MEPS 601:253-267 (2018)  -  DOI: https://doi.org/10.3354/meps12668

ABSTRACT: Overwintering conditions often impact an individual animal’s breeding performance in the following season. These so-called carry-over effects have been demonstrated in birds, including penguins. We studied carry-over effects in Magellanic penguins Spheniscus magellanicus, a species of conservation concern, breeding at Punta Tombo, Argentina, and wintering from northern Argentina to southern Brazil. We characterized oceanographic conditions in the penguins’ wintering grounds from 1982 to 2012 using principal component analysis on weekly sea surface temperature (SST) anomalies. The first principal component represented a weak Rio de la Plata plume and warm SST. The Rio de la Plata plume carries cool, productive, low-salinity water north from the river mouth through the penguins’ wintering area. The plume is stronger (extends farther north) when winds blow from the southwest than when winds blow from the northeast. When the Rio de la Plata plume was weak in late winter, females arrived earlier to breed and were in better condition, likely because prey was concentrated in a smaller plume area closer to Punta Tombo. Females that arrived earlier laid eggs earlier, and females laid larger eggs when they arrived earlier and were in better condition. In contrast, body condition of breeding males did not vary with winter conditions. The effects on individual females varied, likely reflecting in part individual foraging ability. A weaker Rio de la Plata plume probably increased prey encounter rates closer to breeding colonies in winter, directly and indirectly improving female body condition, increasing egg size, and resulting in earlier arrival and egg laying.

KEY WORDS: Carry-over effect · Spheniscus magellanicus · Magellanic penguin · Arrival date · Body condition · Egg-laying date · Egg size