Margaret Stanley, Ellery McNaughton, Rachel Fewster and Josie Galbraith talk us through their recent research that uses reports of lost pet birds to estimate the cumulative propagule pressure that the pet trade exerts on the establishment of introduced bird species.
Although concerns about the billion-dollar global pet trade industry have usually focused on issues associated with the trade of endangered species, the pet trade also plays a critical role in moving invasive species around the globe. For birds, the pet trade is now the primary source of invasive birds.
Most studies use trade and sales of pet birds as an indirect measure of propagule pressure, rather than directly measuring the number of escaped or released birds. To gain a more direct insight, we used websites from Aotearoa–New Zealand where owners report their lost pet birds.
Our study highlights just how many pet birds, particularly parrot species, are reported as lost by their owners, contributing to a consistently large pool of escapees in our city suburbs, with the potential to breed and spread.
An ill-fated history of introductions
Unfortunately, Aotearoa–New Zealand is famous for its history of deliberate introductions of new bird species through well organised Acclimatisation societies. The meticulous record-keeping of these early British settlers has created one of the best global datasets for analysing the effect of propagule pressure on the establishment and spread of new species. We now know that propagule pressure (number of healthy individuals released) is a critical factor in whether a species becomes invasive.
Although the days of acclimatisation societies releasing new species are long gone, the pet trade has spurred a new wave of companion bird imports, some leading to the escape or even deliberate release of new bird species.
What we discovered from website loss reports was staggering. During our 3.5 year monitoring period, 1205 birds and at least 33 species were reported as lost, 92% of which were parrots. Given that not all owners will list their lost pets on websites, and given that some birds are released deliberately, these numbers are likely to be a considerable underestimate.
The parrot problem
Globally, parrots have a well-documented history of invasion and impacts. Ring-necked parakeets (rose-ringed parakeets; Psittacula krameri) have established in 47 countries and form large populations that have severe impacts on orchards and crops, as well as on other bird species via competition for food and nest sites.
Although not yet officially established in Aotearoa, there are currently management programmes underway to eradicate two small populations that have been detected. This is the same species that was reported as lost by about 100 pet owners in our study.
Cumulative propagule pressure
Worryingly, 23% of the birds reported as lost were part of a group, including male–female pairs. We used the data to run 50-year simulations that investigated the cumulative propagule pressure exerted by lost pet birds in Auckland city. We found that in any given month in Auckland there is an average of least 491 escaped birds, including 136 potential breeding pairs.
For seven species of parrots, we found there was more than an 80% chance of having a male–female pair at large in the same Auckland locality (city districts) at the same time. For the ring-necked parakeet, this figure was a stark 100%, with an average of 10 different Local Board Areas (city districts) hosting a male–female pair at any point in time.
Prevention is key
Clearly, the pet trade poses a major risk for the invasion of new parrot species. While the impacts of invasive birds can be substantial, there are currently very few options for controlling birds, and potentially little public support for lethal control.
The only viable and cost-effective approach to preventing the economic and environmental risks that invasive parrots pose is a preventative one. Regional bans will not be enough to prevent spread beyond regions, especially given the ease with which these birds can be bought online from outside the regulated zones. We need to enact regulation at a national, and even international, level banning the sale of parrot species that pose the highest risk.
