Whether made by hoaxers or unexplained visitors from outer space, crop circles have been hard to find in Oxfordshire fields this summer.

As the crop circle season draws to a close, the county has suffered one of its most barren periods for years. Only three have been spotted compared to seven last year and 13 in 2005.

Blame for the dearth of circles springing up around the county has been placed on the major summer floods, which made the most prolific week of the season a wash-out.

Geoff Ambler, of Oxfordshire Centre for Crop Circle Studies, from Wheatley, has been tracking the phenomenon for 20 years.

He said: "Two years ago it was very prolific and last year was rather good. But they don't seem to have come back to Oxfordshire this year.

"After the terrific storm on July 20 the crop circles seemed to dramatically stop. Usually in that period up to July 30 we have a huge influx of circles but after the big floods there wasn't much anywhere in the region for five or six days.

"But there's no rhyme or reason for it. Some years are better than others. It may be that we have missed some this year and they have been chopped down by farmers before they have been found."

The only three circles spotted this summer include an elaborate creation boasting ten crescents and three small circles found at Southend, Garsington on June 29.

Then on July 7, a second hexagon-shaped circle was found in a field at Garsington.

The latest circle was a butterfly image in Hailey Wood near Ashbury which was found on July 16.

At this time last year there were seven crop circles found in Botley, Rollright Stones, Ashbury, Uffington White Horse, Blowingstone Hill and two at Toot Baldon.

In 2005 there were 13 crop circles in the county but this weekend marks the end of the crop circle season when crops are chopped down.

Mr Ambler believes around 10 per cent of them are man made while the rest are created by 'non-humans'.

He said: "They remain very strong in Wiltshire, but everywhere else it has died a death now."

If anyone spots a crop circle, contact the Oxfordshire Centre for Crop Circle Studies on 01865 872628.

Crop circles first appeared in the English countryside in the late 1970s, often near ancient sites. Enthusiasts offered various explanations, from visits by alien spaceships to freak weather conditions or whirlwinds.

In 1991 Doug Bower and and Dave Chorley admitted making crop circles in England since 1976 after being confronted by their wives who thought they were out having affairs.

The duo revealed they made the circles using planks, rope and wire. Many other enthusiasts have since joined groups to make more and more intricate designs but some sceptics doubt all are man-made.

Circles have also been seen in Russia, Japan and the US. The 2002 movie Signs saw Mel Gibson star as a farmer visited by aliens after discovering crop circles.