Seagrass (Zostera spp.) as food for brent geese (Branta bernicla): an overview

Brent geese (called brant in North America) are among the smallest and the most marine of all goose species, and they have very long migration routes between high Arctic breeding grounds and temperate wintering grounds. Like all other geese, brent geese are almost entirely herbivorous. Because of these ecological characteristics they have a high food demand and are strongly dependent on stopover sites to ”refuel” during the migration period. Three subspecies of brent geese are distributed around the Holarctic, forming seven populations with distinct migration routes. Most or all of these populations make heavy use of Zostera spp. during migratory stopovers on spring and/or autumn migration. Examples of Zostera stopover areas being used by large numbers of brent geese for several weeks each year are Izembek Lagoon (Alaska), lagoons in Baja California, the German/Danish Wadden Sea, the Golfe du Morbihan (France), British estuaries, and the White Sea (Western Russian Arctic). Brent geese feed on Zostera wherever they can, but they can only reach the plants at low tide or in shallow water. Changes in Zostera abundance affect brent goose distribution, and the ”wasting disease” affecting Atlantic Zostera stocks during the 1930s was at least partly responsible for a steep decline in brent goose population sizes on both sides of the Atlantic. While Zostera is of outstanding importance as food for brent geese, the impact of the geese on Zostera stocks seems to be less important – at many sites, the geese consume only a small amount of the available Zostera, or, if they consume more, the seagrass can regenerate fully until the following season. Received: 6 December 1998 / Received in revised form: 6 August 1999 / Accepted: 9 August 1999     

Changes in abundance and spatial distribution of geese molting near Teshekpuk Lake,Alaska: interspecific competition or ecological change?

Goose populations molting in the Teshekpuk Lake Special Area of the National Petroleum Reserve—Alaska have changed in size and distribution over the past 30 years. Black brant (Branta bernicla nigricans) are relatively stable in numbers but are shifting from large, inland lakes to salt marshes. Concurrently, populations of greater white-fronted geese (Anser albifrons frontalis) have increased seven fold. Populations of Canada geese (Branta canadensis and/or B. hutchinsii) are stable with little indication of distributional shifts. The lesser snow goose (Anser caerulescens caerulescens) population is proportionally small, but increasing rapidly. Coastline erosion of the Beaufort Sea has altered tundra habitats by allowing saltwater intrusion, which has resulted in shifts in composition of forage plant species. We propose two alternative hypotheses for the observed shift in black brant distribution. Ecological change may have altered optimal foraging habitats for molting birds, or alternatively, interspecific competition between black brant and greater white-fronted geese may be excluding black brant from preferred habitats. Regardless of the causative mechanism, the observed shifts in species distributions are an important consideration for future resource planning.     

Intercolony variation in growth of black brant goslings on the Yukon-Kuskokwim Delta,Alaska

Recent declines in black brant (Branta bernicla nigricans) are likely the result of low recruitment. In geese, recruitment is strongly affected by habitat conditions experienced by broods because gosling growth rates are indicative of forage conditions during brood rearing and strongly influence future survival and productivity. In 2006–2008, we studied gosling growth at 3 of the 4 major colonies on the Yukon-Kuskokwim Delta, Alaska. Estimates of age-adjusted gosling mass at the 2 southern colonies (approx. 30% of the world population of breeding black brant) was low (gosling mass at 30.5 days ranged 346.7 ± 42.5 g to 627.1 ± 15.9 g) in comparison to a third colony (gosling mass at 30.5 days ranged 640.0 ± 8.3 g to 821.6 ± 13.6 g) and to most previous estimates of age-adjusted mass of brant goslings. Thus, our results are consistent with the hypothesis that poor gosling growth is negatively influencing the brant population. There are 2 non-mutually exclusive explanations for the apparent growth rates we observed. First, the population decline may have been caused by density-independent factors and habitat capacity has declined along with the population as a consequence of the unique foraging feedback between brant and their grazing habitats. Alternatively, a reduction in habitat capacity, as a result of changes to the grazing system, may have negatively influenced gosling growth, which is contributing to the overall long-term population decline. We found support for both explanations. For colonies over habitat capacity we recommend management to enhance foraging habitat, whereas for colonies below habitat capacity we recommend management to increase nesting productivity. © 2010 The Wildlife Society.     

Latitudinal variation in population structure of wintering Pacific Black Brant

ABSTRACT.   Latitudinal variation in population structure during the winter has been reported in many migratory birds, but has been documented in few species of waterfowl. Variation in environmental and social conditions at wintering sites can potentially influence the population dynamics of differential migrants. We examined latitudinal variation in sex and age classes of wintering Pacific Black Brant ( Branta bernicla nigricans ). Brant are distributed along a wide latitudinal gradient from Alaska to Mexico during the winter. Accordingly, migration distances for brant using different wintering locations are highly variable and winter settlement patterns are likely associated with a spatially variable food resource. We used resightings of brant banded in southwestern Alaska to examine sex and age ratios of birds wintering at Boundary Bay in British Columbia, and at San Quintin Bay, Ojo de Liebre Lagoon, and San Ignacio Lagoon in Baja California from 1998 to 2000. Sex ratios were similar among wintering locations for adults and were consistent with the mating strategy of geese. The distribution of juveniles varied among wintering areas, with greater proportions of juveniles observed at northern (San Quintin Bay and Ojo de Liebre Lagoon) than at southern (San Ignacio Lagoon) locations in Baja California. We suggest that age-related variation in the winter distribution of Pacific Black Brant is mediated by variation in productivity among individuals at different wintering locations and by social interactions among wintering family groups.     

Factors influencing route choice by avian migrants: a dynamic programming model of Pacific brant migration

We used stochastic dynamic programming to investigate a spectacular migration strategy in the black brant Branta bernicla nigricans, a species of goose. Black brant migration is well suited for theoretical analysis since there are a number of existing strategies that easily can be compared. In early autumn, almost the entire population of the black brant gathers at Izembek Lagoon on the Alaska Peninsula to stage and refuel before the southward migration. There are at least three distinct strategies, with most geese making a spectacular direct migration more than 5000km across the Gulf of Alaska to their wintering grounds in southern Baja California or mainland Mexico. This is a potentially dangerous strategy since foraging is not possible during the overseas passage. Some individuals instead use shorter flights to make a detour along the coast, a longer route that all individuals use for northwards migration in spring. Since flight costs accelerate with increasing body mass, migration by short flights is energetically cheaper than long-distance flights. A small but increasing part of the population has recently begun to winter at Izembek. We investigated this migration under two different suppositions using a dynamic state variable model. First, if the geese are free to make a strategic choice, under what assumptions should they prefer direct migration and under what assumptions should they prefer detour migration/winter residency? Second, provided that the dominating direct migration strategy is optimal, what conditions will force the geese to go for detour migration/winter residency? In the second case the geese may try to follow an optimal direct migration strategy, but stochastic events may force them to choose a suboptimal policy. We also simulated possible effects of global warming. The model suggests that the fuel level at arrival in Izembek and fuel gain rates are key factors and that tail winds must have been reliable in the past, otherwise direct migration could not have evolved. It also suggests that a change to milder winters may promote an unexpectedly abrupt change from long-distance to short-distance migration or winter residency. Finally, it produced a number of predictions that might be testable in the field.     

Time energy budgets and food use of Atlantic brant across their wintering range

We conducted extensive behavioral and food sampling of Atlantic brant (Branta bernicla hrota) across their winter range and used time–activity budgets for brant to determine daily energy expenditure (DEE). Sampling occurred 1 December–31 May 2006–2008 in 11,225-km² sites between Rhode Island and Virginia containing important estuarine and upland habitat. To calculate DEE we used instantaneous scan sampling to estimate time–activity budgets. We also determined foods eaten by brant and energy density of food plants. Last, we quantified body condition of brant, which differed among years, months, regions, and ages, and sexes. Overall DEE for brant was 1,530 ± 64 kJ/day. There was considerable variation in time–activity budgets among years, months, regions, habitat, tide, temperature, and time-of-day, but we detected no significant difference in DEE of brant between years or among regions. However, DEE in January (2,018 ± 173 kJ/day) was nearly double the DEE of brant in May (1,048 ± 137 kJ/day). Brant spent their time feeding (32.3%), swimming (26.2%), resting (16.2%), and flying (14.5%). The percent of brant foreguts sampled contained macroalgae (53%) eelgrass (Zostera marina; 18%), salt marsh cordgrass (Spartina alterniflora; 17%), and terrestrial grass (Poa. sp.) and clover (Trifollium sp.; 9%). Energy density differed by vegetation type: macroalgae (12.6 ± 0.1 kJ/g), eelgrass (14.1 ± 0.1 kJ/g), new-growth salt marsh cordgrass (16.9 ± 0.2 kJ/g), and terrestrial grass and clover (17.7 ± 0.1 kJ/g). Atlantic brant exhibited behavioral plasticity thereby allowing modification of daily activity budgets to meet seasonally varying energetic requirements associated with wintering and spring staging. Recognizing a variable DEE can be used along with eventual estimates of food biomass and total metabolizable energy on the landscape to calculate carrying capacity (goose use days) on state, region, or range-wide scales. © 2011 The Wildlife Society.     

Using body mass dynamics to examine long-term habitat shifts of arctic-molting geese: evidence for ecological change

From 1976 onward, molting brant geese (Branta bernicla) within the Teshekpuk Lake Special Area, Alaska, shifted from inland, freshwater lakes toward coastal wetlands. Two hypotheses explained this redistribution: (1) ecological change: redistribution of molting brant reflects improvements in coastal foraging habitats, which have undergone a succession toward salt-tolerant plants due to increased coastal erosion and saltwater intrusion as induced by climate change or (2) interspecific competition: greater white-fronted geese (Anser albifrons) populations increased 12-fold at inland lakes, limiting food availability and forcing brant into coastal habitats. Both hypotheses presume that brant redistributions were driven by food availability; thus, body mass dynamics may provide insight into the relevance of these hypotheses. We compared body mass dynamics of molting brant across decades (1978, 1987–1992, 2005–2007) and, during 2005–2007, across habitats (coastal vs. inland). Brant lost body mass during molt in all three decades. At inland habitats, rates of mass loss progressively decreased by decade despite the increased number of greater white-fronted geese. These results do not support an interspecific competition hypothesis, instead suggesting that ecological change enhanced foraging habitats for brant. During 2005–2007, rates of mass loss did not vary by habitat. Thus, while habitats have improved from earlier decades, our results cannot distinguish between ecological changes at inland versus coastal habitats. However, we speculate that coastal forage quality has improved beyond that of inland habitats and that the body mass benefits of these higher quality foods are offset by the disproportionate number of brant now molting coastally.     

Decadal Response of Arctic Freshwaters to Burgeoning Goose Populations

The Arctic is faced with rapid climatic changes, but in some areas, drastic changes in the abundance of herbivores represent an even greater agent of change. Increasing goose populations, especially midcontinent lesser snow geese (Chen caerulescens), have led to an extensive loss of vegetation in terrestrial habitats in the Arctic through heavy grazing and destructive foraging. Our aim was to evaluate the effect of geese on the freshwater systems in their Arctic breeding grounds. We sampled the water chemistry of lakes and ponds across a major goose breeding area in the Eastern Canadian Arctic and compared results to samples taken 13 years earlier to determine whether the changes in water chemistry, if evident, were consistent with effects of geese or of climate. Our results suggest that nutrient loadings have increased while most other parameters associated with the underlying geology and hydrology of the region have stayed in a similar range as a decade ago. The most significant changes were linked to nitrogen and phosphorus; phosphorus concentrations doubled between 2001/2002 and 2015, with the highest levels and greatest changes observed for wetlands inside versus outside of goose breeding areas. Our results suggest that geese are most strongly affecting nutrient loads in freshwaters inside breeding areas, which show evidence of ornithological eutrophication. Nutrient changes of this magnitude, especially in typically oligotrophic Arctic lakes, can have profound consequences on ecosystem structure and function and demonstrate how burgeoning waterfowl populations can act as a vector of rapid environmental change in Arctic freshwaters.     

Potential for an Arctic‐breeding migratory bird to adjust spring migration phenology to Arctic amplification

Arctic amplification, the accelerated climate warming in the polar regions, is causing a more rapid advancement of the onset of spring in the Arctic than in temperate regions. Consequently, the arrival of many migratory birds in the Arctic is thought to become increasingly mismatched with the onset of local spring, consequently reducing individual fitness and potentially even population levels. We used a dynamic state variable model to study whether Arctic long‐distance migrants can advance their migratory schedules under climate warming scenarios which include Arctic amplification, and whether such an advancement is constrained by fuel accumulation or the ability to anticipate climatic changes. Our model predicts that barnacle geese Branta leucopsis suffer from considerably reduced reproductive success with increasing Arctic amplification through mistimed arrival, when they cannot anticipate a more rapid progress of Arctic spring from their wintering grounds. When geese are able to anticipate a more rapid progress of Arctic spring, they are predicted to advance their spring arrival under Arctic amplification up to 44 days without any reproductive costs in terms of optimal condition or timing of breeding. Negative effects of mistimed arrival on reproduction are predicted to be somewhat mitigated by increasing summer length under warming in the Arctic, as late arriving geese can still breed successfully. We conclude that adaptation to Arctic amplification may rather be constrained by the (un)predictability of changes in the Arctic spring than by the time available for fuel accumulation. Social migrants like geese tend to have a high behavioural plasticity regarding stopover site choice and migration schedule, giving them the potential to adapt to future climate changes on their flyway.     

An Integrated Population Model for Harvest Management of Atlantic Brant

Atlantic brant (Branta bernicla hrota) are important game birds in the Atlantic Flyway and several long-term monitoring data sets could assist with harvest management, including a count-based survey and demographic data. Considering their relative strengths and weaknesses, integrated analysis to these data would likely improve harvest management, but tools for integration have not yet been developed. Managers currently use an aerial count survey on the wintering grounds, the mid-winter survey, to set harvest regulations. We developed an integrated population model (IPM) for Atlantic brant that uses multiple data sources to simultaneously estimate population abundance, survival, and productivity. The IPM abundance estimates for data from 1975–2018 were less variable than annual mid-winter survey counts or Lincoln estimates, presumably reflecting better accounting for observer error and incorporation of demographic estimates by the IPM. Posterior estimates of adult survival were high (0.77–0.87), and harvest rates of adults and juveniles were positively correlated with more liberal hunting regulations (i.e., hunting days and the daily bag limit). Productivity was variable, with the percent of juveniles in the winter population ranging from 1% to >40%. We found no evidence for environmental relationships with productivity. Using IPM-predicted population abundances rather than mid-winter survey counts alone would have meant fewer annual changes to hunting regulations since 2004. Use of the IPM could improve harvest management for Atlantic brant by providing the ability to predict abundance before annual hunting regulations are set, and by providing more stable hunting regulations, with fewer annual changes. © 2021 The Wildlife Society.     

Energetic consequences of a major change in habitat use: endangered Brent Geese Branta bernicla hrota losing their main food resource

Coastal seagrasses are declining at increasing rates worldwide, forcing herbivores previously reliant on these habitats to abandon them in search of alternative ways to fulfil their daily energy budgets. After two decades of declining seagrass abundance in Mariager Fjord, Denmark, the Svalbard breeding population of Light‐bellied Brent Geese Branta bernicla hrota has experienced substantial changes in habitat use at this traditional autumn staging area. Declines in seagrasses have caused birds to depend increasingly on Sea Lettuce Ulva lactuca in recent years, and forced birds into terrestrial habitats such as saltmarsh and winter wheat. In contrast to those birds exploiting aquatic habitats, birds relying on these new habitats showed higher energy expenditure and failed to balance their energy budget. Eelgrass (Zostera) was energetically superior to other food resources, with marine Ulva being second best. Predicted body mass development under two different scenarios indicate that present habitat use resulted in a midwinter body mass around 122 g lower than just 20 years ago, equivalent to c. 9.4% of Brent Goose body weight. Even after controlling for inter‐annual differences in thermoregulatory costs, the effect of changes in habitat use translated into a body mass reduction of c. 56 g, which could adversely affect survival and future reproduction. Flyway‐wide declines in Zostera abundance and further reductions in traditional habitats due to climate change give cause to reassess projected population trends and consequent management implications for the East Atlantic flyway population of Light‐bellied Brent Geese.     

Distribution and Habitat Use of Ross's and Lesser Snow Geese During Late Brood Rearing

ABSTRACT We assessed spatial distribution and habitat use by Ross's and lesser snow geese (Chen rossii and C. caerulescens caerulescens) during late brood rearing to begin understanding goose-habitat interactions and monitoring key habitats around a rapidly growing nesting colony located at Karrak Lake, Nunavut, Canada. We conducted aerial surveys to count geese and georeference locations, then used Landsat Thematic Mapper satellite imagery to identify habitats associated with each flock. We observed 435 and 407 flocks and 36,287 and 32,745 birds in 1994 and 1995, respectively. Birds were somewhat uniformly distributed over the 5,000-km² study area, with larger aggregations occurring closer to the coast, about 70 km from the colony. We assessed habitat use using Bonferroni intervals at both the flock and individual scales. At the flock level, birds avoided lichen-heath, used other terrestrial habitats as available, and selected freshwater. At the individual level, geese selected lowland habitats: wet sedge meadow, hummock graminoid tundra, and freshwater, which accounted for about 70% of the birds observed, and avoided upland habitats. Selection of lowland habitats is likely due to greater availability of food and easier predator avoidance compared to drier upland areas. Because most geese in our study used freshwater habitats, our results demonstrate that assessment of carrying capacity, at least in the central Arctic, must be expanded beyond the coastal salt marshes traditionally considered by researchers and managers as primary brood-rearing habitat for mid-continent light geese.     

Temperature and precipitation at migratory grounds influence demographic trends of an Arctic‐breeding bird

Anthropogenic climate disruption, including temperature and precipitation regime shifts, has been linked to animal population declines since the mid‐20th century. However, some species, such as Arctic‐breeding geese, have thrived during this period. An increased understanding of how climate disruption might link to demographic rates in thriving species is an important perspective in quantifying the impact of anthropogenic climate disruption on the global state of nature. The Greenland barnacle goose (Branta leucopsis) population has increased tenfold in abundance since the mid‐20th century. A concurrent weather regime shift towards warmer, wetter conditions occurred throughout its range in Greenland (breeding), Ireland and Scotland (wintering) and Iceland (spring and autumn staging). The aim of this study was to determine the relationship between weather and demographic rates of Greenland barnacle geese to discern the role of climate shifts in the population trend. We quantified the relationship between temperature and precipitation and Greenland barnacle goose survival and productivity over a 50 year period from 1968 to 2018. We detected significant positive relationships between warmer, wetter conditions on the Icelandic spring staging grounds and survival. We also detected contrasting relationships between warmer, wetter conditions during autumn staging and survival and productivity, with warm, dry conditions being the most favourable for productivity. Survival increased in the latter part of the study period, supporting the possibility that spring weather regime shifts contributed to the increasing population trend. This may be related to improved forage resources, as warming air temperatures have been shown to improve survival rates in several other Arctic and northern terrestrial herbivorous species through indirect bottom‐up effects on forage availability.     

Interactions between land use,habitat use,and population increase in greater snow geese: what are the consequences for natural wetlands?

The North American greater snow goose population has increased dramatically during the last 40 years. We evaluated whether refuge creation, changes in land use on the wintering and staging grounds, and climate warming have contributed to this expansion by affecting the distribution, habitat use, body condition, and migration phenology of birds. We also reviewed the effects of the increasing population on marshes on the wintering grounds, along the migratory routes and on the tundra in summer. Refuges established before 1970 may have contributed to the initial demographic increase. The most important change, however, was the switch from a diet entirely based on marsh plants in spring and winter (rhizomes of Scirpus/Spartina) to one dominated by crops (corn/young grass shoots) during the 1970s and 1980s. Geese now winter further north along the US Atlantic coast, leading to reduced hunting mortality. Their migratory routes now include portions of southwestern Québec where corn production has increased exponentially. Since the mid‐1960s, average temperatures have increased by 1–2.4°C throughout the geographic range of geese, which may have contributed to the northward shift in wintering range and an earlier migration in spring. Access to spilled corn in spring improved fat reserves upon departure for the Arctic and may have contributed to a high fecundity. The population increase has led to intense grazing of natural wetlands used by geese although these habitats are still largely undamaged. The foraging in fields allowed the population to exceed limits imposed by natural marshes in winter and spring, but also prevented permanent damage because of their overgrazing.     

Forage plants of an Arctic‐nesting herbivore show larger warming response in breeding than wintering grounds,potentially disrupting migration phenology

During spring migration, herbivorous waterfowl breeding in the Arctic depend on peaks in the supply of nitrogen‐rich forage plants, following a “green wave” of grass growth along their flyway to fuel migration and reproduction. The effects of climate warming on forage plant growth are expected to be larger at the Arctic breeding grounds than in temperate wintering grounds, potentially disrupting this green wave and causing waterfowl to mistime their arrival on the breeding grounds. We studied the potential effect of climate warming on timing of food peaks along the migratory flyway of the Russian population of barnacle geese using a warming experiment with open‐top chambers. We measured the effect of 1.0–1.7°C experimental warming on forage plant biomass and nitrogen concentration at three sites along the migratory flyway (temperate wintering site, temperate spring stopover site, and Arctic breeding site) during 2 months for two consecutive years. We found that experimental warming increased biomass accumulation and sped up the decline in nitrogen concentration of forage plants at the Arctic breeding site but not at temperate wintering and stop‐over sites. Increasing spring temperatures in the Arctic will thus shorten the food peak of nitrogen‐rich forage at the breeding grounds. Our results further suggest an advance of the local food peak in the Arctic under 1–2°C climate warming, which will likely cause migrating geese to mistime their arrival at the breeding grounds, particularly considering the Arctic warms faster than the temperate regions. The combination of a shorter food peak and mistimed arrival is likely to decrease goose reproductive success under climate warming by reducing growth and survival of goslings after hatching.     

Trends in volume migration chronology in spring staging Pacific black brant

We used a robust dataset of count and mark-resighting data for Pacific black brant from 1989–2004, and a novel mark-recapture model capable of analyzing such data, to calculate the annual variability and timing of brant as they migrated through the Parksville–Qualicum Beach area, a traditional spring staging site in coastal British Columbia, Canada. Our analysis indicated that the date of departure from this site to northern breeding sites advanced between 10 and 20 days over this period because of a combination of earlier arrival and shorter residence times. Given this change in migration behavior, and the potential implications for population dynamics, we recommend that targeted research on brant wintering, migration, and reproductive strategies should be examined within a greater Pacific-wide context. In this way, the consequences of proximate factors (e.g., disturbance, food, and climate) can be understood in terms of individual fitness and population dynamics. Finally, at the local level, conservation actions are needed to ensure the long term sustainability of Parksville–Qualicum Beach as an important spring staging site for Pacific black brant. © 2011 The Wildlife Society.     

Life‐history attributes of Arctic‐breeding birds drive uneven responses to environmental variability across different phases of the reproductive cycle

Animals exhibit varied life‐history traits that reflect adaptive responses to their environments. For Arctic‐breeding birds, traits related to diet, 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. 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. We monitored aspects of reproductive performance related to the timing of breeding, reproductive investment, and chick growth from 2011 to 2018. In response to early snowmelt 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 nestlings 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. Higher temperatures, however, may negatively affect the quality of herbaceous foods and slow gosling growth. 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.     

Winter Movement Dynamics of Black Brant

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 Niña and El Niño 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.     

若尔盖湿地水鸟资源季节变化

若尔盖湿地位于青藏高原东缘,是我国最大的高寒泥炭湿地之一。2010年从3月至12月,对若尔盖湿地水鸟种类、数量和分布进行了较为系统的调查。共记录到48种26 050只水鸟,隶属于6目12科,其中雁鸭类水鸟最多,共统计到21 408只,占水鸟总数的82.2%。3月和10月是若尔盖湿地水鸟数量的高峰期;11月是低谷期,主要是由于水鸟的迁离和越冬水鸟尚未到达的缘故。尕海是若尔盖湿地的重要组成部分,全年物种数和水鸟数量占了整个若尔盖湿地较大的比例。卫星跟踪的结果表明,青海湖斑头雁(Anser indicus)在若尔盖湿地与云南和贵州的越冬水鸟汇合,因此加强若尔盖湿地禽流感的防控是非常重要的。