You can get a sharp sign of the mass intelligence of Fort Cobb Lake crows by watching them come into the roost at night. The lake was formed six years ago by an earth dam that backed up the water seven miles. Inlets and crevices give the mile-wide lake a saw-tooth shoreline. Near the north end of the lake, where one of these inlets reaches back two miles, the crows make their roost on a jagged point of land. The lake gives them protection on two sides, the inlet gives them protection on another. On the remaining side the only approach is through an almost impenetrable growth of blackjack. Napoleon could not have picked cut a better defensive location.
Coming in to roost, the crows make no such display as they make in leaving. Half an hour before sunset there is not a crow in sight. Then a few scouts fly over the roost. About two miles from the roost, radiating out like the spokes of a wheel, the crows assemble at staging points in the fields. Just at sunset they stream in over the trees in long wavering lines, very fast and nearly silent. If a hard wind is at their backs they swoop along with it in swaying motions that suggest ice skating. As they drop out of the sky you cannot see them landing on the trees, but you can see the top branches getting bigger, until they look like girders for a building.
Nor can you see the ones that arrive late, find the no-vacancy sign up and sleep on the ground. But they are there. The night after Gerald Iams shot his cannon net and got his big haul, he went back and found that there was a vacant space all around his blind deep in the roost. You could crouch down in the sand there, look up and see crows everywhere except overhead. Regardless of what the behavior tests indicate on crow intelligence, the crows in the Fort Cobb Lake roost look like the world's least threatened species.