Survival Of The Fattest: Heaviest Parrot Nestlings Survive Better

Juvenile survival of critically endangered orange-bellied parrots is positively related to nest body condition

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There are only two species of parrot in the world whose entire populations migrate annually between breeding grounds in Tasmania and wintering grounds in southeastern Australia. Their migratory route takes them through Australia’s treacherous Bass Strait, which is 240 kilometers (150 miles) wide. This stretch of water is very rough, so crossing it is a dangerous journey for these parrots.

These two migratory parrot species are the orange parrot, Neophema chrysogasterand the swift parrot, Lathamus discolorboth of which are listed as Critically Endangered (largely due to Australians’ penchant for cutting down these parrots’ native trees to make toilet paper), so both are the subject of intensive captive breeding programs to bolster their dwindling populations.

For reasons that are poorly understood, orange-bellied parrots bred in captivity tend to misbehave after being released into the wild (for example, more here). Furthermore, the low survival rate of young during migration is the main factor limiting the recovery of this species. Currently, the entire population is restricted to a single breeding site at Melaleuca in south-west Tasmania (ref).

This raises an important question: Which parrots bred in captivity are most likely to survive their migration journey? Can they be easily identified so that only those captive-bred individuals most likely to survive are released into the wild?

The study on orange parrots, led by biologist Laura Bussolini, a PhD student at Australian National University, attempted to answer these questions by examining and comparing juvenile survival rates for both wild and captive-bred parrots. Ms. Bussolini’s main interest is to bridge the gap between scientific research and conservation management of critically endangered species by exploring practical research questions, tools and techniques that could directly contribute to endangered species management and recovery actions.

“Surprisingly, both groups were equally likely to survive their first migration,” Ms. Bussolini reported in statement.

“But the birds that were heavier as nestlings were much more likely to survive – regardless of whether they came from a wild or captive population,” Ms Bussolini then explained (Figure 1).

Heavier nestlings have better body condition.

“There was little variation in the body condition of chicks by age in the wild population – this is not surprising as they respond to so many changing conditions such as the amount of food available, predators and wild weather,” Ms Busolini explained.

The order in which chicks are hatched also plays a role in their body condition, with hatchlings having the best body condition (Figure 2).

“But wild-born nestlings were almost always in better body condition than captive parrots – this identified a clear new research target aimed at improving the quality of captive-bred parrots.”

The orange parrot captive breeding program consists of several hundred birds distributed in five facilities. But choosing which young parrots to release into the wild is difficult and complicated.

“There are many different factors involved in choosing who gets released into the wild, but this study shows that nestling body condition is a handy tool for identifying individuals with the best chance of survival after release,” Ms Bussolini explained. “It could also help identify those birds that are struggling.”

What will happen to the cubs that are in poorer body condition?

“Just because individuals are at the lower end of the bell curve when it comes to physical condition does not mean they are not valuable to the entire population,” Ms. Bussolini replied.

Unfortunately, orange parrots are just one of a growing number of species whose survival depends on effective conservation interventions. On the one hand, we know that captive-bred individuals can differ significantly from wild species (ref), but on the other hand, this study shows that captive-bred individuals can survive just as well as those born in the wild. This study suggests that the age-corrected weight-to-size ratio can be a useful and easily implemented tool to help identify candidates for release, improve post-release survival and thereby increase the success of animal reintroductions.

“These results demonstrate the importance of thinking strategically when it comes to our breeding programs and using all available evidence in the hope of improving survival outcomes for critically endangered species.”


LT Bussolini, R. Crates, A. Herrod, MJL Magrath, S. Troy and D. Stojanovic (2023). Carryover effects of nest physical condition predict first-year survival of a critically endangered migratory parakeet, Animal Conservation | doi:10.1111/acv.12878

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