July, 1917 THE OSPREYS OB THE YELLOWSTONE 119 dred and twenty pairs of ospreys regularly breeding there. There are also two old, or abandoned, nests for each occupied one. Most ornithologists would surely rank this bird as abundant here, and I believe this abundance is due to the large quantities of easily obtainable fish as much as to the absolute protec- tion afforded. As trout are the only large fish to be had, sportsmen-tourists are sometimes antagonistic to these rivals of the air. But there are certainly fish enough for all; and when it is considered that the ospreys catch mostly the
- vormy fish whose malady makes them an easy prey by bringing them near the
surface, and less alert to the plunging danger from above, we see that they are really improving the stock by removing the diseased members. Ospreys arrive at the low-altitude Gardiner River Canyon about April 17 (my earliest date is April 15, 1915), but it is apt to be two weeks later before they reach the Yellowstone Canyon and Lake; even so, early May is well on the snowy side of the year. The birds are already paired off (in fact they are be- lieved to mate for life), and immediately start their hunt for a nest site. Al- though they may have nested at a certain place for years, they go through the form of site-hunting each year and then finally return to the old nest. Un- doubtedly the normal nesting site of an osprey is the tip of a tall spruce, pine, or fir on or near the water's edge. I do not think there is any preference shown for either living or dead trees, but it is likely that the nesting often kills the tree. In certain canyons, notably the Gardiner, Gibbon, and Yellowstone canyons, the ospreys have chosen to build their homes on the tips of sheer, out- jutting pinnacles of rock whose tips are completely covered by the nest. That these prove reasonably safe can be deduced from their eontinued use over a long term of years; yet I have observed that the mortality among the young is high, only about one-half reaching maturity. Repairing the nest (I eannot corroborate from my own observation the statement that this bird repairs its nest in the fall) is soon f, inished. It is then four feet or more in diameter and made of a great mass of sticks some of which may be as large as a man's wrist, usually secured by the bird dropping heavily on the dead limb of a tree and at the same time giving it a peculiar wrench with his strong feet. Coarse grasses, pine needies, pieces of bark and other rubbish are placed on top. Most of the nests are close to the water, but some are a mile or more from it. As a rule there is quite a delay from the finishing of the nest to the laying of the eggs. I have found sets of eggs as early as May 20, and have known of other sets not completed until June 25. Even the ear- lier of these dates is very late; but is evidently due to the late date (often mid- June) that ice remains in the lake; and the stream-haunting birds are delayed by the June rise of the streams. Fish is to be had in these streams before the rise, but evidently the birds do not consider it safe to risk their young against the usual conditions of May and June; perhaps also the late snows of June might have their effect on the exposed birds. About Yellowstone Lake, with an altitude of 7800 feet, nesting is fully as early as in Gardiner Canyon at 5500 feet. Two or three eggs constitute a set and they are brooded for twenty-eight days by the female, who remains continuously on the nest except that during a warm, sunny day she may venture to leave for a short time. I have often won- dered why the nests were so large. Can one of the reasons be to afford the young room to find a cool spot ? While the temperature in the shade reaches a maxi?num of only 80 degrees, on the sun-baked floor of the exposed nests it is
