THE LEVEL OF RESERVE PROTEIN AS THE PROXIMATE FACTOR CONTROLLING THE TIMING OF BREEDING AND CLUTCH‐SIZE IN THE RED‐BILLED QUELEA <i>QUELEA QUELEA</i>

SUMMARY Changes in the fat and flight muscle protein reserves of adult Red‐billed Queleas Quelea quelea were followed in two colonies in Tanzania and Botswana. At the start of a breeding attempt the protein reserves were higher that at any other time of the year, particularly in females which had heavier flight muscles (non‐fat dry weight) than did the (larger) males at that time. The pre‐breeding increase in the labile component of the muscle protein (the actual protein reserve) is calculated at 80% for females, but only 14% for males. The fat reserve was only increased slightly at the beginning of the breeding attempt. In both sexes, though for different reasons, the protein and fat reserves fell rapidly during the first few days of the attempt, in some individuals to dangerously low levels. During the incubation period there was rapid recovery while the situation during the rearing period appeared to vary between colonies. It is proposed that the proximate control of breeding is provided by the individual's own body condition, and particularly the state of its protein reserves. No environmental releasers are required for the birds to breed at the appropriate time of the year. Individual females producing two, three and four egg clutches differed in the rate at which their reserves fell during egg formation. The results are used to support the view that in this quelea the actual clutch‐size produced on any occasion is the largest the female can produce before becoming too enfeebled. Thus, clutch‐size appears to be determined phenotypically downward from a maximum which is indirectly under genetic control.