Campbell, B.& Lack, E.(1985) A Dictionary of Birds, T & AD Poyser, 670p.
Cramp, S.& Brooks, D.(eds)(1992) The Birds of the Western Palearctic, Vol. VI, Oxford UP, 728p.
Fujimaki, Y.(2008) Check-list of the Birds of Hokkaido (2nd ed., Supplement), http://www16.ocn.ne.jp/~bonasa/list.html (accessed 2008-8-25)(in Japanese).
Kotaka, N.& Matsuoka, S.(2002) Secondary users of great spotted woodpecker (Dendrocopos major) nest cavities in urban and suburban forests in Sapporo City, northern Japan, Ornithological Science, 1, 117-122.
Martens, J.(1980) Lautäuβerungen, verwandtschaftliche Beziehungen und Verbreitungsgeschichte asiatischer Laubsänger (Phylloscopus), Advances in Ethology 22, 1-71p.