. The Canadian field-naturalist. 1999 West and Swain: Hydrothermally-heathd Maieknii y Colony 427. 2130 2230 2330 0030 0130 0230 0330 0430 Time (DST) Figure 1. Mean number of Myotis lucifiigus captured per hour at White Sulfur Hot Springs, Chichagof Island, Southeast Alaska, 23 -25 July 1992. environment of the maternity roost may offset daily thermoregulatory costs more effectively than torpor would in nonheated tree or cavity roosts. This adap- tive strategy could occur if the energetic costs of arousal from torpor in nonheated roosts were greater than the costs of not entering torpor, or of
. The Canadian field-naturalist. 1999 West and Swain: Hydrothermally-heathd Maieknii y Colony 427. 2130 2230 2330 0030 0130 0230 0330 0430 Time (DST) Figure 1. Mean number of Myotis lucifiigus captured per hour at White Sulfur Hot Springs, Chichagof Island, Southeast Alaska, 23 -25 July 1992. environment of the maternity roost may offset daily thermoregulatory costs more effectively than torpor would in nonheated tree or cavity roosts. This adap- tive strategy could occur if the energetic costs of arousal from torpor in nonheated roosts were greater than the costs of not entering torpor, or of entering shallow torpor (, to 26°C), in the hot springs roost. In natural roosts of drier interior environ- ments. Little Brown Bats commonly select day roosts with southwestern exposures where solar heat- ing provides exogenous heat for arousal from torpor (Fenton 1970; also see Vonhof and Barclay 1997). In Southeast Alaska persistent rain and fog can pre- clude solar heating as a source of regular, depend- able heat. Under these conditions it may be energeti- cally more efficient for males not to use unheated natural roosts, but to seek shelter during the day in the warm environment of the hydrothermally-heated maternity colony. While limited, our capture data also suggest that male bats at White Sulfur Hot Springs may not use the maternity roost at night between foraging bouts. No males were recaptured during this study until just before sunrise. By contrast, females regularly returned to the roost during the night, undoubtedly to nurse their young. This nocturnal separation of the sexes is consistent with the behavior of other M. lucifugus colonies (Anthony et al. 1981). However, we cannot exclude the possibility that the distur- bance of capture during this study may have caused the males to temporarily abandon the site each night until dawn. Of the five species of bats that occur in Southeast Alaska, only M. lucifugus is common and widespread (West 1994; MacDonald a
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