They are bug eaters and like to glean caterpillars, aphids, beetles and other invertebrates from leaves as they flit from branch to branch on the edges of woodlands.
Unfortunately their nests are among the most parasitized by the Brown-headed cowbird. Cowbirds deposit their eggs in nests of other birds’ species so that their cowbird chicks will be fostered. The cowbird eggs typically hatch earlier than their host’s eggs which gives them a competitive advantage over the other hatchlings.
Some Yellow Warblers will abandon their nest once a cowbird has left an egg. To just kick the out the cowbird egg could result in a cowbird attack on the nest and holes pecked in all the warblers own eggs. So warblers try to avoid the cowbirds all together or another tactic the warblers take is to build a new nest on top of an old nest that has a cowbird egg. Some nests end up looking like a bizarre, multi-layered high-rise nest.
- Attracting Michigan Songbirds http://goo.gl/Gmn0b
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