Climate change is changing behavior and habits of a variety of animal and plant life. These are clear signs of global climate change, but until recently many of these behaviors are not well documented for individual animals but rather for whole populations. Scientists from Nelson Mandela University, the Farallon Institute, and Hokkaido University, are now studying seabirds and using their results to demonstrate how this category of birds are individually adapting to climate change.
The effect of climate change on individual seabirds
Balearic shearwaters (Puffinus mauretanicus) are a relatively small population of seabird with a limited breeding area, which allows them to be more easily monitored by scientists to see how climate change is affecting their behavior.
Previous studies have indicated that the timing of natural events, like flowering or migration (phenology), influences the way animal and plant populations are distributed. Numerous studies have looked at how these population groups are shifting their living areas to adapt to new food sources and habitats due to ongoing climate change.[1]
Seabirds in particular have been shown to adjust their range based on predator-prey dynamics as food sources change their range.[2] However, what this recent work does is also focus on not only population-level change but also individual members displaying selective adaptation.
Individual shearwaters are adjusting how far noter they migrate in response to climate change
Shearwaters appear to individually adjust the range of migration by going further north, but also return faster from their migration areas, likely because they are returning to their natural breeding grounds. These changes appear to show that these birds understand the need to migrate further north and compensate the timing of their return based on changes to migration distances.
These birds also develop migration memory that enables spatial cognitive mechanisms that adjusts to the distances needed for travel. This would affect migrations as the timing of when birds return from a given migration is adjusted.[3]
Published in PNAS, this study by Lewin et al. (2024) used long-term geolocators to map the migratory movements of 145 individual birds. Shearwaters were studied in the Balearic Islands of Ibiza and Mallorca, with 274 migrations over a period of ten years tracked. The study found that the seabirds increasingly migrated northward, but not all individuals went as far north and the timing of their returns to the Balearic Islands varied.
For most of the birds, differences in timing of the returns are based on route learning and their migration. In other words, the birds realize that they are migrating further, leading these birds by compensating the more distant travel by returning earlier. However, even if birds leave their northern migration earlier, they still generally return later given the distance needed to travel.
Ocean surface temperatures influence how far north shearwaters migrate
Using linear regression, the researchers show that sea surface temperatures in July and August most affect the range that birds travel. This then influences the timing of returns as birds learn the new route they travel. However, individual flexibility was found as birds time their migrations and distances individually. Using a binomial generalized linear mixed effects model with a logit link function, the researchers show a 1 °C increase in sea surface temperature leads to a 1.79 increase in more northern migration.
Shearwater migration timing indicates spatial and temporal awareness
What is unexpected is the relationship between the speed of outbound migration and return migration do not appear to be related. This indicates different behavior mechanisms might be affecting each of these migrations. Individual flexibility appears to most affect the return migration.
Generally, birds that travel the farthest leave two days earlier than birds that do not travel as far north. This shows temporal as well as spatial awareness for these migratory birds. The island of origin also seems to affect specific populations. Mediterranean Sea shearwater returned on average 9.8 days earlier than Ibizan shearwaters.
Study indicates individual seabirds make adjustments in migration timing based on climatic factors
While this study focused solely on shearwaters, the results are potentially significant for other seabirds. First, it shows that individual as well as group behavior is beginning to be affected by climate change, where birds are adjusting their routes and migration timing. Seabirds generally are well adapted to change, given their spatial and temporal cognition.
Second, it might not be temperature specifically that influences bird migrations, but changes in food availability are probably impacted by sea surface temperature changes. Finally, overall migrations are moving more north as temperatures are increasing. The study also suggests individual as well as larger populations should be studied as individual and populations make phenological decisions on how to best adapt to climate change.
References
[1] For more on changing behavior of seabirds due to climate change, see: J. A. Gill, J. A. Alves, T. G. Gunnarsson. (2019). Mechanisms driving phenological and range change in migratory species. Philos. Trans. R Soc. B Biol. Sci. 374, 20180047.
[2] For more on seabird range change due to predator-prey change, see: Pistorius, P. A., Sydeman, W. J., Watanuki, Y., Thompson, S. A., & Orgeret, F. (2023). Climate change: The ecological backdrop of seabird conservation. In Conservation of Marine Birds (pp. 245–276). Elsevier. https://doi.org/10.1016/B978-0-323-88539-3.00020-0.
[3] For more on individual seabird migrations, see: Lewin, P. J., Wynn, J., Arcos, J. M., Austin, R. E., Blagrove, J., Bond, S., Carrasco, G., Delord, K., Fisher-Reeves, L., García, D., Gillies, N., Guilford, T., Hawkins, I., Jaggers, P., Kirk, C., Louzao, M., Maurice, L., McMinn, M., Micol, T., … Padget, O. (2024). Climate change drives migratory range shift via individual plasticity in shearwaters. Proceedings of the National Academy of Sciences, 121(6), e2312438121. https://doi.org/10.1073/pnas.2312438121.
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Fonte : National Geographic
