I was particularly interested in this race of the Eurasian Skylark. I had studied geographic variation
in this species with respect to a vagrant which occurred in California and came to the conclusion that japonica
was misclassified as a race of A. arvensis. I had thought it was better classified as a race of the Oriental
Skylark (A. gulgula) or possibly a separate species. Russian ornithologists have reported sympatry between
japonica and other races of arvensis in Sakhalin and the Kuriles. If valid, the Japanese bird cannot
be a race of arvensis. (Brazil 2009). I was impressed by the buffy tips to the secondaries (in flight), the proportionately long, thin bill and short primary projection compared to A. arvensis. All of these features are more like A. gulgula which is resident in China. Also japonica is non-migratory unlike all other races of A. arvensis but like most populations of gulgula. This photo shows the rusty wing panel formed by the edges of the primaries typical of A. gulgula.
These birds called frequently and their vocalizations sounded thinner, drier, and higher pitched than what I expect from A. arvensis. Canon PowerShot SX50 HS.
References:
Brazil, M. 2009. Birds of East Asia. Princeton Univ. Press.
Campbell, R. Wayne, L. M. Van Damme and Stephen R. Johnson.(1997). Eurasian Skylark (Alauda arvensis), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/skylar
Donald, P. & Garcia, E.F.J. (2017). Eurasian Skylark (Alauda arvensis). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/57680 on 19 June 2017).
Morlan, J. and R. A. Erickson. 1983. A Eurasian Skylark at Point Reyes, California, with notes on skylark identification and systematics. Western Birds 14:113-126. [PDF]