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?2o THE CONDOR VoL. V ing a loud noise for a few moments. The female remained on duty until we were directly over the nest. They made but little fuss this time, probably owing to the fog. Upon lying down and looking well over the edge of the ledge, the eggs were seen on the sandy floor of a small pothole. They were five in number and so far advanced that the embryos were covered with down. Incubation must have been at least two weeks, causing this set to be the earliest laid o[' any in the latitude. Bendire's "Life Histories of North American Birds" records.a set taken by Mr. W. E. Bryant on March 25, incubation fresh, some years ago at the place hereinbefore mentioned, at the foot of Mt. Diablo. In ?9oo, March 3?, we arrived at the ranch house and were told the birds had left the locality because one of the party had passed up the canyon last week and failed to see the birds. This was far from encouraging news after our long trip and it seemed our informant knew what he said, but I surmised he failed to see any birds because the female was a close sitter and the male might have been off on a hunting excursion, and we therefore decided to labor over the steep and winding route once ?nore and not return without investigating more closely than a hunter would. When on the opposite hill, before the ledge appeared to view, we breathed a sigh of relief, for wasn't that the music we were anxious to hear, the notes of a prairie falcon? In a short time we saw the female reconnoitre from the nest-hole and after crossing the canyon and adjusting the rope, soon had five eggs in our possession; incubation fully one week. The male had alighted on a dead snag across the canyon and now and then uttered his "chug" notes, described where he allowed his mate to fly to and fro along the canyon, and once as she flew rather close to him he joined her for a short flight, then resumed his perch and uttered a sort of cackle unlike any I ever heard, neither can I _emember it nor de- scribe it after hearing it, except that it varied considerably from the usual sounds. An advanced or retarded spring apparently cuts no figure with these birds. This year spring was well advanced while nidification was later. In x9o?, March 30, the site was tenanted by a pair of duck hawks, but no eggs were found althongh we worked the length of the ridge very thoroughly, nor did the birds raise any disturbance, as is the rule. One of them was sitting in the nest-hole when seen across the canyon, and the pair allowed us to approach sur- prisingly close before taking wing for a resting place further along the ridge, instead of making any sort of demonstration or flying about overhead. They were flushed again but only made a half-hearted fuss. From its superior size and fiercer habits I judged they had driven the prairie falcons into a new precinct, for we were not able to obtain a glimpse of them. It is probable that no pair of duck hawks or even prairie falcons dwell within a few miles of each other's domain owing to mutual antagonism. Once while robbing a duck hawk's nest in a dizzy cliff over a canyon the male had settled on a dead tree half a mile along the ridge leaving the angry female to swoop at us and do all the screeching. She took but little interest in abusing a couple of turkey vultures that came too close, but all at once a prairie falcon chanced across the zone of her short flights and she imme- diately attacked him, about 250 feet over the side hill. Both birds clinched with their talons, and in each others grip fell straight down like dead weights. Seem- ingly in an inextricable position they were about to meet with injury or death by contact with the ground below, bnt when within a few feet of the hill they simul- taneously and deftly parted, swinging gracefully aside, the prairie falcon continu- ing its original course and the duck hawk resuming her swoops and invectives at us, with increased energy. In ?9o2 we did not arrive at the prairie falcon nest until April ?5, so as to