Predation strategies in aerial feeding birds

• Main Author: Waugh, David R.
• Other Authors: School of Natural Sciences, Department of Biological Science
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Stirling 1978
• Subjects: Birds Behavior; Birds Food; Apus apus
• Online Access: http://hdl.handle.net/1893/2402; http://dspace.stir.ac.uk/bitstream/1893/2402/1/Waugh-1978-thesis.pdf

The predation strategies of four species of aerial feeding bird, the Swallow, Hirundo rustica, Sand Martin, Riparia riparia, House Martin, Delichon urbica and Swift, Apus apus, are examined during their breeding season in Britain. The abundance of aerial insects upon which they feed increases in April and reaches a plateau in May which is maintained until September. Aerial insect density is higher nearer the ground, the spring rise in abundance occurs earlier, a greater proportion of larger insects are available and insect numbers fluctuate less than at higher levels. The arrival times of the different predator species into the breeding area are staggered and this is linked to their preferred prey and feeding station, and to the distribution of aerial insects. Throughout the breeding season the four species of bird are ecologically isolated with respect to feeding station in the air-space and various characters of the insect prey, primarily size and mobility. It is suggested that to coexist they segregate along a combination of axes of the feeding niche, although segregation in air-space may be the most effective. Morphological adaptation to feeding niche is shown for tail shape, wing-length and bill shape, which respectively influence manoeuvrability, mode of flight and prey handling ability of the predators. Both Sand Martin and Swallow show increases in their prey size and mobility niche breadths in favourable feeding conditions whilst all four species simultaneously show decreases in air-space niche breadths. It is postulated that both within and between species there is a tendency to switch between patch specialisation and prey specialisation. Current theories of optimal patch and prey choice are discussed in relation to this hypothesis. Under very adverse conditions prey size overlaps are small and, when they increase, air-space overlaps simultaneously decrease. This suggests competition between aerial feeding birds in adverse conditions. Swallows deliver more meals per unit time to larger broods, with an ...