The enormous structure with its multiple nest chambers looks like a large haystack in a thorny tree. Up to a 100 pairs may nest in it. Oilbirds in Venezuela nest in the pitch dark of caves. The ledges behind the mile wide Iguacu Falls on the Brazil-Argentina border are among the most secure nesting places of all. In the permanent damp inches from a constant deluge the great dusky swifts have found the last word in safe houses.
Some birds actively cooperate with other species.
By nesting close to animals better equipped to deter predators, the birds are inadvertently protected by their neighbors. A very unusual cooperation in breeding has evolved between members of two different bird species. The small red-breasted goose breeding on the Siberian tundra is extremely vulnerable to predation by arctic foxes. The geese have established a working relationship with another inhabitant of the arctic tundra. The peregrine falcon nests on the tundra at the same time, and this small but fierce bird of prey is able to ward off the hungry arctic fox.