The roots of a colony: establishment and growth of a Magellanic Penguin breeding site in Patagonia, Argentina

The unique opportunity to record the establishment of seabird colonies provides key insights into population dynamics and habitat use. This is the case of the Magellanic penguin (Spheniscus magellanicus ) colony El Pedral. Located in Patagonia, Argentina, this colony was reported from its first 6 pairs in 2008, and was monitored continuously over 15 years. Annual surveys of breeding pairs were conducted to calculate population growth ( λ ). A remarkable increase in population size, with an average annual growth of 50%, was observed during the study period. Breeding success was measured by recording the number of breeding pairs and fledglings produced, with fluctuations observed between years. Additionally, the expansion of the colony into two main areas was detected, and spatial occupancy was evaluated using GPS mapping. Gradual colonization of available habitat was observed, with the first established sector expanding more rapidly than the other. The rapid growth and expansion, along with the variable breeding success observed in our results, highlight the important contribution of immigration in new colonies.