Chemical threat to birds and mammals in The Netherlands.

This article reviews the impact of xenobiotic substances on wild birds and mammals in The Netherlands, as recorded in the field over the past 25 yr. First, a brief survey is given of population trends during this period, using a few illustrative examples to indicate the role played by "environmental policy themes" other than diffusion. The present review of the policy theme diffusion is not intended to be exhaustive, but to provide a broad summary of the nature of the problems involved. Based on this review, conclusions are drawn about the ecological compatibility of various groups of xenobiotics with respect to birds and mammals. Because policy-makers are interested in the relative significance of both the various groups of substances and the various environmental themes for the decline of bird and mammal populations in The Netherlands, a provisional estimate of these contributions is also presented. The main conclusion is that, in the context of the policy theme diffusion, PCBs and pesticides have the greatest impact on birds and mammals. PCBs have an impact up to the species level, whereas the main impact of pesticides today is probably ecological, that is, foraging and habitat changes. It is also concluded that the share of the theme diffusion in the sum total of negative environmental influences is approximately one-quarter.