Magellanic Penguins, Spheniscus magellanicus, spend half of the year in open waters and the other half at their colonies. Except on remote islands, this species is easy to study whilst breeding. However, little is known about the complete migration trips and their habitat use in winter.
Magellanic Penguins breed from Isla Algorrobo (in Chile-Pacific Ocean) through Cape Horn to Islote Lobos (in Argentina-Atlantic Ocean). They are currently categorised as Least Concern by the IUCN, and are excellent sentinels of the oceans due to their long latitudinal distribution and abundance.
In a recently published article, we studied the migration trips of three colonies along its Atlantic distribution using geolocators.
Magellanic Penguin with geolocator attached to right foot by Melina Barrionuevo
We found that the distances covered were similar among the colonies, but the penguins used various areas of the Shelf depending on the breeding colony, which are subject to different oceanic features (Sea Surface Temperature, Depth, Chlorophyll-a). Penguins from different colonies also exploited different isotopes niches, partially segregating in all these niches. Additionally, the penguins from northern and central colonies experienced more similar oceanic features whilst foraging within the anchovy range, whereas the southern colony experienced lower SST and lower depths while foraging on sprat.
Figure 2 (adapted) from Barrionuevo et al. 2023: Smoothed first-passage time (in hours) versus sea surface temperature (SST) and colony locations. Peaks in first-passage time are a proxy indication of where tracked penguins found favourable environmental conditions and food. The 2 top bars represent the range and mean thermal preference of the 2 major prey species
Delving into the migratory trips of the southern colony, Cabo Vírgenes, we found a behaviour previously unreported for this species: partial migration. In the paper concerning this we discovered that some penguins travelled as far as 2000 km, whilst 43% of the tracked penguins stayed resident and dispersed within 290 km of the colony. The resident and migratory groups experienced marked differences in their habitats (residents lower Chl-a and 2°C cooler). There appears to be a bias towards females being resident (80% of the residents and 50% of the migrants were female), but further work needs to be done to find out if this behaviour is fixed within the individuals or caused by environmental issues.
The non-breeding dispersals of Magellanic Penguins from three colonies (top) and the different movements of migrants and residents from the Cabo Vírgenes colony (bottom). Adapted from Figure 1a (top; Barrionuevo et al. 2023) and Figure 1a, 1b (bottom; Barrionuevo and Frere 2023)
These studies indicate that Magellanic Penguins breeding along the latitudinal range of Argentina express a broad variation in habitat use (space, oceanic features, and isotopes) during the non-breeding period, and even not migrating when food supplies appear to be enough. It also highlights the importance of the Patagonian Continental Shelf (waters south of 40°S) for this species, not only during breeding season, as it was already known, but also during winter. The Patagonian Continental Shelf is known to be one of the world’s most productive marine areas, however, the region is also a focus for fisheries and economic development (including seismic activities, and offshore exploitation), creating several threats to wildlife. To date, we have not seen a strong effect of these activities on Magellanic Penguin populations. However, we cannot discard cumulative effects in the future, especially since climatic and ocean changes are believed to affect their prey distribution.