New Program to Aid American Black Duck Research
The research project conducted by White (1994) during the winter seasons of 1990-91 and 1991-92. This study looked at body composition, activity budgets, and food habitats of black ducks on the Duck River Unit. Body fat was excellent during both years of this study. However, a decline in body mass was detected during the later part of the winter of 1992 which were probably due to a reduction in available food, requiring movement to and from feeding areas off the refuge. During this year and abnormally early drawdown of the impoundments was initiated during the second week of January, resulting in a loss of available habitat. Evaluation of the activity budgets determined that black ducks spent about 48% of their time feeding, which ranged from 24% during the early winter to 59% during late winter. Moist-soil and waters along levees were the preferred foraging habitats. Black ducks rested 28% of the time and preferred more open habitats, including mudflats and open water. The food habit analysis portion of this study is a continuation of the research conducted by Byrd (1991) and was only conducted in 1991-92. Mallards were also compared to black ducks. This study examined foods consumed by twenty-three black ducks and eighteen mallards. Plant seeds (other than agriculture grains) were again the dominant food source for black ducks (54%) and mallards (50%), but declined from the previous winter. Water smartweed ( Polygonum hydropiperoides), primrose-willow (Ludwigia sp.), wild millet ( Echinochloa crusgalli), and lovegrass ( Eragrostis hypnoides) were the dominant seeds consumed by black ducks. Mallards preferred wild millet, lovegrass, flat sedge ( Cyperus sp.), and smartweed ( P. lapathifolium). The amount of agriculture grain consumed by black ducks (4%) was similar to that of the previous year, but increased to 38% of the diet of mallards. The amount of vegetation other than seeds consumed by black ducks was 33%, which was an increase from 17% found by Byrd (1991). Animal mater made up 8% of the black duck and less than 1% of the mallard diet.
During the winters of 1992-93 and 1993-94 Clark (1996) studied the habitat preference differences between black ducks and mallards on six sites in Tennessee, with the refuge being one of these sites. Clark found that black ducks selected open water habitats more frequently than mallards, which preferred more densely vegetated areas. Black ducks were found in higher densities relative to mallards in moist-soil and scrub/shrub habitats that contained a substantial open water component than similar habitats without.
Chipley (1995) studied the habitat use and survival of female black ducks captured on the Duck River Unit and equipped with radio transmitters during the winters of 1990-91 (n=20 adults) and 1991-92 (n=24 adults & 23 juveniles). Chipley found that moist-soil was the preferred habitat during nocturnal periods. During the early winter periods moist soil and lacustrine habitats were the predominate locations utilized by black ducks. Most late winter locations still occurred in moist soil and open water areas but a shift towards forested wetlands, scrub/shrub wetlands, and agricultural habitats was noticed. Birds in poorer condition preferred agricultural areas during the late winter. Each year the majority of the early winter locations occurred on the refuge (90% in 1990-91 and 59% in 1991-92). During the late winter the locations started shifting to areas away from the refuge (43% off refuge in 1990-91 and 90% in 1991-92). The excessively high percentage of use off the refuge in 1991-92 may be attributed to the abnormally early drawdown that occurred in mid-January of 1992. The survival rate was 0.94 during the years of this study. Chipley suggested that this high survival rate may be attributed the mild winters that occurred during the study, a diverse mix of habitat types both on and off the refuge, and the low human disturbance that occurred on the refuge.
Black Duck Blood Lead Concentrations
Two studies have been conducted on the refuge to measure lead exposure in black ducks from ingesting lead shot. The first study occurred in 1986-88 (Samuel et al., 1992) prior to the nation-wide lead shot ban and a followup study took place in 1997-99 (Samuel and Bowers, 2000). During both studies blood samples taken from black ducks captured on Tennessee and Cross Creeks NWRs. In the first study 11.7% of the ducks had lead exposure above normal levels ( $ 0.2 ppm) as compared to 6.5% detected in the later study. This represents a 44% decline in elevated blood lead levels.
Byrd, V. E. 1991. Food habits of black ducks wintering in west central Tennessee. M.S. Thesis. Tennessee Technological University, Cookeville, TN. 41pp.
Chipley, W. H. 1995. Habitat use, daily movements, and survival of female American Black Ducks wintering in west-central Tennessee. M.S. Thesis. University of Georgia, Athens, GA.
Clark, W. S. 1996. Habitat differences between Mallards and American Black Ducks wintering in Tennessee. M.S. Thesis. Tennessee Technological University, Cookeville, TN.
Samuel, M. D., and E. F. Bowers. 2000. Lead exposure in American Black Ducks after implementation of non-toxic shot. Journal of Wildlife Management 64(4):947-953.
Samuel, M. D., E. F. Bowers, and J. C. Franson. 1992. Lead exposure and recovery rates of Black Ducks banded in Tennessee. Journal of Wildlife Diseases 28:555-561.
White, T. O. 1994. Body composition, activity budgets, and food habits of American Black Ducks wintering in west-central Tennessee. M.S. Thesis, Tennessee Technological University, Cookeville, TN. 82pp.