[1] ALSTRÖM, P., SAITOH, T., WILLIAMS, D., NISHIUMI, I., SHIGETA, Y., UEDA, K., IRESTEDT, M., BJÖRKLUND, M. and OLSSON, U. (2011), The Arctic Warbler Phylloscopus borealis– three anciently separated cryptic species revealed. Ibis, 153: 395-410. https://doi.org/10.1111/j.1474-919X.2011.01116.x.