Insect and Bird Interactions

Auk, The, Jul 2005 by Cooper, Robert J

Insect and Bird Interactions.- Helmut F. van Emden and Miriam Rothschild, Editors. 2004. Intercept Limited, Andover, Hampshire, United Kingdom, xx 301 pp., 5 color plates. ISBN 1-898298-92-0. Hardback, $140.00.-Although this volume stems from a conference run by the Entomological Club at the University of Reading in 1997, the editors point out in the preface that this is not strictly a conference proceedings. New authors were recruited to increase the coverage of certain topics in the form of review papers that were inappropriate for the conference. The volume is described as a first, and thus unique, compilation of information on insectbird interactions. Although the title is unique, the latter statement is not exactly true, because there have been two edited volumes that largely covered insect-bird interactions, albeit with a more restricted focus than the current volume. Dickson et al. (1979) edited the proceedings of a conference on the role of insectivorous birds in forest ecosystems; all the contributors were from the United States and Canada. Morrison et al. (1990) edited the proceedings of a conference on foraging theory, methodology and applications; again, most of the papers were North American in emphasis, with a focus on methodology of studies on bird foraging, diet, and the like. The strong emphasis of both previous volumes was on birds; such is not the case here. There is a much more balanced approach to examining the relationships between birds and insects than any previous effort; for that reason alone, this book is unique.

The volume is divided into four parts. Part 1, on population management issues, largely focuses on agricultural systems in Great Britain, which are under government pressure to become more productive. As in other regions of the world, unproductive parts of the landscape such as hedgerows and field borders are being put into agricultural production, and there is increased reliance on mechanization and chemical inputs such as fertilizers and pesticides. Associated declines in many bird populations are blamed on decreasing food supplies, especially insects. However, except for some experimental evidence of Grey Partridge (Perdix perdix) populations being thus affected via decreased chick survival, most of the evidence that bird population declines are caused by food reduction is correlative. As several of the authors point out, large-scale manipulative experiments are badly needed in this area. The idea that terrestrial arthropod management can be a means of managing songbirds is promoted in several chapters; this notion has not been developed enough in U.S. wildlife management programs. We definitely need to learn more about terrestrial arthropod management.

Interestingly, the first chapter in Part 1, by Goss-Custard and West, does not involve insects but rather the interactions between aquatic invertebrates and their shorebird predators and is offered as a model to strive for in achieving a better understanding of the interactions of insects and birds, especially with regard to understanding avian population dynamics. I agree that the work of Goss-Custard and colleagues has been exemplary in understanding bird predatorinvertebrate prey relationships, but there are some important differences between mudflats and terrestrial systems that make this model a difficult one to achieve for those of us working in the latter. First, prey sampling becomes much more difficult as additional layers are added to the essentially two-dimensional substrate in which shorebirds forage. Forest arthropod sampling is especially challenging. Tidal inundation is a major factor affecting invertebrate prey availability and is predictable, but the factors affecting terrestrial arthropod availability are highly variable and unpredictable, or largely unknown. Birds are harder to count, find, and observe in scrub and forest than in open areas. The list goes on. Still, this is a great chapter.

Part 2, which covers the effects of insecticides on bird populations, continues with the agroecosystem emphasis. It is recognized that most modern pesticides used in agriculture and forestry do not kill or otherwise harm birds directly. Rather, they affect them indirectly through reduction of nontarget prey such as caterpillars or by killing the plants that are fed upon by herbivorous insects. Another chapter features a case study by Colin Walker, who, in an ecotoxicological "whodunit," assigns the blame for British raptor declines not to DDT but to cyclodiene insecticides, principally aldrin, dieldrin, and heptachlor, which were used as sprays and seed dressings in the 1950s and 1960s.

Part 3, which covers foraging behavior of birds on insects, differs markedly from the Morrison et al. (1990) volume mentioned above. Here, the focus is on the basic biology of avian vision, warning coloration, smells, and the chemical defenses of insects. The chapter on the avian retina is written by James Bowmaker, an ophthalmologist. Two other papers at the end of the section focus on studies of diet and prey availability.