Bird-watchers in the South Downs, in Sussex and Hampshire, are being urged to keep a look out for lapwings.
Lapwings are a common farmland bird, but numbers are waning (Image: RSPB)
The Royal Society for the Protection of Birds (RSPB) is hoping to establish how many there are as records suggest numbers are down since a study in 2002.
So far this year the public has reported only 28 pairs in comparison to more than 120 found five years ago.
The bird is traditionally known as the "farmer's friend", and the RSPB wants to find where lapwings are breeding.
Spokesman Richard Milsom said: "We're hopeful that there are still plenty of pairs out there waiting to be found.
"Just let us know where you went and how many you saw.
"We'd even like to hear from you if you saw none at all - it all helps to build up a picture of where lapwings now are, and aren't," he said.
The lapwing is a relatively large and conspicuous bird that has bold black and white markings, glossy green sheen and a long crest on the back of the head.
Once possible breeding sites have been reported, the RSPB will send a team of trained volunteers to make further observations.
The South Downs of Hampshire, West and East Sussex are known as a stronghold for a number of declining farmland bird species, which include the skylark, yellowhammer and linnet.
Last year, the RSPB launched a five-year project to halt the decline of the lapwing.