On several days over the past winter small and large groups of cormorants hve been seen. Below I give some of my records.
Very large flocks were recorded on 18th November 1987 in the Zirku area; three on south-facing slopes on the Island and two about two miles offshore to the west. All had disappeared the next day and I have not been able to discover when they arrived. On 2nd February 1988 there was a large flock on the south-east tip of Qarnayn Island. On 1st March 1988 there was an almost perfectly circle-shaped group adjacent to the north end of the airstrip on the island. The diameter of the group must have been at least 200 feet. On 19th April 1988 another large group was noticed on Qarnayn Island.
Estimating the number of cormorants in one large flock gives an unbelievably large number. For instance, one group in the sea, seen on 18th November 1987, easily had a surface size equal to a large tanker, which we visit often. The tankerís length is 320 meters and its width 52 meters (1000 by 150 feet). One bird per square foot is rather on the high side. Let us accept one third of this figure, which is certainly possible. But on that day, there were five flocks of roughly equal number in the Zirku area, giving a minimum total of 250,000, a quarter of a million and a very large number indeed. Smaller flocks were seen at sea in Umm Shaif oilfield on 31st March 1988 (three flocks) and one on a well-head on 7th April in the same field. There was one more flock of cormorants completely covering the helideck of a wellhead in the Zakum field on 9th April 1988. The dimensions of a helipad are about 40 feet by 40 feet. When cormorants roost on them, helidecks appear to be painted black. The birds appeared to be touching each other, so there could have been anywhere between 2 000 and 4 000 of them.
Every so often cormorants are seen flying in large numbers. From ground level they are seen as an undulating line, up to 200 feet high. This happens occasionally in the neighborhood of Abu Dhabi. A few times I have seen this offshore between Abu Dhabi and Zakum and between Zakum and Zirku.
When flying at 1 500 feet, you sometimes see them in long lines in a V-formation with branches inside the V (see Figure A). One of the legs of such a formation has been followed for three minutes at an airspeed of 90 kts, giving a distance of roughly 4.5 miles. Between two birds is an open space, where another bird could more or less fit. The end of the other leg could not be seen. The wingspan of the Socotra Cormorant is about three feet, so in three minutes at least 4 000 birds can be seen.