Trumpeter swans at Kelly Warm Springs, near Kelly, Wyoming, USA

Have they forgotten to fly south?

Trumpeter swans live near rivers, lakes and coastal roads in northern and western US states, Canada and Alaska. Trumpeters tend to stay put year-round if they have access to enough open water. But if the water freezes in winter, they'll migrate far enough south to find wetlands where they can eat the aquatic plants that make up the bulk of their diet. That may be why the swans in this image are drawn to the waters of Kelly Warm Springs in the US state of Wyoming, which don't freeze, even if snow lines the banks. Trumpeters are among the largest types of swan. The biggest known cob - that's a male swan - weighed nearly 18kg (almost three stone) and had a 10ft (3m) wingspan.

Although in the early 20th century they came perilously close to extinction, today there's an estimated 35,000 trumpeters. Even with the tremendous recovery, it remains illegal to hunt them. And yes, their calls do sound like trumpets, but Miles Davis they aren't. Click below to listen