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Late summer and early autumn bring large numbers of skewers passing by our shores as they migrate south away from their high latitude breeding grounds.
Sightings of these birds from shore is often a very distant specks and this can lead to significant difficulty and identification.
Much has been written on the details of separating close-seen individuals on subtle plumage characteristics and indeed seeing a single juvenile skewer inland, out of context, on a reservoir for instance, is a true identification challenge.
But in this guide we shall be concentrating on birds flying and seen some way offshore where overall light and dark markings and jizz will help us.
There are four species to consider, great skewer or bonxi, pomeran, arctic and long-tailed skewer.
Of these, great and arctic skewers are by far the most frequently encountered and the key to becoming confident in identifying all four species is to become truly familiar with these two.
Let's look at great skewer first as this is usually the most distinctive species.
Great skewer has a similar body length and wingspan as a herring gull although it is worth remembering that all the skewers are dark and so when compared to nearby white or grey sea birds they will probably appear larger.
Although similar in size to a herring gull, great skewer is much stockier and overall is much darker than a juvenile gull.
Appearing almost black out to sea, broad white wing flashes are visible both above and below.
In sunshine, paler scapulas or shoulders can sometimes be surprisingly obvious as well.
Great skewers fly like heavy gulls and give the impression of power rather than of agility, a real bruiser of a bird.
The other three species can appear more similar to each other with confusion added with light and dark-faced birds as well as adults and juveniles.
Again, it is familiarity with arctic skewer and jizz that will be the most helped to us.
Arctic skewer is a much smaller bird than great skewer with a body size only slightly larger but again more stocky than a black-headed gull but with much longer wings.
There are very elegant birds with attenuated rear ends especially in adults.
Their flight is elegant and buoyant giving a falcon-like or raptorial impression.
In all plumages there is a clear white wing flash on the underwing whereas the flash on the upper wing is much less obvious and on some few individuals almost missing.
This difference between the white on the upper and lower sides is obvious as the birds shear from side to side as they pass by or harass gulls and terms.
It is useful to use arctic skewer as the default smaller skewer and compare the remaining two species back to this one.
Pomeran skewer is larger again and although closer in size to arctic skewer than great skewer with a body size similar to a common gull, it gives a more great skewer-like impression.
Poms as they are often known are heavy set thug-like skewers with deep barrel chests.
Their wings are wider and not as elegant as arctic skewer with a modest white flash above and a distinctive double white flash below.
On some adult birds the central tail extensions can be seen throughout the winter and some even retain the twisted feathers or spoons which can look like trailing feet.
Many poms, both adults in winter and juveniles, have a noticeably paler barred rump which stands out against the dark back, tail and wings.
Generally the rarest longtailed skewer is also the smallest species although very occasionally large numbers pass our shore but more usually you will be lucky to pick one or two longtailed skewers out amongst a stream of passing arctic skewers.
If familiar with arctic skewer you will be struck on seeing a longtailed skewer by its small size, lithe proportions and incredibly buoyant and agile flight, more like a turn than a gull.
Indeed longtailed skewer has a similar body size to a sandwich turn but even longer wings.
Juveniles which make up almost all of the individual seen off shore in autumn do show significant white primary bases underneath, more so than arctic skewer.
Juveniles can also be strikingly pale with noticeable pale heads which again will show up when the birds are far out to sea.
This video is a general guide of the major differences and should help you separate many individuals.
But especially when first starting out and until you are truly familiar with arctic skewer you will probably misidentify some individuals and others will appear unidentifiable.
As you watch more skewers you will become more tuned in to the subtle differences in structure, markings and jizz but skewers are very difficult to separate and there is no shame in admitting that you are not 100% certain of the identity of a bird that has just flown past.
It happens to us all.
