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Spatial variation in Brown-headed Cowbird (Molothrus ater) abundance and brood parasitism in Flint Hills Tallgrass Prairie

Investigators:
William E. Jensen, Ph.D. Student

Project Supervisor:
Dr. Jack F. Cully, Jr.

Funding:
Kansas Department of Wildlife, Parks,
and Tourism
Natural Resources Conservation Service

Cooperators:
Kansas Department of Wildlife, Parks, and Tourism

Location:
Flint Hills of eastern Kansas and Oklahoma

Completion:
2003

Status:  Completed


Brown-headed Cowbird (Molothrus ater)

Objectives:

Examine how habitat selection, species-specific habitat requirements and general aspects of intraspecific competition might affect cowbird distribution among tallgrass prairie-woodland edge and tallgrass prairie interior habitats within the Flint Hills of eastern Kansas and Oklahoma.

Results:
Environmental factors affecting habitat selection range from species-specific habitat requirements to general aspects of intraspecific competition. Different proximate factors may affect spatial patterns of host selection by the brood parasitic (Molothrus ater) brown-headed cowbird within grasslands. Here I examined how such factors might affect cowbird distribution among tallgrass prairie-woodland edge and tallgrass prairie interior habitats within the Flint Hills of eastern Kansas and Oklahoma. First, I experimentally tested the hypothesis that the presence of elevated perches—similar to those provided by trees and shrubs—increases the abundance of cowbirds in grasslands and their parasitism of grassland-nesting birds (Chapter 1). However, cowbird abundance and parasitism levels of dickcissel (Spiza americana) nests were similar among experimental perch plots, prairie interior plots (>100 m from wooded edges), and plots near (<100 m) wooded edges when averaged across eight study sites. As cowbird habitat use patterns might be distorted by density-dependence in their habitat selection, I also examined cowbird use of these three habitats in relation to geographic variation in cowbird abundance across the Flint Hills (Chapter 2). Cowbird abundance and parasitism rates were higher near wooded edges than in prairie interior on study sites where cowbirds were less abundant and parasitic, but increased within open prairie interior at faster rates as the magnitude of these measures increased geographically. Experimental perch and open prairie habitats were used equally by cowbirds across the region. Density-dependent selection of edge and interior habitats by cowbirds might result from observed negative density-dependent effects of multiple parasitism on cowbird reproductive success. As local cowbird parasitism rates on dickcissel nests varied greatly across the region (from 0% to 92% of nests parasitized) an attempt was made to identify possible ecological correlates with local parasitism levels (Chapter 3). However, parasitism levels were unrelated to habitat structure at local and landscape scales and local host community attributes, being positively correlated only with local female cowbird density. Dickcissel reproductive success was negatively related to local cowbird parasitism levels. This study demonstrated that habitat-specific and overall cowbird parasitism levels can vary greatly with geographical variation in cowbird abundance, independently of geographical variation in habitat or host community attributes.




Dickcissel (Spiza americana)





Nest with Dickcissel eggs




Dickcissel nest with a cowbird egg





Dickcissel nest with many Brown-headed Cowbird eggs


Products:
Peer-reviewed Publications:

Rivers, J.W., W.E. Jensen, K.L. Kosciuch, and S.I. Rothstein. 2010. Community-level patterns of host use by the Brown-headed Cowbird, a generalist brood parasite. Auk 127:263-273.

Jensen, W. E., and J. F. Cully, Jr. 2005. Density-dependent habitat selection by a brood-parasitic cowbird in tallgrass prairie. Oecologia 142:136-149.

Jensen, W. E., and J. F. Cully, Jr. 2005. Geographic variation in cowbird parasitism and dickcissel nesting success in great plains tallgrass prairie. The Auk 122:648-660.

Thesis or Dissertation:

Jensen, W.E. 2003. Spatial Variation in Brown-Headed Cowbird (Molothrus ater) Abundance and Brood Parasitism in Flint Hills Tallgrass Prairie. Ph.D. Dissertation, Division of Biology, Kansas State University. (Advisor: Cully).

Professional Presentations:
Rivers, J.W., W. E. Jensen*, K. L. Kosciuch, and S. I. Rothstein. 2008. Community-level patterns of host use by the brown-headed cowbird, a generalist brood parasite. 126th Stated Meeting of the American Ornithologists Union, Portland, OR.

Jensen, W. E., and J. F. Cully, Jr. 2003. Evidence for density-dependent habitat selection by brown-headed cowbirds in tallgrass prairie. Paper presented at the Cooper Ornithological Society Annual Meeting, Flagstaff, AZ.

Jensen, W. E.* and J. F. Cully, Jr. 2003. Density-dependent habitat selection by brown-headed cowbirds in tallgrass prairie. 121st Stated Meeting of the American Ornithologists' Union. University of Illinois at Urbana-Champaign. -- Invited paper to symposium: Ecology and evolution of host-parasite interactions and cowbird management.

Jensen, W. E. and J. F. Cully, Jr. 2003. Latitudinal variation in cowbird parasitism and productivity of grassland songbirds across the Flint Hills. Paper presented at the Kansas Chapter of The Wildlife Society meeting, Kansas State University, Manhattan, KS. -- Recipient of Best Paper Award, Ph.D. Research.

Jensen, W. E. and J. F. Cully, Jr. 2003. Evidence for density-dependent habitat selection by brown-headed cowbirds (Molothrus ater). Kansas State University, Division of Biology 29th Annual Graduate Student Research Forum, Manhattan, KS. -- Recipient of Chris Edler Memorial Award for Outstanding Konza Prairie Graduate Student.

Jensen, W. E.* and J. F. Cully, Jr. 2002. Do brown-headed cowbirds exhibit density-dependent habitat selection in tallgrass prairie landscapes? 3rd North American Ornithological Conference, New Orleans, LA.

Jensen. W. E.*, D. Miller, J. Bowers, and M. Leonard. 2002. Experimental test of host song in attracting the brood parasitic brown-headed cowbird. Annual Meeting of the Kansas Ornithological Society, Meade, KS.

Jensen, W. E.* and J. F. Cully, Jr. 2002. Evidence for density-dependent habitat selection by brown-headed cowbirds in tallgrass prairie landscapes. Annual Meeting of the Kansas Ornithological Society, Meade, KS. -- Recipient of Outstanding Student Paper Award.

Jensen, W. E.* and J. F. Cully, Jr. 2001. Use of grassland bird communities by brown-headed cowbirds in tallgrass prairie landscapes. 63rd Midwest Fish and Wildlife Conference, Des Moines, IA.

Jensen, W. E.* and J. F. Cully, Jr. 2001. Use of grassland bird communities by brown-headed cowbirds in the Flint Hills. Annual Fall Meeting of the Kansas Ornithological Society, Wichita, KS. -- Recipient of Outstanding Student Paper Award.

Jensen, W. E. and J. F. Cully, Jr. 2001. Brown-headed cowbird distribution among host habitats in a grassland-dominated landscape. 71st Annual Meeting of The Cooper Ornithological Society, Albuquerque, NM. (Poster)

Truman, C., W. E. Jensen*, and J. F. Cully, Jr. 2000. Use of experimental perches by brown-headed cowbirds in tallgrass prairie. 12th Annual Konza Prairie LTER Workshop, Kansas State University, Manhattan, KS.

Schmitt, R., W. E. Jensen*, and J. F. Cully, Jr. 2000. Association of brown-headed cowbird foraging flocks with grazing ungulates in tallgrass prairie. Annual Fall Meeting of the Kansas Ornithological Society, Overland Park, KS.

Truman, C.*, W. E. Jensen, and J. F. Cully, Jr. 2000. Use of experimental perches by brown-headed cowbirds in tallgrass prairie. Annual Fall Meeting of the Kansas Ornithological Society, Overland Park, KS.