Monitoring Breeding Performance of the Black-tailed Gull<i>Larus crassirostris</i> on Kabushima Island, Japan, from 2012 to 2020

We monitored the breeding performance of Black-tailed Gulls Larus crassirostris on Kabushima Island, which has been connected to Honshu Island by a manmade isthmus since the 1940’s, from 2012 to 2020. The mean number of eggs per nest on 13–20 May between 2014 and 2020 (2.01‒2.16 egg/nest), except for 2019, was higher than that in 2012, 2013, and 2019 (1.57‒1.80 egg/nest). However, the number of chicks on 5–15 July per number of eggs on 13–20 May in 2014 and 2020 (0.01‒0.17 chick/egg) was lower than that in 2012 and 2013 (0.23‒0.29 chick/egg).