General Discussion

Kleindorfer decided to study bird eggs and early development, which were then neglected research topics. "Maybe this was because only females have eggs and I was a woman in science," she told me. "I don't have a better reason." Kleindorfer had noticed that mustached-warbler chicks seemed to respond to the alarm calls of adult warblers, even though the thinking at the time was that such calls were directed at other adults, or possibly at predators. "If I put a snake nearby, the parental alarm call made the chicks in the nest jump," she said. "If I put a marsh harrier"—a hawk like predatory bird—"nearby, the response to the parental alarm call was that the chicks would duck." The chicks were responding appropriately to different alarm calls—a satisfying finding.

Kleindorfer also studied the superb fairy wren, a songbird that weighs about as much as a walnut and sports a flirty, upright tail. Despite their fanciful names, fairy wrens are commonplace in Australia. They are socially monogamous but sexually promiscuous—they are essentially in open marriages—and they bring up their young collectively. Arguably, they have even more to chat about than geese do. Fairy-wren nests are about the size of cupped human hands, built to contain pale, speckled eggs that are smaller than thumbnails. Kleindorfer and her team wired up nests with cameras and microphones and soon discovered something that they hadn't known to look for. "The mothers in nests were producing an incubation call—a call to the eggs," she told me. It was like a lullaby. Why would a mother bird make any sound that could attract predators to the nest? "Songbird embryos don't have well-developed ears, so this was completely unexpected," she said. "That started a twenty-year project—why is she calling to the eggs?"

The team compared incubation calls to the begging calls of young chicks. "It was very odd," Kleindorfer recalled. "Each nest had its own distinct begging call." What's more, each begging call matched an element from the mother's incubation call. This suggested, startlingly, that birds could learn a literal mother tongue while still in ovo. (Humans do this, too; French and German babies have distinct cries.) Even "foster" chicks, who as eggs were physically moved from one nest to another, learned begging calls from their foster mothers, rather than from their genetic mothers. This was big news in the ornithology world. "The paradigm of how songbirds learn—after hatching, from their father's song—was overthrown," she said. The same process was soon documented in more songbird species.

https://www.newyorker.com/magazine/2024/10/21/how-scientists-started-to-decode-birdsong