laying became less frequent, but 9% of birds still laid rim eggs as of 2011. Conservationists have faced some criticism that they may inadvertently do harm, if they allow organisms with deleterious traits to survive and perpetuate what is maladaptive. All of the surviving black robins are descended from "Old Blue", giving little genetic variation among the population and creating the most extreme population bottleneck possible. However, this does not seem to have caused inbreeding problems, leading to speculation that the species has passed through several such population reductions in its evolutionary past, and has lost any alleles that could cause deleterious inbreeding effects. It was generally assumed that the minimum viable population protecting from inbreeding depression was around 50 individuals, but this is now known to be an inexact average, with the actual numbers being below 10 in rapidly reproducing small-island species, such as the black robin, to several hundred in long-lived continental species with a wide distribution (such as elephants or tigers). Nest predation by introduced common starlings is the most common cause of nesting failure for black robins on Rangatira Island, with almost 21% of nests failing due to starlings. Incidents of failure caused by starlings are more common when black robins nest in cavities compared to open nests. The species is still vulnerable, but now numbers around 300 individuals in populations on Mangere Island and South East Island. Ongoing restoration of habitat and eradication of introduced predators is being undertaken, so that the population of this and other endangered Chatham endemics can be spread to several populations, decreasing the risk of extinction by natural disasters or similar stochastic events. Attempts made to establish another population in a fenced covenant on Pitt Island have failed so far. References Cited text Further references Attenborough, D. 1998. The Life of Birds. BBC External links Black robin BirdLife Species Factsheet black robin black robin Birds of the Chatham Islands Bird conservation black robin black robin Endemic birds of New Zealand Birds with names in Moriori