Evolutionary influences on avian clutch size

I conducted a series of studies which looked at influences on avian clutch size. Firstly I examined the traditional view that the demands of rearing chicks create a bottleneck at which clutch size is shaped by natural selection. I considered whether instead other stages such as incubation might also be important. I proposed that reproductive demands at each stage of the breeding season may be interdependent, and by developing a mathematical model, I formalised the argument and showed that data on the relationship between the number of offspring and the expenditure of resources at many stages of the season could reveal the importance of natural selection on clutch size at each stage. I then reviewed the literature on the importance of incubation for clutch size determination. Results indicated that metabolic demands of incubation were appreciable and that the incubation of enlarged clutches imposed penalties on the adults. In a field study of kittiwakes I found that breeding success was depressed during incubation and chick rearing by enlargement of clutches and broods respectively. I measured metabolic rates of kittiwakes during incubation and found them to be comparable with those during chick-rearing. Secondly, I examined whether individual adults within populations differed in their reproductive capacities (i.e. whether there was a range of 'adult quality') and whether this could then affect clutch size. In a study of kittiwakes I found clusters of birds with similar breeding performance, but found that these clusters did not persist between years. In a study of swifts, I found that some individuals were consistently good breeders but that this had negligible effects on the distribution of lifetime reproductive success between individuals. I then examined whether the low clutch sizes and high survival of swifts might reflect a bet-hedging strategy in a fluctuating environment, but found little evidence of this. I looked at whether differences in the amount of space available at the nest site could account for differences in clutch sizes of kittiwakes, but could find no such evidence. Lastly I developed a theoretical model to look at how clutch size might be affected by changes in reproductive effort with age. I examined whether the predictions of optimality models were borne out by the more appropriate population genetics approach and found that in birds the optimality models are robust