First Insights into the Breeding Behaviour of an Ex Situ Population of Northern Rockhopper Penguins (Eudyptes moseleyi)

The northern rockhopper penguin (Eudyptes moseleyi) is an endangered species undergoing continued population decline, making ex situ conservation and evidence-based breeding management increasingly important. Yet, behavioural data from ex situ populations remain limited. We provide the first systematic assessment of selected breeding-related behaviours in 13 pairs at Vienna Zoo during the 2024 breeding season using focal video observations. We quantified sex-specific investment in incubation, brooding and nest building, recorded agonistic interactions and nest-material competition, and derived composite indices of pair bonding, coordination, conflict exposure, and aggression initiation. Females contributed significantly more to incubation, whereas males invested more time in nest building, initiated more contact aggression and stole nest material more frequently. Males also received more non-contact aggression but fewer contact aggression events. Higher pair coordination was associated with lower conflict exposure, but the behavioural indices did not reliably predict reproductive success. Birth-origin composition (zoo versus wild-born) was associated with breeding outcome, with mixed-origin pairs showing lower breeding success than same-origin pairs. This exploratory association should be interpreted cautiously given the small sample size and possible confounding by demographic or pair-history characteristics. Our findings identify complementary sex-specific roles, nest-material competition and pair-level coordination as components of ex situ breeding behaviour.