Do mourning doves nest in trees or on the ground?

Doves do not nest in tree cavities or nest boxes.
Mourning dove prefer to nest on the horizontal branches
of pine and cedar trees,but will nest in shrubs and even on the ground.Doves typically nest in trees along
the edges of fields,pastures or clearings and are seldom found in densely wooded areas.To create nesting cover for mourning doves,plant small clumps of two to three trees or even several single coniferous trees around open fields or your front yard.

They seem to prefer nests in trees.


http://www.crypto.com/photos/dove/

The mourning dove uses a very wide choice in selecting a site for its nest. Perhaps the site most nearly typical is not far from the trunk on a horizontal branch of an evergreen tree--a pine or cedar--affording a firm foundation for the flimsy nest. The bird frequently nests on the ground, however, even on a clump of grass, sometimes on the stump of a tree, and there are several recorded instances where the nest has been found placed on a wooden ledge attached to an inhabited building.

http://birdsbybent.com/ch11-20/mourning.html

Doves (a type of pigeon) will nest almost anywhere, but prefer horizontal limbs near fields or clearings. I have a feeder in my yard that attracts a dozen or so on a semi regular basis, so I've gotten to know them pretty well over the years. They become tame fairly quickly, I can approach them within 15-20 feet now, and they even play brinksmanship games with my cat, much to her frustration!