Increasing Frequency Of El Nino Takes Toll On Northern Hemisphere's Only Penguins

May 26, 1998

El Nino means milder winters for some in the United States and flooding and mudslides for others. For the penguins living in the Galapagos Islands off South America, it means possible starvation.

The increasing number and strength of warm-water El Nino events, along with a decline of colder-water La Nina events, have reduced the population of Galapagos penguins by half since 1970, says researcher Dee Boersma, a University of Washington zoology professor and a leading authority on temperate- and equatorial-zone penguins. Only recently had the penguins shown signs of recovery from drastic losses during the last two decades, she says. That was before the current El Nino.

Boersma's most recent analysis of the long-term effects of El Nino on the Galapagos penguin population was published in the May issue of the journal Condor.

Additionally, she returned to the Galapagos for two weeks in early May to examine the impact of the current El Nino, the strongest this century, on the penguin population. Her observations were striking: dead marine iguanas and sea lions, undernourished flightless cormorants and a generally emaciated penguin population in which no juveniles were seen.

"What that suggests is that none of the penguins bred in the last six months, or if they did breed none of (the chicks) survived to become adults," said Boersma. In the equatorial Pacific Ocean surrounding the islands, she measured water temperatures of 83 to 84 degrees Fahrenheit, much warmer than usual and too warm to sustain the food supply for animals that normally feed in the water. Some of the marine iguanas that normally forage in intertidal basins were observed feeding on land.

"The islands were very lush, green and verdant, which is unusual," Boersma said. "It's like the ocean is the desert right now and the land is the garden. It's usually the other way around."

Boersma is concerned that the increased intensity and frequency of El Nino events, combined with fewer and milder La Nina events, could continue reducing the islands' penguin population.

"I'm certainly not at all convinced that the Galapagos penguin is going to go extinct because of this," Boersma said. "But I am concerned that the numbers are going to become increasingly low, and we know that with smaller populations they're just more vulnerable to extinction."

The flightless birds are among the smallest penguins, typically standing 20 to 24 inches high and weighing 4 to 5 pounds. They live primarily on two islands in the Galapagos Archipelago off the coast of Ecuador. Since they can range to the northernmost reaches of the chain, above the equator, they are the only penguins whose natural habitat is in the Northern Hemisphere.

Boersma says the birds' current population is likely in a range of 4,250 to 8,500, half the total when she first studied their population and nesting patterns in the early 1970s. Recent population counts have been conducted by the Ecuadorian National Park and the Charles Darwin Research Station using the methodology she established.

There are two primary reasons for the population decline, both linked to food shortages because of El Nino, Boersma says. In some instances, adults simply don't attempt to lay eggs. In other cases, they don't have enough food to sustain themselves and so abandon their nests. Such food shortages affect females more severely because they have less ability to store reserves. The Galapagos penguins are the only ones that molt before breeding. Sometimes they don't get enough nutrition to sustain them through that physically taxing feather-shedding process, which Boersma says could leave some of the birds too weak to survive, let alone breed. During her latest trip, some of the 100 penguins she observed were starting to molt, which she says is an encouraging sign the food supply might be returning.

The situation is complicated further by increasing human activity in the islands. More boats increase the likelihood of oil dumping, Boersma says, and a larger number of people engaged in fishing make it more likely for penguins to get caught in the nets.

Evidence suggests that El Nino Southern Oscillation, or ENSO, events cause changes in the ocean that deprive the penguins of the schools of small fish, mostly mullet, on which they feed. Typically a Cromwell current, basically a deep undersea cold-water river, is forced to the top by underwater volcanoes in the area of Fernandina and Isabella islands, where the penguins live. The current carries nutrients that sustain zooplankton and phytoplankton, which attract the fish.

But during El Nino, the Cromwell current disappears and the fish go elsewhere in search of food. That in turn deprives the penguins of nutrition or forces them to forage farther from home, Boersma says. They can't simply move to a new home because the nearest land is more than 600 miles away.

"I think the concern is that perhaps the frequency and the extreme nature of (ENSO events) is different now in this period than what the birds have historically or evolutionarily been exposed to," Boersma said.

The penguins' sharpest population decline appears to have come during the El Nino of 1982-83, the strongest recorded before the current El Nino started. Boersma originally studied the Galapagos penguin population in 1970, 1971 and 1972. In 1971, during a La Nina event, she found that 80 penguin chicks had fledged from 62 nests. The following year, during an El Nino, she found that all but one of the 92 nests failed in a winter breeding period and all 108 nests failed in the fall breeding period. She also visited breeding sites in 1978, 1988 and 1991.
-end-


University of Washington

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