The afterlives of wildlife tracking devices
by Alexandra Palmer, University of Oxford
Much has been said about wildlife tracking devices (known by various names such as ‘tags’ and ‘loggers’), which researchers attach to, or implant in, animals to monitor their movements. At the Digital Ecologies conference for example, we heard of how such devices are used to make sure animals are where they’re supposed to be (von Essen), and to monitor human activities that affect wildlife (Hartman Davies). For example, albatrosses armed with loggers are used as ‘ocean sentinels’ for monitoring the locations of undeclared fishing vessels (and hence the likely hotspots for bycatch) and plastic waste (Phillips and Waluda, 2020; Weimerskirch et al., 2020). Albatrosses are thereby enlisted in their own conservation.
Tracking devices have a complex history, with their use prompting debates about topics ranging from animal welfare to the ethics of monitoring legal and illegal animal harvests (Benson, 2010). But a question that has received less attention is: what happens to tracking devices once they’re no longer useful for science and conservation—when a device stops working, the animal dies, or the movement of interest (e.g. migration) comes to an end? In other words, where do tracking devices go when they (or the animals to which they’re attached) die? This is an important question given its implications for animal welfare, environmental health, and the economics, ethics, and politics of wildlife tracking.
My recent work with the Animal Research Nexus has explored various questions around tracking technologies in wildlife research. This work has examined how one decides whether a device is sufficiently harmful (from the animal’s perspective) to require regulation under the UK’s Animals (Scientific Procedures) Act (A(SP)A), and what these regulatory decisions mean for citizen scientists’ ability to use trackers (Palmer et al., 2020; Palmer and Greenhough, In Press). While I didn’t think to ask my professional and citizen scientist participants specifically about where their used tracking devices go, I did hear various stories about tag loss and recovery, and how the lives and deaths of tags relate to those of the animals they track. These stories can help us to understand why the afterlives of tracking devices matter.
One possibility is that tracking devices end their lives exactly where they began: in the hands of researchers. Tag recovery might be motivated by science or animal welfare. Data-logging devices store information directly onto the tag for download, allowing researchers to collect more data (Lear and Whitney, 2016). It’s also well-known that tracking devices can pose risks to animal welfare, for example from the initial attachment (which might involve implantation or puncturing the skin) and effects of tag shape and weight on animal movement (e.g. see Vandenabeele et al., 2012 for birds).
There is therefore an incentive to not only reduce tag weight and size, but also to ensure that the device will eventually come off, either through introducing weak links in harnesses (meaning the tag eventually falls away) or re-capturing the animal and removing its tag. Re-capture is inherently difficult with some animals (e.g. those that are highly mobile), but is easier with others, such as those that regularly return to the same breeding spot or live in a fixed home range.
However, even for theoretically ‘easy’ animals, tag recovery can be confounded, including by animal agency. For example, some British mammal researchers told me that after their study ended they meticulously re-trapped each animal and removed their heavy GPS tag collars. All animals but one, that is: a specific female has become sufficiently wary of traps that she can’t be caught, yet they know she is still alive because she can be seen (collar and all) on their camera traps. So, every few years the researchers engage in a kind of “ritual” (as one put it) where they go to the field site and attempt to re-trap the female, to no avail.
Tag recovery can also be confounded by animals being caught by third parties. A game bird researcher told me that he deliberately conducted his research on a farm where there would be no hunting. Yet in practice his birds were occasionally hunted and eaten, meaning that he needed to form good relationships with neighbouring farmers to ensure that if they do happen to shoot his research subjects, they will at least give him the tag. He also encourages them to check whether the battery has been crushed before eating potentially poisoned meat.
Recovering tracking data can therefore involve potentially awkward alliances between researchers and hunters. For example, prior to the use of radio tags, ‘discovery marks’ were sometimes used for tracking whales: thin metal tubes imprinted with serial numbers, which could only be retrieved when whales were killed and processed for oil. The use of discovery marks therefore required collaboration between researchers and whalers, and amounted to “tacit approval of the whaling industry” (Benson, 2010: 143).
The lives and deaths of tags and animals
Often though, tracking devices never fall away or are recovered; rather, a dead tag remains with a live animal, or a live tag with a dead animal. In the former case, the animal continues to live, but the death of the tag renders the animal’s movements invisible to researchers. Animals therefore continue to carry tags for the rest of their lives, but this burden no longer serves any scientific purpose.
In the latter case, tag stasis can come to stand in for animal death. A fish researcher explained that his satellite tags detect if a fish has sunk to the ocean floor, and that if a tag sinks in shallow water, animal death can be deduced through lack of movement. The tags also become hotter if the animal is eaten.
While for this researcher animal death provided useful data, this isn’t always the case. For example, some researchers studying fish migration noted that ideally every tagged fish would survive the journey, to provide more data points on the migration distance and route. Scientific and animal welfare considerations therefore encouraged them to tag only healthy-looking fish. Economics pushed them in the same direction: a researcher in the team noted that if a tagged fish immediately dies, they may as well have just thrown £250 (the cost of one acoustic tag) into the water.
Conversely, tag movement can come to stand in for evidence of life. In a previous research project on orangutan rehabilitation, I found that post-release monitoring doesn’t always involve visually checking in on the animal, but may involve checking for radio tag movement. This practice was subject to debate, since while movement means an animal is alive, it doesn’t necessarily mean they’re doing well or thriving. Yet it was also the only option for some groups that had a lot of orangutans to monitor and insufficient resources to watch each individual closely (Palmer, 2020).
There are therefore complex relationships between the lives and deaths of tags and animals. Tag death can render animals’ burden purposeless, and tag stasis and movement can stand in (albeit controversially) for animal life or death. Researchers’ decisions about which animals to tag are also shaped by expectations around which animals (and tags) are expected to live long enough to produce useful data and justify the financial investment.
When tags fall away, or remain with animals when they die, they are lost, perhaps into an ocean or forest. This can cause environmental problems, for example from leaking toxic batteries. There is therefore a need to develop more environmentally-friendly tag technologies. Writing about the future of wildlife tagging, a group of ecologists point to the possibilities of new technologies such as batteries made from cuttlefish ink, salt, paper, algae, and sugar (Lennox et al., 2017).
Another possibility for reducing environmental harms could be to encourage researchers to prioritise tag retrieval, though recovery can be extremely difficult (or even impossible) depending on the species under study. Use of tags could also be discouraged unless deemed absolutely essential, though this could mean foregoing important scientific information that only tagging can provide.
Until ‘eco’ tags are developed, or tagging activities cease, used tags will gradually build up in the landscape as material reminders of science of the past, much like the increasingly problematic ‘space junk’, mostly comprising ‘zombie’ satellites that risk colliding with space vessels and infrastructure (Witze, 2018). Indeed, some space junk is itself wildlife tracking junk as well, since satellites are required for the functioning of various kinds of wildlife tags (e.g. those relying on GPS). In a (perhaps foreseeable) twist, this space tracking junk is now itself the subject of tracking, with the new field of space traffic management aimed largely at monitoring the locations of zombie satellites to prevent collisions (Witze, 2018).
Wildlife tagging is probably still sufficiently small-scale that ‘tracking junk’ is not yet a serious environmental threat. However, we don’t actually know how many tags are lost (intentionally or otherwise) each year. Plus, tracking is increasing in popularity and often championed as a vital new tool for science and conservation. In this context, conversations about tracking junk will likely become more important over the coming years, and there may come a time when we need to think about tracking the earth-based tracking junk.
The afterlives of wildlife tracking devices are interesting and important for at least four reasons. First, the challenges posed by tag recovery highlight the importance of animal agency in shaping not just the results of tracking studies, but also the process and practice of science: animals not only determine where the tags go once attached (though their movements may also be subject to human control; Hodgetts and Lorimer, 2020), but they must also allow themselves to be caught before any tracking can occur.
Second, tag recovery stories highlight the potentially difficult relationships that wildlife researchers must often forge with hunters. These alliances may raise important questions about the ethics of tracking, particularly given that tracking is sometimes aimed at monitoring the activities of those involved in killing animals (e.g. fishing vessels involved in bycatch).
Third, the lives and deaths of tags and animals are intertwined in complex ways, and these complexities highlight important economic, ethical, scientific, and animal welfare considerations in tracking studies. For example, tag stasis provides valuable scientific information for some researchers, but for others it represents a waste of effort and money. Similarly, tag movement is understood as an adequate sign of animal life for some, but a relatively meaningless signal for others, depending on their financial and ethical circumstances.
Finally, the accumulation of ‘tracking junk’ in the environment may become important in future if tracking studies become more common. Addressing this issue may involve the development of new tag technologies, further regulation of tracking (potentially at the expense of science), or even tracking the tracking junk, in much the same way that zombie satellites are now tracked by space traffic managers.
Benson E (2010) Wired Wilderness: Technologies of Tracking and the Making of Modern Wildlife. Baltimore, MD: Johns Hopkins University Press.
Hodgetts T and Lorimer J (2020) Animals’ mobilities. Progress in Human Geography 44(1): 4–26. DOI: 10.1177/0309132518817829.
Lear KO and Whitney NM (2016) Bringing data to the surface: recovering data loggers for large sample sizes from marine vertebrates. Animal Biotelemetry 4(1): 12. DOI: 10.1186/s40317-016-0105-8.
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Witze A (2018) The quest to conquer Earth’s space junk problem. Nature (News Feature), 5 September. 7721. Nature Publishing Group. DOI: 10.1038/d41586-018-06170-1.
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