day there is a note to the effect that "No. 2 female seems to be of no interest to No. 5 male (the new arrival); its purpose seems to be to drive away intruders." On the 2nd April and subsequent days, this bird attacked every other male that approached, and not only maintained its position but ultimately succeeded in securing a mate. Here then we have two territories occupied by two males, both of which had obtained a mate. The relation of these two birds was normal, a month's routine had defined their boundaries, and conflicts were less frequent than formerly. But upon this comparatively peaceful scene a strange male intrudes. Observe the manner of the intrusion. The stranger does not wander about first in this direction and then in that, but acts as if it had some definite end in view, and establishing itself in a small alder bush which it uses as a base or headquarters, it gradually extends its dominion, gains the mastery over the surrounding ground, part of which belonged to No. 1 male and part to No. 2, and finally drives a wedge, so to speak, between the two territories.
How is its behaviour to be explained, and why did its presence cause such commotion? No one could have watched the gradual unfolding of this incident day by day and not have been impressed by the persistent endeavour with which this male maintained its position in one small part of the meadow. This is the first and most important consideration. Then there is
