What's a good treat to use as positive reinforcement for training diamond doves?

I just started working at an aquarium that has two diamond doves on exhibit. I've been told that no one has ever really handled these birds beyond vet checks as far as they know, but I would like to attempt to train them to perch on my hand to maybe be used during animal presentations. I realize this is a high goal for birds of an unknown age that have possibly never been handled in their lives (they were someone's pet and given as a gift to the aquarium, and their past history beyond that is unknown), but I would like to try. I am familiar with the training of other bird species but have never worked with doves. Does anyone have any advice, especially in terms of a good, quick, low-calorie treat that would work well as positive reinforcement while trying to teach them to step up?