FITNESS CONSEQUENCES OF PARENTAL BEHAVIOR IN RELATION TO OFFSPRING NUMBER IN A PRECOCIAL SPECIES - THE LESSER SNOW GOOSE

We investigated the relationship between parental behavior and brood s ize, and the consequences of this relationship in terms of parental fi tness (timing of molt and body mass at onset of molt in same year as b reeding, and probability of return, timing of breeding, and clutch siz e in following year) in the precocial Lesser Snow Goose (Chen caerules cens caerulescens) at La Perouse Bay, Manitoba. The percentage of time parent birds spent feeding decreased with increasing brood size, from greater than 90% for pairs without off-spring to less than 80% for br oods of seven and eight. The number of vigilant (head-up) postures per minute by parental birds increased up to brood size five and then dec reased. Parental females also spent significantly less total time feed ing and more time in alert behavior as brood size increased from one t o five goslings. The relationship between parental behavior and brood size remained significant for small brood sizes even if pairs without goslings were excluded (range one to five goslings), and this relation ship was independent of female age. Males (but not females) rearing la rger broods molted later than those with smaller broods, although only by one to two days. This was directly related to rearing of offspring ; in both sexes, birds that hatched four or more goslings and subseque ntly lost one or more goslings during brood-rearing molted significant ly earlier than birds rearing all of their hatched goslings. There was no relationship, in either sex, between number of goslings reared and the adult mass five to six weeks posthatch (molt) in the same year, o r probability of return or timing of breeding (laying date or hatch da te) in the following year. Partners of males that reared the largest n umber of goslings laid significantly larger clutch sizes the following year, suggesting that these were ''better-quality'' pairs. Over the r ange of naturally observed brood sizes, the effect of increasing brood size on parental behavior does not appear to be associated with any n egative effects on residual parental reproductive effort or fitness in this species.