Relative Effects of Hatching Order, Egg-Size Variation, and Parental Quality on Chick Survival in Common Terns

Abstract

I examined the relative importance of factors influencing chick survival in manipulated and natural broods of Common Terns (Sterna hirundo). In nonmanipulated broods of three (modal brood size), egg mass decreased with laying order, siblings hatched asynchronously, and chick survival declined with hatching order. The ratio of a chick's mass to that of its siblings, at the time of brood completion, explained the greatest portion of variation in chick survival in these broods and in manipulated broods in which survival also varied with hatching order. Hatching order was an important component of mass ratio at brood completion. Egg mass did not influence survival in these brood types. In contrast, egg mass was important in manipulated broods in which chicks hatched synchronously and in natural broods of two, for which hatching order did not affect survival. Parental quality, as indicated by the number of a chick's siblings that survived, also had a positive effect on chick survival that was more important than the negative effect of increasing brood size. Length of the incubation period was positively correlated with size of last-laid eggs. My data did not strongly support the brood-reduction hypothesis of hatching asynchrony and egg-size variation. A smaller egg may benefit the last-hatched chick by reducing hatching asynchrony.

Serum immunoglobulin G levels are positively related to reproductive performance in a long-lived seabird, the common tern (Sterna hirundo)

“…In 17 broods, one or two chicks died or disappeared (''brood reduction''). As in earlier studies of common terns (Nisbet 2002), most of the chicks that died or disappeared were the third-hatched (''C-chicks'') or second-hatched (''B-chicks'') within the brood; most had lost body-mass and appeared to have died from starvation, reflecting sibling competition that favors the oldest chick (''A-chick'') in each brood (Bollinger 1994). We classified each brood according to whether brood reduction occurred or not.…”

Telomere length reflects phenotypic quality and costs of reproduction in a long-lived seabird

“…Main causes of early chick mortality are chick abandonment and starvation [36,37]. Chick mortality is highest during the first week of life, and quality differences in parental care become apparent at this stage [37]. The reproductive success in our study colony was on average 0.5 fledglings pair 21 yr 21 between 2002 and 2009 [38], and thus in most years only high quality individuals succeeded in raising chicks to fledging.…”

“…Both sexes provide parental care, but in the first days after hatching females are mainly brooding and, over the entire chick-rearing period, chick feeding effort of males exceeds females' by a factor of three [35]. Main causes of early chick mortality are chick abandonment and starvation [36,37]. Chick mortality is highest during the first week of life, and quality differences in parental care become apparent at this stage [37].…”

Early mortality saves energy: estimating the energetic cost of excess offspring in a seabird

“…Although mortality hazards indeed declined from hatching onwards, relative differences between HOs remained relatively stable with age (figure 1b). Perhaps this increased vulnerability of later hatchlings throughout the pre-fledging phase is an unavoidable epiphenomenon of parents promoting brood reduction with lower baseline investment in later hatchlings, as evident from egg size decreasing with laying order in common terns [35,39]. Alternatively, food shortage may sometimes only occur late in the pre-fledging phase and delay brood reduction.…”

“…This is typical for common terns [34,35] and not indicative of a population with poor reproductive success, as the study population is thriving and numbers of natal philopatric breeders are growing. Instead, producing offspring in excess most likely reflects an evolved response to stochastic offspring mortality (e.g.…”