Why loathsome Brown Cowbird?
Because they the female Cowbird lays her eggs in the warbler nests. Our Warblers are dimenishing in numbers. Not so the cowbirds. This is partially because unsuspecting folks put out bird feeders with millet in the seedmix. Not many of our native birds like millet, but Cowbirds too. Thus, they are getting extra food provided by humans. While the Wablers are not seed eaters at all and eat insects such as caterpillars.
The result is that there are more Cowbirds than ever, and they are parasitizing our Warblers. That's why I consider them loathsome even though they are native birds.