Date of Award

Fall 12-1-2006

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Advisor

John O. Whitaker Jr.

Second Advisor

Peter E. Scott

Third Advisor

George S. Bakken

Abstract

I investigated the use of torpor and arousals during winter of 2005 - 2006 by freeliving big brown bats (Eptesicus fuscus) by measuring skin temperature (remotely using data loggers) and used those measurements to estimate winter energy expenditure. Torpor bouts lasted for a mean of 3 .3 days ( d) with a mean of 3 .6 d and 2.2 d for males and females, respectively. There was no correlation between ambient temperature (Ta) during torpor and torpor bout length, but there was a significant correlation between Ta and length of the active period. Arousals lasted on average 5.0 hours (h). The mean time to warm and cool from torpor was 0.9 hand 2.6 h, respectively. A larger proportion of bats aroused on warm days. Mean arousal time was 6:44 PM EST. Most arousals occurred after sunset. For a hypothetical 90-d hibernation period bats used a total of 93.6 kJ: 40.1 kJ during torpor, 22.4 kJ in the active arousal, 16.1 kJ in the active phase, and 15.0 kJ cooling. Bats used 93.2 % of their time and 42.0 % of their energy in torpor. They used the remaining energy in active arousals, the active phase (period when bats are euthermic ), and the cooling phase. It was assumed that bats were not in flight, but if flight is considered energy consumption increases. Partial passive rewarming was used by five of seven bats and passive rewarming bouts lead to 19.9 % energy savings over comparable active arousals. For a 90-d winter bats save an average of 95.2 mg of fat (3.6 d of torpor with the average arousal) with one individual saving 266.6 mg (10.1 d). When including passive rewarming bouts, the total energy used in 90-d fell to 89.8 kJ. The lV torpor, arousal, active, and cooling phases cost 40.1, 18.7, 16.1, and 15.0 kJ respectively for 90-d. Arousals occurred more frequently than previously recorded for most bat species. Bats maintained a pattern of arousing around dusk, which would allow for activities outside of the roost. Bats used partial passive rewarming causing them to arouse after the peak daily ambient temperature (Ta) as their body temperatures warmed with the increasing Ta• In addition I investigated winter feeding in this roost. I placed clear plastic sheeting under hibernating bats to collect fecal pellets dropped from above from 27 October 2005 - 31 March 2006. I collected pellets containing fresh insect remains (normal pellets) in each sampling period indicating feeding had occurred. The number of normal pellets/bat/day was different in winter and non-winter months showing a reduction in defecation. While the number of pellets was reduced in winter, I found feeding provided an important energy source for maintaining an energetic balance. Further studies on winter feeding should consider the energetic perspective which may largely influence this behavior. Insect remains were mostly coleopterans and hemipterans until March when lepidopterans and dipterans were more common. Hard black-green pellets (winter pellets) and soft, sand-like pellets sometimes containing insect remains (transition pellets) were also found throughout the winter. The purpose of these pellets is still uncertain but could be due to more efficient digestion by bats in times of low food resources. I provide numerous suggestions for future work such as: winter feeding studies for all bats across their ranges, energy sources other than fat and feeding, fat accumulation and loss in the wild, assimilation efficiency across seasons, and frequency/quantity of food consumption.

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