Getting fat in Alaska – how migratory shorebirds prepare for trans-global flights1 August 2005 - 15 October 2005
The Arctic summer offers huge and highly productive areas for reproducing shorebirds. However, the summers are short and the breeding areas are far away from suitable wintering grounds at temperate and tropical latitudes. The birds are therefore forced to make long, rapid and demanding flights each year back and forth from the Arctic. The aim of our project was to investigate how the birds in the Arctic prepare for such long migrations and to find out which routes they take.
The Bering Strait region is at the crossroads of multitudes of migratory flyways of tundra-breeding shorebirds, from the Taymyr Peninsula in the west to central Canada in the east. There is probably no place in the world where so many exciting migratory phenomena co-occur in a relatively small region. We focussed our work on two shorebird species: the Sharp-tailed Sandpiper Calidris acuminata and the Bar-tailed Godwit Limosa lapponica baueri. Preliminary work had indicated that both species might have an extraordinary migration ecology.
The Bar-tailed Godwits breed on the tundra in western Alaska. In late summer they congregate on the rich mudflats along the Alaskan shorelines (Gill and Handel, 1990), where they put on large amounts of fat fuel. Circumstantial evidence strongly suggests that in September the birds make an 11,000 km long non-stop trans-oceanic flight down to the wintering grounds in New Zealand (Piersma and Gill, 1998, Gill et al., 2005). We aimed at studying the birds’ preparation for the long jump, by sampling the food abundance on the coastal mudflats and by making behavioural observations of the birds. By putting radio transmitters on birds we planned to follow in detail both the departure from Alaska and the arrival in New Zealand, to seek direct evidence for the trans-oceanic flights.
Juvenile Sharp-tailed Sandpipers (also known as ”Sharpies”) arrive in Alaska in early September from breeding grounds in northeast Russia. They stay in Alaska for about a month to put on fuel for further migration towards wintering grounds in Australia. In contrast adult birds almost never migrate to Alaska, but rather fly a more direct route due south to Australia. Why do the juveniles make this long detour over Alaska? What do they eat and how much fuel do they put on? Do they also go for long trans-oceanic flights (as do the godwits)?
Other shorebird species were also studied, either for comparison with the godwits and Sharpies, or to be included in comparative analysis of genetic variation in arctic shorebirds.
Important preparatory fieldwork in Alaska started as early as June. The main work was carried out between 20 August and 26 September 2005 in two areas of southwest Alaska: the Yukon Delta National Wildlife Refuge (YDNWR) and Egegik Bay on the Alaska Peninsula (figure). Field operations did not terminate completely until late October. The project was not represented on the icebreaker Oden.
Most of the work in the YDNWR took place at the Tutakoke River Field Camp, a tent camp situated on the coast about 500 m from the shoreline. In periods of severe tidal flooding (see below) we also worked at the Kanaryarmiut Field Station about 25 km eastnortheast of Tutakoke. One person also stayed for two weeks at Tern Mountain, an observation camp about 100 km south of Tutakoke. At Egegik, a known staging site for Bar-tailed Godwits, the scientists stayed in a small wooden hutclose to a tidal lagoon, and most work was carried out in the immediate surroundings.
All transports of people and supply within the YDNWR were carried out using either float-planes or small boats with outboard engines. The float-planes belong to the US Fish and Wildlife Service (USFWS), the governmental body responsible for the management of the refuge, and therefore also our main collaborator in the YDNWR.
A large number of methods and techniques were used in the field. A major sampling scheme was launched to investigate the food base for the godwits (mud samples). The potential food for Sharptailed Sandpipers was collected more opportunistically, based on cues from feeding birds. Hundreds of hours were also spent looking for marked birds and collecting detailed data on feeding behaviour.
Birds were trapped in various kinds of nets and traps. Trapped birds were weighed, measured and ringed with plastic colour rings to enable recognition in the field. We also collected blood and small pieces of feather on some birds for various types of analyses. A number of Bar-tailed Godwits and Sharpies were supplied with radiotransmitters and their movements were followed locally, using hand-held receivers, automatic tracking stations and aerial surveys. A few godwits were also supplied with transmitters to be tracked by satellite. A large amount of work analysing blood and feathers for DNA and stable isotopes still remains to be completed in the lab.
Birds of this species are among the most difficult birds in the world to trap. Despite bringing together an experienced team from literally all over the world, a combination of bad luck and extremely bad weather throughout the whole study period resulted in no birds being caught during the postbreeding period. This was a major disappointment for us all. Having trapping difficulties in mind, however, we had already marked five birds with satellite transmitters during the breeding season. In line with our bad luck in the field, all five transmitters stopped working before the birds had left Alaska. A small light in the darkness was that one of the five birds was later seen in New Zealand, proving that the birds can make the flight carrying this kind of transmitter. We will try again! Four more birds were supplied with conventional radio transmitters during the breeding season, allowing tracking while still within Alaska. Whether any of these later were picked up in New Zealand remains to be seen.
The other parts of the godwit work went very well. Thousands of mud samples were collected on the tidal shores both in the YDNWR and at Egegik. The preliminary view is that the Alaskan tidal flats have among the highest densities of evertebrates recorded in this kind of habitat anywhere in the world. About 30 godwits colour-ringed by colleagues in New Zealand and Australia were identified through telescopes, shedding new information about the migration patterns of the birds. Observations of feeding birds, combined with information from food sampling, revealed that juvenile (birds born the same year) and adult godwits were spatially segregated both on a large and small scale. Certain areas – such as the ones around Tutakoke and at Egegik – were primarily used by young birds, while the Tern Mountain mudflats held large concentrations of adults. At a local scale, young birds often fed in sub-optimal areas and then with low intake rates. Adults chose the best areas and accordingly had the highest feeding rates. This inability of juveniles may explain why it takes juveniles more time (about a month longer) to fatten up prior to the long flight and why survival is low during the godwits’ first year of life. The foraging studies also revealed that prey choice differed between study sites, in a seemingly opportunistic pattern, with the most available prey being preferred.
Juvenile Sharpies started to appear in good numbers around 1 September. They are much easier to trap than godwits, and 228 birds were trapped from 1–26 September. From the birds in the hand we got information about size and body mass. Birds will be sexed molecularly (from sampled blood) which will allow us to draw detailed conclusions about sex-specific patterns of behaviour. Overall, the birds roughly doubled their body mass over the study period, with a fuelling rate that was ten times higher in the second compared to the first half of September (photo 1).
To follow the birds’ local movements we supplied 30 birds with radio transmitters. All survey data together indicated that the Sharpies were relatively site-faithful, with the majority of birds staying for a prolonged period of time until early October, when the major exodus apparently started. It seems clear from our preliminary data and observations in the field that varying parts of the diet of the Sharpies consist of seeds and invertebrates. The fact that seeds make up a considerable part of a shorebird’s diet during migratory fattening is very unusual. We strongly believe that the seeds play an important role in the explanation as to why the juvenile Sharpies make this long detour via Alaska during their first autumn migration, but this remains to be properly evaluated.
Smoke, storm, rain and floods
The weather in southwest Alaska during our stay in August–September was straight out bad by almost any standards. Smoke from extensive forest fires in August covered the tundra for weeks. A more or less continuous row of lows brought strong wind and rain to an extent that we did not think was possible. Sunny calm days were simply in very short supply. This of course complicated our research efforts and was one reason why the godwit catching failed. Suitable days for mistnetting, the only possible trapping method for godwits, were very few. Two flooding events in August and early September also forced us to evacuate the Tutakoke camp for a few days each time.
As if the Arctic wanted to set an example, our stay ended somewhat prematurely because of a severe storm in late September. It coincided with the month ’s highest tides, which resulted in the sea rising to a level of 1.5 m above the coastal tundra, covering hundreds of km² of land. The accompanying waves swept our whole coastal camp away (and all the gear inside). Luckily we had then already evacuated the people and the most precious samples to higher grounds at Kanaryarmiut Field Station where we could ride out the storm in safety (photo 2).
Despite being smoked, rained at, blown away and flooded out, our Alaskan experience was great. We look upon our field season as being overall very successful.
We are most grateful to Mike Rearden and his personnel at the USFWS in Bethel for their superb logistic and moral support during the expedition. Additional support was kindly provided by the US Geological Survey, Alaska Science Center, Anchorage. Several people helped in the field, including Sarah Jamieson, Jesse Conklin, Patrick Lemons, Lee Tibbitts, Nils Warnock, Alexandra Hoffmann, Dan Ruthrauff, Marnie Shepherd, David Melville, Dick Veitch and Adrian Riegen. The co-operation regarding radio tracking with Phil Battley and Martin Wikelski is warmly acknowledged.
- The Dutch Science Foundation
- Stiftelsen Ymer-80
- Kungl. Fysiografiska Sällskapet in Lund
- Gill, R.E. and Handel, C.M. 1990. The importance of subarctic intertidal habitats to shorebirds: a study of the central Yukon-Kuskowim Delta, Alaska. Condor 92, 709–725.
- Gill, R.E. Jr, Piersma, T., Hufford, G., Servranckx, R. and Riegen, A. 2005. Crossing the ultimate ecological barrier: evidence for an 11,000-km long nonstop flight from Alaska to New Zealand and eastern Australia by Bartailed Godwits. Condor 107, 1–20.
- Piersma, T. and Gill, R.E., Jr. 1998. Guts don’t fly: Small digestive organs in obese Bar-tailed Godwits. Auk 115, 196–203.