- In strict usage in Europe and Asia, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks, sparrowhawks, the Sharp-shinned Hawk and others. These are mainly woodland birds with long tails and high visual acuity, hunting by sudden dashes from a concealed perch. See Eagle.
- More generally (especially in North America) to mean falcons or small to medium-sized members of the Accipitridae – the family which includes the "true hawks" (Accipiters) as well as eagles, kites, harriers and buzzards.
- Loosely, to mean almost any bird of prey outside of the order Strigiformes (owls).
The common names of birds in various parts of the world often use hawk in the second sense. For example, the Osprey or "fish hawk"; or, in North America, the various Buteo species (e.g., the Red-tailed Hawk, B. jamaicensis).
In February 2005, the Canadian ornithologist Louis Lefebvre announced a method of measuring avian "IQ" in terms of their innovation in feeding habits.[1] Hawks were named among the most intelligent birds based on his scale.
Hawks are widely reputed to have visual acuity several times that of a normal human being. This is due to the many photoreceptors in the retina (up to 1,000,000 per square mm for Buteo, against 200,000 for humans), an exceptional number of nerves connecting these receptors to the brain, and an indented fovea, which magnifies the central portion of the visual field
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