History of a Nesting Colony of Caspian Terns on San Francisco Bay

Abstract

It was in 1924 that information was first brought to Mlr. Chase Littlejohn, veteran naturalist of Redwood City, that a colony of Caspian Terns (Hydroprogqne caspia imperator) was breeding somewhere in the southern reaches of San Francisco Bay. The man who brought Mr. Littlejohn the information stated that a few of the birds had been noted in 1922 and again in 1923, but it was not until 1924 that they became numerous. He was asked to bring in a few of the eggs the next time he came to town, which he did the following week. These eggs, together with a vivid description of the birds, convinced Mr. Littlejohn and myself that Caspian Terns were breeding in the Bay district. It was not until July 4, 1926, however, that we were able to affirm positively our earlier convictions, by making a trip to the nesting colony. Leaving Redwood City by automobile about five-thirty on the morning of the fourth it did not take us long to reach a group of salt ponds on the southeastern side of the Bay, where the colony had previously been located. These ponds were enclosed and subdivided by a series of dikes or levees and it was upon one of the latter that the birds had been reported nesting. The question was, which one of the many miles of dikes had the birds selected: not an easy problem, as the dikes all looked exactly alike. With the aid of a field glass we eventually picked up a rather steady flight of birds all of which seemed to be headed toward a single point on one of the dikes, some half-mile distant. Upon closer scrutiny of this particular area we were quite sure that we could see a closely massed colony of nesting birds. Eagerly anticipating the pleasure of stepping into the center of a breeding colony of this species we put on full steam ahead. As we approached our destination we could clearly see an ever increasing number of terns flying to their breeding grounds. Several of them came quite close to us, making it possible to identify them as Caspian Terns. Each one seemed to be heavily laden with fish, which evidently it was carrying home to a hungry family. When we were still a hundred yards from the colony all of the adults sailed into the air emitting a rather startling, if not terrifying, chorus of tern blasphemy. The more daring members came right out to meet us, some of them actually swooping down to within a few inches of our heads. Each time one darted at us it let out