A quick recap.
So far we've got the strikingly white head (hopefully breast and belly too), the very dark brown crescent of tertials with discrete white tips, and brown coverts that are beautifully plain* and un-fussy, and where each tract of feathers is clearly discernable from its neighbour.
More coverts stuff
Before moving on to the mantle/scapulars, there is more to glean from the coverts. As well as being plain brown* with whitish borders, the greater coverts especially are also darker at the base. The line of dark-based feathers graduating into whitish tips (broadest on the inner coverts) produces a lovely wing bar on the resting bird. Before the feathers get too worn at the tips, thereby reducing its definition and impact, that wing bar can bear a striking resemblance to the logo of a well-known sporting goods brand. This tram sheds Casp from December 2009 illustrates it quite well...
SWOOSH!!™ ...Sporty Casp
Amazingly the coverts have even more to offer, because the effect of dark base/pale tips is also there on the median coverts to some extent, so you actually get a double wing-bar. If I post up the collage which I used to illustrate tertials, but draw loads of arrows on it, you can see the wing-bars. It may seem a bit subtle on a photo, but honestly it's pretty obvious in the flesh.
Lovely, lovely wing-bars
Mantle and Scapulars
Not really sure why I'm mentioning 'mantle' at all, because it's just the scapulars I'm worried about. The mantle is the small area of feathers between the shoulders, and who cares about them? Not me. In the next collage there are three 1st-winter Caspian Gulls on the left and three 1st-winter Herring Gulls on the right. The Casps range from one with the least marked scaps I've seen, to the most heavily marked. But even on the most strongly marked bird, note that the darkest markings are at the base of the feathers rather than the tips - unlike Herring Gull.
Generally speaking, a 1st-winter Casp has light grey scaps, showing some dark basal diamonds, some thin, dark shaft streaks, and fine terminal anchors [feather pedants please note - technically, sub-terminal, but I've gone and labelled the collage now and I can't be bothered to correct it]. There may be a few plain, mid-grey feathers admixed - certainly two of our birds have shown this. Basically, the less markings on the scaps, the better - the top left bird is a beauty in this respect.
Compare this patterning with Herring Gull...
This pic also excellent for showing contrast between plain coverts of Casp (left) and 'fussy' coverts of Herring (right)
One more thing before we move on. All five 1st-winter Casps I've seen have shown a 4-colour zoned appearance, as follows...
- White head
- Grey mantle/scaps
- Brown coverts
- Black(ish) tertials and primaries (again, pedants might quibble about the tertails, but let them, I don't care)
If you find a Herring or Yellow-legged Gull with the combination of features discussed so far, I'll eat my red hat. Except I probably won't have to because it will no doubt be a Casp!
There is so much more to say, and I'll probably get around to jizz, bill, legs, tail pattern, upperwing, underwing etc, etc, but there's plenty to be getting on with for the moment. So I'll close part 4 with...
A Final Thought or Two
It would be easy to accuse me of being simplistic. Apparently Caspian Gulls can be much more variable than I might have implied and sometimes really hard to ID for sure, with some horribly tricky and border-line birds. My response to this fact is 'so what?' I'll worry about them if I ever come across one. In the meantime, I will happily accept all the easy ones that fall in my lap, and offer a word of encouragement...
Although I have read quite extensively about Caspian Gull ID, and am therefore well aware of what 1st-winter Caspian Gulls should look like, everything in these posts so far is based on experience, ie., what I have seen with my eyes. Initially I thought writing a Casp ID series based on five birds might make me a presumptuous fraud, but have since realised that if I can find and identify Caspian Gulls from scratch, then any fule kan, and perhaps my experience as a beginner (rather than a slick and awesome expert from another universe) might inspire others to think it could actually be within reach, and therefore worth a go after all.
I hope so.
* The coverts may not be 100% plain, and may even have some quite obvious chequering, as on the inner greater coverts of this beast that we had in December 2011, but still not a patch on a Herring Gull (or YLG) and certainly plain enough for me, thanks :o)