A new settlement for the Magellanic penguin species has been found in Tierra del Fuego, Argentina. The colony at San Juan de Salvamento, Staten Island embodied the fourth colony in the area after the known Franklin Bay (also in Staten Island), Observatorio and Goffré Islands colonies (Schiavini et al. 2005, Raya Rey et al. 2014, Balza et al. 2022). The southern rockhopper penguin colony at San Juan was reported in historical records at least from mid-1800 (Payro 1898). None of these chronicles mention Magellanic penguins nesting in this locality, though individuals from this species were documented swimming in nearby waters and nesting in Observatorio Island (Payro 1898). Since then, the colony was surveyed from the air and boat censuses for other species were performed at the colony entrance without noticing Magellanic penguins breeding (Schiavini 2000, Schiavini and Raya Rey 2001, Schiavini et al. 2004). Thus, we hypothesized that this newfound colony might have been founded in recent years. Population abundance was probably underestimated as the survey occurred during chick rearing instead of during the peak of laying, thus some individuals must have failed by that time and abandoned the nest area (Yorio et al. 1998).
The “seabird paradox” avowed that most seabirds exhibit high rates of philopatry despite their long-distance movements outside the breeding season (Milot et al. 2008). Although the expression of philopatry, quantified by Coulson (2016), is variable among taxa, and within species and influenced by environmental conditions. Nevertheless, evidence of colonization and range expansion have been documented for several penguin species (Frere et al. 1993, Ghys et al. 2008, Kush and Marin 2012, LaRue et al. 2013) including Magellanic penguins (Pozzi et al. 2015, Borboroglu et al. 2022). Magellanic penguins presented a northward expansion in the septentrional limit of the Atlantic range up to 40ºS over several decades (Boersma et al.1990, Carribero et al.1995, Bertellotti and Yorio 2005, Borboroglu et al. 2022). The small colony of Bahia Franklin together with this new colony, 58 km apart from each other, could represent an expansion toward other locations that mirror the situation in the north. Extra evidence is the higher growth rate of the Franklin Bay colony in comparison to the biggest ones (Raya Rey et al. 2014, Balza et al. 2022) as shown for newly settled northern colonies (Pozzi et al. 2015).
Two hypotheses have been offered as drivers to immigration to other breeding sites. The "Habitat Quality" hypothesis proposes that individuals choose to colonize other places when habitat (nest sites or foraging areas nearby) decrease in the natal breeding site. Then the “Individual Quality” hypothesis suggests that poor or less experienced competitors could increase their fitness by pioneering at new sites (Kildaw et al. 2005). Although, we still cannot confirm this colony probably was founded by individuals from the nearby Año Nuevo Islands colonies, Observatorio or Goffré, which by historical records seemed to be older (Schiavini et al. 2005, Balza et al. 2022). These colonies are only 20 km away from the new site and thus within the foraging range for the species during chick rearing (Rosciano et al. 2018), this precludes to lean toward the habitat quality hypothesis at least regarding foraging habitat. However, habitat quality in terms of nesting sites in Observatorio island could be deteriorated given bio-erosion by introduced rabbits (Balza et al. 2022) and probably Magellanic penguins themselves (Quiroga et al. 2020). Bio-erosion leaves a lower quality nesting area at least in terms of available free space for new burrows to dig (Quiroga et al. 2020). As a newly discovered colony we have no trend data, but the point-centered quarter method was reliable to estimate the population size of colony, and it will represent a consistent method for the long-term monitoring of this population.
In northern Patagonia there was no evidence for the individual quality hypothesis given the higher breeding success and growth rate from younger colonies (Pozzi et al. 2015). Nevertheless, productivity alone cannot explain trends with dispersal having a key role (Pozzi et al. 2015).
Seabirds use the presence of conspecific to gather information on new settlement (Reed and Dobson 2993), and penguins are known to establish in places where other penguin species breed (Ghys et al. 2008). Southern rockhopper penguins whose known presence at this locality has been recorded could have been the cue for the first individuals to reach that place. Southern rockhopper and Magellanic penguins sharing nesting areas, although not intermingled, have been registered in other areas (Pütz et al. 2001, Schiavini et al. 2005). However, to our knowledge this is the first location where both species share the entrance to reach the nesting area, which is a rocky ledge typical for southern rockhopper penguins in comparison with the sandy or rocky beach normally occupied by nesting Magellanics. In fact, this would be the Magellanic penguin colony found at the highest altitude.
While detrimental at the individual level, migration and colonization leading to the establishment of colonies at new locations can provide long-term benefits such as gene flow, increased effective population size, and overall, enhanced viability of populations and species (Clobert et al. 2001) and is advantageous in a changing world (Kokko and López Sepulcre 2006). However, that which could represent an advantage for some species could be in detriment of other potential competitors such as these two sibling species. Following the climate change “winners and losers” concepts extended from Antarctic penguins (Forcada et al. 2006, Ainley et al. 2010, Clucas et al. 2014), we may speculate that in subantarctic islands the more generalist in terms of breeding and foraging range, habitats, and diet such as the Magellanic penguins (Boersma et al. 2013) could eventually displace a more restrictive species like southern rockhopper penguins (Pütz et al. 2013). In the Antarctic Peninsula generalist gentoo penguins as climate change winners in recent time expanded their range southward, while chinstrap and Adelie populations as losers of climate change are decreasing (Clucas et al. 2014). Rockhopper populations are suffering considerable declines and although some populations seem to be stable, mass-mortality events related to water temperature mediated food availability are occurring too frequently for populations to recover and thus are considered vulnerable (Birdlife International 2022). In this case Magellanic penguins overlapping ecological niches pose additional stress for this species that already face loss of habitat by invasive species (Pütz et al. 2013).
Penguins are seriously threatened with most species’ populations decreasing throughout their breeding range (Borboroglu and Boersma 2013). In this sense a new colony must be good news for conservation in times of a profound biodiversity loss crisis (Singh 2002). Nevertheless, we need to address implications for other species within the expansion range to have the bigger picture. Lastly, this finding highlights the importance of accounting for the connectivity among colonies and the need to consider metapopulation structure for conservation status of species (LaRue et al. 2013, Pozzi et al. 2015).