With climate change impacts, many species are forced to alter their behaviour and distributions over time, due to the scarcity of natural resources essential for the population’s survival. In some cases, the abundance of the species less efficient in exploring the resources may decrease, or even lead to their local extinction. This impact has become more evident in the polar, Arctic and Antarctic regions, where the climate has undergone the greatest changes over the last few decades.
For that reason, this study evaluated the distribution and trophic ecology of two guillemot species: the common guillemot Uriaaalge and the Arctic’s Brünnich guillemot Urialomvia. Both species are very similar morphologically, with the Brünnich guillemot reaching a larger size and wingspan, presenting a shorter and thicker bill than the common guillemot. The common guillemot can be found in coastal areas situated at temperate latitudes of the Atlantic and Pacific Oceans, the Brünnich guillemot can be more easily found along the arctic coasts of Europe, Asia and North America. Therefore, Iceland is one of the regions where the distribution of the two species overlaps and understanding how they are adapting to the changing habitat becomes crucial to better predict the future of these species.
For the study, the team used telemetry techniques to obtain GPS data of the habitat used by the species, by monitoring the movement of selected individuals during their foraging. The GPS devices that were placed on the birds had very low weight, to not interfere with normal behaviour. GPS data were recorded for one month, coinciding with the beginning of the nesting season, and then collected when the selected individuals were recaptured. In addition, the team also collected about 1ml of blood to analyse the ratio of stable isotopes of carbon and nitrogen in red blood cells. Through the differences in these ratios, we can have a better perception of the habitat used by individuals, whether more coastal or more pelagic, and about the trophic level occupied, from a producer to a top consumer. The analysis also considered some environmental factors such as water temperature.
From the data, the team found that both species’ abundance varied with the recorded water temperature, decreasing in regions with warmer waters such as southern Iceland. This decrease was particularly evident for the Brünnich guillemot, as their populations have declined since the 1990s. The decrease in abundance of Brünnich guillemot is in line with geographic projections of the species’ niche in response to climate changes. It was also found that populations of Brünnich guillemot moved further to feed in open sea and ocean ice areas in the Arctic region. This behaviour was mainly recorded in the populations of Látrabjarg (Northwest Iceland) where they have access to polar water currents such as the East Greenland Current. These results were also confirmed by the stable carbon isotopes that would differ significantly between both populations. Where access to these areas was difficult, populations of the Brünnich guillemot tend to take refuge in the Icelandic fjords which, due to their preservation of waters with lower temperatures, act as a refuge for this species.
Contrary to expectations, the results of this study did not show any effect between the abundance of common and Brünnich guillemot in relation to the habitats used by both. Regarding their trophic ecology, the isotopic signatures recorded suggest that both species have similar diets. For this reason, the research team concluded that the competition between the two species of arose is similar to intraspecific competition, with environmental conditions being the main limiting factors in their geographical distribution. In short, the impacts of climate change in the Icelandic region will have negative impacts on both species, in particular the Brünnich guillemot.
Bonnet-Lebrun, AS., Larsen, T., Thórarinsson, T.L. et al. Cold comfort: Arctic seabirds find refugia from climate change and potential competition in marginal ice zones and fjords. Ambio 51, 345–354 (2022).
Author: Ricardo Matias