Multidecadal comparison of Red-footed Booby Sula sula diet at Ulupa'u Crater, O'ahu, Hawai'i

We describe the diet of Red-footed Boobies Sula sula nesting at Ulupaʻu Crater, Oʻahu, Hawaiʻi based on 106 regurgitations collected during 2014 and 2015. We also compare our results to a diet study at this colony five decades earlier. Both studies indicate that flying squid (Ommastrephidae) and flyingfish (Exocoetidae) are important prey for this population while provisioning chicks. In particular, purpleback flying squid Sthenoteuthis oualaniensis occurred in the majority (>70%) of the recent regurgitation samples, and their size (mantle length <11 cm) indicates that they were mostly juveniles. Moreover, the size distribution of the squid prey varied by year, indicating interannual variability in phenology of spawning and larval development. This study highlights the Red-footed Boobys reliance on the juveniles of this poorly-studied squid, and underscores their value as biological samplers of epipelagic fish and squid within their foraging areas.