The prairie grasslands of the Midwest and Great Plains range from tall-grass prairie in the east, through mixed-grass and short-grass prairie in the drier west. These great native grasslands covered at least 1 million square miles of the interior of North America prior to European settlement. Settlers found this ecosystem to provide ideal conditions for farming and ranching - as a result the prairies have been heavily modified by human activities and most remaining examples of native prairie exists as relatively small fragments embedded in an agricultural landscape. This is especially true of the remaining tall-grass prairie. The range of tall-grass prairie, with its spectacular head-high grasses and wildflowers once covered the rich soils of what is now the US Corn and Soybean belt. As a result, all but a small percent of this ecosystem has fallen under the plow. Estimates are that 95 to 99% of tall-grass prairie has disappeared, making this one of the globe's most critically endangered ecosystems.
The plants and animals of the prairies have varied in how well they have been able to adapt to the rapid changes in habitat brought about by the transition to agriculture. A high proportion of the species in the grassland bird community have given indications of population declines over the past decades. As a result these birds have become a focus of conservation concern for government and non-governmental organizations.
Many of the species of conservation concern now survive in the small prairie fragments in the agricultural landscape or are able to breed in the heavily modified grasslands at the edges of farm fields. A central component to the conservation strategy for grassland birds must involve an understanding of the ecology of grassland birds in agricultural ecosystems. This will include understanding the effects of agriculture on adjacent native prairie reserves, the importance of marginal grass habitats bordering agricultural fields (or even within fields in the case of terraces and waterways), and the restoration of former farm fields. Restoration will include both long-term attempts to restore the conditions of native prairie and shorter term conservation strategies such as USDA's Conservation Reserve Program (CRP) that encourages private land owners to plant grasses.
The over-all aim of our research program is to provide timely, relevant information to meet the research needs of resource managers and policy makers.
Our current focus of grassland bird research addresses two sets of questions: (1) how do changing farming practices influence grassland birds breeding in and around agricultural fields? and (2) how does management of grassland fragments at a landscape-level impact grassland birds?
Agricultural ecosystems can provide critical habitat for birds and other wildlife. However, intensity of land use and farming practices vary greatly and can have important implications for the value of agricultural lands to wildlife. One of the most note-worthy changes in farming in recent decades is the large-scale adoption of herbicide tolerant crops and their accompanying agricultural practices. These changes have the potential to produce environmental changes that alter avian communities and reproduction. In particular, avian communities and populations are affected by habitat structure, food supply and nest predators. In the Great Plains, grassland and riparian ecosystems have declined and represent a small percentage of land within an agriculturally dominated landscape, but these habitats are disproportionately important to birds. Because of the limited habitat availability to species depending on grassland or riparian ecosystems, agriculturally-mediated changes can have profound implications for the management and sustainability of bird populations. For example, the adoption of glyphosate tolerant soybeans has disproportionately increased the use of glyphosate, meaning in an absolute sense more herbicide is being applied. On the other hand, glyphosate is considered to be environmentally friendly because of its low toxicity to vertebrates and relatively low soil persistence. We are studying the effects of adoption of transgenic glyphosate tolerant soybeans and their accompanying agricultural practices on avian communities, reproduction, their food supply, the vegetation structure within the habitats they use, and nest predation. With respect to herbicide usage, the increased amount of glyphosate relative to other herbicides could cause negative or positive effects on avian species composition, reproduction, and other ecological factors. These hypotheses remain untested at a landscape level, and the data to address these will have considerable use to policymakers as glyphosate-tolerant crops are submitted for deregulation.
This project, funded by USDA, looks at multiple levels of ecological organization. At the population-level, the reproductive ecology of Dickcissels breeding in grasslands, and of cavity nesting birds such as Tree Swallows, Eastern Bluebirds, and House Wrens breeding in riparian zones is being monitored adjacent to fields of conventional and transgenic crop varieties. These species are linked to community level processes through interactions with their food supply and the community of nest predators. We are monitoring these aspects though a combination of environmental monitoring and through as series of artificial nest experiments (designed to provide and index of nest predator activity). Finally, we have initiated long-term monitoring of the grassland and riparian bird communities to evaluate larger spatial and temporal scale differences associated with the adoption of new crop varieties.
The widespread conversion of natural grasslands to agriculture means that most of the habitat for grassland birds that remains exists in relatively small, isolated fragments. This is especially true of the tall-grass prairie ecosystem of eastern Nebraska and Iowa. We are looking at how the size of grassland fragments and the composition of the surrounding landscape influences grassland birds. Much of this work is being conducted with the support of Boyer Chute National Wildlife Refuge and DeSoto National Wildlife Refuge in the Missouri River Valley of Iowa and Nebraska.
These wildlife refuges provide important habitat for grassland birds and support populations of a number of grassland species of conservation concern. Today these grasslands exist in a fragmented mosaic of grassland, woodland, and agricultural fields. However, one of the land management goals for the future development of these refuges is a reduction in the degree of fragmentation and an increase in the size of grassland plots available.
Our research at the wildlife refuges is looking at the composition of the grassland bird community at the refuges. This work will provide information on how the current landscape configuration correlates with the diversity and abundance of grassland species. This work will also serve as a baseline for long-term monitoring of the avian community as the wildlife refuges implement changes in their management regime. An important part of this project is the graduate work of Shannon Engberg, who censused grassland parcels for grassland birds of conservation concern in 2002 and 2003. Shannon successfully defended her thesis in the summer of 2004 (Engberg, S. E. 2004. Landscape and habitat effects on grassland birds. MS Thesis, Department of Biology, University of Nebraska at Omaha.). Shannon's results showed that both the size of grassland restorations and the type of vegetation restored significantly influenced that abundance and species richness of grassland bird species of conservation concern.
Additional work at the National Wildlife Refuges focuses on the population ecology of Dickcissels in grasslands of varying size. We are monitoring reproductive success, of this species with a special emphasis on documenting predation rates and nest parasitism by Brown-headed Cowbirds. This work will help document ecological changes across the refuges and will provide insights into the mechanisms behind any community level differences that occur.
The 2005 season again combined work on birds and butterflies. Graduate student Page Klug defended her thesis in May (Page Klug. 2005. The effects of local grassland habitat and surrounding landscape composition on the predators of grassland bird nests. MS Thesis, University of Nebraska at Omaha.) but continued to collect data on snakes in grasslands before moving to Kansas State University to start a Ph.D. program. Nichollette Rider collected a second year's data on grassland butterflies.
Another member of our lab, Katy Simmons, is exploring the impact of recreational trails on bird abundance and diversity.
Four members of the lab presented research at the 2005 Natural Areas conference. Both student awards were won by members of our lab: Katy Simmons was awarded the Best Student Poster Award and Joel Jorgensen earned the Best Student Paper Award.
For the 2004 field season we added investigations of grassland butterflies to the work we are doing with grassland birds. Graduate student Nichollette Rider is looking at the abundance and diversity of butterflies in relation to farming practices. The grassland bird work continued, with Lorelle Berkeley and Page Klug collecting their second year's data. Lorelle successfully defended her master's thesis in November and graduated in December (Berkeley, L. I. 2004. The postfledging ecology of Dickcissels (Spiza americana). MS Thesis, Department of Biology, University of Nebraska at Omaha.). Lorelle found that the first few days after leaving the nest are a critical period for young Dickcissels. Habitat was an important determinant of survival, with juveniles in fields with a higher density of forbs surviving longer. Lorelle is currently at the University of Minnesota.
With the help of our field crew we were again able to monitor over 230 Dickcissel nests and greatly expanded our collection of information on the food supply and habitat of birds using both agricultural lands and conservation lands.
Also in 2004, graduate student Joel Jorgensen started his work on the stop over ecology of migrating Buff-breasted Sandpipers. Joel's work has found that a significant proportion of the world's population of Buff-breasted Sandpipers stops in Nebraska's Rainwater Basin during migration. His research is focused on trying to understand habitat use and the relationship between this species and agriculture. You can learn more at Joel's website.
The Grassland Bird Project completed its second field season in 2003, with support from the US Department of Agriculture and the US Fish and Wildlife Service's Boyer Chute National Wildlife Refuge and DeSoto National Wildlife Refuge.
The 2003 field season expanded on the efforts of our first season by doubling the number of sites censused and increasing our efforts at monitoring Dickcissel reproductive success. Thanks the efforts of our dedicated field crew we were able to monitor over 230 Dickcissel nests as well as nests of Field Sparrows, Common Yellowthroats, Eastern Meadowlarks, and Red-winged Blackbirds.
Two new graduate students joined the project in 2003. Page Klug is studying the distribution of potential and actual nest predators across the landscape, while Lorelle Berkeley is focusing on the post-fledgling habitat use and survival of Dickcissels. In her first field season, Page Klug monitored the abundance of the major members of the predator community at our field sites, including birds, snakes, small mammals, and medium-sized mammals such as raccoons. She also documented the species actually responsible for predation on Dickcissel nests using time-lapse, infra-red video. She is currently analyzing her data to determine how members of the predator community might interact and how the distribution of habitats across the landscape influences the risk of nest predation.
Lorelle Berkeley is studying the post-fledging ecology of Dickcissels using radio-telemetry. In her first field season she marked and tracked young Dickcissels to determine what types of habitats they use and to understand their patterns of survival. Her preliminary results suggest that, while dispersal from the natal site is low during the first few weeks after fledging, survival is also low. Her work will help us to understand this critical phase in the life history of grassland birds.
The Grassland Bird Project started its first season in May 2002. With support of the University Committee on Research (UCR) at University of Nebraska at Omaha and from the US Fish and Wildlife Service, collected data on the population, community, and landscape level ecology of grassland birds in eastern Nebraska and Western Iowa. We are just beginning to review the data collected in this season but provide an overview of our projects below.
A major focus of this first season was to begin to understand the population ecology of Dickcissels. We found approximately 125 nests on grasslands at DeSoto National Wildlife Refuge, Boyer Chute National Wildlife Refuge, and at UNOmaha's Allwine Prairie Preserve.
As part of this project we captured and marked adult Dickcissels and followed reproductive success. It is apparent that both predation and parasitism by cowbirds are major factors limiting reproductive success of Dickcissels in these populations.
In collaboration with Marlon Ortega, an undergraduate Environmental Studies major at University of Nebraska at Omaha, we also completed a major study of nest-site selection by Dickcissels.
Another member of our lab, graduate student Shannon Engberg, began her work this season, censusing the grassland bird populations. Shannon's work takes a landscape-level perspective and focuses on the species identified by the National Wildlife Refuge managers as being of greatest conservation concern. Her work will provide valuable information about how these species are responding to current land management practices and will serve as a vital baseline for monitoring future changes in the avian community as Boyer Chute and DeSoto NWRs implement their management plans.