How to identify the Arctic Warbler

To correctly identify the Arctic Warbler (Phylloscopus borealis), check each of these features. Birds can be tricky: habit, habitat, and call often confirm a sighting that a single photo cannot.

Size at a glance

Length

11.5-13 cm (4.5-5.1 in)

Wingspan

18.5-22 cm (7.3-8.7 in)

Weight

7-12.5 g (0.25-0.44 oz)

Physical features to check

1. 1

   Plumage

   Overall feather coloration and pattern.

   Adults are typically plain olive-green on the upperparts, including the crown, nape, back, and rump. The underparts are whitish, often with a grayish wash on the flanks and breast. A key feature is a prominent yellowish-white supercilium (eyebrow stripe) that extends well beyond the eye. There is also a distinct pale wing-bar on the greater coverts, and often a fainter or less complete bar on the median coverts. The flight feathers and tail are dark brown with narrow pale edgings. The tertials have prominent pale edges, creating a pale panel on the folded wing.

2. 2

   Beak shape

   Shape and color of the bill: a key field mark.

   Small, slender, and pointed; typically dark brown to black above and yellowish or orange at the base of the lower mandible.

3. 3

   Eye color

   Iris color and any distinctive eye markings.

   Dark brown.

4. 4

   Leg color

   Leg and foot color.

   Pale flesh-colored or yellowish-brown.

5. 5

   Distinguishing features

   Standout features that separate this species.

   Erect posture, prominent yellowish supercilium, single distinctive pale wing-bar (sometimes a fainter second bar), and pale legs. Its overall appearance is quite 'plain' compared to many other warblers, but the combination of its wing-bar and supercilium is key.

6. 6

   Juvenile appearance

   How young birds differ from adults.

   Juveniles resemble adults but often have a slightly brighter, more yellowish wash on the underparts, especially the flanks and throat. The wing-bar might be slightly less distinct than in adults, but still present.

7. 7

   Seasonal changes

   Plumage variation between breeding and non-breeding seasons.

   Plumage does not undergo significant seasonal changes. Birds appear slightly fresher and greener after the complete post-breeding molt in autumn, and can look a bit duller and browner by spring due to feather wear.

8. 8

   Sexual dimorphism

   How males and females differ.

   Males and females are visually identical in plumage.

Key field marks

• Supercilium. Look for a very prominent, long, yellowish-white stripe above the eye, extending well behind it.
• Wing-bar. Observe for a distinct single pale wing-bar (on the greater coverts). A fainter second bar on the median coverts can sometimes be present but is less reliable.
• Leg Color. Note the pale, flesh-colored or yellowish-brown legs, which contrast with the darker legs of many similar warblers.
• Plumage Color. Olive-green upperparts and pale whitish underparts. It generally has a 'cleaner' and slightly brighter overall appearance compared to some duller leaf warblers.
• Song. Listen for its characteristic loud, rapid, and whirring 'zhweezh-zhweezh-zhweezh' song, which is quite distinctive and insect-like. This is often the best identification feature in breeding areas.
• Behavior. Observe its active foraging style, constantly moving and gleaning insects from foliage or making short sallies.

Explore the Arctic Warbler