Izu Thrush: Tokara Islands 2004
Fergus Crystal, 15 February 2005
In 2004 I visited the Tokara Islands in the northern Nansei Shoto (Kagoshima-ken) eight times: islands visited were Nakanoshima, Tairajima, Suwanosejima and Akusekijima. I counted the number of singing males of Izu Thrush, Turdus celaenops. along certain trails on the islands. I plan to return in March/ April 2005 to census the same trails. Below is a description of the songs and calls, followed by observations.
Song: Like a deeper, more thrush-like version of Japanese Robin, Erithacus akahige, trilling, 'tsurrrrrr.. turrrrrr.. tzurrrrrrr...(tsizi)', but less distinct and here often drowned out by the more melodious trills of Ryukyu Robin (E. komadori). (The densest population of the latter species in the world is to be found on Nakanoshima: around 1000 pairs.) The trills vary in pitch, with those at mid-pitch sounding a sharper 'inhaling'. Some individuals omit the closing 'tsizi' or 'chizzle' sound, and some males intersperse the trills with an abrupt 'chik!' Song perches are often situated two meters or more up in the umbrella spokes of pine crowns on Suwanosejima (where this species is common), or additionally in darker forest on perches/ buttress roots of dark evergreen trees in the lusher forest of Nakanoshima (where it is less common). Singing occurs from mid-March to early July. The place to see this species is without doubt Suwanosejima, where it is commonly encountered in woodland (including in the village near plots, etc.) right up to the tree line not far from the crater of the active volcano there. The bubbling alarm call is deeper and more guttural than that of Pale Thrush (T. pallidus) or Brown Thrush (T. chrysolaus). This is often a good identification feature when trying to separate female or first-year celaenops from chrysolaus (particularly similar ssp. orii, which has been recorded on migration in the Tokara Islands). Males exhibit a strange alert posture, freezing near an intruder with their breasts puffed out, heads tucked back and tails cocked.
Nakanoshima: seven males noted along a 3-km track through forest from the village up to the farm fields, 17 April 2004. Two were also heard near Oike Pond in the north-central area of the island. Population estimate is about 20 pairs for the whole island (judging by habitat availability) although I have still not checked the pine-clad slopes of the volcano, which may prove to be more productive. Tairajima: I have not yet recorded this species here, on 5 visits in different seasons, but individuals are recorded annually (last was in June 2004 at the school, per Imai Noboyuki). Akusekijima: not noted in apparently suitable habitat 8th and 9th May 2004. I am unaware of any records for this island yet. Suwanosejima: 27 males heard along an 8-km circular walk around the south of the island, up to the crater, 26-27 June 2004. Males perched more in the open and were less wary than on Nakanoshima. Population estimate about 120 birds with 40-50 singing males. The north of the island, as a result of lava flows, has little suitable habitat.