How to identify the Changeable Hawk-Eagle

To correctly identify the Changeable Hawk-Eagle (Nisaetus cirrhatus), 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

55-75 cm

Wingspan

100-160 cm

Weight

1.0-1.9 kg (males), 1.3-2.3 kg (females)

Physical features to check

1. 1

   Plumage

   Overall feather coloration and pattern.

   Highly polymorphic, ranging from very pale (whitish underparts, pale brown upperparts) to very dark (dark brown to blackish overall). Intermediate morphs show varying degrees of streaking and barring. Underparts can be plain white, streaked, or heavily barred. Upperparts are typically dark brown. The 'changeable' aspect refers to these significant individual variations, not seasonal changes.

2. 2

   Beak shape

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

   Strong, hooked beak, typical of raptors; dark grey to black with a yellow cere.

3. 3

   Eye color

   Iris color and any distinctive eye markings.

   Bright yellow to orange-yellow in adults; paler in juveniles.

4. 4

   Leg color

   Leg and foot color.

   Yellow legs and feet with powerful talons.

5. 5

   Distinguishing features

   Standout features that separate this species.

   Key features include its robust build, relatively long tail, and broad, rounded wings. The presence or absence of a crest (a short, shaggy crest of feathers on the nape) is variable even within the same morph. The underwing pattern often shows dark flight feathers and a paler underwing coverts, though this also varies with morph. In flight, it often holds its wings in a shallow dihedral.

6. 6

   Juvenile appearance

   How young birds differ from adults.

   Juveniles are typically paler than adults, often with whiter underparts and less distinct markings. The head and underparts may be buffy or rufous, and the eyes are paler yellow. The crest, if present, may be less developed. They gradually acquire adult plumage over 2-3 years.

7. 7

   Seasonal changes

   Plumage variation between breeding and non-breeding seasons.

   No significant seasonal plumage changes. The 'changeable' refers to individual polymorphism, not seasonal variation.

8. 8

   Sexual dimorphism

   How males and females differ.

   Females are generally larger and heavier than males, but plumage coloration is similar between sexes.

Key field marks

• Overall Size and Build. Look for a medium-large, robust raptor with broad wings and a relatively long tail. It appears powerful in flight and perched.
• Plumage Polymorphism. Be aware of the wide range of plumage variations. It can be very pale (whitish underparts, pale brown upperparts) to very dark (dark brown/blackish overall). Intermediate morphs are common, showing streaking or barring on the underparts. Do not expect a single 'typical' plumage.
• Crest (Variable). Check for a short, shaggy crest on the nape, though its presence and prominence are variable even within the same morph and age. Some individuals are uncrested.
• Underwing Pattern. In flight, observe the underwing. It often shows dark flight feathers contrasting with paler underwing coverts, though this can vary with morph. Look for a dark trailing edge to the wing.
• Flight Profile. Note its powerful flight with strong wing beats and glides. When soaring, wings are held in a shallow dihedral. It can appear quite agile for its size.
• Vocalizations. Listen for its distinctive, loud, high-pitched, and far-carrying 'ki-ki-ki-ki-ki-ki-ki-ki-keee' or 'klee-klee-klee-klee-klee' calls, often accelerating and rising in pitch.
• Habitat. Consider the habitat – it prefers a mix of tall trees and open areas, often in lowlands and foothills across tropical Asia.

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