Mortality of Little Brown Bats Following Multiple Pesticide Applications

Autor: W. Timothy Rumage, Thomas H. Kunz, Edythe L. P. Anthony
Rok vydání: 1977
Předmět:
Zdroj: The Journal of Wildlife Management. 41:476
ISSN: 0022-541X
DOI: 10.2307/3800519
Popis: This study documents the mortality of little brown bats (Myotis lucifugus) at a nursery colony in southern New Hampshire in a 2 year period following multiple applications of pesticides (DDT, chlordane) for extermination. Mortality among adult females was greatest in the second summer (principally in the parturition period) following the last pesticide application. Two major peaks of mortality occurred in young bats, one soon after birth and another as they reached adult size. Significant age differences in mortality were observed between the first and second years after spraying. The percentage of young bats dying as they approached adult size was highest in the second year. Mortality was nearly 9 times higher in young than among adult bats in the first year, whereas proportionately more adults died in the second year. We suggest that the prolonged and latent mortality of bats following pesticide applications increases the short and long-term health risk to humans and therefore necessitates the reevaluation of current extermination practices. J. WILDL. MANAGE. 41(3):476-483 Most efforts to document accumulation of pesticide residues in insectivorous bats (Jefferies 1972, Reidinger 1972, 1976, Clark et al. 1975, Clark and Lamont 1976a,b, Clark and Prouty 1976, Geluso et al. 1976) arose out of concern for declining bat populations (Cockrum 1970, Stebbings 1970, Mohr 1972, Braaksma and van der Drift 1972, Findley 1973). These studies assumed that the principal route of pesticide entry was via the food chain, with bats as "non-target" species (Pimentel 1971). The application of DDT, chlordane, and similar compounds directly on bats or their roosting places has become common practice in the name of "public health" and "vermin control." With the exception of a follow-up study by Greenhall and Stell (1960), the effectiveness of these compounds for such purposes is virtually unknown. Agencies authorizing the use of pesticides for extermination usually assume that once they have been applied, the vermin have been controlled and the related public health problems resolved. We challenge this assumption. We thank Frank, Joni, and Mark Miller, formerly of Amherst, New Hampshire, for their assistance and hospitality in the course of this study. We gratefully acknowledge the field and laboratory assistance of R. Diafuku, G. Glass, J. McGuire, N. Murray, G. Rogowitz and A. Simpson. J. Pestana of the J. P. Chemical Company, Amherst, New Hampshire, and C. A. Wilber of the Abalene Pest Control Company, Shelburne, Vermont, kindly provided information on the history of pesticide applications at the treated colony. Drs. D. R. Clark, Jr., M. B. Fenton, and S. R. Humphrey reviewed an early version of this paper and suggested several improvements. We also wish to thank Drs. D. G. Constantine and C. V. Trimarchi for their comments. This study was partially supported by grants from the American Philosophical Society, the Boston University Graduate School, and the National Science Foundation, Undergraduate Research Program (GY 11245) to T.H.K. (Project Director). BACKGROUND AND METHODS We studied a colony of little brown bats occupying a barn near Amherst, Hillsborough Co., New Hampshire. The barn 476 J. Wildl. Manage. 41(3):1977 This content downloaded from 157.55.39.54 on Thu, 30 Jun 2016 05:35:20 UTC All use subject to http://about.jstor.org/terms BAT MORTALITY DUE TO PESTICIDES * Kunz et al. 477 and attached house are over 150 years old, and judging from recollections of former owners, records kept by exterminators, and the appearance of roosts, bats have probably used it for nearly as many years. In the past, numerous attempts were made to exclude bats by sealing potential access routes. According to a local exterminator the interior walls and roost areas of the barn were sprayed with DDT in 1967, and Lindane on subsequent occasions. At these times "numerous" bats were killed, but each year the barn was reinhabited. In 1973 a new owner of the property contacted an exterminator, and 3 sprayings were conducted on 13 and 21 August and "some time in early September" 1973. Reportedly a 2 percent wettable solution of Diazinon (volume unknown) was applied to the interior walls and rafters of the barn on these 3 dates. However, laboratory analyses of crystalline deposits scraped from the walls and roost areas indicate that DDT and chlordane were used (Clark et al. 1978). We became aware of this bat colony (and the first 2 of the 3 recent applications) on 27 August 1973, when the owner of the property notified us of dead and moribund bats on the floor of the barn. We first visited the colony in early September, soon after the third spraying. We discovered that some of the bats which apparently had been killed during and after the applications of pesticides had been disposed of by the exterminator, and others had been disposed of by the owner and the family cat. Because 2 of the 3 pesticide applications were made in late August and early September, the majority of bats which occupied this barn in the summer of 1973 probably had already departed for transient roosts and swarming sites (Fenton 1969) at the time of spraying. Judging from our studies at other colonies in southern New Hampshire in the same year, we suspect that no more than 10 percent of the maximum 1973 summer population remained at the time of spraying. Thus, the initial pesticide exposure to most residents probably was to residues in the roost the following spring and summer (1974). On 30 May 1974 we began regular visits to this site at 9 day intervals which continued through mid-September. On each visit in 1974 we trapped bats (Tuttle 1974) as they departed at dusk from a small windowlike opening (0.71 x 0.79 m), as they returned from their initial feeding (around midnight), and again before sunrise. Individuals were weighed, sexed, aged (adult vs. young), and reproductive condition was determined. Most were released at the site of capture; those retained were assigned identification numbers, individually packaged, frozen, and later assayed for pesticide residues (Clark et al. 1978). Following evening departures, we recovered all dead and moribund bats lying on the floor and rafters of the barn. In 1975 we also collected dead and moribund bats at 9 day intervals (April through September), and 2 trap samples were taken on 20 July and 15 August as bats departed at dusk. Forearm measurements of dead and moribund bats were taken in both years and each animal was examined for sex, age, and reproductive condition. No weights were taken because most bats, at the time of collection, were badly decomposed or dehydrated. Where reproductive condition could not be determined for adults at the time of death, we assigned them to the reproductive condition expected for that period. Adults were distinguished from young in having fused phalangeal epiphyses. Ages of juvenile bats (in days) were assigned for the first 3 weeks of post-natal growth, based on extrapolations from the equation for forearm length, FA = 37.9 (1 0.649e-0.?09t), after Kunz and Hamill (In preparation). J. Wildl. Manage. 41 (3):1977 This content downloaded from 157.55.39.54 on Thu, 30 Jun 2016 05:35:20 UTC All use subject to http://about.jstor.org/terms 478 BAT MORTALITY DUE TO PESTICIDES Kunz et al.
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