No. What you are probably seeing is the male wren building several nests at the same time in hopes of pleasing his very finicky mate.
Yes, some birds lay eggs in nests of other birds when they have hatched their eggs and are done raising their chicks.
No, they build their own.
The cactus wren
The cactus wren nests in cholla crevasses as well as suguaros and a couple of other desert plants
2to 4
3weeks
I'm assuming that you are asking for notable facts about the Cactus Wren. The Cactus Wren is a small bird that lives in the southwestern United States and Mexico. Its scientific name is Campylorhynchus brunneicapillus, which means "bent bill with a brown cap." It is the largest U. S. wren and the state bird of Arizona. It lives in desert regions and like all wrens eats mostly insects with the occasional seed or fruit. As its name suggests, it often makes its nests in the left-over nests in saguaro cacti made by Gila Woodpecker. I'm assuming that you are asking for notable facts about the Cactus Wren. The Cactus Wren is a small bird that lives in the southwestern United States and Mexico. Its scientific name is Campylorhynchus brunneicapillus, which means "bent bill with a brown cap." It is the largest U. S. wren and the state bird of Arizona. It lives in desert regions and like all wrens eats mostly insects with the occasional seed or fruit. As its name suggests, it often makes its nests in the left-over nests in saguaro cacti made by Gila Woodpecker.
North American Wrens which there are 9 types, are secretive. They (House Wren, Carolina Wren, Rock Wren, Canyon Wren) will nest in holes, trees and birdhouses. The Marsh Wren makes a globe-shaped nest which are attached to plants just above the water. Cacus Wren builds a nest shaped like a football in cacti.
Sedge wren, marsh wren, Carolina wren, winter wren, cactus wren, rock wren, Bewick's wren, canyon wren, house wren.
They share the characteristics of all birds, feathers, warm blood, laying of eggs.
Brown-headed Cowbird
What you saw was more likely a wren feeding a Brown-headed cowbird. Cowbirds are dark in color like crows but as adults are more blackbird-like in size. Cowbirds often lay their eggs in the nests of songbirds and allow them to hatch and raise the cowbird fledglings. This is a behavior known as brood parasitism and is normal for cowbirds. A cowbird fledgling oftentimes grows to become larger than the host parent that is raising it.