W. Sean Boyd

SURVIVAL, EMIGRATION, AND WINTER POPULATION STRUCTURE OF HARLEQUIN DUCKS

Abstract A population of individually marked Harlequin Ducks (Histrionicus histrionicus) at White Rock, British Columbia, Canada was examined to measure the degree of population differentiation among birds which pair during the winter months. This required an understanding of the patterns of emigration among wintering sites in different segments of the population. Some juveniles arrived at the wintering grounds accompanied by their mothers, thus initially arriving into the same winter population as their parents. Young males were more likely than young females to disperse during the first two years of life. Adult males had higher local survival than adult females during the summer months, probably because of the greater mortality risks to nesting females. During the nonbreeding seasons, local survival was the same in both sexes. Paired males had a local survival of more than 90%, suggesting both high survival and strong philopatry. Unpaired males had a lower local survival rate, suggesting they have higher mortality and/or emigration rates. Young females had the same local survival rate as adult females, suggesting that they did not disperse during the winter. These winter philopatry patterns are similar to the general pattern of breeding philopatry in waterfowl, with females showing stronger philopatry than males, and paired adults stronger philopatry than unpaired and young birds. The dispersal of young males makes local population differentiation unlikely in this species.

A COMPARISON OF THE CHARACTERISTICS AND FATE OF BARROW'S GOLDENEYE AND BUFFLEHEAD NESTS IN NEST BOXES AND NATURAL CAVITIES

Abstract Barrows Goldeneye (Bucephala islandica) and Bufflehead (B. albeola) are cavity-nesting waterfowl that have received considerable attention in studies using nest boxes, but little is known about their nesting ecology in natural cavities. We found larger clutch size, lower nesting success, and different major predators for Barrows Goldeneyes nesting in boxes versus those nesting in natural cavities, but few differences for Bufflehead. These differences are attributed to the location and physical differences between Barrows Goldeneye nest boxes and natural cavities that affect their conspicuousness to predators and conspecific nest-parasitizing females. Goldeneye boxes were concentrated in highly visible locations such as trees at water or forest edge. Natural cavity nests, on the other hand, were often abandoned Pileated Woodpecker (Dryocopus pileatus) cavities, which were more dispersed throughout the forest interior and concealed under dense canopy cover. Bufflehead natural cavity nests were typically closer to edges, which may account for their similarity with boxes. We conclude that in some respects, studies of Barrows Goldeneye that use nest boxes may not be representative of birds nesting in natural cavities, whereas those of Bufflehead are more likely to be so. Comparación de la Ecología de Nidificación de Bucephala islandica y B. albeola en Nidos Artificiales y en Cavidades Naturales Resumen. Los especies de patos Bucephala islandica y B. albeola anidan en cavidades, por lo que con frecuencia han sido estudiadas usando nidos articificales, pero poco se conoce sobre su ecología de nidificación en cavidades naturales. Los individuos de B. islandica que anidan en nidos artificiales presentaron nidadas más grandes, menor éxito reproductivo y distintos depredadores que los individuos que anidan en cavidades naturales, pero detectamos pocas diferencias para B. albeola. Estas diferencias son atribuidas a la ubicación y a las diferencias físicas entre los nidos artificiales y las cavidades naturales de B. islandica que afectan su visibilidad para deprededores y hembras coespecíficas que parasitan los nidos. Los nidos artificiales de B. islandica estuvieron concentrados en lugares muy visibles como árboles al borde del bosque o a la orilla del agua. Por el contrario, las cavidades naturales frecuentemente fueron cavidades abandonadas de Dryocopus pileatus, las cuales se presentaron más dispersas por el interior del bosque y ocultas bajo un dosel denso. Las cavidades naturales de B. albeola se ubicaron típicamente más cerca del borde, lo que tal vez explica la semejanza con los nidos artificiales. Concluimos que en algunos casos, los estudios de B. islandica que utilizan nidos artificiales pueden no ser representativos de individuos que anidan en cavidades naturales, mientras que los estudios de B. albeola probablemente sí sean más representativos.

Spacing patterns, mating systems, and winter philopatry in Harlequin Ducks

Abstract Many species of waterfowl form pair bonds during the nonbreeding season, yet current descriptions of mating systems and patterns of philopatry in waterfowl focus on the breeding grounds. We studied wintering Harlequin Ducks (Histrionicus histrionicus) in southwestern British Columbia to examine mating systems and philopatric behavior outside of the breeding season. The number of males at our study area was far more variable than that of females. Males that were unsuccessful in obtaining a mate were observed over a larger area than were paired males. Habitat use overlapped considerably among paired males, and no territorial boundaries were formed. Annual return rates to the nonbreeding grounds were high for both sexes (62% for females, 77% for males). Individuals not only returned to the general study area, but also to specific sections within the study area. Males that did not pair in the previous year returned to the study area in the subsequent year with the same frequency as males that had obtained mates; however, they tended to leave the study area prior to courtship. Therefore, it is possible that males return to the same wintering grounds each year to reunite with a previous mate. High levels of philopatry by both sexes allow pairs to reunite in fall, potentially increasing the benefits of philopatry for both sexes.

NOCTURNAL FORAGING BEHAVIOR OF WINTERING SURF SCOTERS AND WHITE-WINGED SCOTERS

Abstract We studied the nocturnal foraging behavior of Surf Scoters (Melanitta perspicillata) and White-winged Scoters (Melanitta fusca) during winter in coastal British Columbia, Canada. Using radio telemetry, we collected nocturnal and diurnal data documenting the frequency of foraging dives and the location of scoters in relation to their intertidal foraging grounds. We found that dive foraging rarely occurred during nocturnal periods for either species. Only 2% of nocturnal observation blocks for both scoter species contained diving, compared with 98% of diurnal observation blocks. This corresponded to an average of only 0.1 min spent underwater per half-hour observation block during the night and over 7 min during the day. Both species of scoters were located farther offshore and in deeper waters during nocturnal hours, indicating that they were not using intertidal foraging areas at night. Our results suggest that Surf Scoters and White-winged Scoters face daylight-imposed limits on the amount of available foraging time. These potential day-length restrictions should be considered when reviewing human activities that potentially alter the amount of available foraging time or food supplies in winter habitats. Comportamiento de Forrajeo Nocturno de Melanitta perspicillata y M. fusca Resumen. Se estudió el comportamiento de forrajeo nocturno de Melanitta perspicillata y M. fusca durante el invierno en la costa de British Columbia. Utilizando radio-telemetría, se colectaron datos nocturnos y diurnos sobre la frecuencia de buceos para alimentarse y la ubicación de las aves con relación a la zona intermareal. Se encontró que los buceos nocturnos son infrecuentes para ambas especies. Sólo en el 2% de las observaciones nocturnas de ambas especies se presentaron instancias de buceo, en comparación con el 98% de las observaciones diurnas. Esto corresponde a un promedio de 0.11 minutos bajo el agua por cada 30 minutos de observación durante la noche y más de 7 minutos durante el día. Ambas especies se ubicaron más alejadas de la costa y en aguas más profundas durante la noche, indicando que los individuos no utilizaron zonas intermareales durante este periodo. Estos resultados sugieren que M. perspicillata y M. fusca enfrentan restricciones en el número de horas disponibles para alimentarse en función de la cantidad de luz. El efecto de la duración del día debe ser considerado cuando se estudia el impacto de actividades humanas que pueden alterar el tiempo disponible para forrajeo o la cantidad de alimento durante el invierno.

Movements of wintering surf scoters: predator responses to different prey landscapes

The distribution of predators is widely recognized to be intimately linked to the distribution of their prey. Foraging theory suggests that predators will modify their behaviors, including movements, to optimize net energy intake when faced with variation in prey attributes or abundance. While many studies have documented changes in movement patterns of animals in response to temporal changes in food, very few have contrasted movements of a single predator species naturally occurring in dramatically different prey landscapes. We documented variation in the winter movements, foraging range size, site fidelity, and distribution patterns of a molluscivorous sea duck, the surf scoter (Melanitta perspicillata), in two areas of coastal British Columbia with very different shellfish prey features. Baynes Sound has extensive tidal flats with abundant clams, which are high-quality and temporally stable prey for scoters. Malaspina Inlet is a rocky fjord-like inlet where scoters consume mussels that are superabundant and easily accessible in some patches but are heavily depleted over the course of winter. We used radio telemetry to track surf scoter movements in both areas and found that in the clam habitats of Baynes Sound, surf scoters exhibited limited movement, small winter ranges, strong foraging site fidelity, and very consistent distribution patterns. By contrast, in mussel habitats in the Malaspina Inlet, surf scoters displayed more movement, larger ranges, little fidelity to specific foraging sites, and more variable distribution patterns. We conclude that features associated with the different prey types, particularly the higher depletion rates of mussels, strongly influenced seasonal space use patterns. These findings are consistent with foraging theory and confirm that predator behavior, specifically movements, is environmentally mediated.

Waterfowl-wetland relationships in the Aspen Parkland of British Columbia: comparison of analytical methods

We explored the relationships between aquatic bird abundance and various pond features (physical and chemical) using data from 112 ponds located in the Aspen Parkland of British Columbia. As expected, pond size was the most important factor influencing the number of aquatic birds present. Total dissolved nitrogen, conductivity and calcium were positively associated with the abundance of several species whereas chloride tended to be negatively associated. The abundance of dabbling ducks was positively associated with turbidity and total dissolved nitrogen and negatively with percent of forested shoreline, percent of marsh and chloride. The abundance of diving ducks was associated positively with pond depth, conductivity and total dissolved nitrogen and negatively with percent of marsh and phosphorus levels. Pond area influenced more the abundance of diving ducks than dabbling ducks. Relationships between bird density and pond features were affected significantly by the area unit used to calculate density. For example, the density of Bufflehead (Bucephala albeola) was correlated positively with pH and conductivity when expressed per area of water 0–2 m deep but negatively when expressed per total area of pond. Results highlight the problems associated with interpreting correlative type studies especially the difficulties in assessing the biological significance of the observed correlations. It underscores the urgent need for experimental approaches to bird-habitat studies.

Foraging Behavior of Surf Scoters (Melanitta Perspicillata)and White-Winged Scoters (M. Fusca) in Relation to Clam Density: Inferring Food Availability and Habitat Quality

Abstract Birds are known to modify their foraging behavior in relation to food availability. Once understood, these relationships can be used to draw inferences about relative food availability and habitat quality. We measured foraging behavior of Surf Scoters (Melanitta perspicillata) and White-winged Scoters (M. fusca) feeding on clams during winter in the Strait of Georgia, British Columbia, to evaluate the relative quality of the foraging landscape for wintering scoters. Because clam biomass does not increase appreciably during winter through growth or recruitment, scoters are faced with a depleting and potentially exhaustible food supply. Along with this temporal variation, clam densities vary widely by site. We considered the influence of variation in clam density on scoter foraging behavior, along with other factors known to affect foraging in other sea duck species, such as season, sex, age, and environmental attributes. Clam-capture success (clams captured per dive) and foraging effort (minutes underwater per hour) of Surf Scoters were not related to variation in clam density. Clam-capture success of White-winged Scoters was unrelated to clam density; however, their foraging effort was negatively related to clam density, though varying by only 4 min across the range of observed clam densities. For both species, foraging behavior was generally more strongly related to other factors, especially seasonal and age effects. These results suggest that (1) observed variation in clam density was relatively minor from the perspective of foraging scoters and (2) our study site constituted high-quality winter habitat in which scoters were not constrained by food availability. Comportamiento de Forrajeo de Melanitta perspicillata y M. fusca con Relación a la Densidad de Almejas: Inferencias sobre la Disponibilidad de Alimento y la Calidad del Hábitat

Habitat Use by Wintering Surf and White-Winged Scoters: Effects of Environmental Attributes and Shellfish Aquaculture

Abstract Shellfish aquaculture is an expanding industry in coastal British Columbia, Canada, and occurs in important wintering areas for surf scoters (Melanitta perspicillata) and white-winged scoters (M. fusca). We quantified habitat use by scoters in relation to natural environmental attributes and habitat modifications associated with shellfish aquaculture. We found that, despite the extensive clam and oyster farming in our study area, densities of wintering surf scoters and white-winged scoters were related primarily to natural environmental attributes, particularly intertidal area, clam density, and sediment type; shellfish aquaculture variables were generally poor predictors of bird densities. We conclude that current levels and forms of shellfish aquaculture in our study site were not an important determinant of scoter distribution and abundance, suggesting that winter scoter populations and the shellfish aquaculture industry may be mutually sustainable. We caution that intensification or further industrialization of shellfish aquaculture in British Columbia could eventually lead to detrimental effects if some threshold level of habitat modification is exceeded.

Plumage Characteristics as an Indicator of Age Class in the Surf Scoter

Abstract We assessed reliability of plumage as an indicator of age class in the Surf Scoter (Melanitta perspicillata) for demographic and behavioral studies. Three age classes were distinguished among male Surf Scoters, based on the degree of concordance between plumage characteristics and known age-related features (bursal depth and tail feather notching). Males in their first year (1Y) were distinguishable from older males (>1Y) with nearly total accuracy. Discriminating between second year (2Y) and after second year (>2Y) males had an error rate of 11%. Female Surf Scoters could not be reliably aged using plumage characteristics. Field observations suggested the timing of feather changes is an important variable affecting accurate age class determination. First year male Surf Scoter plumage is brown and female-like at the time of fledging, and gradually becomes more adult male-like during the first year. Observations of plumage changes throughout the annual cycle on wild birds suggested that females and 1Y males may be confused in early autumn, and that 1Y males and 2Y males may be misidentified during late spring and summer. Further, variation in timing and speed of pre- and post-breeding molt among 2Y and older males is uncertain. Therefore, mid-January until the end of March is the period when age class determinations based on plumage are most reliable.

Foraging behaviors of Surf Scoters and White-Winged Scoters during spawning of Pacific herring

Abstract ABSTRACT Winter diets of Surf (Melanitta perspicillata) and White-winged Scoters (M. fusca) are composed primarily of bivalves. During spawning of Pacific herring (Clupea pallasi) in early spring, scoters shift their diets to herring eggs. Using radio-telemetry, we contrasted scoter foraging behaviors between winter and herring spawning periods. Scoters increased their dive durations during herring spawning, likely to maximize the amount of roe consumed per dive; in winter, dives were typically terminated upon clam capture. Scoters spent approximately 50% less time foraging (min underwater hr−1) and decreased their dive rate (dives hr−1) by 70% when feeding on roe. The observed reduction in time spent foraging was presumably caused by the abundance of herring eggs, and thus a reduction in prey search-time. Scoters were able to meet energetic requirements with reduced effort, despite potentially increased demands related to spring fattening. Less time spent foraging may also allow more time for premigratory courtship behaviors.