Excerpt from the Crystal Desert: Penguins (2)

I had the pleasure of spending time with David G Campbell during a cruise to the Antarctic. I love his book and will be posting excerpts from it from time to time.

The book is called “The Crystal Desert:  Summers in Antarctica” and is published by the Houghton Mifflin Company.

“A superior personal account of place, a remarkable evocation of a land at the bottom of the world (Boston Globe)

PENGUINS (2)

There are eighteen species of penguins, all from the Southern Hemisphere and all from Gondwana. Only two – the Adélie and the emperor – are truly Antarctic, spending their entire lives on the continent or close to it. The emperor, which breeds in the Antarctic on top of fast ice, is a wholly oceanic species – indeed the only species of bird that need never alight on land in the course of its life. The other species of penguins which nest in the Antarctic – the chinstrap, gentoo, king, macaroni, and royal penguins – have ranges that include the subantarctic islands. These seven species comprise 70 percent of the avian biomass in Antarctica.

King George Island is as cosmopolitan a place for penguins as any on earth. Chinstrap, Adélie, and the gentoo penguins all breed at Point Thomas and nearby Sphinx Hill, at the western entrance of Admiralty Bay. The three species are close relatives, all members of the family of “brush-tailed” penguins. In comparison to Bailey Head, this rookery is modest: only 18,000 Adélies, 2,800 gentoos and 300 chinstraps. At first it would seem that they all make their living the same way: crowding into the same low hills and beaches, vying for the same finite number of nesting pebbles and feeding on the same populations of krill in the bay. Careful long term study at Point Thomas has revealed important differences in the lifestyles of the three species, which have carved distinct temporal and spatial niches. It is only because Point Thomas is neither extremely Antarctic nor clemently subantarctic that they manage to coexist there. The Adélie penguin is adapted to the hostile conditions of the Antarctic and is near the northern edge of its range. The gentoo, a subantarctic species that is common as far north as the Falkland Islands, is at the southern edge of its range. Only the chinstrap, a species of the maritime Antarctic, is truly at home. The social structure of each species is woven into instinct and is adapted to the exigencies of place and time. The chinstraps have a strong perennial fidelity to both their nesting sites and their mates. This loyalty is probably due to the inclement  and variable conditions of their breeding sites along the Scotia Arc: a known nesting site and a tested mate are advantages in an unpredictable world, but only if the breeding season is long enough – and benign enough – to find another partner should last season’s consort not return in the spring. By contrast, the southerly Adélie penguins retain an attachment to their nest sites but not necessarily to their mates of the previous season; time is too short for the luxury of fidelity. Like the chinstraps, the gentoos maintain a strong pair bond over the season, but having evolved in a relatively warm sea with a surfeit of nesting beaches, they waste little energy in squabbling over real estate.

Adélie Penguin (photo: flickr)

Adélie Penguin (photo: flickr)

The reproductive sequences of the three species at Point Thomas are separated by intervals of several weeks. The first ashore, in late September, are the Adélies. The gentoos arrive in mid-October and the chinstraps three or four weeks later. Courtship, egg laying, and the nurturing and fledging of the chicks are therefore staggered; when the gentoos are at the peak of hatching in middle December, the Adélie chicks are two weeks old and the chinstraps are still incubating. Competition among the penguin species for krill – especially during the demanding period when the chicks are being nurtured – is therefore diminished. The three species also reduce competition by having different foraging ranges. Gentoos are homebodies that stay inside Admiralty Bay or close to its mouth in Bransfield Strait. Chinstraps range as far as 34 kilometers into the Strait; Adélies up to 50 kilometers. Their vertical ranges are different as well: gentoos dive to 150 meters, which explains why they can catch sufficient krill in Admiralty Bay; chinstraps and Adélies make much shallower dives, to a maximum of about 100 meters.

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