KEEL-BILL—KESTREL 477 
vertical bony septum between the great pectoral muscles, which 
mainly rise from it. Its size, and especially its depth, stand in 
direct correlation with these, the chief motor muscles of the wing. 
Great power of flight, as in Gannets, Petrels, Swifts and Humming- 
birds is associated with a deep Keel, while disuse of the wing- 
muscles tends to reduce it, as is strikingly illustrated by the thin 
and inconspicuous ridge which it takes in Stringops (KAKAPO). In 
the fatitz the Keel is altogether absent, without even the least 
trace of it in the embryo, and there is no sign of it in the fossil 
Hesperornis (ODONTORNITHES). In this last, its absence is in keep- 
ing with the very slender humerus, indicating that the well- 
developed paddle-like feet were the only organs of locomotion. 
On the other hand, its great size in the Penguins is easily explained 
by the use they make of their wings, with a semi-rotatory or screw- 
like action, as the means of propulsion under water. The con- 
figuration of the anterior margin of the Keel is of some taxonomic 
value (see STERNUM). 
KEEL-BILL, Shaw’s name (Gen. Zool. viii. p. 380) for the ANI 
KESTREL (French Cresserelle or Crécerelle, Old French Quer- 
cerelle and (uercelle, in Burgundy Cristel), the English name! of one 
of the smaller FALCONS, originating probably from its peevish and 
languid cry. This bird, though in the form of its bill and 
length of its wings one of the true Falcons, and by many ornitho- 
logists placed among them under its Linnean name of Falco 
tinnunculus, is by others referred to a distinct genus Tinnunculus as 
T. alaudarius—the last being an epithet wholly inappropriate. We 
have here a case in which the propriety of the custom that requires 
the establishment of a genus on structural characters may seem 
open to question. The differences of structure which separate 
Tinnunculus from Falco are slight, and, if insisted upon, in the way 
some systematists have done, must lead to including in the former 
genus birds which obviously differ from Kestrels in all but a few 
characters arbitrarily chosen; and yet, if structural characters be 
not required, the Kestrels form a group readily distinguishable by 
several peculiarities from all other Falconidx, and a group that the 
instinct of real ornithologists (though this is treading upon danger- 
ous ground) does not hesitate to separate from the true Falcons of 
the genus Falco, with its subsidiary sections or genera, salon 
(MERLIN), Hypotriorchis (HOBBY), and the rest. Scarcely any one 
outside the walls of a museum or library would doubt for a moment 
whether any bird shewn to him were a Kestrel or not; and the 
late Mr. Gurney believed (/dis, 1881, p. 277) that the aggregation 
1 Other English names are Windhover and Staniel of which Stannell is a corrup- 
tion, and often by mistaken etymology written Standgale (cf Skeat, Zrans. 
Etymol. Soc. 1888-90, p. 21). 
