THE CASPIAN TERN

Forest and Bird, Issue 57, 1 August 1940, Page 12

THE CASPIAN TERN

(By Wesley Sanderson.)

THE Caspian tern is the largest tern in the world. It is like its smaller relatives in that «t has a forked tail and pointed wings, also a dagger-like beak. The colour of the Caspian is white except for slate-grey on the wings and shoulders and a blue-black cap in summer or a grey one in winter. The young ones have spotted wing feathers and grey caps. The feet and legs are small, black and webbed, while the three-and-a-half-inch beak is light, bright red.

The Caspian tern is a fish-eater. It flies along about thirty feet above the water with its beak pointing downward at right angles to the body. Every now and then, perhaps to see where it is going, it looks up with a jerk of the head and then goes flapping on until it sights a fish; it flutters above the water for perhaps half a minute, then closing its wings it drops down on top of its prey, and a second later it is in the air swallowing the fish. When diving, the tern often keeps the . tips of its pointed wings above water.

In early spring, about August or September, the terns collect in groups of two or three hundred or in still smaller groups. In late September they set about their work of nest-building. About a mile out on the beach in front of our home on the Whangarei harbour there is a shell bank about a foot above high spring-tide level, and on this about three hundred terns usually nest. All I know about the Caspian tern I learned from this colony. After they have been at the colony for about a month they start to pair up for the nesting. The courtship is interesting. They bow to each other, run round in small circles and come to a stop facing each other. Next they bend their legs until their breasts reach the earth and their beaks touch each other on the ground; then they raise their heads very slowly and stretch them far back, uttering curious noises in their throats at the same time.

The nest, which is a hollow about three inches deep scratched in the shells, is sometimes lined with seaweed. In this the female usually lays two eggs and on rare occasions —never more- These are dirty, whitish brown, blotched with dark brown. After

about two to three weeks of incubation, which is carried on by the sun alone on hot days, the chicks poke their tiny beaks through the shells and start to squeak. This is a period of danger for the tiny creatures. Some can’t force their way through the shell, while the shell sticks to the wet down of others and they die. I have often helped the chicks out of the eggs. When first hatched they are very ugly, but after an hour in the sunshine they are beautiful snowy white chicks with pink legs and beak. When the chicks hatch, the parent birds are kept very busy searching for food, bringing to their young mainly herring or piper, which is placed head first in the baby’s open beak. Often these fish are as big as the chick, so the little fellow props itself up and goes to sleep, and as the fish digests the rest slips down until finally the tail has disappeared and the fish is digested. As the chicks grow the beak quickly develops, while the feet hardly grow at all. When the chick is a month old its legs have turned black, and it wanders all over the colony. I remember on summer Sundays we used to walk out to the colony, which is near a deep tidal creek about a mile across the beach from the house. When we were within half a mile of it a group of half a dozen old terns would fly out and have a look at us, then return.

Then when we were within a couple of hundred yards of the colony a mob of about twenty males would rise up and attack us. They would hover about thirty feet above our heads and then dive at us, missing our heads by inches only. If we took our dog with us he sometimes received a peck or two. As soon as we arrived every pair of wings would be raised skywards, and then with a whirl they would all rise and we would be subjected to a fierce attack. As the birds hovered above our heads they would utter harsh short crackly notes, and as they dived they would let out an ear-splitting, crackling call. As this was happening, all the chicks over a week old had either sought shelter in the mangroves or had run down the beach and taken to the sea, where they could be seen swimming to the opposite shore some hundred yards away. Then the parents would fly over to their young and encourage them along on

their perilous voyage. When on the other side, they would wait until we left, then return with their parents fluttering over their heads. Some of the youngsters were in difficulties when we arrived, for many of them had fish six inches long in their throats. Most of these were disgorged, but others were swallowed. Some of the larger chicks were so full that they could not run.

Their greatest enemy is the tide. Some four seasons back, after it had been blowing hard from the east for nearly a week and had been raining heavily most of the time, the spring tide banked up and came high above its usual mark. By 11 a.m. the tide reached its highest, completely covering the shell bank. Alas, it was the middle of the nesting season and there were hundreds of young birds there in various stages of development, and dozens of eggs. Presently the rain stopped and the wind died down completely, so father and I went for a walk when the tide went out. Dozens of young dead terns were lying amongst the seaweed, and also a pair of little blue penguins, starkly cold in death. We went on to the nesting place. The shell bank had partly washed away, and all that remained of the once happy colony of young birds was about a dozen big youngsters. When coming home, I noticed a white thing on a small islet, so I went over and found a young tern almost dead. I took it home, and after about an hour it was quite lively again. As I had no fish or meat I was forced to give it a slug. This it would not eat until salted.

I kept the baby bird until the first fine day and then returned it to its birthplace. So far I have only mentioned the terns’ unconquerable foe, but now I turn to rats. About a quarter of a mile from the nesting place there is a small islet situated in the midst of huge hollow mangroves ideal home for rats. Every night dozens of huge brown rats used to steal through the dark desolate wastes to the colony, there to rob, murder, and carry off eggs and young ones. We noticed this happening, so one day we went a-hunting and caught twenty-five of these rats.

As can be guessed, all the terns are not always successful in their quest for food. Then they turn pirate and rob the other terns of their prey. Often I have seen a tern with a fish being pursued over the land. Of course both strive for the highest position, the result of which is that they both rise to a great height. Often the pursued is so hard pressed that he has to drop his prey, which falls rapidly earthwards. The terns drop after it, and before it has gone fifty yards have caught up with it. The bird that arrives there first seizes it in its beak and, spreading its wings, shoots upwards and off he goes with the loser in hot pursuit. Occasionally, however, they both reach the fish at the same time and fight for possession. When terns fight, they do not continue fighting for long. After a few seconds one can usually be seen to be getting the worst of the combat, and this one soon flies away, hotly chased by the other.