Trappings of Success: Predator Removal & Habitat Associations with Dabbling Duck Nest Survival in Alberta Parklands

• Author / Creator

  Blythe, Emily M

• In mallards and other upland-nesting duck species in the prairies, nest survival is the vital rate most influential to population dynamics, with 15% - 20% survival required for maintenance of stable populations. Nest survival is most limited by nest predation, which often is enhanced by anthropogenic causes including habitat fragmentation, mesopredator release, and predator subsidies. Predator removal during the nesting season has successfully increased duck nest survival on township-sized areas in agricultural ecosystems in the eastern portions of the prairie pothole region. However, predator removal has not been evaluated in western parkland habitats where three-dimensional habitat is considerably greater. During 2015 – 2017, we evaluated nest survival on control and predator-removal plots at two study areas in the central Alberta parklands. In the second year of the study, we transposed predator removal to control for habitat effects. Estimates of 34-day nest survival did not significantly differ between trapped (x̅ = 20.9%, 95% CI = 13.2% - 33.7%) and control (x̅ = 17.8%, 95% CI = 10.5% - 30.0%) plots in any year. Age of nest upon discovery was the most influential factor on, and had a weak positive association with, nest survival. In the final year of study, crows and ravens might have recognized investigator and nest-marking patterns, leading to exceptionally low nest survival in some plots. For one of our two study areas, the odds of nesting hen mortality were significantly higher on trapped plots (OR = 2.60, 95% CI = 1.03 – 6.58, n = 467), contrary to expectation. Predator removal may not have depressed nest predator populations sufficiently to improve nest survival, but potentially drove changes in predator community assemblage in favour of hen predators. In the Canadian prairie pothole region (PPR), waterfowl management often aims to increase the productivity of duck populations through the acquisition and stewardship of nesting habitat. Relating habitat characteristics to nest-site selection and nest predation risk can identify source and sink habitats, thereby informing management strategies for lands managed for duck production. We evaluated selection by comparing nest sites monitored in 2016 and 2017 with random locations, and evaluated habitat associations with nest survival by comparing sites of hatched and depredated nests. Based on the best model, hens nested selectively in relatively smaller patches of grassland (hay, pasture, and idle cover combined). Hens selected nest sites that were farther from aspen stands and characterized by taller vegetation that was more homogeneous in height. The best model for nest survival indicated that nests were more likely to hatch in relatively larger patches of grassland characterized by lower wetland edge-to-area ratios associated with large wetlands. Our findings indicate that smaller grassland patches are attractive sinks for upland duck nests, and do not provide evidence of adaptive habitat selection. We recommend that predator removal not be implemented in Alberta parklands due to its ineffectiveness at improving duck nest survival, and that future predator removal programs standardize and quantify removal effort. We recommend prioritization of relatively larger tracts of land for habitat acquisition and suggest management for hay rather than grazing is more effective for duck production in central Alberta parklands. Duck nest success is influenced by greater landscape composition and benefits from a greater proportion of grassland on the landscape, so we recommend greater use of easements and spring-seeded crops.

• Subjects / Keywords

  • Alberta parklands
  • mesopredators
  • nest success
  • predator management
  • corvid predation
  • Anas spp.
  • nesting hen survival

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-2wb0-m511

• License

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