Survival and brood rearing ecology of emperor geese

Thesis (Ph.D.) University of Alaska Fairbanks, 2000Emperor Geese (Chen canagica) breed on the Yukon-Kuskokwim Delta in an area inhabited by three other goose species. Whereas populations of other geese increased since the mid 1980s, Emperor Goose numbers remained low. Because survival and habitat selection by broods of Emeperor Geese had not been studied previously and numbers of predatory Glaucous Gulls (Larus hyperboreus) had recently increased, I studied brood rearing ecology of Emperor Geese during 1993-1996 to assess whether this seasonal period could be limiting population growth. Survival of goslings to 30 days varied among years from 0.32 to 0.70 and was primarily influenced by mortality during the first five days after hatch. Other goose species with similar rates of gosling survival are increasing rapidly. Survival of Emperor Goose goslings was lowest in 1994, when unusually heavy rainfall occurred during early brood rearing. Using a long-term data set from Izembek National Wildlife Refuge, sizes of families in fall (n=23 years) were related to rainfall during early brood rearing. Gosling survival was lower and gull disturbance of broods greater in 1993-1994 than in 1995-1996. Although goslings wer commonly consumed by Glaucous Gulls, gull diets during 1993 were similar to those observed in the 1970s. Across a broad scale, broods of Emperor Geese (n=56) strongly selected habitats dominated by Carex subspathaceae, Carex ramenskii, and unvegetated areas interspersed among these forage species, as determined from telemetry. These selected habitats comprised one-third of all available habitat. Habitat selection by the composite goose community (dominated by Cackling Canada Geese [Branta canadensis minima]) was assessed by feces collections and differed substantially from that of Emperor Geese. Broods of Emperor Geese spent more time feeding during 1993-1996 than during an earlier study in 1985-1986. During 1994-1996, feeding rates of gosling and adult females was related more to total goose density than to Emperor Goose density. Although Cackling Canada Geese exhibited strongest selection of other habitats, their greater overall abundance resulted in numerical equivalence to Emperor Geese in habitats preferred by Emperor Geese. Interspecific competition for food has impacted behavior in Emperor Geese, which may impact growth and survival of juvenile geese

The Emperor Goose: An Annotated Bibliography

This bibliography contains more than 500 published and unpublished references relevant to the emperor goose (Chen canagica). The referenced works date from the early exploration of Beringia and Alaska through the formal description of the species in 1802 to 1993

The Annual Migration Cycle of Emperor Geese in Western Alaska

Most emperor geese (Chen canagica) nest in a narrow coastal region of the Yukon-Kuskokwim Delta (YKD) in western Alaska, but their winter distribution extends more than 3000 km from Kodiak Island, Alaska, to the Commander Islands, Russia. We marked 53 adult female emperor geese with satellite transmitters on the YKD in 1999, 2002, and 2003 to examine whether chronology of migration or use of seasonal habitats differed among birds that wintered in different regions. Females that migrated relatively short distances (650–1010 km) between the YKD and winter sites on the south side of the Alaska Peninsula bypassed autumn staging areas on the Bering Sea coast of the Alaska Peninsula or used them for shorter periods (mean = 57 days) than birds that made longer migrations (1600–2640 km) to the western Aleutian Islands (mean = 97 days). Alaska Peninsula migrants spent more days at winter sites (mean = 172 days, 95% CI: 129–214 days) than western Aleutian Island migrants (mean = 91 days, 95% CI: 83–99 days). Birds that migrated 930–1610 km to the eastern Aleutian Islands spent intermediate intervals at fall staging (mean = 77 days) and wintering areas (mean = 108 days, 95% CI: 95–119 days). Return dates to the YKD did not differ among birds that wintered in different regions. Coastal staging areas on the Alaska Peninsula may be especially important in autumn to prepare Aleutian migrants physiologically for long-distance migration to winter sites, and in spring to enable emperor geese that migrate different distances to reach comparable levels of condition before nesting.La plupart des oies empereurs (Chen canagica) nichent dans une étroite région côtière du delta Yukon-Kuskokwim (DYK), dans l’ouest de l’Alaska. Cependant, l’hiver, leur répartition hivernale s’étend sur plus de 3000 km, depuis l’île de Kodiak, en Alaska, jusqu’aux îles Commander, en Russie. Nous avons apposé à 53 oies empereurs femelles adultes du DYK des transmetteurs satellites en 1999, 2002 et 2003 dans le but d’examiner si la chronologie de la migration ou l’utilisation des habitats saisonniers différaient chez les oiseaux qui hivernaient dans des régions différentes. Les femelles dont la migration se faisait sur des distances assez courtes (de 650 à 1010 km) entre le DYK et les lieux d’hivernage du côté sud de la péninsule de l’Alaska contournaient les haltes migratoires de la côte de la mer de Béring de la péninsule de l’Alaska ou s’en servaient pendant de plus courtes périodes (moyenne = 57 jours) que les oiseaux dont les migrations étaient plus longues (de 1600 à 2 640 km) vers les îles Aléoutiennes de l’Ouest (moyenne = 97 jours). Les migrants de la péninsule de l’Alaska passaient plus de jours aux lieux d’hivernage (moyenne = 172 jours, 95 % IC : 129–214 jours) que les migrants des îles Aléoutiennes de l’Ouest (moyenne = 91 jours, 95 % IC : 83–99 jours). Les oiseaux dont la migration se faisait de 930 à 1 610 km vers les îles Aléoutiennes de l’Est passaient des intervalles intermédiaires aux haltes migratoires de l’automne (moyenne = 77 jours) et aux aires d’hivernage (moyenne = 108 jours, 95 % IC : 95–119 jours). Les dates de retour au DYK ne différaient pas chez les oiseaux qui hivernaient dans des régions différentes. Les haltes migratoires côtières de la péninsule de l’Alaska pourraient revêtir une importance particulière à l’automne, en ce sens qu’elles permettent aux migrants des Aléoutiennes de se préparer physiologiquement à la migration de longue distance menant aux lieux d’hivernage, et le printemps, elles permettent aux oies empereurs qui migrent sur diverses distances d’atteindre des degrés de condition comparables avant la nidification

Effects of Fish Populations on Pacific Loon (Gavia pacifica) and Yellow-billed Loon (G. adamsii) Lake Occupancy and Chick Production in Northern Alaska

  Predator populations are vulnerable to changes in prey distribution or availability. With warming temperatures, lake ecosystems in the Arctic are predicted to change in terms of hydrologic flow, water levels, and connectivity with other lakes. We surveyed lakes in northern Alaska to understand how shifts in the distribution or availability of fish may affect the occupancy and breeding success of Pacific (Gavia pacifica) and Yellow-billed Loons (G. adamsii). We then modeled the influence of the presence and abundance of five fish species and the physical characteristics of lakes (e.g., hydrologic connectivity) on loon lake occupancy and chick production. The presence of Alaska blackfish (Dallia pectoralis) had a positive influence on Pacific Loon occupancy and chick production, which suggests that small-bodied fish species provide important prey for loon chicks. No characteristics of fish species abundance affected Yellow-billed Loon lake occupancy. Instead, Yellow-billed Loon occupancy was influenced by the physical characteristics of lakes that contribute to persistent fish populations, such as the size of the lake and the proportion of the lake that remained unfrozen over winter. Neither of these variables, however, influenced chick production. The probability of an unoccupied territory becoming occupied in a subsequent year by Yellow-billed Loons was low, and no loon chicks were successfully raised in territories that were previously unoccupied. In contrast, unoccupied territories had a much higher probability of becoming occupied by Pacific Loons, which suggests that Yellow-billed Loons have strict habitat requirements and suitable breeding lakes may be limited. Territories that were occupied had high probabilities of remaining occupied for both loon species.  Les populations de prédateurs sont vulnérables aux changements de répartition ou de disponibilité des proies. En raison du réchauffement des températures, on prévoit que les écosystèmes lacustres de l’Arctique changeront pour ce qui est du régime hydrologique, des niveaux d’eau et de la connectivité avec d’autres lacs. Nous avons examiné des lacs du nord de l’Alaska pour comprendre comment les changements en matière de répartition ou de disponibilité des poissons peuvent avoir des incidences sur le taux d’occupation et sur le succès de reproduction du huart du Pacifique (Gavia pacifica) et du huart à bec blanc (G. adamsii). Ensuite, nous avons modélisé l’influence de la présence et de l’abondance de cinq espèces de poissons de même que les caractéristiques physiques de lacs (comme la connectivité hydrologique) par rapport au taux d’occupation lacustre des huarts et à la production d’oisillons. La présence du dallia (Dallia pectoralis) avait une influence positive sur l’occupation et la production d’oisillons chez le huart du Pacifique, ce qui suggère que les espèces de poissons au petit corps constituent une proie importante pour les oisillons. Aucune caractéristique de l’abondance des espèces de poissons n’a eu d’influence sur l’occupation lacustre du huart à bec blanc. L’occupation du huart à bec blanc a plutôt été influencée par les caractéristiques physiques des lacs qui contribuent aux populations de poissons persistantes, comme la taille du lac et la proportion du lac qui ne gelait pas en hiver. Toutefois, aucune de ces variables n’a exercé d’influence sur la production d’oisillons. La probabilité qu’un territoire inoccupé devienne occupé par le huart au bec blanc au cours d’une année subséquente était faible, et aucun oisillon huart n’a été élevé avec succès dans des territoires d’oisillons anciennement inoccupés. En revanche, les territoires inoccupés avaient une beaucoup plus grande probabilité de devenir occupés par les huarts du Pacifique, ce qui suggère que les huarts à bec blanc ont des exigences strictes en matière d’habitat et que le nombre de lacs convenant à la reproduction risque d’être limité. Les territoires qui étaient occupés avaient de fortes probabilités de rester occupés par les deux espèces de huarts

Using Videography to Quantify Landscape-Level Availability of Habitat for Grazers: An Example with Emperor Geese in Western Alaska

We present a videography approach to estimating large-scale availability of grazing lawns, an important food resource used by broods of emperor geese (Chen canagica) on the Yukon-Kuskokwim Delta, Alaska. Sampling was conducted in 1999, 2003, and 2004 at six locations that encompassed ~40% of the North American population of breeding emperor geese. We conducted ground truthing in 2003 and 2004 to estimate how accurately grazing lawn was classified. Overall, classification accuracy for grazing lawn and non-grazing lawn habitat was greater than 91%. Availability of grazing lawns was stable among years, but varied both among and within locations. Some locations have up to three times as much available grazing lawn, which in combination with densities of geese, likely represents dramatic variation in per capita food availability. Our results suggest that videography is a useful way to sample quickly across a large region and accurately identify fine-scale habitats. We present its use for estimating the availability of a preferred food resource for emperor geese, but the method could be applied to many other cases.Nous présentons une méthode vidéographique pour évaluer, à grande échelle, la disponibilité des pâturages, une importante ressource alimentaire pour les couvées d’oies empereurs (Chen canagica) du delta Yukon-Kuskokwim, en Alaska. Des échantillonnages ont été effectués en 1999, 2003 et 2004 à six emplacements visant environ 40 % de la population nord-américaine d’oies empereurs nicheuses. Nous avons réalisé des vérifications au sol en 2003 et en 2004 dans le but d’estimer dans quelle mesure les pâturages étaient bien classés. Dans l’ensemble, l’exactitude du classement des habitats destinés au pâturage et de ceux qui ne sont pas destinés au pâturage dépassait les 91 %. La disponibilité des pâturages était stable au fil des ans, mais variait d’un emplacement à l’autre et au sein de ceux-ci. Certains emplacements ont trois fois plus de pâturages disponibles que d’autres. Cela, allié aux densités d’oies, représente vraisemblablement des écarts remarquables pour ce qui est de la disponibilité de nourriture par tête. Nos résultats laissent supposer que la vidéographie représente une bonne manière de faire des échantillonnages rapides dans de grandes régions et de repérer avec prévision les habitats à petite échelle. Nous présentons l’emploi de cette méthode pour évaluer la disponibilité d’une source alimentaire préférée de l’oie empereur, méthode qui pourrait être employée dans bien d’autres cas

Interactions among climate, topography and herbivory control greenhouse gas (CO2, CH4 and N2O) fluxes in a subarctic coastal wetland

High-latitude ecosystems are experiencing the most rapid climate changes globally, and in many areas these changes are concurrent with shifts in patterns of herbivory. Individually, climate and herbivory are known to influence biosphere-atmosphere greenhouse gas (GHG) exchange; however, the interactive effects of climate and herbivory in driving GHG fluxes have been poorly quantified, especially in coastal systems that support large populations of migratory waterfowl. We investigated the magnitude and the climatic and physical controls of GHG exchange within the Yukon-Kuskokwim Delta in western Alaska across four distinct vegetation communities formed by herbivory and local microtopography. Net CO2 flux was greatest in the ungrazed Carex meadow community (3.97 ± 0.58 [SE] µmol CO2 m−2 s−1), but CH4 flux was greatest in the grazed community (14.00 ± 6.56 nmol CH4 m−2 s−1). The grazed community is also the only vegetation type where CH4 was a larger contributor than CO2 to overall GHG forcing. We found that vegetation community was an important predictor of CO2 and CH4 exchange, demonstrating that variation in regional gas exchange is best explained when the effect of grazing, determined by the difference between grazed and ungrazed communities, is included. Further, we identified an interaction between temperature and vegetation community, indicating that grazed regions could experience the greatest increases in CH4 emissions with warming. These results suggest that future GHG fluxes could be influenced by both climate and by changes in herbivore population dynamics that expand or contract the vegetation community most responsive to future temperature change

Early Goose Arrival Increases Soil Nitrogen Availability More Than an Advancing Spring in Coastal Western Alaska

An understudied aspect of climate change-induced phenological mismatch is its effect on ecosystem functioning, such as nitrogen (N) cycling. Migratory herbivore arrival time may alter N inputs and plant–herbivore feedbacks, whereas earlier springs are predicted to increase N cycling rates through warmer temperatures. However, the relative importance of these shifts in timing and how they interact to affect N cycling are largely unknown. We conducted a 3-year factorial experiment in coastal western Alaska that simulated different timings of Pacific black brant (Branta bernicla nigricans) arrival (3 weeks early, typical, 3 weeks late, or no-grazing) and the growing season (ca. 3 weeks advanced and ambient) on adsorbed and mobile inorganic (NH4+–N, NO3-–N) and mobile organic N (amino acid) pools. Early grazing increased NH4+–N, NO3-–N, and amino acids by 103%, 119%, and 7%, respectively, whereas late grazing reduced adsorbed NH4+–N and NO3−–N by 16% and 17%, respectively. In comparison, the advanced growing season increased mobile NH4+–N by 26%. The arrival time by geese and the start of the season did not interact to influence soil N availability. While the onset of spring in our system is advancing at twice the rate of migratory goose arrival, earlier goose migration is likely to be more significant than the advances in springs in influencing soil N, although both early goose arrival and advanced springs are likely to increase N availability in the future. This increase in soil N resources can have a lasting impact on plant community composition and productivity in this N-limited ecosystem

Cloud Cover and Delayed Herbivory Relative to Timing of Spring Onset Interact to Dampen Climate Change Impacts on Net Ecosystem Exchange in a Coastal Alaskan Wetland

Rapid warming in northern ecosystems over the past four decades has resulted in earlier spring, increased precipitation, and altered timing of plant–animal interactions, such as herbivory. Advanced spring phenology can lead to longer growing seasons and increased carbon (C) uptake. Greater precipitation coincides with greater cloud cover possibly suppressing photosynthesis. Timing of herbivory relative to spring phenology influences plant biomass. None of these changes are mutually exclusive and their interactions could lead to unexpected consequences for Arctic ecosystem function. We examined the influence of advanced spring phenology, cloud cover, and timing of grazing on C exchange in the Yukon–Kuskokwim Delta of western Alaska for three years. We combined advancement of the growing season using passive-warming open-top chambers (OTC) with controlled timing of goose grazing (early, typical, and late season) and removal of grazing. We also monitored natural variation in incident sunlight to examine the C exchange consequences of these interacting forcings. We monitored net ecosystem exchange of C (NEE) hourly using an autochamber system. Data were used to construct daily light curves for each experimental plot and sunlight data coupled with a clear-sky model was used to quantify daily and seasonal NEE over a range of incident sunlight conditions. Cloudy days resulted in the largest suppression of NEE, reducing C uptake by approximately 2 g C m−2 d−1 regardless of the timing of the season or timing of grazing. Delaying grazing enhanced C uptake by approximately 3 g C m−2 d−1. Advancing spring phenology reduced C uptake by approximately 1.5 g C m−2 d−1, but only when plots were directly warmed by the OTCs; spring advancement did not have a long-term influence on NEE. Consequently, the two strongest drivers of NEE, cloud cover and grazing, can have opposing effects and thus future growing season NEE will depend on the magnitude of change in timing of grazing and incident sunlight