Gulls are variable. They are the most diverse bird-group concerning plumage variation within species and age-classes. To add more confusion to the aspect of identifying gulls, they also differ in the timing of their moult. On top of this, some birds loose feathers without "wanting" it. These are some of the aspects why gulls are the most intriguing birds todo in-depth observations off.
At first glance a normal first winter Common Gull, but really strange when studying the details.
An odd white tail
Yesterday I saw this freaky Common (Mew) Gull in Bergen. The plumage and bare parts tells me it is a bird that is less than a year old. At first glance it gives the impression of being in its first winter (first basic) plumage. Scrutinizing the bird a bit more careful reveals a nearly white tail. Common Gulls at this age should have a wide black terminal band on the tail. In second winter plumage they can look like this, although usually completely white. Has the tail been shed? We'll leave the tail-feathers for a moment, and go on studying more plumage characteristics. The wing looks a bit strange.
Yesterday I saw this freaky Common (Mew) Gull in Bergen. The plumage and bare parts tells me it is a bird that is less than a year old. At first glance it gives the impression of being in its first winter (first basic) plumage. Scrutinizing the bird a bit more careful reveals a nearly white tail. Common Gulls at this age should have a wide black terminal band on the tail. In second winter plumage they can look like this, although usually completely white. Has the tail been shed? We'll leave the tail-feathers for a moment, and go on studying more plumage characteristics. The wing looks a bit strange.
 The primaries on both left and right wing. |  This is how the primaries should look like. |
Strange set of primaries
There is something about the outer primaries. Some feathers are brighter than normal, and both p9 and p10 show small mirrors (the two outermost primaries). P9 has a larger mirror than p10, which only has traces of one. Mirrors are rare in first winter Common Gulls, but second winter birds show mirrors on these two feathers, but with a large mirror on p10 and a smaller one on p9 (sometimes not present). From p7 and inwards the primaries have large light grey areas, giving the hand a rather unfamiliar look. When zooming in, some interesting features are revealed. P10 is lighter brown than p9, and the latter seem a bit short compared to p10 and p8, indicating a not fully grown feather.
Two generations primaries
Gulls moult their primaries from the center of the wing (starting with p1, the inner primary, working its way gradually to p10. Does this mean that the bird has shed p1-p9? Apparently, but once again when looking on each feather you can see a contrast between the dark areas on p5-p1 and p6. P5 does also show dark smudging on the outer web, which is perfect for a first generation feather. Summing the feather features up the conclusion is that p9 and p7-p6 have been shed and regrown. I think P8 on the left wing is an old first generation feather, and it is missing completely on the right wing.
When birds accidentally loose feathers, they try to replace them as fast as possible. In particular feathers crucial for their flying ability, such as primaries, secondaries and tail-feathers. Did this gull experience something that made it unintentionally loose some feathers? Probably. I am sure that the primaries p9-p6, minus p8, are moulted into second generation, but I am not completely sure about the tail, since all are the same generation. It may be an aberrant first generation tail, but probably not. The really strange thing is that it has moulted the same three primaries on both wings! This is how gulls moult of course, synchronous on both wings, but this is not the right order of things, and it is not at all the season to observe second generation flight feathers on first-winter Common Gulls.
So, what happened to this gull? Did it hit a wire, interact with a predator, or maybe was shot by a hunter? Did it walk around with no tail and seven central primaries missing some time last autumn? Whatever happened the result is a second calendar year Common Gull with seven (4+3) shed primaries, six of them regrown, and a really aberrant tail that probably is also renewed. Beautiful!
There is something about the outer primaries. Some feathers are brighter than normal, and both p9 and p10 show small mirrors (the two outermost primaries). P9 has a larger mirror than p10, which only has traces of one. Mirrors are rare in first winter Common Gulls, but second winter birds show mirrors on these two feathers, but with a large mirror on p10 and a smaller one on p9 (sometimes not present). From p7 and inwards the primaries have large light grey areas, giving the hand a rather unfamiliar look. When zooming in, some interesting features are revealed. P10 is lighter brown than p9, and the latter seem a bit short compared to p10 and p8, indicating a not fully grown feather.
Two generations primaries
Gulls moult their primaries from the center of the wing (starting with p1, the inner primary, working its way gradually to p10. Does this mean that the bird has shed p1-p9? Apparently, but once again when looking on each feather you can see a contrast between the dark areas on p5-p1 and p6. P5 does also show dark smudging on the outer web, which is perfect for a first generation feather. Summing the feather features up the conclusion is that p9 and p7-p6 have been shed and regrown. I think P8 on the left wing is an old first generation feather, and it is missing completely on the right wing.
When birds accidentally loose feathers, they try to replace them as fast as possible. In particular feathers crucial for their flying ability, such as primaries, secondaries and tail-feathers. Did this gull experience something that made it unintentionally loose some feathers? Probably. I am sure that the primaries p9-p6, minus p8, are moulted into second generation, but I am not completely sure about the tail, since all are the same generation. It may be an aberrant first generation tail, but probably not. The really strange thing is that it has moulted the same three primaries on both wings! This is how gulls moult of course, synchronous on both wings, but this is not the right order of things, and it is not at all the season to observe second generation flight feathers on first-winter Common Gulls.
So, what happened to this gull? Did it hit a wire, interact with a predator, or maybe was shot by a hunter? Did it walk around with no tail and seven central primaries missing some time last autumn? Whatever happened the result is a second calendar year Common Gull with seven (4+3) shed primaries, six of them regrown, and a really aberrant tail that probably is also renewed. Beautiful!
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