A new study has highlighted how a helping hand for nesting native birds almost made a species incapable of surviving in the wild.

When 1980s conservation workers came across eggs of the Chatham Island Black Robin teetering on the edge of a nest, they thought they were doing the right thing by nudging them back into the centre where they would be looked after - eggs left on the rim of the nest were not incubated and never hatched.

However a new study shows that this seemingly benevolent act was in fact reshaping the evolution of the birds, allowing the survival of evolutionarily unfit 'edge-of-nest-laying' genes in successive generations of robins.

Repositioning of these edge eggs by Wildlife Service staff inadvertently resulted in the rapid spread of this maladaptive trait throughout the population.

Conservation staff ceased repositioning eggs in 1990 and, according to the new research, this lead to a large drop in edge-laying as the behaviour literally died out.

Had this trait become more established in the population, the black robin would have become utterly dependent on continued human assistance for reproduction.

The story has come to light following genetic research from University of Canterbury scientists, lead by Dr Melanie Massaro, published this week in the journal PLOS ONE.

Dr Maassaro said: "Our study reveals how this valiant effort nearly ended in disaster, and highlights the thin line that conservation efforts must walk between saving a species and rendering it irreversibly dependent on humans.

"It is important that such information enters the public consciousness, so this risk may be avoided in other conservation efforts."