William L. Hohman

Shot prevalences and diets of diving ducks five years after ban on use of lead shotshells at catahoula lake, louisiana

Catahoula Lake, central Louisiana, is a RAMSAR Convention Wetland of International Importance and among the most important wintering and staging areas for waterfowl in North America. To evaluate exposure rates in Catahoula Lake waterfowl 5 years after a ban on use of lead shot, we determined the prevalence of ingested shot and diets of canvasbacks (Aythya valisineria) and lesser scaup (A. affinis) salvaged from commercial fishing nets in winter 1992-93. Plant material composed >77% of the midwinter diet of canvasbacks. Consumption of belowground plant material (e.g., chufa flatsedge [Cyperus esculentus] and arrowhead [Sagittaria spp.] tubers) exceeded 47% in 1992-93, but was lower than in 1987-88. Male lesser scaup fed almost exclusively on plant material, especially bearded sprangletop (Leptochloa fascicularis) and millet (Echinochloa spp.). Prevalence of ingested lead or steel shot was similar in canvasbacks (38%) and lesser scaup (34%) in spite of differences in foraging behavior, suggesting that ducks actively selected shot as grit. Shot (lead or steel) prevalence in diving ducks at Catahoula Lake was similar in winters 1987-88 and 1992-93, but the proportion of birds with lead in their gizzards was greatly reduced in 1992-93 (6%) compared to 1987-88 (27%). Because ingestion of lead shot deposited in wetlands prior to steel shot regulations remains a problem at some sites, we suggest that provision of nontoxic grit may serve to reduce lead shot prevalence in waterfowl at contaminated sites.

Influence of ingested lead on body mass of wintering canvasbacks

The authors determined the prevalence of lead shotgun pellets in gizzards of canvasbacks (Aythya valisineria) collected at Catahoula Lake and the Mississippi River Delta, Louisiana, during winter 1987-88 to assess the influence of ingested lead shot on canvasback body mass. The prevalence of ingested lead shot was significantly higher at Catahoula Lake (27%) than at the Mississippi River Delta (4%). Canvasbacks collected at Catahoula Lake showed significant differences in prevalence of ingested lead shot by age and month. The authors attributed age-related and seasonal variations to differences in foraging effort and exposure time. Body mass of canvasbacks at Catahoula Lake, after accounting for age, monthly variation, and body size, was significantly reduced (120 g or 10%) in birds that had lead shot in their gizzards.

Responses of Plants and Arthropods to Burning and Disking of Riparian Habitats

Abstract Alteration of Iowa, USA, landscapes for agricultural production has resulted in a loss of >99% of the original prairie and >95% of native wetlands. This conversion has included riparian areas, which, as interfaces between terrestrial and aquatic ecosystems, are important to many wildlife species. Farm Bill programs have resulted in the reestablishment of millions of hectares of grasslands and wetlands nationwide, including >100,000 ha in riparian areas of the Midwest. We assessed plant and arthropod responses to burning and disking of riparian grasslands in east-central Iowa in 2001 and 2002. Burning altered the plant community by removing litter and standing dead vegetation and had negative effects on several arthropod taxa, including Hemiptera and Lepidoptera. However, we observed no differences in vegetation or arthropods between burned and unburned fields during the second year postburning (P > 0.05). Disking decreased the cover of grasses, litter, and standing dead vegetation and increased plant species richness and the cover of forbs and bare ground (P < 0.05). Arthropod abundance and dry biomass were greater on disked than undisked portions of fields (P < 0.05). Increases in the abundance and biomass of arthropods associated with changes in vegetation structure and composition likely improved habitat quality for a number of breeding bird species. Both burning and disking appear to be effective management options for maintaining or enhancing riparian grasslands for wildlife.

Butterflies and Continuous Conservation Reserve Program Filter Strips: Landscape Considerations

Abstract Filter strips or buffers are areas of grass or other perennial herbaceous vegetation established along waterways to remove contaminants and sediments from agricultural field runoff. In the heavily cultivated regions of the Midwestern United States, these buffer zones established under the Farm Bill provide important habitat for wildlife such as butterflies. The question of how the landscape context of these plantings influences their use has not been adequately researched. We used multiple regression and Akaikes Information Criteria to determine how habitat width and several landscape-level factors (i.e., landscape composition [total herbaceous cover, amount of developed area, and amount of wooded cover] and configuration [herbaceous edge density]) influenced the abundance and diversity of the butterfly community using filter strips in southwestern Minnesota, USA. Habitat-sensitive butterfly abundance and all richness and diversity measures were positively correlated with filter-strip width. Butterfly abundance was negatively associated with the amount of developed areas (cities, towns, and roads) within the area of a 1-km radius (3.14 km2) surrounding the sites. Percentage of wooded cover in the landscape was an important variable explaining individual species abundance, although the direction of the relationship varied. Our finding that landscape context influences butterfly use of filter strips highlights the importance of landscape-level approaches to wildlife conservation in agroecosystems.

Winter survival of immature Canvasbacks in Inland Louisiana

In spite of management efforts, population indices for canvasbacks (Aythya valisineria) declined during 1955-93. Since 1985, Catahoula Lake, located in central Louisiana, has attracted more wintering canvasbacks than any other site in North America. Canvasbacks are attracted to Catahoula Lake because of its consistent flooding regime and abundant below-ground plant foods, but are at risk of lead (Pb) toxicosis because of the high density of spent Pb shot contained in sediments. To estimate survival rates and determine sources and timing of mortality, we radiomarked 172 immature canvasbacks during winters 1991-94. Half of our sample had blood Pb concentrations ≥ 0.2 parts per million (ppm) at time of capture and were considered Pb exposed. Blood Pb concentrations of others (unexposed) were initially at background levels (i.e., Pb < 0.2 ppm). Year had no effect on canvasback survival (P = 0.357), but survival was positively related to body mass (P = 0.014) and negatively related to the interaction of blood Pb concentration and body mass (P < 0.001). Winter survival estimates for Pb-exposed immatures were lower (P ≤ 0.045) than those for unexposed immatures in 1992-93 (0.569 vs. 0.815, respectively) and 1993-94 (0.578 vs. 0.923, respectively) but did not differ (P = 0.34) in 1991-92 (0.747 vs. 0.857, respectively) when Pb-exposed canvasbacks had greater body mass and lower blood Pb concentration. Causes of mortality were gunshot (31%), Pb toxicosis (16%), drowning in commercial fishing nets (6%), and unknown (47%). Survival estimates for Catahoula Lake canvasbacks, especially Pb-exposed individuals, were lower than those previously reported for immature females wintering in coastal Louisiana or Chesapeake Bay. Most immatures that were initially exposed to Pb apparently survived the winter; however, subsequent survival and performance of annual cycle events may have been affected because exposed birds weighed less than unexposed birds. We recommend that Pb exposure in waterfowl be periodically monitored and managers give priority to reducing Pb shot availability at concentration areas

Age-class determination of ring-necked ducks

A quantitative technique was developed to distinguish adult from yearling ring-necked ducks (Aythya collaris) during the breeding season using wing feather criteria. This method requires removal and measurement of the 5th secondary (S 5) and 12th greater secondary covert (GSC 12). Bursal and other plumage characteristics were evaluated for use in the field during the breeding season. Cloacal characteristics are of no value in distinguishing adult and yearling males after arrival on breeding areas (Apr), but bursal depth >10 mm is characteristic of yearling females into their Ist breeding season. Although not all adult females have white head feathers (e.g., flecking), the presence of flecking on mature females strongly indicates adult status. J. WILDL. MANAGE. 50(3):442-445 The ability to distinguish age classes within waterfowl populations is important in understanding aspects of their reproductive biology and population dynamics (Serie et al. 1982). However, determining age classes of waterfowl that reproduce in their 1st year often is difficult, especially during the breeding season. Cloacal (Gower 1939) and rectrix (Pirnie 1935) characteristics are commonly used during the fall and winter to distinguish immatures from adults but are unreliable for birds captured in spring (Hochbaum 1942). Use of qualitative wing feather criteria for determining age class and sex is possible for some species: mallards (Anas platyrhynchos) (Krapu et al. 1979, Gatti 1983), blue-winged teal (A. discors) (Dane 1968), American wigeons (A. americana) (Wishart 1981), canvasbacks (Aythya valisineria) (Serie et al. 1982), and redheads (A. americana) (Dane and Johnson 1975). Unfortunately, these methods do not work well for ring-necked ducks (Carney 1964). Remiges and associated coverts are retained by juvenile waterfowl until the prebasic II molt and are replaced annually thereafter during the prebasic molt (Humphrey and Clark 1961). Multivariate statistical procedures using wing feather measurements have been used to determine age of springand summer-caught mallards (Krapu et al. 1979, Gatti 1983), gadwalls (Anas strepera) (Blohm 1977), American wig ons (Wishart 1981), canvasbacks (Serie et al. 1982), and redheads (Dane and Johnson 1975). Here we describe a quantitative technique for accurate age class separation of male and fema e ring-necked ducks in spring and early summer. Additionally, bursal and other plumage characteristics are evaluated for use in the field during the breeding season. We wish to thank B. D. J. Batt, R. D. Crawford, and M. W. Weller for their helpful comments on earlier drafts of the manuscript. We were assisted in the field or laboratory by J. S. Barzen, D. O. Carlson, L. A. Fluggeman, and J. W. Grimm. Financial support was provided by the North Am. Wildl. Found. through the Delta Waterfowl and Wetland Res. Stn., Univ. Minnesota (Dep. Fish. and Wildl., Comput. Cent., Agric. Exp. Stn., and Graduate School), Minn. Dep. Nat. Resour., and Minn. Waterfowl Assoc. This is J. Pap. 13837 of the Minn. Agric. Exp. Stn., St. Paul, Minn.

Indices of Fat and Protein for Ring-Necked Ducks

Indices of ash-free lean dry body weight and body fat using easily obtained tissue weights and structural measurements were developed for ring-necked ducks (Aythya collaris) collected throughout the annual cycle. The linear regression model incorporating eviscerated carcass weight, wet leg and breast muscle weights, and bill length measurements explained 81% of the variation in ash-free lean dry weight. Wet weights of the abdominal (omental) fat and shared skin tissues accounted for 96% of the variation in body fat. Comparison of direct and indirect measures of nutrient composition confirmed that indices may be used to accurately estimate body protein and fat content of ring-necked ducks. J. WILDL. MANAGE. 50(2):209-211 The ability to assess nutrient reserve levels in waterfowl is important in understanding their strategies for survival and reproduction and in managing habitats to meet changing waterfowl needs. Laboratory assays commonly used to determine fat and protein content of animal tissues are expensive and time intensive. Indices of fat and protein using easily obtained tissue weights and morphological measures have been developed for several waterfowl species to circumvent costly laboratory analyses (Woodall 1978, Bailey 1979, Wishart 1979, Campbell and Leatherland 1980, Chappell and Titman 1983, Thomas et al. 1983). The objective of our study was to develop simple, accurate methods for estimating fat and protein content of ringnecked ducks. We are grateful to W. A. Chappell, M. W. Weller, and R. A. Wishart for their helpful comments on earlier drafts of the manuscript. Financial support was provided by the North Am. Wildl. Found. through the Delta Waterfowl and Wetland Res. Stn., the Univ. Minnesota (Dep. Fish. and Wildl., Comput. Cent., Agric. Exp. Stn., and Graduate School), Minn. Dep. Nat. Resour., and the Minn. Waterfowl

The efficacy of protoporphyrin as a predictive biomarker for lead exposure in canvasback ducks: Effect of sample storage time

We used 363 blood samples collected from wild canvasback dueks (Aythya valisineria) at Catahoula Lake, Louisiana, U.S.A. to evaluate the effect of sample storage time on the efficacy of erythrocytic protoporphyrin as an indicator of lead exposure. The protoporphyrin concentration of each sample was determined by hematofluorometry within 5 min of blood collection and after refrigeration at 4 °C for 24 and 48 h. All samples were analyzed for lead by atomic absorption spectrophotometry. Based on a blood lead concentration of ≥0.2 ppm wet weight as positive evidence for lead exposure, the protoporphyrin technique resulted in overall error rates of 29%, 20%, and 19% and false negative error rates of 47%, 29% and 25% when hematofluorometric determinations were made on blood at 5 min, 24 h, and 48 h, respectively. False positive error rates were less than 10% for all three measurement times. The accuracy of the 24-h erythrocytic protoporphyrin classification of blood samples as positive or negative for lead exposure was significantly greater than the 5-min classification, but no improvement in accuracy was gained when samples were tested at 48 h. The false negative errors were probably due, at least in part, to the lag time between lead exposure and the increase of blood protoporphyrin concentrations. False negatives resulted in an underestimation of the true number of canvasbacks exposed to lead, indicating that hematofluorometry provides a conservative estimate of lead exposure.

Survival of female canvasbacks wintering in coastal Louisiana

Annual survival probabilities of female canvasbacks (Aythya valisineria) are lower than those of males, but sources and timing of mortality are poorly understood. To further elucidate causes of reduced annual survival in female canvasbacks, we estimated survival rates for radio-tagged females in coastal Louisiana during winters 1988-91. Survival estimates For winters 1988-91 were 0.946 ± 0.072 (estimate ± 95% CI) for adults (n = 82) and 0.952 ± 0.065 for immatures (n = 51). High survival by females wintering in coastal Louisiana suggests that sex- and age-related differences in canvasback survival occur during other periods of the annual cycle or at other wintering or staging sites

Short-term Effects of Burning and Disking on Songbird Use of Floodplain Conservation Easements

Abstract Extensive conversion of Midwestern riparian areas for agricultural production has had many consequences including reduced habitat for nesting birds. However, more than 120,000 ha of riparian habitat have been restored in this region through USDA conservation programs. In 2001 and 2002, we assessed songbird responses to burning and disking for management of conservation easements in east-central Iowa. We randomly assigned herbaceous riparian fields to burning and disking treatments and collected data on density and species richness of songbirds in these habitats. Total density of grassland and wetland species and red-winged blackbirds (Agelaius phoeniceus) were reduced by burning in the first and second breeding seasons after burning; common yellowthroat (Geothlypis trichas) density decreased with burning only in the first season. Disking led to increased density of grassland and wetland birds and greater overall avian conservation value on treated relative to untreated fields in the year after treatment. Changes associated with burning and disking treatments were likely related to changes in both vegetation structure and abundance of arthropod food resources. Despite decreased bird densities with burning, fire is a necessary management tool to control woody vegetation. Overall, both burning and disking appear to be effective management practices for maintaining herbaceous riparian habitats for grassland birds.