Michael G. Brasher

Breeding-Season Survival of Male and Female Mallards in Canada's Prairie-Parklands

Abstract Despite greater harvest rates of males, mallard (Anas platyrhynchos) populations exhibit male-biased sex ratios, presumably because females experience greater mortality during breeding seasons than do males. Nest success and adult female survival during the breeding season greatly impact mallard population growth; however, no study has evaluated breeding-season survival of males and females simultaneously using radiotelemetry. We captured, radiomarked, and monitored 90 male and 272 female mallards during 2 breeding seasons in the Prairie-Parkland region of Canada (Manitoba 1998, Saskatchewan 1999). Model-averaged estimates of female breeding season (i.e., 15 Apr–14 Jul) survival probabilities were 0.84 (SE = 0.031) in 1998 and 0.71 (SE = 0.040) in 1999. Estimated survival probabilities of paired males were 0.99 (SE = 0.016) in 1998 and 0.98 (SE = 0.025) in 1999; survival estimates for unpaired males were 0.92 (SE = 0.052) in 1998 and 0.85 (SE = 0.083) in 1999. Female mortality was greatest during periods of intensive nesting, whereas limited male mortalities precluded identification of attributes linked to mortality. Our results suggest that breeding-season survival of males has little impact on mallard population growth, and that management efforts to increase female survival rates offer greater potential to enhance mallard production.

Evaluation of indicated breeding pair criteria to estimate mallard breeding populations

Indicated breeding pair (IBP) criteria have been used since the 1950s to estimate breeding duck populations, yet few studies have evaluated these criteria for accuracy of population estimation. During spring aerial and ground surveys, observed pairs of ducks, lone males, and groups of 2-4 males are enumerated as IBPs, and assumed to reflect breeding pairs. We radiomarked and observed 36 paired and 44 unpaired male mallards (Anas platyrhynchos) in Manitoba in 1998 and Saskatchewan in 1999 to document their sociability and evaluate accuracy of IBP criteria. Paired male mallards occurred with their mates ≥54% of the time, whereas unpaired males occurred as lone males and in groups of 2-4 males 80% of the time from 21 April to 30 May. Based on these data, we calculated that mallard breeding populations in our study areas may be overestimated by approximately 7%. Inflated population estimates could promote underestimated production indices, overestimated fall population indices, and overly liberal harvest regulations. We suggest development of correction factors or modified survey criteria to improve accuracy of breeding population estimates for mallards and other duck species.

A New Method to Predict Seed Yield of Moist-Soil Plants

Multiple linear regression can be used to predict seed yield of moist-soil plants; however, measurement of multiple predictor variables is tedious, subject to variation, and these models can exhibit multi-collinearity. Thus, we tested if simple linear regression models could predict seed yield of 5 species of moist-soil plants as precisely as multiple linear regression models. The single predictor variable was number of dots on a grid covered by seed. Simple regression models explained as much variation in seed mass (R 2 adj = 0.92-0.97) and predicted (R 2 pred = 0.91-0.96) as well as or better than multiple regression models. Precision of models was attributed to the strong positive linear relation between the dependent variable and the predictor, accurate dot counting, and lack of multicollinearity. Dot counting also was easier and more efficient than measuring multiple phytomorphological variables. This new method is useful for researchers and managers estimating seed yield of moist-soil plants; however, additional models should be developed for other plant species, and the method should be tested in other regions.

Reproductive effort and success of wild female mallards: does male quality matter?

In accordance with the differential allocation hypothesis, females are expected to increase their reproductive investment when mated to high-quality males. In waterfowl, reproductive, investment increased when captive female mallards (Anas platyrhynchos) were mated to more attractive males, but information for wild ducks is lacking. Studies of waterfowl mating systems have focused primarily on the importance of plumage coloration of males and female mate choice, whereas investigations of reproductive ecology examine female attributes and virtually ignore the role of males in investment decisions. Here, we used unique data for 253 pairs of wild mallards to test whether females mated to high-quality males would increase reproductive effort and reproduce more successfully. We derived measurements of female and male body size and condition, and indices of male plumage quality, and related these traits to patterns of reproductive effort and performance of females. Consistent with predictions, yearling females nested earlier and had higher nest survival when mated to males with better plumage scores. Furthermore, when paired with larger bodied males, yearling females renested more often, and nest and brood survival increased among older females. Although the strength of male effects varied with breeding stage and female age or experience, this is one of a few studies to demonstrate an additive effect of male quality on investment and success of females, in free-ranging birds.

Density of Lead and Nontoxic Shotshell Pellets in Gulf Coast Prairie Ricelands

Abstract Waterfowl ingest residual lead or nontoxic shotshell pellets while foraging for food in agricultural and other habitats. The Chenier Plain of Louisiana and Texas and the Texas Mid-Coast provide important habitats for wintering waterfowl, yet these regions are characterized by long traditions of waterfowl and other game-bird hunting, which potentially exposes waterfowl to historical lead pellets remaining in the environment. Recent evidence suggests that migrant and resident waterfowl within the Chenier Plain and Texas Mid-Coast regions continue to ingest lead pellets despite strict shotshell regulations. Thus, we randomly collected and radiographed soil cores (10-cm diameter and depth) from production and idled ricelands (n = 500 from each type) in the Chenier Plain (n = 760) and Texas Mid-Coast (n = 240) during November 2013 to estimate density of lead and nontoxic pellets in important waterfowl habitats of these regions. Across all regions and field types, we detected only one lead pellet and z...