The Rise of Black Robins Laying Rim EggsHow Human Conservation Efforts Can Cause Unforeseen EffectsBy Simone Scully
The black robins on Chatham Islands were in trouble. By 1980 only five birds remained, including a single breeding pair. Introduced rats and cats had devoured the birds nearly to the point of extinction. Given the dire circumstances, researchers felt they had no choice but to step in and encourage the survivors to get busy.
Black robins are known to re-lay if a clutch is lost, so they removed the eggs laid by the last fertile female, “Old Blue,” from her nest, and placed them with birds of a related bird species to be hatched and raised. It worked; Old Blue quickly laid another clutch.The meddling didn’t end there, though: Scientists also moved black robin eggs that were laid on the edges of nests, which usually don’t hatch, into the middle of the nest to increase their chances of survival.
But the scientists’ well-intentioned intervention nearly backfired. Because they were moving the eggs to the center of the nest, the bad egg-laying trait was passed on to future generations. By 1989, 50 percent of all black robins were laying “rim eggs,” even though the species had begun to recover.
The black robin’s situation demonstrates how conservation interventions can have unforeseen, and potentially dangerous effects on the recovery of a species, researchers from Australia and New Zealand write in the latest issue of PLoS One. It’s a dilemma that conservationists face: Species have to recover quickly to avoid extinction, yet human efforts to help might, as the authors write, “unintentionally relax selection by allowing the ‘survival of the not-so-fit’.”
more at: http://mag.audubon.org/articles/birds/rise-black-robins-laying-rim-eggs