Egg production, flight velocity and predation risk in birds

Veasey, Jake S (1999) Egg production, flight velocity and predation risk in birds. PhD thesis, University of Glasgow.

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Abstract

The costs of reproduction can be defined as the trade-off between present and future reproduction, where current reproduction may diminish future reproductive success of the parent and/or of the parent's offspring. One potential cost of reproduction in birds may be a reduction in the ability of the female to escape from predators due to a reduction in maximal flight velocity. Such a reduction in flight performance may come about in laying females as a result of an increase in mass over the laying period, and a reduction in flight muscle condition. The result of such a reduction in the flight velocity of wild birds would be to increase the susceptibility of those birds to capture by predators once attacked. To investigate the potential of egg production to affect flight velocity and consequently predation risk, the individual effects of body mass and muscle condition needed to be determined. Contrary to theoretical studies which have indicated that body mass might significantly affect flight velocity in birds, no such relationship was found in startled zebra finches (Taeniopygia guttata), a finding supported by a number of other empirical studies on other species. To determine whether muscle loss is significant in affecting flight velocity, the physiological costs of reproduction and consequently the extent to which females lost muscle condition were manipulated. This was achieved by encouraging females to lay large or small clutches on high or low quality protein diets, and measuring the changes in muscle condition and flight velocity during the course of laying a clutch. A strong positive relationship was found to exist between changes in muscle condition and changes in flight velocity. Treatments in which birds exhibited the largest declines in muscle condition, were associated with the largest declines in flight velocity, hi contrast to this, those treatments in which birds lost the least muscle condition were associated with actual improvements in flight performance, that is to say, birds flew faster at the end of a clutch than at the beginning. These changes were independent of body mass and occurred post-laying indicating that it is the cost of egg production that is critical in affecting flight velocity rather than the cost of carrying eggs as had previously been suggested. Moreover, it is demonstrated that independently of diet and changes in body mass, increased reproductive output decreases maximal flight velocity mediated by an increase in muscle loss. This is the first demonstration of a physiological trade-off between resource allocation to reproduction and the maintenance of musculature critical to an animal's escape response. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Neil Metcalfe
Keywords: Ecology
Date of Award: 1999
Depositing User: Enlighten Team
Unique ID: glathesis:1999-71801
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 09:31
Last Modified: 17 May 2019 09:31
URI: http://theses.gla.ac.uk/id/eprint/71801

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