July, 1917 THE OSPREVS OF 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 

 wormy 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 continued 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 cannot corroborate from my own observation the 

 statement that this bird repairs its nest in the fall) is soon finished. 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 Avrench 

 with his strong feet. Coarse grasses, pine needles, 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 J ? While the temperature in the shade reaches a 

 maximum of only 80 degrees, on the sun-baked floor of the exposed nests it is 



