Research

Black Ducks Down Home on Dairy Farms
by Charles Maisonneuve, Société de la faune et des parcs du Québec, Luc Bélanger, Canadian Wildlife Service, and Jason Beaulieu, Ducks Unlimited Canada

Aerial surveys in southern Quebec lowlands during spring 1998-1999 have revealed surprising results. The highest densities of American black ducks, generally associated with forests, were obtained in agricultural landscapes dominated by dairy farms. These surveys were carried out under the Eastern Lowlands Initiative, in partnership with Ducks Unlimited Canada, the Canadian Wildlife Service, the Institute for Wetland and Waterfowl Research, and the Société de la faune et des parcs du Québec.

Regions targeted were agricultural lowlands of the St. Lawrence Valley and Lake Saint-Jean, and agricultural sectors of Abitibi-Témiscamingue in northwestern Quebec. The objectives were to estimate waterfowl populations, determine distribution, and build a predictive model of the relationship between breeding pair densities and multiple habitat variables obtained through satellite imagery analysis. This will help predict breeding pair densities in areas not covered by surveys carried out under the Black Duck Joint Venture and produce a waterfowl habitat map for southern Quebec lowlands. The map will become a tool for identifying Eastern Habitat Joint Venture priority areas and for planning and evaluation.

The highest breeding pair densities (178/100 square kilometers) were recorded in Abitibi-Témiscamingue, and the lowest (74/100 square kilometers) in the western part of the St. Lawrence Valley. American black duck and mallard were the dominant species, with more than 70% of the estimated 38,000 indicated pairs breeding. Within the St. Lawrence Valley, five main landscapes—cash crop, dairy farm, heterogeneous agriculture (mix of the two previous), agro-forested landscape, and forested landscape—were delimited based on land-use types with the use of LANDSAT-TM satellite images. Mallards were evenly distributed within these landscapes, but black duck densities in the dairy farm and forested landscapes were over three times those obtained in areas of extensive agriculture. In fact, these landscapes harbour the highest densities of breeding black duck in Quebec. Some forested habitats used by black ducks, like woodlots and fencerows, are still covering adequate areas of the dairy farm landscapes, which is not the case in the cash crop and heterogeneous landscapes.

Habitat modifications in southern Quebec may have had a marked influence on black duck population declines at the regional and continental scale. If studied lowlands in Quebec support only 10% of the continental black duck population, this is probably the segment of the population most at risk. Modifying agricultural practices and creating cultivars that grow in harsher conditions may represent a threat for black duck populations still nesting in dairy farm landscapes.

Thus, the black duck could eventually become an excellent indicator species in evaluating the environmental quality of agricultural landscapes, both from water quality and biodiversity standpoints. The species could also be an indicator of wetland availability and riparian strip, fencerow, and woodlot conditions. Continuation of the analyses will lead to a model and map showing black duck habitat potential.

For more information, contact Charles Maisonneuve, Société de la faune et des parcs du Québec, 675 Boulevard René-Lévesque Est, 11ième etage, Québec, Québec G1R 5V7, (418) 521-3940 extension 4457, charles.maisonneuve@fapaq.gouv.qc.ca.

Native Warm-season Grass Habitat in One Season
by Thomas G. Barnes, University of Kentucky

Native warm-season grasses (NWSG) provide excellent nesting and winter cover for a variety of grassland birds, but, until recently, this vegetation type was difficult to establish, taking 3 to 5 years. It was hypothesized that before above-ground productivity was seen these grasses spent years establishing productive root systems that allowed them to compete with existing vegetation. The proposition became: If competing vegetation is removed will NWSG seedlings grow above and below ground at the same rate?

Over the past 5 years, University of Kentucky scientists have developed standard methodologies for establishing NWSG using imazapic, the primary active molecule in a variety of relatively new herbicides, including Plateau® and Oasis®. Biologically, imazapic stops photosynthesis by inhibiting the biosynthesis of branched-chain amino acids through the inhibition of acetohydroxyacid synthase. Use of imazapic results in little residue, and thus, effects on the environment and wildlife are minimized. In studies where the imazapic was fed to mammals and birds, no toxicity resulted. Its mobility in earth is limited because it binds to soil particles. In addition, at maximum label-rate application, approximately one-tenth of imazapic is present when compared to maximum label rates of products using glyphosate.

Field trials show that tall fescue is effectively eliminated with imazapic using a full label rate (12 ounces per acre) with one quart of surfactant and one quart liquid 28-0-0 nitrogen fertilizer. There is enough residual herbicide activity to provide full weed control for 45 to 60 days, a critical factor in successfully establishing NWSG. Protocol calls for idle grassland fields to be burned in March, followed by herbicide application in mid April, when tall fescue is 6 to 8 inches tall. Native warm-season grass seed is planted with a no-till NWSG drill in mid May. Through 2000, this process has resulted in the successful establishment of NWSG in a single growing season, with flowering and seed production.

Conservation Reserve Set Aside acres are restricted to the use of 4 ounces of imazapic per acre. A change in protocol will result in a stand of NWSG that is comparable to using the 12 ounce rate in no-till situations: Follow burning with the application of glyphosate at the maximum label rate, then apply 4 ounces of imazapic at the time of NWSG seeding.

With conventional tillage and a good seed-bed, a 4-ounce application of imazapic at the time of NWSG seeding will provide adequate weed control for the entire growing season in mid to northern latitudes.

For exotic cool season grass invasion into NWSG stands or for prairie restoration, it was found that prescribed burning followed by an application of 10 ounces of imazapic with a non-ionic surfactant provided excellent tall fescue control and bolstered growth of NWSG and numerous forbs.

There is a downside to imazapic use. Few forbs or wildflowers can tolerate the herbicide, and some prairie grasses like the wild ryes, switchgrass, and eastern gamagrass may not be tolerant. Nonetheless, imazapic herbicides have revolutionized the establishment of native warm-season grasses.

For more information, contact Thomas G. Barnes, Associate Extension Professor and
Extension Wildlife Specialist, Department of Forestry, University of Kentucky, Lexington, Kentucky 40546-0073, (859) 257-8633, tbarnes@ca.uky.edu.

Diving Ducks Trends in Chesapeake Bay
by Matthew Perry, Peter Osenton, and Edward Lohnes, U.S. Geological Survey

Based on aerial surveys during the past 50 years, diving ducks wintering in Chesapeake Bay have accounted for 23% of Atlantic Flyway and 9% of North American populations. Continental and local factors have affected population changes. Factors such as human population increases, water quality, and food availability have been implicated in the changes in distribution, abundance, and food habits of some species of diving ducks.

Mid-winter aerial surveys, conducted by U.S. Fish and Wildlife Service and state wildlife agencies, determine the distribution of and estimate the size of the bay's waterfowl populations. The bay has annually wintered approximately 1 million waterfowl on average during the past 50 years. Diving ducks have declined significantly during this period; the bay now winters approximately 200,000 diving ducks. Survey results show a decline in pochards (canvasback, redheads, and scaup), ruddy duck, and goldeneye. Although there have been major changes during some periods, the long-term trends of long-tailed duck (oldsquaw) and scoters show that numbers in the 1990s are similar to those of the 1950s, but bufflehead and mergansers have shown population increases.

Scientists have determined present food habits by analyses of the gullets and gizzards removed from ducks obtained from hunters or law enforcement officers. They separated organisms by species and measured dry weights and volumes for each sample. They also determined frequencies of occurrence, average weight, and average volume of the food items for each duck species. For comparison purposes, they reexamined historic food habits data for the bay's sea ducks.

Some species of diving ducks have shown major long-term changes in the food eaten, whereas other species show no change in diet. The percentage of invertebrates in the diet of most pochards and ruddy ducks has increased as submerged aquatic vegetation (SAV) has declined. The Baltic clam constitutes over 90% of the food of canvasbacks. Both species of scaup feed on hooked mussels, but also rely on clams and barnacles. The redhead did not alter food preference for SAV, and populations of this species have declined from over 100,000 to less than 1,000 in the bay.

Baltic clam and hooked mussels are important foods of goldeneye. Bufflehead also feed on the Baltic clam, but they feed heavily on the dwarf surf clam, too. The sea ducks rely heavily on mollusks, especially the hooked mussel and several species of clams. Long-tailed duck appears to select the gem clam at rates higher than other divers, but food habits of this species show a diverse diet of other mollusks and crustaceans.

While some species of diving ducks have modified feeding habits to accommodate changes, other species show little changes in food habits. Species, like the pochards, that feed in shallow water are probably more affected by environmental changes in the bay than those that feed in deeper water.

Contributing human factors affecting diving duck populations include development in the bay's tributaries, increased year-round boat traffic, and increased levels of contamination of the bay's waters.

For more information, contact Matthew Perry, U.S. Geological Survey, Patuxent Wildlife Research Center, 11410 American Holly Drive, Laurel, Maryland 20708, (301) 497-5622, matt_perry@usgs.gov.

Getting to Know Oaxaca's Coastal Island Seabirds
by Juan Meraz, Universidad del Mar

The coast of Oaxaca is characterized by rocky beaches interspersed along extensive sandy portions of coastline. Just off the coast is a series of small islands, keys, and rocky formations concentrated throughout Bahías de Huatulco. Highly mobile organisms, such as birds, occur along the coastal mainland as well as on adjacent islands. In theory, if there is a large number of species migrating between the two, the islands should maintain a high level of diversity. An assumption could also be made that there should be a great degree of resemblance between species that inhabit both areas.

The Resources Institute at the Universidad del Mar in Oaxaca initiated a project to study seabird communities on four small islands near the coast: Montosa, Cacaluta, San Agustín, and Roca Blanca. Interestingly, concentrations of brown booby were found on Isla Roca Blanca in the surroundings of Zipolite beach, which is within the tropical zone where reproductive conditions for this species are not usually appropriate. It also was surprising to find many wintering migrant groups of brown pelican and magnificent frigatebird throughout most of this zone.

On islands closer to sandy portions of the coastline, elegant tern was found, together with snowy egret and laughing gull. Of particular interest were osprey and American kestrel, located in the prominent portions of the islands. Less frequently seen species included spotted sandpiper, great blue heron, American oystercatcher, red-billed tropicbird, and belted kingfisher. Numerous groups of storm-petrels and shearwaters were registered in the open sea. Although these birds were closer to the islands, none were spotted on them.

At this time, studies have been developed mainly for species identification and census. In the future, researchers hope to conduct annual inventories as well as comparisons between species diversity and abundance on the islands and mainland coast. The importance of studying these areas is based on two points: studies on Oaxaca's seabirds are limited and tourism activities are increasing. The modification of the coastline by hotel construction and the growing number of tourist vessels will make the islands increasingly important refuges for seabirds. The future well-being of Oaxaca's seabirds is tied to the protection of these islands.

To date, there has been little or no interest in the islands as tourist destinations; for this reason, they are still well-conserved areas. Research projects that gain knowledge about the bird populations there and their insular habitats will provide the basis for sound conservation strategies now and in the future.

For more information, contact Juan Meraz, Instituto de Recursos, Universidad del Mar,
Carr. A Zipolite, km 1.5 Puerto, Angel, Oaxaca, México, C.P. 70902, (529) 584-3047 or 3049, revista@angel.umar.mx.