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 14 THE .C. ONDOR Vol. XIII For a moment we felt dubious as to the nest being occupied. As we approached the tree, however, a Great Horned Owl flew from oue of the higher branches, aroused either by the squirrel or, more likely, by our own approach. This was more favorable. We gave the tree a few kicks, when the sitting bird hopped up lightly to the rim of the cavity, looked across the white landscape for several secouds, then spread her nearly five feet of wings and flew silently away. Our first mistake for 1907 wasin not looking iuto the uest on this first day. Our reasons for not doing so were the belief that the set of eggs could hardly be complete at this time and especially the fear that the egg or eggs could not stand exposure even for a short time on so cold a day. My present belief is that this fear was unfounded. Just two days later, on February 9, at about three o'clock in the afternoon, I visited the nest again and found the set of three eggs complete. Fig. 1o. APRIL 18. lq07; AT THE BASE OF THE OLD NEST TREE; VOUNG THIRTV-SEXEN TO VORTX'-OE VAX'S These were lyiug in a slight hollow as before, but as far back ill the cav'ity as possible. Except for n small space about the eggs the house was filled. even to the door sill, with suow. It was a picture indeed, but one over which we did not dare tarry in freezing weather. All the eggs were nest-stained and it did not look ns if any one of them had beeu laid that day. However, this was uncertain nnd I had lost n possible opportunity of learning just wheu the set became complete. This was regrettable, for no one seems to know the period of incubation of an egg of the Great Horued Owl. The older ornithologists made their guess at three weeks. Bendire later expresses his belief that this period is too short nnd that four weeks is probably nearer to the truth. I have not determined the point though my datn stillpossesses some interest. Toward the end of the month I