Research Article Winter Movement Dynamics of Black Brant MARK S. LINDBERG, 1 Department of Biology and Wildlife and Institute of Arctic Biology, P.O. Box 757000, University of Alaska Fairbanks, Fairbanks, AK 99775, USA DAVID H. WARD, Biological Science Office, United States Geological Survey–Alaska Science Center, 1011 E. Tudor Road, Anchorage, AK 99503, USA T. LEE TIBBITTS, Biological Science Office, United States Geological Survey–Alaska Science Center, 1011 E. Tudor Road, Anchorage, AK 99503, USA JOHN ROSER, 390 Binscarth Road, Los Osos, CA 93403, USA ABSTRACT Although North American geese are managed based on their breeding distributions, the dynamics of those breeding populations may be affected by events that occur during the winter. Birth rates of capital breeding geese may be influenced by wintering conditions, mortality may be influenced by timing of migration and wintering distribution, and immigration and emigration among breeding populations may depend on winter movement and timing of pair formation. We examined factors affecting movements of black brant (Branta bernicla nigricans) among their primary wintering sites in Mexico and southern California, USA, (Mar 1998–Mar 2000) using capture– recapture models. Although brant exhibited high probability (.0.85) of monthly and annual fidelity to the wintering sites we sampled, we observed movements among all wintering sites. Movement probabilities both within and among winters were negatively related to distance between sites. We observed a higher probability both of southward movement between winters (Mar to Dec) and northward movement between months within winters. Between-winter movements were probably most strongly affected by spatial and temporal variation in habitat quality as we saw movement patterns consistent with contrasting environmental conditions (e.g., La Nin ˜a and El Nin ˜ o southern oscillation cycles). Month-to-month movements were related to migration patterns and may also have been affected by differences in habitat conditions among sites. Patterns of winter movements indicate that a network of wintering sites may be necessary for effective conservation of brant. ( JOURNAL OF WILDLIFE MANAGEMENT 71(2):534–540; 2007) DOI: 10.2193/2006-051 KEY WORDS brant, goose management, movement, population dynamics. Geese in North America are managed based on their geographic distribution during the breeding season because populations or subpopulations of geese are often identiﬁable during this phase of their life cycle (U.S. Fish and Wildlife Service and Canadian Wildlife Service 1986). Although much research has focused on the factors affecting goose populations during the breeding season, events during the winter may also affect the dynamics of breeding populations (Hestbeck et al. 1991, Sedinger et al. 2006). Many geese are capital breeders, at least during some years, and the nutrients that they acquire in winter or during spring migration can inﬂuence the probability of breeding and reproductive performance (Ankney and MacInnes 1978, Be ˆty et al. 2003, Gauthier et al. 2003). Mortality may be affected by timing of migration and wintering distribution (Hestbeck et al. 1991). Finally, immigration and emigration among breeding areas may ultimately be affected by wintering distributions, if pairs are formed during this period (Raveling 1970, Robertson and Cooke 1999, Esler 2000). Therefore, a complete understanding of factors affecting the dynamics of breeding populations and their management requires knowledge of movement patterns of these geese during the winter. The effects of winter distributions and movements may be particularly important for the few goose species that still use nonagricultural environments during the winter because food resources may be more limiting. Most goose species have shifted to a diet primarily composed of agricultural grains during the winter and this food source is widely distributed (Malecki et al. 1988, Gauthier et al. 2005). For geese like black brant (Branta bernicla nigricans; hereafter brant), which do not use agricultural grains and instead rely on marine food sources, loss of wintering sites or changes brought about by environmental or anthropogenic events can have profound affects on winter movements and ultimately dynamics of breeding populations (Ward et al. 2005). Using multistate models (Brownie et al. 1993), we analyzed the movement of marked brant (Sedinger et al. 1998) wintering in discrete coastal lagoons in Mexico and southern California, USA, to more fully understand the processes that may ultimately affect the management of the breeding populations of these birds. Brant are small geese that breed in colonies in Alaska, USA; northeastern Russia; and the western Arctic of Canada (Reed et al. 1998). Brant spend the winter in coastal bays and lagoons from Alaska to Mexico with the majority wintering in California and Baja California, Mexico (Ward et al. 1997). Movements of brant among wintering sites may have important consequences for population dynamics, pair formation, and genetic structure of these birds (Rockwell and Barrowclough 1987, Robertson and Cooke 1999). Furthermore, some wintering sites used by brant are threatened by activities, such as development (Ibarra-Obando and Escofet 1987, Ward et al. 2003), and understanding brant use of these sites is critical for the future conservation of this species. Finally, our goal was to advance our understanding of metapopulation dynamics of migratory bird species by examining hypotheses about ecological factors inﬂuencing avian movements during the winter (Esler 2000). Our objectives were to 1) estimate spatial and temporal variation in movement of brant among wintering sites and 2) determine the relative importance of 1 E-mail: ffmsl1@uaf.edu 534 The Journal of Wildlife Management  71(2)