Non-breeding gull-billed tern, Gelochelidon nilotica (protonym, Sterna nilotica), sometimes known as the marsh tern, photographed at Awash Lake, Ethiopia (Africa).
Question: This African mystery bird occurs on every continent in the world except Antarctica. There also is a small and isolated population in northern Germany and Denmark. Can you name this bird and tell me something unusual about its habits or life history?
Response: This is either an immature or an adult non-breeding gull-billed tern, Gelochelidon nilotica. (Immature birds can be distinguished from adults by faint brown mottling on the mantle -- back).
Gull-billed terns are colonial breeders on freshwater and brackish waters, including swamps, lakes, beaches, mudflats, floodwaters, sewage farms, irrigated croplands and grasslands, and they especially favour salt-pans, coastal lagoons and inland saline lakes. They are only rarely found over the ocean. Basically, this is an inland species, but they are nomadic so when they are not breeding, they show a distinct preference for salt marshes and lagoons near a coast.
Terns were once mostly placed into one genus, Sterna, but recent DNA work shows they are sufficiently distinct to be split into a number of smaller genera within the family, Sternidae. These studies show that the gull-billed tern is distinct enough to warrant its own genus, Gelochelidon.
The gull-billed tern is distinguished from most other terns by the shallow fork in its tail, broader wings and thicker, fairly short, black bill. Its name recalls the shape of its bill, but its leisurely flight closely resembles that of gulls, too. It especially can be confused with the sandwich tern, but the gull-billed tern's stouter black bill lacks the sandwich tern's pale bill tip and its wings are broader than the sandwich tern's wings, too.
One habit that I find interesting about this species is they do not normally plunge-dive for fish as other white terns do, nor do they settle onto water, despite having webbed feet. Instead, they feed on insects that they catch in flight. They also hunt over wet fields, grabbing amphibians, small mammals and small birds.
Here's an adult in breeding plumage and a juvenile gull-billed tern sitting next to each other in a rice paddy [Portugal; digiscoped]:
Just to give you an idea of how breathtaking their hunting flight is, here's a video from spring 2011 of a breeding-plumage adult gull-billed tern hunting over a field in Cornwall, England [filmed at the Trevilly Farm, Sennen, 07/04/2011]:
The videographer writes: "This Gull-billed Tern was found in a field near Sennen by local birdwatcher Martin Elliot on Wednesday 6th April, I caught up with it the following day a short distance away at Trevilly Farm."
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