02369nas a2200205   4500008004100000245014500041210006900186300001300255490000800268520160400276653002101880653002501901653001501926653002501941653001901966653002001985100001702005700001602022856012502038       2005                        eng d00aGeographic variation in Brown-headed Cowbird (Molothrus ater) parasitism on Dickcisssels (Spiza americana) in Great Plains tallgrass prairie0 aGeographic variation in Brownheaded Cowbird Molothrus ater paras  a648 -6600 v1223 aThe incidence of brood parasitism by Brown-headed Cowbirds (Molothrus ater; hereafter “cowbirds“) within host species typically reflects the continental pattern in cowbird abundance across North America, where parasitism is heaviest in the Great Plains. However, we found considerable variation in cowbird parasitism on Dickcissel (Spiza americana) nests within a subregion of the Great Plains (the Flint Hills), where the highest levels of cowbird parasitism on grassland bird nests had been previously reported. Local parasitism frequencies on Dickcissel nests varied latitudinally across the Flint Hills, ranging from 0% to 92% of nests parasitized. Interestingly, we found no obvious patterns in habitat or host attributes that were associated with this steep geographic gradient in brood parasitism. Cowbird parasitism on Dickcissel nests was not correlated with the vertical density of local prairie vegetation, mean nest distance to edge, proportion of forest to grassland habitat surrounding study sites (≤5 to 10 km), geographic variation in host abundance, or Dickcissel density or nest initiation dates. Parasitism frequencies and intensities (number of cowbird eggs per parasitized nest) on Dickissel nests were only significantly related to variation in local female cowbird density. Dickcissel clutch size and apparent fledging success were negatively correlated with local cowbird parasitism levels. Geographic patterns in cowbird abundance within and among regions should be considered when establishing conservation areas for grassland birds or other cowbird hosts of concern.10abrood parasitism10abrown-headed cowbird10aDickcissel10ageographic variation10aMolothrus ater10aSpiza americana1 aJensen, W.E.1 aCully, J.F.  uhttp://lter.konza.ksu.edu/content/geographic-variation-brown-headed-cowbird-molothrus-ater-parasitism-dickcisssels-spiza