HATCHING ASYNCHRONY IN GREAT TITS: A BET-HEDGING STRATEGY?

Abstract

Previous studies have shown that asynchronous hatching in birds tends to result in fewer, but higher quality, offspring than does synchronous hatching. However, very few studies have considered the consequences of such a pattern for the recruitment of offspring as subsequent breeders. We recorded nestling survival and fledgling body mass in experimentally synchronous and asynchronous broods of the Great Tit, Parus major. Using six different juvenile survival models, taken from published studies of the species, we calculated the expected number of offspring recruited with each hatching pattern and survival function. The sex of fledglings was included in the analysis. When comparing the estimates of surviving juveniles between synchronous and asynchronous broods, we found no significant difference in the means with any of the six models. However, the distributions of recruitment were different: the expected number of recruits was more variable with synchrony than with asynchrony. This suggests that hatching asynchrony in the Great Tit may serve as a bet-hedging strategy. A larger proportion of asynchronous broods than of the synchronous broods experienced brood reduction, but fledgling body masses for the reduced synchronous broods were lower than those for the reduced asynchronous broods. This suggests that synchronous hatching inhibits adaptive brood reduction in the Great Tit. There was considerable individual variation in the level of brood reduction within the same area and season. We argue that conditions also may be unpredictable at a small scale (parental abilities, territory quality, or parasite load). In consequence, high-quality parents may benefit from synchrony, but low-quality parents benefit from asynchrony, within the same year.