Penguin Dispatch 4: How to Study a Penguin Egg
Females guard their eggs closely, so scientists must tread carefully when temporarily extracting the eggs for research
- By Eric Wagner
- Smithsonian.com, June 04, 2009, Subscribe
Antarctic skuas are close relatives of gulls, albeit larger and a good deal more menacing. I first saw them in late September doing lazy circuits around the colony fringes. They seemed not to fly so much as scull the air with dark blade wings. Now, a couple of weeks into October, they move with a swifter purpose, streaking low over my head in twos and threes, here quick and then gone. I am terrestrially bound and move more slowly, but we are searching for the same thing: penguin eggs.
A female Magellanic penguin will lay a clutch of two eggs. Each is about half again as large as a big chicken egg, and, I’m told, has a subtle fishy flavor. For his part, the male penguin has keenly anticipated them. He has had to sit at the nest for up to a month, fasting, unable to leave for fear of losing either his home or his mate to some eager lothario, of which Punta Tombo has no shortage. But once the second egg is laid and he is reassured that he is likely to have been responsible for both, off he goes.
Wedged in the back of a small burrow, it is a female that scowls out at me when I come to measure her clutch, my trepidation running high, egg cup in hand. Like all classic field equipment, the egg cup is a product of domestic salvage and ingenuity—a tin can wrapped in layers of the ubiquitous duct tape and lashed to a yardstick. So laden, I feel a little absurd as I try to explain to some bemused tourist in my caveman Spanish, with supplemental gestures, that I’m off to “touch egg with cup.”
To retrieve an egg, the egg cup is thrust into the nest, where it must withstand the female’s defensive jabs as the egg is maneuvered inside it. I record the egg’s length and width and relative temperature. For good measure I weigh the female, too. Her weight especially gives a sense of her body condition, and whether she has enough fat reserves to last out her mate’s two-week absence. Penguins lose about 2 ounces per day of fast, and Dee has found that once a female drops below 6.1 pounds, she’ll abandon the clutch. In good years, females will weigh more than 9 pounds between the laying of the first and second egg. But this year, many weigh less than 7 pounds. They are cutting it close.
I now have to return the egg. As one who has enjoyed his share of omelets, I’ve seen plenty of chicken eggs come and go in my time. But to hold an egg that actually contains nascent life is quite another matter, a tremendous responsibility. Part of my anxiety is due to the carnage scattered around. The penguins have been laying eggs for a few weeks and the ground is littered with broken eggshells, the depredations of skuas and kelp gulls. To break the egg through clumsiness would put me in league with those ne’er-do-wells. But the task is further complicated by a quirk of penguin cognition. Once an egg is no longer in the nest—once it is beyond the reach of its parent’s bill—the penguin will not recognize its own egg as an egg. Rather, the egg has become like any other thing not itself in the nest—a predator. The transformation from “Fruit of My Loins” to “Mortal Foe” is shockingly abrupt. As I scoot the cup back, the egg rattling loosely inside, the furious penguin hammers away, grabs the cup, thrashes it. Were the egg to bounce free, she would fiercely peck and break it. And I would feel awful.
Thankfully, though, once they are returned, the female is quick to forgive the eggs their absence. She clucks lovingly at them as if the previous five seconds had never happened, and tucks them back under her the warm, unfeathered area of skin called a brood patch. Settled on her eggs, she stares out at me, wondering what I am doing there. I wait for my pulse to slow, and then move on.
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