Food resource utilisation by the Magellanic penguin evaluated through stable-isotope analysis: segregation by sex and age and influence on offspring quality

Abstract

the species in the study area, did not differ from other fish species (hake) in its δ 15 N value, we used it to represent a fish dietary alternative. Using a 2-source (anchovy and squid) isotopic mixing model, we determined that the mean proportion of anchovy in the diet was 49% for yearlings, 76% for chicks, and 69% and 67% for adult males and females, respectively. Sex and age differences in diet, as revealed by stable isotopes, may be the consequence of individual morphology (sexual size dimorphism) and reproductive constraints imposed by chick development since growing young require more nutritive prey than adults and yearlings. This reasoning would also explain the significant and positive correlation found between proportion of anchovy in the diet and body condition of chicks.

Resource partitioning within a tropical seabird community: new information from stable isotopes

“…Comparison of chick and adult values indicates that adult great frigatebirds foraged in different areas and preyed upon higher trophic level organisms during the non-breeding period. Interestingly, immature great frigatebirds had intermediary δ 13 C and δ 15 N values and segregated from adults by feeding at a lower trophic level, as previously found in the only seabird species so far investigated -the Magellanic penguin (Forero et al 2002).…”

Abrupt recent shift in δ 13 C and δ 15 N values in Adélie penguin eggshell in Antarctica

“…These variations may be due to individual variability in diet, differences by colony, or even the age of the individual. Slight variations in ␦ 15 N (Ϫ0.1 to Ϫ0.3) and ␦ 13 C (Ϫ0.1 to Ϫ0.5) values between adults by sex also were found in the Magellanic penguin (Spheniscus magellanicus) (14), and it is likely that the amount of variation among penguin species is subject to species-specific foraging behavior. Eggshell carbonate carbon and membrane nitrogen data also display a striking decrease in values in the past Ϸ200 years compared with the fossil samples in all three regions of the Antarctic (Fig.…”

“…[reported in either calendar years (cal yr) or 14 C yr] and 57 modern samples from the three regions were analyzed for stable carbon, nitrogen, and oxygen isotopes [supporting information (SI) Tables 2 and 3]. Of the fossil samples, 21 fragments were large enough to divide into two pieces, one for radiocarbon dating and one for stable isotope analysis.…”

“…Since the 1980s, carbon (␦ 13 C) and nitrogen (␦ 15 N) stable isotope values of seabird tissues have been used to address questions on diet and foraging behavior (10)(11)(12)(13)(14). These studies are particularly useful when traditional diet studies (observations of chick feedings and stomach lavage) are difficult to carry out on far-ranging species such as many seabirds.…”

Does location really matter? An inter-colony comparison of seabirds breeding at varying distances from productive oceanographic features in the Bering Sea

“…Parents may therefore feed their offspring higher value prey items than they consume themselves because of the nutritional requirements of growth and development (Forero et al, 2002). It may also benefit central place foragers with limited ability to carry and transport prey to deliver fewer, high quality meals to their offspring while feeding on prey of more variable quality because of the costs of transporting food items (e.g., Davoren and Burger, 1999).…”