Lay Summary & BULL; Migratory birds time their annual migrations to take advantage of temporal and spatial variation in resources, disease, and predation. & BULL; Timing of these migrations is broadly determined by an internal biological clock set by day length, but individuals may refine when and how they migrate in response to environmental conditions. & BULL; We used 11 years of satellite tracking data to investigate migratory cues in Barrow's Goldeneye, a species of sea duck. & BULL; We found that birds used weather conditions as migratory cues, leaving their wintering grounds earlier in warmer springs and arriving on their breeding grounds earlier when the snow melted earlier in the year. & BULL; Because individuals respond to conditions both where they start and where they end spring migration, our results suggest that Barrow's Goldeneye update their migratory decisions during migration. & BULL; Barrow's Goldeneye's ability to respond to environmental cues suggests that they may be able to adapt to ongoing climate change. Timing of seasonal bird migrations is broadly determined by internal biological clocks, which are synchronized by photoperiod, but individuals often refine their migratory timing decisions in response to external factors. Using 11 years of satellite telemetry data, we show that Pacific Barrow's Goldeneye (Bucephala islandica) at higher latitudes initiated spring and molt migrations later and fall migration earlier than individuals at lower latitudes. We further show that individuals refined migratory timing in response to interannual variation in environmental conditions. Individual Barrow's Goldeneye initiated spring migration earlier in years with warmer springs at their overwintering locations and concluded spring migration earlier in years with earlier annual snowmelt on their breeding grounds. Because individuals respond to conditions both where they initiate and where they conclude spring migration, our results suggest that Barrow's Goldeneye update their migratory decisions en route. For all 3 migrations in their annual cycle, birds delayed initiating migration if they had been captured and tagged prior to that migration. Birds that initiated migration late for their latitude were less likely to include a stopover and completed that migration faster, partially compensating for delayed departures. Our results are consistent with the hypothesis that Barrow's Goldeneye uses a combination of endogenous cues and environmental cues in migratory decision making. Sensitivity to environmental cues suggests that Barrow's Goldeneye may have behavioral plasticity that is adaptive when faced with ongoing climate change.

Effective management of migratory animals requires an understanding of individual movement patterns throughout the annual cycle. We used satellite transmitters to track adult Barrow's Goldeneye (Bucephala islandica) captured at five wintering sites, one breeding site, and one molting site from across the species' geographic range in western North America. The data were analyzed to assess the strength of migratory connectivity and determine latitudinal and sex effects on migration phenology. At the range-wide scale, migratory connectivity was high; cluster analyses showed subpopulations aggregated at each stage of the annual cycle. Barrow's Goldeneye from all wintering latitudes traveled north and east to breed. Compared to females, males traveled farther north to molt and consequently traveled longer distances when returning to their wintering areas. Wintering latitude had little effect on migration distance but a large effect on the phenology of migration. Individuals that wintered at northern latitudes arrived on their wintering areas earlier and departed later than individuals that wintered farther south. Individuals that wintered at northern latitudes also arrived on and left their inland breeding areas later but left their molting sites earlier than individuals that wintered farther south. Sex also influenced the phenology of migration at all sites: males left their mates during incubation and consequently spent less time on breeding areas and more time on their molting and fall staging areas. The high level of migratory connectivity observed in this study suggests that the subpopulation of Barrow's Goldeneye in south-central Alaska is demographically independent from subpopulations in southeast Alaska and British Columbia, and could be managed separately.

We quantified the duration and phenology of remigial molt of Barrow's Goldeneyes (Bucephala islandica) in northwestern Alberta, Canada. We estimated that the remiges' average (+/- SE) growth rate was 3.94 +/- 0.13 mm day(-1), slightly slower than that of most waterfowl. Barrow's Goldeneyes regained flight with the ninth primary 77% grown, a percentage similar to or greater than that of most waterfowl. By several metrics, remigial molt of Barrow's Goldeneye was longer than that of most waterfowl. We estimated that it took 6.5 +/- 1.2 days for a new ninth primary to become visible once the old primary was dropped (pre-emergence interval). The periods in which males and females were flightless were 30 +/- 0.4 and 28 +/- 0.5 days, respectively, and 36.5 +/- 0.5 and 34.5 +/- 0.8 days, respectively, including the pre-emergence interval. Complete maturation of primaries after emergence took 39 +/- 0.5 and 36 +/- 0.7 days for males and females, respectively, and 45.5 +/- 0.6 and 42.5 +/- 0.9 days, respectively, including the pre-emergence interval. These results suggest a lack of strong selective pressure to reduce the duration of remigial molt in this species. Initiated over a range of nearly 2 months, remigial molt was asynchronous both between and within age and sex cohorts, suggesting a lack of strong temporal optima for remigial molt of Barrow's Goldeneyes at our study sites.

Postbreeding survival of waterfowl is rarely quantified, despite potential for constraints during this stage of the annual cycle that may subsequently affect population dynamics. We estimated survival of radio-marked adult male Barrow's goldeneyes (Bucephala islandica) during remigial molt and fall staging at Cardinal and Leddy Lakes in the Boreal Transition Zone of northwestern Alberta, Canada. Daily survival rate (DSR) was high during remigial molt (DSR=0.9987, 95% CI: 0.99671.0000), corresponding to a 39-day period survival rate (PSR) of 0.95 (95% CI: 0.881.00). During fall staging, DSR was markedly lower (DSR=0.9938, 95% CI: 0.98980.9978), corresponding to a PSR of 0.68 (95% CI: 0.530.87) over the 62-day period between the end of remigial molt and fall migration. Half of fall staging mortalities observed on Cardinal Lake were directly attributed to hunting. We conclude that remigial molt is a period with high survival in the annual cycle of Barrow's goldeneyes at our study sites. However, in light of low fall staging survival, Barrow's goldeneye harvest management strategies should be carefully evaluated with intent to reduce risk of localized high mortality at significant staging sites in western Canada. (c) 2013 The Wildlife Society.

Molt is a metabolically demanding process in the annual cycle of birds, particularly for species that undergo simultaneous remigial molt because nutritional and energetic costs occur during a short period. Birds that molt remiges simultaneously utilize many different body-mass and foraging strategies to meet the nutritional and energetic costs of remigial molt, and documentation of interspecific variation has contributed to understanding species-specific risks associated with molt. However, little is known about intraspecific variation in body-mass and foraging strategies among birds that molt remiges simultaneously. We documented body-mass dynamics and foraging effort of Barrow's Goldeneyes (Bucephala islandica) during simultaneous remigial molt at two important postbreeding sites, including a large, hypereuthrophic lake and a small, mesotrophic lake in Alberta, to determine whether strategies for meeting nutritional costs of remigial molt varied across sites, years, and cohorts. Average body mass of all age and sex cohorts on both lakes increased during remigial molt in both 2009 and 2010. Birds were heavier on the smaller lake, and heavier in 2010 than in 2009, and adult males were heavier than subadult males. Radiomarked adult males exhibited similar foraging effort on each lake in each year (approximately 120-140 min day(-1)); however, birds foraged primarily diurnally on the large lake and nocturnally on the small lake. We conclude that Barrow's Goldeneyes exhibit considerable intraspecific variation in body-mass and foraging dynamics during remigial molt across sites, years, and cohorts, which suggests that these components of molt strategy are plastic and responsive to local environmental conditions.

Abstract. Sites where Barrow's Goldeneye (Bucephala islandica) undergo remigial molt and fall staging are poorly known, with only two major sites documented in Alaska and the Yukon Territory. Satellite telemetry, aerial surveys and ground surveys were used to identify previously unknown molting and fall staging areas in the Boreal Transition Zone (BTZ) of northern Alberta. Of 816 wetlands surveyed between 2004 and 2006 in the BTZ, 40–45% (105–127 lakes annually) had molting goldeneyes. Of these, 1.3–3.3% were used by large aggregations of goldeneyes (>100 birds). Two wetlands, Cardinal and Leddy Lakes, were particularly important, with an estimated 5,000–7,000 Barrow's Goldeneyes, primarily adult males, using these sites during remigial molt and fall staging. Birds used these sites up to five months or over one-third of their annual cycle. Half of adult males marked with satellite transmitters at a breeding area in interior British Columbia used Cardinal Lake for postbreeding activities. Discovery of these sites represents some of the largest concentrations of molting Barrow's Goldeneyes in North America, and the only major molting sites currently known for the intermountain breeding portion of the western population. Protection of Cardinal and Leddy Lakes, and other significant molting and staging sites within the BTZ, should be a priority conservation effort for this species.

Abstract Naturally occurring stable isotopes in foodwebs can be used to determine the relative contributions of endogenous and exogenous nutrients to avian eggs in cases where birds move between isotopically distinct biomes or habitats to breed. We measured δ13C and δ15N values in somatic muscle tissues and eggs of Barrow's goldeneye (Bucephala islandica) together with those isotope values in amphipods from wetlands used by birds breeding on the Chilcotin Plateau in central British Columbia, Canada. Females that had recently arrived on the breeding grounds had muscle tissue isotope values similar to those found in coastal wintering birds and were considerably more enriched in 13C than were samples from local foodwebs. However, δ15N values of amphipods were highly variable among wetlands, resulting in a nondistinct exogenous δ15N endpoint for our dual-isotope mixing model. Therefore, we only used the model based on δ13C values to estimate nutrient sources to eggs. In 2000, first-laid eggs were more enriched in both isotopes than fourth- or eighth-laid eggs. Considerable endogenous protein input to egg yolk and albumen was detected for the first laid egg (yolk: range = 0–92.7%, median = 23.7%; albumen: range = 0–78.6%, median = 28.7%) with less endogenous contribution of somatic lipids (first egg: range = 0–100%, median = 4.9%). Using archived tissue samples of muscle and developing ovarian follicles from birds collected in 1993–1994, we found no δ13C isotopic evidence for endogenous protein contribution to egg yolk. Our results demonstrate the utility of the stable isotope approach in cases where isotopic endpoints are well established. Barrow's goldeneye showed a mixed strategy of endogenous vs. exogenous nutrient allocation to reproduction that varied by individual females, laying order, and year. We encourage managers to use this approach to quantify nutrient allocations from various biomes to reproduction in waterfowl to better understand the importance of wintering sites to reproduction.