Egg Tooth and Gender Dimorphic Bills

The Bird's Bill or Beak

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Tbe Bird's Beak or Bill and the Rhamphotheca or Horny Sheath

Bird Nostrils

Sifting Bills, Spatula and Spoonbills

Birds with Strong Beaks including Hornbill, Crossbill and Wry Bill

Egg Tooth and Gender Dimorphic Bills

Gender Dimorphic Bills

Gender Dimorphism is mostly restricted to peculiarly shaped bills; for instance, the horn of the male Hornbills is often larger, and differs in shape from that of the female. In the males of Pelicans several unpaired excrescences are formed entirely by the horny coating of the premaxilla; they sometimes reach a height of three to four inches, and are again cast off after the breeding season, resembling in the latter feature the Auks.

The most striking example of dimorphic bills is that of the New-Zealand HUIA, Heterolocha, the bill of the female being slender, about four inches long, and much curved, while that of the male is nearly straight, stout, and scarcely half that length. The knobs or swellings in the Gallinae are mostly restricted to the males; the same applies to Oedemia (SCOTER). Sexual differences in colour are common. For instance, in the male Scoter the bill is black and orange, in the young and in the female it is simply grey, and without the knob. The bill of the adult male Blackbird is orange-yellow; that of the young of both sexes and of the adult males of Buceros malayanus (HORNBILL) is white, but becomes black in the adult female, forming thus an interesting exception to the general rule that the young agree with the females, and that aberrant coloration is confined to the males. The colour of the bill is deposited as a diffused pigment in the horny cells of the epidermal coat, but is occasionally restricted to the deeper layers, or even to the Malpighian layer itself, then shining through the outer transparent layers.

The Egg Tooth

In connection with the bill is to be mentioned the "egg-tooth," which is developed in the embryos of all birds as a small whitish protuberance or conglomeration of salts of calcareous matter, deposited in the middle layers of the epidermis of the tip of the upper bill, without being connected with the premaxilla itself. The sharp point of this "tooth" soon perforates the upper layers of the horny sheath, and then files through the eggshell, a slight crack in the latter being sufficient to enable the young bird to free itself. A similar egg-tooth exists in Reptiles, and is, as in Birds, cast off after hatching. The wearing away of the growing and constantly renewed .horny layers of the bill can be easily observed in the pealing beak of a Parrot.
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