2021 Volume 53 Issue 1 Pages 3-23
The Order Accipitriformes is said to have a standard sequential molt from innermost primary P1 to outermost P10. Recently, a new primary molt pattern has been reported for the Japanese Sparrowhawk Accipiter gularis, starting among the central primary feathers. However, this new sequence has not been fully clarified, and requires further elucidation. Furthermore, other aspects of the species’ molt are poorly known. Here we describe the form of immature Japanese Sparrowhawk molt, including molt sequence, molt timing, and sexual differences in molt. We collected data on the wing molt of immature Japanese Sparrowhawks by means of photographic analysis (146 samples), examination of museum specimens (56 samples), and observations of a captive bird. In order to describe the primary and secondary molt sequence, we used two different approaches: one based on the distribution of feather molt, and the other based on asymmetric molt position. In order to estimate sexual, temporal, and geographical variation in molt, we used statistical analysis. These analyses allowed us to discover several unique aspects of molt. Some individuals undergo divergent molt, in a sequence which begins with one of the middle primaries (P4–P6) and proceeds simultaneously in both directions towards the inner and outer primaries, and some molted while wintering. In addition, among divergent molting individuals, males molted earlier than females. Moreover, they molted secondary S2 before S1. Comparisons between ‘non-standard’ molt patterns (and related phenomena such as migration and molt timing) and ‘standard’ molt patterns, may further our understanding of the evolution of molt.
