Fears are growing for the plight of the tawny owl whose eerie call was once a familiar sound across East Anglia.
People are asked to listen for the tawny owl and report findings
Tidier woodlands and falling numbers of mammals like mice and voles are blamed for a decline in the bird of prey.
The Norfolk-based British Trust for Ornithology estimates that numbers have dropped nationally by more than 30% in the past 10 years.
It is asking volunteers to take part in a survey to try to estimate numbers of birds and where they live.
A special "owlaphone" with recordings of calls has been set up to help people recognise a tawny owl cry.
Mike Toms, the group's garden bird watch coordinator, said: "This survey is so easy that it can be done from the comfort of your own bed, listening through an open window or from an armchair on your patio.
"We are asking for volunteers to record when the owls are calling and the type of calls that are heard.
"For those people unsure what a tawny owl sounds like we have a dedicated owlaphone that you can call to listen to their eerie calls."
The tawny owl is the most common of the five owl species in Britain and is the one most likely to be heard in woodland or suburban areas.