Ticks are very common in collared doves and wood pigeons. They will usually be on the head and look like a soft brown lump. It is important that these are removed, - and removed properly - because they inject an anticoagulant into their host's blood , which can cause haemorrhaging and can also affect the nervous system causing neurological symptoms and often death.
If you find any you will need to ensure that you remove the whole tick including the head which will be buried in the bird's flesh. If you do not have a tick remover you can use tweezers: the claws of the tweezers as close as you can get to the birds body then gently twist anticlockwise. Dabbing the tick with frontline first can weaken it and make it easier to remove.