Many waders breeding in the Arctic tundra regions perform spectacular annual migrations to wintering areas in temperate, subtropical and tropical areas all over the world. In some species, the number of individuals and their distribution are relatively well known, as are the general migration routes and stop-over sites of waders. However, for most species, individuals from different populations cannot be identified. Therefore, the breeding origin of a particular wintering or migrating population is rarely known and the migration patterns of different populations have been difficult to identify, as has the variation in migration strategies between populations.

Intraspecific variation in morphology has been used in some cases as a rough measure to distinguish between populations, but this method has seldom allowed accurate separation below the level of subspecies. However, recent advances in DNA technology have opened up the possibility of identifying the origin of individuals from morphologically similar populations. This may be done by studying mutations in rapidly evolving DNA regions, such as microsatellites or mitochondrial DNA (mtDNA). Another way to differentiate populations may be to use isotope analyses of birds’ feathers. The isotope content of a feather reflects the environment of the bird, through the food that the bird ate at the time when the feather was growing.

During the Tundra Northwest 1999 expedition, we collected information on the occurrence and phenology of a number of wader species at their breeding grounds on the High Arctic tundra regions of North America, as well as during the initial stages of their migration southwards to the wintering grounds in Central and South America. The main focus of the study was on the phenotypic and genetic variation within and between the different populations of each species. Morphological data, chemical analyses of feather composition and studies of the genetic variation will together provide us with a map of existing wader populations and serve as essential background information for tracing the origin of migratory and wintering birds. Genetic analyses will also show the genetic structure of each population, as well as provide information about the population history (bottlenecks, effective population sizes, recent expansions, etc.) and make it possible to estimate the gene flow between the current populations.

The phenological data will be used to investigate the variation between populations in the timing of breeding, migration and moult. The scheduling of these activities is under selection, and hence we can expect the populations to exhibit optimal year cycles. Climatic changes due to anthropomorphic activities on Earth are likely to have most pronounced effects in the Arctic and Antarctic. The breeding conditions are likely to change which will lead to changes in the annual cycles of Arctic breeding waders. We used the geographical variation in breeding conditions to see how it affects the annual cycles of the birds. In order to obtain information of the complete cycle, birds of different breeding origin must be identified and studied at stop-over and wintering sites as well.

So far, only a very limited number of waders have been sampled on their breeding grounds and not much is known about their population structure. During the 1994 Russian-Swedish Tundra Ecology Expedition, we collected information and samples from different populations of waders breeding on the Palearctic tundra. Samples from the Nearctic tundra will now provide a more complete picture of the Holarctic breeding species. The data from the breeding areas will also be compared to similar data collected at various locations along the migratory routes, and we hope that this will provide a better understanding of the migratory behaviour of wader populations.

In addition, we are also interested in the significance of the wax that the waders put on their feathers. A recent study indicates that the content of the feather wax may change during the year, and that it has a unique composition in the spring. It has been suggested that it is used as an equivalent to ’make up’, and thus is of importance for mate attraction during the breeding season. We collected samples of feather wax from the birds for analyses of its chemical composition to investigate this question further.

Field and laboratory methods

In the field, the waders were trapped on their nests with nest cages, and at roosting or feeding places with mist-nets or walk-in traps. The birds were ringed with numbered metal rings, white flags on the left tibia indicating their Canadian origin, and colour ring combinations unique for each site. Several morphological characters were measured and the extent of moult was investigated. Three kinds of samples were taken: preen gland wax and feather samples for chemical analyses, and small blood samples (<50 ml) for genetic analysis.

The timing of the breeding season was measured in the following way: the breeding stage of each clutch of eggs was determined by measuring the density of eggs (measured indirectly by their floating capacity in water). The age of the chicks was determined by weighing them and by scoring the extent of downy feathers.

In this way, a very valuable set of morphological, phenological and genetic data from a number of populations of various waders species has been collected from places from which very little information has been available before.

After the expedition, feather samples of waders from different populations are being analysed for their C12/C13 and N14/N15 content and the chemical constitution of the preen gland wax is being analysed by GCMS, and the genetic variation is being studied by sequencing mitochondrial DNA.

Preliminary results

In total, 17 species of waders were found during the expedition, all of them occurring at more than one site. All of these wader species were breeding in the region and for 13 species the nests or non-fledged chicks were found. Altogether, 310 waders were caught, 42 adults and 268 juveniles.

We found 30 broods with eggs or young still dependent on their parents. The overall picture, including all species, is that a greater proportion of western broods are later than eastern ones (r=0.42, P0.05, N=30). However, the result can still be due to a latitudinal effect but with the picture disrupted by the data from the southerly situated King William Island (69°N, 114°W) which is known for its harsh climate, as witnessed by historic expeditions which have often encountered trouble in the area (e.g. the Franklin and Amundsen expeditions) .

Genetic analyses of mitochondrial DNA of the white-rumped sandpiper, Calidris fuscicollis, show that, as is the case in most other wader species, genetic variation within the species is relatively low. The average sequence divergence between individuals is about 0.4%. This is less than in ruddy turnstone Arenaria interpres (0.9%) and dunlin Calidris alpina (2.0%), but more than in red knot Calidris canutus (0.39%). As in the red knot and the ruddy turnstone, there is extensive gene flow between populations, and most of the genetic variation of white-rumped sandpipers occurs within the populations.