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Platte River Status: An abundant migrant and nesting species; uncommon to rare winter resident. Occurrence dates on the Mormon Island Crane Meadows, Hall County, range from 26 March to 31 October. Tout (1947) reported brown-headed cowbirds from Lincoln County during 27 March to 3 November. Rosche (1979) recorded this species in the lower North Platte River Valley during 14 April to 15 August.

Breeding Range: The brown-headed cowbird is abundant during the breeding season in virtually all physiographic regions west to Lake McConaughy. This species appears to be less numerous in the southern Lincoln and Deuel County areas of the Western Plain physiographic region.

Breeding Population: The mean breeding population in 1979-1980 was 175,000 pairs which made up 6.0% of the total breeding bird population in the study area. Brown-headed cowbirds ranked sixth in total abundance among all species present.

Habitat: We found highest breeding densities in shelterbelts (409.5 pairs/km²), followed by Wetlands (89.7 pairs/km²), river channel island (55.0 pairs/km²), lowland forest (37.2 pairs/km²), residential (15.2 pairs/km²), wet prairie (14.1 pairs/km²), domestic hayland (12.5 pairs/km²), alfalfa (12.2 pairs/km²), upland native prairie (5.6 pairs/km²), wheat (2.7 pairs/km²), and corn (0.5 pairs/km²).

Effect of Habitat Alteration: The brown-headed cowbird evolved in the grasslands of North American (Friedman 1929). Recent alterations of the landscape coupled with great changes in the physical make-up of the habitats has had a positive impact on this species. The largest breeding density in our study area occurred in shelterbelts where the population was nearly four times larger than in the second ranking habitat which was natural wetland vegetation. As is typical of most Icterids, this species demonstrated the ability to adapt to gross changes in the habitat base and to successfully exploit and flourish in the newly formed habitat.

Nesting Data: On the Mormon Island Crane Meadows, Hall County, we have records of brown-headed cowbird parasitising the following species: ring-necked pheasant, upland sandpiper, brown thrasher, dickcissel, lark bunting, grasshopper sparrow, bobolink, red-winged blackbird, and meadowlark sp. Egg dates range from 24 May to 30 June; hatchlings were present by 21 June. Evidence obtained at nest sites indicate that brown-headed cowbirds actively pierce and remove the eggs of their host. Some hosts do likewise, or they cover the cowbird eggs with additional nest material. In several cases, we have recorded nest abandonment by the host species after their nest was parasitized. Kansas egg dates for this species are from 21 April to 20 July and include 40 host species (Johnsgard 1979).