Rodney W. Brook

Evidence for Black Duck Winter Distribution Change

Abstract The Mississippi Flyway midwinter population survey (MWS) indicates that American black ducks (Anas rubripes) have been rapidly declining for the last 10 years. We found a negative relationship between MWS and Ontario (Canada) midwinter counts for black ducks. Thus, as number of black ducks in the MWS decreased, Ontario midwinter counts increased. A shift in midwinter distribution of black ducks may be partly responsible for the decreasing trend in MWS counts. We recommend that midwinter black duck surveys be expanded to more sites in southern Canada and northeastern United States that currently are not sampled to better assess winter habitat use and improve the midwinter black-duck population index.

Effects of small mammal cycles on productivity of boreal ducks

Abstract North American boreal nesting waterfowl (and their eggs and ducklings) share a number of generalist predators with small mammals and non-migratory birds that could indirectly link fluctuations in these coexisting prey. We surveyed pairs and broods to determine an index of productivity for lesser scaup Aythya affinis breeding near Yellowknife, Northwest Territories, Canada. We also calculated a mallard Anas platyrhynchos productivity index for birds from northern Saskatchewan, Canada. Small mammal abundance was estimated by snap trapping rodents and by counting pellets of snowshoe hares Lepus americanus in the Yellowknife area. Because small mammal data were not available for the same area as mallard harvest survey data, correlation with an estimate of ruffed grouse Bonasa umbellus harvest was used because small mammal abundance and grouse are known to correlate positively. We found a positive correlation between the abundance of rodents and lesser scaup productivity suggesting a prey switching relationship for predators between their main prey (rodents) and alternative prey (lesser scaup, eggs and ducklings). A negative correlation between snowshoe hare abundance and lesser scaup productivity was also found as well as a negative correlation between ruffed grouse abundance and mallard productivity. Negative correlations suggest a possible shared predation relationship, where changes in main prey abundance (hares) may cause a numerical response in predators that influences predation rates of shared alternative prey (ducks, eggs and ducklings). Although our conclusions are based on correlations, they indicate that a great deal of variation in boreal duck productivity might be explained by the indirect effects of coexisting prey abundance. Further work is needed to determine causal mechanisms contributing to these relationships, the effect of cycles in small mammal populations and the overall importance of top-down predator regulation for regulating duck productivity in boreal forest.

Retention and effects of nasal markers and subcutaneously implanted radio transmitters on breeding female Lesser Scaup

Abstract Forty-seven wild female Lesser Scaup (Aythya affinis) were marked with nasal markers and radio transmitters (implanted subcutaneously on the back) just prior to breeding near Yellowknife, Northwest Territories, in 1999 and 2000. Retention rates of both marker types were evaluated, and their effects on specific behavior categories were assessed by comparison of marked birds with unmarked control birds. Significant effects of nasal markers on behavior were detected; females often removed vegetation from nasal markers after diving, and consequently marked females tended to shake their head more frequently than unmarked birds. No nasal markers were lost during the study. Five females lost radios, producing an average retention time of 39 d. Daily retention rate was 0.997, being 0.85 when extrapolated to 60 d. The survival rate of 42 females radio-tracked consistently was constant for six 7-d intervals, suggesting no immediate adverse effect on survival. Because the technique is invasive, use of subcutaneous transmitters may not be appropriate for all applications, but it could be a preferred alternative to other transmitter-attachment methods for short-term tracking of waterfowl.

Patterns of Wetland Use by Brood-rearing Lesser Scaup in Northern Boreal Forest of Canada

Abstract Little is known about wetland selection by Lesser Scaup (Aythya affinis) during any phase of the breeding cycle, particularly in the northern boreal forest region, where most of the North American population of scaup breeds. We used survey data (1989-98) for 402 wetlands near Yellowknife, Northwest Territories, Canada to assess frequency of scaup brood occurrence. In 1999, features of 80 randomly selected wetlands (21 used and 59 not used by scaup broods) and 27 wetlands used repeatedly by brood-rearing scaup were evaluated (N = 107 total). Discriminant function analysis using all wetland measurements was used to classify scaup use of 77 randomly selected wetlands; classification criteria were subsequently used to predict brood use of the remaining 30 hold-out wetlands. This randomization procedure was repeated 100 times, producing an average classification success of 88% (95% CI = 77% to 97%). Broods occurred more often on larger, deeper wetlands with water lilies and amphipod crustaceans, the latter being an important food for adults and ducklings. Wetlands created during road construction were used less often, possibly because these tended to be smaller, shallow, less likely to have amphipods, and had a different vegetation regime than natural wetlands.

Risk of Agricultural Practices and Habitat Change to Farmland Birds

Many common bird species have declined as a result of agricultural intensification and this could be mitigated by organic farming. We paired sites for habitat and geographical location on organic and nonorganic farms in Ontario, Canada to test a priori predictions of effects on birds overall, 9 guilds and 22 species in relation to candidate models for farming practices (13 variables), local habitat features (12 variables), or habitat features that influence susceptibility to predation. We found that: (1) Overall bird abundance, but not richness, was significantly (p < 0.05) higher on organic sites (mean 43.1 individuals per site) than nonorganic sites (35.8 individuals per site). Significantly more species of birds were observed for five guilds, including primary grassland birds, on organic vs. nonorganic sites. No guild had higher richness or abundance on nonorganic farms; (2) Farming practice models were the best (∆AIC < 4) for abundance of birds overall, primary grassland bird richness, sallier aerial insectivore richness and abundance, and abundance of ground nesters; (3) Habitat models were the best for overall richness, Neotropical migrant abundance, richness and abundance of Ontario-USA-Mexico (short-distance) migrants and resident richness; (4) Predation models were the best for richness of secondary grassland birds and ground feeders; (5) A combination of variables from the model types were best for richness or abundance overall, 13 of 18 guilds (richness and abundance) and 16 of 22 species analyzed. Five of 10 farming practice variables (including herbicide use, organic farm type) and 9 of 13 habitat variables (including hedgerow length, proportion of hay) were significant in best models. Risk modeling indicated that herbicide use could decrease primary grassland birds by one species (35% decline from 3.4 to 2.3 species) per site. Organic farming could benefit species of conservation concern by 49% (an increase from 7.6 to 11.4 grassland birds). An addition of 63 m of hedgerow could increase abundance and richness of short distance migrants by 50% (3.0 to 4.8 and 1.3 to 2.0, respectively). Increasing the proportion of hay on nonorganic farms to 50% could increase abundance of primary grassland bird by 40% (6.7 to 9.4). Our results provide support for alternative farmland designs and agricultural management systems that could enhance select bird species in farmland. RESUME. De nombreuses especes d’oiseaux ont decline en raison de l’intensification des pratiques agricoles, mais ces declins pourraient etre attenues grâce a l’agriculture biologique. Nous avons apparie des sites (habitat et situation geographique) sur des fermes biologiques et des fermes non biologiques en Ontario, Canada, afin de tester des previsions a priori d’effets sur l’avifaune dans son ensemble, 9 guildes et 22 especes d’oiseaux, en relation avec des modeles candidats testant les pratiques agricoles (13 variables), les caracteristiques locales de l’habitat (12 variables) ou les caracteristiques de l’habitat qui influencent le risque de predation. Nous avons trouve que : 1) l’abondance totale d’oiseaux, mais pas la richesse, etait significativement plus elevee (p < 0,05) aux sites biologiques (moyenne de 43,1 individus par site) qu’aux Aquila Conservation & Environment Consulting, Environment Canada, Ontario Ministry of Natural Resources Avian Conservation and Ecology 6(1): 5 http://www.ace-eco.org/vol6/iss1/art5/ sites non biologiques (moyenne de 35,8 individus par site). Un nombre significativement plus eleve d’especes d’oiseaux ont ete observees chez cinq guildes, dont celle des oiseaux specialistes des prairies, aux sites biologiques. Aucune guilde n’a presente une plus grande richesse ou abondance sur les fermes non biologiques; 2) les modeles prenant en compte les pratiques agricoles etaient les meilleurs (∆AIC < 4) pour prevoir l’abondance totale d’oiseaux, la richesse des oiseaux specialistes des prairies, la richesse et l’abondance des insectivores aeriens qui chassent a l’affut et l’abondance des oiseaux nichant au sol; 3) les modeles prenant en compte l’habitat etaient les meilleurs pour prevoir la richesse dans l’ensemble, l’abondance des migrateurs neotropicaux, la richesse et l’abondance des migrateurs de courte distance (Ontario-E.-U.-Mexique) et la richesse des residents; 4) les modeles prenant en compte la predation etaient les meilleurs pour prevoir la richesse des oiseaux generalistes des prairies et des oiseaux se nourrissant au sol; 5) une combinaison de variables issues des modeles-types representait la meilleure option pour prevoir la richesse ou l’abondance dans leur ensemble, chez 13 des 18 guildes (richesse et abondance) et 16 des 22 guildes examinees. Cinq des dix variables decrivant les pratiques agricoles (y compris l’utilisation d’herbicides et le type de fermes biologiques) et 9 des 13 variables touchant l’habitat (y compris la longueur des haies et la proportion de foin) etaient significatives dans les meilleurs modeles. La modelisation du risque a indique que l’utilisation d’herbicides pouvait toucher les oiseaux specialistes des prairies, a raison d’une espece (declin de 35 %, de 3,4 a 2,3 especes) par site. L’agriculture biologique pourrait favoriser les especes dont la conservation est preoccupante, jusqu’a 49 % (augmentation de 7,6 a 11,4 oiseaux de prairie). Un ajout de 63 m de haie permettrait d’augmenter l’abondance et la richesse des migrateurs de courte distance de 50 % (de 3,0 a 4,8 et de 1,3 a 2,0, respectivement). Une hausse de 50 % de la proportion de foin sur les fermes non biologiques permettrait d’augmenter de 40 % l’abondance des oiseaux specialistes des prairies (de 6,7 a 9,4). D’apres nos resultats, une attention particuliere portee a la configuration des fermes et a la gestion agricole permettrait d’ameliorer le sort d’especes d’oiseaux selectionnees dans les paysages agricoles.

Fine-Scale Analysis Reveals Cryptic Patterns of Genetic Structure in Canada Geese

Abstract. In migratory birds, population-genetic structure is generally low, but philopatric species can have fine-scale patterns of differentiation. We investigated the population-genetic structure of the Canada Goose (Branta canadensis) across multiple spatial scales to determine whether genetic data support current delineations of subspecies and populations for management. We collected samples from two subspecies (B. c. interior and B. c.maxima) and four management populations across Ontario and Quebec. Using 7 microsatellites and 442 base pairs of mtDNA we found that genetic structure varied with scale. FST revealed low levels of genetic differentiation between subspecies and management populations, and individual-based clustering revealed no genetic differentiation. However, fine-scale spatial autocorrelation revealed significant levels of relatedness at distances <85 km. The lack of clear genetic structure may reflect recent human management. That our fine-scale analysis revealed significant genetic relationships suggests that genetic structure may increase and in time reflect that revealed by banding data. As our markers were unable to accurately distinguish between subspecies they will be of little use in estimating subspecific contribution to harvested stock. Alternative molecular markers under selective pressure may be more informative in assess targets for harvest.

Changes in Annual Survival Estimates for Black Brant from the Western Canadian Arctic, 1962-2001

Abstract Numbers of Black Brant (Branta bernicla nigricans) have declined dramatically in at least one important breeding area in the Western Canadian Arctic (WCA) and the regional population is small and widely scattered. The overall Pacific Flyway Population, to which the WCA Brant belong, has declined historically as well, probably in part due to high rates of harvest and low rates of survival during the 1960s and 1970s. To better understand how changes in survival rates may have influenced WCA Brant, band recoveries and recaptures were used to estimate historical (1962-67 and 1975-79), and more recent (1991-2001) survival rates. On the mainland WCA, adult survival rates (derived from band recoveries) averaged 0.719 ± SE 0.045 and 0.693 ± 0.082 in the 1960s and 1970s, respectively but increased significantly (P < 0.05) to 0.884 ± 0.052 (based on band recoveries of both sexes) or 0.886 ± 0.025 (based on recaptured females) during 1991-2001. Comparable survival rates for juvenile Brant, derived from band recoveries only, were 0.216 ± 0.051, 0.460 ± 0.112, and 0.694 ± 0.205, and increased significantly over time. On Banks Island, located 250 km northeast of our mainland study site, adult survival rates averaged 0.945 ± 0.037 during 1992-94. The harvest of Pacific Flyway Brant has declined substantially since the 1960s which possibly explains much of the observed increase in survival estimates in WCA Brant. The most recent survival estimates for WCA Brant are as high as, or higher than, those for other areas in arctic North America or Eurasia. Managing harvest to maintain current levels of survival, and maintaining or increasing current levels of productivity (known to have declined in at least one important breeding area) may be required to maintain WCA Brant at present population levels.

Assessing Seasonal Variation in Counts and Movements of Bonaparte’s Gulls Larus philadelphia on the Niagara River, Ontario

Abstract We assessed potential factors contributing to variation in counts of staging Bonaparte’s Gulls (Larus philadelphia) on the Niagara River in southern Ontario. Much of the Mississippi Flyway population of this species stages each autumn at this site, en route to the Gulf coast and Mexico. Between 1986-96, weekly or bi-weekly counts were made of gulls flying to their nocturnal roost at the mouth of the Niagara River entering Lake Ontario, to assess the seasonal and temporal patterns of movement. Counts began each year in early October, corresponding to the ‘second wave’ of gulls. Generally, this second wave of autumn movements began in early October to late November (median 1 November) and continued until late January or mid-February (median 5 February). Model selection based on a repeated measures analysis (Generalized Estimating Equations) demonstrated a quadratic relationship between counts and time of year and a linear relationship with daily count duration. Less evidence existed for the role of mean daily temperature in explaining variation (positive relationship) in counts; more data, or inclusion of different weather variables (e.g., wind, cloud cover), may demonstrate that it is more important than our models suggest. Maximum counts were from early November to late January (median 6 December). Peak daily totals per season varied between 6,300 (1993/94) and 40,000 (1990/91). Migration counts may be useful to help monitor populations of this species, provided that variables affecting seasonality in counts are accounted for and the turnover rate of individual gulls staging in the area is determined (e.g., through mark-recapture or radio-telemetry studies).