Feeding Strategies of the Little Brown Bat, Myotis Lucifugus, in Southern New Hampshire

Abstract

Feeding strategies of the little brown bat, Myotis lucifugus, were investigated in southern New Hampshire USA from early May through late 1974. Nightly food consumption was estimated by comparing mean prefeeding body weights with postfeeding weights taken as individuals returned to the roost from their first feeding period (at 2200 to 2400h) and from a subsequent foraging period (at 0330 to 0500 h). Pregnant bats consumed an average of 2.5g of insects (2.72kJ/g prefeeding body weight) nightly. lactating females ate 3.7 g (4.23 kJ/g), and juveniles ingested 1.8 g (2.47 kJ/g). Increased food consumption in lactating bats accommodated reproductive energy demands and was facilitated by rising food availability. Increasing levels of independent food consumption in juveniles accompanied weaning. Fecal analysis revealed that diets of individual bats were diverse. All available insects 3 to 10 mm in body length were accepted as food items. Nematoceral Diptera were by far the most common insects taken in light—trap samples, and constituted a major portion of the diet throughout the summer. Coleoptera, Trichoptera, Lepidopter, Ephemeroptera, and Neuroptera were also consumed in appreciably numbers. Comparison of dietary composition with prey availability indicates that pregnant bats consumed 3—10 mm prey in approximate proportions encountered during June, when insect availability was low and unpredictable. However, lactating, postlactating, and nonproductive ♂ ♂ exhibited more selective feeding in July, when insects were more abundant. This increase in selectivity reflected exploitation of beetles and mayflies, which were uncommon in trap samples. In August, juveniles approximated random feeding patterns, as they learned to forage. We suggest that increased resource availability allowed selective feeding in adult bats during July, as predicted by presy selection models. However, reduced discriminatory abilities may prevent similar levels of prey selection in juveniles.