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Migratory Bird Study Could Identify Species Most at Risk From Climate Change

Birds flying in a distant V formation over large hills
Credit: DICSON / Unsplash.
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In a new study of more than 600 bird species, researchers have identified the different strategies that migratory birds use to track their preferred climatic conditions – also called their environmental "niche" – as the seasons change.

According to the study, published in the journal Global Ecology and Biogeography, traits such as a bird’s size and diet can predict which species are likely to frequently seek out newer climates, and which can withstand more extreme conditions.

As climate change pushes many species into conditions that they have not experienced before, the researchers say their work could also help scientists understand how animal populations are coping with climate change.

Niche tracking, explained

An animal’s niche refers to the physical environment where it lives – whether it is tree-dwelling or prefers arid regions, for example – as well as the temperature and climate in which it thrives. For many species, the changing of the seasons can make their current niche uncomfortably cold, which is why migrating birds will begin to fly south for the winter.

As these birds migrate, they will travel to new locations that match up with their preferred environmental niche. This so-called niche tracking behavior – how birds seek out the same weather conditions all year long – is now the subject of a new study by researchers at Yale University.

“We found that some migratory species can track temperature or rainfall throughout the year, going out of their way to experience the same weather all year long, while others experience strong variation in seasonal conditions throughout the year,” said Dr. Jeremy Cohen a postdoctoral associate and ecologist at Yale.

Working with Walter Jetz, a professor of ecology and evolutionary biology at Yale, Cohen was able to analyze a large volume of animal records and satellite weather data to determine how different bird species react to the change of the seasons. Similar studies have been done previously that worked with average temperature assessments, but in this study, the Yale team also decided to factor in measurements of weather variability to get a better idea of how circumstances were changing as the months rolled on.

“For the first time, we can determine which species require strict consistency in both the average and variability of weather conditions throughout the year,” Cohen said. “This is critical information when trying to determine vulnerability to climate change, which is shifting both the average and variability (or unpredictability) of weather conditions.”

Bird size and diet play a significant role in migration

For this new study, Cohen and Jetz analyzed millions of occurrence records for over 600 bird species, along with 22 years of weather data from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) instrument and CHELSA climate data set.

The team also utilized a new tool developed by colleagues in the Yale Center for Biodiversity and Global Change which, according to Cohen, allowed them to “easily annotate millions of observations with fine-scale weather data across hundreds of species.”

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They found that long-distance migratory birds, as well as small-bodied birds and insect-eating birds all tended to closely track their preferred niches over the course of a year. Conversely, large-bodied birds and birds that had a herbivorous or omnivorous diet tended to be more hardy and would not track so closely, instead preferring to simply withstand the large seasonal variations between their breeding grounds and overwinter locations.

“Knowing who has narrow requirements and who can withstand a broader range of conditions can help us predict climate change vulnerability,” Cohen explained.

Niche trackers – animals that seek out very specific climates and environments – will potentially suffer more under a changing climate as their preferred conditions become harder to seek out. By contrast, the hardier species that already endure much more variable conditions may be less affected.

In tying species-level traits to these niche-seeking or flexible behaviors, the researchers say that they have established a more reliable way to estimate how species will react to different weather conditions.

“Now we have a framework that can predict vulnerability to both changes in mean and variability based on the traits of different species of birds, even among species we were unable to cover in our study,” Cohen said.

What about other migrating animals?

Birds are certainly the most classical example of an animal that migrates to different pastures as the seasons change. Deer, moose, wildebeest and similar large mammals do also undertake significant migrations between the summer and winter months. For the Yale researchers, their study of birds is just the beginning.

“The recent explosion in tracking data for many of these other species will soon allow us to ask these questions [about seasonal niche tracking and climate change vulnerability] in other taxa as well,” said Cohen.

“It’s important to understand how wildlife may be handling the ongoing consequences of accelerating climate change so that, as climate change accelerates, we can prevent the collapse of ecological communities and biodiversity while avoiding the loss of ecosystem services.”


Reference: Cohen J, Jetz W. Diverse strategies for tracking seasonal environmental niches at hemispheric scale. Global Ecol Biogeogr. 2023. doi: 10.1111/geb.13722

This article is a rework of a press release issued by Yale University. Material has been edited for length and content.