Offspring body condition and immunocompetence are negatively affected by high breeding densities in a colonial seabird: a multiscale approach

Abstract

Why avian colonies vary in size and how food competition among nearby colonies a¡ects o¡spring quality are still not completely understood. We simultaneously examined the e¡ects of four scales of breeding density on two measures of o¡spring viability (body condition and T-cell-mediated immunity) in the colonial Magellanic penguin. Body condition of £edglings was inversely correlated with breeding density within 100 m 2 of nests, and decreased with increasing numbers of breeding pairs competing within the parental foraging ranges (100 km), probably as a result of density-dependent food depletion. The T-cell-mediated immune response was positively correlated with body condition, re£ecting, to some extent, the previous breeding-density e¡ects, and was negatively correlated with colony size, which may be related to social stress. However, given the e¡ect of protein intake on cell immunity, this result could also indicate a thus far neglected cost of coloniality, namely the consumption of low-protein food to compensate for the depletion of optimal prey. These results were not in£uenced by other traits, nor by the current exposure of birds to parasites and diseases, as measured by serological variables. Since body condition and the T-cell-mediated immune response of £edgling birds are indicators of their survival and recruitment prospects, the costs we have identi¢ed can explain variability in colony size in relation to food competition with surrounding colonies, as well as the skewed distribution toward small colonies in this species.

Opposing selective pressures may act on the colony size in a waterbird species

“…Hötker 2000), constraining such activities as foraging and food provisioning, which may reduce chick growth rates and their physical condition (Phillips et al 1998). Our results are consistent with patterns observed in the Magellanic Penguin, where offspring raised in large colonies showed lower body condition and poorer immune response in comparison to chicks from smaller colonies (Tella et al 2001). Since the studied tern colonies were located at the same site and adults used the same foraging grounds, differences in food availability could be excluded as a potential explanation for colony-related variation in chick growth rates and condition.…”

“…Finally, the physical condition of chicks raised in large and dense breeding aggregations may be negatively affected by increased social stress [e.g. in the Magellanic Penguin Spheniscus magellanicus (Tella et al 2001)]. …”

Sex-specific development of cell-mediated immunity under experimentally altered rearing conditions in blue tit nestlings

“…In the majority of studied species, including barn swallows (Hirundo rustica), American kestrels (Falco sparverius), Magellanic penguins (Spheniscus magellanicus), Alpine swifts (Apus melba) and white stork (Ciconia ciconia), male and female nestlings do not differ in cellular immune response (Tella et al 2000(Tella et al , 2001Saino et al 2002;Jovani et al 2004;Bize et al 2005), in Eurasian kestrels and great tits females develop stronger cellmediated immunity than males (Fargallo et al 2002;Tschirren et al 2003) and in blue tits males show stronger cellular response (this study). In some species, sex-related variation in immune function is more complex, e.g.…”

Natural and anthropogenic factors affecting the feeding ecology of a top marine predator, the Magellanic penguin

“…In addition, the abundance and distribution of conspecifics and fishing vessels were expected to influence the diet and foraging distribution of penguins through a density-dependent depletion of optimal (i.e., high-protein) prey types (Tella et al 2001, Forero et al 2002a). We used remote sensing and geographic information systems (GIS) to derive several explanatory variables likely informing marine productivity patterns (Acha et al 2004), fishing pressure (Skewgar et al 2007, Yorio et al 2010, and intra-specific competition (Tella et al 2001, Forero et al 2002a. A species distribution model was used to quantitatively infer the role of different environmental features in explaining the at-sea distribution of penguins and general linear models were used to evaluate the effect of food availability on different dietary metrics (inferred from penguin blood d 13 C and d 15 N values).…”

“…iucnredlist.org; accessed on December 2012), and interacts with humans through fisheries and ecotourism (Yorio et al 2001, Villanueva et al 2012. Magellanic penguins have been the subject of several studies aimed at investi-gating the link between prey availability and diet (e.g., Forero et al 2002a, Wilson et al 2005, spatial distribution of conspecifics (e.g., Wilson et al 2005, Boersma et al 2009, Yorio et al 2010 and reproductive performance (e.g., Tella et al 2001, Forero et al 2002a). However, most previous studies have not addressed large-scale ecological mechanisms in an integrative way.…”