SIZE-SPECIFIC RESOURCE USE IN JUVENILE LITTLE BROWN BATS, MYOTIS-LUCIFUGUS (CHIROPTERA, VESPERTILIONIDAE) - IS THERE AN ONTOGENIC SHIFT

This paper correlates shifts in habitat use and diet with morphologica l transitions occurring during postpartum growth and development (onto genetic niche) in little brown bats, Myotis lucifugus. Juveniles were captured in mist nets as they foraged in different microhabitats that were defined and quantified using ''clutter indices'' ranging from 0 ( least cluttered) to 5 (most cluttered). I analyzed fecal samples from captured individuals to assess diet. Chi-squared analyses showed that there was a significant difference in habitat use and diet among juven iles captured in early, mid, and late July. Juveniles with smaller win gs foraged in the least cluttered habitats, whereas juveniles with lar ger wings foraged in habitats with a high degree of clutter. Juveniles with larger wings were captured in all microhabitats, whereas those w ith smaller wings were captured predominantly in open microhabitats. J uveniles with relatively higher aspect ratios and lower wing loadings used a greater diversity of habitats than those with lower aspect rati os and higher wing loadings. In addition, differences in diet were sig nificant and correlated with wing size. My results suggest resource pa rtitioning between juveniles as a function of wing size. These data ha ve important implications regarding how relative size among juveniles may effect intraspecific structuring of populations.