Breeding in captivity can affect birds wing shapes, reducing their chances of survival on migratory flights when they are released to the wild, new research suggests.
In a study of the critically endangered orange-bellied parrot, researchers found that in captive birds those with altered wing shapes had a survival rate 2.7 times lower than those born with wings close to an ideal wild type wing.
The total population of orange-bellied parrots once dropped as low as 17 in the wild, but their numbers have been bolstered in recent years by captive breeding and release efforts in Tasmania and Victoria.
The bird breeds in Tasmania and migrates for the winter to mainland Australia's southern coast.
The study author Dr Dejan Stojanovic, of the Australian National University, said there was natural variation in wing feather lengths in both wild and captive-bred orange-bellied parrots.
He said that there is a significant difference between the lengths of feathers in captive wings and wild wings when you look at the lengths of all the feathers on the wings.
Stojanovic has previously shown that captive-bred orange-bellied parrots tend to have less pointed and shorter wings than their wild counterparts.
He said there was variation within captivity from a perfect wild type wing to very suboptimal.
In captive-bred birds whose wings resembled the ideal wild wings, the wings most closely resembled the ideal wild wings, and were more likely to survive a feather known as the distal primary flight feather, which was longer by a single millimetre.
The change for orange-bellied parrots is a 1 mm difference in the length of a feather. It is so easy not to detect it, but it has a major downstream consequence, Stojanovic said.
Few other recovery projects have the scale and resourcing that orange-bellied parrots do.
These changes went unnoticed despite all of that care. These results show that these undetected changes were impacting on survival, which is a key success measure for whether we are benefiting the wild population. Stojanovic also looked at the wings of 16 other birds, finding evidence of altered captive wing shapes in four other species budgerigars, turquoise parrots, sundown parrots and Gouldian finches.
He said that this phenomenon was a lot more widespread and might actually be a pattern that had gone undetected. The next phase is to understand what is driving the changes.
Maybe it is an environment trait or a family trait that we don't know. We need to be better at looking at the quality of the animals we are breeding rather than just focusing on their quantity.