Increased sensitivity of common murres to top-down disturbance by bald eagles during poor foraging conditions of a marine heatwave

• Main Authors: 3rd World Seabird Conference 2021, Orben, Rachael, Porquez, Jessica
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Underline Science Inc. 2021
• Subjects: Climate Change; Ecosystem; Animal Science; Animal Biology; Medina; Pacific; Uria aalge; Alaska; uria
• Online Access: https://dx.doi.org/10.48448/xpgw-4s13; https://underline.io/lecture/35476-increased-sensitivity-of-common-murres-to-top-down-disturbance-by-bald-eagles-during-poor-foraging-conditions-of-a-marine-heatwave

Abstract: Common murres (Uria aalge) are expected to buffer activity budgets during poor conditions to compensate for low prey availability. However during a marine heatwave (2014-16) in the eastern North Pacific, we found that common murres nesting at Yaquina Head, Oregon, USA had near zero reproductive success (2015-17). Breeding success during this time was compounded by top down pressure from avian predators, primarily bald eagles (Haliaeetus leucocephalus), and while disturbance rates were highest in 2016 (0.495/hr), rates were slightly lower during the other heatwave years (0.29/hr) than preceding (2011-2013, 0.37/hr), when reproductive success was 0.41±0.06. Murres showed multiple signs of prey limitation during heatwave years. Birds caught at-sea near the colony and fitted with Argos-PTTs (2015-2016, n=15) typically foraged 174 km north at the mouth of the Columbia River. Daytime dives and central place foraging trips were notably longer in duration in 2015 than 2013. Feeding delivery rates during heatwave conditions in 2016 were on average the lowest in our time series ~0.15/hr (1999-2002, 2010-present). Fish length was not notably different from average in 2016, thus it appears murres did not compensate by increasing the size of delivered. In assessing heatwave impact, colony structure was also important, as a small subset of birds in nesting locations protected from eagle disturbance hatched chicks, at reduced rates, during peak heatwave years. The effects of the heatwave persisted into 2017, but in 2018 and 2019 reproductive success was high despite the continued occurrences of bald eagle disturbances. This suggests that predation can impede reproductive effort when prey availability was poor, potentially benefiting individuals by preventing investment in breeding, with reduced effect as foraging conditions improve. Our results indicate that murre reproductive success may be more stochastic as marine heatwaves become more common and the impact of these events may be exacerbated by predation at colonies. Authors: Jessica Porquez¹, Rachael Orben¹, Jane Dolliver¹, Stephanie Loredo¹, Ana Medina Roman¹, Donald Lyons², Robert Suryan³ ¹Oregon State University, Hatfield Marine Science Center, ²National Audubon Society, ³NOAA Alaska Fisheries Science Center