Barnacle geese migrate annually from the UK to Svalbard to breed. The birds need energy both to fly to Svalbard and to produce eggs, and they carry much of that energy with them in the form of fat. But fat also tends to accumulate pollutants. Can stored pollutants teach us anything about the geese?
Our project followed the geese on their journey north, investigating their potential energy and pollutant sources. We want to know if feeding at different sites and timing of energy acquisition and allocation also affect how pollutants are taken up and transferred from mothers to eggs.
Travelling to breed
Over 2 500 km of land and ocean separates the summer and winter grounds for barnacle geese. In winter, the birds spend most their time at Solway Firth wetlands on the west coast of the United Kingdom. During late spring, they fly northwards along the Norwegian coast and across the southern Barents Sea to Svalbard. Many of the geese make a pit stop along the Helgeland coast and Vesterålen in northern Norway.
Goose migration varies in terms of when the birds leave their overwintering grounds, which route they take, and how long they spend at the different feeding sites. The timing and route of migration can tell us when and where energy is acquired to produce eggs. From an ecotoxicological perspective, this makes the geese an exciting study species, since we can use pollutants as chemical tracers to track migration and energy source.
A migration of research
From May to June in 2016, we joined the geese on their journey towards the Arctic. A small team of scientists flew from the Netherlands and southern Norway to Svalbard to study some of the goose populations living on island colonies accessible only by boat. We had hoped to arrive at the Svalbard breeding grounds before the geese did, but were beaten to the chase. It was an exceptionally early year for the geese, with most females laying eggs already on the 1st of June, about a week earlier than a decade ago.
The researchers competed with the geese for grass samples along the flyway. Bird watchers equipped with telescopes and notebooks recorded sightings of ringed birds during their stopover in northern Norway. And at the Svalbard breeding grounds, scientists ventured forth onto the breeding island, recorded biological details of the colony, and sampled eggs from the nests.
We brought egg and grass samples back to Tromsø where NILU – Norwegian Institute for Air Research analysed for pollutants, including fat-soluble substances (such as PCB and HCB) and protein-associated chemicals (PFASs and Hg). In grass and eggs we also measured the composition of stable isotopes of carbon and nitrogen to determine where along the flyway geese acquired their energy to produce their eggs. Combining this with our biological data we get a picture of where the geese were travelling, when they were arriving in Svalbard, and if the energy placed into the eggs was also reflected by the pollutants we were detecting.
The chemicals we investigated include persistent organic pollutants (POPs), which contains an organochlorine structure and take decades to break down in the environment. POPs are regulated globally under the Stockholm Convention and mercury (Hg) under the Minamata Convention. Many scientists are interested in how animals are exposed to such pollutants, and what effects they might cause. These chemicals serve as model pollutants in ecotoxicology – we understand much about their chemical properties and association with fats and protein in biological material.
Fortunately for the goose eggs, the levels of these pollutants were quite low. We often report pollutant concentrations on a nanogram per gram basis (ng/g), which is the same as parts per billion. Imagine if everyone on earth wore blue t-shirts, except seven who wore red t-shirts – those seven would be roughly equivalent to 1 ng/g. And that’s the amount of pollutants we detected in the eggs.
Pollutants as carry-on baggage
The stable isotope results suggest that geese acquire a large proportion of their resources towards egg production from southern regions, including the United Kingdom and Norway. However, we cannot rule out additional feeding sites along the coast of Svalbard, closer to the breeding grounds. Even though pollutant concentrations in eggs are low, our preliminary results allow us to track the migration of pollutants within geese from southern up to their breeding grounds in Svalbard.