Bonaparte's Gull vs Black-headed Gull

Bonaparte's Gull and Black-headed Gull are both small gulls, but Bonaparte's Gull is smaller and more delicate. The most reliable field mark is the bill: Bonaparte's Gull has a thin, black bill, while Black-headed Gull has a thicker, reddish bill. Both species show a dark head in breeding plumage, but Bonaparte's Gull's head is more uniformly black.

1. Bill: Bonaparte's Gull has a thin, black bill; Black-headed Gull has a thicker, reddish bill. 2. Size: Bonaparte's Gull is smaller and more delicate. 3. Head Color in Breeding: Bonaparte's Gull has a black head; Black-headed Gull has a chocolate-brown head. 4. Flight: Bonaparte's Gull has a more tern-like flight. 5. Habitat: Bonaparte's Gull nests in trees and is often inland; Black-headed Gull is more coastal.

Bonaparte's Gull is smaller and more delicate than Black-headed Gull.

In breeding plumage, Bonaparte's Gull has a black head, while Black-headed Gull has a chocolate-brown head. In non-breeding plumage, both have white heads with dark ear spots, but Bonaparte's Gull retains a more delicate appearance.

Bonaparte's Gull often exhibits a more tern-like, buoyant flight compared to the more typical gull-like flight of the Black-headed Gull.

Bonaparte's Gull nests in trees in boreal forests and is often found inland during migration, while Black-headed Gull is more commonly found in coastal and wetland areas.

Bonaparte's Gull has a more lilting call, whereas Black-headed Gull's call is harsher and more gull-like.