periods usually were evident in summer with a major period of activity soon after sunset and a reduced secondary period before sunrise. Pregnant females emerged sooner than lactating females and adults departed before juveniles when the latter first began to fly. Adult—like emergence and foraging behavior developed in juveniles within 2 wk after flight was initiated. Adult females consumed greater quantities of food than adult males, and juveniles were less efficient at insect capture than adults. Nearly 80% of daily food consumption can be accounted for in the first 2 hr following emergence. Seasonal changes in consumption corresponded to changing energy demands imposed by pregnancy, lactation, molt, and the availability of food resources. Levels of food consumption in both sexes were lowest in spring and autumn when insect densities were low. Adult females increased their daily levels of consumption throughout most of gestation, although in the terminal days of pregnancy daily food consumption was reduced. Maximum daily levels of food consumption in adult females (approximately 25—30% of body weight) was reached near the time that young were weaned in late July and early August. Adult males achieved maximum levels of consumption (20—25% of body weight) in June, at the time molt and spermatogenesis were initiated. Young bats began foraging for insects at the age of 4 wk although their meager diet of insects was supplemented with milk for 2 wk after foraging was initiated. By the age of 6 to 8 wk their daily level of consumption increased to adult proportions. Food habits based on stomach content analysis revealed that in volume and in actual numbers, beetles (Coleoptera) and moths (Lepidoptera) comprised the major prey items in the diet. Colony size and dispersal distances may be adjusted to reduce intraspecific competition, with most individuals from large colonies dispersing nightly to greater distances than individual from smaller colonies. Emigration of males from nursery colonies in late spring and early summer and emigration of adult females soon after young were weaned may provide a mechanism to reduce competition for available food. Small and widely—scattered transient colonies in early spring and later autumn may be important in reducing competition for food at a time when food resources are scarce.