Results for “Marine Onithology”

USGS2021

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.

Hawaii↗

USGS2024

Predator disturbance contributed to Common Murre Uria aalge breeding failures in Cook Inlet, Alaska following the 2014–2016 Pacific marine heatwave

The 2014-2016 Pacific marine heatwave caused unprecedented die-offs and multi-year reproductive failures for Common Murres Uria aalge along the west coast of North America. Lingering impacts, such as declines in colony attendance and productivity, have persisted at some colonies following the heatwave and are attributed largely to changes in prey availability and quality. Here, we present evidence of an additional, top-down mechanism contributing to Common Murre breeding failures on Gull Island (Alaska): disturbance of nesting birds by aerial predators and associated egg depredation. We collected time-lapse images over five murre breeding seasons (2016-2020) on Gull Island to document the frequency, duration, and intensity of disturbances caused by aerial predators, as well as to quantify disturbance-associated egg depredation. To identify seasonal and inter-annual variability of disturbances, we calculated a daily disturbance index and compared years using generalized additive models. In all years, Bald Eagles Haliaeetus leucocephalus were the primary cause of disturbance, which led to periods of prolonged colony abandonment by murres and facilitated high levels of murre egg depredation by Glaucous-winged Gulls Larus glaucescens and Herring Gulls L. argentatus . We found that the seasonality of disturbance was an important factor in determining egg depredation rates. In years when disturbance levels were high and persisted later in the season, the colony experienced complete breeding failures due to disturbance-associated egg depredation. Our study revealed that the response of nesting murres to a strong environmental perturbation, such as the Pacific marine heatwave, can be complex and involve multiple stressors from both bottom-up and top-down factors.

Alaska↗