Abstract
To estimate age (days old) of Japanese Marsh Warbler Locustella pryeri nestlings, I recorded daily developmental patterns (e.g., pin-feather eruption and eye opening) for 64 nestlings from 14 nests, from hatching to fledging, in Hotoke-numa wetland during the breeding season in 2008 and 2009. These patterns were age-specific, and can be used for estimation of nestling age. In addition, I measured tarsus and natural wing lengths of nestlings and weighed them from 1 to 8 days after hatching. These traits had large variance, and thus were not age-specific; a logistic model might account for the growth patterns of these traits.
