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Abstract

Eboshijima, Japan is a small island in the Tsushima Strait that hosts a small colony of Japanese Murrelet Synthliboramphus wumizusume, an endangered seabird that breeds in the warm Kuroshio Current region around Japan and South Korea. We conducted a study to investigate the effects of depredation by Large-billed Crows Corvus macrorhynchos on murrelets after discovering 29 carcasses and 50 eggshells depredated by crows in four survey plots at Eboshijima in 2022. Trail cameras captured crows during daylight hours from 06h59 to 16h45. To estimate the existing population of Japanese Murrelet and predict scenarios that demonstrate the effects of corvid depredation on the murrelet population, we used a return-time (RET) capture-mark-recapture model. We evaluated the murrelet population using the best-fitting RET model and the capture histories of 187 murrelets mist-netted on Eboshijima during 2013–2022. We then simulated 1 000 iterations of a 50-year population using scenarios based on the parameters obtained from the best-fitting model. Our simulations indicate that corvid depredation could lead to the extirpation of the murrelet population, with no individuals remaining within 17 years. However, by reducing the corvid depredation effect by 50%, the probability of extinction can be lowered to less than 50% over the next 50 years. Therefore, we recommend implementing a crow translocation or removal program to protect the Eboshijima murrelet population. Additionally, further research should be conducted to identify breeding and non-breeding individuals, as well as active nesting sites.

DOI

http://doi.org/10.5038/2074-1235.51.2.1530

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