Sanderling Project ~ Background
Current research at the University of Groningen (Netherlands), in close collaboration with the Royal Netherlands Institute for Sea Research (NIOZ) and the Centre for African Wetlands (Ghana), under the umbrella of the Global Flyway Network focuses on four main themes:
(1) Costs and benefits for sanderlings that spend their non-breeding period at different latitudes
By colour-ringing sanderlings and putting a lot of effort in resighting the individual birds, we aim to estimate survival probabilities of sanderlings in the Netherlands, Mauritania and Ghana. The research on survival is combined with ecological studies to understand possible differences in survival chances, such as predation risk (number of falcons), food availability and the likelihood that sanderlings get ill or have to invest in a costly immune defense.
(2) Contrasting investments in reproduction
Sanderlings have an interesting, but poorly understood, breeding system. Some females lay two clutches of four eggs of which the first is incubated by the male and the second by herself. The advantage of this breeding system is a possible larger number of young within that year, but the draw-back is that the parents have to work very hard to incubate a clutch by themselves. After all, they only have limited time to leave the nests to find food because the eggs cool down rapidly in the absence of a partner that can take over the incubation duties. The research focuses on what drives the differences in reproductive investment between pairs. Is it mainly influenced by the circumstances in the High Arctic, such as annual variation in snow, temperature, prey availability and/or predator abundance, or do conditions in the wintering grounds (disease, food availability etc) and during the northward migration (wind direction & force, feeding conditions etc) play a role as well?
(3) Migration: timing and routes
The migratory journeys that sanderlings undertake twice a year belong to the longest known in the avian world. The length of the flights, the number and duration of stops between flights, as well the timing of the journeys will depend on the latitude of the non-breeding area and probably also that of the breeding area. Yearly variation in the circumstances during migration (both natural and caused by human) will further influence the success of the migratory flight and might thereby selectively favour sanderlings that winter closer or further away from the breeding area through their survival (see 1), as well as through reproductive output (see 2).For long it has been suggested that sanderlings from Greenland and NE Canada mix with sanderlings breeding on the Taimyr Peninsula in Siberia during the non-breeding period. However, the evidence for Siberian sanderlings wintering in W Europe and/or W Africa is very poor. With our colour-ring scheme we hope to get a better view on the apparent mixing of both breeding populations.
(4) Monitoring sanderling populations by colour-ringing
Due to the worldwide scattered occurrence of sanderlings on many beaches, sanderlings are particularly difficult to monitor. Also during migration periods, the birds are hard to count and peak numbers counted on important stopover sites do not accurately represent the real numbers passing through due to asynchronous arrival and departures at those locations (high turn-over).The size of the sanderling flyway populations are influenced by the survival and reproduction of the birds. Survival probabilities can be measured by marking sanderlings with colour-rings and observing how many of the marked birds have survived until a next time step (a year, a season, or even a day). The annual reproductive output can be measured by the fraction of young birds in a population, which can be determined in the field and by catching sanderlings.
More counts of sanderlings in more different areas and in additional times of the year are needed.
