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Every year barnacle geese embark on an epic 6000-kilometre
migration from Scotland to the Arctic and back again.
Tamera Jones meets Steve Portugal to find out how.

       efore embarking on an epic                requires a lot of effort and energy, so much      It is midway between the north of Norway
       3000-kilometre journey from Svalbard      so that it acts as a key population control for   and the North Pole. The sun stays above the
       in the Arctic to Caerlaverock in          barnacle geese. ‘Having fledged their nests,      horizon from late April until late August,
Scotland, you’d think that barnacle geese        young geese are more likely to perish on their    giving continuous daylight.
would do everything they possibly could to       first migration than at any other time of the          The geese leave Scotland for the Arctic in
build up their fat reserves. On the contrary,    year, often being blown off course by strong      April. They follow spring up the Norwegian
research in captive geese suggests that          winds,’ says Portugal. Even so, many birds        coast to take advantage of the new foliage
around six weeks before migration, the geese     migrate, so there must be something in it.        growth. The availability of daylight and
mysteriously lose about a quarter of their            Birds migrate in response to the             food in Svalbard gives the geese the perfect
body mass.                                                                                         opportunity to build up their fat reserves
    Dr Steve Portugal at the University of
Birmingham spent his PhD working out
                                                 Migrating is a risky                              and breed. They put on a lot of weight
                                                                                                   during this time, reaching their summer peak
why the geese lose weight at such a crucial      business and requires a                           around the end of June.
time. It turns out that almost everything                                                               By June, the ice has melted, so the birds
a barnacle goose does is exquisitely timed       lot of energy.                                    can feed to their hearts’ content. Piling on
to the seasons. And losing weight so soon                                                          the pounds in June and July is crucial for the
before migration is closely related to another   availability of food and to find the best         birds. The annual wing moult – when old
important event in the goose’s calendar –        breeding grounds. This improves their             wing feathers fall out and are replaced by new
growing new wing feathers.                       chances of producing a large clutch of chicks     ones – starts in July. Shortly afterwards, they
    One large population of barnacle geese       – or goslings if you’re a barnacle goose. Geese   quickly lose weight.
spends the majority of the year over-            consider Svalbard one of three ideal Arctic            Once feathers have finished growing
wintering at the Solway Firth in Scotland.       spots for their summer residence. Food is         – like hair – they are dead. Over time they
The geese feed on winter stubble crops to        widely available, and the conditions are ideal    become worn and abraded, so need replacing.
bulk up, reaching their heaviest around the      for breeding because there are fewer land              Barnacle geese go through a fairly rapid,
start of February before migrating to the        predators.                                        simultaneous wing moult from the start of
Arctic around April.                                 The Svalbard archipelago lies in the          August to mid-September before migrating
    Migrating is a risky business and            Arctic Ocean well within the Arctic Circle.       south in October. They are completely

24      Planet Earth • Spring 2009
                                                                                           Steve Portugal’s supervisor Professor Pat Butler has monitored
                                                                                           the autumn migration of six geese by satellite. Their heart rates
                                                                                           rocketed to around 250 beats per minute in flight compared with
                                                                                           a resting rate of around 50 beats per minute. Most of the geese
                                                                                           stopped periodically, probably along the coast of Norway. Some
                                                                                           particularly fit birds completed the journey in just four days, flying
                                                                                           non-stop for 24 hours in some cases.
                                         Steve Portugal.

                                                                                           Intriguingly, their metabolism also shot up a
                                                                                           massive 80 per cent during the wing moult.

                                                                           to monitor their metabolic                   condition. Indeed research has shown
                                                                           rate – as well as behaviour – at             that birds in good condition grow feathers
                                                                           different times of the year.                 quicker than birds in poor health. The
                                                                               The captive geese had                    flightless period is shorter in birds that are
                                                                           constant access to food, no                  in good condition, which means they are
                                                                           predators and, importantly,                  vulnerable for a shorter period of time.
                                                                           don’t migrate. So if changes                 Barnacle geese that have failed to put on
                                                                           in metabolic rate, weight and                enough weight and are in poorer condition
                                                                           behaviour are important for                  are less likely to weather the weight loss
                                                                           wild geese, Portugal surmised                during wing moult.
                                                                  David Whitaker / Alamy

                                                                           that he might see similar                         Once the new wing feathers have
                                                                           changes in the captive geese.                grown, the geese set to work to replace the
Barnacle geese consider Svalbard one of three ideal Arctic spots
for summer residence.                                                          Portugal found that captive              weight they’ve lost. With only six weeks
                                                                           barnacle geese lost weight at                before their 3000-kilometre trip back to
                                                                           the same time – during the                   Scotland, it’s a race against time. The most
flightless during the moult, making them                    wing moult, even when they have unlimited                   effective way the geese can put weight on
particularly vulnerable until new feathers                  and unrestricted access to food and no                      in a short period of time is by going into
grow back.                                                  predators to worry about. Intriguingly, their               a state of anapyrexia – they decrease their
     During this time, foraging for food is a               metabolism also shot up a massive 80 per                    body temperature by nearly five degrees
struggle and escaping from predators, like                  cent during the wing moult.                                 centigrade. Maintaining a higher body
Arctic foxes or polar bears, is considerably                     ‘Growing a whole bunch of new wing                     temperature uses energy, so keeping it lower
trickier. In contrast, passerines – much                    feathers uses up a lot of energy, so metabolic              helps them conserve valuable energy for
smaller perching birds – lose their wing                    rate and oxygen consumption both rise                       their imminent migration.
feathers one at a time over a period of                     to take account of this. The energetic cost                      ‘Geese that have been in captivity for
months. This doesn’t hamper their ability                   of moulting means the birds need more                       more than five generations and have very
to fly. It seems to make sense then for the                 nutrients to make feathers. Amino-acid                      different environmental cues compared to
wing moult to pass as quickly as possible for               metabolism goes up, as well as blood volume                 their wild counterparts still appear to carry
barnacle geese.                                             and heat loss, all of which need energy,’                   on as if they were summering in the Arctic
     ‘Simultaneous wing moult has only                      Portugal adds.                                              and migrating like wild geese,’ says Portugal.
evolved in birds that can feed and avoid                         He noticed that the birds tend to rest                      Arriving back in Scotland in October,
predators while flightless. Barnacle geese still            and stay put a lot more than before the                     they have just over half a year before they
have access to grasses and mosses, and can                  wing moult. ‘It’s as if the birds sense their               have to repeat the remarkable journey all
use water for safety,’ says Portugal.                       vulnerability when they’re unable to fly                    over again. ❖
     Many other waterfowl lose weight                       and they put as much energy as they can
during wing moult, but until now it wasn’t                  into moulting to get it over with as quickly
clear exactly why. Some researchers have                    as possible,’ he says. This, together with                    Steve Portugal is a researcher in the School of
suggested that a lighter bird would be more                 hampered foraging opportunities, means the                    Biosciences at the University of Birmingham.
able to fly sooner – once its new feathers                  birds inevitably lose weight.                                 Email: sxp320@bham.ac.uk
had grown – than a heavier bird.                                 It seems bingeing before wing moult
                                                                                                                          Tamera Jones is a science writer at the Natural
     To figure out why the birds lose                       starts is crucial. Being in the best possible                 Environment Research Council.
weight, Portugal checked the rate of oxygen                 condition is likely to help the geese grow                    Email: tane@nerc.ac.uk
consumption in captive geese. He wanted                     feathers quicker than birds not in tip-top

                                                                                                                                 Planet Earth • Spring 2009                 25

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