I found two robin's nests in my back yard this past week. One fell to the ground, the other is still up in the Tahiti lime tree. At least I think they are robin's nests, because I saw a grown robin bringing worms and such to the tree on a regular basis a few weeks back. No sign of the fledglings, though, although I'm sure they are about. If the cat got them, there'd be feathers everywhere. And I don't think the cat has ever tried to climb the lime tree - too many thorns.
The nests are quite sturdy. They have a strong clay mud bottom basin, reinforced with straw, and then a nice bedding of more straw/grasses.