Opinion: Torments of tagging

Is marking the wild animals we study skewing our results? And if so, what can we do about it?

By | February 3, 2011

A female African Penguin with a green tag on its left flipperWIKIMEDIA, BROKENSPHEREIn 1971, NASA and the Smithsonian Institution deployed the first ever satellite collar, using a female elk they named Monique in the Grand Tetons in Wyoming. They spent months testing the collar, bright red and over 10 kilograms, to make sure it could survive everything an elk would put its way. The collar was well-armored, expected to make it through a frozen river without problems. Within a week after collaring Monique, she was dead.

NASA dubbed it a coincidence, but it illustrates an important concern that plagues most field biologists: Are the methods we use to research our animal subjects harming them, or inadvertently altering the biological systems we study?

As with most sciences, the main limit to knowledge in ecology is an observational problem: Our inability to fly, swim in arctic waters, run 120 kilometers per hour or sit in one place for a century creates serious barriers to understanding. In place of superhuman powers, wildlife biologists have spent many years developing methods for observing the natural world without having to be in constant contact with our animal subjects.

By marking individuals, we can recapture them later to estimate a suite of important ecological characteristics, such as survival, movement, age, and change in body condition. Plastic leg bands, ear tags, radio collars, toe clipping and PIT tags—small electronic transponders implanted underneath the animals' skin—are all considered standard tagging methods. Hippopotamus researchers have even used different combinations of colored paint balls, a simple, safe (and, I assume, less monotonous) method for marking individuals.

The assumption, of course, is that these methods have no significant effects on the target species. And yet we must all have nagging doubts. How on earth can a 20 gram bird handle a 5 gram radio collar? What if the seed we use in our traps provides a significant nutritional benefit to the individuals we capture? Or what if the individuals we capture tend to be in poorer health, more willing to risk crawling into a cold, dark, box for what smells like a good meal? It becomes necessary to push these thoughts aside in order to continue the research at hand. There simply isn't enough time or money to conduct a meta-study on the effect our research has on our research subjects. And besides, how would such a thing even work?

The problem is neatly zen: how can you measure the effect of not studying a species? Some recent research, however, has suggested that such unspoken concerns may be warranted. Saraux and colleagues found, for example, that penguins with flipper bands experienced serious reductions in fecundity (39% fewer chicks) and survival compared with PIT-tagged, non-banded, birds. It may be easy to shrug off these results as an obvious consequence of the highly invasive tagging practice, as flipper bands are known to cause short-term injury and, long-term, increased drag while swimming. But other research has shown that even a small PIT tag can have behavioral consequences. In bivalves, for instance, PIT tagged individuals spent more time burrowing, possibly resulting in increased predation and dislodgment. Even individuals handled but not PIT-tagged were negatively affected. If the mere act of picking up a mussel can have negative consequences, how can we ever hope to study any species and not affect it?

As technology continues to improve, wildlife research will become less invasive. Today, elk collars weight about 1 kilogram, and have been designed to reduced chafing and to fall off if the animal's neck grows. Universities now have strict review boards to ensure proper animal care, and continuing applied research offers insight into the problems. Indeed, the most hands-off approach is becoming a reality: researchers can use scat-sniffing dogs to collect samples for genetic analyses, which are often as good as, if not better than, traditional mark-recapture studies. These results will be stronger, more robust, and less influenced by our presence. (Although, for now, we choose to ignore the effect of introducing Canis familiaris into our study system, and the effects of removing feces that would otherwise have enriched the soil.) But until analyzing a single genetic sample is cheaper than paying an undergraduate to pierce individuals with a five-cent ear tag, we will continue probing our systems in ways we don't fully understand. Funding agencies would do well to request more information on the effects a study design would have on the focal species—and, more importantly, provide funding for such research.

Timothy Bean is a PhD candidate at the University of California, Berkeley's department of Environmental Science Policy and Management, and an F1000 Member since 2010.


February 3, 2011

Much like the boy in Hans Christian Andersen's tale "The Emperor's New Clothes," Mr. Bean makes some excellent points and while causing some well-earned embarrassment. Truly, the Heisenberg uncertainty principle applies to wildlife science, just as it does to quantum mechanics.\n\nI would just like to expand a bit on one point. In discussing the use of scat-sniffing dogs to collect samples for genetic analyses, Bean says, "Although, for now, we choose to ignore the effect of introducing Canis familiaris into our study system, and the effects of removing feces that would otherwise have enriched the soil." \n\nI would add that collecting the sample also deprives members of the focal species, as well as their prey and their predators, from the rich olfactory information contained in the scat. \n\nIn our studies of the behavior and ecology of the timber wolf (Canis lupus) in Northern Wisconsin, we make it a rule to collect no more than 1/4 of the feces an animal deposited, leaving the rest to provide information vital to the system.
Avatar of: Richard Patrock

Richard Patrock

Posts: 52

February 3, 2011

There was a paper 20 or so years ago demonstrating that butterflies like being marked, that is, those who were marked were more likely to show up multiple times than what was expected. For an animal that is drugged and tagged, it is very likely they will be punished naturally. A mammal is most likely to remember the event and disassociate from it in one way or another. Schrödinger's cat doesn't like Verschränkung at a quantum or a quartered scale.
Avatar of: Christopher Lee

Christopher Lee

Posts: 50

February 3, 2011

This story reminds me of a discussion a while back about allowing whole regions remain totally wild, with no humans allowed (the southern half of Florida was mentioned;-). I seem to remember we were discussing the forms of malaria that are specific to humans.\n\nIs it politically correct nowadays to permit the continued existence of untagged wild animals (bearing in mind that humans may well fit into this category)?
Avatar of: anonymous poster

anonymous poster

Posts: 1

February 3, 2011

Recently I saw a wild goose tagged with an at least 3-inch high neck band. I could read the numbers on the band without binoculars from across the pond, and it appeared to me that the band was very obviously interfering with the animal's normal behaviors (for one thing, it kept trying, and failing, to groom itself). At the time I wondered why scientific inquiry would require such a large, colorful (bright yellow) marker or why an ethics board would permit so intrusive a device. Years ago, wee leg bands would have been regarded as sufficient.
Avatar of: Mike Waldrep

Mike Waldrep

Posts: 155

February 3, 2011

Interesting! I hope that everyone had a happy Groundhog Day!
Avatar of: anonymous poster

anonymous poster

Posts: 69

February 4, 2011

The US consular official there has apparently declared that tagging humans (in this case, hapless students embroiled in a bogus American University scam) is quite an in-thing to do since celebrities in US get that! Apparently she did not know about this or she knew that animal/bird studies are not relevant to humans.Wise consul!


Posts: 1

February 15, 2011

Mr. Bean raises many important points about the impact of "intervention" on a species being investigated. One concern that has not been raised are the effects of the stress of capture and handling on the immune defense systems of the species being studied. For example, I doubt that the capture of birds in mist nets and their subsequent banding is physiologically neutral, especially species that may be captured while they are already physiologically impacted by a long distance migration.

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