side, the strings which the Old Crow had pulled scores of times in earlier tests. Would he have done so without his previous experience? This Young Crow showed signs of imitating the Old Crow most often only when the efforts of the latter were similar to those previous efforts of the former which had resulted in opening the door and thus obtaining food. English Sparrows, Cowbirds, Bluejays, Baltimore Orioles, and Crows when submitted to experiment by negative as well as positive results, exhibit behavior w r hich makes it advisable to use the criterion as stated above. If bird No. 1 has not previously opened the box it is unlikely that it will try vigorously to do so unless the experimenter can in some way delay action on the part of bird No. 2. But, if No. 1 has previously obtained food in its own way it not only will be more likely to struggle, fight, etc., with bird No. 2, but has given the experimenter, by its previous behavior, a standard by which to judge its present behavior. As a working hypothesis and standard of interpretation the reader is asked to hold in mind throughout this paper the criterion as stated above.
III. Results of Experiments
Series A. English Sparrows and Cowbirds
These birds, several pairs of each species, were forwarded to me in the same small box. While the large cage in which they were to be kept when experimented upon was being built they were placed in smaller cages and supplied with plenty of food, sand and water. It was interesting to see that the Cowbirds began at once on being liberated to bathe in the large water pans while the Sparrows showed a strong preference for the sand bath.
The Cowbird is much easier to keep in good condition than the English Sparrow and, I believe, than most other birds. Early in my work it was noted that the Cowbird was very attentive to the Sparrows. See Fig. 1, A. It soon developed that they were looking for parasites. Judging from the fact that I have never seen a single parasite really taken by them one would conclude that we may have to deal here with a very strong habit or probably an instinct. They look over very carefully the perches, window 7 sashes, etc., in fact all objects where parasites might be found. It is probable that many times the Sparrows need the good offices of the Cowbird; but very early the male Sparrow learned always to keep a safe distance away. The little female Sparrow was able whenever she wished to so use her beak that the Cowbird refrained for a time from coming too near. Fig. 1 B. It is not impossible that a part of this behavior of the male Cowbird was due to the mating instinct.
