October 19, 2021

I, Science

The science magazine of Imperial College

Argh! Detag!
Argh! Detag!

You wake up.  There’s a glorious moment of tranquillity as the world slowly begins to reshape and you realise, aaah, it’s Sunday.  Then, like a burly-but-affable, check-shirted, sledgehammer-wielding navvy, last night hits.

What did I…?  Who did I…?  How did it…?

You sit up and another brief triumph shatters as the brick in your brain catches up.  Yup, definitely hung over.

Water… coffee… laptop… browser… popular social networking site…

Oh no…  No no…  Really?  Is that me??

Well at least you’re not alone, because thousands of miles away in the freezing Southern Ocean, king penguins are also suffering from ill-advised tags.

A study published in this week’s Nature shows that penguins tagged for research are 16% less likely to survive and 39% less likely to produce offspring than untagged birds.  The findings raise serious ethical questions and undermine the reliability of penguin data.

But why are we tagging penguins?

In its 2007 report, the Intergovernmental Panel on Climate Change made an urgent call for research into the impact of global warming on cold-water marine ecosystems.  Scientists have responded; studying penguins because, as top-level predators, any disturbances lower in the food chain ultimately affect their success, making them excellent indicators of ecosystem health.

Accurately studying penguin behaviour means repeatedly identifying the same birds, so researchers tag penguins’ flippers with metal bands to make them easy to spot.  However, the bands cause problems.

Penguins beat their flippers three times per second when swimming and the metal chafes, causing severe injury.  In addition, tags disrupt water flow over the birds’ elegantly hydrodynamic bodies, causing drag.  Experiments show that banded penguins use 24% more power to swim than their unbanded brethren and, since swimming is a penguin’s main means of getting about, the implications aren’t good.

Tagged birds are observed arriving later at mating sites.  In the penguin world, if you’re late for the party you’re less likely to pull.  Some do get lucky, but with the metal band slowing them down, they suffer longer, more arduous trips to find food for their chicks.  King penguins take it in turns to forage and fast and if one parent’s away too long, the hungry mate may abandon its vulnerable offspring to go find a meal.

Worse still, tagged penguins are more likely to die.  Mortality in banded birds is 30% higher for up to 4.5 years after tagging.  At this point the death rates even out and it was initially assumed that penguins had learned to deal with the impairment.  However, now it appears that tags weed out lower-quality individuals, in effect accelerating natural selection.  After ten years, even the strongest penguins haven’t got used to the handicap.

So are these birds dying in vain or will their sacrifice eventually save all penguins from climate change?

Sadly, the former seems true: environmental impacts on the penguins’ food supply forces the birds to forage further, so scientists measure penguin dispersal as a key indicator of climate effects.  However, seabirds that are struggling to breed also disperse, moving to new colonies where they stand a better chance.

It seems that tagging birds for climate research makes them behave exactly as if they were being affected by climate change – an ironic bias that’s impossible to untangle from the data.

Are there any parallels to be drawn with Facebook?  Will a bad tag hamper your reproductive success?  Maybe…  Will it kill you?  Probably not.  So next time you’re hastily detagging your drunken hideousness, spare a thought for the penguins.