【英语时差8,16】鸟类荷尔蒙映射其生活策略(下)（在线收听）

Researchers wondered if corticosteroid variability was somehow related to life strategies. Would birds like the short lived great Tit, which lays twelve eggs at a time, have different hormone levels than the Spotted Ant bird which lays only two eggs and lives as long as eighteen years? Researchers collected blood samples from many bird species in North America and Panama, and used additional research data to compare corticosteroid levels to life strategies. They measured both baseline and stress induced hormone levels, and found that species with long life spans had lower baseline hormone levels, but higher stress induced levels than short lived species. Scientists think there is a physiological reason for this. Hormone levels are costly to maintain. The “hares” of the bird world pay that cost because they have few chances to have offspring. They can’t afford to make a mistake. The “tortoises”, on the other hand, have more breeding time and don’t need to keep their hormones on alert continuously. Instead, they wait until the threat is present and then ramp up their hormone levels. It’s all a matter of strategy.