House wrens are feisty and pugnacious animals considering their tiny size. They are known to occasionally destroy the eggs of other birds nesting in their territory by puncturing the eggshell. Females that sang more songs to conspecifics that were simulated by playback lost fewer eggs to ovicide by other wrens. Female bird song in this species is therefore thought to have a function in competition and is not only displayed by males. They are also known to fill up other birds' nests within its territory with sticks to make them unusable..
Seen at Mt Diablo
This wren had a nest full of babies .She was cleaning up the nest. A fecal sac can be seen in her mouth.