The kittiwake (Rissa tridactyla) is not actually flying upside down at all. You can tell because the bird's upper wings are visible in the photo, showing the silvery grey feathers with the classic dipped-in-black-ink wing tips. If it were upside down we would see the under wings, which are white with black tips. The twist of the bird's head is interesting, though. Clearly the bird has turned its head a long way to the right, so that it seems initially to be flying upside down.

Many birds can rotate their heads to this degree or more - owls and other birds of prey are the best known examples. In these species, head-turning helps them to detect their prey. Specifically, it allows owls to orientate their ears to obtain the best possible reception when listening for the faint rustling of a rodent moving through vegetation in the dark.

In the kittiwake, however, this doesn't happen. A possible explanation is that the bird is trying to cough up a particularly sharp piece of fish bone or something else it has swallowed. Many birds, including gulls, which are relatives of the kittiwake, regurgitate indigestible pellets.

Another explanation is that the bird is shaking off excess salt water from its beak. Most seabirds take in varying amounts of salt water when feeding, which they have to get rid of before it reaches harmful levels in the body. Finally, the bird may simply be twisting as it calls out to other individuals in the same area, or just keeping a lookout for potential predators, such as skuas.

Kevin Elsby, Norwich, Norfolk, UK

If you get a chance to look at the photos in the websites below - especially the first - do so - Ed

The bird is flying normally and twisting its head around, perhaps to preen itself or to loosen a morsel of fish that it may be eating. The under-wing pattern of the kittiwake looks nothing like the upper wing at all, and a cursory inspection of the structure of the flight feathers of this bird reveals a normally aligned gull.

Birds do not generally fly upside down, but they may momentarily invert, such as when wildfowl "whiffle" to lose height rapidly, spilling air from under their wings (see bit.ly/3wfoqV). Additionally, some birds may roll during mating displays, such as the aptly named roller birds, part of the order Coraciiformes, while others might in play (see bit.ly/90q8PT).

Simon Woolley, Winchester, Hampshire, UK

Bird could be blind in the right eye. Using its left eye to look right.