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Breeding Range. (Fig. 153). Common throughout the state.

Breeding Habitat. This ubiquitous species is characteristic of edge complexes that are composed of woodlands, wood margins or brushy thickets, and various types of open country that lie adjacent to them. Occupied areas include natural forest-prairie marginal areas or ecotones, and tree growth-cropland combinations that have been created by man.

Nesting. Breeding season: Early May to mid-August; peak, late May to mid-July. Extreme egg dates (117 parasitized nests): May 10 [1969] in Kidder County (RES) to July 15 [year ?] in North Dakota (Bent 1958). Extreme nestling dates (14 parasitized nests): June 15 [1895] in Towner County (Bishop egg collection catalog, Peabody Museum) to July 25 [1974] in Kidder County (RES). Extreme dates of dependent young out of the nest (8 records): June 24 [1970] in Pembina County to August 16 [1973] in Stutsman County (RES).

A total of 133 instances of cowbird parasitism have been recorded in North Dakota, including 69 on sparrows (Emberizinae), 33 on icterids (Icteridae), 10 on warblers (Parulidae), and 21 on miscellaneous species. Records of parasitism by species are as follows: 23, Red-winged Blackbird; 16, Chestnut-collared Longspur; 14, Clay-colored Sparrow; 9, Western Meadowlark; 8, Yellow Warbler; 6 each for Lark Bunting and Song Sparrow; 5 each for Horned Lark, Le Conte's Sparrow, and Vesper Sparrow; 4, Savannah Sparrow; 3 each for American Goldfinch, Baird's Sparrow, and McCown's Longspur; 2 each for Eastern Kingbird, Least Flycatcher, Red-eyed Vireo, Spotted Rufous-sided Towhee, and Chipping Sparrow; 1 each for Upland Plover, Brown Thrasher, Gray Catbird, American Robin, Veery, Ovenbird, American Redstart, Yellow-headed Blackbird, Dickcissel, Rose-breasted Grosbeak, Grasshopper Sparrow, Lark Sparrow, and Brewer's Sparrow. In addition, Alfred Eastgate reported somewhat questionable records of host species that include the Ferruginous Hawk, California Gull, and House Wren (Friedmann 1963).

Indicated clutch size (69 parasitized nests): 1 to 6 cowbird eggs; mean, 2.0 eggs. An unusually large clutch of six cowbird eggs was recorded with two host eggs in a Horned Lark nest in Stutsman County on June 10, 1969 (RES).

Figure 153. Breeding Range of Brown-headed Cowbird.