Police were forced to close a busy dual carriageway after up to 1,000 chickens were scattered across the road.
The birds escaped from a lorry when it was involved in a collision with four other vehicles on to the A420 just outside Oxford at 0950 BST on Friday.
RSPCA officers helped to catch the birds, enabling police to deal with the crash in which one person was seriously hurt and three received minor injuries.
Police estimate that between 500 and 1,000 chickens escaped onto the road.
Two lorries and three cars were involved in the accident which closed the road in both directions between the Botley Interchange and Cumnor.
It intensified traffic problems in the area as thousands of people made their way to the CLA Game Fair at Blenheim Palace.
A Thames Valley Police spokesman said the escaped birds "are all over the carriageway."
"The game fair is on and we are going to ask if there are any wagons or nets that we can use to get the chickens together."
He said that although it was a priority to deal with the people injured in the accident, officers would also be helping round up the wayward flock.