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What 5,000-year-old penguin poo can tell us about climate change
Understanding when and why huge breeding colonies of seabirds first arrived on south Atlantic islands could give us clue as to what might happen as climate change gathers pace.
By looking at the record of bird poo preserved for thousands of years researchers are showing how the sudden appearance of such bird colonies lead to a dramatic shift in the vegetation and in turn altered the entire nutrient cycle of an island.
The islands that are scattered throughout the southern Atlantic are globally important nesting sites for millions of sea birds that take advantage of the rich southern oceans full of food.
How long these birds have been taking advantage of these isolated nurseries is not really known, yet could be crucial in figuring out what will happen to these populations as the climate crisis continues to unfold.
But new research is now revealing not only exactly when large colonies of birds showed up on the Falkland Islands, but also showing just how interconnected the marine and terrestrial ecosystems are, and how little we know about the potential impacts of climate change.
It seems the secret is in the poo.
Dr Dulcinea Groff is a postdoctoral researcher at the University of Wyoming who was looking back through a 14,000-year record of life preserved in the peat bogs of the Falklands for her PhD while at the University of Maine.
'Our work emphasizes just how important the nutrients in seabird poo are for the ongoing efforts to restore and conserve their grassland habitats,' explains Dulcinea. 'It also raises the question about where seabirds will go as the climate continues to warm.'
The study has been published in the journal Science Advances.
The southern oceans are rich in food, which in turn fuels millions of breeding seabirds ©David Stanley/Flickr CC BY 2.0
The rich southern seas
The Falkland Islands, found off the eastern coast of southern Argentina are home to internationally important populations of birds, including four species of penguin, great sheerwaters, white-chinned petrels and 70% of the global population of black-browed albatross return every year to breed.
These birds nest amongst a distinctive plant known as tussac grass, which forms one of the most important wildlife habitats on the islands. Growing up to three metres in height, it provides not only shelter but also food for some of these species.
In many places this vital habitat has been damaged, mainly due to overgrazing by sheep.
But new research is showing just how interconnected the tussac grass and the seabirds are. Not only do the birds need the grass to breed, but the grass needs the birds to grow.
Lots of species that breed on the Falkland Islands use the tussac grass to breed, including birds and seals ©Falkland Islands/Flickr CC BY-NC-ND 2.0
By taking a core sample from the island that was over four and half metres long, the team were able to look in astonishing detail at how the plant and bird community has changed over a period of 14,000 years.
The core showed that for the first 9,000 years there was little change, with the plant community dominated by grasses, ferns and small diddle-dee shrubs. But around 5,000 years ago there was a sudden shift.
The team found that the chemical make-up of the soil dramatically changed, with a particular spike in nitrogen. This is thought to be from huge amounts of guano, or bird poo, indicating the sudden appearance of a breeding colony of seabirds.
What is extraordinary is what followed. Within less than 200 years of this bird colony being established, the researchers were able to see a spike in pollen from newly dominant tussac grass, showing that the presence of the birds precipitated this shift in the vegetation.
By around 2,000 years ago there was another alteration in the types and proportion of nutrients in the soil as a result of changes in the bird poo, which could indicate that there was change in which species of birds were breeding there.
There was a second shift in the nutrients, suggesting that there was a change in which seabirds were nesting at the site ©Katie Crafts/Flickr CC BY-NC-ND 2.0
Today, there are no birds breeding in this particular bay of the Falklands, due in part to the grazing of sheep. But this work shows how quickly these fragile habitats can shift as situations change.
It also demonstrates the vital links that connect the oceans and land, feeding in to our growing understanding of how the health of the oceans is intimately linked to the health of the lands.
Where did the birds come from?
The sudden appearance of seabirds breeding on the Falklands around 5,000 years ago corresponds with a cooling of the general climate at that time. This suggests that previously the waters were simply too warm to support such large colonies of birds.
As the climate has now started to warm again, it could be a window on the future of these south Atlantic islands.
Where the birds came from, and so where they may then go as the climate warms, is still not known ©Liam Quinn/Flickr CC BY-SA 2.0
Dr Jacquelyn Gill is an associate professor of paleoecology and plant ecology at the University of Maine and coauthor of the paper.
'As the world warms, our study is a powerful reminder of why we need to understand how different ecosystems are connected,' explains Jacquelyn. 'We know that many seabirds in the South Atlantic rely on these unique coastal grasslands, but it turns out that the grasses also depend on the nutrients seabirds provide.
'Because they rely on ecosystems in the ocean and on land for their survival, seabirds are really good sentinels of global change. We just don't have good long-term monitoring data for most of these species, so we don't know enough about how sensitive they are to climate change.
'The fossil record can help us fill in the gaps.'
But the researchers note that while they know the birds appeared during a cooler period in Earth's history, they do not know where they came from.
This is of concern as temperatures rise, because if that results once more in a shift of these communities we simply have no way of knowing where they might be headed to and so cannot predict which regions will need future protection.
