Earth

How Animal Movements Help Us Study the Planet

Scientists have been underutilizing a key resource we can use to help us understand Earth: animals. Our fellow Earthlings have a much different, and usually much more direct, relationship with the Earth. They move around the planet in ways and to places we don’t.

What can their movements tell us?

Humanity has a fleet of satellites orbiting Earth that tell us all kinds of things about the planet. Satellites track temperature, CO2 emissions, rainfall, forest fires, drought, volcanic eruptions, etc. We know more about Earth than ever, and a lot of it is thanks to satellites.

Climate change is our biggest concern right now, and new research shows that sensors attached to animals can elevate our climate change data to a new, more granular level.

The research perspective is titled “Animal-borne sensors as a biologically informed lens on a changing climate,” published in Nature Climate Change. The lead author is Diego Ellis-Soto, a graduate student at Yale University and a NASA FINESST (Future Investigators in NASA Earth and Space Science and Technology) fellow.

The first animal tracker was probably just a piece of coloured string. In 1803, American Naturalist John Audobon wanted to know if birds migrated and returned to the same place yearly. So he attached a piece of string around a bird’s leg before it flew south for the winter. Next spring, he spotted the bird and knew it had returned to the same place.

The tools at scientists’ disposal now are much more powerful than Audobon’s piece of string. Ellis-Soto studies animal movements and what they can tell us about rapid environmental change. He uses remote sensing, GPS tracking, and citizen science to try to forecast environmental changes at fine spatio-temporal scales.

This type of research has its roots in things like the Great Backyard Bird Count, where citizen scientists spend four days each February recording what birds they see. Participants spend only a few minutes each day recording what they see and uploading it to a website. The result is a massive collection of data unattainable by any other method.

The Bird Count is a more passive example of animal movement studies that the authors advocate. They’re pursuing more active methods of studying animal movement and gathering data to get around some of the roadblocks scientists face when studying the climate.

“Traditional climate measurements are often constrained by geographically static, coarse, sparse and biased sampling, and only indirect links to ecological responses,” Ellis-Soto and his co-authors write in their research. “Here we discuss how animal-borne sensors can deliver spatially fine-grain, biologically fine-tuned, relevant sampling of climatic conditions in support of ecological and climatic forecasting.”

A 130-pound wolf watches biologists in Yellowstone National Park after being captured and fitted with a radio collar on 1-9-03. Tracking wolves as they move through their territory can also tell researchers about the environmental and climate conditions that motivate their movements. Image Credit: By William C. Campbell – U.S. Fish & Wildlife Service, Public Domain, https://commons.wikimedia.org/w/index.php?curid=30609

Even though we have a fleet of powerful satellites and a massive number of ground-based data collectors, they each have a weakness of some type. Ground stations can only sample data from a single location. Satellites have their own limitations. They can collect data in fine spatial resolution, across multiple wavelengths, or at high temporal frequency. But they don’t do it all at once. They’re also inhibited by cloud cover and, in some cases, the darkness of night. The result is data that though powerful, has gaps in it.

Animal sensors can bridge those gaps, according to Ellis-Soto. “Animals are an integral component of Earth observation,” he said.

Animal-borne sensors (ABS) aren’t new. They’ve been used for decades to track various animals, including predators like lions, ocean-going animals like orcas, migrating birds, and even insects. These trackers monitor and report an animal’s movements in places that satellites can’t monitor, and humans can’t easily access. But Ellis-Soto says we can use trackers to gather other data, like temperature.

In South Africa’s Kruger National Park, scientists used temperature and movement trackers on elephants to monitor the animals as they moved around in the park for one year. They combined it with satellite temperature data. Two maps from that effort show how the elephant sensors filled in gaps in the satellite data and created a much more complete picture.

These two maps show satellite temperature data (top) and elephant location and temperature data from ABSs. Image Credit: NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey and elephant-borne sensor data from Thaker, M. et al. (2019).

Ellis-Soto sees the issue in terms of bias. Each satellite has a sampling bias. Sampling bias is unavoidable when designing satellites and their instruments. But animals have a sampling bias, too, and scientists can use that bias for their own purposes.

“These animals are extremely biased sensors, and this bias is called animal ecology and behaviour,” said Ellis-Soto.

The elephants in Kruger National Park are just one example. The use of ABSs is widespread.

This image shows how ABSs are used to collect different environmental data. 1 to 9 show ABSs used to estimate measurements ranging from wind speed and direction to air temperature. 10 to 16 shows ABSs used to measure sea surface temperature and salinity. 17 and 18 show ABSs used to measure near-surface temperature in terrestrial realms. Image Credit: Ellis-Soto et al. 2023

Ellis-Soto and his colleagues see many opportunities to expand this kind of monitoring and combine it with other data, including satellite data. “Technological advances in ABSs offer an ever-increasing number and quality of auxiliary on-board sensors that collect climatic variables,” they write. Technological advancements in ABSs combined with animal movement are powerful tools that can play a larger role. “Animals can access and monitor remote areas and detect rare events and hard-to-measure environmental conditions of potential importance for climate change projections.”

The authors highlight the issue of snowmelt. Around the world, snowmelt is an important indicator in understanding the coming growing season. Snowmelt provides irrigation water for millions of farmers around the world. For example, in India and Pakistan, 130 million farmers rely on meltwater to irrigate their crops.

“In many areas of the globe, snowmelt is a crucial component of the natural hydrological cycle,” they write. “A biological warning system of earlier snowmelt under climate change by ABSs may improve estimates of the contribution to mountain hydrology, a critical area of improvement for climate change projections and water runoffs for food production.”

In the Arctic, researchers used ABSs to track the movements of three types of birds: snowy owls, rough-legged buzzards, and peregrine falcons. The ABS data showed how these animals follow the snowmelt during migratory journeys. The data was more granular than satellites could provide. “Spatially fine-scaled capture of patches of snowmelt as homed in on by animals is otherwise hard to attain but highly useful for understanding the phenology and distribution of Arctic species under changing climate conditions,” the authors write.

There are many examples of ABSs being used to gather otherwise unattainable or difficult-to-obtain environmental data. But there are also many more opportunities waiting to be realized.

This figure shows how harp seals can be fitted with ABSs to record and transmit data while going about their business. ARGOS is a satellite network dedicated to wildlife monitoring. Image Credit: McMahon et al. 2021.

“We see a real opportunity for the ecological and meteorological community to employ ABSs for a strongly expanded, representative and biologically interpretable measurement of meteorological
and climatic conditions under current and future climate,” the authors write.

Our fellow Earthlings are like an army of unwitting citizen scientists. As long as the ABSs don’t hamper or harm them, they can greatly contribute to Earth’s well-being without even knowing it.

“The thousands of animals today swimming, running and flying around the globe carrying electronic tags are agile earth observers with the potential to provide transformative data collection in support of global change research, meteorology, climate forecasting and ecology,” the authors conclude.

Evan Gough

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