Tina Yerkes

Stable Isotopes (δD, δ13C, δ15N) Reveal Associations Among Geographic Location and Condition of Alaskan Northern Pintails

Abstract Information on spring migration routes, geographic linkages among winter, spring, and breeding locations, and potential geographic effects on arrival body condition of northern pintails (Anas acuta) are currently unknown. Through a combination of stable-isotope measurements of tissues representing different periods of dietary integration and body composition analyses, we examined these linkages for pintails breeding in Alaska, USA. We collected 77 females at 4 locations upon spring arrival. We performed carbon (δ13C), nitrogen (δ15N), and hydrogen (δD) isotope measurements on flight feathers, breast feathers, and whole blood, and we conducted body composition analyses. Inference based on stable-isotope values in pintail tissues suggests that philopatry to Alaska was strong, as most of the collected females had stable-isotope values consistent with the boreal forest of Canada or western Alaska and most spring migrating females had whole-blood values indicating use of a food web in the boreal forest before collection. These patterns highlight the importance of the boreal forest for production and staging of pintails. Breast feather isotope values grown during prealternate molt were variable and covered the currently documented distribution of wintering pintails. Our results indicate associations among specific geographic areas, habitat use, and arrival condition of female pintails settling in Alaska. Females that wintered or staged in coastal habitat (as indicated by elevated δ13C values) arrived with less body fat compared to those that we inferred to have wintered or staged on inland freshwater habitat. Those females we inferred to use coastal areas appeared to rely more heavily on agricultural fields for nutrient acquisition (as indicated by elevated δ15N but low δ13C values). Our results provide the first link between low-condition females and inferred use of specific geographic areas before arrival. Conservation on wintering grounds should focus on restoration and protection of wetland complexes that provide adequate natural food resources in proximity to coastal systems that are heavily used by wintering pintails. Conservation efforts should also focus on the boreal forest, not only for pintail, but for other boreal-dependent species such as lesser scaup (Aythya affinis)

Population Dynamics of Breeding Mallards in the Great Lakes States

Abstract Mallard (Anas platyrhynchos) populations in the United States portion of the Great Lakes region increased through the 1990s but have since declined. To promote sustainable growth of this population, managers need to understand how perturbation of vital rates will affect annual population growth rate (λ). We developed a stage-based model representing the female mallard population in the Great Lakes using vital rates generated from a landscape-level study documenting reproductive parameters from 2001 to 2003. We conducted perturbation analyses (i.e., sensitivity analyses) to identify vital rates that most influence λ and variance decomposition analyses to determine the proportion of variation in λ explained by variation in each vital rate. Perturbation analyses indicated that λ was most sensitive to changes in nonbreeding survival, duckling survival, and nest success. Therefore, changes in these vital rates would be expected to result in the greatest Δλ. Process variation in breeding season parameters accounted for 63% of variation in λ. Breeding season parameters explaining the most variation were duckling survival (32%) and nest success (16%). Survival of adult females outside the breeding season accounted for 36% of variation in λ. Harvest derivation, high harvest, and high sensitivity of λ to nonbreeding survival for Great Lakes female mallards suggests there is a strong potential for managing the Great Lakes mallard population via harvest management. Because λ was highly sensitive to changes in duckling survival, we suggest programs that emphasize wetland protection, enhancement, and restoration as a management strategy to improve population growth for breeding mallards.

MALLARD DUCKLING SURVIVAL IN THE GREAT LAKES REGION

Abstract Survival of young in waterfowl is poorly understood, particularly in regions outside of the traditional prairie breeding areas. Further, traditional methods of survival estimation lack the ability to statistically characterize between the extremes of random and catastrophic mortality events. We estimated Mallard (Anas platyrhynchos) duckling survival rates for 121 broods at nine study sites across the Great Lakes region from 2001–2003, using a novel statistical method that allows for the partitioning of random and correlated mortality processes. Results indicated that survival increased rapidly with age, did not change with hatching dates, did not differ among years, but varied across site-by-year replicates. Rates of random mortality were found to vary among site-years, while rates of correlated mortality varied little across site-years. In contrast to most studies of Mallard duckling survival, seasonal increases in duckling survival were not detected. We speculate that the observed patterns in survival rates with hatching date are related to productivity in Great Lakes brood-rearing wetlands and temperate regional climate.

Food Resources for Wintering and Spring Staging Black Ducks

Abstract A bioenergetic approach has been adopted as a planning tool to set habitat management objectives by several United States Fish and Wildlife Service North American Waterfowl Management Plan Joint Ventures. A bioenergetics model can be simplified into 2 major components, energetic demand and energetic supply. Our goal was to estimate habitat-specific food availability, information necessary for estimating energy supply for black ducks (Anas rubripes) wintering on Long Island, New York, USA. We collected both nektonic and benthic samples from 85 wetland sites dispersed among 5 habitat types (salt marsh, mud flat, submersed aquatic vegetation, brackish bay, and freshwater) commonly used by black ducks in proportion to expected use. Biomass varied among habitats (F4,5 > 7.46, P < 0.03) in 2004–2005, but there was only marginal variation in 2005–2006 (F3,4  =  5.75, P  =  0.06). Mud flats had the greatest biomass (1,204 kg/ha, SE  =  532), followed by submersed aquatic vegetation (61 kg/ha, SE  =  18), and salt marsh (34 kg/ha, SE  =  6). In the second year of the study, freshwater had the greatest biomass (306 kg/ha, SE  =  286), followed by mud flats (85 kg/ha, SE  =  63), and salt marsh (35 kg/ha, SE  =  4). Our results suggest food density on wintering grounds of black ducks on coastal Long Island is considerably lower than for dabbling ducks using inland freshwater habitats, indicating black duck populations are more likely than other species of dabbling ducks to be limited by winter habitat. We recommend targeting preservation, restoration, and enhancement efforts on salt marsh habitat.

Effects of Habitat on Mallard Duckling Survival in the Great Lakes Region

Abstract Habitat provides food and shelter resources for prefledgling waterfowl and thus plays a critical role in their growth, development, and survival. However, few studies have examined whether and how particular elements of habitat affect duckling survival. We investigated relationships of duckling survival rates with distance of overland travel, wetland vegetation composition, water permanency, and surrounding upland vegetation for 116 mallard (Anas platyrhynchos) broods in the Great Lakes region from 2001 to 2003. We found that the probability, on hatch day, that a mallard duckling will survive to 55 days was positively related to the proportion of wetland area that was vegetated and negatively related to the proportion of forest cover within 500 m of duckling locations. We found little support for relationships between duckling survival rates and the proportions of grasslands or seasonal wetlands or to distances traveled overland by broods. Our results suggest that conservation groups and wildlife managers in the Great Lakes region can improve mallard duckling survival rates by managing for, creating, and protecting vegetated wetlands and focusing efforts within lightly-forested areas.

Return rates and reproductive output of captive-reared female mallards

From 1993 to 1995, we evaluated the se of captive-reared, released female mallards (Anas platyrhynchos) to increase local breeding populations. A total of 146 females in 1992, 480 in 1993, and 1,140 in 1994 was released onto pothole habitat. Return rates for females released in 1992 and resighted in 1993 were 18-24%. Return rates for females released later were much lower, ranging from 2 to 10%. Released females homed to an average of 1.17 km (SE = 0.28, n = 28) from their original release site. Released birds had low direct recover rates, which suggests poor prefledging or premigratory survival. Comparisons of reproductive output of released females to wild conspecifics were limited by low return rates. Attempting to increase local breeding populations of mallards with released birds is not a viable management technique.

Occurrence of Second Broods in Mallards in the Midwest

Abstract Mallards (Anas platyrhynchos) typically hatch no more than one nest per year. Herein, we document two cases of re-nesting by radio-marked mallards after hatching a nest earlier in the breeding season in northern Ohio during 2001. One radio-marked female hatched 13 eggs during her first nesting attempt and, subsequently, lost her brood. She then initiated a second nest that was later depredated during incubation. A second radio-marked female hatched 11 eggs during her first nesting attempt and, after losing her brood, initiated a second nest, hatched 5 eggs and reared her second brood to fledging. Double brooding may be associated with age of the female (AFY), early nest initiation date, loss of initial brood and breeding season length.

Predicted Distribution and Characteristics of Wetlands Used by Mallard Pairs in Five Great Lakes States

ABSTRACT Understanding the relationship between wetland types and waterfowl distribution in the Great Lakes States of Wisconsin, Michigan, Illinois, Indiana and Ohio is complicated because basin specific waterfowl survey data do not exist. We used data from breeding waterfowl surveys in Michigan and Wisconsin during 1993 to 2002 and digital wetland data within buffered transect routes to develop a predictive model of mallard distribution within the 5 Great Lake States. The most parsimonious model based on AICc was used to map predictive distributions of breeding mallards. Based on the positive influence of palustrine emergent, palustrine unknown and palustrine unconsolidated shore and the negative influence of palustrine forested wetlands, the highest densities of breeding mallards were predicted in southeastern Wisconsin and southeastern Michigan. Additionally, we flew helicopter surveys in spring of 2003 to characterize wetland basins used by mallard pairs. Individual pairs were observed most often on small palustrine emergent and palustrine forested wetlands. The resulting models and maps can be used by a variety of agencies to plan conservation and management actions for mallards breeding in the Great Lakes States.