AVIS-IBIS

Birds of Indian Subcontinent

Economics of Experimentally-Induced Territorial Defence in a Gregarious Bird, the Fieldfare Turdus pilaris

Publication Type:Journal Article
Year of Publication:1986
Authors:Tye, A
Journal:Ornis Scandinavica
Volume:17
Issue:2
Date Published:1986
ISBN Number:00305693
Keywords:Sturnidae, Sturnus, Sturnus vulgaris, Turdidae, Turdus, Turdus pilaris
Abstract:Fieldfares wintering in eastern England have a flexible social structure ranging from highly gregarious to near-territorial according to their food supply. Feeding experiments were carried out to investigate this variability. In experiments using apples, previously-gregarious Fieldfares established large exclusive territories, of a kind hitherto unknown in this species. Territory-owners spent more time on aggression and eating experimental apples and less time hunting invertebrates than non-territorial birds did. Within the range used, apple density and distribution had little effect on feeding and territorial behaviour. Increasing intrusion by Fieldfares and Starlings reduced the amount of time which owners spent eating apples, while increasing the time which non-territorial birds spent eating them. Increasing intrusion increased agonistic behaviour time for all birds. Estimated net energy gain of territory-owners declined with increasing intrusion rate while that of non-territorial birds did not. Territories shrank and were abandoned when non-territorial birds enjoyed higher net energy gain than owners, possibly following a period of assessment of the value of defence after defence had become uneconomical. Territoriality permitted accumulation of reserves in preparation for food scarcity and was thus part of an adaptation to unpredictable, rather than stable, food supplies.
URL:http://www.jstor.org/stable/3676864
Short Title:Ornis Scandinavica
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith