I initially thought this was a tern but think, perhaps, it is a gull due to it's white head. (Correct me if I am wrong.)
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Thanks for the help. I am still a little confused. The Gull I photographed did not have a 'black head' and was small, compared to the Herring Gulls nearby. Can someone assist me with understanding this a little more?
Herring Gulls are very large...up to 2ft long, with a wingspan well over 4ft. In contrast, Black-headed are smaller...not much over one foot long, with a wingspan of three feet or so. In other words, Black-headed is obviously smaller than Herring. Little Gull is a step down again, less than a foot long and a wing span of two feet or so.
Both Black-headed and Little Gulls have dark heads in breeding plumage (Little Gull has the black head, Black-headed has it brown!). However, they both lose that in autumn and through the winter. Most of the year, they lack a dark head.
Little Gull does behave very much like a tern, with dipping flight and quick wingbeats.
One obvious difference is that Little Gulls have blackish underwings. Really, it is one of those species where you will know it when you see it. :)
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Thanks you Ophrys, I appreciate the identification help, especially the note about autumn plumage. I need to learn a little more about Gulls, and take more photos when I do get to see them.
Lat/Lng: 54.96969, -1.60025
OS grid ref: NZ256639
Flying around the Millennium Bridge.