Chick and juvenile survival of Japanese rock ptarmigan Lagopus muta japonica

Abstract

We estimated clutch size, hatching success, chick survival before independence from hens and juvenile survival after independence in Japanese rock ptarmigan Lagopus muta japonica during 2006‐2012 on Mt. Norikura, Honshu, Japan. The tame behaviour of this subspecies provided us a unique opportunity to observe them at a close range throughout the period from hatching to adulthood. The average clutch size was 5.7 ± 0.1 (± SE). We estimated the average hatching success to be 0.602 ± 0.880, the average nest hatching success to be 0.733 ± 1.071, the average hatchability of successful nests to be 0.907 ± 0.017 and average female survival during June, as an indicator of their survival during laying and the incubation periods, to be 0.905 ± 0.055. We attributed all egg losses to predation by carnivores. Clutch size, nest success, hatchability and female survival during June did not vary among years. Chick survival decreased sharply during the first four weeks of the brooding season. The average annual chick survival until independence was 0.278 ± 0.097, but it varied from 0.096 ± 0.051 to 0.639 ± 0.084. Survival of juveniles after independence was higher than for chicks before independence. Average over‐winter survival of juveniles was larger and was 0.902 ± 0.015. We estimated the average reproductive success of Japanese rock ptarmigan from egg‐laying to one year old to be 0.586 ± 0.883 birds/breeding female. Weather conditions, especially rainfall, during the first two weeks of the brooding season appeared to negatively affect chick survival.