Identifying captive escapes of Rainbow Lorikeets at different stages of the pet-release pathway

When an animal is traded in the pet trade, they are taken outside of their native ranges to new environments. That pet can escape from captivity into that new environment. If that bird survives in the wild, finds another escaped pet and has chicks, it can lead to a new invasive population.

Not all captive escapes lead to an invasive population. A bird may not survive in the wild, or it may never find a mate to reproduce. However, we currently have no way to quickly identify between a bird which has recently escaped captivity, and a bird which has been living in the wild for some time and is reproducing.

Being able to tell the difference between a recent escape and a true wild bird can help with preventing these populations from becoming a conservation problem. For example, if a non-native bird is a recent escape from captivity, efforts could be on making sure there are no more escapes in that area. Or, if it is a true wild bird, efforts should be on controlling that wild population to make sure it does not grow in size or spread. 

For this project, we used feathers collected through the Feather Forensic project. We focussed on Rainbow Lorikeets; an abundant native species which has formed invasive populations in Australia.

Rainbow Lorikeets: a domestic non-native

Rainbow Lorikeets (Trichoglossus moluccanus) are one of Australia’s most well-known native parrots, being the most observed species in the Aussie Backyard Bird Count for nine years running. They are also one of the most popular native parrot species kept by Australians, desired for their bright plumage and fun personalities. However, because of their popularity, they have now established invasive populations within Australia.

Rainbow Lorikeets are one of the most popular native pet birds in Australia, which means they’re kept in large abundances in captivity across the country. Consequently, they have escaped and established invasive populations. Despite being native to the eastern and southern coasts in Australia, they are not native in the remaining environments and can cause significant damage to ecosystems and agriculture. They are very aggressive birds, which outcompete native species for nesting hollows and resources.

In Western Australia, the invasive population is so large, they are now the most observed species around Perth. This population most likely formed after a small numer of escapes in the 1960s, which very rapidly grew in numbers and spread.

Meanwhile in Tasmania, Rainbow Lorikeets have started to appear as recently as 2007, when one breeding pair was observed in the wild. While there are ongoing efforts to prevent this population from growing and spreading, there are now three self-sustaining populations around Tasmania.

For this project, we used feathers collected through the Feather Forensics program. We selected feathers from wild birds in Western Australia (an invasive population), Tasmania (a recently established population), and in South Australia (within their native range). We compared the stable isotope ratios of these feathers to those of captive birds, to see if we could identify birds which have recently escaped captivity.

Results: identifying recent captive escapees in a new, established population

We found that while this method has potential, especially in smaller or recently established populations like the one in Tasmania, it's less useful in large, widespread groups like those in Western Australia.

Two birds in Tasmania stood out with unusually high δ¹³C levels, matching those of captive birds, suggesting they may be recent escapees.

This kind of tool could help manage early-stage invasions, but it's not foolproof in populations that have had time to adapt to wild food sources. Captive diets, and particularly commercial nectar supplements made with sugar cane (a C₄ plant), likely drive much of the isotopic variation we see in captive birds, so knowing more about these diets could sharpen our ability to identify escapees.