Fitness Consequences of Parental Behavior in Relation to Offspring Number in a Precocial Species: The Lesser Snow Goose

Abstract

We investigated the relationship between parental behavior and brood size, and the consequences of this relationship in terms of parental fitness (timing of molt and body mass at onset of molt in same year as breeding, and probability of return, timing of breeding, and clutch size in following year) in the precocial Lesser Snow Goose (Chen caerulescens caerulescens) at La Pérouse Bay, Manitoba. The percentage of time parent birds spent feeding decreased with increasing brood size, from greater than 90% for pairs without offspring to less than 80% for broods of seven and eight. The number of vigilant (head-up) postures per minute by parental birds increased up to brood size five and then decreased. Parental females also spent significantly less total time feeding and more time in alert behavior as brood size increased from one to 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 relationship was independent of female age. Males (but not females) rearing larger 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 subsequently lost one or more goslings during brood-rearing molted significantly 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, or probability of return or timing of breeding (laying date or hatch date) in the following year. Partners of males that reared the largest number of goslings laid significantly larger clutch sizes the following year, suggesting that these were "better-quality" pairs. Over the range of naturally observed brood sizes, the effect of increasing brood size on parental behavior does not appear to be associated with any negative effects on residual parental reproductive effort or fitness in this species.