Avian predator control led to increased breeding success of Common Murre Uria aalge on Teuri Island, Hokkaido

Abstract

The population of Common Murre Uria aalge on Teuri Island, northern Hokkaido, Japan declined until nearly extirpated (15 birds with no fledglings) in 2005, despite restoration actions being conducted based on social attraction in a safer nesting site in a cave. Large-billed Crow Corvus macrorhynchos and Slaty-backed Gull Larus schistisagus, predated both eggs and chicks. Since 2011 culling of these avian predators has been conducted and the breeding activities of murres nesting in the cave were monitored with direct observation in 2011 and with video cameras in 2012–2016. The maximum number of birds in the cave increased at an annual rate of 24.4% from 2007 to 2016, raising the population to 38 birds in 2016. The number of fledglings per egg-laid (74%) was higher than that before 2010 (33%). Pairs laying earlier and occupying rock wall, which seemed to be more secure against avian predators, produced more fledglings per egg-laid. Culling of avian predators seemed to allow the increase in productivity. Population viability analysis with this increased productivity indicates that immigration from other colonies is likely, and predicts that in 50 years the population may reach 2,099 birds in the case of sustained adequate conditions of the quality and quantity of habitat including nest sites.