Nearly the entire (98%) and over a third of the East Asian population of Brent Geese stage in Notsuke Bay and nearby sites of eastern Hokkaido, Japan, during autumn and spring migration, respectively,. Despite the region’s importance as a refueling site for migrating Brent Geese, little is known about how these migrants use specific sites within this region. In this study, we investigated the seasonal variation in the movements and use of four key sites in the eastern Hokkaido using radio telemetry. Notsuke Bay was the primary staging area for Brent Goose in both seasons, but there were frequent movements between Furen Lake in fall and between Kunashiri Island in spring. The three sites lie in close proximity to one another in the Nemuro Strait, enabling relatively quick (<30 minutes) flights between sites. Consequently, these sites may be considered as one continuous habitat during migration. Brent Geese primarily foraged on eelgrass beds at night in fall and during the day in the spring. The occupancy rates of marked geese within the protected areas of Notsuke Bay and Furen Lake were 74% and 71% during autumn, and 64% and 87% during spring, respectively. However, extending the buffer to 3 km from the boundaries of the protected areas resulted in residency rates exceeding 90% during both seasons. To effectively conserve these important staging sites in the Nemuro Strait, we recommend expanding the protected areas and including connecting waters between Notsuke Bay and Kunashiri Island and Furen Lake.

1. Animals exhibit varied life-history traits that reflect adaptive responses to their environments. For Arctic-breeding birds, traits like foraging guild, egg nutrient allocation, clutch size, and chick growth are predicted to be under increasing selection pressure due to rapid climate change and increasing environmental variability across high-latitude regions. 2. We compared four migratory birds (black brant [Branta bernicla nigricans], lesser snow geese [Chen caerulescens caerulescens], semipalmated sandpipers [Calidris pusilla], and Lapland longspurs [Calcarius lapponicus]) with varied life histories at an Arctic site in Alaska, USA, to understand how life-history traits help moderate environmental variability across different phases of the reproductive cycle. 3. We monitored aspects of reproductive performance related to the timing of breeding, reproductive investment, and chick growth from 2011–2018. 4. In response to early snow melt and warm temperatures, semipalmated sandpipers advanced their site arrival and bred in higher numbers, while brant and snow geese increased clutch sizes; all four species advanced their nest initiation dates. During chick rearing, longspur chicks were relatively resilient to environmental variation whereas warmer temperatures increased the growth rates of sandpiper chicks but reduced growth rates of snow goose goslings. These responses generally aligned with traits along the capital-income spectrum of nutrient acquisition and altricial-precocial modes of chick growth. Under a warming climate, the ability to mobilize endogenous reserves likely provides geese with relative flexibility to adjust the timing of breeding and the size of clutches. Warmer temperatures, however, may negatively affect the quality of herbaceous foods and slow gosling growth. 5. Species may possess traits that are beneficial during one phase of the reproductive cycle and others that may be detrimental at another phase, uneven responses that may be amplified with future climate warming. These results underscore the need to consider multiple phases of the reproductive cycle when assessing the effects of environmental variability on Arctic-breeding birds.