Assessing the Relationship Between Stable Isotopes and Grassland Bird Productivity on Great Plains National Park Service Properties

National Park Service (NPS) units in the Great Plains provide breeding habitat for many grassland birds. However, little is known about the quality of this habitat and more extensive study into the avian breeding ecology at these sites has been recognized as necessary. A short-term study on songbirds at three NPS properties complemented current NPS monitoring, providing an among park comparison of nest success – a prohibitively labor-intensive and expensive process when conducted on a regional scale. Park managers need lower-cost data for informed decision-making, and measuring site fidelity is a potentially less expensive means of monitoring breeding site quality.

Goals

Avian nest survival will be intensively monitored in three NPS units (Pipestone National Monument, MN; Homestead National Monument, NE; and Tallgrass Prairie National Preserve, KS). Stable isotope values will be determined for feather and blood samples taken from nestlings and breeding adults. The two target grassland bird species are meadowlarks (eastern and western), and dickcissels.

Current Status

This project is complete with results compiled into a master's thesis.

The project used unique methods – stable isotope analyses of avian tissues – to evaluate variability in site fidelity of grassland birds at three NPS units in the Great Plains: Homestead National Monument, Nebraska; Pipestone National Monument, Minnesota; and Tallgrass Prairie National Preserve, Kansas. Birds that breed successfully at a location will often return to that location again (site fidelity). Current extrinsic markers used in monitoring site fidelity were inadequate for small birds; stable isotope analyses provided an alternative approach. This project evaluated the extent to which stable isotope analyses could be utilized to measure site fidelity in breeding grassland birds, specifically four target species: dickcissel (Spiza americana), grasshopper sparrow (Ammodramus savannarum), eastern meadowlark (Sturnella magna), and western meadowlark (Sturnella neglecta).

All years of field research have been completed at all three sites. Grassland bird species richness was highest at Pipestone and Tallgrass. Grassland obligate nest success for both years was 39% at Homestead and 6–29% for target species at Tallgrass. No target species nests were found at Pipestone. Mean adult feather hydrogen ratios (δD) were separable among study sites (P<0.05). Site fidelity tended to be higher at the large site, Tallgrass (63%), and lower at the small site, Homestead (50%). Mean blood δD values were 46% more depleted than mean δD feather values. Analyses of nest success, site species richness, avian density, site fidelity, and stable isotopes have been completed. Results were compiled and reported in a master's thesis available at: http://digitalcommons.unl.edu/natresdiss/11.