Devices worn by wild animals that record their location, and in some cases their behavior and environmental conditions, are known as biologgers. They have vastly increased our knowledge of animal movements and generated data on their use of space that have led to numerous conservation applications.

A growing class of biologging devices incorporates sensors that not only track an animal’s movements but also gather other environmental data. These geo-referenced data sets are then incorporated by scientists into oceanographic databases, such as NOAA’s World Ocean database. But as researchers tag an increasing number of species, a debate has arisen over the consequences for animal welfare, conservation and technology.

Animals as oceanographers

Most environmental biologging work happens in marine environments, using the conductivity-temperature depth satellite relay data logger (CTD-SRDL). Developed by the Sea Mammal Research Unit at the University of St. Andrews in Scotland, the device measures water temperature, pressure and salinity, and transmits the information through the Argos satellite network when the tagged animal surfaces to breathe.

This male spotted seal (Phoca largha) in the Bering Sea wears a biologging tag on its head, which facilitates data transmission when the animals surfaces. The tag’s Argos satellite transmitter estimates its location and sends data to scientists. Its pressure gauge measures how deep the animal dives, and a conductivity sensor measures the percentage of time the tag is out of the water. The tag is attached to the seal’s hair to study its use of sea ice and remained on the animal for 6 to 8 weeks. Photo credit: National Oceanographic and Atmospheric Administration (NOAA).

Fabian Roquet, a physical oceanographer at the University of Gothenburg, Sweden, who helped develop the CTD-SRDL tags, told Mongabay their greatest contribution to date was in helping researchers “understand what is happening around the Antarctic continent.”

“It’s hard for the general public to understand how little we know about these remote regions,” said Roquet, who is also the acting head of Marine Mammals Exploring the Oceans Pole to Pole (MEOP), an international consortium that coordinates marine tag deployments. “It would be easy to think that science is all-powerful and that we are trying to know just a bit more or something. But no, it’s much deeper than that. We are lacking very basic information to understand what’s happening right now.”

MEOP also standardises and centralises oceanographic biologging data, which have been incorporated into NOAA’s and other oceanographic databases and which Roquet said could be supplemented by data from other sensors as additional biologging devices are developed.

Roquet said researchers deploying marine environmental biologgers “are not using the animals as some kind of instrument” to collect data. “It is always managed by ecologists who have their own scientific objectives in terms of biology, and incidentally we get physical data,” he said. Roquet added that physical data help us understand animal behavior and create better conservation plans for marine environments.

Sensing on the wing

Biologgers on birds have demonstrated potential to assess human activity and air quality. In a 2017 study, Henri Weimerskirch and colleagues combined GPS tracking devices and radar detectors into a device that they attached to 53 wandering albatrosses (Diomedea exulans) to help detect radar-emitting fishing vessels in the Indian Ocean. Knowing that albatrosses often follow fishing vessels, and that entanglement in fishing equipment is a leading form of human-caused mortality in seabirds, the scientists measured the spatial overlap between foraging albatrosses and fishing vessels.

A wandering albatross (Diomedea exulans) in flight off Tasmania, Australia. These birds have the wingspan of up to 3.5 meters (11.5 feet) of any bird and can soar for hours without flapping. Photo credit: JJ Harrison ( via Wikimedia Commons, CC 3.0.

Some 80% of the tags on the albatrosses were able to detect fishing vessels up to 2 kilometers away during the animals’ foraging trips. The authors suggested that these biologgers could be used to detect illegal fishing vessels, which also emit radar to navigate safely.

Following the study, the French navy deployed 250 tags on wandering albatrosses to pinpoint illegal fishing vessels. The EU-funded project, called Ocean Sentinel, uses a modified version of the biologger that can relay information on illegal fishing ships over the Argos network.

In 2006, homing pigeons in San Jose, California, took off wearing biologgers for a project called Pigeon blog. The devices included sensors that detected carbon monoxide, nitrous oxide and temperature, as well as a GPS device and a cellular transmitter that relayed pollution readings to a website and Google maps database in real time. The project aimed to “re-invoke urgency” about urban air pollution as well as “broaden the notion of grassroots scientific gathering,” as stated on its website.

A group called Plume labs repeated the exercise in 2016 for three days in London to bolster funding and interest for the development of human-worn pollution sensors. Both projects reached a massive audience, including international media outlets, and provided an educational platform on the dangers of urban air pollution and the possibilities of environmental sensing.

A member of the Plume Labs pigeon air patrol wearing a tiny backpack biologger that collected data on air pollutants across London over several days during the city’s rush hour periods. The information was disseminated via an app and Twitter to raise awareness of air quality. Screenshot image from a project video.

Scientists have shown that movement of a tagged bird through air or water alone can help assess environmental phenomena, such as wind speed and ocean current. In a 2018 study led by Rick Thomas, the authors tested a biologger on two species of captive eagles that recorded GPS location, humidity, pressure and wind speed. Despite the study’s limited success, the authors suggested bird-mounted environmental sensors could help us understand weather in urban areas, within which governments may prohibit use of drone- and ground-based sensors.

The ICARUS project has stated plans for sensor-equipped biologgers. “In the future, we’ll use every animal that flies as a meteorological drone,” stated Martin Wikelski of the ICARUS project. “To measure the temperature in the middle of the Pacific at 20-metres [66-feet] altitude is impossible, but birds do it all the time.”

Ethics of biologging

Animal welfare is a central factor of biologging research. “If you’re significantly impacting the behavior, health or welfare of the animal that’s terrible from the welfare perspective, but also if that animal is not acting or behaving normally, the actual scientific data you’re getting would be useless as well,” said Steven Portugal, a professor at the Royal Holloway University of London, who deploys biologging devices on captive animals.

To use biologgers on animals, scientists require permission from academic institutions, government agencies and scientific journals, depending on study location and the species involved. The society for biologging’s ethics working group and past research help scientists determine ethics and best practices. Portugal said it was common now, but not in the 1990s, for studies to include a control population, not equipped with biologgers, to help determine whether the biologgers were having an impact on significant life-history traits.

A Swainson’s thrush wearing a backpack-like geolocator data logger is about to be released after capture in Alaska, USA. The tiny tags monitor and record light levels. Using the time of sunrise and sunset, researchers can estimate the bird’s location to within a few dozen miles. The devices do not transmit their data, so the researchers (and the bird) must return in future years to the capture location and retrieve the tag. Photo credit: Nina Chambers, U.S. National Park Service.

All biologging devices have some impact on the animals being tagged, says Penny Hawkins in her 2004 review. Capturing, restraining or sedating the animal to attach and, in some cases, remove the device, can stress it, and carrying a device can cause stress and require additional energy expenditure.

A growing body of scientific papers finds that current methods inadequately measure the impact of biologging devices on animals, limiting scientists’ ability to make informed decisions in using the technologies.

One increasingly scrutinized “best practice” is that tags must be less than 2 to 5 percent of an animal’s body weight. “There’s no real evidence for it,” said Portugal. “I think partly it was a very conservative estimate that people felt like they were being very safe by choosing that figure.”

A 2018 meta-analysis by Thomas Bodey and colleagues analyzed results from 214 biologging studies using wild birds. The authors found that tagging birds produced small but significant impacts on the birds’ survival, reproduction and foraging behavior. The researchers also identified numerous publications with insufficient information to quantify these impacts and suggested that biologging studies provide specific data to facilitate comparisons among studies, dissemination of best practices, and robust conclusions that ensure protocols can be improved.

Swansea University professor Rory P. Wilson, who has published extensively on the ethics and impacts of biologging, told Mongabay that measuring life-history traits to understand device impacts shows progress, but that this effort lacks a consistent framework. He called for modeling physical impacts of biologgers on animals, saying that predicting whether carrying a tag causes an animal to fly, climb or run more slowly will greatly inform tag deployment. “When scientists get to that stage, and ethical bodies can follow them, that will be great,” he added.

Wilson said longer-lasting tags allowed scientists to attach devices for longer periods, potentially increasing their impact. In a 2015 study, he and collaborators also showed that device impact could change with environmental variability. Impacts of tags are also species-dependent, so a device’s mass, shape and location on the animal’s body are key design criteria to minimise its impact, writes Hawkins and other scientists.

Large, terrestrial mammals can carry tags that collect more data over longer time periods. This female white-tailed deer fitted with a GPS-enabled radio tracking collar stands in the back dune habitat of Fire Island, where scientists studied the influence of deer on post-storm vegetation regeneration. Photo credit: U.S. National Park Service.

Then there’s the biologger configured in such a way that it generates data about how it’s affecting the tagged animal. Wilson calls it the “daily diary,” which he says “allows you to derive things like the energetics associated with movement [and] determine animal behavior, the trajectories of the animals, and how much their behavior varies. It’s this particular configuration of sensors, where you can actually put them together and pull out tons and tons of metrics, that can help you identify animal well-being.”

Data standardization

Although standardising these and other biologging data can provide researchers access to timescales and sample sizes beyond individual research projects, challenges for standardizing data abound due to the diversity of research projects and biologging devices.

In a 2016 paper, Hamish Campbell and colleagues outlined the need for biologging data standards, finding that the lack of standards in variable names and definitions, file formats, and other aspects of data may increase the possibility of errors and inhibit sharing. Database projects such as Movebank and MEOP have already begun to standardize and store biologging data, making them available to the research community and the public.

The ethical questions of adding additional sensors to biologgers remains. “On the one hand, I would always advocate put more sensors on if it doesn’t adversely increase the size of your tag. Put it on because you can get that much more information that may be valuable to the animal itself,” Wilson said.

On the other hand, he added, biologging must primarily help the animal wearing the device. “No animal likes being tagged,” he said, “and I think it would be much more difficult to explain to that animal, if it could be explained to, that you were tagging it because you were more interested in glacial melt-water than you were in seals, so that’s a tricky one.”

This article first appeared on Mongabay.