Why do birds fly south? Well actually, it turns out they don’t much - in the case of the Common Myna . . .
Common (aka Indian) Mynas are a bit of paradox. Although these accomplished songbirds are popular pets worldwide (and symbols of undying love in India), they are reviled in Australia with the dubious distinction of being voted our most-hated bird. Presumably this is because of their invasive potential - they are one of only three bird species on the list of the top 100 global invasives. But how invasive are they?
Common Mynas are reported as having been introduced to Melbourne in the early 1860s to control insect pests; and subsequently to Sydney, Townsville, inland from the Gold Coast and Canberra. For nearly a hundred years their Australian populations were confined to those locations, and it is only since the 1940s that their distribution has expanded along much of the urbanised eastern zone of Australia. The timeline of this expansion is hardly what we would expect from an invasive dynamo.
Perhaps because of their cohabitation with humans, negative impacts of Mynas on both people and native fauna are often stated, although there is remarkably little scientific evidence. But given their potential impacts and expanding range, it is important to find out more about the dispersal capacity of this species.
One way of measuring the effective dispersal of a species is to analyse the DNA of its constituent populations. If animals are moving between populations their gene pools will mix and homogenise, while isolated populations will have distinct genetic signatures. We used genetic techniques to test the accuracy of historical reports of Common Myna translocations and to determine their patterns of effective dispersal, with the overall goal of informing population management of this exotic species.
Responding to our calls, volunteers trapped 462 Myna specimens from 26 sites between Cairns and Melbourne. We then compared their genetic signatures using 4156 variable markers across the genome. Our results demonstrated conclusively that populations occupying the original sites of colonisation remain genetically distinct from each other, and with the exception of the Gold Coast population, these populations were founded by translocation from the sources recorded historically. (The founders of the Gold Coast are a bit mysterious, but appear to result from a mixture of translocated birds from Melbourne and birds from a novel introduction.)
Satellite populations in Victoria, and New South Wales have been colonised from Melbourne and Sydney respectively, and it was only on the New South Wales/Queensland border that we detected mixing of different genetic stocks. These “admixed” populations now have higher genetic diversity than their parent populations, and in theory this should improve their evolutionary potential.
Our study indicates that Common Mynas do not disperse effectively over long distances in Australia – “flying south” is not something they are prone to do; nor is “flying north”, or “east” or “west”. Ironically, Mynas relied on human transport to spread across eastern Australia, rather than using autopilot. We recommend that any population control should now be focussed on the slow-moving invasion front, rather than the largest population centres which also coincide with the largest human centres. In particular, merging of populations with different genetic stock, as is happening in northern New South Wales, should be discouraged to prevent genetic diversification.
Kyle Ewart (PhD Candidate, School of Life and Environmental Sciences, University of Sydney; and AMRI, Australian Museum)
Prof Rebecca N. Johnson (Director, AMRI, Australian Museum)
Dr Richard E. Major (Principal Research Scientist, AMRI, Australian Museum)
- Ewart, K. M., Griffin, A.S., Johnson, R. N., Kark, S., Magory Cohen, T., Lo, N. and Major, R.E. (2019). Two speed invasion: assisted and intrinsic dispersal of common mynas over 150 years of colonization. Journal of Biogeography 46: 45-57. https://onlinelibrary.wiley.com/doi/full/10.1111/jbi.13473