If you’ve called recently about booking an encounter with one of our Magellanic penguins, you know that the birds are molting. We suspend the penguin encounters during this two- to three-week period while the birds refeather.
For penguins, molting is an annual process during which they completely replace their plumage. (Some bird species have a second either partial or complete molt during the year.)
“The Magellanics look like shorn sheep,” says Lana Vanagasem, Shedd's supervisor of sea otters and penguins, shown above leading a penguin encounter. The birds probably feel like it, too. She speculates that the sensation of the new feathers emerging from the follicles in the skin is itchy. “They definitely can be irritable during molt,” she says.
They’re messy, too, as each bird drops thousands of feathers that drift around the rockwork, float on the water and settle into the drains. “We constantly collect feathers from the drains,” Lana says.
Scientists call this all-at-once whole-body changeover a "catastrophic molt," a graphic and only slightly hyperbolic term. A penguin in the midst of a molt has been described as looking like a down pillow that exploded.
New feathers emerge under the old ones before the latter fall out, so at least the bird is never naked. But it’s a patchy process. In areas where the new feathers have grown in completely, the old ones are finally pushed out. So when a bird looks its “exploded” worst, it’s actually in the home stretch.
Penguin feathers are small and densely packed—about 70 on a square inch of body surface. Fuzzy down at the base of each feather shaft traps body-temperature air next to the penguin’s skin, creating an insulating layer. The stiff, shiny feather tips overlap tightly to keep water out. Penguins carefully maintain their feathers, cleaning them, rearranging them and preening. When penguins preen, they spread oil from a gland at the base of the tail to make their bodies as waterproof as a rain slicker. The oil also reduces friction in the water, enabling them to zoom like greased lightning with the least expenditure of energy.
After 12 months of swimming, hunting, clambering over rocky terrain and raising the kids in a burrow, however, a Magellanic’s feathers are pretty worn, and even broken. Because feathers are “dead” structures, made out of keratin like our hair and fingernails, they don’t heal, so they have to be
Molting is tied to seasonal changes, including shortened photoperiod, or day length, which triggers hormonal changes in the birds. At Shedd, we re-create the penguins’ natural photoperiod, albeit flipped to match Northern Hemisphere seasons (or else they’d be in winter dusk during your summer visits), using lights on a programmed timer to lengthen and shorten their “daylight” through the year.
Molt also coincides with the relative downtime between nesting and returning to the sea. In their native Southern Hemisphere range, along the coast of Chile, around the Straits of Magellan and halfway back up the Argentine coast, the young of the year begin molting in January, which is midsummer, acquiring their first adult plumage. They are followed by young adults in late February and the older adults in late March, after their chicks have left the nest.
During this lull between fledging and migrating back to their winter territory, the birds start gorging themselves on fish, both to support the energy-intensive feather-building process and to lay on additional blubber to tide them over during the molt. For the 19 or so days that the new and old feathers are changing places, penguins are not waterproof, so they can’t hunt.
That instinct carries over at Shedd. Lana says, “Usually our birds eat a lot of fish before getting ready for molt. Each bird’s diet can increase from 20 to 30 fish a day up to 50 to 60 fish. They bulk up because they won’t be able to go in the water. And while we’re able to offer them fish out of the water, during this period they might snack on a few, but they usually don’t eat very much at all.”
Appetites—and good humor—return at the end of the molt.
So do our penguin encounters. The 30-minute programs resume Friday, Sept. 14. Encounters are offered on Fridays, Saturdays and Sundays. Each session is limited to 10 people, so book your encounter in advance by calling 312-692-3355.
But the resumption of encounters doesn’t mark the end of molt season in the penguin habitat. While the Magellanics are almost finished, Lana says, the rockhoppers have just started.
Karen Furnweger, web editor