Their name contains their most distinctive feature: the flare of brilliant yellow feathers on their rumps as they fly away. The rest of their bodies are primarily gray with black streaks and speckles, white wing bars and yellow patches on their chests, throat and forehead. The female’s coloration is more subdued and muted.

A typical warbler, adults measure about 5.5 inches (14 centimeters) long.

Flexible and adaptable birds, yellow-rumped warblers can thrive in a variety of environments. In the summer months they mainly inhabit forests wherever pine trees grow. In the winter they prefer shrubs, trees or vines with berries, especially in more open woodlands including parks, residential neighborhoods and streams. 

They have an average lifespan of about seven years. 

In the summer, they eat mainly insects including beetles, weevils, ants, aphids, spiders and ants. They also eat spruce budworm—a native moth species that can devastate millions of trees during their periodic outbreak. They can catch insects on the wing by darting from branches. 

Yellow-rumped warblers can survive colder winter temperatures compared to other warblers due to their ability to rely on seeds and cold-hardy berries. They have high concentrations of bile salts, substances made in the liver, that dissolve the waxy coating of berries including those from wax myrtle, poison ivy , grapes, Virginia creeper, dogwood, juniper and bayberry. Eating berries boosts their metabolism and supplies a large portion of their diet in the winter months. In winter they will eat the fleshy coating surrounding coffee beans, and drink honeydew, a sweet substance secreted by aphids.

Yellow-rumped warblers are active during the day except when it migrates. During migration, it flies by night, as is the case with many migratory birds.

Flocks of yellow-rumped warblers form during migration and in the winter, often including birds of other species. 

Monogamous during the breeding season, yellow-rumped warblers live in pairs and build their nests on horizontal perches in pine trees. The female builds the nest, with the male sometimes bringing her materials. The nest takes about ten days to build and resembles a small cup, woven of twigs, barks and roots which are lined with grass, feathers and animal hair. The female lays one to six pale speckled eggs, with an average clutch size of four. Eggs are incubated for 12 to 13 days before hatching, followed by a nestling period of 10 to 14 days before fledging. Pairs can have two broods per breeding season.