52 TIlE CONDOR Vol. XVI Turner-Reich lens of eighteen-inch focus, stopping down to 64 U.S., and giving an exposure of ten seconds on a Seed nmnber 3 plate, I secured a negativ.e of her in this position which is the best one of all. Some idea of the value of a good convertible lens in this work may be secured by comparing the picture of the sit- ting bird with that of the nest and surrounding rocks (fig. so), both taken from the same spot. The double combination of the lens of six and one-half inch focus was used in the latter picture. A slight movement of the focusing cloth after this exposure was too much for the nerves of the bird, and she was off like a flash, but so quietly as to be unheard even at the short distance I was from the nest. Both birds put in an appearance after the one left the nest, but beyond cat- oq Fig. 23. PACIFIC ltORNED O?VLS THREE WI?EKS OLD; PORTION OF RABBIT IN FOR]?GROUND calling and "who-who"-ing around, made no disturbance. The mate of the sitting bird flexv out from a small sumac bush on the steep hillside directly above. I had always supposed there was considerable difference in appearance between the male and the female birds, but I could not tell one from the other except for one having an unusually white feather in its "horn". This feather shows up very plainly in the picture of the sitting bird. One was nmch wilder than the other and could not be approached very closely. indicating that they took
- urn about in the incubation of the eggs.
The cause of the extreme bravery of the sitting bird was at once apparent upon looking into the nest. One owlet was out of the shell and the remaining egg was pipped. This is conclusive evidence that the period of incubation is
