Factors affecting nestling growth in the great tit Parus major.

Full article

Published:

Volume 40(2), December 1993. Pages 121-131.

Language:

English

Keywords:

asymptotic weight, eastern Spain, growth rate, nestlings, Parus major.

Abstract:

The nestling growth of the Great Tit Parus major was studied in Sagunto, eastern Spain, by periodic weighting of individually marked nestlings in 24 successful first clutches. The logistic equation was used to model weight gain, and the growth constant (k) and the asymptote (A) computed, using an iterative least square fitting technique. The variability of these parameters was studied within broods, between broods, and between populations. Most clutches hatched asynchronously. Late-hatched young died more frequently than early-hatched ones. Those late-hatched young that survived grew at a lower rate than their early-hatched siblings, but reached the same asymptotic weight. Considering brood means as sample units, the relationships between some variables (including reproductive parameters and ambient temperatures during growth) and the nestling weight at different ages, growth rate, and asymptotic weight were analysed by stepwise multiple regression. Weights at days 0 and 4 were not significantly related to any studied variable. Weight at day 8 was negatively related to the number of hatchlings, and weights at 12 and 16 days were negatively related to the number of fledglings. The asymptotic weight was positively related to the mean egg volume, while the growth rate was negatively related to the clutch size. The partial regression coefficients of other variables were all non-significant after removing the effect of these factors. It is concluded that the mean asymptotic weight of a brood is mainly determined by the "quality" of the parents, while its mean growth rate is affected by sibling competition. Including only successfully fledged young, k was 0.39 g/day per g, and A was 17.86 g in the population of Sagunto. We compared the growth parameters of this and four other European Great Tit populations to examine the hypothesis that the growth rate is physiologically maximized and therefore does not vary geographically. We found significant differences in growth rate and asymptotic weight between the studied populations. These results do not support this hypothesis, suggesting that the nestling growth rate could vary between populations depending on the particular conditions in which they live.