Organic life in all its forms is flexible; instinct is flexible; the habits of all the animals change more or less with changed conditions, but the range of the fluctuations in the lives of the wild creatures is very limited, and is always determined by surrounding circumstances, and not by individual volition, as it so often is in the case of man. In a treeless country birds that sing on the perch elsewhere will sing on the wing. The black bear in the Southern States "holes up" for a much shorter period than in Canada or the Rockies. Why is the spruce grouse so stupid compared with most other species? Why is the Canada jay so tame and familiar about your camp in the northern woods or in the Rockies, and the other jays so wary? Such variations, of course, have their natural explanation, whatever it may be. In New Zealand there is a parrot, the kea, that once lived upon honey and fruit, but that now lives upon the sheep, tearing its way down to the kidney fat.
This is a wide departure in instinct, but it is not to be read as a development of reason in its place. It is a modified instinct,--the instinct for food seeking new sources of supply. Exactly how it came about would be interesting to know. Our oriole is an insectivorous bird, but in some localities it is very destructive in the August vineyards. It does not become a fruit-eater like the robin, but a juice-sucker; it punctures the grapes for their unfermented wine. Here, again, we have a case of modified and adaptive instinct. All animals are more or less adaptive, and avail themselves of new sources of food supply. When the southern savannas were planted with rice, the bobolinks soon found that this food suited them. A few years ago we had a great visitation in the Hudson River Valley of crossbills from the north. They lingered till the fruit of the peach orchards had set, when they discovered that here was a new source of food supply, and they became very destructive to the promised crop by deftly cutting out the embryo peaches. All such cases show how plastic and adaptive instinct is, at least in relation to food supplies. Let me again say that instinct is native, untaught intelligence, directed outward, but never inward as in man.