Swooping, diving, skidding through the air, dodging, jinking and turning, the two birds tumbled through the Arabian sky in a spectacular display of excited high spirits. One held a small silver fish in its beak, the ostensible reason for this dazzling aerobatic performance. But as we watched, the pair alighted briefly on the beach, the silverling was ceremoniously transferred from one orange-yellow bill to the other - and the chase began all over again.
These were terns, also called sea swallows - slimmer and more graceful than their close relatives the gulls; and the aerial fireworks we were watching were the first display flight of this breeding season, performed above a coral island in the Arabian Gulf. More and more birds would join this first pair in the hours and days to come, as the excitement they generated crackled through the colony, until the sky was full of a tumbling mass of screeching gray-and-white birds with black caps
Terns are found practically all over the I world - though you are much less likely to see terns during a walk on the beach than gulls. Terns' longer, narrower wings and weaker, shorter legs make them truly creatures of the air: they perch but hardly ever walk, and they only even settle on the water for a few moments at a time to bathe. Only the compelling urge to breed forces them to the land; then these wanderers of the oceans - select isolated islands, near good fishing grounds, for their breeding colonies in which hundreds or even thousands of pairs of terns mate, scrape out their minimal nests, brood and raise their chicks.
Warm and teeming with fish and shellfish, the Arabian Gulf is also dotted with uninhabited sandy islands topping some of its many coral reefs (See Aramco World, November-December 1978). So it is not surprising that Saudi Arabia plays host to thousands of breeding terns every May and June on six or more of the Gulf islands.
That terns nest and breed in the Gulf has been known to Westerners since at least 1878. In those days, ornithology was a science in its infancy, decorously pursued in their leisure time by gentlemen travelers and far-flung military officers; one of them, a Colonel E. A. Butler, obtained eggs of Caspian and gull-billed terns collected for him on an island off Kuwait and, three months later, added several hundred eggs of another tern species to his bag on al-'Arabiya and al-Farisiya Islands, off what is today Saudi Arabia. The eggs ended up in the British Museum; by the close of the century Colonel Butler, and others like him, had identified eight species of terns breeding on Gulf islands.
Last summer we located one of the most elusive: the swift tern (Sterna bergii), which had been known to breed off Iran and Kuwait but had only rarely been sighted - and never recorded as breeding - in Saudi Arabia's Eastern Province. On a trip to the islands of Karan and Harqus, we found and photographed sizeable colonies of these noisy 19-inch crested birds with their distinctive lemon-yellow bills.
We visited those islands, and others in the Gulf, for several reasons. For one thing, data on the distribution of terns are still a long way from complete: the birds are shy, they spend most of their time over water, they move around a great deal - either in migration or within their breeding and wintering areas - and they are notoriously fickle about where they breed, abandoning and re-establishing breeding grounds from year to year without any good reason that frustrated ornithologists, at least, can detect.
Beyond filling in some ornithological blanks, though, and beyond our own pleasure in watching and photographing the family life of these graceful birds, the presence of these thriving tern colonies is a measure of the level of pollution; we were very pleased at how many large and busy breeding colonies are still flourishing.
One was just being established when we first visited Karan Island in mid-May. We found many bridled terns that wheeled around us or perched uneasily in the salt bushes, looking as if we had interrupted something important. We had; the birds were establishing their nesting territories by the old method of claim, counter-claim, threat and quarrel; later on each pair would nest in the middle of its little space, which would be just as big as one brooding tern could defend with pecks and lunges without getting off the eggs. Right under the straggly vegetation we found some of the first "scrapes" of these bridled terns.
Terns don't build elaborate nests. Soon after they arrive at the breeding grounds, both males and females start building the scrapes: the bird presses its breast to the ground while its long wings and forked tail are held vertically upward out of the way. Then it scratches with its toes, pushing the soil out behind it, and sometimes rotating as it scratches to produce a shallow, round depression in the sand or silt. Sometimes both birds of a pair work on the same scrape, which on compacted coral sand is often hardly visible at all; sometimes a pair makes a number of scrapes and then selects one of them to lay the eggs in.
Later that day we moved to the south end of Karan's mile-and-a-quarter length to photograph a colony of what we thought were lesser crested terns that had already laid their eggs. As we drew nearer, we saw that we had made a mistake: these birds had yellow bills, not orange ones; they were white and slate gray, not dove gray; and they were bigger than the 14-inch lesser crested terns that had nested on Karan Island in past years.
The birds had their eggs on their minds and paid little attention to us. Their scrapes were unprotected by shrubbery, and the terns simply stood over them with the "elbows" of their wings drooped to the ground, shading the eggs from the baking heat of the Arabian sun. We photographed from closer and closer until finally the whole colony flew up at the same instant in an explosion of wings and calls. They revealed to us about 400 eggs on the dry coral sand - some of the most incredibly varied eggs we had ever seen.
The background color was either pinkish buff or yellow-gray or bluish white - and in one case bright blue! - and there were blotches and scribblings of reddish brown, umber and black superimposed on lilac shell markings. This wide color variation is characteristic of swift tern eggs and confirmed our identification of a species that no one had ever before recorded as breeding in the Eastern Province.
Both that colony - and another we found the same day on Harqus Island - had a difficult breeding season, though. The 50-egg colony on Harqus had already been wrecked once when we first saw it; waves had swept over the breeding area and left the eggs wet, sand-covered and dented - and already beginningto smell. On another visit on May 25, we found the terns had laid new eggs in scrapes further from the shoreline; terns normally replace lost eggs if they've been recently laid and its not too late in the breeding season. But when we returned to Harqus the last time, early in July, a severe storm in the Gulf had brought heavy seas that had clearly swept right over the island, carrying everything with them. The only remaining sign of life was a disconsolate line of lesser crested terns standing on the beach; there were no nests and no eggs. The swift terns had moved to the greater security of Karan Island.
Karan's original swift tern colony had had its own share of tragedy. When we revisited it on May 25, the sand was littered with broken eggshell; not one whole egg remained of the 400 we had seen earlier and black Socotra cormorants stood sentinel on the sandspit. Probably, the cormorants were not guilty of destroying the colony - they are mainly fish-eaters - and the eggs had been broken and eaten by the versatile, predatory ghost crabs common on the islands. Baby turtles and other crabs make up part of their diet, so surely they are capable of making a meal of terns' eggs.
Elsewhere on Karan Island, though, a colony of several thousand bridled terns was doing better— perhaps because they seemed to prefer making their scrapes on the higher ridges, away from the beach-roaming crabs and deep in the protection of the thickest of the salt bushes. Not far from them was a colony of a few hundred white-cheeked terns, one of the species in which both the male and the female of the pair sit on the eggs, tern and tern about. Most of their nests, unshaded, contained two eggs, which we noticed frequently had small drops of water on them. Apparently the bird that relieves its mate on the nest returns from the sea with a little water trapped in its breast feathers; the water is transferred to the eggs and - "intentionally" or not - helps keep the eggs cool and the embryo inside from drying and dying in the heat.
On the bare plateau above Karan Island's steeply sloping west beach, two colonies of lesser crested terns, each about 1,000 pairs strong, had laid their single eggs on the sand. The compact masses of the tern colonies help protect the birds from predators like falcons, who can't easily single out one target from a whirling mass of identical birds—and who are also intimidated, as we were, by the terns' swooping, diving mob - aggression tactics when they're alarmed. For, make no mistake, terns may come together in large groups to breed, but their loners' instincts are only barely suppressed during that time. In the colonies, very clearly, one good tern disturbs another, and occupants of adjoining territories are constantly testing the "stabbing distance" between them with pecks and beak-fencing.
This is especially true when both terns of a pair are at the nest at the same time, provoking spreading ripples of dissension and irritation in the colony-and providing a better target as well. We even found the fresh corpse of an adult tern, killed by a blow from the beak of one of its neighbors.
Similarly conflicting instincts even cause tensions between mates. During the approximately three weeks that lesser crested and swift terns sit on their eggs, the bird on the nest is fed by its mate, usually with small fish presented in an atmosphere of much excitement. Necks are stretched and bills are held vertically as the sitting bird tries to reach the fish without getting off the eggs and its mate seems torn between its own appetite and its instinct to feed its partner. After a little fencing and lunging, though, the fish is given to the sitting bird - or, more frequently, simply snatched.
Despite tension and conflict, though, the colonies grow in size because they do provide relative security to the birds in them, and the two 1,000-pair lesser crested tern colonies on Karan Island grew, in only about a week, to an enormous quarreling carpet of birds: 15,000 to 20,000 pairs, with some 1,000 additional pairs of swift terns - mostly refugees from the colonies destroyed earlier - in their own adjoining group. It was an impressive sight, and we set up a blind from which to photograph it.
As we did, I saw two fishermen in the distance collecting tern eggs, and I set out to reach the swift tern colony at the same time they did. Each man had a 30-inch metal bowl piled high with eggs; when they had filled them full, they hoisted the bowls onto their heads and set off across the island back to their dhows. I walked the stretch of beach they had harvested; in two densely populated sections of the colony of lesser crested terns, every egg but one had been taken.
Birdwatchers - and conservationists generally - find it easy to get emotional about an event like this, but there is room and reason for second thoughts. The fishermen, quite correctly, regard the tern eggs as a gift from a bountiful God, and have harvested them as long as there have been terns - or men. And the terns, for their part, readily replace the eggs in about 10 days, so - barring repeated harvesting of the same parts of the colony - there is no harm done to the terns either individually or as a species. The real danger lies in more intense commercial exploitation: that would deplete the stock of birds even more rapidly than it seems to have depleted the stocks of Gulf shrimp in recent years.
The eggs that were left - and of course there were thousands - began to hatch in mid-June, and hatching went on for weeks. In early July we still found terns sitting on unhatched eggs; many of them were already pipped by the chick's struggles to get out, with the hard, temporary "egg tooth" on the end of the hatchling's bill showing in the hole. The effort of pecking and fighting its way out of the shell takes the chick to the very end of its strength, and it spends its first few hours after hatching in a wet-looking, bedraggled heap at the bottom of the scrape. Once the membranes covering the individual downy feathers have been rubbed off, the chicks show the markings of their species on their down: mottled pale silver-gray for the swift terns, grayish white with black spots and streaks for the lesser crested terns, and sandy fawn with black markings for the white-cheeked terns.
There in the scrape, lesser crested and swift tern chicks spend their first three or four days, fed on bits of fish regurgitated by their parents, who defend them furiously and fearlessly. Yet those are the young birds' most critical days, for if the adult birds are forced away from the nest - by curious humans, for example - the chicks may wander into a neighboring nesting territory. We watched an unlucky bridled tern chick wander from its scrape under a salt bush into the nesting area of a small group of swift terns. Bowled over by a savage lunge from a pointed lemon-yellow beak, it picked itself up only to be struck again and again as it blundered from one nesting territory to another. Eventually, squealing with fright, weakened and confused, it was carried off by an adult swift tern and dropped, limp, into the undergrowth.
Things are not so brutal once the chicks are older than a few days. Swift tern chicks all hatch at about the same time, and territorial defenses are abandoned by the adults when the hatchlings - still in down -are ready to leave the nest. Their parents lead them to scattered patches of protective cover on the edge of the colony. Even so, some of the chicks get separated from their parents during the trek - but by some sudden genetic miracle the adult swift terns are now no longer viciously aggressive toward strange chicks, but actually protective. Though, on Karan Island, only a tiny percentage of the swift terns had hatched two eggs, we now found many terns brooding two or even three chicks: their own as well as a temporary "foster child."
Lesser crested tern chicks of the same where relatively few adult birds babysit while the parents go fishing. Yet on their return the adult terns can identify their own chicks among thousands of identical balls of fluff, and only rarely succumb to the pleading gape of another hungry beak. The nursery on Karan Island must have contained at least 10,000 chicks, all hungry - a scene of considerable confusion.
Any close approach to the nursery causes deaths among the chicks, which panic, run into the sea and - though they can swim - soon become waterlogged and drown. The adult babysitter terns on Karan spotted us at a distance and attacked with utter determination, flying directly at our faces. It would take a determined intruder to come any closer, and we did not.
Man's less direct approaches, however, could pose a serious threat to the tern. Although rats, mice, crabs, airborne predators, and the tank-like turtles - which can crush eggs and chicks as they plow ashore to lay their own eggs - also pose threats these are all forces as natural as heavy seas, and the terns have successfully coped with them since they evolved. What they can't cope with is the destruction of their breeding grounds, or of the isolated and undisturbed character of the breeding grounds. Thus oil spills and visitors are what could do the terns in.
So far, the Arabian Gulf has been spared all but the most local pollution; indeed, the terns' continued presence in the Gulf testifies to the current low level of pollution. But controls on visitors to the breeding islands may still have to come - if only for the annual two to three months of the breeding season - since casual visitors, all unaware, can harm eggs or chicks or keep adult birds away from their nests. If it keeps these beautiful birds in the Gulf, that modest additional protection will have reaped a rich return.
Raymond J. Connor, formerly a Detective Chief Superintendent of Scotland Yard, has been an ornithologist for 35 years and has contributed numerous papers to specialist publications.