Sept., 1918 167 



EVIDENCE THAT MANY BIRDS REMAIN MATED FOR LIFE 



By F. C. WILLARD 



ONE OF THE strongest impressions I had as a boy, and later as a student, 

 in reading various books and papers on the Life histories 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 1 turned this over in my mind 

 every time I met the statement I 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 

 stretch as I began to do in Arizona. Here three special fields drew my atten- 

 tion 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, I 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. 

 Having 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 the sections above mentioned and other 

 species that are found in but one. The Vermilion Flycatcher (Pyroccphnl >us 

 rubinus 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. Seldom 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 comparison 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 willow 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 when I collected a nest of this bird I always tried to take 

 it on the fork if possible. One pair always selected such a large fork that I 

 could not collect it, and the result was that the same few forks were used by 

 this pair 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 1 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 pertinax pallid iventris) were, 

 particularly reliable 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 



