Division of Bird Habitat Conservation

Birdscapes: News from International Habitat Conservation Partnerships

Research

How Landscape Factors Affect Duck Hatching Rates
by David Howerter, Institute for Wetland and Waterfowl Research

Editor: This is the first in a series of articles on the findings of the 8-year Prairie Habita Joint Venture Assessment Project.

Southern Canada's Prairie Pothole Region remains one of the world's most important duck-producing areas, despite the fact that 77% of the pre-settlement prairie has been converted to agriculture since the 1870s. Gone, along with the grasslands, are the vast herds of bison and the wildfires that periodically roared across the plains, shaping the vegetation and impacting all the region's inhabitants. Gone, too, is the predator complex dominated by grizzly bears, gray wolves, and swift foxes. It has been replaced with a suite of mid-sized carnivores such as raccoons, striped skunks, and red foxes better adapted to living near humans and adept at finding and eating ducks and their eggs.

Natural habitats have been reduced to minuscule remnants surrounding wetlands and along roadside ditches. For decades, biologists have surmised that waterfowl forced to nest in these small, easily searched patches of cover were more susceptible to predation. Modern computing technology and geographic information systems (GIS) now allow complex analyses of how the spatial arrangement of habitat features affect duck population dynamics. Armed with these sophisticated tools, the study determined how these sweeping landscape changes have affected duck populations and searched for solutions that will allow waterfowl and prairie agriculture to coexist.

As part of the Prairie Habitat Joint Venture Assessment Project, between 1993 and 2000, Ducks Unlimited Canada (DUC) researchers radio-marked between 111 and 137 female mallards at 27 sites across Manitoba, Saskatchewan, and Alberta. Using truck-mounted receiving equipment, researchers determined where mallards nested, renesting rates, and nest-hatching success. In the process they also found over 15,000 nests of other duck species. Detailed analyses were completed on about 9,000 nests. Habitat maps were created within the GIS form high-resolution aerial photographs, and a global positioning system mapped nest locations.

The study assessed statistical relationships between hatching rates and various habitat features, including habitat type; size of habitat patch containing the nest; cropland in proximity to the nest; and nest distance from wetlands, farms, and habitat "edge" (the boundary where habitat types meet—hypothesized to be "high-travel" predator zones).

Generally, hatching rates increased with distance from a habitat edge. Similarly, hatching rates were higher in larger patches of habitats, especially early in the nesting season. Hatching rates increased with distance from wetlands. Conversely, other analyses indicate that survival of ducklings is higher for nests near wetlands. Ducks, then, may face a tradeoff—an increased chance of losing a nest if they nest close to a wetland versus an increased change of losing ducklings if they nest farther away.

An understanding of the most important habitats and how the spatial arrangement of habitat features affects duck production will allow DUC managers to maximize their habitat-investment efficiency. For example, if all else is equal, securing or restoring habitats in large blocks appears to be a sound strategy. The relationship between hatching rates and proximity to wetlands, however, poses a dilemma. Is it better to restore previously drained wetlands to augment pair numbers and duckling survival, or do lower hatching rates nullify these benefits? Work continues to better understand the implications of these trade-offs.

For more information, contact Michael G. Anderson, Director, Institute for Wetland and Waterfowl Research, Ducks Unlimited Canada, P.O. Box 1160, Stonewall, Manitoba, Canada R0C 2Z0, (204) 467-3231, m_anderson@ducks.ca.

Food for Thought
by John Eadie and Luke Naylor, University of California-Davis, and
Michael Eichholz, Central Valley Habitat Joint Venture

In the past decade, private landowners and federal, state, and non-governmental organization partners have acquired, restored, and enhanced thousands of acres of wetlands in California's Central Valley. These habitats and associated agricultural lands support the largest single concentration of wintering waterfowl in North America—3 to 4 million birds. The foraging value of the wetlands is the primary concern of the North American Waterfowl Management Plan's Central Valley Habitat Joint Venture.

The joint venture is using a bioenergetic approach to aid conservation planning. Researchers calculate total energy requirements of projected waterfowl populations and estimate the total food value provided by wetland and agricultural habitats to determine the acreage needed to provide the required foraging habitat. This approach provides a biologically sound basis for establishing habitat objectives.

Well managed marshes can produce more than 1,500 pounds of combined seeds, tubers, green forage, and invertebrates per acre. However, food production is extremely variable depending on the vegetation present, the length of time since disturbance of vegetation and soils, and the management strategies used. Joint venture partners, funded by a North American Wetlands Conservation Act evaluation grant, recently conducted studies to determine the amount of food available in moist-soil habitats and the rate at which food is depleted during the winter.

Researchers measured moist-soil seed abundance in 30 wetland units having different habitat types and management regimes. Results indicate that Central Valley wetlands appear to produce less food than was previously assumed, averaging slightly over 500 pounds per acre. A simulation analysis suggested that at this level of food production only 67% of the energy requirements of waterfowl populations would be met by current joint venture implementation plan objectives.

The study also revealed that food production was highly variable among sites. Some wetland units produced over 1,400 pounds per acre of moist-soil seeds, while others produced less than 200 pounds per acre. This variability occurred despite a common goal among wetland managers to produce high levels of waterfowl food. It has been assumed that restored and protected wetlands will provide quality waterfowl habitat. If moist-soil seed production is a reliable indicator, some wetlands may not be meeting this objective.

One of the most striking results of the study was the extent to which food in moist-soil habitat was depleted by waterfowl and other consumers. Levels of food depletion over winter were high and sites that produced the greatest abundance of moist-soil seeds experienced the highest levels of depletion. There was remarkably little variation in this relationship, suggesting that food production alone—rather than distance to refuge, habitat complexity, or a myriad of other factors—may be the single most important factor influencing habitat use by wintering waterbirds.

Collectively, the results of this study suggest that the joint venture's planning objectives would be supported through habitat-enhancement activities that increase food production on existing wetlands. Partners would not only provide the critical food resources needed to sustain wintering bird populations, but also they would ensure that the wetlands acquired are serving their intended purpose.

For more information, contact John Eadie, University of California-Davis, Department of Wildlife, Fish and Conservation Biology, One Shields Avenue, Davis, California 95616, (530) 754-9204, jmeadie@ucdavis.edu.

Evaluating Foraging Needs Project Partners

Central Valley Habitat Joint Venture
University of California-Davis
Ducks Unlimited, Inc.-Western Regional Office
California Department of Fish and Game
California Waterfowl Association
U.S. Fish and Wildlife Service
U.S. Bureau of Reclamation

Why the Decline of Forest Birds?
by Allison Wells, Cornell Laboratory of Ornithology

The wood thrush, with its haunting, flute-like song, is among the many forest-dwelling bird species showing declines. Birds in Forested Landscapes (BFL), a study being conducted by the Cornell Laboratory of Ornithology (Laboratory) with the help of volunteer birders across the continent, is working to better understand the reasons for declines and to develop guidelines that may help reverse these trends.

The study's objectives are to understand the effects of forest fragmentation to determine the amount of habitat various forest-dwelling bird species require for successful breeding; how habitat requirements are affected by land uses in the surrounding landscape; and how habitat requirements of a species vary across its range.

To find these answers, Laboratory researchers are relying on the help of volunteer birders. Participants in BFL select study species that occur in the region where they live. They then choose survey points in forest patches of different sizes, visit each point twice during the breeding season to search for the selected species, look for evidence of breeding success, and record characteristics about the study site.

During both visits, volunteers look and listen for the birds they are studying as well as for potential nest predators and brown-headed cowbirds, nesting parasites. These citizen scientists also conduct a short playback-and-behavior watch for each study species using a compact disk containing songs, calls, and drums of study species. Observations are recorded on field data forms provided to volunteer researchers, and they either enter data at the BFL Web site or send it to the Laboratory.

Preliminary results indicate that veery, Swainson's, and hermit thrushes appear to be negatively affected by forest fragmentation. These species are much less likely to attempt to breed in regions where forest cover has been reduced to many wooded patches that are small in size. This is true even when the area of remaining patches is several times larger than the minimum size needed for a breeding territory. There is often enough space for more than one pair to breed, but that is not occurring. This pattern is consistent for both eastern and western North America.

Wood thrushes do not appear to be strongly negatively affected by forest fragmentation. Instead, decline may be related to acid rain in the Appalachian Mountains and to predators and cowbirds elsewhere where landscapes are fragmented. In addition to thrushes, data are being collected for almost 50 different bird species from all regions of the continent, including Cooper's and sharp-shinned hawks, yellow-billed cuckoo, oak titmouse, Lewis's woodpecker, olive-sided flycatcher, and many warbler species.

The Laboratory and the U.S. Department of Agriculture's Forest Service have formed a partnership to help determine the effects of recreational development on forest thrushes. In 2001, study volunteers collected data on 28 national forests and 137 campgrounds.

Obtaining data for the BFL requires the help of birders from across the continent. Volunteering to help with this project is a meaningful way to help in the recovery of forest-dwelling birds.

For more information, contact Sara Barker, Cornell Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, New York 14850, (670) 254-2473, toll free inside the United States (800) 843-2437, forest_birds@cornell.edu, www.birds.cornell.edu/bfl, or for the recreational study, Barb Kott at Zigzag Ranger Station, 70220 E. Highway 26, Zigzag, Oregon 97049, (503) 622-3191 extension 687, bkott@fs.fed.us.

The Predator's Edge
by Rebecca Phipps, U.S. Geological Survey

Declines in North American grassland bird populations are largely due to loss of habitat. As grassland areas are divided into smaller tracts of land, there are more "edges" and fewer large, open grassland areas for birds to nest in. Biologists have suggested that predators looking for food near these "edges" might be more likely to prey on grassland bird nests, making it more difficult for birds to successfully raise chicks.

From 1998 through 2001, graduate students Rosalind Renfrew and Jamie Drossel, along with their major professor Christine Ribic with the Department of Wildlife Ecology at the University of Wisconsin-Madison, placed miniature cameras at 89 nests of five grassland bird species in southwestern Wisconsin pastures. They found that most of the nest predators were raccoons, thirteen-lined ground squirrels, and snakes. More than one-third of the nest failures were caused by species that prefer the woody edges of grasslands, such as raccoons and opossums.

In 2000 and 2001, the scientists monitored sand-track stations placed at regular intervals along the eggs of pastures and found that the same species that preyed on nests near woody edges were predators that frequented those edges.

The scientists concluded that grassland fragmentation is making it more likely that edge predators will find nests and that this may be contributing to population declines among grassland birds. However, the second and third most common nest predators were species that live in grasslands, suggesting that removal of edge species may not significantly improve grassland bird nest success.

For more information, contact Christine Ribic, U.S. Geological Survey, Wisconsin Cooperative Wildlife Research Unit, Department of Wildlife Ecology, University of Wisconsin-Madison, 204 Russell Labs, 1630 Linden Drive, Madison, Wisconsin 53706, (608) 263-6556, caribic@facstaff.wisc.edu.

Understanding Great Lakes Mallards
by Tina Yerkes and Tildy La Farge, Ducks Unlimited, Inc.

Understanding basic biological requirements and limiting factors is fundamental to effective habitat conservation programs. To that end, Ducks Unlimited, Inc., and the North American Waterfowl Management Plan's Upper Mississippi River & Great Lakes Region Joint Venture, along with other partners, launched a landscape level study in 2001 to determine limiting factors and habitat use of breeding mallards in the Great Lakes states.

From the early 1960s to the early 1980s, breeding mallards were increasing in the Great Lakes region. Based on age-ratio data, a decline began to occur in the late 1980s. Habitat conservation organizations in this area want to understand the factors that are limiting population growth and to create habitat programs that address them.

While we have extensive knowledge of mallards on the prairies, we are starting from scratch in the Great Lakes region. The prairies and the Great Lakes landscape may be an apples and oranges comparison, because birds breeding in the Great Lakes area likely experience dissimilar threats, including different habitat mosaics and urban growth disturbance. Information from our study will facilitate the development of habitat programs tailor-made for the Great Lakes area and will enhance decision-making related to the allocation of limited financial resources used to achieve the joint venture's habitat conservation goals.

Now in its second season, the study will take 3 years to complete. Each year, sites are located in different areas of the five Great Lakes states to capture spatial variability so that knowledge gained can be inferred across the entire area. In 2001, sites were located in Ripon, Wisconsin, Riverdale, Michigan, and Port Clinton, Ohio. The 2002 sites are in very different landscapes: Shiocton, Wisconsin, the tri-state area of Indiana, Ohio, and Michigan, and north of Battle Creek, Michigan.

Nest success in the first year varied little; whereas, brood survival was highly variable among sites. Mayfield nest-success values ranged from 13 to 16%. Habitat-specific variability saw nest success highest in haylands (18%), but that was a very wet year and cropping was delayed, and lowest in scrubland (11%). The proportion of broods that survived varied from a low of 47% in Ohio to a high of 87% in Michigan. This is likely due to different wetland types dominating the landscape. Scrub-shrub wetlands dominated the Michigan site but were scarce elsewhere.

The habitat-specific production information obtained in this study will be integrated with multiple data layers, such as projected urban sprawl and historic wetland sites, to develop a Decision Support System (DSS) specifically for the Great Lakes landscape. The DSS will use geographic information system modeling technology to identify the landscapes where partners can most effectively target conservation efforts that are based on sound science.

For more information, contact Tina Yerkes, Director of Conservation Planning, Ducks Unlimited, Inc., Great Lakes/Atlantic Regional Office, 331 Metty Drive, Suite 4, Ann Arbor, Michigan 48103, (734) 263-2000, tyerkes@ducks.org.

Great Lakes Mallard Research Partners

Ducks Unlimited, Inc.
Upper Mississippi River & Great Lakes Region Joint Venture
Ohio Department of Natural Resources, Division of Wildlife
Michigan Department of Natural Resources
Wisconsin Department of Natural Resources
Indiana Department of Natural Resources
Winous Point Conservancy
West Rosendale Hunt Club
Kellogg Bird Sanctuary of Michigan State University
The Bruning Foundation
Christel-DaHaan Family Foundation