Jj. Sanz et Jm. Tinbergen, Energy expenditure, nestling age, and brood size: an experimental study ofparental behavior in the great tit Parus major, BEH ECOLOGY, 10(5), 1999, pp. 598-606
A brood manipulation experiment on great tits Parus major was performed to
study the effects of nestling age and brood size on parental care and offsp
ring survival. Daily energy expenditure (DEE) of females feeding nestlings
of 6 and 12 days of age was measured using the doubly-labeled water techniq
ue. Females adjusted their brooding behavior to the age of the young. The d
ata are consistent dth the idea that brooding behavior was determined prima
rily by the thermoregulatory requirements of the brood. Female DEE did not
differ with nestling age; when differences in body mass were controlled for
, it was lower during the brooding period than later. In enlarged broods, b
oth parents showed significantly higher rates of food provisioning to the b
rood. Female DEE was affected by brood size manipulation, and it did not le
vel off with brood size. There was no significant effect of nestling age on
the relation between DEE and manipulation. Birds were able to raise a larg
er brood than the natural brood size, although larger broods suffered from
increased nestling mortality rates during the peak demand period of the nes
tlings. Offspring condition at fledging was negatively affected by brood si
ze manipulation, but recruitment rate per brood was positively related to b
rood size, suggesting that the optimal brood size exceeds the natural brood
size in this population.