Robert B. Emery

Effects of transmitters on reproduction and survival of wild mallards

Radiotelemetry is an important tool in many studies of waterfowl ecology and management, but some studies have indicated that harnessed-radiopackages affected the behavior and survival of marked birds. Transmitters attached mid-dorsally with sutures, glue, and a subcutaneous, stainless steel anchor-shaped wire (hereafter anchored backpacks) may eliminate such problems. Therefore, we compared various measures of reproduction and survival rates of wild mallards (Anas platyrhynchos) radiomarked with abdominal implants and anchored backpacks at 5 study sites located in the aspen-parkland biome of the Prairie Pothole Region of Canada. We also compared our tracking ability between abdominal implants and anchored backpacks and determined retention time of anchored backpacks. Females with anchored backpacks devoted significantly fewer days to egg laying and incubation and initiated fewer nests than did females with implants. At one site, females with backpacks had significantly lower survival rates than females with implants. At 3 of the remaining 4 sites, females with anchored backpacks had lower survival rates than females with implants, but these results were not significant. We detected no difference in our tracking ability between anchored backpacks and abdominal implants (63 of 136 [46%] with anchored backpacks, and 140 of 319 [43%] with implants were monitored successfully from the time they were trapped to 30 June at each site). Two anchored backpacks were known to have fallen off and 11 were suspected to have fallen off, out of 198 backpacks (average retention time for anchored backpacks was 43 ± 5.8 days for those that lost their transmitter). Our results suggest that anchored backpacks may have negatively affected reproduction and survival rates of wild mallards.

Waterfowl Use of Dense Nesting Cover in the Canadian Parklands

Abstract Dense nesting cover (DNC) has been a conspicuous component of habitat management for upland-nesting ducks for >30 years, but its benefits for nesting ducks have been contentious. During 1994–1999 we monitored 3,058 dabbling duck (Anas spp.) nests in 84 DNC fields located throughout the Canadian Parklands to examine sources of among-field variation in nest density and nesting success. Nest density averaged 1.51 (SE = 0.15) nests/ha and overall nesting success was 20.4%, but there was pronounced annual variation in both estimates. Nesting success increased with increasing field size (range = 6–111 ha), but nest density remained constant. Nest density increased with percent wetland habitat within DNC fields and declined with percent perennial cover in the surrounding 2.4 × 2.4-km landscape, but these variables were not important for predicting nesting success. Nest abundance and nesting success roughly doubled in fields seeded with alfalfa (Medicago sativa) or sweet clovers (Melilotus spp.), but there was no benefit from using native as opposed to tame grasses. We recommend that waterfowl managers in the Canadian Parklands establish DNC with alfalfa in large fields in landscapes with abundant wetlands but minimal competing cover.

Probability of Survival and Breeding for Juvenile Female Canvasbacks

Few studies have examined factors affecting the probability of recruitment into breeding populations by juvenile ducks. We were able to do this for juvenile female canvasbacks (Aythya valisineria) at Minnedosa, Manitoba, Canada, 1983-1988 by combining estimates of duckling survival, annual survival, and breeding probability. Annual survival probability increased with duckling weight, declined with advancing hatch date, and was lower in years with more liberal than conservative harvest regulations. Breeding probability was lower during years with relatively dry wetland conditions than years with wetter conditions, and it also declined with advancing hatch date. Estimates of breeding probability ranged from 0.54 to 0.94 for juveniles and 0.74 to 0.95 for adults. Recruitment probability for juveniles ranged from 0.12 to 0.28 at the mean of the covariates (body mass and hatch date) and from <0.01 to 0.43 at the extremes. More than 54% of the recruits were ducklings produced in nests that hatched early. The per-capita contribution of recruits by hens that hatch nests early may be even more disproportionate because clutch size and nest success generally decline with advanced laying date. Managers should recognize that late, dry breeding seasons will likely result in poor recruitment of hatched ducklings. Where possible, habitat management should facilitate early nesting by canvasbacks.

Survival and Philopatry of Female Redheads Breeding in Southwestern Manitoba

Understanding the relationships between survival and philopatry of adult and juvenile waterfowl is fundamental information for developing effective management programs. We used combined recovery-resighting models to estimate band-reporting (r), fidelity (F), survival (S), and resighting (p) probabilities of female redheads (Aythya americana) breeding in southwestern Manitoba, Canada, during 1983-1993. We banded and nasal-marked 194 hatch-year (HY) females during 1983-1988 and 149 after-hatch-year (AHY) females during 1984-1990 and subsequently obtained 298 resightings and 26 band recoveries during 1984-1993. Recovery data were sparse, and band-reporting rates were best modeled as a constant (r= 0.082, 95% CI: 0.055 to 0.121). Breeding-site fidelity (F = 1 - permanent emigration) averaged 0.899 (95% CI: 0.703 to 0.971) across age classes, or 0.744 (95% CI: 0.287 to 0.955) and 0.923 (95% CI: 0.665 to 0.986) for models that treated HY and AHY females as different. Annual survival rates varied by age, averaging 0.417 (95% CI: 0.311 to 0.532) for HY females and 0.722 (95% CI: 0.610 to 0.812) for AHY females in a model with constant F, or 0.487 (95% CI: 0.273 to 0.705) and 0.708 (95% CI: 0.597 to 0.799), respectively, in models with age-specific estimates of F. Resighting estimates varied by age and year, averaging 0.513 (95% CI: 0.263 to 0.764) for HY females returning as yearlings and 0.724 (95% CI: 0.604 to 0.843) for AHY females. We suspect that lower resighting rates by HY versus AHY females were the result of greater temporary emigration by HY females (i.e., lower breeding propensity), and that some among-year variation in resighting rates was also caused by temporary emigration (i.e., drought avoidance). Our data demonstrate that temporary and permanent emigration are important processes affecting local redhead populations, and that failure to model these processes can lead to biased estimates of survival, especially among HY females.

Survival and Movements of Canvasback Ducklings

Because canvasback (Aythya valisineria) breeding areas have been reduced by wetland drainage and because density-dependent factors that limit survival of ducklings are poorly understood, we studied brood and duckling survival during 1983-90 and overland brood movements during 1988-89 on 2 study blocks (15.8 km 2 each) near Minnedosa, Manitoba. One block was designated as the experimental area where canvasback duckling production was experimentally enhanced, whereas the other block was an unmanipulated control. Individually marked female canvasbacks with ducklings were monitored to test the effects of canvasback brood density, presence of parasitic redhead (A. americana) ducklings, hatching date, and pond water levels on canvasback duckling survival. We observed no between-block differences in mean daily survival rates of canvasback ducklings during 1983-86. The experimental high-density area had higher (P < 0.05) duckling survival probabilities during 1987-88. Duckling survival was significantly related (P = 0.033) to duckling density but not (P = 0.56) June wetland water levels. Duckling survival probabilities were highly variable among years (range = 0.027 ± 0.007 [SE] to 0.623 ± 0.004 [SE]); survival rates in 1989-90 during severe drought were much lower than in previous years. We observed no consistent effect of hatching date on duckling survival among years. On the experimental study block in 1988, canvasback ducklings in broods containing parasitic redhead ducklings had lower (P = 0.013) survival during the first 7 days of life. Canvasback broods were observed on an average of 4 different ponds and traveled an average total overland distance of 1.5 km with no between-block differences. Density-dependent mortality of ducklings was not a factor in limiting recruitment of canvasbacks in the Minnedosa area.

CONTINUOUS LAYING AND CLUTCH-SIZE LIMITATION IN MALLARDS

Abstract We assessed nutritional constraints on clutch size in Mallards (Anas platyrhynchos) by observing incidence and consequences of continuous laying—the sequential production of eggs in two or more nest bowls. Continuous laying behavior was detected in 278 of 3,064 radiotracked Mallards (9.1%). Continuous laying females produced an average of 12.12 total eggs (SD = 2.70, range 5–18, n = 69), versus 8.90 eggs for normal nesting females (SD = 1.67, range 4–14, n = 587). On average, continuous laying females were 25 g heavier than noncontinuous laying females, and body mass was positively correlated with egg production among continuous laying females. Nest success was not affected by continuous laying, but continuous laying females that abandoned their nests were more likely to be young or to have laid a greater number of eggs. A large component of the breeding Mallard population can lay more eggs than they typically do, and there appear to be minimal consequences of that behavior. These observations appear inconsistent with the egg-formation hypothesis.

Social Indices of Breeding Productivity in Parkland Mallards

Abstract Social indices were developed to assess breeding productivity of waterfowl based on weekly roadside surveys of social groupings (i.e., pairs, lone M, flocked M). We calculated social indices for mallard (Anas platyrhynchos) populations breeding on 16 study sites in the Canadian parklands from 1993 to 1998 using 7 previously developed indices. We also calculated duckling:pair ratios from our roadside counts, and we obtained independent measures of nesting effort, nesting success, female success, and fledging rate for these same 16 sites from a concurrent telemetry study. Social indices were correlated (r2 = 0.28–0.67) with telemetry-based measures of breeding productivity in 5 of 7 cases, with the strongest relationships deriving from indices that emphasized renesting effort. The 2 ineffective social indices (r2 ≤ 0.13) both measured early onset of nesting activity. Duckling:pair ratios could be calculated more easily from the same survey data and also were correlated (r2 = 0.26–0.48) with measures of breeding productivity. Because surveys measuring late-nesting effort also can enumerate early hatched ducklings, we recommend that waterfowl researchers use duckling:pair ratios rather than social indices because ducking:pair ratios are more easily interpretable. Development of sightability-adjustment factors for pair and duckling surveys could further enhance the utility of duckling:pair ratios as indices of breeding productivity in mallards.