Dark-bellied Brent Geese Branta bernicla bernicla, as recorded by satellite telemetry, do not minimize flight distance during spring migration

Nine Dark-bellied Brent Geese Branta bernicla bernicla were equipped with satellite transmitters during spring staging in the Dutch Wadden Sea in 1998 and 1999. The transmitters (in all cases less than 3% of body mass) were attached to the back by a flexible elastic harness. One juvenile female was tracked to the Yamal peninsula in 1998. Eight adult males were selected from a single catch of 75 to span the range of body mass observed on the date of capture (11 May 1999) and all but the lightest individual completed the first lap of the migratory flight to the White Sea, Russia, according to the time schedule normal for this species. Six birds were successfully tracked to Taymyr for a total distance averaging 5004 km (range 4577-5164) but judging from later movements none bred (although 1999 was breeding year). Although the routes chosen during spring migration were closely similar; none of the tagged birds migrated together. On average the geese used 16 flights to reach their summer destinations on Taymyr. The longest uninterrupted flights during the first half of the journey (Wadden Sea to Kanin) covered 1056 km (mean of seven adult males, range 768-1331), while the corresponding value for the second half of the migration (Kanin-Taymyr) was only 555 km (mean of six adult males). Only 7% of total time during spring migration was spent in active flight, as contrasted to c. 80% at long-term stopovers. Overall average travelling speed was 118 km/day (range 97-148). Including fattening prior to departure the rate of travel falls to 62 km/day (range 49-70), in keeping with theoretical predictions. Routes followed deviated from the great circle route, adding at least 700 km (16%) to the journey from Wadden Sea to Taymyr, and we conclude that the coastal route is chosen to facilitate feeding, drinking and resting en route instead of minimizing total flight distance

Population development and breeding success of Dark-bellied Brent Geese Branta b. bernicla from 1991-2011

The Dark-bellied Brent Goose Branta bernicla bernicla is the largest of the six Brent Goose populations, which collectively number around 600,000 birds globally. After a major decline to 16,500 geese in 1958, numbers recovered during the 1970s and 1980s to a peak of c. 330,000 individuals between 1992 and 1994. From 1994 onwards the population declined again to 200,000–250,000. This decline has been attributed to poor breeding, associated with faltering cycles of Siberian Brown Lemming Lemmus sibiricus (predominantly) and Palearctic Collared Lemming Dicrostonyx torquatus abundance on the breeding grounds on the Taimyr Peninsula, where lemmings are a main food resource for potential predators of goslings. Darkbellied Brent Geese only breed well in peak lemming years (Summers & Underhill 1991), and this usually occurs every three years, but the frequent failure since 1994 of lemming numbers to peak (except in 2005) has resulted in the absence of very good breeding years for the geese (Nolet et al. 2013). The mid-winter distribution has shown a marked shift towards France over the last decade. France currently supports 50% of the population in January, Great Britain 35–40%, the Netherlands 15–20%, and Germany and Denmark 2%. In spring, almost the entire population gathers in the Wadden Sea, leaving only 4% of the population in Great Britain, and virtually none in France, with the Dutch part of the Wadden Sea supporting 40–45%, the German section 45–50% and Denmark 6%

Contrasting consequences of climate change for migratory geese:Predation, density dependence and carryover effects offset benefits of high-arctic warming

Climate change is most rapid in the Arctic, posing both benefits and challenges for migratory herbivores. However, population-dynamic responses to climate change are generally difficult to predict, due to concurrent changes in other trophic levels. Migratory species are also exposed to contrasting climate trends and density regimes over the annual cycle. Thus, determining how climate change impacts their population dynamics requires an understanding of how weather directly or indirectly (through trophic interactions and carryover effects) affects reproduction and survival across migratory stages, while accounting for density dependence. Here, we analyse the overall implications of climate change for a local non-hunted population of high-arctic Svalbard barnacle geese, Branta leucopsis, using 28 years of individual-based data. By identifying the main drivers of reproductive stages (egg production, hatching and fledging) and age-specific survival rates, we quantify their impact on population growth. Recent climate change in Svalbard enhanced egg production and hatching success through positive effects of advanced spring onset (snow melt) and warmer summers (i.e. earlier vegetation green-up) respectively. Contrastingly, there was a strong temporal decline in fledging probability due to increased local abundance of the Arctic fox, the main predator. While weather during the non-breeding season influenced geese through a positive effect of temperature (UK wintering grounds) on adult survival and a positive carryover effect of rainfall (spring stopover site in Norway) on egg production, these covariates showed no temporal trends. However, density-dependent effects occurred throughout the annual cycle, and the steadily increasing total flyway population size caused negative trends in overwinter survival and carryover effects on egg production. The combination of density-dependent processes and direct and indirect climate change effects across life history stages appeared to stabilize local population size. Our study emphasizes the need for holistic approaches when studying population-dynamic responses to global change in migratory species.</p

Breeding in a den of thieves : Pros and cons of nesting close to egg predators

Breeding success of many Arctic-breeding bird populations varies with lemming cycles due to prey switching behavior of generalist predators. Several bird species breed on islands to escape from generalist predators like Arctic fox Vulpes lagopus, but little is known about how these species interact. We studied brent geese Branta bernicla bernicla that share islands with gulls (Larus spec.) in Taimyr, Siberia (Russia). On one hand, gulls are egg predators, which occasionally steal an egg when incubating geese leave the nest for foraging bouts. On the other hand, gulls import marine resources to the islands, enriching the soil with their guano. We considered three hypotheses regarding clutch size of brent geese after partial nest predation. According to the "predator proximity hypothesis", clutch size is expected to be smallest close to gulls, because of enhanced predator exposure. Conversely, clutch size is expected to be largest close to gulls, because of the supposedly better feeding conditions close to gulls, which might reduce nest recess times of geese and hence egg predation risk ("guano hypothesis"). Furthermore, gulls may defend their nesting territory, and thus nearby goose nests might benefit from this protection against other gulls ("nest association hypothesis"). We mapped goose and gull nests toward the end of the goose incubation period. In accordance with the latter two hypotheses, goose clutch size decreased with distance to the nearest gull nest in all but the lemming peak year. In the lemming peak year, clutch size was consistently high, indicating that partial nest predation was nearly absent. By mapping food quantity and quality, we found that nitrogen availability was indeed higher closer to gull nests, reflecting guanofication. Unlike predicted by the nest association hypothesis, a predation pressure experiment revealed that egg predation rate decreased with distance to the focal gull nests. We therefore propose that higher food availability close to gulls enables female geese to reduce nest recess time, limiting egg predation by gulls.</p