Interannual variation in breeding performance, chick growth, and feeding parameters in a small pelagic seabird (Hydrobates melania, Hydrobatidae)

Abstract Changing environmental conditions affect the breeding biology and feeding parameters of seabirds. Understanding how species and populations respond to ocean climate variations and extreme events is crucial for evaluating their vulnerability. This study examined how the breeding performance, chick growth, and provisioning rates of black storm-petrels ( Hydrobates melania ) at San Benito Oeste Island, Mexico (28°18’12’’ N, 115°35’24’’ W), varied interannually over six breeding seasons (2012–2017), and how they were affected by variations in ocean conditions. Large-scale climate indices, including the Oceanic Niño Index, Pacific Decadal Oscillation, and North Pacific Gyre Oscillation, were analyzed alongside local oceanographic conditions (sea-surface temperature, coastal upwelling, chlorophyll- a concentration). Oceanographic conditions fluctuated across breeding seasons with warming anomalies in 2014 and 2015. Despite these changes, the population maintained high hatching and fledging success rates (71–90%), except in 2013, when chick mortality reached 48% due to a tropical storm. The timing of hatching and fledging remained consistent across seasons. Conversely, feeding parameters varied significantly across years, with reduced feeding rates observed in 2013 and 2014, leading to chicks with lower body masses at fledging. No significant relationships were found between large-scale climate indices or local oceanographic conditions and chick provisioning and chick growth. These results indicate that the black storm-petrel is resilient to environmental variability but vulnerable to extreme weather conditions and food availability. Further research is needed to understand the role of fine-scale processes and preceding oceanographic conditions in chick provisioning, as well as to evaluate long-term impacts of global warming.