Aden: breeding of Swift Terns

>>Salt Pans: 4 August 1946

Life list now 216 species 

On 1 June 1946 I noticed a new species of tern of which there was a flock of about 25. At first I could not name it but later identified it as the Swift Tern* Sterns bergii. On 10 July I estimated about 200 of these birds in two flocks on large pools where there was exposed mud. A flock remained in one of the pools (c. 400 by c. 500 metres) and numbered c.80 on 22 July and c.60 on 28 July. Then, on 4 August, in the same pool, I found the water level higher, all but three of the terns gone, but 37 eggs along the east side. “They were all either floating or lying on exposed mud at the edge. The wind was blowing strongly from the west (as usual) and I suspect that the eggs had been blown across the surface from a colony of Swift Terns nests in the centre of the pool. I have seen the species there in numbers not less than 60 for a month or two.

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There were 15 eggs in one corner. 8 had white grounds, 3 pinkish stone (paler than III) and one ordinary stone. Spots on the latter were very small, like the egg of a Coot [Fulica atra]. I was able to retrieve three eggs (which seemed representative), sketch and measure them. I also took down the following descriptions.
I: ground colour white; spots mixed medium and very dark rich brown; a few medium to pale grey.
II: ground colour white, spots mostly medium to dark brown, the majority having grey edging.
III: ground colour fairly pale pinkish stone, spotted as in I but browns redder and greys bluer.
In all three, the surfaces were matt. When broken, I and III revealed respectively a clear red ball (yolk?) and an opaque orange mass; II was practically empty.”

Barnes (1893) has a similar description of Swift Terns eggs. His average size was 62 x 43 mm; mine 63 x 43 mm.

*Description on 1 June 1946: “Most noticeable feature at a distance on the ground was the contrast of white neck with dark body. At shorter range it was possible to see that the crown was very black; this rather crested cap extended to the nape in some some cases. The back, rump, upper tail and upper wing surfaces were quite dark grey or grey-brown appearing darkest on the primaries and lightest on the upper tail. In flight this dark plumage was much less noticeable. The neck and underparts seemed white. Bill: long, slightly down-curved and yellowish, feet and legs black or very dark. Their size was about equal or a little less than that of the Caspian Tern, the flight rather resembled that of this species. The call heard once or twice when one bird was disturbed by another was a very harsh “ark-ark”, quite unlike the quaver of the Caspian Tern.”  On 10 July 1946 I described the call: “resembles that of a breeding Black-headed Gull [Larus rhidibundus, which call I knew from England] only more grating.July 20, 2010.”

Aden: a summer visitor

>>Aden summer 1946

Life list now 215 species

Even though Aden seemed to have eternal summer to someone coming from northern climes, there were seasons. It was hotter in July than January and, more important for the birds, there was an alternation of wet and dry influences. As already mentioned, southwest Arabia is a continuation eastwards of the Sahel zone of Africa and is subject to monsoon rains. These generally fall in the summer, April to October, with a peak in July and August. In fact, a belt of rain follows the sun in the equatorial zone and moves north in the northern summer and south in the southern summer. Though Aden experiences little of this rain, it falls heavily in the mountains of Yemen to the north. The rain causes vegetation to grow and insects to flourish. Birds follow the rain belt and travel north from Africa to take advantage of the plentiful food.

Many birds anticipate the seasonal change in the area to which they are migrating so as to have young birds already hatched when the peak of food abundance arrives. It was one such bird that amazed me by its exotic appearance, even from a brief glimpse at Steamer Point on 5 May 1946. “From the billet I saw an unidentified species fly from the hillside to near Tarshyne. Size about as Starling [Sturnus vulgaris] or thrush, general colour very bright cobalt blue, apparently black or dark shoulders and bright red bill and head (?)” Because of the arid habitat I did not guess that it was, in fact, a kingfisher, though the brilliant blue in the plumage should have given me a clue. A few years previously I had found a dead Kingfisher Alcedo atthis in England and had made a display of the iridescent turquoise feathers from the back and wings. In fact, as I found out later, the Aden bird was a ___________________________*. I was not the first to observe this species in Aden. It had been reported by Barnes (1893) in January and by Yerbury (1896) in April. 

At about the time I saw this bird, there were, as already recounted, obvious signs of migration of birds through Aden bound for their breeding grounds far to the north, where the return of warm weather would bring about a vast increase in food supply. I had been very familiar with this type of migration in England. I did not realize that the bird I had just seen was my first encounter with a different class of migration, intra-tropical, which takes place within the tropics and is driven by the annual passage north and south of the rains. I would later in life come across the _______________ performing its migration in other parts of the Sahel right across Africa, almost as far west as the Atlantic coast of Mauritania. 

I obtained proof of its destination further north when I visited Lahej on 7 July 1946. Lahej was 15-20 miles north of Aden and was watered by a river that flowed down from the mountains of Yemen even further north. Surprisingly, I did not apparently link these birds with what I had seen at Steamer Point on 5 May >>> 
"Another bird was quite common and about the most striking there. In size it equaled, approximately, a Starling but the head and bill were comparatively very large and the tail a little longer. Head, neck and upper breast were a very light grey or grey-pink, black around eye (?), mantle (?), part of upper wings and primaries (only) black or very dark blue, rest of upper parts (including tail) very vivid blue. In flight this combination of black and blue on the upper parts was very noticeable. I'm not quite clear on the colour of the underparts but they were definitely darkish and showed up the whitish neck etc. Bill was a bright coral or orange red, legs a pinkish red. In flight this showed plainly together with a white patch beneath each wing. This bird spent a great deal of time calling "chwik" repeatedly as "jek-ek-ek-ek-.." or "jek-je-je-jek..." making the notes jumbled when calling them in fast succession. Once it dived with a splash into a pool of water rather like a kingfisher."

QUIZ: If you think you know what species this bird was, please put its name, your name, how you identified it and the date (5 May 1946) in the comment box at the end of this post.