From recruitment to senescence: food shapes the age‐dependent pattern of breeding performance in a long‐lived bird

Abstract

We used a long-term data set (26 years) from Audouin's Gull (Larus audouinii), a long-lived seabird, to address the relationship between the age-dependent pattern of reproductive performance and environmental conditions during breeding. Although theoretical models predict that the youngest and oldest breeders (due to inexperience and senescence, respectively) will perform less well than intermediate age classes, few empirical data exist regarding how this expected pattern varies with food availability. To assess the influence of age and food availability (corrected by population size of the main consumers to take into account density dependence) on a number of breeding parameters (laying dates, egg volume, clutch size, and hatching success), we modeled mean and variances of these parameters by incorporating heterogeneity into generalized linear models. All parameters varied with age and to different degrees, depending on food availability. As expected, performance improved with increased food supply, and the observed age pattern was quadratic, with poorer breeding performances occurring in extreme ages. For most parameters (except for laying dates, for which age and food did not interact), the pattern changed with food somewhat unexpectedly; the differences in performance between age classes were higher (i.e., the quadratic pattern was more noticeable) when food was more readily available than when food availability was lower. We suggest that, under poor environmental conditions, only high-quality individuals of the younger and older birds bred and that the differences in breeding performance between age classes were smaller. Although variances for egg volume were constant, variances for laying dates were highest for the youngest breeders and tended to decrease with age, either due to the selection of higher-quality individuals or to a greater frequency of birds skipping breeding with age, especially when food was in low supply. Our results show that mean and variances of breeding parameters changed with age, but that this pattern was different for each parameter and also varied according to food availability. It is likely that, other than food, certain additional factors (e.g., sex, cohort effects, density dependence) also influence changes in breeding performance with age, and this may preclude the finding of a common pattern among traits and among studies on different taxa.

Forage fish abundance is a predictor of timing of breeding and hatching brood size in a coastal seabird

“…This is an important finding because it strongly indicates that the population increase in years of peak prey abundance mainly reflects re duced nonbreeding among experienced breeders and is not caused by increased recruitment of young birds that would tend to lay late and smaller clutches (e.g. Saether 1990, Oro et al 2014 dropped to only 60 to 71% of that in the adjacent years and the biomass of 1 yr old saithe in the shag diet (24%) was nearly one third of the average (61%) for the other years in the period 2007 to 2012 (S.-H. Lorentsen unpubl. data).…”

Telomere length is a strong predictor of foraging behavior in a long‐lived seabird

“…In addition, we predict birds with deteriorated telomeres will spend less time underwater, indicating decreased foraging efficiency. Foraging efficiency declines with age in several seabird species (Oro et al 2014) and may be a driver of aging patterns overall (Lecomte et al 2010), although in some species foraging efficiency or success increased with age (Desrochers 1992, Rutz et al 2006, Le Vaillant et al 2013. Lastly, we predict that the stable isotope signatures of birds with short telomeres will indicate more inshore prey (if they forage closer to the colony) and lower trophic levels, since they cannot specialize on high quality, high trophiclevel prey.…”

The influence of environmental conditions on the age pattern in breeding performance in a transequatorial migratory seabird

“…Aside from the increase in breeding performance with age, several studies of long-lived animals have reported a decline in performance as a result of senescence (Vieyra et al, 2009;Pardo et al, 2013;Oro et al, 2014). We did not find a similar pattern, however the lack of senescence in our study may either be due to the small sample size (i.e., a lack of statistical power owing that there were only 4 individuals older than 20 years of age), to an increase of skip breeding with age, or to within-cohort phenotypic selection hiding senescence patterns (Cam et al, 2002).…”

“…Despite this, few studies have ever examined at the same time how environmental conditions affect age patterns in breeding performance (Bunce et al, 2005;Pardo et al, 2013;Oro et al, 2014). Depending on environmental conditions, different age patterns can exist (see Oro et al, 2014): in most studies, either (a) differences among age classes in breeding performance were found to decrease under better environmental conditions (Sydeman et al, 1991;Laaksonen et al, 2002;Barbraud and Weimerskirch, 2005;Bunce et al, 2005) or (b) environmental conditions had no clear influence on breeding performance (Nevoux et al, 2007;Vieyra et al, 2009;Lee, 2011;Pardo et al, 2013); just one study found that differences between age-classes were greater under favorable environmental conditions (Oro et al, 2014).…”