August 4th   Leave a comment

It has been a month since I added a new bird to the Crail year list. Today it was a roseate tern: quite a special Crail bird, and I have only seen them in 6 of the last 19 years. Roseate terns are very rare breeders in Scotland. They used to breed in the inner Forth in small numbers and there are one or two birds around the May Island most summers. The best time to see them in Crail is late summer with the arctic terns that gather in big flocks at Balcomie and Kingsbarns after breeding. So it was again this morning. I diverted from corn bunting nest monitoring to look at the terns gathering at Balcomie, hoping to find a roseate. I was feeling low as another late corn bunting nest had fallen foul of potato harvesting: I watched the pair return to their destroyed nest site just ten minutes after the tractor had cut away all the potato vegetation. It is hard to register stunned disbelieve from a corn bunting but it was hard not to imagine that this is what they were feeling. Corn bunting nests must always have been instantly destroyed by herds of grazers or wildfires so corn buntings are evolutionarily prepared for the complete habitat transformation that occurs in literally seconds with modern farming equipment. Nevertheless, I expect it still hurts.

Anyway – the antidote to dwelling on the narrow margins between life and death that animals live by – is to sit on sunny beach and work your way through 200 Arctic terns looking for a roseate tern. The Arctic terns themselves are wonderful and they were an even mix of adults and juveniles suggesting a great breeding season. There were also a few adults and juvenile common and sandwich terns in the flock. After about half an hour I got lucky and heard the distinctive “choo-wit” call of a roseate a few times when the flock flew up in response and circled round in alarm as a heron went by. I couldn’t get eyes on it though. After a couple more alarm flybys I finally saw an adult roseate amongst the Arctic. The thing to look for is a black leading edge to the primaries on the upperwing – Arctic terns pretty much have unmarked wings (very clean looking) and common terns have blackish inner primaries (and so the back of the wing). I picked up this feature and followed the bird down to land on the rocks, conveniently next to both an Arctic and a common tern. I could go through all the features (although the call is good enough for me for a firm identification). Long legs (Arctic have short); a very black, long bill with only red at the very base (Arctics have short, all dark coral red bills and commons have long, brighter red bills with a black tip); a paler, nearly white looking back (Arctic and common have slightly darker grey backs, although in the strong sunlight today everything was bleaching white); and the best feature of all, the division of black and white on the folded wing. Roseate terns have the lower half of the wing black and the top half white, so a black and above a white line extending above the tail. Arctic terns have a greyish line with no contrast, and common terns have the opposite pattern, lower half white and top half blackish. It is a subtle suite of characters, but they combine to make a different looking bird to an Arctic or common tern, and the flight shape is also distinctive: more like a sandwich tern, more head than tail. But as I have said the thing that really makes them distinctive to me is the call – so much like a spotted redshank at times that I actually double checked a whimbrel passing through the terns, just in case.  

Roseate tern (right) and Arctic tern
The three very similar looking terns handily together for comparison R = roseate, A = Arctic and C = common. The other terns are Arctic with a juvenile from this year in the foreground.

The Arctic tern flock was on the rocks just north of Balcomie Beach. They are likely to stay here for several weeks, and roseate terns in the past that have associated with these flocks have also stayed around. So, if you feel like a find the needle in a haystack challenge, then the opportunity is likely to be there for a while. Another good bird today. A juvenile marsh harrier hunting over Crail airfield, probably on its way slowly down to Africa.

Pick out the roseate tern…

Posted August 4, 2021 by wildcrail in Sightings

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