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 Batitx 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 CrS^erelle, Old French Quer- 

 cerelle and QuerceUe, 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 i:)laced among them under its Linnaean 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 Falconidse, 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 (Ihis, 1881, p. 277) that the aggregation 



■^ Other English, names are "Windhover and Staniel of which Stannell is a coiTup- 

 tion, and often by mistaken etymology written Standgale (c/. Skeat, Trains. 

 Etymol. Soc. 1888-90, p. 21). 



