The birds which we group here under the name Hawks, agree with the harriers in the slender form, weak and un-toothed bill, long tail and legs, tarsus about the same length as the tibia, and superciliary shield prominent. The absence of the facial 'ruff' would at once separate them from the Circinee, but an equally important difference, not only from the harriers but from the falcons and buzzards, is seen in the wings, which instead of being long, straight, and tapering, as in the harriers and falcons, or broad, fiat, and obtuse as in the buzzards, are short and rather rounded, but very concave beneath, so that their flight is rapid and almost 'whirring,' without the power of lofty soaring or of long continued and easy gliding. The cutting edge of the bill is also usually furnished with a prominent lobe or 'festoon;' the middle toe is often very long, the 'pads' under the joints on all the toes very strongly developed; and the tarsal envelope very various, usually more or less leathered, and the bare part scutellate in front or behind or both, sometimes with the plates fused together to form a 'booted ' tarsus (as in the true thrushes), or even in some cases partially reticulate.
The hawks, while numerous individually and even specifically (there are sixty or seventy species), are all contained in a very few genera, probably nine tenths of them in the genera Astur (goshawks), and Accipiter (sparrow-hawks). The distinctions between these two groups, moreover, are very slight, so slight indeed that there are very many species which to ordinary eyes seem to have as good a right under one name as the other. In general, Astur contains the larger and especially the stouter forms, in which the tarsus is more extensively leathered. There are, moreover, other points, such as the condition of the tarsal envelope, which should be taken into account. As an illustration of the lack of uniformity among systematists with regard to these genera, it may be mentioned that of two prominent authorities who published their views at about the same time (1874), one refers but six species to Astur, while another includes thirty-one. The latter author, however, allows but twenty-three to the genus Accipiter, while the former admits forty-five. For our present makes little difference which we follow in this respect, though there seems to be little doubt now that only a few species ought to be included among the gos-hawks.
