The largest living tortoise is helping the Galapagos Islands’ biggest bird – an endangered master aerialist of the Pacific Ocean – the Waved Albatross.
By Rex Graham
Only about 34,000 of the birds with 8-foot (2.4 m) wingspans survive. The Waved Albatross is the only tropical albatross in the world. It breeds almost exclusively on Española Island. The fish- and squid-eater, like other seabirds, takes advantage of the island’s geographic position at the confluence of three ocean currents and the rich marine ecosystem there.
Waved Albatrosses have no trouble flying 60 miles to lunch at ocean upwellings. However, their 8-foot wingspans make ground takeoffs and landings notoriously clumsy. Unfortunately, the overgrowth of vegetation at its nesting sites interfered with the birds’ ability to come and go to feed their hungry chicks.
Another albatross, another vegetation issue
The Tristan Albatross faces a similar, but direr situation on Gough Island in the South Atlantic. An invasive perennial shrub (Sagina procumben), which grows in cracks in concrete in the Northern Hemisphere, has invaded Gough Island. The plant spreads as a dense, 1-foot-thick moss-like layer of impenetrable twigs. The birds can’t dig nesting burrows through the tangle. Albatrosses and other seabirds, invertebrates and plants are in danger of being shoved out by the shrub.
The mostly pristine and undisturbed 91-square-km (35-square-mile) volcanic island about midway between South Africa and Argentina is the only breeding site of the entire world populations of Tristan Albatrosses, Spectacled and Atlantic Petrels and Gough Buntings. The Royal Society for the Protection of Birds (RSPB) is leading an effort to remove the invasive plant. The RSPB also is eradicating an introduced mouse that bites and eats albatross and petrel chicks on the UNESCO World Heritage site.
Galapagos goat crisis
On Española Island, vegetation had grown unchecked after thousands of endemic Española Giant Galapagos Tortoises were eliminated by humans. The last 15 tortoises were evacuated decades ago to a captive breeding facility on another island.
Introduced goats made matters worse for the albatrosses. The goats quickly devoured the prickly pear cactus forests and other plants that had benefited tortoises. However, the goats ignored woody plants, which grew tall enough to interfere with the albatrosses’ takeoffs and landings.
The Charles Darwin Foundation for the Galapagos Islands has repopulated the island with tortoises from its captive-breeding facility. The reptiles are munching their way through the vegetation, removing woody-plant seedlings before they grow tall enough to impede the birds. Scientists call it “ecosystem engineering.” More work is needed to clear all the tall, old brush, but conservationists and tortoises make a good team.
Benefits of ‘Ecosystem Engineers’
About 1,500 tortoises now live on the island. They remove woody plants, scatter seeds of beneficial plants, and act as bulldozers to continually prune vegetation in albatross nesting areas. The albatrosses have learned to roll their eggs out of the paths of tortoises.
“Española tortoises and Waved Albatross may have a long co-evolutionary relationship,” said a team of scientists in an October 28, 2014, paper in PLoS ONE. “The effects of giant tortoises on terrestrial ecosystems of oceanic islands are potentially on par with those of mega-herbivores as drivers of savanna structure and function.”
So far, most tortoises have restricted themselves to remnant cactus patches with few woody plants. However, the Charles Darwin Team is planning large-scale habitat restoration to help the tortoises expand into more areas that will overlap with nesting albatrosses.
The Waved Albatross population has declined as much as 19 percent in the past 84 years.
The birds are often killed when they get hooked while pursuing fish-baited longline fishing sets as they are lowered from boats into the water or reeled up later. “Even if immediate action was taken to curb adult mortality, the population will continue to decline for a decade or so until the current cohort of juveniles reach breeding age,” says a BirdLife International species description.
Fisherman with taste for albatross
Small-scale fishing operations off northern Peru are particularly hazardous. Based on 36 interviews in 2008 at the port of Salaverry, Peru, researchers said fishermen kill 16-24 Waved Albatrosses a year. “Reasons for capturing albatrosses included insufficient food supplies onboard during long fishing trips, collection of rings from ringed birds, the development of a taste for the bird’s meat and even boredom,” researcher from Peru, the U.K., and Sweden reported in the Pan-American Journal of Aquatic Sciences.
Despite the albatrosses’ predicament, Española Island offers birdwatchers unique opportunities to observe Waved Albatrosses and Giant Tortoises. Albatross pairs perform elaborate bowing and bill-clacking displays during courtship. Females lay a single egg in April through June, and the eggs hatch after a two-month incubation. The young congregate in large nurseries and begin to fly late in the year.