ENVIRONMENTAL RESEARCH
Biosecurity Event - Environmental Disaster
The word “pigeon” evokes thoughts of gentle cooing, fluttering in rafters, and poo-encrusted statues. The species responsible for the encrustation is deeply familiar to us, having ridden waves of European expansionism to inhabit every continent, including Australia. First domesticated thousands of years ago, urban pigeons have turned feral again.Less familiar are the native species that are not your stereotypical pigeons: a posse of pointy-headed crested pigeons in a suburban park, or a flock of topknot pigeons feeding in a camphor laurel.Australia and its neighbouring islands are the global epicenter of pigeon and dove (or “columbid”) diversity with the highest density of different columbids – an impressive 134 species – found in the region. Twenty-two of these native species are found in Australia alone, in just about every habitat.These native species play an important role in ecosystem functioning: they forage for and disperse seeds, concentrate nutrients in the environment, and are a source of food for predators. Fruit doves for example, are zealous fruitarians, and the region’s tropical rainforests depend on them for tree diversity. Where fruit-doves have disappeared in the South Pacific, numerous plant species have lost an effective dispersal mechanism.The future of Australia’s native pigeons however, may depend on our domestic pigeons. Australia’s domestic pigeon population — both feral and captive - is large and interconnected by frequent local and interstate movements. Pigeon racing, for example, involves releasing captive birds hundreds of kilometers from their homes only so they may find their way back. While most birds do navigate home, up to 20% will not return, of which some will join feral pigeon populations. Birds are also traded across the country and illegally from overseas. These movements, together with poor biosecurity practices, mean that captive pigeons can and do mingle with feral domestic pigeons.And here’s a paradox. Could Australia’s feral domestic pigeons become the vector for a dramatic decline of columbids – native species on which Australian ecosystems rely?
Emerging Viral Epidemics
In recent years, two notable infectious diseases have been found to affect our captive domestic pigeons: the pigeon paramyxovirus type 1 (PPMV1) and a new strain of the pigeon rotavirus (G18P). These diseases are notable because in captive domestic flocks they are both spectacularly lethal and difficult to control.
PPMV1, although likely to have originated overseas, is now endemic in Australia. This virus has jumped from captive to feral domestic pigeon populations on several occasions, but fortunately has yet to establish in feral populations.
Avian paramyxovirus type 1 (PPMV1) is a very serious disease that can kill up to 100% of pigeons in some lofts. Some of the signs of PPMV1infection include lethargy, vomiting or regurgitation, green diarrhoea, twisting of the neck, circling, head flicking, labored breathing and runny eyes and beak. Sick birds can die within three days. The infection spreads easily between birds and there is no specific treatment.
Infected birds may shed the virus in their faeces and other discharges, contaminating the environment (including feed, water, equipment and human clothing) and allowing transmission to other birds. Avian paramyxovirus 1 can survive for several weeks in the environment, especially in cool weather.
The spread of PPMV1is typically due to the movement of birds, but transmission can occur through direct contact with faeces and respiratory discharges or contaminated food, water, equipment and human clothing. Infected birds may shed the virus in their faeces, contaminating the environment (including food and water).
G18P is thought to have spread to Victoria and South Australia from a bird auction in Perth in 2016. PPMV1 also spread rapidly to multiple states following its first appearance in Melbourne in 2011. The movements of captive pigeons, and their contact with their feral counterparts, can be the routes through which virulent and lethal diseases – such as the PPMV1 and the G18P – may spread to Australia’s native columbids.
Signs of PPMV1 include: 1
* high morbidity and mortality
* loss of appetite, lethargy
* gastrointestinal signs including regurgitation and diarrhoea
* neurological signs such as head shaking, torticollis
* respiratory signs.
What Have We Got To Lose?
Potential ecological impacts:2 The pigeon paramyxovirus (PPMV1) now considered endemic in Australia3 causes an often fatal disease in many bird species worldwide, not just pigeons. Overseas it has infected raptors, pheasants, swans, cockatoos and budgerigars (the latter Australian species in captivity overseas). So far in Australia the virus has infected racing, show and feral pigeons (rock pigeons and one spotted turtle dove).
The one native species so far diagnosed with the disease was a collared sparrow-hawk in a Melbourne park, which presumably ate a diseased pigeon.
Overseas, it has caused sporadic large die-offs in wild doves and pigeons, and in Australia several hundred (600 estimated) feral pigeons died at a grain storage facility in Geelong. With feral pigeons so widely distributed, we have cause to be concerned about their potential to spread it to native birds.
We can’t say how serious the consequences would be, because we have not previously observed such viral infections among our native pigeons. New diseases can have catastrophic consequences. A very high rate of mortality (up to 100%) has been recorded in pigeon lofts. Schuler et al. (2012) warn that ‘transmission events may be rare, but single spillover occurrences could have dire consequences for native species.’
If the viruses prove equally lethal to native columbids as they are to domestic pigeons, we could see catastrophic population declines across numerous columbid species in Australia over a short period of time.
Should these viruses spread (via feral domestic pigeons), the control and containment of losses among our native pigeon species would be near impossible.
Maps of Australia showing the overlapping distribution of our 22 native pigeon and dove species (left) and the distribution (in orange) and verified individual records (red dots) of introduced feral domestic pigeons (right). Atlas of Living Australia, Birdlife International
Maps of Australia showing the overlapping distribution of our 22 native pigeon and dove species (left) and the distribution (in orange) and verified individual records (red dots) of introduced feral domestic pigeons (right). Atlas of Living Australia, Birdlife International
What Does Protection Look Like?
Agricultural poultry is routinely screened to check their vulnerability to threats like the PPMV1 and G18P. Such screening is an appropriate response to protect our agricultural industry.
Although Avian paramyxovirus is a notifiable disease in Australia under the Queensland Biosecurity Act 2014, for our native pigeons and doves no similar testing is planned. Based on progress in veterinary vaccine development and advancements in understanding of feral pigeon control, the knowledge and technology required to mitigate this threat should be relatively inexpensive. The threat for these species can be actively managed, now, by improving our biosecurity and vaccination programs for captive domestic pigeons, and eradicating feral domestic pigeons.
AFPP is dedicated to protecting the Australian environment and its fauna by eradicating feral pigeons in an discreet and effective manner.
Department of Agriculture, Fisheries and Forestry (Qld) (2012).
Aldous et al. (2004), Kim et al. (2008), Schuler et al. (2012), Ujvari et al.(2003), Australian Wildlife Health Network reports.
Cowan et al. (2014)
