Abstract:
Grassland birds have benefitted from the Conservation Reserve Program (CRP),
which creates grassland habitat through restoration of marginal cropland. Grazing by
domestic cattle (Bos taurus), which is currently restricted in CRP, might improve habitat
structure for some bird species. However, changes in habitat structure, and the presence
of cattle, might hinder nest concealment from predators, attract brood-parasitic brown
headed cowbirds (Molothrus ater), and alter invertebrate food availability for birds.
Higher abundance of arthropods, which constitute the diet for most songbird nestlings in
grasslands, might allow greater parental provisioning and, consequently, improved
nestling condition and survival. During the summers of 2017–2019, I investigated the
effects of experimental grazing on nest survival and brood parasitism (where appropriate)
of five bird species that utilize grassland habitat in Kansas. Additionally, I examined
nestling condition of dickcissels (Spiza americana) in relation to abundance of arthropod
prey across sites. Experimental grazing by cattle, which occurred during the first two
years of study, had inconsistent effects on nest success and parasitism by cowbirds
among the bird species analyzed. Negative consequences of grazing included reduced
nest success and increased brood parasitism in dickcissels, as well as reduced nest
success in meadowlarks (Sturnella spp.), but some effects varied over years or were
conditional upon conservation practice. Management had no effect on arthropod biomass,
and nestling condition showed no clear relationships with field-level variation in food
availability. Instead, nestlings in larger broods were generally in poorer condition than
those in smaller broods. Thus, parents might be more limited in their capacity to feed
nestlings in large broods than limited by the availability of food within CRP fields.
Negative consequences of grazing tended to be weak, so short-term grazing, as might be
implemented for mid-contract management of CRP fields, might not have long-lasting
effects on grassland bird reproduction
