The sounds are similar to "motherese," the high-pitched, sing-song noises human mothers around the world use to communicate with their babies.

Photograph by James Warwick/Getty Images

EMAIL NEWSLETTER Photos and News of the Week Get the top photos and news of the week from National Geographic News, plus occasional breaking-news alerts. See Sample >> Please enter a valid email address Thank You! Subscription accepted. An email confirmation will be sent. Privacy Policy MOST VIEWED NEWS Earth's Core, Magnetic Field Changing Fast, Study Says Even Modest Increases in MPG Can Equal Big Gas Savings Amazon Tribe Attacked by Masked Gunners NEWS FEEDS      Get our news delivered directly to your desktop—free. How to Use XML or RSS