Wayne H. Davis

Biology and Migration of the Bat, Myotis lucifugus, in New England

Female bats typically end hibernation in Aeolus Cave in southwestern Vermont from early April to mid-May and males between 7 May and 7 June. They scatter to summer colonies as far distant as 172 miles, predominantly to the southeast. The cave is frequented by bats from mid-July through August. After a nights visit individual bats leave, but return in September and October to hibernate. In Vermont, maternity colonies of a dozen to 1,200 bats start forming in attics as early as 22 April. Adult males compose up to 6% of a colony in June, and up to 34% in September. Parturition occurs between 7 June and 10 July. Old bats give birth earlier than yearlings. Most young can fly by mid-July. Yearlings can sometimes be recognized through June by the shape of the finger joints. Colony breakup is gradual, from late July to mid-September. Juvenile bats and some adults seem to lack homing ability. Old bats become fat in August and enter hibernation before juveniles, many of which appear emaciated. Two abandoned mines appear to serve more localized populations than does the cave most intensively studied. In summer, bats appear to be most abundant in an area of overlap known to be served by these three retreats. The summer population density of an area of approximately 8,600 square miles served by the cave is estimated to be 26 bats per square mile. The population wintering in the cave is estimated to be 300,000 ± 30,000.

Population Dynamics of the Bat Pipistrellus Subflavus

Populations of pipistrels hibernating in two West Virginia caves were studied over a 14-year period. Methods are developed for determining the percentages of surviving bats not recaptured in the caves, the annual survival percentages, survival rates for each sex and age group and the structure of the populations by age and sex. Sex ratios observed in the caves, which fluctuate between 69.5% and 85.1% males, do not show the sex ratio of the species; analysis of survival rates indicates that the true sex ratio is 61♂: 39♀. Life tables are presented for the species and for random cohorts of adults. Annual survival rates are different for each age group. Survival is low in youngest bats, climbs to a peak at 3.5 years and then decreases, falling rapidly as maximum life span is approached.

Colonial Behavior of Eptesicus fuscus

Big brown bats, Eptesicus fuscus , were studied at maternity colonies in buildings in Kentucky. Bats arrived at the colonies in May, and colonies contained few adult males before the young were weaned. Young were born in early June. Mothers left even the youngest babies behind during feeding flights, and mothers retrieved their fallen babies from the floor and recognized their own. Young bats grew rapidly; growth curves are presented. After parturition mother bats fed close by and returned soon to their babies; as the young matured the mothers stayed away longer. When 3 weeks old the young could fly, and by mid-June mothers and young were using a night roost. Adults filled their stomachs in about an hour of feeding. Big brown bats were not tolerant of heat, and left a roosting spot at temperatures above 92°–95°F. This is a rather sedentary species; most movements recorded were of a few miles or less.

RESPONSES OF BATS FROM TEMPERATE REGIONS TO CHANGES IN AMBIENT TEMPERATURE

1. Responses to upward and downward changes in ambient temperature from 5° C. were studied in dormant bats of the species E. fuscus, P. subflavus, M. sodalis, M. lucifugus and L. borealis. Rectal temperatures and heart rates were recorded.2. Except for L. borealis which did not arouse until ambient temperature reached about 20° C., all species responded by arousal from dormancy when the temperature was increased to 15° C.3. The effects of decreasing ambient temperature varied considerably among species. E. fuscus invariably aroused from dormancy. L. borealis never aroused but showed a thermoregulatory response by increasing its metabolism to compensate for the increase in heat loss. The responses of the other species depended upon the abruptness of the temperature change. Abrupt lowering of ambient temperature tended to induce arousal in M. lucifugus and M. sodalis, whereas these species responded similarly to L. borealis when exposed to gradually decreasing temperature. P. subflavus usually aroused in re...

Thermoregulation in Bats Exposed to Low Ambient Temperatureis

Summary Heart rates and rectal temperatures (Tr) were recorded from inactive bats exposed to stepwise changes in ambient temperature (Tn) in the range between —5°C and 10°C. An increase in heart rate and in the difference (ΔT) between rectal and ambient temperature (ΔT — Tr — Tu) with decreasing ambient temperature below 5°C was found. The bats remained in the dormant state but were able to arouse from dormancy in response to mechanical stimuli. The results indicate that the species of bats studied possess thermoregulatory ability during dormancy and that this ability is a homeostatic mechanism and thus different from the process of arousal. We thank Dr. Loren D. Carlson for suggestions and criticism during preparation of the manuscript.

Burrow Systems of the Prairie Vole, Microtus ochrogaster, in Central Kentucky

We examined burrow systems of prairie voles ( Microtus ochrogaster ) in fields of fescue ( Festuca elatior ) in central Kentucky. Burrow systems were associated with patches of lush vegetation and consisted of numerous surface entrances, extensively branched and interconnected tunnels and dead end passages, and nest chambers, feeding chambers, and chambers that were plowing artifacts. Most vole burrowing was within 20 cm of the surface.