How Do Magellanic Penguins Cope With Variability in Their Access to Prey?

Abstract

Abstract. Movements of animals provisioning offspring by central place foraging extend from short, highly local trips where food is brought back essentially unchanged from its normal condition to extensive interseasonal movement where the offspring are nourished from body reserves built up during the adult's absence from the breeding site. Here, appropriate strategies for maximizing lifetime reproductive success depend on the abundance and location of prey in relation to breeding sites and the energetics and speed of travel of the animal. Magellanic Penguins Spheniscus magellanicus undertake central place movements that are particularly variable during the incubation period; trips may last from a single day to over three weeks depending on colony locality. We reasoned that site-specific variability in prey distribution and abundance is responsible for this. Remote-sensing systems attached to 92 penguins from six different colonies over the species distributional range over the Patagonian Shelf were used to determine space use and foraging patterns in an attempt to understand the observed patterns. Birds in the north and south of the latitudinal range were essentially monophagic, feeding primarily on anchovies Engraulis anchoita and sprats Sprattus fuegensis, respectively, both species that are to be found relatively close to the colonies. Penguins in the center of the distributional range, where these pelagic school fish prey are essentially absent at that time of the year, traveled either north or south, to the same regions utilized by their conspecifics, presumably to exploit the same prey. A simple model is used to clarify patterns and can be used to predict which movement strategy is likely to be best according to colony location. During chick rearing, southerly movement of anchovies and northerly movement of sprats mean that Magellanic Penguins in the center of the distributional range may benefit, although the abundance of these fish is considered to be less than that closer to the Magellanic Penguin range limits. The extensive time involved in the foraging trips during incubation coupled with the postulated poorer prey conditions during the chick-rearing phase may help explain why Magellanic Penguin colony sizes in the center of the range are not elevated.

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

“…Flexible time budgets allow murres to maintain chick-feeding rates and breeding success (Kitaysky et al, 2000) at fairly constant rates over a range of foraging conditions, by allocating more time to foraging when conditions are poor . However, very little is known about how foraging distances vary under different conditions of food availability (e.g., Wilson et al, 2005). While at-sea surveys are useful for broadscale measures of abundance and foraging distribution (Clarke et al, 2003;Trathan et al, 1998), birds enumerated in these surveys can include a high proportion of non-breeding individuals , and it is impossible to determine breeding location when multiple colonies are within commuting distance.…”

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

“…Magellanic penguins occur at Argentinean Patagonia in 29 colonies on the mainland and islands from about 428 S to almost 558 S (Yorio et al 1998, Wilson et al 2005. Our study area extended along ;1000 km of the coast of Chubut province (from 428 S to 468 S latitude; Fig.…”

“…However, inter-colony dietary differences were also reported and these differences followed a latitudinal gradient (Scolaro et al 1999, Wilson et al 2005, Boersma et al 2009 related to the abundance of anchovy (Engraulis anchoita; Scolaro et al 1999, Hansen et al 2001, Wilson et al 2005, Boersma et al 2009). At northern colonies penguins consume anchovy almost exclusively, whereas squid (Loligo spp.…”

“…and Illex spp.) or hake (Merluccius hubbsi ) become much more important in penguin diet at southern colonies (i.e., North Puerto Deseado; Scolaro et al 1999, Forero et al 2002b, Wilson et al 2005.…”

“…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.…”