2 Feb 1989 - Caspian Terns

When we arrived here Peter said it was a good two hour walk to go around both the marshes along the sea walls. Today we actually make it the whole way round ‑ it takes eight hours! There are just too many things to stop and look at.

The first excuse for a stop is Jim scoping the estuary while I photograph more flowers ‑ algarve toadflax, salad mustard, asphodel, etc, where they grow behind a bush and are sheltered from the wind. The estuary birds are much as usual, but no sign of raptors today.

We stop frequently to scan the marshes. Some chiffchaffs are feed­ing on insects over the drainage channels. Some seem to be taking insects off the surface too. I notice one place where a bird regularly uses a perch just below where we stand. After a while I climb half-way down the bank and sit with the camera aimed at the perch. The chiffchaff seems to patrol about fifty metres of channel, using four or five perches along the way to watch for insects. It ignores me as I climb on down to the bot­tom of the bank and take photo­graphs from there. Beyond the ends of its territory there are other chiffchaffs in their territories.

Jim concentrates on watching the Caspian terns fishing. One bird flies into the strongish east wind, often hanging or hovering before flex­ing its wings and plunging vertically, disappear­ing in a splash of water. At the end of its run it flies back with the wind and repeats the pro­cess. It catches two items and dips its bill in the water three or four times after each. The third item proves to be quite a mouthful for, ten seconds after swallowing, it brings the fish up again, attracting the attention of black-headed gulls. It downs the prey even­tually but this time doesn’t wash its bill after­wards. Another bird also has three consecutive successful dives and flies off looking decidedly heavy in the crop.

Terns are the focus of our attention for the rest of the walk. There is one roosting on its own out on a sandbank with nothing, not even a gull, for size comparison and the sun is behind it. The bird appears buffy-pink under­neath and when it shows its head the forehead was white and the bill long and dark, though it looks reddish with the sun behind. It is difficult to work out whether the tail or primaries extend furthest ‑ I think it is holding one wing lower than the other just to confuse the issue. We decide it is a sandwich tern ‑ definitely not a Caspian and the other species should not be here yet anyway ‑ but it high­lights more gaps in our knowledge.

On another sandbank off the western marsh holds a roost of gulls with half a dozen Caspian terns. The terns are either in pairs comprising an adult plus a juven­ile, or as single adults. The juveniles occasionally turn face to face with their parent and beg half-heartedly ‑ they remain partly dependent for up to eight months. We do not see a youngster actual­ly being fed but they still give whistling begging calls in flight as well as on the ground. They are all in different scruffy stages of moult, show­ing some dark-marked feathers on the tertials, coverts and secondaries. Although they do not breed until three or four years of age, the juven­iles attain adult non‑breeding plumage within a year and are then indistinguishable from their parents except in the breeding season.