Rodway M.S.,Wildwing Environmental Research |
Regehr H.M.,Wildwing Environmental Research |
Boyd W.S.,Environment Canada |
Iverson S.A.,Carleton University
Marine Ornithology | Year: 2015
In research on sea ducks, winter age and sex ratios provide valuable demographic data that are difficult to obtain by other means. Our objectives were to determine spatial, temporal, and density-related variability in (1) age and sex ratios for five sea duck species and (2) proportions of adult males for eight species that winter in the Strait of Georgia, British Columbia, Canada. Kilometre-long shoreline sections (n = 49–62) were surveyed in early February in three years: 2003, 2004, and 2014. Annual estimates for male age ratio (first year:adult male) varied significantly for Black Scoter Melanitta americana (0.071 to 0.170), Surf Scoter M. perspicillata (0.064 to 0.101) and Harlequin Duck Histrionicus histrionicus (0.068 to 0.138). Regional differences in male age ratio were found for Barrow’s Goldeneye Bucephala islandica (0.034 to 0.197) and Common Goldeneye B. clangula (0.033 to 0.165), and more complex interactions were found between regions by year for Surf Scoter. Sex ratios were less variable than age ratios and varied consistently by year and region only for Common Goldeneye. Adult male proportions were correlated with but varied more than sex ratios and showed significant differences by year for Surf Scoter, Common Goldeneye and Bufflehead B. albeola and by region for Surf Scoter, Common Goldeneye, Bufflehead and Red-breasted Merganser Mergus serrator. Based on previous research that calculated expected confidence limits from different numbers of occupied survey sections, the sampling intensity for each species obtained in this study provided age ratio estimates with 95% confidence limits likely within ± 5% for Surf Scoters and ± 3% for Harlequin Ducks. Regional and density-related differences in age ratios, sex ratios and adult male proportions indicated segregation and emphasize the need for broad-scale sampling to achieve representativeness. Inter-annual differences may indicate demographic changes, but few comparative data exist, and several consecutive years of surveys are needed to provide baseline data. © 2015, Marine Ornithology. All rights reserved.
Rodway M.S.,Wildwing Environmental Research |
Lemon M.J.F.,Environment Canada
Marine Ornithology | Year: 2011
We describe the use of permanent plots for monitoring population trends of burrow-nesting seabirds in British Columbia and test the assumption that trends in plot counts mirror trends in overall population size. A total of 97 plots for Ancient Murrelets Synthliboramphus antiquus, Cassin's Auklets Ptychoramphus aleuticus, Rhinoceros Auklets Cerorhinca monocerata, and Tufted Puffins Fratercula cirrhata were established in the 1980s. Plots were subjectively distributed in higher-density nesting areas of major colonies. Since then, numbers of Ancient Murrelet, Rhinoceros Auklet, and Tufted Puffin burrows increased or remained stable at monitored colonies, except on Pine Island, where burrows decreased for Rhinoceros Auklets. Declines were apparent for Cassin's Auklets, especially on Triangle Island, where numbers of burrows in plots declined 2.5% per year, resulting in a 40% decline in 20 years-a potential loss in that region of more than 20% of the estimated world breeding population. A serious threat to a majority of the world's Ancient Murrelet population from introduced predators was undetected by the permanent plot scheme because colonies with predators were not sampled. This highlights the need for a broad sampling of colonies and the importance of additional surveillance and study of breeding populations. Close agreement was found in the trend information provided by permanent monitoring plots and full-colony transect surveys. Both methods revealed significant differences when burrow numbers changed 3-4% annually. Results suggest that six to eight subjectively placed permanent plots reveal accurate trends in burrow numbers within a colony.
Hipfner J.M.,Environment Canada |
Lemon M.J.F.,Environment Canada |
Rodway M.S.,Wildwing Environmental Research
Bird Conservation International | Year: 2010
The Scott Islands, British Columbia, Canada, support the largest aggregation of breeding seabirds in the eastern Pacific Ocean south of Alaska. However, large seabird populations were eradicated by American Mink Neovison vison and Raccoons Procyon lotor introduced to Lanz and Cox islands in the 1930s, while the ecological consequences of the introduction of European Rabbits Oryctolagus cuniculus to Triangle Island in the 1920s are unknown. We have seen dramatic changes in the vegetation on Triangle Island in recent decades, chiefly a decrease in Tufted Hairgrass Deschampsia cespitosa cover and a concomitant increase in Salmonberry Rubus spectabilis cover. We carried out vegetation surveys at Triangle Island (1989 and 2004) and its nearest neighbour, rabbit-free Sartine Island (1987 and 2006), to test the hypothesis that rabbits have caused these changes. We found, however, that similar changes have occurred at Sartine Island as at Triangle Island over the same time period. Because these two islands support the bulk of the world's breeding population of Cassin's Auklet Ptychoramphus aleuticus, a small seabird that selects grass-covered habitat but avoids tall Salmonberry for nesting, the vegetation changes raise serious concerns for a species that has experienced dramatic population declines in recent years. Restoration of seabird nesting habitat by removing American Mink and Raccoons from Lanz and Cox islands will be vital for long-term seabird conservation in the Scott Islands. Copyright © BirdLife International 2010.
Rodway M.S.,Simon Fraser University |
Rodway M.S.,Wildwing Environmental Research
Waterbirds | Year: 2013
Previous theory to explain pairing behavior in waterfowl suggested that timing of pairing was constrained by costs to males of being paired and assumed that males incur most of the cost of defense after a pair bond is formed. An alternative hypothesis predicts that male and female partners will mutually defend their pair bond and that an individual will assume a greater share of defense when paired to a relatively high than low quality partner. Behavior of wintering Harlequin Duck (Histrionicus histrionicus) pairs was consistent with the latter hypothesis. Females and males shared equally in pair-bond defense in new pairs involving young females, while males assumed a greater share of defense when paired to an older female. Overall, males performed more aggressive displays in defense of the pair bond than females, but displays by females were more frequently of higher intensity than those of their mate. The relative share of pair-bond defense also varied between females and males depending on the target of the aggressive display. In some pairs, females performed virtually all defensive displays and bore the primary cost of pair-bond defense. Even when sex ratios are male-biased, differences in male quality probably make females willing to protect a pair bond with a high-quality male. Mutual mate choice and shared defense of a pair bond indicated that "pair-bond defense" would be a more appropriate label than "mate-defense" for the mating system of Harlequin Ducks and likely most monogamous avian species.
Regehr H.M.,Simon Fraser University |
Regehr H.M.,Wildwing Environmental Research
Waterbirds | Year: 2011
Population structure of Harlequin Ducks (Histrionicus histrionicus) wintering in the Strait of Georgia, British Columbia, was evaluated by generating age, sex, paired status and distance-specific movement rates with multi-stratum mark-recapture analyses, and age and sex-specific movement distances through surveys of marked individuals. Annual movement distances and rates did not differ by sex, but only 2-4% of adults (third year and afterthird year) compared to 7-11% of subadults (hatch year and second year) moved among locations per year and distance moved decreased with age. Adults were highly site faithful regardless of sex and paired status. The stepping stone gene flow model estimated the among population component of genetic variance (FST) at 0.005, suggesting that winter movement by subadults was sufficient to explain results of previous genetic analyses that detected no fine scale genetic structuring. Seasonal movement rates indicated that at least 95% of individuals molt and winter in the same location, and that annual aggregation at Pacific Herring (Clupea pallasi) spawning sites facilitates demographic mixing and gene flow. Low annual movement rates (0.001) between the northern and southern Strait of Georgia and dispersal by both sexes suggest that a metapopulation distribution may function within the Pacific Coast range, which is relevant to the geographic scale of management. Movement rates and distances suggest that subadult survival rates are particularly vulnerable to underestimation.