Page:Condor13(2).djvu/20

58 THE CONDOR Vol. XllI construction of numerous large storage reservoirs, with the consequent seepage aud marsh land, suitable breeding grounds have increased in number many fold; and in the case of the Barr Lake region at least, these birds are now common summer resi- dents and breeders, and so far as my own observations go I should say that a fair proportion of migrants make this the terminus of their northward migration. The first appearance of'the terns in the spring was about May first; our earliest record was April 27, 1907, on which date a total of fifteen birds was noted, at dif- ferent points along the Barr chain of lakes. We did not note any extensive migra- tion of these birds immediately following this date, and in fact we did not see any migrating flocks of terns which we did not have good reason to believe were a part of the local breeding colony. However, northward moving flocks might easily have passed through between our weekly visits to the lakes, or during the night. By May 10, or a few days later, the full quota of breeding birds had apparently arrived, and nest building was .begun within a few days. May 11, 1907, the nest- ing sites had apparently been selected, as the birds made a great commotion when we visited the spot, and the first egg was found May 17. Fig. 24. THE INJURED FORSTER TERN AND NEST The nesting site was a large musk-rat "house", standing in the dense cat-tail swamp surrounding a small rush-bound lake. The house which stood in about two feet of water, projected about two feet above the water, and the eggs were laid in a slight cavity among the dry cat-tail stalks composing the house. These nests corresponded exactly in location and construction with those we had examined the preceding year. On this date (June 9, 1906) we examined fifteen nests, all located on musk-rat houses, and containing eggs exhibiting all stages of incubation. The fifteen nests contained one set of six, two sets of five. nine sets of three, and one nest a single egg. On May 24, 1907, (a week after the first eggs were found) the breeding colony was in full swing, and we were surprised to find a number of nests, containing complete sets, which had been built by the birds upon floating masses of decay- ing cat-tails. These structures were all made entirely of dead cat-tail stalks, and while they varied greatly in size and bulk, the general plan of construction was the same in all, being a compact pile of material of irregular outline, apparently floating on the