In nearly every instance the nest of this Hawk has been constructed in trees. It is usually large in proportion to the size of the bird, and its materials are somewhat elaborately put together; it is composed chiefly of large sticks and twigs, and the whole platform is covered with a thin lining of dry leaves, mosses, grass, etc. Mr. John Krider, of Philadelphia, found a nest in New Jersey, in the vicinity of that city, which was built on the edge of a high rock. Mr. Robert Kennicott met with the nest of this species at Fort Resolution. It was composed entirely of small dry spruce twigs, with the exception of a half-dozen small flat bits of the scaly outer bark of the spruce, laid in the bottom, and forming a sort of lining. No feathers or other softer materials were used. The nest was shallow and broad. The base was about eighteen inches in diameter, and was about eight feet from the ground. It was in a small spruce in a thick wood and on high ground. When disturbed, the female flew off a short distance; but on Mr. Kennicott’s hiding himself returned and flew near the nest, continually uttering a harsh rapid note. Near the nest were marks indicating the place where the male passed the nights perched on a dry stick near the ground. Mr. B. R. Ross observed these birds nesting thickly along the cliffs of the Upper Slave River. They were more rare northward of Fort Simpson than _F. columbarius_. Mr. William Street, of Easthampton, informs me that he has found this Hawk nesting on Mount Tom, where he has known of six of their nests in one season. In the spring of 1872 he found three nests, on the 24th and 25th of May. They contained two eggs each. One of these, on the 27th contained three eggs, of which he took one; on the 3d of June two more eggs had been laid. Two of these were taken, after which the birds deserted the nest and resorted to an old squirrel’s nest, where they had four more eggs, depositing one every third day. They arrive at Mount Tom about the 1st of May. Their nests are made entirely of sticks, larger on the outside, and smaller within. They usually build in a hemlock-tree, selecting a thick clump. They are very noisy when they are at work building their nest, and often betray their presence by their cries. The younger the pair the more noisy they are. This Hawk appears to live nearly altogether on small birds. Mr. Street mentions having found ten or twelve skeletons in a single nest of this species. Nisus cooperi (BONAP.). =Var. cooperi=, BONAP. COOPER’S HAWK.