Variation in mallard vital rates in Canadian Aspen Parklands: The Prairie Habitat Joint Venture assessment

Abstract

The Prairie Habitat Joint Venture (PHJV) delivers conservation programs for the Canadian portion of the Prairie Pothole Region under the North American Waterfowl Management Plan. The PHJV Assessment was designed to evaluate biological assumptions and effectiveness of PHJV conservation activities. Our objectives were to 1) test whether waterfowl reproductive success increased in response to the full suite of PHJV habitat treatments, and 2) quantify the relationships between mallard (Anas platyrhynchos) vital rates and landscape variables. We focused on examining the association of mallard vital rates with covariates measured at the study‐area scale. We collected information on vital rates from 3,214 radio‐marked female mallards at 27 study areas mainly throughout the Aspen Parkland ecoregion of Manitoba, Saskatchewan, and Alberta in 1993–2000. We used a modeling framework and information‐theoretic techniques to test hypotheses about putative effects of environmental covariates on adult female and duckling survival, nesting effort, and nest survival. Additionally, we constructed a stage‐based matrix projection model of mallard population growth (λ) to estimate the sensitivities of population growth rates to variation in vital rates. Nest survival was positively related to the amount of herbaceous vegetation on study areas and total precipitation for the 12 months prior to nesting. Nesting effort was positively related to wetland inundation in July. Duckling survival was positively related to the proportion of seasonal wetlands holding water in July and negatively related to the number of days in June and July when the minimum air temperature dropped below 10° C. Adult female survival rate was positively related to both the proportions of grassland and wetland habitats measured at the study‐area scale (65 km2), though these factors interacted such that the positive relationship with proportion of wetlands was strongest on study sites with high proportions of grassland. The stage‐based projection model constructed using mean vital rates indicated that populations were declining (mean λ = 0.95, median λ = 0.98, 5th percentile = 0.68, 95th percentile = 1.38). Variance‐stabilized sensitivities indicated that population growth was most responsive to variation in vital rates for after‐second‐year birds and that nest survival was the single vital rate to which populations were most sensitive. A prospective simulation revealed that, as expected, sensitivity to nest survival is likely to decrease at higher levels of nest survival. Despite evidence that nest survival was higher in PHJV habitat treatments than surrounding habitats, our a priori PHJV treatment index was unrelated to mallard vital rates estimated at the 65‐km2 scale. Although mallard populations were affected by several weather variables and land uses, efforts to increase populations should focus on improving nest survival rates, which currently are below approximately 30%. © 2014 The Wildlife Society.

Banding age ratios reveal prairie waterfowl fecundity is affected by climate, density dependence and predator–prey dynamics

“…We suspect that spatial patterns of population declines as well as higher fecundity exhibited by gadwalls, mallards and pintails at more southwestern sites and by teal at more southern sites reflects the earlier pursuit and greater effectiveness of upland and wetland conservation programmes in the United States (Reynolds, Shaffer, Renner, Newton, & Batt, ) and the lower rates of upland conversion in the west (Wright & Wimberly, ). This pattern is corroborated by recent investigations of nest success in parkland Canada (Howerter et al., ) and the western U.S. prairies (Stephens et al., ). Efforts should be taken to protect wetlands that are inconsistently flooded and most vulnerable to agricultural conversion, because of the positive benefits to fecundity when these wetlands reflood.…”

“…However, if this were the case we would have expected a negative effect of previous‐year prey abundance ( BPL1 , SOL1 ) on fecundity, but this effect was only observed in teal. Although within‐season precipitation and evapotranspiration, as indexed by PDSI , was a poor predictor of fecundity, local effects of precipitation or temperature on fecundity, such as decreased brood survival during rain events (Howerter et al., ; Krapu, Pietz, Brandt, & Cox, ), are likely dampened by the broad spatial and temporal scale of this metric (Zhao, Boomer, & Kendall, ).…”

“…Spring wetland inundation drives increases in invertebrate richness (Szalay et al., ), which are hypothesized to improve fecundity through higher clutch size, renesting propensity and duckling survival (Arnold, Devries, & Howerter, ; Cox et al., ; Krapu, Reynolds, Sargeant, & Renner, ). Low summer precipitation and excessive evapotranspiration can lead to loss of flooded wetland habitat, in turn reducing renesting propensity and brood survival (Howerter et al., ). In addition to wetland conditions, density‐dependent effects on fecundity have been identified in North American dabbling ducks at continental scales, although the ecological mechanism remains obscure (Gunnarsson et al., ).…”

Population dynamics of mallards breeding in eastern Washington

“…Our overall survival rate of adult female mallards during the breeding season (0.895) was higher than estimates from the Prairie Pothole Region (0.65–0.87; Devries et al , Brasher et al , Arnold et al , Howerter et al ); Southern Ontario (0.65–0.84; Hoekman et al a ); Great Lakes Region (0.74; Coluccy et al ); New Brunswick, Canada (0.80; Petrie et al ); and northeast California (0.59; Mauser et al ). On the prairies, female mortality is highest during incubation when females are exposed to a range of terrestrial predators and breeding season survival is most influential on annual survival (Arnold et al ).…”

“…Robust modeling requires accurate estimates of key population metrics (e.g., nest success, female survival, brood survival) and an approach that allows for modeling the tradeoffs among such estimates simultaneously (Nicolai et al 2014). The mallard is among the most well-studied birds in North America (Drilling et al 2002) and many studies have estimated vital rates for breeding mallards (Simpson et al 2005, Devries et al 2008, Arnold et al 2012, Howerter et al 2014. Results of these studies indicate that vital rates and the relative importance of each metric to mallard population growth can vary among regions of North America (Hoekman et al 2002(Hoekman et al , 2006bColuccy et al 2008).…”