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Missing in Costa Rica: female crocodiles

Male crocodiles suddenly outnumber females. That's not good news for the species.

American crocodile
A crocodile, which lost part of his upper jaw during a fight with another crocodile, eats at the crocodiles farm inside the San Carlos Technological Institute on June 20, 2008. (Yuri Cortez/AFP/Getty Images)

SAN JOSE, Costa Rica — Where have all the female crocodiles gone?

Scientists in Costa Rica are concerned about the dwindling number of female crocodiles on the Pacific coast.

They warn that a dramatic switch-up in the sex ratio could lead to the crocodile's demise in that region within the next 25 to 30 years.

The sex of the American crocodile (Crocodylus acutus) is determined by temperature during egg incubation, with males hatching in warmer temperatures. Scientists say that climate change and deforestation are raising temperatures enough to create a sex imbalance.

While the ratio usually skews toward females by 3:1, a study of the Tarcoles River found the ratio had shifted to 1:1. Then a study in the Tempisque River showed males are dominating by as much as 5:1.

Laura Porras, the biologist who led the Tempisque studies, said the difficulty in finding female mates has spurred aggressive behavior among the males.

Costa Rica sees an average of eight crocodile attacks per year, which she says is high for such a small country. An average of three fatal attacks occur each year, said Juan Rafael Bolanos, a statistician and member of the Association of Central America Crocodile Specialists.

When a crocodile attacks a human or livestock, people tend to retaliate by killing off the nearby crocodiles, Porras said.

Beyond the threat of slaughter, the male-female ratio could tip the balance too far for the population to sustain itself. Bolanos gives Tampisque’s crocodiles until 2040 at the latest to survive under these conditions.

The United Nations forecasts the planet’s temperatures will rise one to six degrees over the next century. Many scientists predict hotter and drier days could decimate plant and animal life in Costa Rica, one of the world’s most biologically diverse regions. Amphibians and other types of species have already disappeared.

Researchers in Costa Rica say local environmental damage is creating localized climate change. They say over-farming and land development have encroached on the rivers, clearing away vital plant cover that provides shade for crocodile nests, heating the eggs enough to create a sex imbalance in a species whose females are expected to outnumber males.

“There are very large companies — producers of watermelon, cantaloupe, rice, sugar cane — and they don’t respect the riverbanks. The crops grow right up to the river,” said Bolanos, who participated in the Tempisque study.