Birds of Indian Subcontinent

Removal Experiments and the Limitation of Breeding Density in Sparrowhawks

Publication Type:Journal Article
Year of Publication:1991
Authors:Newton, I, Marquiss, M
Journal:Journal of Animal Ecology
Date Published:1991
ISBN Number:00218790
Keywords:Accipiter, Accipiter nisus, Accipitridae, Columba, Columba palumbus, Columbidae
Abstract:(1) When the breeding population had settled, female sparrowhawks were removed from seven different nesting territories, and males from seven other territories in southern Scotland. In the same season, three of the removed females were subsequently replaced by other females, and three or four of the males were replaced by other males. (2) All three replacement females laid eggs, but only one (the oldest with previous breeding experience) produced young. Only one of the pairs with replaced males got beyond nest-building, but none raised young. The breeding success of the replacement birds was significantly lower than that of the remaining population. (3) As no movements were recorded from surrounding territories, and migrants were unknown in the area, it was assumed that the replacement birds were resident sparrowhawks that would otherwise not have attempted to breed that year. They included some first-year birds and some older ones, at least one of which had bred in the area in previous years. Replacement occurred even though unused nesting territories existed nearby. This raises the question why these birds had not already taken one of these unused territories and nested. Quality of available territory may be involved, as all replacements were on territories where previous use and nest success had been high. It is suggested that certain (mainly young) birds which are less efficient hunters can attempt to breed only if they can find a vacancy in good habitat (with a rich food supply), but not if the only habitat available to them is poor. In other words, an interaction between habitat quality and bird quality influences whether breeding occurs.
Short Title:Journal of Animal Ecology
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith