of a feather
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.
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: firstname.lastname@example.org
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: email@example.com
consumption in captive geese. He wanted feathers quicker than birds not in tip-top
Planet Earth • Spring 2009 25