The Grey Wagtail is a common bird by flowing water, preferring the mid to upper stream of a river. Along with displaying the characteristic tail pump of the wagtail family, the Grey Wagtail is one of three species with yellow on its underside, but is the only one that is commonly seen throughout the year (however, it is only a summer bird in Hokkaido, and a winter bird in the southern islands). Its repeated call of “Chi-chin, chi-chin” is similar to the White Wagtail, and its song sounds like “Tzi-tzi-tzi.”
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Wagtails are commonly found in watery habitats and all share a similar diet mainly consisting of insects, but the Grey Wagtail prefers the mid to upper stream of narrow rivers while the Japanese Wagtail prefers the midstream, and the White Wagtail can often be seen in downstream reaches and other areas away from water completely. The Yellow Wagtail, which is yellow on its underside like the Grey Wagtail, breeds in the northern part of Hokkaido only, and the Citrine Wagtail is a rare passage migrant. Such differences among relatives that have very similar food sources and habits are vital to avoid competition between them.
The background of biodiversity is the reality that many creatures become food for other creatures, and since rivalry in mating (passing on DNA) and other areas of life occurs even among individuals of the same species, there is a constant battle for survival and also securing a mate. On the other hand, it can be said that in the harsh natural world there is also a mechanism for avoiding conflicts.
When asked why wagtails wag their tail, some say in a fit of desperation, “If they shake their neck it will make their eyes spin.” In the profile of the White Wagtail, it was explained that the reason why is not really known, but it seems that the action of wagging or pumping the tail has nothing to do with gender, the season, or for catching food, rather, the tendency to pump the tail vigorously occurs when in a state of alarm, so it is believed to most likely be a warning signal of predators nearby.
Incidentally, in Japan the Grey Wagtail is called ki-sekirei (which means yellow wagtail in Japanese). The bird known as the Yellow Wagtail in English is called tsumenaga-sekirei in Japanese. The reason for this is that the English name of many birds has been decided in the United Kingdom, and since the tsumenaga-sekirei commonly breeds in the United Kingdom, it could be that it was named Yellow Wagtail first there.
The summer plumage of the male includes a black throat (some females also have a black throat but it is not completely black). Both the male and female Yellow Wagtail and Citrine Wagtail have black legs in summer and winter, and their voice is less sharp.
Winter plumage has lighter yellow coloring and less yellow part than summer plumage (Most males have darker yellow coloring than females, but there is also individual difference). At the time of autumn migration when their winter plumage has come in, they can also appear in places where they are not usually seen.