When does the Japanese Bush Warbler sing?

The most distinctive feature of the Japanese bush warbler is its 'Hohokekyo' call.

Only males sing, primarily to declare their territory to other birds or to signal safety to females bringing food. 'Ho' is the intake of breath, and 'Hokekyo' is the exhale.

On the other hand, its soft call, expressed as 'Jaja', is used to intimidate intruders into its territory.

When females hear this soft call, they stop transporting food and hide for the safety of themselves and their nest, a behavior also known as 'crossing the valley.'

In human habitats, this call can be heard in early spring, but in the mountains where they nest, it is heard from early spring through summer. Early spring calls are somewhat awkward, as the birds are still practicing. By the breeding season in summer, they are ready to perform at their peak in the mountains.

Male Japanese bush warblers spend most of their day patrolling their territory, continually calling, often singing over a thousand times a day.

Interestingly, the day when a Japanese bush warbler sings for the first time in the year is known as 'the first singing day,' a sign that spring has arrived.

What is the origin of the Japanese Bush Warbler's name?

The origin of the name 'Uguisu' is subject to various theories, most of which derive from its distinctive call.

While nowadays it is described as 'Hohokekyo', it was once called 'Uguisu'.

Another theory suggests that the name combines 'Ugui', a version of its call, with 'su', a suffix denoting a bird, similar to other birds like crows (Karasu) or jays (Kakesu).

Apart from the call, some believe the name comes from the bird emerging from deep valleys in spring, hence 'deep emergence' morphed into 'Uguisu'.

Its other name, 'Harutsuge-bird', is derived from its habit of starting to sing in lowland areas in early spring. It has other spring-related names like 'Spring Bird' or 'Spring Herald'.

The kanji for 'Uguisu' was adopted from Chinese, but in China, it refers to a different species, the Korean bush warbler, which has a different call and appearance.

In English, it's known as 'Bush Warbler', which refers to its habit of singing from within bushes, aptly describing its natural behavior.

What does the Japanese Bush Warbler eat?

The Japanese bush warbler is omnivorous, varying its diet with the seasons.

In summer, it primarily feeds on small insects, larvae, and spiders, thanks to the abundance of life.

In winter, when fewer living things are available, it relies on seeds and fruits from plants as its main source of nutrition.

When is the breeding season for the Japanese Bush Warbler?

The breeding season for the Japanese bush warbler is in early summer.

They practice their singing in populated areas during early spring and start their courtship behavior and nest-building in the mountains once the breeding season begins. Nests are made from materials like dead bamboo leaves, and a typical clutch contains 4-6 eggs.

The female incubates the eggs for about half a month, and the chicks leave the nest approximately two weeks after hatching.

Japanese bush warblers practice polygyny, where one male may have several female partners who build nests. This strategy increases their chances of leaving more descendants, as eggs and chicks are highly susceptible to predation.

Are Japanese Bush Warblers and White-eyes related?

Japanese bush warblers and white-eyes are often confused, but they belong to different families; the Japanese bush warbler belongs to the Cettiidae family, and the white-eye to the Zosteropidae family.

This confusion likely stems from their similar habitat patterns and the overlap in their depiction with flowers like plums, which are culturally significant but biologically unrelated.

Interestingly, while the uguisu is depicted with plum blossoms in art, it has no real association with plums, unlike the white-eye, which feeds on plum nectar.

Their physical coloration also adds to the confusion. The Japanese bush warbler is generally depicted as vibrant green in confections like 'uguisu mochi,' though its actual color is a duller brownish-green. The white-eye's bright green plumage more closely matches the mochi's color.

Both birds are also visible in spring, furthering the mix-up. Though their calls are quite distinct, visually they can be difficult to distinguish, making it better to identify them by sound rather than appearance.

Who are the predators of the Japanese Bush Warbler?

Predators of the Japanese bush warbler include small birds of prey and snakes, which often prey on their eggs and chicks.

Another significant threat is the cuckoo, which practices brood parasitism by laying its eggs in the nests of bush warblers, often leading to the destruction of the warbler's own eggs and chicks.

However, recent studies have shown that Japanese bush warblers can sometimes detect and expel the intruding cuckoo eggs, although not all individuals possess this ability.