On Anzac Day in 1949, 15-year-old Len Robinson went to pay homage to a little Aussie battler. After making the considerable trip from his home outside Melbourne to the CBD, he walked a mile through the mixture of wasteland and remnant salt marsh known as Fishermans Bend. There, within sight of the Yarra, alongside the proving ground for General Motors Holden, he found what he had been looking for. "I can still remember those two little green parrots sitting on that wire fence," he says warmly, as if describing a first love.

Decked out in bright grass-green, with splashes of yellow below and sapphire on the wings and face, the Orange-bellied Parrot is undeniably cute. Sure, it doesn't have the take-your-breath-away colours of a bird of paradise, but its subtler hue is a matter of necessity. This unassuming creature spends most of its life in open country, where too gaudy a plumage would make it a sitting parrot, so to speak, for any predator. It has, not surprisingly, a nervous disposition, and will take off on its streamlined wings at the first sign of trouble.

It is also credited with the ability to shut down infrastructure projects worth billions of dollars. And because of this, and a name that sounds as if straight out of a Monty Python sketch, the Orange-bellied Parrot has replaced gay whales as the favoured symbol of unfettered environmentalism for bone-headed talkback hosts and op-ed columnists.

Yet the OBP (even birdwatchers prefer to call it something less starchy) has never stopped a single major development project. The former Victorian premier Jeff Kennett abandoned a proposal to relocate the Coode Island petrochemical plant for purely economic reasons, but the innocuous bird still copped the blame. And when the former federal environment minister Ian Campbell expressed concern that the blades of the Bald Hills wind farm might chop up the birds, it needed to be pointed out that this was, at worst, only likely to happen once every 143 years. (The project went ahead.)

Recently, amid arguments about the dredging of Port Phillip Bay, Peter Garrett, who had to give approval for the state-based project, said that channel deepening could actually be beneficial for the OBP, as the resulting "hydrological changes" may increase its salt-marsh habitat. This was nonsense of the highest order, but no doubt politically expedient, helping to stall legitimate environmental arguments a bit longer.

The OBP, according to Chris Tzaros, conservation manager for Birds Australia, has become "a much-maligned little beast". At the same time, the outlook for the bird has never been more uncertain. Today there are more giant pandas in the wild than there are OBPs. There are more blue whales. There are even more Liberal politicians sitting in parliaments around the nation. Thanks to a stupid evolutionary strategy of choosing two of the least hospitable of Australian regions for its habitat - the rain-soaked moors of south-west Tasmania and the windswept coastal salt marshes of the southern mainland - the OBP was never a common bird. And to move between the two habitats, of course, it has to fly across Bass Strait, one of the most treacherous stretches of water in the world. It is perhaps surprising that there are any OBPs left at all.

Today the Fishermans Bend salt marsh is gone, covered by dusty landfill awaiting further industrial development; at the site of Len Robinson's first encounter stands one of the pylons supporting the West Gate Bridge. All along the west coast of Port Phillip Bay, the OBP's former habitat has been replaced with anything from housing developments to armaments compounds. The few remaining patches of salt marsh are being overrun by invasive weeds. Thick with feral predators, trashed by illegal recreational vehicles and horse riders, and after ten years of below-average rainfall, they have failed to produce the kind of prolific seeding that keeps a parrot going through a long, hard winter.

In Tasmania, where some of the more remote breeding grounds were spared the settlers' axe, the removal and killing of the Indigenous peoples ended the regular burning that had left the open patches which the birds had come to rely on to successfully raise their young. Within a few decades, as thick scrub encroached, suitable nesting sites all but disappeared.

By the 1980s, though, things seemed to be going the parrot's way. An intergovernmental management plan, the first of its kind in Australia for a single species, was established. A captive breeding program began, and the majority of sites favoured by the birds were given conservation status. But still the ungrateful buggers kept disappearing. While it was thought that roughly the same number of birds (around 140) were leaving the breeding grounds each year, less than a third of them were being spotted on the mainland during winter.

Chris Tzaros sought to find out why. He followed up every reported sighting and analysed each site for clues as to why the birds may have been using it, as well as checking any likely habitat the parrots could be hiding in. Over the course of two winters he must have visited every patch of degraded salt marsh from Sale to Victor Harbour, but he was still unable to discover the long-dreamt-of "golden paddock" where all the missing OBPs gather to feast on some unknown food source.

His conclusion? Perhaps we are seeing fewer parrots at the traditional winter grounds because there are simply fewer parrots to find. The relatively stable numbers reported from the Tasmanian breeding grounds are estimates based on the birds that researchers can locate. While they may be finding approximately the same number each year, it doesn't necessarily follow that the rest of the population is similarly stable. It is not certain, but the indications are that the OBP is in even worse shape than anyone thought - despite the media depiction of a privileged, pampered parrot.

The OBP is a species that has been kept alive by human intervention: habitat and population monitoring by volunteers (Len Robinson still takes part in surveys and has been known to commando-roll under fences, despite a dodgy hip, to confirm an OBP sighting), which led to conservation reserves being declared; management of breeding grounds, to optimise nesting success; and supplementation of the wild population. This summer, 80 birds raised in captivity were released into the wild. If they survive and join their brethren, it could be the boost needed to raise their critically low numbers. Right now, these birds are braving the roaring forties, making their way over wind farms and hydro-electric dams, channel dredges and desalination plants. They'll be hoping that there has been enough rain to make glasswort fruit grow, so they can eat - and enough friends like Len Robinson and Chris Tzaros to keep the tractors and motorbikes, cats and foxes, politicians and op-ed columnists out of their salt marshes for another season.