Too few males driving antelope to extinction
Selective poaching of male saiga antelope has pushed the endangered species closer to extinction, scientists say.
Saiga antelope are one-metre tall, weigh about 35 kilograms, have skinny legs and large eyes and noses. The nomadic herds live in the semi-arid rangelands from central Asia to Russia.
Males have long, ringed horns prized for traditional Chinese medicine. Hunting of males for their horns has led to a gender bias, where females outnumber males by a ratio of 100 to 1.
In 2002, aerial surveys suggested the world's population of saiga antelope had shrunk by 95 per cent since the 1970s down to 50,000 individuals.
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Scientists had assumed a shortage of males isn't necessarily a problem since one male can mate with many females. Saiga herds are organized in harems of females.
"Our observations indicate that if the percentage of males in the population falls below one per cent, reproductive collapse will result," said the study's leader author, Dr. E.J Milner-Gulland of Imperial College London.
Milner-Gulland and her colleagues in Russia and Kazakhstan collected population data on saigas in Kalmykia, Russia, between 1992 and 2002.
They found changes in population density or climate didn't account for the drop in number of offspring. The team concluded the heavily skewed sex ratio must be driving the decline.
In 2000, the researchers saw single males were surrounded by dominant females, who drove away younger females. The observation could explain why most first-year females failed to become pregnant.
All may not be lost, though. Historical data suggests a similar crash happened at the beginning of the 20th century, but a strict hunting ban allowed the saiga population to recover.
The study appears in Thursday's issue of the journal Nature.