Up in the sky, under the sea, deep inside an animal society—researchers can’t go these places themselves, so they attach tracking devices to wildlife in order to gather the data. But are these gizmos invisible to the creatures themselves, and can they go about their lives the same way they would if they didn’t have a tracker stuck on their fin or wing? Or do some of these electronic devices interfere with the animals’ ways of life, and therefore send back bad data to the scientists?
This week there’s a new entry into this long-running debate, regarding one of the most-tracked animals in the world: the king penguin of Antarctica. A study published in Nature that tracked 100 penguins found that those wearing flipper bands lived different lives than those without, and less successful ones to boot.
In terms of survival, banded penguins had a 16 44 percent lower rate [survival rate dropped from .36 to .20, a drop of 16 percentage points, or 44 percent] over the entire 10 years, but there is a breakpoint at 4.5 years. In the first 4.5 years, banded penguins actually had a 30 percent higher mortality rate. After that, the difference in mortality between banded and unbanded birds levels off. The authors propose that flipper-banding acts as an artificial selector for the strongest penguins, creating a bias in data collected from banded birds. Over the decade, banded birds were less successful in breeding. Banded penguins produced a total of 47 chicks, while unbanded penguins had 80 chicks. [Ars Technica]
This study presents a practical problem: Studying the effects of clipped-on tracking tags means your control group must be free of them, but you have to track the group without the flipper bands somehow. So Yvon Le Maho’s team implanted small, newer-style tags that lie under the skin on all the penguins in their study. That way they could give half of the birds a dummy tracking tag clipped on the fin to see if the equipment itself changes their behavior.
Why should the tags hamper the penguins? One possibility—which any human climber, diver, or adventurer could confirm—is that extra gear simply slows them down. It’s not just inconvenience. If the penguins swim slower and must work harder, then they’re less efficient in foraging. And if they’re less efficient in foraging, then they arrive later than other penguins when it’s time to mate. From DISCOVER blogger Ed Yong:
[Study author Claire] Saraux found that banded birds arrived at their breeding grounds about two weeks later than their electronically tagged peers. Their delayed arrival coincides with the end of Antarctic summer, when food supplies are dwindling and rearing chicks is more difficult (and that’s for birds that aren’t slowed down by a metal band). As a result, the banded latecomers were less likely to breed successfully, or even to try to mate at all. Slowed by their bands, would-be parents had to make longer foraging trips to find enough food for their chicks. Overall, they reared 39% fewer young than the unhindered birds.
You can check out Ed’s full post at Not Exactly Rocket Science for more details about this study.
As noted above, scientists now have the option to use newer devices like under-the-skin tags that would appear to interfere with the animals’ daily life to a lesser degree. The problem with penguins is that fin bands have been available for decades, and thus scientists have deployed tens of thousands of them to study the Antarctic birds. If fin bands really do alter the penguin lifestyle, it means that researchers have not only been getting skewed data, but they also have been harming the birds they intended to help.
But the new tags are not perfect, either, according to lead researcher Yvon Le Maho.
“The only difficulty is that once a bird is only with an electronic tag you need an antenna for identification – so to study immigration you need antennas in different colonies – you cannot do it simply by observation as you do with flipper bands but again [flipper bands] skew the data,” he said. [The Guardian]
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