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 Mar., 1919 NOTES FROM THE FEATHER RIVER COUNTRY 77 I had expected to find the Calaveras Warbler and the Sierra Hermit Thrush (Hylocichla guttat a sequoiensis) fairly numerous near Mohawk or Johns- ville, but found none of the former and identified but one of the latter, which was the only one whose note was recognized as belonging to that species, .its song leading to its capture for identification purposes. Sa Francisco, Jauary 22, 1919. THE MARITAL TIE IN BIRDS By LOYE HoLMEs MILLER N THE CONDOR for October, 1918, Mr. F. C. Willard contributes a most stim- ulating article dealing with the question "Do birds mate for life ?" In sup- port of his affixhnative contention he brings forward 'some observations re- sulting from his extended field work in southern Arizona. His article is good and the facts recorded are unimpeachable. The inter- pretation of facts, however, introduces the human element into science, and hence offers a basis for divergence of honest opinion. It is not my desire to dispute Mr. Willard's conclusions but to offer, wholly in good faith, some re- marks in support of the opposite side of the question, so that each reader may be his own judge, jury, and court of appeal.. I am free to say that I do not know whether or not birds mate for life, which statement is equivalent to admitting that I do not consider my own argu- ment as conclusive. In all probability it often falls out that the same individ- uals come together in successive reproductive cycles, but such may be quite a fortuitous'occuence, due wholly to propinquity and not therefore proof of the truth of a more general conclusion. For some time it has been my own opinion that birds do not, as a rule, retain the same mates from one season to the next. At the risk of stepping from the realm of knowledge to that of spec- ulation, I am offering in support of my position the following points, scarcely to be dignified by the name of evidence. My first contention is that a bird's' activities are almost wholly the result of instincts. These instincts are racial characters and are transmitted from generation to generation, no less truly, though perhaps more variably, than is color, size, or wing area. Only occasionally can even the layman contend that what we call intelligence enters in as a factor of behavior. Instinct bids a Hooded Oriole choose plm or yucca fiber as her nesting material, even though she place the structure in a gum tree or on a corn stalk, and failure of this in-' stinct is almost as rare as is that failure in pigment formation which results in albinism. My second contention is that instincts are dependent for their stimulus upon the physiological condition bf the animal. Recent experiments on internal secretions have been performed by the transplantation of reproductive glands or by the infusion of tissue extracts directly into the blood stream. These ex- periments have some bearing upon our problem in that they go to prove that plumage differences between the sexes of poultry are directly controlled by the presence in the body of these germ cells, and that many instinctive acts are dependent, for their immediate stimulus, upon the activity of these glands. A