Since hatching three weeks ago, the Zoo’s harpy eagle chick has grown from a helpless little ball of fluff to, well, a significantly larger ball of fluff. (Read Beau’s previous blog, Harpy Eagle Chick.) The chick doubled in size in just about a week and now (at almost three weeks) weighs nearly a pound.

Its little legs, barely wider than a toothpick at hatching, have grown wider than a Bic pen. They’re not even strong enough yet to support the rapidly growing chick, but as the talons grow in and begin to curve downward, the feet are becoming weak, miniature versions of the adult harpy eagle’s lethal killing tools. The adult harpy eagle’s foot can have a span as large as a man’s hand and is capable of exerting over 500 pounds (225 kilograms) per square inch of pressure. That’s more pressure than a gray wolf’s bite and about five times the grip of an average man’s hand!

As the baby eagle has grown, its appetite has kept pace! The Avian Propagation Center’s (APC) animal food preparers are now providing skinned mice and rats that are minced into bite-sized pieces before being fed to the hungry chick. Yum! We supplement the chick’s meals with vitamin B and calcium and set them outside each day (weather permitting) to soak up vitamin D from the sunlight. The temperature in the eagle’s brooder is reduced little by little as the chick is able to better regulate its own body temperature. Soon the medium-white fluff ball will be moved out of the brooder’s confines and into a larger nest tub. There, as it gains strength, the eaglet will be able to stand up, stretch its wings and eventually “branch.” (To branch means to leave the nest and begin to climb out onto the surrounding branches.)

Nobody knows yet if the eaglet is a boy or a girl. Adult female harpy eagles are significantly larger than their male counterparts, but the only way to definitively sex a baby is with a DNA test. Fortunately, such a test can be performed without laying a finger on the eaglet. As the chick developed inside the egg, blood vessels also formed on the inner surface of the shell. That vascular tissue was left over after hatching and the broken eggshell has been sent off to a lab where technicians will be able to recover enough DNA from the tissue to determine the chick’s sex.

Beau Parks is a keeper at the San Diego Zoo.

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