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Platte River Status: A common (locally abundant) migrant and nesting species. Dates of occurrence at the Mormon Island Crane Meadows, Hall County, are 5 May to 12 October. Tout (1947) considered grasshopper sparrow an irregular spring migrant and rare fall migrant in Lincoln County. Extreme dates for spring migration in Lincoln County are 26 April to 21 May. Rosche (1979) found grasshopper sparrow in the lower North Platte River Valley during 3 June to 10 September.

Breeding Range: A common (locally abundant) and widely distributed nesting species in the Sandhills physiographic region; common on the Western Plain, Eastern Plain, and Platte River Valley; uncommon and local on the Dissected Plain. An apparently recent increase in abundance and distribution in the western half of the study area is suggested because Tout (1947) considered the grasshopper sparrow a rare summer resident and breeding species in Lincoln County, citing only a 26 July 1942 record.

Breeding Population: The estimated population in 1979-1980 was 248,500 pairs which made up 8.4% of the total bird numbers on the study area. Grasshopper sparrow ranked third in abundance among all nesting species present in the Platte River Valley those years.

Habitat: Grasshopper sparrow is a characteristic breeding species of lightly to moderately grazed upland native prairie. We found highest breeding densities on lightly to moderately grazed upland native grasslands and in wet meadows along the Platte, North Platte, and South Platte rivers. The largest mean breeding densities throughout the study area occurred on upland native prairie (18.0 pairs/km²), followed by wet prairie (14.7 pairs/km²), domestic hayland (12.5 pairs/km²), alfalfa (7.2 pairs/km²), wheat (4.5 pairs/km²), wetland (3.7 pairs/km²) and corn (0.1 pairs/km²). Kantrud and Kologiski (1982) reported highest breeding densities among grasshopper sparrows on the northern Great Plains occurred in lightly to moderately grazed native prairie associated with high moisture soils. Only western wheatgrass was of more than average abundance on native prairie tracts supporting highest densities of grasshopper sparrows. Other grasses indicative of optimum breeding habitat in Kantrud and Kologiski's study were Kentucky bluegrass and green needlegrass. Grasshopper sparrow is a fairly common to common nesting species in shortgrass prairie and sandhill prairie in western Kansas (Rising 1974).

Effect of Habitat Alteration: Our data suggest that grasshopper sparrow is negatively impacted by the conversion of native upland grasslands to other uses. De-watering of the Platte River system and the resultant increase in the occurrence and distribution of wooded vegetation in wet meadows is also detrimental to this species. The complete absence of grasshopper sparrow from any habitat supporting wooded vegetation suggests that this species is not able to adapt positively to great alteration in the structure of prairie vegetation. Continued conversion of grasslands to agricultural production, along with increased rates of wooded vegetation establishment within the channels of the Platte River will produce additional negative impacts on this species in the future. On the other hand, Graber and Graber (1963) speculated that the future of grasshopper sparrow in Illinois was "reasonably bright" because although the extent of pastureland was declining, hayfields offered a good reservoir habitat.

Nesting Data: Active nests containing eggs or young have been found on the Mormon Island Crane Meadows, Hall County, during 6 June to 24 July. Among 6 grasshopper sparrow nests found on Mormon Island, 4 were parasitized by brown-headed cowbird. Benckeser (1950) found a young grasshopper sparrow 6 km N.W. Brule, Keith County on 9 June 1948. Johnsgard (1979) reported Kansas egg dates ranging from 1 May to 30 June, with a peak about 21 May. Extreme egg dates from North Dakota range from 30 May to 21 July (Stewart 1975).