We have just published a new paper in the Journal of Animal Ecology on the causes of declines in puffin populations in the northeast Atlantic. By using innovative technology to study the feeding ecology of puffins, we found that a lack of prey near some major breeding colonies is driving puffin chicks to starve, ultimately leading to population declines.
Puffin populations have been in decline for decades, especially in the northeast Atlantic, e.g. in Norway and southern Iceland. For example, the Norwegian colony of the Røst archipelago, which we included in this study, has declined by over 80% since the 1970s. However, some smaller populations, such as Skomer Island in Wales where my main puffin long-term field study is taking place, seem to be thriving. We wanted to understand which mechanisms are driving poor breeding success in declining puffin populations, in particular relating to food availability.
In a collaboration with colleagues Tycho Anker-Nilssen in Norway and Erpur Hansen in Iceland, we studied and compared the feeding movements and behaviour of four puffin populations with contrasting success: Grimsey and Westman islands in Iceland, Røst in Norway and Skomer Island in Wales. We used miniature GPS trackers weighing only 3g to track for the first time the feeding movements of puffins in these countries. Some of these trackers could automatically upload data onto the base station installed at the colony, so we did not need to catch the birds again to collect data, hereby minimising disturbance to the birds and also maximising our chance of collecting data (the trackers fell off naturally within a couple of weeks).
Left: puffin with GPS tag (photo: T Anker-Nilssen). Right: base station deployed on the colony on Westman Islands in Iceland (photo: A Fayet)
We combined the GPS tracking with automated camera traps near the puffins’ nests. We also collected poop samples from the birds and their chicks and collaborated with my colleague Gemma Clucas to do what is called a DNA metabarcoding analysis of the droppings, which identifies what prey the birds have eaten by sequencing the remains of prey DNA in their faeces. By combining these techniques, we were able to explore where the puffins were feeding, how often they fed their chicks, and what prey they were eating.
Left: collecting puffin poop in Norway (photo: T Anker-Nilssen). Centre: puffin faecal samples in tubes (photo: A Fayet). Right: deploying camera traps in Norway (photo: T Anker-Nilssen)
We found that at the colonies with poor breeding success (Norway and southern Iceland), puffins had to travel much further to find food than at more stable colonies in Wales and northern Iceland. Some of these trips were > 100km long overall, a huge distance for a small puffin. These longer travels required puffins to spend more time in flight, which is energetically costly for them, and caused chicks to be fed less often.
Examples of feeding trips from the four colonies, with a scale for comparison. The red dots indicate points of high speed (i.e. flight) and blue lower speed, when the birds are sitting on the water and are either feeding or resting. Image from the Supplementary Material of the paper. A Fayet.
The camera trap analysis also showed these birds brought back smaller fish loads to their chick, and the diet analysis show their diet was more diverse and less dominated by one preferred lipid-rich prey, which suggest they fed on a lower quality diet. Together, this caused high chick mortality from starvation.
Left: a puffin on the declining colony of Heimaey (southern Iceland) bringing tiny fish larvae back to its chick. Right: A typical fish load on Skomer Island, Wales, a thriving colony. Photos from camera traps, A Fayet.
Together these results indicate that a lack of prey near some puffin colonies in the northeast Atlantic has a major impact on the breeding success of these colonies, ultimately leading to population declines. Climate change is at least partly responsible for this lack of prey, with changes in currents and sea temperatures affecting the abundance and availability of fish that the puffins rely on to rear their chick.
Our study highlights the major impact that climate-driven changes in prey availability can have on seabird populations – here forcing birds to feed much further away than they normally would, and preventing them from feeding their offspring sufficiently, which ultimately causes chick starvation. Many other seabird species in the region feed on similar prey, so the effects we detected in puffins are also likely to occur in other species.
This research was funded by grants from the National Geographic Society, the Royal Society, SWBG Conservation Fund and Sky Ocean Rescue. The paper is freely available here: https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2656.13442