A Two-Part Egg Mystery May Have One Answer

Chris Gash

By SINDYA N. BHANOO

Published: July 19, 2010

Every year, the female macaroni penguin lays two eggs. Peculiarly, the first is smaller than the second. Stranger still is that she kicks the first egg out of the nest before it hatches.

The second is incubated until birth.

The puzzle of the abandoned egg has occupied biologists for six decades. Now, a new study, which will appear in the American Naturalist, offers a partial solution. The first egg’s smaller size may be because of a drop in protein levels as the penguin returns to land (South Georgia, in the case of the penguins in the study) from the sea.

Researchers found that penguins who lay their first egg within days of arriving on land for breeding season have particularly small eggs — sometimes 50 percent the size of their second egg. Those that wait have first eggs closer in size to the second egg.

The penguins that lay earlier may produce their eggs as they are migrating across the ocean and are not yet ready for reproduction. During this time they have lower amounts of vitellogenin, the primary protein in egg development, said Glenn T. Crossin, a sea bird biologist at Simon Fraser University in Vancouver and the Centre for Ecology and Hydrology in Britain and the study’s lead author.

Why the penguin goes through the effort of producing the first egg is still puzzling. It may be an example of maladapation — or evolution gone awry, Dr. Crossin said. “The thinking is that evolution works perfectly, but that’s not always the case, and the macaroni penguin is one good example of that,” he said.

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