BLUE HERON. 155 



half of the upper mandible, are light greenish-blue, the rest black; the lower 

 mandible yellow, with a patch of black an inch and a quarter in length on 

 each side at the end. Legs, tarsi, and toes greenish-blue, the sides yellow- 

 ish; claws dusky. The feathers of the head are slightly elongated; those of 

 the back are also elongated, but much broader and shorter than in the adult. 

 The feathers on the upper part of the head are of a faint bluish-grey; and 

 the alular feathers and eight outer primaries are tinged with the same colour. 

 At this period, the length to the end of the tail is 22 inches, to end of claws 

 2S^; bill along the ridge 2^-; wing from flexure 11; tail 4—%. 



In November, when the moult is advanced. The bill is black, dull blue 

 at the base. The feet are nearly black, as are the claws, The occipital 

 feathers are now two inches and a half in length, and some of the dorsal 

 feathers extend as far as the tips of the wings; those of the lower part of 

 the neck have also a length of about three inches. The general colour of 

 the plumage is white; the upper part of the head, the hind neck, back, 

 anterior edge of the wing, and outer primaries at the end, of a faint bluish- 

 grey tint; some of the elongated feathers of the back darker. 



Length to end of tail 22 inches; to end of claws 29-J; bill 3; wing from 

 flexure 11^. 



A year old. Bill nearly as in the adult; feet bluish-black, the plumage is 

 white, with the upper parts pale greyish-blue as in November, but the whole 

 interspersed with numerous feathers of a deep greyish-blue, similar to that 

 of the adult; the primaries and tail being still white. 



Length to end of tail 23^; extent of wings 32^; bill 3^. Weight 9 oz. 



At the age of a year the bird propagates, so that individuals in the white, 

 mottled, or blue plumage, may be seen breeding together. 



When only a few weeks old, the serrature of the claw of the middle toe 

 is scarcely perceptible, exhibiting merely faint indications of points upon a 

 very slight margin. This margin enlarges, and when the bird is com- 

 pletely fledged the serratures are perfectly formed. 



In this bird, as in most other Herons, the crura of the lower mandible are 

 thin, flexible, and elastic, the angle filled by an elastic membrane covered by 

 the skin. The tongue is 1 inch long, sagittate at the base, tapering to a 

 point. The roof of the mouth has a median prominent ridge, and two 

 lateral lines; the palate is convex; the posterior aperture of the nares 10 

 lines in length. The pharynx may be dilated to 1^ inches; the oesophagus, 

 which is 12 inches long, is, when dilated, 10 lines in diameter at its upper 

 part, and gradually contracts to 7 lines; at the curvature of the neck it lies 

 directly behind, having passed down on the left side, along with the trachea. 

 Its walls are extremely thin, contrasting in this respect with the oesophagus 

 of the Great Northern Diver and other swimming piscivorous birds. The 



