Moderator: Moderators
Chads93GT wrote:Easy. Don't touch them. I shine my lights at them, talk, etc who cares. Whomever gave you the impression that the slightest peep will disturb a bat gave you the wrong impression.
Although intentional disturbance of roosts is well documented, unintentional disturbance often poses an even greater threat. In the temperate zone, aggregations of bats which cavers typically encounter are either hibernating groups that occur in late fall, winter, and early spring, or maternity colonies that occur in late spring or summer. There is no question that disturbances as seemingly trivial as merely entering a roost area, or shining a light on hibernating bats or on a maternity group of females and their pups, can result in decreased survival, perhaps outright death, and possible abandonment of the roost site. Although there is some controversy about the significance of this apparently "innocent" disturbance, my own experience and reading of the literature lead me to the opinion that it can be extremely significant. however, there is no question that the impact of such disturbances are somewhat species-specific, and that the timing of the disturbance is very important.
The results of "innocent" disturbance of a maternity colony can include the following> (1) It can cause individuals to abandon roost sites, particularly early in the reproductive season when females are pregnant. This may result in females moving to other, perhaps less ideal, roosts were their success at reproducing is reduced. (2) disturbance raises the general level of activity within roosts. This may result in greater expenditure of energy and less efficient transfer of energy to nursing you. This, in turn, may cause slower growth of young and increase the foraging demands on females, thus increasing the time females are outside of the roost and vulnerable to predation. (3) Disturbance can cause outright death of young that lose their roost-hold and fall to the cave floor. (4) maternity aggregations often result in thermoregulatory benefits. Clustering bats gain thermal benefits from being surrounded by other warm bodies However, individuals also may receive thermal benefit because the accumulated body heat of all individuals present serves to raise temperatures within the roost area. Therefore, if the size of a colony decreases, the accumulated thermal advantes to the individuals in that colony may likewise decrease, and it may become energetically less advantageous, or perhaps even energetically impossible for females to raise pups in that roost. Thus, there may be a "threshold," where after a population reaches a certain lower size, roost temperatures cannot be raised sufficiently for rearing young and that roost must be abandoned as a maternity site. (Peter's note: with WNS severely depleting bat populations, we're seeing much smaller maternity roost sizes begging this question. Dr. Tom Kunz is experimenting with simple wooden baffle systems in several New England buildings that are historical maternity roosts to re-create levels of heat formerly maintained by larger maternity colonies in order to help assist reproductive rates of WNS survivors and the recovery of the species.)
Problems caused by disturbing hibernating bats also relate to their energy requirements. During winter, temperate zone bats go long periods without eating, and allow their body temperatures to drop, often to near freezing. the energy reserves that bats accumulate prior to hibernation are often close to what is needed to survive the winter. disturbance during hibernation may cause bats to arouse prematurely, elevating their body temperatures and utilizing stored energy reserves which should not be spared. The bats may go back into torpor after the disturbance, but then they may not have sufficient energy to survive the rest of winter. this may not be apparent to the person causing the disturbance."
Abstract
I measured natural baseline activity and the response of hibernating bats to human presence in a hibernaculum containing ca. 1,300 bats of the species Myotis lucifugus and Myotis septentrionalis. Infrared detectors registered baseline flight movements in the hibernaculum over 62 days in January to March and over 8 days in April, when no observer was present, and they also registered the increase in flight movements following six visits of 1-2 h each to the hibernaculum. Visits to the mine resulted in a dramatic increase in flight activity of bats beginning within 30 min of the visit, peaking 1.0-7.5 h later, and remaining significantly above baseline level for 2.5-8.5 h. These results show that, contrary to previously published studies, hibernating bats are sensitive to nontactile stimuli and arouse and fly following human visits. To avoid increased mortality due to the premature depletion of fat reserves, human visits to hibernacula should be kept to a minimum.
Abstract
(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 Natterer's bat (Myotis nattereri Kuhl), Daubenton's 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 6.17 mW. (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 4.5 h, and was 104 h for each tactile disturbance. (7) Each non-tactile disturbance was predicted to decrease fat stores by 0.001 g. Each tactile disturbance was predicted to decrease fat stores by 0.05 g.
Users browsing this forum: No registered users