Arctic Warbler (Phylloscopus borealis) — Vorstman's Guide to the Birds of North America

Voice

The song is a fast, dry rattle on one pitch, two to four seconds long, suggesting an insect or a sewing machine rather than a songbird. It comes from the top of a willow, after which the bird drops straight back into the bush. The call is a hard, short dzik, like a spark jumping, and that sound betrays it more often than the song does. Nothing else in Alaskan scrub sounds like it: the Ruby-crowned Kinglet, the only other singer there that is as loud, sings in tumbling melodic phrases instead.

Listen: SongXC1173319

Recording: Anne McCormack — CC BY-NC-SA 4.0 · Nome, Nome Census Area, Alaska, United States · xeno-canto

Identification

Eleven to thirteen centimetres, and sturdily built for a leaf warbler: a large head, a broad-based bill and a short tail. It is olive-grey above and dirty white below with a greyish wash on the flanks. The face decides it: a long yellowish-white eyebrow stripe running from the bill to well behind the eye, often curling up slightly at the end, with a dark eyestripe beneath it. There is usually one narrow, faint wingbar, which wears away as the summer goes on. The lower mandible is orangey with a dark tip and the legs are pale brownish pink; male and female look the same.

Confusion species

In Alaska the mistake is nearly always the Orange-crowned Warbler (Leiothlypis celata): yellower, with yellow undertail coverts, a thin pointed bill and never a wingbar, and its face lacks the sharply drawn eyebrow stripe. The Ruby-crowned Kinglet has a bold white eye-ring, a broad white wingbar with a black bar behind it, and a minute bill. On the Bering Sea islands the Kamchatka Leaf Warbler (Phylloscopus examinandus) may turn up, counted as the same species until 2015; it is known by its slower, lower song and its slightly longer bill. All three cases are settled by sound in a second and sometimes not by sight in ten minutes.

Habitat

Dense willow and dwarf birch scrub along creeks, lake edges and wet hollows, and the shrubby transition to scattered, stunted spruce. It needs shrubs of head height: bare tundra it passes by, and closed forest as well. The scrub must also be damp; on dry slopes it is absent. In the wintering areas of Southeast Asia it keeps to forest, forest edge and old second growth, from the coast to high in the mountains.

Where the bird is most often found, arranged by the USNVC — the vegetation classification of the United States and Canada — and CMECS for sea and coast.

Range and movements

It breeds in western and central Alaska — the Seward Peninsula, the lower Yukon and Kuskokwim, and the foothills of the Alaska Range and the Brooks Range — and beyond that across northern Eurasia from Scandinavia to Kamchatka. In August it leaves westward across the Bering Strait and then travels through eastern Asia to the Philippines, Indonesia and mainland Southeast Asia. Those wintering grounds lie outside this map; the map therefore shows only its breeding range in Alaska. In the rest of North America it does not appear, apart from the odd autumn record on the coast of California — it shares with the Northern Wheatear the trait of leaving the continent in the wrong direction.

Breeding (summer)
Passage
dark = core range, pale = thinly spread

The map is a density field, not a drawn range boundary: it is built from the records themselves and therefore does not follow state or national borders. Both the seasonal colour and the depth of colour come, cell by cell, from the records of GBIF (2006–2026), counted per 0,7° cell and divided by all bird records in that same cell, so that the density of birdwatchers does not count. Every cell is counted separately for June–July, December–January and the migration months, and takes the colour of the season that wins there; a cell is only called summer or winter where the other season is nearly empty. Country outlines: Natural Earth (public domain).

Where and when to look

The last week of June on the Seward Peninsula, along the roads that run inland from Nome: stop at every willow thicket beside a creek and listen for the rattle. Before about 5 June it is not there yet; it is one of the last birds to arrive in Alaska, and by late July it sings little. After the first song, wait: the singer comes briefly to the top of a willow every few minutes, and that is the moment for the eyebrow stripe.

Conservation

Least Concern (LC): worldwide this is a matter of more than eighty million birds, of which an estimated 2.5 million breed in Alaska. The Alaskan population has nonetheless fallen steeply over the past thirty years — enough to place the species on the list of common birds in steep decline. The causes are sought above all in the wintering areas, where forest in Southeast Asia is disappearing fast; what warming is doing to its Alaskan scrub has not yet been worked out.

Scientific name

Phylloscopus borealis | (Blasius, 1858)

Blasius described the species in 1858 as Phyllopneuste borealis, from a bird taken in the Sea of Okhotsk; because it was later placed in another genus, author and year stand in parentheses. The genus Phylloscopus was introduced by Boie in 1826, from Greek phullon, 'leaf', and skopos, 'searcher': the bird that searches the leaves. borealis is Latin for 'northern'. The type locality is not a place but a position at sea — 59°38' north, 147°30' east — because the first specimen was collected aboard a ship.