The male has a gray and black plumage on the back, the black belly with an inverted "U" spot. It has a yellow patch on crown, shoulder and rump. He has a black mask. The female is gray-brown in color with pale yellow shoulder patches and yellow rump. She has a greyish mask. This warbler has a wingspan of 21 cm, measures about 15 centimeters and weighs about 12 grams, which is about the weight of a strawberry! This warbler lives about 6 years.

Yellow-rumped Warbler, like most warblers, is primarily insectivorous and loves butterflies, caterpillars and flies. It's the only warbler able to digest the waxes found in bayberries and wax myrtles. It is often seen fluttering to catch insects in flight or resting on leaves. It is one of the first warblers that we see in the spring, at the end of April it is back in Quebec, thanks to it's ability to digest berry waxes.