Timber treatments and bats

TIMBER TREATMENTS AND BATS P. A .

RACEY

The numbers of bats are declining dramatically throughout Western Europe.

There are many reasons for such a decline. The reduction in insect abundance due to water pollution, changing agricultural practices, and increased use of agricultural pesticides may have significant effects on bats' survival and breeding success. The change from haymaking to silage and loss of permanent meadows prevents the maturation of some insects and reduces their diversity. The effect of these changes is difficult to quantify, although experimental work has shown that bats are highly sensitive to organochlorine pesticides (Jefferies, 1972; Clark, 1981). Insects that do not succumb to repeated applications of insecticides and fungicides often carry sublethal doses of these chemicals. Bats feeding on such insects accumulate the poisons, stĂśre them in fat, and metabolise them during hibernation when they exert their harmful effects.

Insecticides and fungicides also kill bats in other ways. We have long since cut down most of the deciduous trees that once covered our country in order to build ships and houses, and in doing so we have deprived bats of natural roost sites in rot holes and beneath peeling bark. However, because of their preference for roosting in bodily contact with wood at least during the summer period of pregnancy and lactation, bats have moved into the roof spaces of houses which are now their commonest roost sites. Some species Cluster or hang from the roof apex, others are crevice-seekers and squeeze into gaps behind soffit boards, or between joists and gables. The roof timbers of most older houses contain infestations of wood-boring beetles of varying severity, and if they have fallen into disrepair, outbreaks of timber-rotting fungi may also be present. The commonest treatment for these problems consists of applying a mixture of an insecticide (gamma HCH = lindane) and a fungicide (pentachlorophenol). In Britain the estimated number of dwellings treated annually rose from 35,000 in 1972 to 100,000 in 1979, and 500,000 in 1983 (Stebbings & Griffith, 1984). The treatment chemicals are applied at far higher concentrations than that required to destroy the infestation so that the Company concerned can provide a long-term guarantee against reinfestation.

My colleague Dr Susan Swift and I have shown that these timber treatments are rapidly lethal to bats, even when they are applied to the roof timbers over a year before the bats take up residence. Chemicals on the surface of the wood become transferred to the fĂźr of the roosting bat, and are ingested during grooming. Even if the bats are prevented from roosting in contact with the treated wood, death still occurs, because the chemicals volatilise and are breathed or absorbed across the skin (Racey & Swift, 1986).

The death of bats due to timber treatments is unnecessary because alternatives exist to the chlorinated hydrocarbons. These are the pyrethroids, a family of insecticides based on pyrethrum which occurs

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TIMBER TREATMENTS A N D BATS

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naturally in an African Chrysanthemum. They are as effective against the wood-borers and as persistent when used in roof spaces as lindane (Berry, 1977; Baker & Berry, 1980). An additional advantage to using pyrethroids is that they can be applied in water-based emulsions so avoiding the necessity for the increasingly expensive and highly inflammable solvents required for the application of lindane. A variety of alternative chemicals also exist to replace pentachlorophenol as a fungicide. Asypetacs and naphthenates, octoates and borates are all effective fungicides.

The Wildlife and Countryside Act 1981 made it an offence to cause the death of bats and there have been five successful prosecutions of individuals and companies who treated roof timbers which were used as bat roosts with toxic chemicals. Most timber treatment companies are more responsible and now use pyrethroids in bat roosts. However, it would be preferable if pyrethroids replaced lindane in all timber treatments. All roof spaces are potential bat roosts, and the continued use of high concentrations of highly toxic chemicals in such close proximity to human inhabitants of dwellings is no longer acceptable. There have been instances where cats accidentally trapped in roof spaces after treatment have died gruesome deaths, and the long-term effects of chlorinated hydrocarbons on man is the subject of increasing disquiet.

1986 is National Bat Year. It should also be the year of safer timber treatments.

References Baker, J. M. & Berry, R. W. (1980). Synthetic pyrethroid insecticides as replacements for chlorinated hydrocarbons for the control of wood-boring insects. Holz als Roh- und Werkstoff 38, 121.

Berry, R. W. (1977). The evaluation of permethrin for wood preservation.

Pestic. Sei. 8, 284.

Clark, D. R. (1981). Bats and environmental eontaminants: a review. United States Department of the Interior, Fish and Wildlife Service. Special Scientific Report - Wildlife, No. 235.

Jefferies, D. J. (1972). Organochlorine residues in British bats and their significance. J. Zool., Lond. 166,245 Racey, P. A. & Swift, S. M. (1986). The residual effects of remedial timber treatments on bats. Biol. Conserv. 35, 205.

Stebbings, R. E. & Griffith, F. (1984). Distribution and status of bats in Europe. Report prepared for the NCC for inclusion in the E E C threatened species list. Peterborough, Nature Conservancy Council.

Prof. P. A. Racey Department of Zoology, The University of Aberdeen.

Footnote As a Student, Professor Racey's interest in bats was encouraged by the late Lord Cranbrook and he carried out much of the fieldwork for his doctorate in Suffolk churches. He still Visits Suffolk where his wife's family lives. (Editor) Trans. Suffolk Nat. Soc. 22