Gentoo Penguins
 World-wide there are about 320,000 breeding pairs of Gentoo penguins,
with breeding colonies on the Antarctic Peninsula, and the islands of
Falklands, South Georgia, Kerguelen, Heard, South Orkney, Macquarie, Crozet,
Prince Edward and South Sandwich.
Gentoo penguins have an average length of 80cm and an average weight of 5kg.
They have a reddish orange bill and orange feet. White patches above each
eye meet across the crown, with white speckling in the adjacent black
plumage around the head. Females are slightly smaller than the males, but
have similar markings.
Photo by Jason Wright
Colonies rarely comprise more than a few hundred breeding pairs, breaking up
into smaller subcolonies when numbers exceed this. The preferred nesting
sites are low coastal plains, fairly close to a sandy or shingle beach,
which is used to gain access to the open ocean. A substantial amount of
guano and waste accumulates around the nesting area during the breeding
season, and colonies usually move a short distance onto fresh ground each
season, retaining the same path to the sea.
Photo by Don Reynolds
Gentoo penguins are ground nesting birds, making rudimentary nests from
stones, sticks, grass, feathers, or practically any material that they can
find suitable for the purpose. Egg-laying is usually completed by late
October, with two equally sized eggs of about 130g being laid. Incubation
takes about 34 days, with both parents sharing incubation duties, and nest
changes occurring every one to three days. Despite the two eggs being laid
four days apart from each other, they both hatch within the space of 24
hours.
 The young chicks remain in the nest until they grow their first feathers at
about three to four weeks of age. During this period both parents brood the
chicks alternately, feeding the chicks and changing over on a daily basis.
Adults usually set out to forage in the early morning, returning later the
same day, and foraging generally occurs within 20km of the breeding site.
The time spent foraging increases as chicks get larger, and their demand for
food gets greater. Photo by Scott Olmstead
After the brood period, chicks are able to leave the nest and form into
large creches, allowing both parents to collect food to meet the ever
increasing demand. The beginning plumage has similar markings to the adult
plumage, except that the dark areas are a brown/gray rather than black, and
there is no white head patch.
Gentoo penguins put equal effort into raising both chicks, and have the
ability to produce large numbers of chicks in seasons of high food
availability. During such seasons of plenty, even deformed chicks that are
unable to walk properly may be reared to the point of fledging. By contrast,
when food is scarce there is strong competition for food between chicks, and
only the strongest survive. Adults are often observed running through the
colony, closely pursued by one or two hungry chicks. This may well be part
of the selection procedure, whereby the strongest, hungriest or most
determined chick gets fed.
Chicks fledge at around 14 weeks of age, but may continue to be fed by the
parents for several weeks after fledging. After completion of the breeding
season, adults spend time at sea building up body fat reserves prior to
undergoing their annual molt. The molt takes around two to three weeks,
and during this time birds spend considerable amounts of time tending to
their plumage. Gentoo penguins do not allopreen.
Gentoo penguin populations are characterized by large annual fluctuations in
population size and breeding success, with the later ranging between 0.5 and
1.5 chicks fledged per breeding pair. Gentoo penguins are capable of
breeding at just two years of age.
Because Gentoo penguins at most sites tend to move the colony a few meters
each year, they do not retain the same nests from year to year. On occasion,
whole colonies that have remained at one site for years will up and move to
a new site many kilometers away, for no apparent reason. This may happen
suddenly during a single year, or gradually over a number of years.
By comparison with other penguins, Gentoo pair-bonds are often long-lasting,
despite annual nest changes. Many adults remain around the colony throughout
the year, while others take the opportunity during the winter months to make
longer foraging trips further afield. Gentoo penguins generally forage close
to shore at depths of 20 - 100m, although they have been recorded diving to
depths of more than 200m. They may make as many as 450 dives during a single
days foraging. Penguins all look clumsy on land, but in fact Gentoo penguins
can out-run a man over short distances. Gentoo penguins are
opportunistic feeders, and around the Falklands are known to take roughly
equal proportions of fish, crustaceans and squid.
At sea, Gentoo penguins are subject to predation by sea lions, leopard seals
and orcas. On occasion, sea lions have been known to come inland after
penguins, and even fur seals can disrupt breeding colonies on occasions.
Nevertheless, such incidents are rare, and Gentoo colonies are usually
placed far enough inland to avoid such threats. On land, healthy adults have
no natural predators, but skuas, gulls and birds of prey, such as caracaras,
will steal eggs and small chicks if they get the opportunity. Chicks are
also at risk from fluctuations in food supply and weather. The baby
plumage provides good insulation when dry, but if it becomes saturated by
prolonged rain, chicks can die from hypothermia. By contrast in periods of
very hot weather, chicks become too hot, and may die from heat stress.
The Falklands is the only Gentoo penguin breeding site with human
habitation. Although farming has greatly modified the landscape around the
Falklands, Gentoo penguins prefer open plains to breed, and consequently
have not been greatly affected by the loss of the tall tussac grass. Gentoo
penguins are also very tolerant of grazing animals, such as sheep, cattle
and horses, which often wander around Gentoo colonies without causing alarm.
The expansion of roads throughout the Falklands, along with the increase in
resident population and tourism, has greatly increased the level of
disturbance at many Gentoo colonies. Nevertheless, studies of population
numbers and breeding success show no evidence that Gentoo penguins are at
risk from current levels of disturbance. Gentoo penguins become tolerant of
human presence, and do not generally become alarmed unless people approach
within about 15m of the nest site.
There is considerable commercial fishing activity in Falklands waters for
squid and finfish. Diet analysis shows that there is some overlap between
those species being commercially harvested, and those which make up the diet
of Gentoo penguins. While it is true to say that the Falklands fisheries
industry is well managed by international standards, the main aim of this
management is to ensure that stocks are not over exploited commercially,
rather than to consider the effects on wildlife.
Source: International Penguin
Conservation Work Group
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