As the world heats up and life adapts or vanishes, some birds are ready with a solution that humans hadn’t considered. Zebra finch parents sing to their eggs, triggering development of heat-tolerant babies before the eggs hatch. These incubation songs seem to alter growth and development of the embryos who become smaller baby finches with bodies and long-lasting behaviors adapted to warmer temperatures. Zebra finches’ designer babies were discovered accidentally, a unexpected finding that motivates more studies.
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This serendipitous discovery resulted when behavioral ecologists were recording finch sounds at an Australian outdoor aviary. They noticed that sometimes, when sitting alone on the eggs, parents made distinctive high pitch calls. So they analyzed 600 hours of recorded calls and associated data, and found a surprise.
Both mom and dad zebra finch sing incubation songs, but only only during the last days before hatching when the embryo's temperature regulation system is developing, and only if it is hotter than normal outside the nest (above 78.8°F). Because finch parents keep eggs at a constant temperature by sitting on the nest, eggs don’t experience outside temperatures.
Ecologists wanted more information. They set up a controlled study with eggs in an incubator set at the usual nest temperature. During the last five days, researchers played to the eggs either the finch’s normal calls (control group) or the special incubation calls.
Upon hatching, those babies who heard the special calls weighed less and were more vocal than the babies who heard normal finch contact calls. These smaller finches are more resilient to hot climates.
“With a smaller body size, they’re better at losing heat,” [...] their lower body mass might also reduce oxidative damage, the harmful buildup of unstable molecules in proteins, fats, and DNA that can adversely affect reproduction.
The two sets of finch babies also behaved differently as adults and changes persisted at least two years.
When kept in hot conditions, the lower weight chicks did indeed go on to produce more fledglings in their first breeding season than did the control birds. But the control birds were more successful in cooler conditions. And the incubation calls may have other lasting effects. For two breeding seasons, the males that heard these sounds preferred nesting boxes that were hot, whereas the control males chose cooler homes.
Are finches designing their babies? Could the parents’ song trigger embryonic change? This may be part of the zebra finch’s normal life strategy as they live in hot dry regions of Australia and Indonesia. They have no fixed breeding season and the region’s temperatures vary.
Scientists agree this is an example of animals having greater control over their lives than humans realize. Perhaps embryos can learn more than we expect. Solutions like incubation calls and embryo changes may be widespread in other birds, but we don’t know because we haven’t been looking for them.
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