Bulletin 27 - November 1985: Notes on the Birds Breeding on Qarneyn Islands

Notes on the Birds Breeding on Qarneyn Islands

There is one regular breeding pair of ospreys on the island, using the same nesting site each year. This is situated on sand about 20 feet in from the sea, on the low-lying and flat southwest corner. A further two pairs have taken over sites for varying periods during the nesting season, but no eggs have been produced. There are about eight old nesting sites on the island, though the one used by the successful pair is by far the largest, consisting of a mound of sticks about 3 feet high and the same in diameter. Tastes in nest-lining are very catholic, and include cormorant skeletons, sea urchin cases, rags, seaweed, nylon rope, even an old broom head and part of an accumulator plate. Ospreys are winter breeders, and in the two seasons observed, 1982/83 and 1983/84, had already begun breeding when I arrived on the island. On December 25th 1982 there were already two eggs in the nest when discovered. One chick hatched on 24th January; the remaining egg was infertile. The chick grew rapidly and had left the nest by 4th April, when I returned after a three week absence.

The 1983/84 season was more successful. Two eggs were laid by 8th December and a third was present when the nest was inspected a week later. On 13th January the first chick hatched, followed by another on 15th. The last chick did not hatch until 20th, and the considerable size difference among the three was visible throughout the fledgling period. All the young flew from the nest when approached on 23rd March -- a minimum nesting period of approximately nine weeks, though they returned to the nest occasionally over the next few days. Once they had left the nest it was difficult to distinguish the young from the adults, and they were rarely seen together, preferring to skulk in the scrub until they could fly strongly.

These are also winter breeders, and I estimate that approximately 200 pairs breed on Qarneyn. Natural holes and crevices two feet or more in length and situated on raised ground, are preferred, but any suitable hole is accepted, including hollows under stones in the flat areas; two were discovered nesting only a few inches above the normal high tide mark on a rocky section of the shore. Only one egg is laid, from which a somewhat immobile grey down-covered chick emerges.

If this breeding season was typical, the first adults arrive on the island at the end of October. I found eggs at the end of the first week in December, though I suspect laying commenced earlier. The first chick was discovered in the second week in February, though I feel sure they were present before that date. Interestingly, when the chicks are only just beginning to sprout feathers, their parents leave them alone at night. The breeding season is virtually over by the time the terns commence laying, and the Tropic birds have left the island. though I found the odd chick at the rear of a tunnel that was also occupied by a Bridled tern chick in the second week in June.

There is a winter population of 100 or so of these predatory gulls on the island, though this figure is doubled by an influx of further breeding birds in the spring. The breeding cycle is synchronised to that of the terns, as the chicks seem to be fed almost exclusively on eggs and young from the tern colonies; the first chicks hatch just as the terns begin laying. The nest site is usually against some cover, often in the lee of a boulder, and normally well away from other nests, though exceptionally in a couple of favoured sites a number of nests can be found within a few yards of each other. The pair occupies its territory some time in advance of egg laying; in 1984 many I scrapes were present by the second week of March, though the first eggs didn't appear until the third week of April, three comprising the usual clutch. Accurate records kept for one nest in 1983 show the first egg laid on 10th April, followed by one on 14th and one on 18th, the chicks all hatching on 10th May. Some youngsters were already on the wing by the end of June and by mid-September all gulls had left the island, only the very occasional straggler being observed in November.

Four species of tern breed on the island -Swift, Lesser Crested, Bridled, and White-cheeked. All except the Swift terns were successful; these suffered total losses due to egg-collecting by visiting 'locals'. The terns are non-resident but from the end of March there is a- rapid build-up, mainly of Swift and Lesser Crested terns, which congregate on the offshore rocks. By the end of April they are joined by numbers of White-cheeked terns. Early May sees the arrival of the Bridled terns, but from the outset their behaviour is totally different, for they pair up and disperse immediately over most of the island. When I returned on 17th May 1984 after a month's absence, the Bridled terns had chosen their territories and many nest scrapes were in evidence, but only one nest containing an egg was found.

The nest sites are all under some kind of cover, hollows under boulders being preferred, though the shelter of dense patches of undergrowth was also utilised extensively in the flatter sandy parts. The loose colonies in some areas seemed to occur solely by a close proximity of suitable sites rather than any sociability on the part of the birds, and in the areas where they nested in the undergrowth the nests were fairly regularly spaced some 20 -30 yards apart. Most nests only contain a single egg, though occasionally two are found. The first chick was discovered on 8th June, but eggshells had been found a few days prior to this. The chicks remained in, or close to, the nest site for the whole of the fledgling period when able to fly they moved to the shore, preferring offshore rocks. All had left by mid September.

On 17th May, the first two colonies of White-cheeked terns were found. As most nests at this stage contained only one egg, and many scrapes were still without eggs, I estimated the colonies to be no more than three days old. The first few colonies, presumably occupying preferential sites, were all on slightly raised areas with plenty of fine gravel which was collected to form the nest. Later colonies were found throughout the island. the nests usually consisting of small chips of wood. Probably 30 - 40 colonies, of 50 - 200 pairs each, were eventually formed. Average spacing between nests was about two feet, and the average clutch was two, occasionally three. Even within a colony there was a wide variation of egg colour and colour of' downy chicks. The first chick was seen on 30th May. Even when well-grown the chicks kept to the vicinity of the nest, though as soon as the colonies were approached the alarm calls of their keen-eyed parents sent them scuttling for the nearest cover, and th9se whose nests were nearest the shore readily took to the water when alarmed. The laying period in anyone colony may be anything up to a fortnight~ any birds further out of synchronisation presumably join another colony. By late June many chicks were well-feathered, though even as late as the second week in July there were some small groups still incubating. By mid-August many young were flying, but when observation was resumed in mid-September the only birds remaining were a few parents that had lingered with injured chicks.

The other two species, Lesser-crested and Swift terns, nest in medium-size to large mixed colonies. The two main colonies were many thousand strong within the colony the two species keep themselves in discreet groups, the Lesser-crested outnumbering the Swift terns. Their laying is extremely well-synchronised -- one day bare ground, the next, the colony is in residence with eggs already laid. From the outset the eggs are laid at the regulation distance apart, about 15 inches, the colony simply expanding outwards as more birds lay. The majority lay within the first three days, only one egg per pair being produced. Other birds sometimes join the colony for a couple of days. Observations of the Lesser-crested tern colonies were very sketchy due to the havoc caused by close approach. The original colony started on 18th May.

Within a week or so of hatching the chicks formed into huge crèches and deserted the nesting sites for rocky areas, both on adjacent hillsides and the shoreline, but they were very nervous. Many of the chicks on the shore suffered a horrible death by being trapped in large areas of glutinous oil that had been washed up and then being broiled by the midday sun. Unlike the White-cheeked chicks, they were loath to enter the water, though a few would if sufficiently frightened. By mid-July the vast majority of chicks were well-feathered, though there were still two tiny colonies still incubating. Many birds were still present in September, but the last stragglers had left by the end of that month.