Izu Thrush

Izu Trush, May 2013, Miyake Is., Japan

It’s not widely known, but Japan’s capital, Tokyo, extends far to the south through a long chain of volcanic islands. The northern part of this chain is called the Izu Islands, home to several bird species and subspecies found nowhere else.

Among them, one of the most iconic is the Izu Thrush. It inhabits only certain islands in the Izu group, as well as some of the Tokara Islands far to the west. How did this bird end up split between such distant archipelagos over the course of evolution?

It is thought that the ancestor of the Izu Thrush once ranged over a wider area, but was separated into isolated populations by climatic changes. The group isolated in the Izu Islands evolved into the present Izu Thrush. Later, some individuals may have dispersed farther south to the Tokara Islands and Yakushima (where it no longer occurs today). Genetic studies have shown several base-pair differences between the Izu Thrushes of the Tokara and Izu populations.

At this point, many readers may have noticed something — that species similar to the Izu Thrush, such as the Island Thrush, are found in Taiwan, Borneo, the Philippines, and New Guinea. Imagining the connections among these island thrushes is another fascinating aspect of their story.