Foraging strategies of Adélie penguins: adjusting body condition to cope with environmental variability

Abstract

Animals modulate breeding effort by balancing investment in self-maintenance against investment in their young, potentially impacting reproductive success when faced with difficult conditions. This life history trade-off model has been evaluated for flying birds, especially those that forage over large pelagic regions of relatively sparse prey availability. We evaluated its applicability to penguins which, lacking flight, depend on reliably available prey relatively close to colonies. We used transponders and an automated weighing system to monitor 40 to 75 breeding Adélie penguins Pygoscelis adeliae per season for 10 seasons, while environmental conditions varied dramatically, measuring foraging trip duration, parental mass change, and total food load delivered to chicks. Parents that lost the most mass during breeding provided more food to chicks while maintaining their own condition. In contrast, in years when adult mass was lower to begin with, parents recovered their own condition and delivered less food to chicks. Food loads were also related to environmental variables, with parents making longer trips and delivering less food when access to prey was more difficult, but delivering more food to 2-chick broods than to 1-chick broods. Penguins did not alternate between short (chick provisioning) and long (self-maintenance) trips, as has been observed in farranging seabirds. Nevertheless, our results indicate they regulated their condition depending on environmental and physiological factors, with impacts on the amount of food delivered to young and pre-fledging mass. Parental choice of multiple foraging habitats and depletion of prey in the nearest habitat due to intraspecific competition have important implications in explaining contrasting patterns observed among studies investigating the life history trade-off model in birds.

Plasticity in foraging strategies of inshore birds: how Little Penguins maintain body reserves while feeding offspring

“…It is interesting to note that this plasticity was not observed in another inshore penguin, the Ade´lie Penguin (Ballard et al 2010), perhaps due to the smaller and inflexible time window to breed at the Antarctic continent. Explanations for bimodal strategies in inshore species thus warrant further investigations, and using data-loggers to investigate potential differences in foraging areas and/or diving behavior between short and long trips, should provide valuable insight on behavioral adaptations to a fluctuating environment.…”

“…offshore seabirds, but virtually never observed in inshore species. Inshore seabirds do not rely on distant food resources and usually perform short foraging trips to coastal areas close to their breeding sites, as, for instance, in Black-browed and Shy Albatrosses, or Ade´lie Penguins (Weimerskirch et al 1986, Hedd 1998, Ballard et al 2010. Some inshore species also exhibit a dual pattern of short and long trips either in duration or distance (see murres in Benvenuti et al 1998 and Gentoo Penguins in Lescroe¨l and Bost 2005).…”

“…Yet, when food supply changes within the foraging range, virtually nothing is known on whether and how inshore seabirds adapt their foraging strategies to continue provisioning food both for themselves and their offspring. A recent study on breeding Ade´lie Penguins, Pygoscelis Adeliae, showed that changes in environmental conditions (such as ice cover or presence of icebergs) affected their foraging behavior, with less food brought back to the chicks, longer foraging trips, and higher body mass loss for the parents along the season (Ballard et al 2010). However, no concomitant change in the foraging strategy was observed (Ballard et al 2010), and Ade´lie Penguins seemed unable to respond to these changes.…”

Trophic cascades in the western Ross Sea, Antarctica: revisited

“…We used the WB data for these (instead of the Splash data) for 2 reasons: (1) WB provided an independent estimate of FTD from a relatively large number of penguins per day, enabling a more complete basis for inferring colonywide patterns (e.g. Ballard et al 2010, Lescröel et al 2010, 2014; and (2) WB data were of higher temporal resolution because sampling was continuous, whereas Splash tag satellite positions are only available when Argos positions are available (on the order of every 1 to 6 h). During this period, we also assessed the chicks' diet by observing the color and consistency of food boluses; pink paste was considered to be krill, and gray, more granular food was determined to be fish (Ainley et al 2006, Whitehead et al 2015.…”

“…First, we used a mixed-effects generalized linear model to assess the effect of time in season (day of year) on FTD from the WB data, controlling for penguin identity as a random effect and sex as a fixed effect (males make shorter duration trips than females; Ballard et al 2001Ballard et al , 2010.…”