by Mike Bingham
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Gentoo Penguin - Pygoscelis papuaBreeding Range: Subantarctic islands and Antarctic Peninsula
World Population: 380,000 breeding pairs
The Gentoo Penguin is numerous and widespread in the Falkland Islands, but has only two very tiny breeding colonies in South America, one on Staten Island (Isla de los Estados) with about 200 breeding pairs, and one on Hammer Island (Isla Martillo) with under 50 breeding pairs as of 2020. World-wide there are about 380,000 breeding pairs of Gentoo, with about 100,000 pairs in the Falkland Islands. Other populations are found on the Antarctic Peninsula, and the islands of South Georgia, Kerguelen, Heard, South Orkney, Macquarie, Crozet, Prince Edward and South Sandwich.
GENTOO PENGUIN: Drawing by Mike Bingham
Gentoos are the second largest Falklands penguin, with an average length of 80cm and an average weight of 5kg. They have a reddish orange bill, apart from the black culminicorn, 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.
Breeding colonies are scattered throughout the Falklands, and rarely consist of more than a few hundred breeding pairs. When colonies exceed this size, they break up into smaller subcolonies adjacent to each other. 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.
Gentoos 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 1 - 3 days. Despite the two eggs being laid 4 days apart from each other, they both hatch within the space of 24 hours.
The female's reproductive tract actually produces three eggs, and she can lay these at 4 day intervals, however the third egg is only laid if she loses her first two eggs. This enables the third egg to be laid within just 4 days of losing the first eggs, and if it is not needed, the third egg is re-absorbed into the body. Even if the third egg is also lost, the female can still produce a completely new clutch of eggs within a month. This is a truly remarkable adaptation to egg-loss from avian predators, and helps to explain the Falkland Islands folklore that Gentoo penguins fare better when colonies have the first eggs removed.
The young chicks remain in the nest until they grow their mesoptile plumage at about 3 - 4 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.
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 mesoptile plumage has similar markings to the adult plumage, except that the dark areas are a browny grey rather than black, and there is no white head patch.
Gentoos 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 which 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 first.
Chicks fledge at around 14 weeks of age, but may continue to be fed by the parents for several weeks after fledging. This is possible because Gentoo penguins do not migrate during winter. After completion of the breeding season, adults spend time at sea building up body fat reserves prior to undergoing their annual moult. The moult takes around 2 to 3 weeks, and during this time birds spend considerable amounts of time tending to their plumage. Gentoos do not allopreen.
Gentoo populations are characterised 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. Gentoos are capable of breeding at just 2 years of age.
Because Gentoos at most sites tend to move the colony a few metres each year, they do not retain the same nests from year to year. On occasions whole colonies that have remained at one site for years, will up and move to a new site many kilometres 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, whilst others take the opportunity during the winter months to make longer foraging trips further afield.
Gentoos generally forage close to shore at depths of 20 - 100m, although they have been recorded diving to depths of more than 200m. Gentoos may make as many as 450 dives during a single days foraging. Penguins all look clumsy on land, but in fact Gentoos can out-run a man over short distances, and often make their colonies 1 or 2 kilometres from the sea.
Gentoos are opportunistic feeders, and around the Falklands are known to take roughly equal proportions of fish (such as Patagonotothen sp., Thysanopsetta naresi and Micromesistius australis), lobster krill (Munida gregaria) and squid (especially Loligo gahi, Gonatus antarcticus and Moroteuthis ingens).
There are 81 breeding sites in the Falkland Islands, with a total of around 100,000 breeding pairs. Breeding populations at these 81 sites range from less than 10 to over 5000 breeding pairs, but sites of more than a few hundred pairs consisted of several sub-colonies of less than 500 nests each.
At sea, Gentoos are subject to predation by Sea Lions, Leopard Seals and Orcas. On occasions 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. Mesoptile 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.
Although human activity 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. Gentoos 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 Gentoos are at risk from current levels of disturbance. Gentoos become tolerant of human presence, and do not generally become alarmed unless people approach within about 15m of the nest.
For many years the rural communities of the Falkland Islands took Gentoo eggs for food. Until recent years these eggs were an important supplement to the diet of many people in the Falklands, but now with regular supplies of hen eggs the tradition is gradually dying out. Penguin eggs are always taken at the start of incubation, and the birds rapidly re-lay, so that colonies which have had eggs taken show little difference in productivity by the time chicks are ready to fledge. This observation, along with the way that Gentoo colonies fluctuate in size without apparent cause, has led to much speculation about the merits of egging.
Many landowners believe that hatching rates are higher for the second brood, because a higher proportion of first brood eggs are infertile, but there is no scientific evidence to support this theory. Another theory is that because all the first brood eggs are removed at the same time, the second brood is more evenly aged than the first, which makes it more difficult for skuas and gulls to pick on smaller, weaker members of the colony. In addition the later brooding puts the colony out of phase with the needs of the predators, which are denied their food source at the start of their brooding period.
This second theory is harder to evaluate, and there could be some merit to it. On balance however, after much study of sites which are egged and those which are not, there is no obvious difference in chick rearing success rates either way, and this centuries old tradition probably has little impact one way or the other, provided it is not abused.
Human impact at sea is more difficult to evaluate. There is considerable commercial fishing activity in Falklands waters for squid and fish. Diet analysis shows that there is 6% overlap between those species being commercially harvested, and those which make up the diet of Gentoo Penguins. Whilst 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.
Food abundance does not so much control penguin populations through the occasional mass starvation, but rather through subtle changes in how effectively penguins are able to raise chicks, survive into adulthood and breed into old age. Any reduction in the abundance of prey will effect the ability of penguins to gather enough food to live and breed.
Life for a penguin is a constant balance between the energy expended hunting for food, and the energy gained by the food caught. Even a small reduction in food abundance means that penguins spend longer, and use more energy, searching for prey. This balance becomes critical during the early stages of chick rearing, when just one adult from each pair can feed at any given time, and yet food is required by both adults and growing chicks. The situation is further complicated by the fact that the foraging range is restricted to how far each penguin can travel in a single day. During chick-rearing Gentoos rely on feeding areas within 20 km of their nest-site.
The Falkland Islands are internationally important as both commercial fishing grounds and seabird breeding sites for essentially the same reason; the richness of the marine food resource. Prior to any commercial fishing activity, seabird and marine mammal population sizes would have been largely controlled by food abundance. Within the overall ecosystem, there would have been many interacting cycles of predator-prey relationships, but all these food webs would have depended on the overall food availability. Any reduction in this level of food availability, be it from natural or human factors, will inevitably lead to a reduction of the populations which it can support.
Prior to the establishment of the Falkland Islands commercial fishing industry, Gentoo penguin populations averaged about 120,000 breeding pairs in the Falklands. This dropped to 65,000 pairs by 1995 following the establishment of the commercial fishing industry in 1988. However Gentoo penguins are very adaptable, and managed to modify their diet to use species not caught by commercial fishing, thereby reducing direct competition for resources to just 6%. This adaptation has allowed the Falklands population to return to a current population of about 100,000 breeding pairs.
Direct mortality from human activities has generally been low. Few penguins are caught by fishing vessels, other than through discarded nets and marine refuse. There has been very little pollution around the Falkland Islands, except during 1998 when a brief period of oil exploration led to three separate oil spills that killed several hundred penguins. Standards must be improved if oil exploration is ever resumed in the Falklands.