S?t., 1918 167 EVIDENCE THAT MANY BIRDS REMAIN MATED FOR LIFE By F.C. WILLARD NE OF THE strongest impressions I had as a boy, and later as a student, in reading various books and papers on the life histor'ies of birds, was the comment frequently made therein that this or that species remained paired or mated for life. It was soon borne in upon me that this assertion was applied practically to raptores only. While I turned this over in my mind every time I met the statementq always wondered why it was so. Not until I went to southern Arizona, in 1896, did I begin real active field collecting. I had collected some in Illinois, but never days or weeks at a ?tretch as I began to do in Arizona. Here three special fields drew my atten- ?:ion annually, the San Pedro River. valley near Fairbanks, the Huachuca Moun- tains, and the vicinity of Tucson. After a few consecutive seasons spent in working these sections, ! began to realize that I could expect to find a pair of some certain species of birds nesting within a very short distance of a given
spot every year, and I at once began .to wonder if it were possible that an occa-
sional pair of birds other than raptores remain mated for life. Not to spend more time in following the processes of my mind in regard 'thereto, I want to give some specific instances which have led me to the opin- ion that it is more usual than unusual for land birds to remain mated for life. IIaving had no experience with water birds, i shall exclude-them from my con- clusions. The flycatchers are a well represented family in Arizona, and there are species that are found in all three of t,he sections above mentioned and other species that are found in but one. The Vermilion Flycatcher (Pyrocephalus rubi?ts mexicanus) is one of the former. A pair nested every year in the trees about our house in Tombstone. We all watched for their arrival. Sel?lom did a third bird of this species appear on the place. though every season the male went through his mating antics just as though he was courting a new spouse. How do I know it wasn't a new spouse ? I don't know it except that my obser- vations have led me to make up my mind to the point of conviction that it was the same pair year after year. The selection of the same forks for the different nests each season, the similarity of the eggs as far as they were examined (I did not collect any from this pair), the lack of fear they possessed, so marked in co?nparison to that shown by others of the same species in other places, all these helped to convince me. Along the San Pedro River I had certain wiIlow trees marked out, in each of which I always expected to find a Vermilion Flycatcher's nest. If it did not happen to be in the exact tree it was sure to be in an adjacent one, and this in spite of the fact that w?en I collected a nest of this bird I always tried to take it on the fork if possible. One pair always selecte'd such a large fork that I could not 'collect it, and the result 'was that the same few forks were used by this Fair each season, sometimes one and sometimes the other. Frequently the same fork was used twice or oftener in the same year. In the Huachuca Mountains there was a certain route I used to cover on a three day's trip. Along this route I .had certain pairs of the various birds "spotted". The Coues Flycatchers (Contopus perti,?ax pallidiventris) were particularly reIiable and in ordinary seasons I could give many of the partic- . ulars in regard to the different nests, before I had actually seen them, with a
