Research

Nest Tunnels: How Many Are Enough?
by Wanda Gorsuch, Delta Waterfowl Foundation, and Matt Chouinard, Mississippi University

The use of artificial structures to increase waterfowl production is not a new idea. Nest success in fragmented habitats often is too low to sustain local populations, and managers continually look for new tools and techniques to improve local production.

Past research on nest structures focused on determining which types of structures and site characteristics were preferred by mallards and other species, and how structures influenced nest success and duckling survival. Managers placed one to three structures in a wetland, because it was assumed that additional ones would not be used due to territorial behaviour of breeding mallard hens. However, the use of multiple structures in a wetland by mallard hens has been frequently recorded. By placing multiple structures per wetland, installation and maintenance time decreases, hence reducing cost while possibly increasing duckling production.

Recent research undertaken by Matt Chouinard, under the direction of Dr. Rick Kaminski at Mississippi State University, and funded by the Delta Waterfowl Foundation, has addressed a fundamental management question: How many nest tunnels should be installed per wetland to produce the greatest number of ducklings at the lowest cost?

This research was conducted on a 20-square-kilometer area near Minnedosa, Manitoba, in 2001 and 2002. This area in Prairie-Parkland Canada is known for abundant breeding mallards but low productivity of nesting ducks. Wetlands in the study area were separated into two size classes of less than 0.4 hectare and 0.4 to 1.4 hectares. Larger wetlands were excluded because ice movement in these wetlands can damage nest structures. Ten wetlands in each size class were randomly selected to contain one, two, or four nest structures. This resulted in six treatment combinations, and a total of 140 structures were erected in March 2001.

Researchers monitored the use of tunnels, nest success, and the number of ducklings produced for each structure. Use of the structures was 42% in 2001, and increased significantly to 75% in 2002. Nest success was 98% in 2001, but dropped to 41% in 2002 due to egg depredation by corvids. However, nest success remained well above the 15% level believed necessary to sustain local populations. In total, 967 ducklings successfully departed structures during the study period. Results indicated that one or two structures per wetland produced about the same number of ducklings (five ducklings per structure), but more than four structures per wetland produced less (three ducklings per structure). Wetland size did not affect occupancy, nest success, or ducklings per structure.

Based on these preliminary results, a current best management practice may be to erect two structures per wetland because of the increased duckling production, and installing, maintaining, and monitoring two structures per wetland is more cost effective.

For more information, contact Wanda Gorsuch, Scientific Assistant, Delta Waterfowl Foundation, Box 1, R.R. #1, Site #1, Portage la Prairie, Manitoba R1N 3A1, (204) 239-1900, wgorsuch@deltawaterfowl.org, or Matt Chouinard, MSc Candidate, Mississippi State University, Box 9690, Department of Wildlife and Fisheries, Mississippi State, Mississippi 39762, (662) 325-2384, mchouinard1@yahoo.com.

A Bird’s Eye View of Oystercatchers
by Stephen Brown and Shiloh Schulte, Manomet Center for Conservation Sciences, and Brad Winn, Georgia Department of Natural Resources

The eastern race of American oystercatcher once ranged from Newfoundland to Mexico, but by the end of the 19th century, market hunters and egg collectors had extirpated this species from New England and Canada and significantly reduced its populations elsewhere. The bird’s numbers rebounded somewhat following passage of the Migratory Bird Treaty Act in 1929, but recovery has been slow. Direct human disturbance, loss of coastal breeding habitat, and increases in nest predators, such as raccoons and gulls, may be likely causes.

The U.S. Shorebird Conservation Plan (Shorebird Plan) designates the American oystercatcher as a high priority species for conservation due, in part, to the lack of reliable information on population status, distribution, and population size. To address this information need, a partnership of scientists embarked on a project in November 2002 to conduct aerial and ground surveys of the entire wintering eastern population of American oystercatchers found in Atlantic and Gulf of Mexico coastal habitats.

From mid-November to mid-February, researchers conducted aerial surveys in Cessna 172 aircraft along the Atlantic Coast from New Jersey to northeastern Florida and along the Gulf Coast from Everglades National Park in southwestern Florida to the Texas/Mexico border. Three strata were surveyed: known oystercatcher wintering sites, probable high-use habitat types, and other intertidal habitats. All aerial surveys were flown at high tide to find the birds at roost. The location of every flock, pair, or individual oystercatcher was recorded using global positioning system (GPS) equipment. Partners carried out ground surveys in New Jersey (two areas), Virginia (entire coastline), North Carolina (two areas), South Carolina (entire coastline), Georgia (intercoastal waterway and barrier islands), and Florida (three areas). No ground surveys were conducted in Alabama, Mississippi, Louisiana, or Texas, where most appropriate habitats are offshore and difficult to reach.

Researchers observed a total of 10,413 oystercatchers: 9,252 birds counted in aerial surveys and 1,161 more in ground surveys. Double counting was avoided by recording each flock location with GPS. Interestingly, no oystercatchers were found in the third strata: other intertidal habitats. Using survey results, numbers will be extrapolated to estimate the numbers of birds in areas with no ground counts. This will provide an estimated upper limit in population numbers.

Partners’ efforts produced the first comprehensive population estimate for the eastern race of American oystercatcher and provided needed winter distribution and habitat association information. Data collected in this study will be used by the North American Waterfowl Management Plan’s (Plan) Atlantic Coast Joint Venture to prioritize areas for habitat conservation that address not only the Plan’s waterfowl population goals but also the Shorebird Plan’s goals for protecting oystercatchers.

It is hoped that this survey’s protocol may be useful to other shorebird monitoring efforts coordinated under the Program for Regional and International Shorebird Monitoring.

For more information, contact Stephen Brown, Director, Shorebird Conservation Research Program, Manomet Center for Conservation Sciences, P.O. Box 1770, Manomet, Massachusetts 02345, (508) 224-6521, sbrown@manomet.org, www.shorebirdworld.org, or Jon Bart, USGS Snake River Field Station, 970 Lusk Street, Boise, Idaho 83706, (208) 426-5216, jbart@eagle.boisestate.edu.

American Oystercatcher Survey Partners

U.S. Geological Survey
U.S. Fish and Wildlife Service
National Fish and Wildlife Foundation
New Jersey Division of Fish and Wildlife
New Jersey Audubon
The Nature Conservancy
Virginia Department of Game and Inland Fisheries
North Carolina Wildlife Resources Commission
Audubon North Carolina
South Carolina Department of Natural Resources
Cape Romain National Wildlife Refuge
Georgia Department of Natural Resources
Florida Fish and Wildlife Conservation Commission
National Audubon Society
Alabama Division of Wildlife and Freshwater Fisheries
Grand Bay National Estuarine Research Reserve
Texas Parks and Wildlife
Houston Audubon Society
Manomet Center for Conservation Sciences

Nest Success Key to Managing Mid-continent Mallards
by Steven Hoekman, University of Alaska-Fairbanks and David Howerter, Institute for Wetland and Waterfowl Research

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

The fundamental assumption underlying implementation of the Prairie Habitat Joint Venture is that nest success is the most important component of mallard population dynamics. Earlier research, mostly conducted in the Dakotas and western Minnesota by biologists from the U.S. Fish and Wildlife Service, suggested that mid-continent mallard recruitment into fall populations was most sensitive to variation in nest success. This result, coupled with numerous studies indicating very low nest success, led managers to focus on bolstering nest success to meet North American Waterfowl Management Plan (Plan) population goals. Furthermore, declining nest success across the Prairie Pothole Region (PPR) has been linked to extensive degradation of upland nesting habitat by agriculture, and to anthropogenic changes in predator communities. Consequently, joint venture partners developed programs to improve upland habitat, thereby providing safer nesting sites for upland nesting ducks and other bird species.

Despite evidence that nest success was crucial to mallard population success, considerable uncertainty remained. Previous studies had not simultaneously considered the relative contributions of all demographic rates throughout the annual cycle to population growth. Recent data from joint venture evaluation and other sources also provided new information. Because evaluation is central to ensuring efficient delivery of joint venture programs, the relative importance of nest success to demographic performance needed examination.

Collaboration between researchers at the University of Montana and Ducks Unlimited Canada’s Institute for Wetland and Waterfowl Research yielded sophisticated analyses using data from the Joint Venture Assessment and other sources to examine the sensitivity of population growth to variation in demographic rates. A model of population dynamics of females was developed based on estimates of demographic rates across the annual cycle. Factors included clutch size, hatch rate, nest success, duckling survival, breeding incidence, renesting intensity, breeding-season survival of adults, and non-breeding season survival. The influence of management and natural variation in demographic rates across space and time on projected population growth for hypothetical sites of 70 square kilometers within the PPR was then assessed.

We found that population growth was indeed most sensitive to nest success. Thus, declines in nest success are likely detrimental to populations. Therefore, management programs that increase nest success will be more likely to increase mallard and other waterfowl populations.

Furthermore, events on the breeding grounds explained most of the expected variation in population growth rate. Nest success explained almost half of this variation, and breeding season survival of adults and ducklings explained most of the remaining variation. In contrast, non-breeding season survival explained only 9% of the variation in population growth. Hence, processes on the breeding grounds, and nest success in particular, appear to be most important to limiting population growth. Predicting spatial variation in nest success is thus critical to identifying productive sites for habitat protection and enhancement. These analyses support the critical assumption underlying joint venture programs: nest success is the key component of population dynamics of mid-continent mallards.

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

Bird and Amphibian Use of Restored Wetlands in Prairie Canada
by Allison Puchniak and Cynthia Paszkowski, University of Alberta and Brian Gray, Ducks Unlimited Canada

Historically, the Prairie Pothole Region (PPR) was dotted with millions of small (less than 1 hectare), shallow (less than 1 meter) wetlands. These pothole wetlands are productive, dynamic ecosystems that provide critical habitat for birds, amphibians, reptiles, and mammals. The loss of wetlands by widespread ditching and the conversion of native uplands to cropland have resulted in a severe loss of wildlife habitat. Wetland loss is estimated at 40% throughout the PPR and as high as 70% near urban centers with more than 90% of remaining wetlands adversely affected by agricultural expansion and urbanization.

There is hope for mitigating these wetland losses. The hydrology of many previously drained prairie wetlands can be restored by placing earth plugs in the existing drainage ditches. Between 1989 and 1997, under the auspices of the North American Waterfowl Management Plan, Ducks Unlimited Canada (DUC) restored the hydrology in over 900 wetlands in Alberta, Saskatchewan, and Manitoba. Recreating waterfowl and wildlife habitat was the primary goal of these restorations. Therefore, a study was launched to evaluate this goal by comparing bird and amphibian assemblages in restored and natural wetlands.

In the PPR of Alberta (1999 and 2000) and Saskatchewan (2000), surveys were conducted on 97 wetlands, which were restored via ditch plug 3 to 7 years prior to the surveys, and 85 relatively unaltered natural or reference wetlands. In all wetlands, bird species richness and composition was determined using modified point count surveys. Amphibians were monitored in a sub-sample of wetlands (30, 15 restored) using a combination of pitfalls with drift fencing and minnow traps.

Overall, the findings were encouraging. Alberta bird assemblages, including both wetland-dependent and upland species, were extremely similar in restored and natural wetlands. In Saskatchewan, although there were differences in species richness between wetlands related to differences in nearby upland habitat, the species composition of wetland-dependent birds, such as waterfowl, was comparable in restored and natural wetlands. Unlike earlier studies on wildlife use of restored wetlands in the United States’ PPR, bird species, such as American bittern, common yellowthroat, and sora, which nest in the wet meadow and low prairie zones in restored wetlands, were observed.

Three species of amphibians were captured in surveyed wetlands: wood frog, boreal chorus frog, and tiger salamander. Amphibian abundance for all species was similar in restored and natural wetlands in Alberta (1999) and Saskatchewan (2000), and wood frogs and boreal chorus frogs were observed to breed successfully in restored wetlands. This was determined by captured larvae. Leopard frog and Canadian toad, species of concern known from historical records to breed in the PPR, were not observed in restored or natural wetlands.

As bird and amphibian assemblages were comparable between restored and natural wetlands, it was concluded that restored wetlands in Canada’s PPR provide suitable bird and amphibian habitat. Bolstered by the findings from this study, wetland restoration will continue to play an important role in DUC’s conservation strategies in the PPR.

For more information, contact Allison Puchniak, Biological Sciences Department, University of Alberta, Edmonton, Alberta T6G 2E9, (204) 888-7256, allison_puchniak@hotmail.com, or Brian Gray, Ducks Unlimited Canada, P.O. Box 1160, Stonewall, Manitoba R0C 2Z0, (204) 467-3349, b_gray@ducks.ca.

In Search of Snags
by Charles Maisonneuve, Société de la faune et des parcs du Québec

Editor: A “snag” is the standing part of a dead tree.

Wildlife species that depend on natural cavities for the completion of their life cycle are among the most threatened species in regions in North America where forestry is a major industry, such as the Province of Quebec. Every year in Quebec, the total area of forest cut covers over 3,000 square kilometers.

Cavity-nesting ducks readily use artificial nest boxes for nesting. Because of this, almost all knowledge of their breeding biology comes from studies of birds breeding in these artificial structures. Consequently, characteristics of natural cavities and surrounding habitats normally selected for nesting are practically unknown. It is, therefore, difficult to determine the possible effects of current forestry practices on the importance of snags to waterfowl populations.

A 3-year study was initiated in 1999 by the Société de la faune et des parcs du Quebec. It aimed to characterize the nesting habitats of the two most abundant cavity-nesting ducks of Quebec’s northern forests: the common goldeneye and the hooded merganser.

At the end of every nesting season, females cavity-nesting ducks often attempt to locate nest-site options for the following season, which assures nesting opportunities should one snag topple. This behaviour helped determine the methods that would be used in the study.

To capture adult females for radio tagging, researchers installed 75 nest boxes throughtout a 365-square-kilometer area of nothern mixed-hardwood forest 70 kilometers northwest of Quebec City. Each box was equipped with a mechanism that triggered a sliding door after the bird entered. Birds captured in and released from these boxes usually did not return to them to nest the following season. Radio tracking led researchers to the birds’ althernative nesting sites.

Snags selected for nesting were of impressive dimensions. Their mean diameter and cavity height were between 50 centimeters and 9 meters, respectively. More than half of the female goldeneyes and mergansers studied showed a preference for nesting in former pileated woodpecker cavities. The remaining cavities were chimney-like, created by breakage of hollow limbs or tree tops. Interestingly, cavities were usually located about 400 meters from the closest lake, challenging the belief that cavity-nesting ducks usually nest close to water.

Results from this study will be useful in determining the effects of forestry practices on snag availability and distribution. The current 20-meter riparian buffer recommendations may need reevaluation. Over time snags are lost, so retention of live trees of adequate size should be considered to secure a bank of potential snags for the future.

For more information, contact Charles Maisonneuve, Société de la faune et des parcs du Québec, 675 Boulevard Réné Levesque East, Québec City, Québec G1R 5V7, (418) 521-3955 extension 4457, charles.maisonneuve@fapaq.gouv.qc.ca.