By Jonathan Fildes
Science and technology reporter, BBC News, San Francisco
Robot ornithologists have joined the hunt for an elusive species of bird.
The robot has so far snapped plenty of geese but no woodpeckers
The automated birdwatcher stands in a US wildlife reserve in Arkansas, scanning the skies for a glimpse of the elusive ivory-billed woodpecker.
The bird was once thought to be extinct, but potential sightings in the area in 2004 renewed the search.
The system uses two video cameras to capture continuous images of the sky that are scrutinised for evidence of bird life by sophisticated software.
Any shot that it does not believe contains a bird is discarded.
"It's been running for three months continuously now and it only keeps one image in every 10,000 it collects," said Dr Ken Goldberg of the University of California, Berkeley, who developed the system.
"We have caught some very exciting images of birds."
No pictures of the charismatic red, white and black ivory-billed woodpecker have yet turned up.
The bird used to be found across the south-eastern US and Cuba but logging and forest clearance squeezed it out of its environment.
The last confirmed sighting of a lonely unpaired female was in 1944.
Since then, decades of searches yielded nothing and any hope of finding the bird diminished.
But a possible sighting in Arkansas in 2004 reinvigorated ornithologists, with researchers from Cornell leading systematic searches of the Cache River National Wildlife Refuge in Arkansas each year.
But the wetland and forest region of the lower Mississippi river valley is 62,000 acres (250 sq km) and human searches can be tricky.
"The problem with field biology is that it is very difficult," said Dr Goldberg.
"You have to go out to somewhere remote, it's lonely, it's cold, it can be downright dangerous; and the presence of a human observer can affect the behaviour of the animals you are trying to study.
"So our idea is that robots can help."
Everything but the bird
The device, installed in the refuge, consists of two high-resolution video cameras connected to a hard disk, all installed in a weatherproof case.
A deliberately conspicuous "radiation hazard" warning sticker is displayed on the outside, "to prevent hunters using it as target practice".
Geese... but no woodpecker, yet
The digital cameras point towards the sky, continuously capturing two-megapixel images.
Advanced algorithms analyse each frame, discarding the images it believes does not contain an image of a bird and saving those that it thinks does.
"We build a statistical model of the sky and look for outliers - pixels that suddenly look very different," said Dr Goldberg.
"Then we look for groups of outliers of a certain size and then we look for things moving at a certain velocity."
The last confirmed sighting of an ivory-billed woodpecker was in 1944
The saved images are stored on hard disks that are routinely removed by a local birdwatcher who, along with other volunteers, scrutinise each frame.
At the moment falling leaves or other flying objects like helicopters can confuse the system.
But it has captured shots of geese, hawks and a heron, proving that when, and if, the time comes, it is capable of capturing a shot of an ivory-billed woodpecker.
However, it does have some limitations, such as only being able to survey one particular site.
The system can also only scan the sky because the algorithms used in the analysis can not cope with staring deep into the forest and trying to pick out moving birds from the gently swaying branches of trees.
Dr Goldberg believes that this will be possible eventually; along with other more advanced analysis.
"The next level is to determine what is a woodpecker versus an average bird, but that's still a long way off," he said.
In time, he believes it could be used to search for other types of elusive wildlife such as bears and gorillas or in security applications, for example monitoring airports for suspicious packages.
The research was presented at the American Association for the Advancement of Science (AAAS) annual meeting in San Francisco, US.