The animal had almost disappeared from the UK after its grey cousin brought the killer squirrelpox virus from America in the 1800s.
But a programme to eradicate the grey squirrel has seen the numbers of reds rise from 40 to 700 on Anglesey.
The Red Squirrels Trust Wales found 48% of deaths since 2004 were on Anglesey's roads, with none from squirrelpox.
A study, conducted alongside the Animal and Plant Health Agency also found a high number died after contracting infectious diseases near squirrel feeders that had not been regularly disinfected.
Road accidents are hampering the resurgence of the red squirrel on Anglesey.