The Factors Influencing the Selection of Food by the House Martin (Delichon urbica (L.))

Abstract

This paper describes part of a 3-year study in southern England of the breeding biology of the house martin (Delichon urbica (L.)). The food of house martin nestlings and the relationship between the prey taken and the food available to the aerial feeding adult martins is discussed. Lack & Owen (1955) investigated the food and feeding habits of the common swift (Apus apus (L.)) in southern Britain. The diet of the house martin in Germany has been examined by von Gunten (1961). The study of Johnson (1967) on the food of the purple martin (Progne subis (L.)) in North America notably compared the stomach contents of feeding birds with samples of flying insects. In a fundamentally similar study of the feeding of the brown trout (Salmo trutta (L.)), the stomach contents showed a high correlation with the occurrence of invertebrates in freshwater drift samples (Elliot 1970). This study also demonstrated the phenomenon of diel variation in the predator's diet associated with diel changes in the composition of the available food. The analogous phenomenon of diel changes in the composition of the aerial fauna, associated with differences in flight periodicity of the constituent insects (Lewis & Taylor 1965), results in different food availabilities at different times of day to aerially feeding birds. This emphasizes the necessity for a continuous diurnal sample of both the available food and the diet. Such a sample was collected in this study, which consequently differs in this respect from earlier work on the diet of swallows (Hirundinidae) and swifts (Apodidae). Hespenheide (1971) described the food preferences of a number of insectivorous birds, including several hirundines. He concluded that the average size of prey taken is always larger than that available. Gibb & Betts (1963) also demonstrated selection of larger prey than those generally available by tits (Parus spp.) feeding on lepidopterous larvae in a pine forest. The purpose of this study was to investigate whether the food taken by the house martin was the result of a similar selection of food items from the available resources, and to assess the influence of the abundance and quality of airborne insects and concurrent weather conditions on food selection.