R. Ian Goudie

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.

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.

Winter Age Ratios and the Assessment of Recruitment of Harlequin Ducks

-Recruitment is the process by which young birds are added to the breeding population. The two most commonly used methods to estimate recruitment in ducks are pair/brood counts, and fall age ratios based on wings returned by hunters. Direct counts on the wintering area to determine the proportion of young males to adult males (age ratios), can be used for species with delayed plumage maturation. This is useful for species that are difficult to study on the breeding grounds and are seldom hunted, such as Harlequin Ducks (Histrionicus histrionicus). Such an approach is only valid if age classes are equally sampled. Between 1994 and 1999, the proportion of male Harlequin Ducks that were immatures in the Strait of Georgia, British Columbia, was estimated at 0.068. The proportions differed across years. Little difference occurred through the winter months until spring, when there was a significant increase in proportions in March. If these age ratios are accurate, then recruitment would not be compensating for annual adult mortality and the population could have been declining during the period of our study. However, if immature males are not distributed evenly among the population, then our assessment may underestimate or overestimate proportions. Delayed breeding means that immature birds experience several additional seasons of mortality prior to breeding, and thus the actual recruitment rate into the breeding population would be lower than that presented here. Received 11 April 2000, accepted 18July 2000.

VIGILANCE BEHAVIOR IN THE HARLEQUIN DUCK (HISTRIONICUS HISTRIONICUS) DURING THE PREINCUBATION PERIOD IN LABRADOR: ARE MALES VIGILANT FOR SELF OR SOCIAL PARTNER?

Abstract Males of several avian species are more vigilant than their female partners, particularly during the preincubation period. Male vigilance may function as a deterrent of extrapair copulation attempts (EPCs) or to ensure male survival, because males of sexually dimorphic species may be more conspicuous to predators than females. However, vigilant males may act as antipredator sentinels to enhance female survivorship, which may also allow females to feed and rest more efficiently, thereby enhancing their ability to form clutches. We attempted to distinguish between the “male benefits” and “female benefits” hypotheses by studying the behavior of unpaired males and paired Harlequin Ducks (Histrionicus histrionicus) during the preincubation period. Paired males were, on average, four times more vigilant than unpaired males and their mates, which suggests that elevated levels of vigilance by paired males does not function primarily for self-protection against predators. Males were not more vigilant during the female’s fertile period, contrary to the “paternity assurance” hypothesis. Male vigilance during feeding bouts was highest when pairs fed alone near shore—a condition in which feeding was likely more “risky.” Male vigilance was positively correlated with female feeding when females fed near shore, but not at other times. During resting bouts, males were vigilant 14 ± 0.01% of the time in all conditions. We suggest that male vigilance may be important to enhance female survival, especially when females feed under risky conditions. Comportement de Vigilance chez Histrionicus histrionicus durant la Période de Pré- incubation au Labrador: Les Mâles Sont-ils Vigilants pour Eux-mêmes ou pour leur Partenaire Social?

Migration Patterns of Black Brant in Boundary Bay, British Columbia

Management strategies to address population declines and changing patterns of winter distribution of black brant (Branta bernicla nigricans) require a better understanding of timing of migration and mixing of migrant and wintering birds along the Pacific Coast of North America. We studied migration patterns of brant in Boundary Bay, British Columbia, using population censuses and sightings of individually marked birds during 1994-95 and 1995-96. There was no detectable turnover of individuals through the area in fall, and brant that first arrived in Boundary Bay in November and early December stayed until at least the first week of March. The first spring transients appeared in mid-February 1995 and 1 week later in 1996. The first spring departures coincided with the opening of brant huntin in Boundary Bay in both years suggesting that early migrants stayed for a shorter period of time in 1996. Spring brant hunting could have adverse effects on reproductive success if migrants depart early from staging areas and opportunities to compensate for decreased nutrient intake farther north are limited. The methods we used could be applied by managers in other areas to establish local hunting regulations appropriate for both wintering and spring staging populations.

Movements of Harlequin Ducks in Eastern North America

Abstract The movements of a total of 948 Harlequin Ducks (Histrionicus histrionicus) banded in eastern North America and Greenland from 1996-2003 (313 breeding, 186 molting/staging, and 449 wintering) were examined. Regular resighting and recapture projects have been underway at the Gannet Islands, Labrador, as well as Jericho Bay, Maine. Less consistent observations have been conducted on the Gaspé Peninsula, Québec, and incidental observations were obtained from the public. Affiliations between breeding, molting and wintering sites were assessed in an effort to determine movement patterns and the level of geographic separation. Population affiliations indicated by past satellite telemetry studies were verified by the capture-recapture data. Absolute geographic separation between the eastern North American wintering population and the Greenland wintering population could not be determined.

Morphological Variation among Harlequin Ducks in the Northwest Atlantic

Abstract Harlequin Ducks (Histrionicus histrionicus) were captured and measured at a variety of staging, breeding, molting and wintering sites across their Northwest Atlantic range from 1996-2002. The consistency in the body measurements taken on the same birds across time and sites, as indexed by repeatability, was adequate (0.4-0.75), with the notable exception of total tarsus, which showed poor repeatability. Correlations among morphological measurements were weak within each sex. Some differences among locations were detected, notably in wing length, with birds breeding in Labrador showing longer wings than birds breeding further south and those wintering in Maine. Overall, however, major differences among sites were not apparent. Recent satellite and banding information indicate that many of these locations are linked and these observations are supported by this morphological data. Harlequin Ducks are similar to other ducks (except eiders) in that they are wide ranging and have disjunct populations, but show, at best, weak morphological differentiation across their range.

Aspects of Distribution and Ecology of Harlequin Ducks on the Torrent River, Newfoundland

Abstract Harlequin Ducks (Histrionicus histrionicus) breeding on the upper Torrent River of the northern peninsula of Newfoundland were studied from 1993 to 2002. This reach of the watershed was proposed for hydro-electrical development in the 1990s. Harlequin Ducks arrive on the Torrent River as soon as ice-out permits in early to late May. Pairs concentrate in the upper watershed that drains the Long Range Barrens ecoregion. Nesting and brood rearing appear to take place primarily in proximity to spring-pair activity, although movements of more than ten km were observed. Young remain in the upper watershed until fledging in late August to mid-September. Counts of Harlequin Ducks breeding on the upper Torrent River increased throughout the 1990s, and the estimated population growth rate for the Torrent River birds was very similar to the growth rate for birds wintering at Cape St. Marys, Newfoundland (1.14 vs. 1.13) during the same period. Paired females spent ∼ 40% of the day in feeding activities whereas paired males allocated less time to feeding (∼19%) and more time to alert or vigilant behaviors while females fed. Birds rested for 35-40% of the day. Harlequin Ducks exploited rapids, riffles and runs, and were especially associated with the boulder-strewn inlets and outlets of ponds. The large quantities of submerged and semi-submerged angular boulders provide increased surface area for attachments of larval insects, and movement of water through boulders assures high rates of oxygenation important to filter-feeding insects. Broods selected areas with flow rates of 1.27 ± 0.24 m/s. The family Chironomidae contained the most taxa and was the most numerous invertebrate group found in the Torrent River. Chironomidae may comprise the most important food items for pre-nesting Harlequin Ducks when considering volume of prey types consumed. A high rate of brood production in 1997 and 1998, compared to adjacent watersheds, suggests the possibility that the Torrent River system may behave as a source population for the general region of northern Newfoundland.