792 



SYSTEMATIC SYNOPSIS. — PYGOPODES 



middle of the back. The marking results from a small spot or stripe near the end of each 

 feiither, on the edge of each web ; there is occasionally a second pair nearer the base of the 

 feather. The amount of spotting is very variable with individuals ; in the young the sj)Ots are 

 always larger and more numerous than in the adults, and usually lengthened into oblique 

 lines, producing a regular diamond-shaped reticulation. Northern Hemisphere at large ; most 

 of the U. S. in winter ; breeds in liigh latitudes. Eggs 2-3, 3.00 X 1-75. 



62. Family PODICIPEDID^ : Grebes. . 

 BUI of variable length, much longer or shorter than head ; culmen usually about straight, 

 sometimes a little concave, or quite convex, especially at the end. Commissure nearly straight, 

 but more or less corresponding with the curve of the culmen, usually sinuate at base. Under 

 outline of bill in general convex, with slight gouydeal angle or none. Sides of bill more or 

 less striate. Nasal fossaj well marked, the nostrils near their termination. Nostrils linear and 

 pervious (broader in PocUlymbus), upper edge straight, not lobed. Frontal extension of 

 feathers considerable, and usually autise run still further into the nasal fossa. A groove along 

 the symphysis of the mandible extends often nearly to the tip. Eyes far forward, with a loral 

 strip of bare skin running thence to base of upper mandible, very narrow iu the typical forms, 

 broader in Tachyhaptes and Podihjmbus. Head usually adorned in the breeding season with 

 variously lengthened colored crests or ruffs ; when these are wanting the frontal feathers may 

 be bristly. Neck usually long, slender, and sinuous. Plumage thick and compact, smoothly 

 imbricated above, below of a peculiar smooth, satiny texture. Wings short but ample, very 

 concavo-convex ; primaries eleven, narrow, somewhat falcate, graduated, the three or four 

 outer ones attenuate on one or both webs ; secondaries short and broad ; tertials very long, 

 hiding the rest of the quills when the wing is closed. Bastard quills unusually long, their tips 

 reaching over half-way to the ends of the primaries. Greater coveits also very long. Tail 

 ruilimentary, represented by a tuft, of downy feathers. Characters of the feet peculiar; for in 

 other lobe-footed birds, as Phalaropes and Coots, the lobatiou is of a different character. Tarsi 

 exceedingly compressed, with only a slightly thickened tract within which the tendons pass. 

 Front edge a single smooth row of overlapping, the hinder ser- 

 rate with a double row of pointed, scales ; sides regularly trans- 

 versely scutellate, as are the upper surfaces of the toes, the latter 

 being inferioi'ly reticulate, with an edging of pectinated scales. 

 Toes flattened out and further widened with broad lobes, espe- 

 cially wide toward the end, and at base connected for a varying 

 distance by interdigital webs. Hind toe highly elevated, broadly 

 lobate, free. Claws short, broad, flat, obtuse, of squarish shape ; 

 that of the hallux minute. 



The Grebes are strongly marked by the foregoing charac- 

 ters, especially of the feet and tail, though they agree closely with 

 the Loons in general structure and economy. Principal internal 

 characters are the absence of one carotid, and of the ambiens, 

 femoro-caudal and accessory semitendinosus muscles, the greater 

 number of cervical vertebrse (19 instead of 13) and shortness of 

 the sternum, with lateral processes reaching beyond the transverse 

 main part (the reverse of the case in Loons). There is a long 

 cnemial process of the tibia, reaching high above the knee-joint, 

 backed by a large patella of about equal altitude (fig. 53U bis.). 

 The gizzard has a special pyloric sac; there are coeca and a tufted oil-gland. These birds are 

 expert divers, and have the curious habit of sinking back quietly into the water when alarmed, 

 like Anhingas. Owing to the virtual absence of the tail, the general aspect is singular, ren- 



F ^^ 



.^'-f 



Fig. 530 bis.—F. fibula; T, 

 tibia, with a, its cnemial process, 

 anil P, large patella, of a grebe; 

 nat. size. 



