LACKS BROOD REDUCTION HYPOTHESIS AND AVIAN HATCHING ASYNCHRONY - WHATS NEXT

Forbes recently argued that extant attempts to test Lack's brood reduc tion hypothesis for asynchronous hatching were of limited value. He ar gued that the hypothesis had to be tested in a two-step process: first , by testing whether brood reduction is adaptive, second, by testing w hether asynchrony pays, provided the first test is fulfilled. Here, we focus on how this protocol can be adopted in empirical work. First, w e identify several theoretical limitations to Forbes's approach: (1) i t is unclear whether the brood reduction threshold should be tested us ing synchronously or asynchronously hatched broods, (2) individuals ar e different and thus have individual ''brood reduction thresholds'', a nd (3) unpredictability may occur at different levels. Second, me disc uss a main practical difficulty in testing the brood reduction hypothe sis, related to the fact that asynchrony may carry a cost when conditi ons are good. When this is the case, tests must be carried out under a wide range of conditions, and during many years. Such a testing progr amme may turn out an almost insuperable task and Lack's hypothesis may be practically untestable using the traditional approach of recording the quantity of fledglings. Instead, we suggest that focus in future research on the issue is turned to consequences of different hatching patterns with respect to offspring quality. Recent evidence suggests t hat asynchrony serves to ensure offspring quality instead of quantity (the Offspring Quality Assurance Hypothesis), and may also lead to les s variable recruitment (bet-hedging).