P. I. Webb

Effects of disturbance on the energy expenditure of hibernating bats

(1) We investigated the effects of a range of stimuli, associated with disturbance by visitors to caves, on the energy expenditure of hibernating bats. (2) Twenty-five individual bats of six species were exposed to 206 separate applications of non-tactile stimuli (head torch, photographic flash, sound, speech, temperature increase). This resulted in only nine significant increases in energy expenditure (4.4%). In contrast, nineteen out of nineteen tactile stimuli, applied to ten individuals of four species, resulted in significant increases in energy expenditure. The difference in frequency of response to the two types of stimulation was highly significant. (3) The extra energy expended by bats in a response following a non-tactile stimulation was low (mean=49 J). Tactile stimulation resulted in much greater energy expenditure (mean= 2038 J). (4) Neither the degree nor the frequency of response to non-tactile stimulation was affected by species, body mass, ambient temperature, season, or metabolic rate during torpor. Degree of response to tactile stimulation increased significantly with increasing body mass. (5) Energy expenditure during torpor (pre-stimulation) was significantly affected by temperature in Natterers bat (Myotis nattereri Kuhl), Daubentons bat (Myotis daubentoni Kuhl), brown long-eared bats (Plecotus auritus L.), and by body mass in these species and pipistrelles (Pipistrellus pipistrellus Schreber). The mean energy expenditure across all species was 6-17mW. (6) By combining the measured energy expenditure in torpor before stimulation with the increase in energy requirements which accompanied non-tactile and tactile disturbance, the mean maximum reduction in potential duration of hibernation resulting from a non-tactile disturbance which elicited a significant response was 4-5h, and was 104h for each tactile disturbance. (7) Each non-tactile disturbance was predicted to decrease fat stores by 0001 g. Each tactile disturbance was predicted to decrease fat stores by 005 g.

The implication of small reductions in body temperature for radiant and convective heat loss in resting endothermic brown long-eared bats (Plecotus auritus)

Abstract 1. 1.|Dorsal surface temperature (Ts) and rectal temperature (Tb) were measured in four captive endothermic brown long-eared bats, Plecotus auritus, resting at ambient temperatures (Ta) of 5, 15 and 25°C. 2. 2.|A heat flux model for the bats was derived and the reduction in radiant and convective heat loss associated with small reductions in Tb were predicted from thoeretical equations. 3. 3.|A drop in body temperature from the maximum (38.2°C) to the minimum (31.5°C) recorded value was estimated to produce energy savings through a reduction in gross radiant and convective heat loss of 25 and 44% of metabolic heat production at ambient temperatures of 5 and 25°C, respectively. 4. 4.|We suggest that small reductions in body temperature offer resting thermolabile bats a compromise between rapid behavioural function associated with high body temperature and low energy demand associated with torpor.

Why do brown long-eared bats (Plecotus auritus) fly in winter?

We investigated the daily food and water consumption of a captive colony of three brown long-eared bats (Plecotus auritus) for 51 d. The bats were kept in a free-flight enclosure exposed to the natural photoperiod and temperature during the winter (January to March 1991) at 57° N. Water was always available, but food was available only on some nights. The mean daily temperature inside a wooden box provided as a hibernaculum was positively correlated with and slightly elevated above (0.6°-2.8° C) the mean daily temperature outside the box in the free-flight enclosure. The mean temperature inside the hibernaculum was 7.1° C and outside was 5.6° C. The mean relative humidity in the hibernaculum was 82% (range 67%-93%). The activity of the bats outside the hibernaculum was monitored by two Doppler radar units. The daily probability of an individual bat emerging from the hibernaculum was between 0.26 and 0.99. Emergence probability increased when there was food available and when it was warmer. The activity of the bats was strictly nocturnal, initial emergence occurring a mean of 64.4 min after sunset (n = 42, SD = 27.0 min). When denied access to food, the bats drank an average of 0.20 mL · bat⁻¹ · night⁻¹ on the nights that at least one emerged (n = 14 nights, SE = 0.05, range = 0.00-0.68). On warmer nights the bats were more active and ate and drank more than on colder nights. We suggest that typically in P. auritus winter flights may not be induced by the onset of starvation (and hence the need to feed) or by the onset of dehydration (and hence the need to drink). Rather, at typical winter temperatures P. auritus may fly frequently, almost daily, to try and ensure that neither energy nor water reserves approach critically low levels. Only during a prolonged cold period (mean night temperature <4° C) might many days pass without a winter flight.

The functional significance of ventilation frequency, and its relationship to oxygen demand in the resting brown long-eared bat, Plecotus auritus.

SummaryMean oxygen consumption and simultaneous ventilation frequency of nine non-reproductive brown long-eared bats (body mass 8.53–13.33 g) were measured on 159 occasions. Ambient (chamber) temperature at which the measurements were made ranged from 10.8 to 41.1°C. Apneic ventilation occurred in 22 of the 59 measurements made when mean oxygen consumption was less than 0.5 ml·min-1. No records of apneic ventilation were obtained when it was over 0.5 ml·min-1. The relationship between ventilation frequency and mean oxygen consumption depended on whether ventilation was apneic or non-apneic. When ventilation was non-apneic the relationship was positive and log-linear. When ventilation was apneic the relationship was log-log. Within the thermoneutral zone ventilation frequency was not significantly different from that predicted from allometric equations for a terrestrial mammal of equivalent body mass, but was significantly greater than that predicted for a bird. A reduction in the amount of oxygen consumed per breath occurred at ambient temperatures above the upper critical temperature (39°C).

Arrhythmic breathing in torpid pipistrelle bats, Pipistrellus pipistrellus

The arrhythmic breathing pattern of torpid female pipistrelle bats (Pipistrellus pipistrellus) was monitored using Doppler radar. A total of 98 h of radar measurements were made on 11 individuals over 17 experiments, during which time 974 apneic intervals were monitored, over ambient temperatures (Ta, degrees C) ranging from -1 to 14 degrees C, and body masses ranging from 4.6 to 7.4 g. As Ta declined, a greater proportion of all breaths occurred in discrete breathing bouts. Apneic intervals lengthened at lower Ta, but were not related to body mass. Mean apneic length, averaged over 1 degree C intervals, was best described by the least squares fit regression equation: ln (apneic length in s) = 7.07-0.811 ln (Ta + 1), (r2 = 0.96, P less than 0.01). Ventilation frequency (breaths.min-1), averaged over a breathing bout and the subsequent apnea, increased as Ta increased, and was not related to body mass. Mean ventilation frequency (f), averaged over 1 degree C intervals, was best described by the least squares fit regression equation: f = 0.812 + 0.499 Ta (r2 = 0.92, P less than 0.01). Using previously published values for O2 consumption (VO2) in torpid pipistrelles, and tidal volume and O2 extraction efficiency at 4 degrees C in torpid bats of the same mean size (6.2 g), we calculated that at 4 degrees C ventilation would, on average, supply only 14.2-21.3% of VO2. This suggests that in torpid pipistrelles the glottis may remain open during apnea, allowing a significant diffusive influx of O2 into the lungs.

Daily energy expenditure in the pouched mouse (Saccostomus campestris Peters 1896)

ABSTRACT Previous studies of the pouched mouse (Saccostomus campestris) have revealed that during reproduction there is no increase in food consumption, although resting energy demands, measured by respirometry, increase substantially. One explanation for this anomalous situation is that these mice may routinely use torpor to compensate their energy budgets. We measured the daily energy expenditure of eleven individual pouched mice over three consecutive days using the doubly-labelled water technique. The mice were housed in cages where they had free access to food and water, at an average temperature of 26.5 °C, and exposed to a natural photoperiod (February Pretoria). There was a large day-to-day variation in energy expenditure within each individual. The coefficient of variation in daily energy demand averaged 24.5%. By comparing the correlation of estimates for consecutive and nonconsecutive days we established that this variation was not a consequence of errors in the isotopic technique. The scaling ...