Documentary Tracks Cuckoo Egg Mystery

Why do cuckoo birds push their own eggs into other nests to hatch? This phenomenon has been studied for over a century, but the answer is still not clear. In Korea, it is an almost forsaken field of study.

The EBS documentary: “Youth Discovering the Secret of Life – Small Devil, The Cuckoo’s Fall” (November 25, 11:05 p.m.) captures it all on tape. The camera follows two youngsters who research the cuckoo’s egg-pushing behavior. Husband and wife Jang Byeong-soon (32) and Lee Yoon-kyung (29), who will be studying in a doctoral program at the University of Manitoba in Canada next year, have picked their brains for the key to the mystery of the cuckoo’s habit of pushing eggs out of its nest. The two have immersed themselves in observing the cuckoo in Yangpyeong-gun, Gyeonggi Province since this April.

The foster mother of baby cuckoos differs for each country. For Korea, it’s the vinous-throated parrotbill, also known as a “crow-tit.” The two researchers, however, say that only parrotbills that lay blue eggs are mothers to cuckoos. Those with white eggs can discern if the cuckoo’s egg is not its own. During the EBS experiment, a parrotbill with white eggs threw away the cuckoo’s egg.

The camera shows a cuckoo making its first visit to the parrotbill’s nest and stealing an egg. Four hours later, it flies back and leaves its own egg, taking another egg from the parrotbill’s nest.

Up until now, it was widely known that the cuckoo took away an egg in exchange for its own, but the observation showed that there were cases where two or more were taken. The young researchers theorized that it was a strategy for raising the survival rate of its own eggs.

A curious fact was that the biological mother displayed no signs of maternal love. She would push her eggs into the parrotbill nest without a second glance. The baby cuckoo also doesn’t recognize its mother and grows to leave the parrotbill foster mother’s nest.

The “why?” question is still a mystery.

Filmed in high-definition format, the show captures the birds and the natural scenery with crystal clarity.

kimjy@donga.com