These images show wrens, nuthatches, and sparrows building and tending nests in both the round and the teardrop models of the Museum Birdhouse. Note the length of the piece of nesting material being brought into the house by a sparrow. It's probably milkweed bark that the birds are fond of using in their nests. The next to the last photo is the beginning of a wren's nest. The male usually starts several nests but doesn't complete one until a female wren that he attracts with enthusiastic singing picks the one nest she likes best. You can watch a streamed video of birds nesting in Museum Birdhouses by clicking here:( Bird Video ).