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 SzPv., x9o3[ THE CONDOR Some Observations on the Nesting Habits of 'the Prairie Falcon xt7 BY DONALD A. COHEN Read before the A. O. U.--Cooper Club Convention, May I6, x9o3 HIS falcon, Fa/co mexicanus, is very rare in the San Francisco Bay region and in a radius of a day's journey about the adjacent territory. Nowhere does it appear to locate its eyry upon the rocky sea coast after the manner of the duck hawk (Falco eregrinus anatum), but prefers the low mountain ranges interspersed with plenty of canyons and rolling valleys. It is hardly necessary to mention that it is less plentiful than in bygone years, having fallen into line with many others of our fauna in their retreat from the encroachments of civiliza- tion. In June x884 while visiting friends in the foothills of Mr. Diablo, Contra Costa county, I was one of a small party in quest of birds' eggs among the cliffs and rocks on the sage-covered slope of the mountain, and incidentally flushed a family of prairie falcons from one of the loftiest cliffs. There were five of them, the iamily of that year, that circled overhead at no great distance during our presence near the cliff. My host, who was present, said they were prairie falcons and said that Walter Bryant had gone over these rocky cliffs by means of ropes and taken their eggs, from time to time. In later years when I made Mr. Bryant's acquaintance he corroborated this. I first noticed the birds here in x88x and have wondered for how many centuries the species nested in that spot. About the last set of eggs taken in this locahty was, from memory, in 889. It was of four eggs taken by a boy living near by and procured for me by my friend and exchanged to the late Chester Barlow. The nest was described as being placed on a ledge and lined with a few sticks and I believe, some grass, while all the prairie falcons and duck hawk sets I have ever taken, about twenty-five sets, were all in small caves or potholes, with a bed of sand or fine gravel and sand with a few bones of small mammals and birds. The birds were either killed off by the numerous campers that infest the region or worried into leaving for more secure quarters. The boulders and cliffs and even the top of the ridge is not so high but that rifle balls will go over from the road in the narrov valley below. Among one of my curios is a partly flattened bullet from a large calibre rifle that I picked up at the base of a boulder near the top of the ridge. In this latitude, I may assume, the birds are constantly resident except for excursions during fall and winter when the young are probably in search of a home, as the old ones will not suffer their presence any longer, so I am told by a mountaineer. On two occasions I have noted single birds in Alameda. One attacked a band of half grown turkeys early in the fall and the other flew from an oak at some pigeons inside their enclosures and struck the wire netting with con- siderable force. Being well acquainted with the duck hawk in adult and iuvenile plumages there is no mistaking a prairie falcon at dose range. The complement to a set of eggs is five and it is hardly possible to confound them with eggs of the duck hawk. As a rule those of the former are plainer and lighter colored, and in exceptional cases some are exquisitely blotched or mot- tled, being gems among gems. In the general run they lack the generous rich coloring of some of our duck hawk eggs but some of the best sets possess such a different style of beauty as to hold their own with any set of duck hawk I have ever seen. They average a trifle smaller although the superior size of the duck hawk over the prairie falcon is greater in proportion.