The flipside of tagging penguins

READERS will be familiar with ‘white -coat hypertension’, a rise in blood pressure triggered by the sight and smell of the doctor’s surgery.

The cull is tightened around the arm and the stethoscope applied but the pressure readings are all over the place. Measurement processes which alter what’s being measured are useless to science. Nor is this just a medical problem; a recent paper in Nature claims that scientists studying penguins have been making a similar error. Information they have been gathering for years is flawed.

Penguins return to their breeding colonies each spring. ‘Roll-calls’ at the sites tell scientists how many birds have made it through the winter and how the species is faring. They study mate fidelity, hatching-success and chick survival rates. But there’s a problem. The birds wear identical uniforms and it’s impossible to tell one individual from another.

To recognise birds, researchers fit marking devices. Traditional metal leg-rings are too small for the numbers engraved on them to be easily read. A marker, from the researchers’ point of view, must be big and bright. Metal or plastic bands wrapped around a wing seemed ideal; marked birds were easy to spot among the crowds at the colonies and the codes engraved on the bands could be read through binoculars.

Banding, though visually intrusive, did not appear to alter a bird’s behaviour. Marked individuals returned to the colonies to nest, rearing young just as successfully as ones which had not been marked. Or so it seemed, until a team of French researchers took a closer look. The team’s results, published recently, have been a bombshell for penguin studies. Claire Saraux and colleagues from the University of Strasbourg argue that wing bands harm the birds and that the results obtained from using them are invalid.

A hundred king penguins were fitted with electronic tags on Possession Island in Antarctica. The devices, normally used to identify dogs and cats, are inserted under the skin. They don’t transmit signals continually but react when a transponder is near them. Fifty of the penguins, half the sample, were given metal wing bands in addition to the electronic tags.

A decade later, 10 of the wing-banded birds were still alive, compared to 18 of those without tags. Carrying a band evidently shortens a bird’s life. Just why this should be so is not known exactly. Perhaps the band impairs a bird’s ability to swim. Penguins are flightless and their wings have evolved into fins. A band on the wing causes drag. Tests carried out with Adélie penguins swimming in tanks showed that birds with wing-bands used 24% more energy than non-banded ones. This could mean that wild penguins are less able to catch fish and escape from predators. Another possibility is that gaudy wing-bands spoil a bird’s camouflage. Penguins have dark backs so that predators don’t spot them from above while white bellies render them less visible to the fish swimming below.

Banding, according to the Strasbourg team, also impairs a penguin’s ability to breed. Wing-banded birds were later than normal arriving back at the breeding colonies and, over the 10 years, they reared 41% fewer chicks than non-banded ones. Reduced swimming and hunting ability seem to be implicated; wing-banded penguins spent on average 12.7 days away from the nest on foraging trips compared to 11.6 for normal ones. The babies of banded parents received less food. They were probably lighter at fledging and, presumably, less well equipped for the trials of life. A similar problem arose closer to home during the 1970s.

Brent geese, captured on the islands of the Canadian Arctic, were fitted with metal neck-collars. Many of the marked birds visited Irish estuaries during the following winters, when I spent a great deal of time tracking them and reading the neck codes through a telescope.

It soon became evident that all was not well. Birds constantly rubbed their necks, trying to remove the collars. Marked individuals were often seen away from the flocks. Either they were ostracised or they had become too weak to keep up with their peers. Collars and wing-bands are not good for birds — or science.