The National Parks and Wildlife service has launched a DeerAware Campaign
Motorists in Mayo are being warned of the risk of collisions with deer, as the mornings and evenings get darker.
The county council says autumn is the 'rutting' season - when lusty stags go off for some female companionship, while younger males are ousted by the more dominant ones.
It says this is bad news for motorists, particularly in a rural counties, where the number of deer and car collisions is a growing concern for National Parks and Wildlife staff.
Car accidents involving deer peak at this time of year. With night falling earlier, the peak commuting time coincides with deer coming out to feed on grass verges near roadsides.
Motorists are urged to drive within the speed limit to give a better chance of stopping.
According to AA Car Insurance in the UK, the average claim payout for a deer strike is stg£1,403 (€1,620).
Some estimates suggest there are as many as 74,000 strikes annually, many unreported in the UK - while in Ireland the latest figures show there are around 400/500 collisions between motorists and deer in Ireland each year, resulting in human injury.
Road safety officer Noel Gibbons says: "At 100km per hour, hitting a deer is serious - not just for the animal but car occupants as well.
"A natural reaction is to try to avoid the collision but as a result, drivers may miss the deer and hit other vehicles or trees which could be even worse."
The national parks body and the Mayo road safety office have joined forces to launch their new DeerAware Campaign.
Denis Strong is the divisional manager of the National Parks and Wildlife Service, based in Ballycroy National Park.
"As days get shorter in the autumn, busy traffic times coincide with dawn and the early part of the night when deer are most active and hardest to spot.
"In wooded areas in particular, there may be very little warning before one or several deer bolt across."
A mature red deer stag can weigh up to 160kg and hinds (or females) will be about 30% lighter.
"Even at low speed they can cause considerable damage to a vehicle and potentially cause life-threatening injuries to the driver and their passengers," Mr Strong warned.
Deer crossing road signs are located in areas known to contain deer population - but are not official crossing points for deer.
But motor vehicles are not the only thing that deer collide with.
If you do hit a deer people are advised to report it to the gardaí, as it may be fatally injured and suffering.