Fenz fire risk management officer, Ashburton, Bevan Findlay said tractor fires at this time of year were usually caused by birds, often starlings, nesting in the engine.
He said the warm, sheltered spot in an engine cavity was ideal for them.
''Our advice is to check and check again. Always check under the bonnet before starting a tractor, even if it's only returning from lunch.
''Birds can quickly gather enough straw and materials to cause a fire when the engine restarts.''
It was a sentiment agreed with by one Mid Canterbury farmer who had such a fire, which destroyed an expensive tractor.
'It can happen so quickly,'' he said.
The farmer said starlings were known to hover and attempt to build nests in the exhaust pipe, within 15 seconds of a tractor being parked and the engine turned off.
They were capable of rebuilding a nest within an hour.
In order to limit any risk, Mr Findlay said having firefighting equipment on tractors and other machinery was a good start and if users left the bonnet up when they finished using a tractor it served two purposes.
''One, it reminds whoever is next using it to check the engine, and two, it may prevent birds thinking it is a safe haven.''
''A fire extinguisher right there could make the difference between a small fire and totally losing a vehicle, especially as most rural properties are further from our fire stations, so it takes us longer to get there. Fires can grow very quickly.''
He also reminded farmers that during harvest, later in the season, fires in other kinds of farming machinery could be caused by dust build-up, so keep up regular maintenance and checking of equipment.
