Results:
Detecting illegal wild harvesting

Feather forensics: tracing the origins of parrots in wildlife trade with stable isotopes and citizen science

K. G. W. Hill, S. Delean, T. Hall, J. J. Tyler, O. C. Stringham, P. Cassey (2025) Animal Conservation.

Read the full peer-reviewed manuscript in Animal Conservation here

Feather Forensics: tracing Australian parrot trade with stable isotopes and citizen science

Native Australian parrots are highly desired as pets in global and domestic pet trade, due to their wide range of colours and sizes, ability to mimic human speech and songs, and high intelligence. To get a new pet parrot to add to the family, buyers would generally purchase a bird through an aviary, where the bird was most likely captive-bred. However, in some cases, the bird may have been taken from the wild (wild-harvesting). This practice is legal and sustainable for some species, provided the birds are harvested responsibly, and the seller has the correct permits and documents.

However, wild-harvesting of many native Australian species is illegal, unsustainable, and may contribute to the decline of wild populations. Some species are notoriously difficult to breed in captivity, so a seller may illegaly wild-harvest a bird, but sell it as “captive-bred”.  While there are laws in place to prevent this practice, there are currently no tools available to quickly and reliably identify if a bird has been illegally wild-harvested. This puts our vulnerable native species at risk, while buyers looking for a new parrot member of their family may be fined for unknowingly purchasing an illegaly harvested bird. 

Wildlife officers from the Queensland Department of Environment and Science (DES) seized three Red-tailed Black Cockatoos in 2022, where the seller did not have the correct permits to sell these protected birds.

Tracing origins with stable isotopes and citizen science

Stable isotopes are a case of you are what you eat: the stable isotopes in an animal’s tissue reflects its diet and environment. We hypothesised that captive and wild birds of the same species would have distinctly different diets, which would reflect in the stable isotopes of their feathers.

For this project, we used feathers collected by citizen scientists through the Feather Forensics. We focussed on the species which had the most feathers collected: Eolophus (galahs), and Cacatua (cockatoos). 

Results: classifying captive and wild origins

We found that dietary stable carbon and nitrogen stable isotopes can differentiate between captive and wild birds, but with varied success.

Captive galahs and cockatoos have higher stable carbon and nitrogen isotope values than their wild populations.

However, there was a large overlap in captive and wild values for cockatoos, which made separating the two groups more difficult.

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In this figure, captive birds (orange points) had enriched stable carbon (δ13C) and nitrogen (δ15N) isotope ratios than the wild (blue triangles) birds. The range of values captive and wild populations showed are enclosed within the ellipses in figures A&C, where in figure C we can see a large overlap between the cockatoo origins.

In plots B&D, we used simple machine learning to draw 1,000 lines between the two groups to identify the best place to separate the two groups for classification (dotted line). The lines are relatively close for galahs, where we could classify birds with 88% accuracy. However, due to the large overlap in captive and wild values for cockatoos, the lines are varied and had only 74% accuracy.

Our results indicate that while can use stable carbon and nitrogen isotopes to identify captive and wild origins, it would work best when combined with other wildlife forensic methods. The large overlap between captive and wild groups means that there is a chance of misclassifying an indicidual bird, which is problematic in criminal investigations. Despite this, stable carbon and nitrogen isotope ratios can still provide valuable information on the potential origins of birds in willdife trade.

Why do we see an overlap in captive and wild populations?

Galahs and cockatoos have very large geographic range sizes and a highly varied diet, which reflects in the stable isotope ratios in their feathers. We likely see the higher stable carbon isotope values in captive birds as pet birds have access to C4 plants (e.g. corn, millet and commercial pet food). Plants in South Australia that wild birds would have access to are mostly C3 grasses and plants. Similarly for stable nitrogen isotope values, it is likely enriched by commercial pet food products.

So why are we seeing such an overlap for cockatoos, and how can we improve these methods? Some of this overlap might be explained by wild birds accessing more “captive-type” diets. Bird feeding is common in urban areas, particularly when people are interested in nature. And wild cockatoos have learnt to open wheelie bins and eat a more “captive-type” diet.

To get around this problem, it is possible to add more isotopes into this reference database. We could look into oxygen and hydrogen, which can tell us their water source like tap or rainwater. Or we could use sulphur, to look at the effect of anthropogenic sources like pollution. And considering we had relatively high success with just carbon and nitrogen, this does look like a promising future tool in the wildlife forensic toolbox to trace captive and wild origins.

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 This research is supported by: