DIETARY ENERGETICS OF THE INSECTIVOROUS MEXICAN FREE-TAILED BAT (TADARIDA-BRASILIENSIS) DURING PREGNANCY AND LACTATION

Stomach content analysis of 20 pregnant (($) over bar x body mass=13.4 g) and 18 lactating (($) over bar x body mass=11.5 g) female Tadarida brasiliensis revealed that the diet, expressed as percent volume, con sists largely of lepidopterans, coleopterans, hymenopterans, and dipte rans, in decreasing order of importance. We found no significant diffe rence in the diet of pregnant and lactating females when expressed as percent volume. However, when expressed as percent frequency, proporti onately more pregnant females fed on lepidopterans, coleopterans, and dipterans than did lactating bats, and proportionately more lactating females fed on hymenopterans. We found no significant differences in t he percentages of water, lean dry mass, fat, and energy density in the stomach contents of pregnant and lactating females. Water in stomach contents averaged 62.7% and fat and lean dry mass averaged 22.2% and 1 5.2%, respectively (expressed as percentage of wet mass); energy densi ty averaged 31.2 kJ g(-1) dry mass. This relatively high energy densit y of stomach contents, as compared to whole insects, can be attributed to the consumption of insects high in fat (especially flying ants) an d the abdomens only of moths and beetles (other body parts being disca rded). Estimates of nightly food intake increased markedly from mid- t o late pregnancy, stabilized or decreased during late pregnancy, and i ncreased again during early to mid-lactation. Average nightly feeding rate doubled from pregnancy to lactation and increased threefold durin g the first half of lactation. By adjusting our gravimetric estimates of nightly feeding rate upwards by 40% (based on estimates of field me tabolic rate), we estimate that the average nightly energy intake of f emale T. brasiliensis ranges from 57 kJ day(-1) in early lactation to 104 kJ day(-1) in mid-lactation. These estimates represent nightly fee ding rates averaging 39% and 73% of a female's body mass in the period from early to mid-lactation, respectively.