Tutakoke River Research Articles

Nest density and competing risks: A long-term investigation of Black Brant (Branta bernicla nigricans) nest survival

Many species of seabirds and waterfowl are predominantly colonial breeders, suggesting that colonial breeding is beneficial in some way. For Arctic nesting geese, colonial breeding may be an adaptive approach to minimize the risk of nest failure through predator swamping. Yet evidence for predator swamping is inconclusive. Species in low-lying coastal zones may have to manage tradeoffs between historical (e.g., predation) and increased frequency of other threats (e.g., coastal flooding associated with storm events). As the climate continues to change, coastal obligates will be subject to rising sea levels and an increase in extreme weather events, which could exacerbate the tradeoff between flooding and predation risk. We studied the effect of nest density on nest success in the colonial nesting Black Brant (Branta bernicla nigricans) on the Tutakoke River Colony in western Alaska and explored how density effects change during years of heavy Arctic fox (Alopex lagopus) predation and coastal flooding associated with storm events. We classified the colony as containing 2 strata that differed in elevation and vegetation, and were separated by the Tutakoke River. The stratum north of the Tutakoke River was 0.25 m lower in elevation and subject to periodic tidal flooding, while the southern stratum never flooded. Nest density positively affected brant nest success in years with high levels of fox predation. Nest success was greatest at the highest density during Normal years (low levels of fox predation and no flooding; northern stratum nest success 0.81 ± 0.01, southern stratum nest success 0.81 ± 0.01) and lowest in areas of low density during Fox years (northern stratum nest success 0.38 ± 0.01, southern stratum nest success 0.31 ± 0.01). Nest success was routinely higher during Normal years at all densities compared to Flood and Fox years. Our results support the hypothesis that colonial nesting, at least in tundra habitats, may have developed as a defense mechanism to swamp mammalian predators.

Changes in behavior are unable to disrupt a trophic cascade involving a specialist herbivore and its food plant.

Changes in ecological conditions can induce changes in behavior and demography of wild organisms, which in turn may influence population dynamics. Black brant (Branta bernicla nigricans) nesting in colonies on the Yukon–Kuskokwim Delta (YKD) in western Alaska have declined substantially (~50%) since the turn of the century. Black brant are herbivores that rely heavily on Carex subspathacea (Hoppner's sedge) during growth and development. The availability of C. subspathacea affects gosling growth rates, which subsequently affect pre‐ and postfledging survival, as well as size and breeding probability as an adult. We predicted that long‐term declines in C. subspathacea have affected gosling growth rates, despite the potential of behavior to buffer changes in food availability during brood rearing. We used Bayesian hierarchical mixed‐effects models to examine long‐term (1987–2015) shifts in brant behavior during brood rearing, forage availability, and gosling growth rates at the Tutakoke River colony. We showed that locomotion behaviors have increased (β = 0.05, 95% CRI: 0.032–0.068) while resting behaviors have decreased (β = −0.024, 95% CRI: −0.041 to −0.007), potentially in response to long‐term shifts in forage availability and brood density. Concurrently, gosling growth rates have decreased substantially (β = −0.100, 95% CRI: −0.191 to −0.016) despite shifts in behavior, mirroring long‐term declines in the abundance of C. subspathacea (β = −0.191, 95% CRI: −0.355 to −0.032). These results have important implications for individual fitness and population viability, where shifts in gosling behavior putatively fail to mitigate long‐term declines in forage availability.

Spatial distribution of band recoveries of black brant

ABSTRACTOn average, band recovery rates of adult black brant (Branta bernicla nigricans) more than doubled between the 2000s and 2010s. However, the spatial distribution of band recoveries of black brant has not been reported. Our objective was to describe the spatial distribution of band recoveries of black brant since 1990. We found that Alaska, California, and Mexico accounted for ≥89% of band recoveries for black brant released from the Arctic and the Tutakoke River Colony in southwestern Alaska, in each decade studied. Although recovery rates increased in each major harvest region from the 1990s to 2010s, increases were not even. For brant released from the Arctic, the recovery rate in Alaska has gone up 7‐fold, whereas the recovery rate in Mexico has increased 1.3‐fold since the 1990s. For brant banded in the Arctic, the increased recovery rates in Alaska resulted largely from a rise in recoveries from the Izembek Lagoon area. For brant banded at the Tutakoke River Colony, the recovery rate in Alaska increased 4.8‐fold, whereas recovery rates in Mexico increased 1.6‐fold. Despite the reduced relative contribution of Mexico to band recoveries in the 2010s, Bahia San Quintin, Mexico, still contributes more recoveries than any other wintering estuary. Because 57–60% of black brant band recoveries occur at the localities of Izembek Lagoon, Alaska; Humboldt Bay, California; and Bahia San Quintin, it is likely that accurate annual estimates of the black brant population using Lincoln's method could be derived from hunter bag checks at these 3 areas. If population managers are interested in managing harvest rates of black brant, they could focus efforts on the main hunting areas we highlight in this paper. Finally, it is unclear if the recent increases in band recovery rates are the result of increased harvest, a declining population, or both; therefore, we suggest refinement of population monitoring programs and continued monitoring of band recovery rates. © 2018 The Wildlife Society.

Declining survival of black brant from subarctic and arctic breeding areas

ABSTRACTSince the mid 1990s, the number of black brant (Branta bernicla nigricans; brant) nests on the Yukon‐Kuskokwim Delta (YKD), Alaska, USA, the historically predominant breeding area of brant, has declined steadily. This has caused researchers and managers to question if arctic breeding populations can compensate for the reduction in brant nests on the YKD. An important component of the assessment of brant population dynamics is having current estimates of first‐year and adult survival. We banded brant at 4 locations in Arctic Alaska and western Canada, and at 1 location in the subarctic, the Tutakoke River (TR) colony on the YKD, 1990–2015. We used joint live and dead mark‐recapture models to estimate first‐year and adult (≥1 yr old) survival of brant. We also used band recovery rates from a Brownie model to assess temporal trends in band recovery rates of adult brant. First‐year survival of brant hatched at TR declined from approximately 0.60 to <0.20 and, although first‐year survival generally was higher for goslings marked in the Arctic, their survival declined from approximately 0.70 in the early 1990s to ≤0.45 in the 2010s. Annual survival of adult females decreased from an average of 0.881 (95% CI = 0.877–0.885) to 0.822 (95% CI = 0.815–0.829) at TR and from 0.851 (95% CI = 0.843–0.860) to 0.821 (95% CI = 0.805–0.836) in the Arctic, from 1990 to 2014. Band recovery rates of adults generally were <1.25% until the last several years of study, when they reached ≤3.5%. Although the current harvest rates may be partially additive to natural mortality, we do not believe that harvest is the main influence on the declines in survival. The general decline in survival rates of brant breeding across a large geographic area may be influenced by a reduction in the quality of migration and wintering ground habitats. We suggest an analysis of seasonal survival of brant to test the hypothesis that declining habitat quality on wintering or spring migration areas is reducing survival. Our results suggest that the number of breeding pairs at TR will continue to decline and also brings into question the ability of arctic breeding populations to grow at a rate necessary to offset the declines on the YKD. Researchers should continue to closely monitor survival and harvest rates of brant, and assess methods currently used to monitor their abundance. © 2017 The Wildlife Society.

Individual heterogeneity in black brant survival and recruitment with implications for harvest dynamics

We examined individual heterogeneity in survival and recruitment of female Pacific black brant (Branta bernicla nigricans) using frailty models adapted to a capture–mark–recapture context. Our main objectives were (1) to quantify levels of heterogeneity and examine factors affecting heterogeneity, and (2) model the effects of individual heterogeneity on harvest dynamics through matrix models. We used 24 years of data on brant marked and recaptured at the Tutakoke River colony, AK. Multievent models were fit as hidden Markov chain using program E-SURGE with an adequate overdispersion coefficient. Annual survival of individuals marked as goslings was heterogeneous among individuals and year specific with about 0.23 difference in survival between “high” (0.73)- and “low” (0.50)-quality individuals at average survival probability. Adult survival (0.85 ± 0.004) was homogeneous and higher than survival of both groups of juveniles. The annual recruitment probability was heterogeneous for brant >1-year-old; 0.56 (±0.21) and 0.31 (±0.03) for high- and low-quality individuals, respectively. Assuming equal clutch sizes for high- and low-quality individuals and that 80% of offspring were in the same quality class as the breeding female resulted in reproductive values about twice as high for high-quality individuals than low-quality individual for a given class of individuals producing differential contributions to population growth among groups. Differences in reproductive values greatly increased when we assumed high-quality individuals had larger clutch sizes. When we assumed that 50% of offspring were in the same quality class as their mothers and clutches were equal, differences in reproductive values between quality classes were greatly reduced or eliminated (breeders [BRs]). We considered several harvest scenarios using the assumption that 80% of offspring were in the same quality class as their mothers. The amount of compensation for harvest mortality declined as the proportion of high-quality individuals in the harvest increased, as differences in clutch sizes between groups decreased and as the proportion of BRs in the harvest increased. Synthesis and applications. Harvest at the same proportional level of the overall population can result in variable responses in population growth rate when heterogeneity is present in a population. λ was <1.0 under every scenario when harvest rates were >10%, and heterogeneity caused as much as +2% difference in growth rates at the highest levels of proportional harvest for low-quality individuals and the greatest differences in qualities between classes of individuals, a critical difference for a population with λ near 1.0 such as the brant. We observed less response in overall survival in the presence of heterogeneity because we did not observe heterogeneity in the annual survival of BRs. This analysis provides a comprehensive view of overall compensation at the population level and also constitutes the first example of a survival-recruitment model with heterogeneity. Individual heterogeneity should be more explicitly considered in harvest management of vertebrates.

Are there trade‐offs between pre‐ and post‐fledging survival in black brent geese?

1. The growth period is an important determinant of fitness later in life through its effects on first-year survival and future reproduction. Choices by adult females about where to rear their offspring strongly affect growth rates and offspring fitness in geese. 2. Individual female black brent (Branta bernicla nigricans) tend to raise their broods in the same areas each year, and these areas are consistently ranked with respect to growth rates of goslings. Therefore, some females consistently rear their broods on areas resulting in lower post-fledging fitness. 3. We explore the potential that growth rates of offspring (and associated fitness consequences) are traded off against other vital rates influencing fitness of either adult females or goslings. Growth of goslings primarily influences fitness after fledging, so one hypothesis is that survival before fledging, which is influenced by predation, is traded off against growth rates and post-fledging survival. 4. We estimated pre-fledging and post-fledging survival for goslings reared on areas used by broods from the Tutakoke River black brent colony. We examined recaptures, recoveries by hunters and resightings of brent marked as goslings with webtags and standard leg rings. These data were analyzed using capture-mark-recapture models in program mark to derive separate estimates of pre- and post-fledging survival for 18 cohorts (1987-2004) of black brent goslings across seven brood rearing areas (BRAs). 5. Estimates of pre-fledging survival probability varied from 0·00 ± 0·00 (mean ± 95% confidence interval) to 0·92 ± 0·1; and estimates of post-fledging survival probability varied from 0·00 ± 0·00 to 1·00 ± 0·08. Substantial variation existed both among BRAs and years but post-fledging survival declined substantially during the study. 6. Pre- and post-fledging survival were positively correlated, exhibiting a quadratic relationship (ß(post-fledging survival) = 1·00 (±0·47)x-0·83 (±0·480)x(2) , where x = pre-fledging survival). Therefore, we did not find a trade-off between pre- and post-fledging survival in black brent goslings across BRAs, suggesting that factors other than foraging conditions and predation on goslings must influence selection of BRAs.

Carry-over effects of winter location contribute to variation in timing of nest initiation and clutch size in Black Brant (Branta bernicla nigricans)

ABSTRACT. We assessed carry-over effects from winter location on timing of nest initiation and clutch size of Black Brant (Branta bernicla nigricans) using observations of individually marked brant breeding at the Tutakoke River colony in Alaska, and wintering along a latitudinal gradient at three areas on the Pacific coast of Baja California: northernmost Bahia San Quintin (BSQ), Laguna Ojo de Liebre (LOL), and southernmost Laguna San Ignacio (LSI). Black Brant initiated nests according to a north—south trend in winter location, although year was a stronger predictor of initiation date than was wintering site. Female Black Brant that wintered at BSQ initiated nests 2.2 days earlier than females from LSI. Conversely, Black Brant showed only a weak south—north trend in clutch size; individuals from LSI laid slightly larger clutches than individuals from BSQ, probably because a smaller proportion of only high-quality females from the southernmost wintering area in Baja California were able to attain the nut...

Carryover Effects Associated with Winter Location Affect Fitness, Social Status, and Population Dynamics in a Long-Distance Migrant

We used observations of individually marked female black brant geese (Branta bernicla nigricans; brant) at three wintering lagoons on the Pacific coast of Baja California-Laguna San Ignacio (LSI), Laguna Ojo de Liebre (LOL), and Bahía San Quintín (BSQ)-and the Tutakoke River breeding colony in Alaska to assess hypotheses about carryover effects on breeding and distribution of individuals among wintering areas. We estimated transition probabilities from wintering locations to breeding and nonbreeding by using multistratum robust-design capture-mark-recapture models. We also examined the effect of breeding on migration to wintering areas to assess the hypothesis that individuals in family groups occupied higher-quality wintering locations. We used 4,538 unique female brant in our analysis of the relationship between winter location and breeding probability. All competitive models of breeding probability contained additive effects of wintering location and the 1997-1998 El Niño-Southern Oscillation (ENSO) event on probability of breeding. Probability of breeding in non-ENSO years was 0.98 ± 0.02, 0.68 ± 0.04, and 0.91 ± 0.11 for females wintering at BSQ, LOL, and LSI, respectively. After the 1997-1998 ENSO event, breeding probability was between 2% (BSQ) and 38% (LOL) lower than in other years. Individuals that bred had the highest probability of migrating the next fall to the wintering area producing the highest probability of breeding.

Differences in growth of Black Brant goslings between a major breeding colony and outlying breeding aggregations

Abstract We compared growth rates of Black Brant (Branta bernicla nigricans) goslings from two dispersed nesting aggregations to those from the large Tutakoke River Colony on the Yukon-Kuskokwim Delta, Alaska during summers, 1999 and 2000. Approximately 20% of the Black Brant population on the Yukon-Kuskokwim Delta, Alaska nests outside of the four major colonies. Dispersal to these outlying breeding locations is hypothesized as a mechanism by which individuals reduce the negative effects of density dependence associated with major colonies. Growth rates of goslings varied among brood rearing areas both associated with dispersed nesting aggregations (n = 4) and associated with the Tutakoke River Colony (n = 7). Mean mass of goslings, adjusted for age, from brood rearing areas associated with dispersed nesting aggregations ranked sixth, eighth, and ninth of nine brood rearing areas sampled in 1999, and sixth and ninth of nine brood rearing areas sampled in 2000. Mean age-adjusted mass of goslings with the ...

Fidelity and breeding probability related to population density and individual quality in black brent geese Branta bernicla nigricans

1. Patterns of temporary emigration (associated with non-breeding) are important components of variation in individual quality. Permanent emigration from the natal area has important implications for both individual fitness and local population dynamics. 2. We estimated both permanent and temporary emigration of black brent geese (Branta bernicla nigricans Lawrence) from the Tutakoke River colony, using observations of marked brent geese on breeding and wintering areas, and recoveries of ringed individuals by hunters. We used the likelihood developed by Lindberg, Kendall, Hines & Anderson 2001 (Combining band recovery data and Pollock's robust design to model temporary and permanent emigration. Biometrics, 57, 273-281) to assess hypotheses and estimate parameters. 3. Temporary emigration (the converse of breeding) varied among age classes up to age 5, and differed between individuals that bred in the previous years vs. those that did not. Consistent with the hypothesis of variation in individual quality, individuals with a higher probability of breeding in one year also had a higher probability of breeding the next year. 4. Natal fidelity of females ranged from 0.70 +/- 0.07-0.96 +/- 0.18 and averaged 0.83. In contrast to Lindberg et al. (1998), we did not detect a relationship between fidelity and local population density. Natal fidelity was negatively correlated with first-year survival, suggesting that competition among individuals of the same age for breeding territories influenced dispersal. Once females nested at the Tutakoke River, colony breeding fidelity was 1.0. 5. Our analyses show substantial variation in individual quality associated with fitness, which other analyses suggest is strongly influenced by early environment. Our analyses also suggest substantial interchange among breeding colonies of brent geese, as first shown by Lindberg et al. (1998).

EFFECTS OF EL NIÑO ON DISTRIBUTION AND REPRODUCTIVE PERFORMANCE OF BLACK BRANT

Climate in low-latitude wintering areas may influence temperate and high-latitude breeding populations of birds, but demonstrations of such relationships have been rare because of difficulties in linking wintering with breeding populations. We used long-term aerial surveys in Mexican wintering areas and breeding areas in Alaska, USA, to assess numbers of Black Brant (Branta bernicla nigricans; hereafter brant) on their principal wintering and breeding area in El Niño and non-El Niño years. We used Pollock's robust design to directly estimate probability of breeding and apparent annual survival of individually marked brant at the Tutakoke River (TR) colony, Alaska, in each year between 1988 and 2001. Fewer brant wintered in Mexico during every El Niño event since 1965. Fewer brant were observed on the principal breeding area following each El Niño since surveys began in 1985. Probability of breeding was negatively related to January sea surface temperature along the subtropical coast of North America during the preceding winter. Between 23% (five-year-olds or older) and 30% (three-year-olds) fewer brant nested in 1998 following the strong El Niño event in the winter of 1997-1998 than in non-El Niño years. This finding is consistent with life history theory, which predicts that longer-lived species preserve adult survival at the expense of reproduction. Oceanographic conditions off Baja California, apparently by their effect on Zostera marina (eelgrass), strongly influence winter distribution of brant geese and their reproduction (but not survival), which in turn affects ecosystem dynamics in Alaska.

Life-History Implications of Large-Scale Spatial Variation in Adult Survival of Black Brant (Branta Bernicla Nigricans)

Abstract We used capture–recapture methods to estimate adult survival rates for adult female Black Brant (Branta bernicla nigricans; hereafter “brant”) from three colonies in Alaska, two on the Yukon-Kuskokwim Delta, and one on Alaska's Arctic coast. Costs of migration and reproductive effort varied among those colonies, enabling us to examine variation in survival in relation to variation in these other variables. We used the Barker model in program MARK to estimate true annual survival for brant from the three colonies. Models allowing for spatial variation in survival were among the most parsimonious models but were indistinguishable from a model with no spatial variation. Point estimates of annual survival were slightly higher for brant from the Arctic (0.90 ± 0.036) than for brant from either Tutakoke River (0.85 ± 0.004) or Kokechik Bay (0.86 ± 0.011). Thus, our survival estimates do not support a hypothesis that the cost of longer migrations or harvest experienced by brant from the Arctic reduced their annual survival relative to brant from the Yukon-Kuskokwim Delta. Spatial variation in survival provides weak support for life-history theory because brant from the region with lower reproductive investment had slightly higher survival.

LIFE-HISTORY IMPLICATIONS OF LARGE-SCALE SPATIAL VARIATION IN ADULT SURVIVAL OF BLACK BRANT (BRANTA BERNICLA NIGRICANS)

Abstract We used capture–recapture methods to estimate adult survival rates for adult female Black Brant (Branta bernicla nigricans; hereafter “brant”) from three colonies in Alaska, two on the Yukon-Kuskokwim Delta, and one on Alaska's Arctic coast. Costs of migration and reproductive effort varied among those colonies, enabling us to examine variation in survival in relation to variation in these other variables. We used the Barker model in program MARK to estimate true annual survival for brant from the three colonies. Models allowing for spatial variation in survival were among the most parsimonious models but were indistinguishable from a model with no spatial variation. Point estimates of annual survival were slightly higher for brant from the Arctic (0.90 ± 0.036) than for brant from either Tutakoke River (0.85 ± 0.004) or Kokechik Bay (0.86 ± 0.011). Thus, our survival estimates do not support a hypothesis that the cost of longer migrations or harvest experienced by brant from the Arctic reduced t...

Age‐specific breeding probability in black brant: effects of population density

SummaryWe estimated age‐specific probability of breeding for black brant (Branta bernicla nigricansLawrence) (hereafter brant) at the Tutakoke River Colony, Alaska, during a series of years in which local breeding density and juvenile mortality both increased. We use these analyses to examine demographic responses to increased population density.Estimates of breeding probability were based on Kendall &amp; Nichols (1995) full‐likelihood modification of Pollock’s (1982) robust design applied to observations of uniquely colour‐banded brant.Breeding probability varied with female age but not across years, indicating lack of response to increased population density. Annual probability of breeding increased from 0·67 ± 0·042 for 2‐year‐old females to 0·90 ± 0·024 for females 5 years old or older.Annual breeding probability of males ≥ 5 years old was 0·78 ± 0·03. Lower breeding probability of males compared to females probably reflects dispersal of males whose mates died.Lower juvenile survival appears to be a general response to increased density in large herbivorous birds and mammals, while changes in adult survival and reproductive investment may be more variable.

Ecological Significance of Brood-Site Fidelity in Black Brant: Spatial, Annual, and Age-Related Variation

-We examined use of brood-rearing sites by female Black Brant (Branta bernicla nigricans) that nested at Tutakoke River, Alaska, 1987 to 1993. Adult females exhibited fidelity to brood-rearing sites; however, we observed site-specific and annual variation in movements among sites. Site fidelity of adults was not related to their hatching date, and hatching dates of females did not vary among brood-rearing sites, suggesting that site selection was unaffected by competition. Movement among sites was affected by distance between sites, but this relationship varied annually and among sites. Variation in forage characteristics may affect movements among sites. Natal-site fidelity was equal to fidelity probability of adults, indicating social inheritance of sites and perhaps facilitation through nepotism. We observed heterogeneity in survival probabilities of goslings and adults among sites. For goslings, heterogeneity in survival was probably related to variation in growth. We observed no relationship between hatching date and use of brood-rearing sites. Previously documented seasonal declines in growth of goslings are more likely affected by declines in forage quality and abundance than by site-specific variation in forage characteristics because use of brood-rearing sites was not related to hatching dates. Received 23 April 1997, accepted 11 November 1997. ENVIRONMENTAL CONDITIONS that precocial young experience before fledging may affect their growth, survival, and future fecundity (Sedinger et al. 1995). The relationship between environment and fitness is particularly evident in northern latitudes where growing seasons are short. Fitness of geese nesting in arctic and subarctic regions is affected by seasonal (Sedinger and Raveling 1986) and spatial variation (Cooch et al. 1993) in forage quality and abundance. Goslings hatching late grow slower (Cooch et al. 1991, Sedinger and Flint 1991, Lindholm et al. 1994) and have lower survival and fecundity than goslings hatching early (Sedinger et al. 1995). Growth of young Lesser Snow Geese (Chen c. caerulescens) and Barnacle Geese (Branta leucopsis) varies among brood-rearing sites (Larsson and Forslund 1991, Cooch et al. 1993). Spatial variation in habitat quality may lead to heterogeneity in survival and subsequent reproductive performance (Cooch et al. 1993, Rockwell et. al. 1993). In addition, fidelity to natal sites may cause genetic-environmental covariance and inflated estimates of heritability I Present address: Institute for Wetland and Waterfowl Research, Ducks Unlimited, Inc., One Waterfowl Way, Memphis, Tennessee 38120, USA. E-mail: mlindberg@ducks.org for growth metrics (Larsson and Forslund 1992). Although the distribution of goslings among brood-rearing sites affects the fitness of these birds, the use of brood-rearing habitats and factors affecting the distribution of birds during brood rearing are poorly described. The distribution of birds among habitats may be influenced by fitness costs and benefits associated with those habitats (Nichols et al. 1983). Birds should occupy the highest quality habitats, but by using these habitats, they may decrease habitat quality. As habitat quality declines, birds should select unoccupied habitats of similar quality as the habitat currently occupied (Fretwell 1972). If all birds occupy habitats of similar suitability, then their distribution may be described as ideal free (Fretwell and Lucas 1970). In an ideal free distribution, all individuals would have similar fitness. The pattern of habitat selection in geese may be particularly complex because geese may initially improve the quality of the habitat through fecal nitrogen deposition, which increases aboveground primary productivity (Hik and Jefferies 1990). Furthermore, movements among habitats may be opposed by competition with conspecifics. Alternatively, advantages of site familiarity may favor fidelity. Ecological advantages of site fidelity and resulting site familiar-

Density-Dependent Effects on Growth, Body Size, and Clutch Size in Black Brant

-We documented gosling size in late summer, adult body size, and clutch size of known-age Black Brant (Branta bernicla nigricans) females nesting on the Tutakoke River colony between 1986 and 1995. During this period, the colony increased from 1,100 to >5,000 nesting pairs. Gosling mass at 30 days of age declined from 764 + SE of 13 g and 723 ? 15 g for males and females, respectively, in the 1986 cohort, to 665 + 18 g and 579 ? 18 g in the 1994 cohort. Gosling size was directly negatively correlated with number of Black Brant broods. We detected no trend in adult body size for individuals from these cohorts; in fact, adults from the 1992 and 1994 cohorts had the largest overall masses. Clutch size increased with age from 3.4 eggs for 2-year-old females to 4.4 eggs for 5-year-old females. Clutch size declined during the study by 0.20 (3-year-old females) to 0.45 (2-year-old females) eggs. Clutch size did not decline between the 1986 and 1990 cohorts for females that were >5 years old. Our results for clutch size and gosling size are similar to those recorded for Lesser Snow Geese (Chen caerulescens caerulescens). Our failure to detect a trend in adult body size, however, differs from the response of other geese to increasing population density. We interpret this difference in effects of density on adult size between Black Brant and other geese as an indication of stronger selection against the smallest individuals in Black Brant relative to other species of geese. Received 19 May 1997, accepted 17 November 1997. ARCTIC-NESTING GEESE are strictly herbivorous during the breeding season (Owen 1980, Sedinger 1992) and are selective of the most nutritious foods and habitats containing these foods (Lieff 1973, Harwood 1975, Sedinger and Raveling 1984, Gadallah and Jefferies 1995a, b). Despite these strong preferences, substantial variation exists in growth rates of goslings, which likely is associated with temporal and spatial variation in habitat quality (Cooch et al. 1991a, Larsson and Forslund 1991, Sedinger and Flint 1991, Aubin et al. 1993). Because gosling growth is associated with future survival and fecundity (Larsson and Forslund 1991, 1992, Francis et al. 1992, Rockwell et al. 1993, Sedinger et al. 1995b), habitat quality likely is directly linked to processes determining population dynamics. Sedinger and Raveling (1986) argued that seasonal declines in nutrient I E-mail: ffjss@aurora.alaska.edu 2 Present Address: Institute for Wetland and Waterfowl Research, Ducks Unlimited Inc., One Waterfowl Way, Memphis, Tennessee 38120, USA. 3Present Address: Alaska Science Center, Division of Biological Resources, U.S. Geological Survey, 1011 East Tudor Road, Anchorage, Alaska 99503, USA. concentration in the diet of Cackling Canada Geese (B. canadensis minima) resulted from reduced availability of the highest-quality foods because of grazing by geese. Lesser Snow Geese (Chen caerulescens caerulescens) substantially reduce the abundance of preferred food plants (Cargill and Jefferies 1984, Hik and Jefferies 1990), as do some Black Brant (B. bernicla nigricans; hereafter brant; Person et al. 1998). The relationship between nutrient intake by goslings and demographic parameters creates the potential for per capita availability of foods of sufficient quality during brood rearing to influence population dynamics. Long-term declines in body size and fecundity have been associated with increased size of a colony of Lesser Snow Geese, and Cooch et al. (1991a, b) and Francis et al. (1992) demonstrated a decline in juvenile survival for this colony over the same period. The number of brant nesting on the YukonKuskokwim (Y-K) Delta declined by more than 60% in the 1970s and early 1980s (Sedinger et al. 1993), likely as a result of human harvest (Sedinger 1996) and predation by arctic foxes (Alopex lagopus; Anthony et al. 1991, Sedinger et al. 1993). Reduced predation and harvest were as-

Ecological Consequences of Nest Site Fidelity in Black Brant

Empirical tests of ecological advantages of site fidelity in birds are few because consequences of dispersal are rarely measured. We examined the relationship between dispersal distance between consecutive nesting attempts and age, nest success, reproductive performance, and spring environment for female Black Brant (Branta hernicla nigricans) nesting colonially at the Tutakoke River, Alaska, 1987-1993. We found little evidence of fidelity to natal sites. Young brant moved towards a peripheral area of the colony. Successfully breeding brant dispersed shorter distances than those failing to nest successfully. Brant that initiated nests early dispersed farther than brant that initiated nests late. Neither nest success nor initiation date in year t + 1 were related to dispersal distance (year t to year t + 1), but clutch size declined with dispersal distance. Although generally not significant, annual variation (interaction) in the relationship between dispersal distance and measures of reproductive performance (i.e., initiation date and clutch size) suggest that this relationship may be influenced by spring weather conditions. Evidence for the advantages of site fidelity in brant was equivocal. Dispersal distance explained little variation associated with reproductive performance. Variation in individual bird quality, environmental conditions, and demographic status may be more important determinants of breeding performance in brant than potential benefits of site fidelity.

Effects of Spring Environment on Nesting Phenology and Clutch Size of Black Brant

We studied the effects of timing of spring snowmelt on nesting phenology, nest site selection, and clutch size of Black Brant (Branta bernicla nigricans) breeding at the Tutakoke River colony, Yukon-Kuskokwim Delta, Alaska. In late springs, brant nested later; however, time between peak arrival at Tutakoke and nest initiation (6 to 12 days) was similar in early and late springs. Nest initiation was more synchronized in late springs than early springs. Height of nests relative to spring meltwater levels was lower in late springs than early springs, indicating that the interval between snowmelt and nest initiation was shorter. Reduced availability of nest sites and increased nesting synchrony in late years may result in greater competition for available nest sites and reduced site fidelity. Clutch size was greater in late springs than in early springs. This increase in clutch size may result from greater accumulation of endogenous reserves on spring staging areas in late springs, or from demographic changes in the breeding population.

Estimating nest site fidelity of adult female black brant with multi-state modeling and geographic information systems

Nest site fidelity of adult female black brant breeding at the Tutakoke River, Alaska was evaluated from 1987 to 1993 by recording nest locations of brant marked (approx. 1500) with individually coded tarsal tags. We used two approaches to study fidelity. First, we examined fidelity to four geographic strata within the Tutakoke River colony. For our second analysis approach, we used ARC/INFO to map and measure distances between successive nesting attempts and then estimated the probability of fidelity to within 200 m of the previous nest site. We used program MSSURVIV to estimate movement probabilities and to test hypotheses about fidelity. Both of our analysis approaches indicate that female black brant exhibit a high (>0.72) probability of fidelity to previous nest sites. Our estimates of fidelity were not biased by the confounding of detection, survival and movement probabilities that have plagued previous studies of fidelity.