Unusual breeding strategies by African Penguins Spheniscus demersus on Robben Island, South Africa

Abstract

African Penguins Spheniscus demersus are typically monogamous with biparental care. However, this long-term study on individuals of known identity and sex on Robben Island from 2001 to 2023 revealed several alternative parental care strategies. In rare cases (n = 3, 0.3% of monitored breeding attempts by marked birds), individual penguins were observed incubating eggs and provisioning chicks at two different nests simultaneously. Cooperative breeding occurred in approximately 4% of monitored attempts, where three birds raised chicks at a single nest. In one-third of these cases, all three individuals participated from the incubation stage. Most notably, in 18% of breeding attempts where both pair members were sexed, both individuals were females, suggesting same-sex pairing as a significant reproductive strategy in this population, possibly due to an adult sex-bias ratio in the breeding population.