by Mike Bingham
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Galapagos PenguinSpheniscus mendiculus
Breeding Range: Galapagos Islands
World Population: less than 1,000 breeding pairs
Galapagos Penguins have the smallest breeding range and population size of any penguin, with less than a thousand breeding pairs. They only occur in the Galapagos Islands, with 90% of the population being restricted to the western islands of Fernandina and Isabela.
Galapagos Penguins are the smallest of the South American penguins, with an average length of less than 50cm, and an average weight of less than 2.5kg. They have a black head and upperparts, with a thin white line running from the throat, up around the head to meet the corner of the eye. The underparts are white, but are bordered by a black line which extends down to the blackish legs. The upper bill and tip of the lower bill are black, with the remainder of the lower bill and surrounding skin around to the eye being pinkish yellow. The females are smaller than the males, but have similar plumage.
Unlike most other penguins, Galapagos Penguins have no particular breeding season, and may have as many as three clutches in a single year. This is an adaptation that allows them to take advantage of periods of high food abundance, and to cope with a very variable and unreliable food resource.
Galapagos Penguins undergo their moult prior to breeding, and may moult twice in a single year. Moulting birds generally avoid the water, but because the equatorial waters are warm, birds that become underweight are able to go to sea to feed, rather than face starvation.
By moulting prior to breeding, Galapagos Penguins are able to ensure that early failure of their food resources will not result in starvation during the moult. Should food supplies disappear prior to the completion of breeding, then breeding success will suffer, but the adults will have the highest chance of surviving the shortage. It is the survival of the adult population that ultimately ensures the survival of the species.
Sea surface temperatures around the Galapagos Islands can vary between 15 - 28 degrees Celsius. During periods of high surface water temperature, primary production is low as a result of the nutrient poor waters, and food becomes short. Such periods of extreme food shortage are called El Niņo Southern Oscillations (ENSO), and during such seasons penguins postpone breeding completely. It is better to delay breeding than to risk adult starvation, which is still the main cause of adult mortality.
El Niņo means "The Boy", and was so named after the Holy Child Jesus Christ because it usually peaks around Christmas time. During ENSO events, cool nutrient rich waters flowing northwards up the coast of Chile and Peru become displaced by warm nutrient poor waters from the central Pacific. The drop in primary production resulting from the low nutrient levels, works its way up through the food chain, causing food shortages for many species that depend on the ocean. The affects of ENSO events are not restricted to the ocean, since weather patterns are also disrupted right across South America and the Caribbean, usually associated with heavy rains.
Breeding is stimulated amongst Galapagos Penguins by a drop in sea surface temperatures to below about 24 degrees Celsius, which corresponds to the presence of nutrient rich currents, and in turn an abundance of prey. Nests are made along turbulent rocky shores within about 50m of the water, mostly on the islands of Fernandina and Isabela. Burrows are sometimes dug in suitable volcanic deposits, but often nests are in caves or crevices in old fissured larva. Adults remain around the breeding sites throughout the year.
Two eggs are laid 4 days apart, but adults do not normally re-lay if the clutch is lost. Incubation of the eggs takes 38 - 40 days, and is shared equally by both parents. Chicks are brooded for the first 30 days, and this is performed by both parents, with daily change-overs. By the end of the 30 days, the chicks have developed a mesoptile plumage that is brown above and white below, which serves more to protect the chicks from the strong sun than to keep them warm. Both adults are then able to forage for food, but chicks do not form into creches.
Chicks fledge at 60 - 65 days of age, and fledging may occur at any time of year. Fledglings have greyish black upperparts and white underparts, but lack the white lines of the adults. Instead they have paler cheeks which indicate where the thin white head line will later develop. Pair-bonds are long-lasting, and this allows rapid reproduction when conditions become favourable. Pair-bonding is constantly reinforced by allopreening and bill duelling.
The main problem that Galapagos Penguins face in relation to weather, is from the strong sun. Entering the water enables penguins to cool off, but when on land they have a number of behavioural adaptations that help them to keep cool. Birds can lose heat from the exposed areas of skin on their feet, and the underparts of their flippers, aided by increases in blood flow to these areas. Birds are often seen standing with out-stretched flippers, hunched forward to shade their feet from the sun. They also lose heat by evaporation from the throat and airways through panting.
Galapagos Penguins do not leave the archipelago, and generally forage close to shore in the cooler Cromwell Current, returning to the land at night. Their diet comprises almost entirely of small schooling fish, particularly mullet and sardines of 1 - 15 cm in length, although some crustaceans are also taken. Co-operative feeding is often employed, and foraging is restricted to daylight hours. Foraging rarely occurs more than a few kilometres from the breeding site.
During periods of food shortage, penguins tend to forage individually, and make no attempt to breed until surface waters drop in temperature once more. During 1982/83, an ENSO event hit the Galapagos Islands so badly that around 77% of the penguin population starved to death, and the population has only gradually been showing signs of recovery.
During 1970/71, the population of Galapagos Penguins was estimated at 6,000 to 15,000 birds. During October 1997, an archipelago-wide census conducted by the Charles Darwin Research Station recorded a total population of just 883 adults, with 184 juveniles and 217 birds of undetermined age. Nevertheless, this was 27% greater than a similar census conducted during 1996.
Unlike larger penguins which have few natural predators on land, Galapagos Penguins must guard against crabs, snakes, owls and hawks, although predation from such sources is generally low. At sea Galapagos Penguins may be killed by sharks, fur seals and sea lions. On Isabela, introduced cats, dogs and rats are also predators. In addition to predation, and other natural hazards associated with an unreliable food resource and volcanic activity, they face a number of man-made hazards.
Tourists and illegal sea cucumber fisherman create disturbance, and affect the marine ecosystem. The illegal fisherman chop down and burn mangrove trees in order to cook the sea cucumbers, affecting the penguins' nesting habitat, and both fisherman and tourists discard refuse that regularly entangles and kills unsuspecting birds. Penguins are also accidentally caught in fishing nets.
The Galapagos Islands are only small, and careful management will be required to balance the increasing pressures from human activities, with the needs of sustaining the fragile and unique ecosystem. Clearly with such a small remaining population, the Galapagos Penguin faces the possibility of extinction, unless such a balance can be successfully achieved.
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