Breeding Habits of the Least Tern in Los Angeles County, California.
By A. I. McCormick.
[Read before the Southern Division of the Cooper Orn. Club, March 26, 1898.]
The beaches of this county, from Santa Monica southward, afford excellent breeding grounds for numberless birds of this species. The coast consists mainly of low sandy beaches, extending back 100 to 200 feet from the water's edge. Back of the beach proper come low sandhills, interspersed with small valleys, and farthest from the ocean are the higher lands, covered with a thick growth of low sage and other shrubs, about 200 feet from the water's edge. Water on the one side and sage brush on the other mark the boundaries of the nesting grounds of Least Terns, most of which last year [1897] arrived from the south about May 10th. For ten days they remained flying high over the sea, seldom if ever coming within gunshot range. My first trip to the beach was made on May 25th, in expectation of collecting eggs of the Snowy Plover, not expecting to find the Terns breeding. Consequently I was surprised on entering the colony, to see numbers of Terns flying wildly about, uttering their shrill notes, indicating that nesting had commenced. The result of information thus conveyed was that my friend and myself at once began to search for their eggs.
So successful were our efforts that during the day we collected twenty sets of two eggs each. The first set taken was in a mere depression in plain sand, about two inches deep and four inches wide, 100 feet from the water's edge. This description answers for the average of all sets taken on this trip—the distance of the nests from the water varying from 75 to 600 feet. Set No. 2 was taken from a hollow in the center of a bed of gravel, lined with small fragments of white shells upon which the eggs were laid. This is quite common with the Snowy Plover, but exceptional with Least Terns.
My second and last trip to the beach was made on June 5, when I was fortunate enough to take fifteen sets of Least Tern's eggs. Six of them consisted of three eggs each. This is exceptional in this county. I have consulted several collectors who have had considerable experience with Least Terns in this locality, and with one or two exceptions two eggs has been the invariable complement found. Several other sets of three were taken in 1897. In all I took 25 sets last season, but could easily have doubled that number had I desired to do so. On each trip we left many nests containing one egg, and many new depressions ready to receive eggs.
All the eggs collected on the first trip were fresh, but many of those taken in June were much incubated. The Terns nest in colonies in common with Snowy Plovers, with eggs of which those of the Terns are often confounded. But upon dose examination they can be easily distinguished; those of the Terns are more nearly oval, and the small end of the Plover's egg comes to a sharper point.
The ground color of the eggs of the Tern is lighter than that of the Snowy Plover's. The spots on the Plover eggs appear like scratches, while in the case of the Tern, the spots are more symmetrical and rounder, and harmonize better with the ground color.
The habits of the two birds during the nesting season are quite different. On one's entering the Tern colony, all the birds at once rise and fly swiftly about overhead, often darting at the intruder within a few inches of his head. They are the most pugnacious and saucy birds that I have yet met during nesting time. The female Snowy Plover often waits until one is within a few feet of the nest before she leaves it, and when she does hop off is generally unobserved. This Plover is a very quiet, unobtrusive bird, in fact, one might tread the beach for hours in the midst of these birds and not know of their presence unless particular pains were taken to ascertain it. Instead of rising from the ground and flying overhead like the Terns, on the approach of a person they run along the sand a few
