Significant variation in plumage coloration of juveniles
Juveniles going into their first winter show remarkable variation in plumage coloration. 3 general types of which can be distinguished while overlap occurs and exact borders are hard to establish.
Type 1 has a fair or pale basic colour and little contrast. There are few shades of brown, mostly warm-noted and reddish, with smooth transients like water colour.
Type 2 is the opposite in most aspects. There are different shades of brown, with a darker brown set on drop-like ornaments which are significantly contrasting with any surrounding colours. From a distance this is resembling juvenile Black-headed Gulls.
Type 3 is similar to type 1 in the lack of contrast, but the basic colour is darker. Along with brown this plumage shows a lot of grey as background pattern.
All 3 types can be seen on the first photo while the second shows two fair coloured individuals, one very pale with low contrast, the other still pale, but with high contrast.
How can those variations be explained that are only present in juveniles? We know that adults in their 3rd calendar year (2nd winter) show very little variations (if any) while older birds all look the same (at least to the human eye). There must be an evolutionary benefit in juvenile plumage variation that is not obvious.
58 chicks on the wing - new all-time high!
End of July is the time for us to strike a balance. How many chicks have made it to fledging and will be leaving the colony on the wing? Those who did are going with good prospects for their future, but until then life is dangerous and all too often a matter of chance. Survival depends on many factors, some of which we are able to control by conservation efforts, some we are not.
So you'll never know and each year is different, but what a surprise - this time was big time! The breeding season 2021 is now closing with the best result ever. Since mid-July we had been quite positive that 52 ringed chicks were alive and about to leave the colony. But, adding up to that, latest reports by Gerd-Michael Heinze (published on ornitho.de) showed that another 6 chicks without rings are being fed on the Lower-Saxony-part of the River Elbe estuary. Most likely they also came from the Neufelderkoog colony, since currently there is no other breeding habitat for Gull-billed Terns in Germany (and Central Europe) than this. We must have missed them at ringing. Anyway, the number of fledged chicks now totals at 58, a marvellous result and a most welcomed reward for all the work that has been put in so far.
This year a surprising lot of chicks and adults went to Holland very early, straight from the colony, with no longer ado. We know about the ways of our terns in the Netherlands thanks to observations and photographs by many Dutch observers and photographers (most notably Renate and Fred Visscher, Harry Kuipers). During migration the first stop is usually taken at certain sandplants close to Groningen where there is plenty of food (mainly Tettigonia-grashoppers) and quiet roosting sites. This year a significant number of terns seemed to be in a hurry for leaving the colony area earlier than usual, perhaps because food was poorer there than in other years.
During midsummer a lot of young fish are migrating upstream into the tidal zones of the River Elbe and connected waters, among those many flatfish. At low tide they are ususally hiding in the mud, enjoying their camouflage and not moving very much - but still enough to be detected by a Gull-billed Tern.
In this scene from the Neufeld harbour basin the retreating waters reveal a flatfish while a Gull-billed Tern is rushing along. Again Fred Visscher found the exact moment to push the trigger on the camera. The precision, speed and aerodynamic control of the tern's action is just breathtaking!