With loose earth a low island with a flat top was built to carry the house. Its top was six inches above high-water mark, and (that would, if accepted) be the floor of the permanent house. A good, practicable tunnel was built to an underwater entrance. Upon that our men set a square, bottomless house of wood, with walls two feet high, and a low roof sloping four ways. Over all this the men piled in a neat mound a lot of tree branches of kinds suitable for beaver food; and with that we left the situation up to the beavers. The finish of our work was made on October 28. For a week there were no developments. The beavers made no sign of approval or disapproval. And then things began to happen. On November 5 we saw a beaver carrying a small green branch into the house for _bedding!_ That meant that our offering was going to be accepted. The subsequent chronology of that beaver house is as follows: Nov. 10. The beavers pulled all our brush away from the house, back to a distance of six or seven feet. The house stood fully exposed. Nov. 11. They began to pile up mud and sticks against the base of the south wall. Nov. 15. Mud-building to cover the house was in full progress. Nov. 17. Much of our brush had been placed in the stock of food wood being stored for winter use in the pond west of the house. Nov. 29. The outside of the house was completely covered up to the edges of the roof. The beavers were working fast and hard. No freezing weather yet. Dec. 15. The roof was not yet covered. Ice had formed on the pond, and house-building operations were at an end until the spring of 1922. XV THE MENTAL TRAITS OF BIRDS In comparison with mammalian mentality, the avian mind is much more elementary and primitive. It is as far behind the average of the mammals as the minds of fishes are inferior to those of reptiles. Instinct Prominent in Birds. The average bird is more a creature of instinct than of reason. Primarily it lives and moves by and through the knowledge that it has inherited, rather than by the observations it has made and the things it has thought out in its own head. But let it not for one moment be supposed that the instinctive knowledge of the bird is of a mental quality inferior to that of the mammal. The difference is in kind only, not in degree. As a factor in self-preservation the keen and correct reasoning of the farm-land fox is in no sense superior to the wonderful instinct and prescience of the golden plover that, on a certain calendar day, or week, bids farewell to its comfortable breeding-grounds in the cold north beyond the arctic circle, rises high in the air and launches forth on its long and perilous migration flight of 8,000 miles to its winter resort in Argentina.