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SEPG 2261 - Date Awarded 2004
Do female great tits adjust egg investment in relation to foraging ability?
Abstract
Animals are expected to have evolved to invest optimally in reproduction; investing too much in any one year will mean decreased future reproductive success, and too little may result in decreased reproductive output. Birds with a variable clutch size may optimise their investment by trading off egg size and clutch size, and adjusting both to thier provisioning ability. Great tits (Parus major) can lay between 2 and 13 eggs in a clutch. Good quality parents should lay more smaller eggs, since they are good at provisioning their chicks can ‘catch up’ later on (‘altricial strategy’). Females that are less good at provisioning should ‘hedge their bets’ by producing fewer large eggs (‘precocial strategy’). Having had a head start before hatching they should be more tolerant of an unpredictable food supply post-hatching. A brood size manipulation showed a trend for a relationship between overall egg investment (clutch size x egg size) and female provisioning levels to a standard brood size, suggesting that good quality females invest more at both egg-laying and chick rearing stages of reproduction. However, there appears to be a trade off within the egg laying phase since clutch size and egg size are negatively correlated. Furthermore, egg and clutch size appear to be optimised according to provisioning ability; egg mass was negatively correlated with provisioning levels to a standard brood size, while clutch size showed a positive correlation. This suggests that although there are between individual differences in quality, individuals apear to trade off aspects of egg investment according to their provisioning potential.
Full report: SEPG2261
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