How much do penguins take care of their habitat? Population regulation in Magellanic Penguin, Spheniscus magellanicus, at Martillo Island, Beagle Channel, Tierra del Fuego

Habitat degradation is one of the major threats to wildlife populations. Several factors have been found responsible for this degradation. Can a species degrade its own habitat? Between years 2004-2016 we performed censuses of Magellanic penguins (MP) at a colony on Martillo Island. The point-transect methodology was used to estimate nest density (Dn: nests/ha) at each point of a permanent grid, registering new areas colonized over years. In 2016 the degree of erosion was estimated at the same points and then extrapolated to the entire colony area, identifying areas with high, medium and low percentage of degradation (aH, aM, aL, respectively) on the island. Reproductive success, adult body indexes and foraging characteristics were compared among areas. The population increased over years in accordance with nest density, being larger to the east of the island and expanding towards the west on aL areas. In areas with higher Dn the erosion degree was higher (GLM p <0.0001). Particularly, in the aH, the Dn increased until 2012 and then decreased. The reproductive success was similar in the different zones (aH= 1.31 ± 0.91, n=51, aM = 1.4 ± 0.84, n=163, aL: 1.30 ± 0.67, n=10, H=0.58, gl=2, p=0.68) and trophic parameters and body indexes differed between zones without a defined pattern. The MP colony of Martillo Island has been increasing during the last years although evidence suggests a deterioration of habitat with potential implications for population regulation.