How to identify the Asian Openbill

To correctly identify the Asian Openbill (Anastomus oscitans), 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

68-81 cm

Wingspan

147-150 cm

Weight

1.3-2.0 kg

Physical features to check

1. 1

   Plumage

   Overall feather coloration and pattern.

   Adults are predominantly white or greyish-white, with black primary and secondary flight feathers, and a black tail. The mantle and scapulars can have a glossy greenish-black sheen in breeding plumage. Non-breeding plumage is duller, often with a greyish wash.

2. 2

   Beak shape

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

   Large, yellowish-grey to horn-colored bill. The most distinctive feature is the prominent gap between the upper and lower mandibles in the distal half of the bill, which develops with age. The tip of the bill meets.

3. 3

   Eye color

   Iris color and any distinctive eye markings.

   Dark brown with a greyish orbital ring.

4. 4

   Leg color

   Leg and foot color.

   Dull pinkish-grey to dark grey, becoming reddish during breeding season.

5. 5

   Distinguishing features

   Standout features that separate this species.

   The unique open bill structure in adults is the primary distinguishing feature. In flight, the broad wings and short neck are characteristic of storks, with the black flight feathers contrasting sharply with the white body.

6. 6

   Juvenile appearance

   How young birds differ from adults.

   Juveniles are duller and browner than adults, lacking the distinct white plumage. Their bill is straight and lacks the characteristic gap, which develops gradually over their first few years.

7. 7

   Seasonal changes

   Plumage variation between breeding and non-breeding seasons.

   Breeding adults show a whiter plumage, sometimes with a faint pinkish wash, and a more pronounced glossy sheen on the black feathers. The legs and facial skin around the eyes may become brighter red.

8. 8

   Sexual dimorphism

   How males and females differ.

   Males and females are generally similar in plumage and size, though males may be slightly larger.

Key field marks

• Bill Structure. The most definitive feature for adults is the unique gap between the upper and lower mandibles of the bill, visible from the side. Juveniles have a straight bill, which develops the gap with age.
• Plumage. Look for a predominantly white or greyish-white body with contrasting black primary and secondary flight feathers and a black tail. The overall impression is a large, pale stork with black wings.
• Habitat. Always found near shallow freshwater wetlands, rice paddies, or marshes. If you see a large stork in such an environment in Asia, check for the bill gap.
• Flight. Observe its flight pattern: slow, deliberate wing beats, with neck extended and legs trailing. The black and white contrast is striking in flight.

Explore the Asian Openbill