USE BY BATS OF OLD-GROWTH REDWOOD HOLLOWS ON THE NORTH COAST OF CALIFORNIA

Use by bats of basal hollows in old-growth redwoods was indexed using the weight of guano collected on water-permeable screens (guano traps) installed inside the trees. Twenty-six trees were systematically sele cted from a stand that flanks both sides of an interstate highway in D el Norte Co., California. Traps were checked for guano once a month fo r 18 months. The quantity of guano collected each month and that every tree was used suggests that the trees served either as day roosts by small numbers of bats or as temporary night roosts. Although bats coul d not be identified on the basis of characteristics of guano, three fe cal morphotypes were identified. Guano was found in all 26 trees durin g most of the sample periods; the greatest deposition occurred May thr ough August. Surprisingly, there was a substantial amount of fresh gua no collected from most trees during winter months. When all trees were considered, weight of guano was not significantly related to diameter at breast height (dbh) of the tree during summer, winter, or annually , but was related to the internal volume of the hollow during summer a nd annually. Trees closer to perennial streams had greater weight of g uano, but only during summer. The most frequently used trees had great er hollow volumes, greater diameters, and were closer to water than th e least-frequently used trees, Although other potential roost sites on redwood trees were not sampled, our work indicates that large hollows are important roost sites. The relationship between weight of guano a nd size of hollow suggests that forests lacking trees large enough to contain these hollows will provide fewer roosting opportunities that c ould affect the abundance and diversity of bats.