Feet highly raptorial, with large, strong, sharp, curved,
contractile claws, adapted for grasping. Hallux perfectly
incumbent, lengthened (more than half as long as the fourth toe),
with large claw. Front toes with slight basal webbing between
outer or middle ones, or none; outer toe often reversible.
Nostrils imperforate. Bill short, stout, not notably contracted
in its continuity, with strongly hooked tip; tomia often
once-twice toothed or lobed. Head feathered wholly or in greatest
part. Lower larynx developed with one pair of muscles. Plumage
with or without after-shafts. Cœca present, as a rule, if not
always.
Physiognomy peculiar by reason of great lateral expansion and
lengthwise shortening of the cranium, causing the eyes to be
directed forward. Eyes surrounded by a disc of radiating
bristly feathers, in front closely appressed to and hiding the
base of the bill, elsewhere bounded by a rim of differently
formed feathers. Tomia never toothed or lobed. Nostrils usually
at the edge of the cere. Outer toe completely versatile,
shorter than the inner toe. Basal phalanx of middle toe not
longer than the second, and much shorter than the next. Legs
commonly feathered or bristly to or on the toes. Plumage
peculiarly soft and lax, without after-shafts; flight perfectly
noiseless. Cranial walls widely separated by intervention of
spongy diploë. Sternum commonly doubly notched. Chiefly
nocturnal … _Strigidæ_.
Physiognomy not peculiar in any lateral expansion of the
cranium; the eyes lateral in direction. No complete facial
disc; base of bill not hidden by appressed bristles. Nostrils
wholly in the cere. Outer toe rarely versatile, except
_Pandion_, etc.; not shorter than the inner. Basal phalanx of
middle toe longer than the second. Legs commonly naked and
scutellate or reticulate in some portion of their length; toes
always bare and scaly. Plumage compact, usually with
after-shafts; flight audible. Cranial walls with little diploë.
Sternum commonly single-notched or fenestrate, sometimes
entire. Diurnal … _Falconidæ_.
Feet scarcely raptorial, with lengthened, little curved or
contractile, weak, short claws. Hallux elevated, shortened, not
more than half as long as the fourth toe, with small claw. Front
toes all webbed at base; middle toe lengthened; outer not
reversible. Basal phalanx of middle toe longer than either of the
succeeding. Nostrils perforate. Bill lengthened and comparatively
weak, little hooked, contracted in its continuity; tomia not
toothed or lobed. Head naked of feathers in greatest part;
sparsely bristly. No lower larnyx developed. No cœca. After-shafts
absent … _Cathartidæ_.