Seasonal Emergence and Historical Contaminant Exposure of Cave Myotis (Myotis velifer) in Central Texas and Current Status of the Population

Tarisha A Land,Charles E Pekins,Donald R Clark,Thomas E Lacher

doi:10.3390/environments6120121

Tarisha A Land, Charles E Pekins + Show 2 more

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https://doi.org/10.3390/environments6120121

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Abstract

We examined the emergence patterns of Myotis velifer in central Texas in 2000 and assessed exposure to pesticide residues. We collected and analyzed guano from three caves for pesticide residues. In addition, bat carcasses were sampled from an active colony of cave myotis (Myotis velifer) in Shell Mountain. Organochlorine residue concentrations were highest in guano from the Egypt and Tippit Caves, whereas organophosphate concentrations were highest in Shell Mountain guano. Residue concentrations of organochlorines and metals in guano and carcasses collected from the three caves are considered low and probably of no biological concern. The study was one of very few to demonstrate the presence of OPs, including 18 different detectable compounds in the two most recent samples of bat guano. Comparisons between spring and fall guano samples from Shell Mountain suggest that HCB (hexachlorobenzene), total chlordanes, dieldrin, endrin, endosulfan II, p,p’-DDE (Dichloro-2,2-bis(p-chlorophenyl) ethylene), and o,p’-DDT (Dichlorodiphenyltrichloroethane) accumulated while bats were absent from the caves at Fort Hood. Lindane appeared to be the only chemical that increased while the bats were present at the site. Organochlorine concentrations in carcasses were generally lowest in lactating females and higher in nursing juveniles. The pattern of emergence coincides with the peak of agricultural activities, therefore, bats forage at a time when the insect pests are most abundant, but also potential to exposure to agricultural chemicals is highest. The current status of the population, however, remains stable in spite of the history of exposure.

Highlights

Conservationists and ecologists have begun to examine more closely the role of biodiversity in providing valuable services to humans, both at a global scale [1] and the local scale [2]
Kunz et al [4] and Jones et al [5] give estimates of the value that bats provide through pollination, seed dispersal, and consumption of agricultural pests; the value provided to cotton production in south-central Texas alone is estimated at $741,000 US/year and could range as high as
The bats typically emerged in pulses, which were most prominent during the months of heaviest emergence

Summary

Introduction

Conservationists and ecologists have begun to examine more closely the role of biodiversity in providing valuable services to humans, both at a global scale [1] and the local scale [2]. Some key benefits include those provided by bats, often overlooked in studies of ecosystem services [3]. Impacts on bats carry a disproportionate economic effect when the magnitude of the ecosystem services they provide is accounted for. Kunz et al [4] and Jones et al [5] give estimates of the value that bats provide through pollination, seed dispersal, and consumption of agricultural pests; the value provided to cotton production in south-central Texas alone is estimated at $741,000 US/year and could range as high as. Hundreds of tropical plants depend upon bats for pollination services [4]. Benefits go beyond agriculture; the Annual Austin Bat Fest, which draws visitors to watch the emergence of Environments 2019, 6, 121; doi:10.3390/environments6120121 www.mdpi.com/journal/environments

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