Náttúra og náttúrutilfeingi
Nýtsla av skúgvaeggum til umhvørviseftiransing í broytingartíðum.
(Using great skua eggs to monitor the changing environment)
University of Glasgow og Umhvørvisstovan
Ruedi Nager og Maria Dam, vegleiðarar
Stuðul úr Granskingargrunninum:
With the increasing empirical evidence for environmental change, the science of understanding wild animals as monitors of environmental change has become vital. However, environmental change can affect many different biological traits which will differ in their sensitivity of environmental variability (Einoder 2009). For birds, various egg parameters have emerged as particularly useful measures of impacts of environmental change. To better understand egg parameters such as size, color and pattern as a tool to assess the marine environment we need to better understand the environmental factors responsible for the variation. Food availability is the most likely explanation for changes in egg size, and this will be experimentally tested using supplementary feeding (Ratcliffe 1999; Blight 2011).
The project aimed to disentangle some of the relationships between the diet, breeding performance and pollution of great skuas in the Faroe Islands. Some research has suggested that dietary specialisation increases breeding performance as the individuals which feed mostly on seabirds tend to lay larger eggs, and lay earlier. Generally such parameters are interpreted as distinguishing individual breeding performance, as early laid and large eggs tend to have a higher success rate. Since some recent research had suggested that there are long term declines in egg sizes in some seabirds, and that this was likely due to changes in food availability, I aimed to investigate if the noted decline in great skua eggs over the past 4 decades possibly also could be food related. For this I designed a supplementary feeding experiment to see if an additional food source would influence the egg sizes. While the absolute size of the eggs didn’t increase, I found a significantly smaller difference between the eggs of the females which had been supplementary fed. This could suggest that while the first laid egg is close to an optimal size, perhaps the size of the second egg shows greater indication of female lack of available nutrients.
Considering that egg sizes can be an indication of food availbility, I set out to study all great skua egg measurements available and eggs from other seabirds in the Faroe Islands. A combination of field measurements and museum egg collections I build up a database of nearly 9000 egg measurements. One interesting finding was that there were significant spatial differences of egg sizes with the largest eggs furthest North, and the smallest ones furthest South. There was also significant temporal variation both in the Faroes and Shetland, but no temporal trends were found for Icelandic great skuas. This is the first study to look at a long term trends (nearly 200 years) and wide geographic scale of egg sizes, and I’m confident that this may become an area of further scientific interest.
In relation to pollution, my study shows that great skuas in the Faroes have higher concentrations of pollutants relative to great skuas in Shetland. Since organic pollutants accumulate up the food chain, it follows the prediction since it is clear from our and other research that great skuas in the Faroes feed higher trophically than great skuas in Shetland. Also can my study and recent publication (see below) illustrate that marine plastic exposure differs between individuals depending on which seabirds they feed on. So overall my study has shown some how some diet related aspects influence breeding performance and pollutant exposure.
Scientific articles, books, thesis etc.
Hammer, S., Nager, R. G., Johnson, P. C. D., Furness, R. W. & Provencher, J. F. Plastic debris in great skua (Stercorarius skua) pellets corresponds to seabird prey species. Mar. Pollut. Bull. (2016). doi:10.1016/j.marpolbul.2015.12.018
Hammer, S. (2016) Feeding ecology and pollutant exposure of the great skua (Stercorarius skua) in the Faroe Islands, PhD-thesis, University of Glasgow
Presentation: World Seabird Conference, Cape Town 2015: Long term and large scale variation in great skua egg sizes.
Poster presentation: World Seabird Conference, Cape Town 2015: Dietary specialisation and egg production of in great skuas in the Faroe Islands
Other results, such as unpublished articles, patents, computer systems, original models and new procedures
Hammer, S., Nager, R. G., Alonso, S., McGill, R. A. R., Furness, R. W., Dam, M. (in review) Legacy pollutants are declining in great skuas (Stercorarius skua) but remain higher in Faroe Islands than in Scotland. Bulletin of Environmental Contamination and Toxicology
Blog post for Naturally Speaking: Research on marine plastic is revealing its spread up the food chain https://naturallyspeakingpodcast.wordpress.com/2015/01/19/research-on-marine-plastics-is-revealing-its-spread-up-the-food-chain/
Publications outside the scientific community, i.e. lectures, periodicals, articles in newspapers, television and radio
Vitan (KVF) – Kári Sólstein http://kvf.fo/netvarp/uv/2015/10/20/vitan-homo-naledi-jhannes-doyparin-og-eggjastd#.VwFK46QrLIU