Age-Specific Offspring Mortality Economically Tracks Food Abundance in a Piscivorous Seabird

Abstract

Earlier offspring mortality before independence saves resources for kin, which should be more beneficial when food is short. Using 24 years of data on age-specific common tern (Sterna hirundo) chick mortality, best described by the Gompertz function, and estimates of energy consumption per age of mortality, we investigated how energy wasted on nonfledged chicks depends on brood size, hatching order, and annual abundance of herring (Clupea harengus), the main food source. We found mortality directly after hatching (Gompertz baseline mortality) to be high and to increase with decreasing herring abundance. Mortality declined with age at a rate relatively insensitive to herring abundance. The sensitivity of baseline mortality to herring abundance reduced energy wasted on nonfledged chicks when herring was in short supply. Among chicks that did not fledge, last-hatched chicks were less costly than earlier-hatched chicks because of their earlier mortality. However, per hatchling produced, the least energy was wasted on chicks without siblings because their baseline mortality was most sensitive to herring abundance. We suggest that earlier mortality of offspring when food is short facilitates economic adjustment of posthatching parental investment to food abundance but that such economic brood reduction may be constrained by sibling competition.

Telomere length is repeatable, shortens with age and reproductive success, and predicts remaining lifespan in a long‐lived seabird

“…This is the stage when the energetic demand of chicks increases (Vedder, Zhang, & Bouwhuis, ), and before which many chicks die, especially in years with low food availability (Vedder, Zhang, Dänhardt, & Bouwhuis, ). As such, our results suggest that telomere shortening serves as a good proxy for the cost of reproduction (also see Bauch et al, ; Bauch et al, ), and that parents may largely escape this cost if their chicks die early (also see Vedder et al, ). Moreover, we found that only reproductive success in the previous year affected telomere length, while reproductive success in years prior to that had no effect (see for details).…”

Contrasting heterozygosity‐fitness correlations across life in a long‐lived seabird

“…Alternatively, strong selection on a non‐heterozygosity‐related trait can mask any effect of heterozygosity if not corrected for (Annavi et al, ; Arct et al, ; Harrison et al, , but see Ferrer, Garcia‐Navas, Jose Sanz, & Ortego, ; Forcada & Hoffman, ; Lesbarreres, Primmer, Laurila, & Merila, ). In our colony, variation in fledging success is to a large extent explained by unpredictable and variable food supplies (Daenhardt & Becker, ; Vedder et al, ) and, owing to an efficient brood reduction strategy, hatchling mortality peaks within the first week of life and is strongly biased towards second and third hatchlings (Vedder et al, ). Moreover, fledging success covaries with laying date, such that hatchlings from earlier broods have an increased fledging probability.…”

“…Later‐hatched chicks receive less food, grow more slowly, have a lower fledging mass (Becker & Wink, ), have a lower fledging probability and die at a younger age (Vedder et al, ) than their earlier‐hatched siblings. In addition, fledging success is known to be affected by brood size, such that a first chick's fledging probability is higher in broods with one or two siblings than when it is alone (Vedder et al, ; Vedder, Zhang, Dänhardt, & Bouwhuis, in revision). To correct for these two aspects of a chick's natal environment, that affect fledging probability, but not later life stages (Vedder et al, in revision), we constructed a six‐level categorical variable of all possible combinations of brood size and hatching order (1.1, 2.1, 2.2, 3.1, 3.2, 3.3), hereafter referred to as BSHO categories.…”

“…In addition, fledging success is known to be affected by brood size, such that a first chick's fledging probability is higher in broods with one or two siblings than when it is alone (Vedder et al, ; Vedder, Zhang, Dänhardt, & Bouwhuis, in revision). To correct for these two aspects of a chick's natal environment, that affect fledging probability, but not later life stages (Vedder et al, in revision), we constructed a six‐level categorical variable of all possible combinations of brood size and hatching order (1.1, 2.1, 2.2, 3.1, 3.2, 3.3), hereafter referred to as BSHO categories. Finally, because fledging success is known to be higher in broods produced earlier in the season (Dobson, Becker, Arnaud, Bouwhuis, & Charmantier, ), we used the Julian date of laying of the first egg of each clutch to describe a chick's natal environment as well.…”

How fitness consequences of early‐life conditions vary with age in a long‐lived seabird: A Bayesian multivariate analysis of age‐specific reproductive values

“…If parents decrease postnatal investment in reproduction, an offspring's competitive rank relative to its siblings becomes an important component of the quality of its developmental conditions (Mock & Parker, 1997). Parents may benefit from promoting competitive asymmetries among their offspring from the start, because by forming stable hierarchies, or inducing rapid mortality of low‐ranked offspring, resources wasted on sibling rivalry can be reduced (Caldwell Hahn, 1981; Lack, 1947; Mock & Ploger, 1987; Vedder et al., 2017, 2019).…”