2020 Volume 52 Issue 2 Pages 63-82
In 2013, we conducted nest monitoring of Japanese Murrelets Synthliboramphus wumizusume at Birojima in Miyazaki, Japan, the largest colony in the world. Our goals were to: (1) establish standardized monitoring protocols for a large sample of nests; (2) determine hatching success, clutch failure, and timing of breeding; and (3) obtain information on egg and adult predation. Monitoring was conducted at 40 nests located in upper-island boulder fields, shoreline caves, and a concrete stairway wall. Peak egg-laying occurred in early March (8 Mar±7 days, 22 Feb–31 Mar; mean±SD, range, n=24 clutches). Mean clutch size was 1.84±0.37 eggs (n=32 clutches). We recorded 30 (77%) hatched clutches, nine (23%) abandoned clutches, and one clutch with an unknown fate. No depredated or missing eggs were recorded at monitored nests. Predation of breeding adults probably accounted for all nine abandoned clutches. We found 19 depredated murrelet eggs and 60–65 adult remains during searches of upper island and shoreline habitats. All depredated eggs and most depredated adults were attributed to Carrion Corvus corone and Large-billed C. macrorhynchos crows, although Peregrine Falcons Falco peregrinus and Ural Owls Strix uralensis were also present and presumably preyed on murrelets. Hatching success was higher in 2013 compared to the limited data available from Birojima and other colonies. More information on the factors affecting breeding success and predation is needed to better protect this vulnerable species; therefore, establishment of a standardized long-term monitoring program at Birojima and other key colonies should be a priority. Basic protocols for monitoring population trends, hatching success, and timing of breeding at Birojima should include: (1) annual nest monitoring conducted throughout the breeding season; (2) a variable 5–10 day interval between nest checks; and (3) checking all potential nests in discrete plots as opposed to monitoring only previously marked nests.
