Complex patterns of food allocation in asynchronously hatching broods of crimson rosellas

In birds, asynchronous hatching typically leads to lower growth and surviva l of last-hatched chicks. However, all crimson rosella, Platycercus elegans , chicks grow at the same rate, although first-hatched chicks can be as muc h as seven times heavier than last-hatched chicks at the end of hatching. W e examined the delivery and distribution of food to 18 rosella broods by vi deotaping feeds and simultaneously recording mass changes in the nestbox us ing a digital balance. Parents visited the nest infrequently and delivered loads of up to 25% of their body weight during a feeding visit. Male rosell as consistently delivered larger loads and consequently had higher feeding rates (g/h) than females. Parents distributed food between chicks by direct regurgitation in a series of up to 51 food transfers. Overall, chicks of a ll hatching ranks received equal numbers of transfers, but parents differed in how they distributed food within the brood. Males fed first-hatched chi cks more than last-hatched chicks, whereas females distributed food equally to all chicks. Selective feeding of small chicks might be costly to female s since they delivered food more slowly than males and spent more time in t he nestbox. Thus female rosellas may invest more in current reproduction th an males. Parents also distributed food differently to male and female chic ks. Large males were fed more than all other nestlings, while female nestli ngs were fed equally irrespective of size. This study confirms that complex patterns of parental allocation occur in wild populations. (C) 1999 The As sociation for the Study of Animal Behaviour.