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Platte River Status: A fairly common migrant throughout the study area; uncommon and local nesting species in the western half. A casual summer resident at Mormon Island Crane Meadows, Hall County, present 7 April to 9 November. Tout (1947) considered double-crested cormorant a rare migrant in Lincoln County; his latest date was 12 November 1938. Rosche (1979) stated that double-crested cormorant was primarily a migrant in the lower North Platte River Valley, present 28 March to 3 June, and 2 September to 6 November. Rosche stated that this species nested formerly in his area, but he doubted that nesting still occurs.

Breeding Range: Nesting colonies have been reported from the upper reaches of the Platte River Valley physiographic region, particularly on Lake McConaughy and near North Platte. Non-breeding individuals occur regularly during the summer in the lower Platte River Valley and in the Sandhills.

Breeding Population: The population is estimated at 200 pairs based on observations made at current nesting areas. Formerly the largest number nesting on Lake McConaughy was 228 pairs (Collister 1948).

Habitat: Most nesting colonies reported from the study area have been in dead cottonwood trees along the periphery of Lake McConaughy. Nests are typically placed 4.5 to 11 m above the water level. Conservation of this bird as a nesting species on Lake McConaughy could be enhanced by establishment of artificial nest platforms.

Effect of Habitat Alteration: Our data indicate that construction of reservoirs to accommodate agricultural irrigation projects has significantly benefited this species. In some cases, creation of reservoirs has provided temporary nesting habitat by killing trees within the impoundment. The colonies are relatively short-lived because the nest trees eventually decay and topple.

Nesting Data: Tout (1946) observed 12-15 nests during 1943 in dead cottonwood trees 5 km east of North Platte, Lincoln County, in an area flooded by a diversion dam. Collister (1948) chronicled the rapid increase in double-crested cormorant nesting on Lake McConaughy after the reservoir started filling in 1939. In 1944, about 50 birds were found on lakes Ogallala and McConaughy. Forty nests were present in 1945, about 14 km west of Kingsley Dam. Sixty nests were present there in 1946. In 1947, the birds moved to 2 different areas due to high water; there were 40 nests east of the mouth of Sand Creek, and 100 nests 0.8 km west of the mouth of Otter Creek. In 1948, 3 colonies totalling 228 nests were on Lake McConaughy. The newest colony was at the mouth of Eagle Canyon. Collister stated that the total number of double-crested cormorants present on Lake McConaughy in 1948 was 1,000 individuals. Egg dates from North Dakota extend from 13 May to 18 July (Stewart 1975).