Black and white tail markings in Rufous Bush Chats Cercotrichas galactotes: size, symmetry and the extent of seasonal abrasion

Authors: Fernando ÁLVAREZ

Published: Volume 51(1), June 2004. Pages 169-175.

Language: English

Keywords: Abrasion, Cercotrichas galactotes, migration, reproduction, Rufous Bush Chat and visual pattern.

Summary:

Aims: An attempt was made to understand the relationship of reproduction with the features of the conspicuous visual pattern in the tail of Rufous Bush Chats Cercotrichas galactotes, especially in relation to its reduction in size during the breeding season.

Location: Southwestern Andalusia (southern Spain).

Methods: In two breeding seasons the size, fluctuating asymmetry and extent of abrasion of the white terminal and black subterminal markings of male and female Rufous Bush Chats were compared until the end of reproduction.

Results: A positive relationship was found in males between the size of their white terminal markings and reproductive success and a negative one between the size of their black subterminal markings and the rate of nest depredation. The size of the white patches was positively related within pairs. Only the size of the white terminal markings is notably reduced over the breeding season.

Conclusions: Since most of the abraded white markings are beyond the point of the maximum width of the tail, the hypothesis is offered of an adaptive reduction of its dragging effect during the birds´ trans-Saharan late-summer southward migration. The black subterminal markings, protected by melanin against abrasion, may function fixing a limit to erosion.

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