Antarctica is possibly the most inhospitable place on earth to rear young, yet millions of penguin parents succeed every year. However, some years the environmental conditions are tougher than others, making raising chicks even more challenging. According to Michaël Beaulieu, from the Institut Pluridisciplinaire Hubert Curien in France, varying sea ice conditions can make rearing chicks harder some years than others. Curious to find out how penguins adapt to fluctuating Antarctic conditions, Beaulieu and his colleagues, André Ancel, Yan Ropert-Coudert and Yvon le Maho, decided to find out how penguin couples cope when foraging is difficult. But instead of manipulating the sea ice and tampering with the birds' food supply, the team decided to subtly alter the manoeuvrability of one partner to see how the animals adapt to difficult foraging conditions (p. 33).

Beaulieu, Thierry Raclot and David Lazin headed south to the French Antarctic research station, Dumont d'Urville in Adélie Land, and attached light Plexiglas backpacks to one half of a penguin duo to impede the penguin's manoeuvrability and foraging. The trio also electronically tagged, weighed and took blood samples from both birds before they laid their eggs and 45 days after egg laying, so that the team could see how both partners responded to the impediment.

Returning to France with the penguin blood samples, Beaulieu teamed up with Marion Spée to measure the levels of a hormone (corticosterone) in the birds' blood to see if the impediment had stressed the birds. He also measured the ratios of stable carbon (13C) and nitrogen (15N) in the birds' blood to see if the birds changed their foraging strategy. Then Beaulieu began looking to see how the hampered penguin couples had coped compared with unimpeded couples.

Not surprisingly, the hindered partner in a foraging pair had spent 70% more time foraging when chick rearing than their unimpeded partners. But had the unhampered partner adjusted the length of his or her foraging foray to compensate for their partner's delayed return? No. And when Beaulieu compared the hampered and unhampered penguins' stress hormone levels, the birds in hampered couples were no more stressed than couples that were unhindered.

So the only birds that had changed the length of time spent foraging were the impeded penguins and the Plexiglas backpacks had not increased the birds' stress levels. But had the impediment changed the range over which the birds foraged?

Analysing the ratios of 13C and 15N in the penguins' blood, it was clear that instead of heading out to sea to catch fish, the hampered partner had taken to foraging on krill close to the sea ice and, amazingly, so had the unhampered half of the partnership. Both members of the couple had changed their foraging behaviour, even though only one of them had supported the backpack.

Beaulieu suspects that both members of a handicapped couple adjust their foraging behaviour to compensate for the hindered partners' inefficiency. ‘This change in foraging decision may optimize feeding time by decreasing travelling time,’ explains Beaulieu. So penguin partnerships are adaptable and are able to adjust their foraging strategies to cope with the constraints they face when breeding.

le Maho
Ecophysiological response of Adélie penguins facing an experimental increase in breeding constraints.
J. Exp. Biol.