Art courtesy of AnMei Little.
In the coldest depths of winter, many of us spend our hours wishing we could move somewhere warmer. Luckily for them, many species of birds have perfected this process. Birds’ seemingly intrinsic ability to navigate has always left us with more questions than answers, especially now as climate change threatens the migration routes and survival of many avian species. To investigate the formation of migratory patterns across thousands of years, and to demystify the relationship between climate and migration, a research team from the Chinese Academy of Sciences collected migratory data to model the effects of rising global temperatures on migratory strategies in years to come.
The peregrine falcons studied here typically live and breed in the Arctic, but every September they embark on a month-long journey to find solace (and warmth) during the winter. These “wintering locations” are mostly located in tropical or temperate areas. In order to study current migration patterns of these falcons, the team strapped satellite trackers to the backs of forty-one peregrine falcons and sent them on their way, monitoring their locations for an entire year. Birds that were tracked for more than this one-year period returned to the same migratory route year after year, settling in the same location each October. Additionally, it was determined that birds from the same population migrated using similar pathways, but not all peregrine falcons wound up in the same wintering areas. This is referred to as “individual migration”—different populations of peregrine falcons have their own unique migration strategies that depend on a variety of factors. Such behavior offers valuable insight into the influence of seemingly tiny changes in climate on overall migration behavior.
Scott Yanco, an incoming postdoctoral researcher at the Max Planck Yale Center for Biodiversity, Movement, and Global Change, praised the methods that the research team used, citing that the transmitters had a spatial error of only a few meters. “We really know where that bird was,” he said, laughing. “We’re in a golden age for that.”
“One of the big holy grails, at least in my opinion for migration, is: why does it happen? There’s all these different adaptations that organisms show to seasonality, and migration is just one of them,” Yanco said.
Towards this question, the team also studied the intrinsic, genetic component of migration. After studying a wide variety of falcon populations with observably different migration patterns (long versus short migratory paths), it was suggested that the ADCY8 gene had a large effect in directing migration of peregrine falcons. An epigenetic modification actually results in over-expression of the ADCY8 gene in falcons that must travel long distances, leading the research team to believe that the gene is directly related to long-term memory. This indicates that migration is a combination of intrinsic ability to remember pathways and learned behavior from other falcons or previous experience. This is also supported by the fact that the level of expression of the ADCY8 gene correlates with the length of the migratory journey.
Yanco thinks this kind of research touches on a question that has been ever-present in the field of migration. “What they’ve been able to do here,” he said, “that is relatively new and I think very few authors are working on, is the sort of ultimate drivers. Why do it? How does it happen? How does something like this emerge in the first place in deep evolutionary time? How is it maintained?” These questions will propel the field forward to looking at the underlying why in migratory patterns.
The research team then set out to determine the history of migration and how it was impacted by large scale climate changes in history, such as the melting of the ice caps. By modelling historical migration paths, they were able to determine that as the ice caps melted, northern falcon populations decreased due to disruptions to their breeding grounds. Breeding grounds shifted north in order to maintain a similar temperature environment for the falcons, lengthening the falcons’ migratory path. As discussed above, the length that a falcon can travel is at least partially genetically determined, meaning that only birds that were genetically predisposed to remember and travel long distances were likely to survive long journeys. This particularly brutal bout of natural selection resulted in a dramatic decrease in the population of peregrine falcons.
In addition to impacting the duration of the migratory journey, changing temperatures and melting glaciers also impacted the directional orientation of migration routes. During the last Ice Age, or the Last Glacial Maximum, there were many more accessible wintering locations to the west, whereas now, there are a relatively equal number of western and eastern locations.
Both of these changes demonstrate that global climate can have a marked impact on migratory routes and relative survival of the peregrine falcon species, and likely other species of Arctic birds as well. The findings offer a grave perspective on the impact of current rising global temperatures on Arctic avian populations.
Having studied how climate change has impacted migration in the past, as well as migratory routes in the present, the research team then directed their attention towards the future. To study how present-day climate change would impact future survival of the peregrine falcon species, they used ecological niche modelling simulations to predict how rising global temperatures would affect potential breeding grounds and wintering areas.
The results were striking. Some groups of peregrine falcons could lose between ninety and one hundred percent of all suitable breeding grounds, a development that would be devastating to those populations. As a result, populations with short migratory routes would see a decrease in migration distance, eventually reaching the point where they wouldn’t migrate at all, while populations with long migratory journeys would see further increases in distance. Longer migration routes are more closely correlated with mortality, so lengthening an already long and harrowing journey could devastate the population size substantially.
According to data from the team, these shifts have already begun. Retroactive analysis of peregrine populations found that population numbers have been declining for the past twenty-five generations: the future doesn’t look bright for peregrines.
What does this mean for the rest of us? While some might hesitate to understand how a peregrine falcon can represent the world, this work has done nothing if not convey how interconnected our planet is. The same climate changes that impact these falcons will undoubtedly have similarly intricate impacts on our ways of life, especially if no steps are taken to slow rising temperatures in the coming years.
The Chinese team’s study is unique in that it focused heavily on one species, using a wide variety of tools and research methods to create a complete and almost definitive picture of the migration patterns of peregrine falcons.
“One of the cool things in this study was that they integrated approaches that are often quite siloed. And I think that this makes a compelling case for putting together teams that can do that stuff—that you’re looking at things behaviorally, environmentally, ecologically, and [with] molecular tools,” Yanco said. “I mean, I think there’s a broad trend in science, that it’s becoming more interdisciplinary and [with] larger teams. As we reach the limits of what we can infer with any given tool, it becomes important to start expanding out.”
Gu, Z., Pan, S., Lin, Z., Hu, L., Dai, X., Chang, J., … & Zhan, X. (2021). Climate-driven flyway changes and memory-based long-distance migration. Nature, 591(7849), 259-264.