One of the more romantic stories in conservation is the tale of the Norfolk Island Boobook. The endemic subspecies of this owl Ninox novaeseelandiae undulata was reduced to a single lonely female in 1986, her calls each night going unanswered.
So, in 1988, she was provided with a male of her closest relative, the New Zealand Boobook N. n. novaeseelandiae. It was just in time. The union produced four offspring which themselves bred amongst each other. Then, when she died in 1996, the male mated with his grand-daughter and produced more young.
Once again boobooks were heard commonly at night in Norfolk Island National Park.
To all intents the intervention was a success. From one owl to forty and the subspecies saved.
Unfortunately, back in 2000 when Gabriel Crowley and I reviewed the status of all Australian birds, the IUCN Red List rules appeared to oblige us to describe the Norfolk Island owl as extinct. Hybridization is a threatening process and hybrids are not generally considered when estimating populations of rare species.
By 2000 all the owls on Norfolk Island were hybrids. Those who had so successfully introduced the male from New Zealand, such as Penny Olsen, were much saddened by this conclusion but we felt it was the logical outcome of the listing rules of the day.
However, when Judit Szabo, Guy Dutson and I again reviewed the status of Australian birds in 2010, owl expert Rod Kavanagh urged us to look at the Norfolk Island Owl again. So I contacted Penny, Stuart Butchart, IUCN Red List specialist at BirdLife International, and geneticist Ari Hoffman to help explore this special case.
Although the Norfolk island owl was reduced to just one individual, the hybridization event was a one off, with one just individual from outside contributing to the gene pool, and is not an ongoing process. Furthermore, if there is a selective advantage for the genes of the original subspecies, then those genes should again come to dominate the population.
We published our results recently in Oryx. We conclude, as we did in the Action Plan for Australian Birds 2010, that the Norfolk Island Boobook is Critically Endangered on the basis of the small size of its population.
They still face problems from a shortage of nest hollows and competition with introduced Crimson Rosellas, but they are now a functioning part of the tiny bit of Norfolk Island left in a state at least vaguely resembling the original.