The author's preference would have been to begin the roll with the most interesting birds, those to which he gave the largest share of his attention, namely, the oscines, but he has decided to follow the order and nomenclature of the Check-List of North American birds as arranged by the American Ornithologists' Union. In deference to the general reader, however, he has placed the English name of each bird first, then the scientific designation. The numbers correspond to the American Check-List. By noting those omitted, the reader will readily discover what species have not been found in Colorado. 1. =Western grebe.= ÆCHMOPHORUS OCCIDENTALIS. Rare migrant; western species, chiefly interior regions of North America. 2. =Holboell's grebe.= COLYMBUS HOLBOELLII. Rare migrant; breeds far north; range, all of North America. 3. =Horned grebe.= COLYMBUS AURITUS. Rare migrant; range, almost the same as the last. 4. =American eared grebe.= COLYMBUS NIGRICOLLIS CALIFORNICUS. Summer resident; rare in eastern, common in western Colorado; breeds from plains to 8,000 feet; partial to alkali lakes; western species. 6. =Pied-billed grebe.= PODILYMBUS PODICEPS. Summer resident, rare; common in migration; breeds in northern part of State; sometimes winters in southern part. 7. =Loon.= GAVIA IMBER. Migrant; occasionally winter resident; not known to breed in State. 8. =Yellow-billed loon.= GAVIA ADAMSII. Migrant; rare or accidental. 9. =Black-throated loon.= GAVIA ARCTICA. Rare fall and winter visitant. 37. =Parasitic jaeger.= STERCORARIUS PARASITICUS. Fall and winter resident; rare. 40. =Kittiwake.= RISSA TRIDACTYLA. Rare or accidental in winter. 49. =Western gull.= LARUS OCCIDENTALIS. Pacific Coast bird; accidental in Colorado; only one record. 51a. =American herring gull.= LARUS ARGENTATUS SMITHSONIANUS. Rare migrant; range, the whole of North America. 53. =California gull.= LARUS CALIFORNICUS. Western species; breeds abundantly in Utah; only three records for Colorado. 54. =Ring-billed gull.= LARUS DELAWARENSIS. Not uncommon summer resident; common in migration; breeds as high as 7,500 feet; range, whole of North America. 58. =Laughing gull.= LARUS ATRICILLA. Bird of South Atlantic and Gulf States; once accidental in Colorado. 59. =Franklin's gull.= LARUS FRANKLINII. Rare migrant; range, interior of North America. 60. =Bonaparte's gull.= LARUS PHILADELPHIA. Rare migrant; not uncommon in a few localities; range, whole of North America. 62. =Sabine's gull.= XEMA SABINII. Rare winter visitant; breeds in the arctic regions. 69. =Forster's tern.= STERNA FORSTERI. Rare summer resident; common migrant; habitat, temperate North America. 71. =Arctic tern.= STERNA PARADISÆA. Very rare migrant; but two records; breeding habitat, circumpolar regions. 77. =Black tern.= HYDROCHELIDON NIGRA SURINAMENSIS. Common summer resident; both sides of range; habitat, temperate North America; in winter south as far as Brazil and Chili.