Like other parulids, Red Warbler is nearly always active. They move quickly and often turn abruptly to cock their heads or jerk their tails. More so, they preen continuously, even fixing the same spot multiple times. Red Warbler forages in the low and midstory, employing a variety of strategies to acquire prey, including gleaning, hovering, and sallying (Elliott 1969).
By late February, males are singing from established territories, which can range from 30-60 m², and average 40 m² (n = 9). Males challenge nearby rivals by flying repeatedly into an adjacent male's territory. These interactions can lead to fights between individuals, but altercations between mated males rarely result in a shift in territorial boundaries. Territorial behavior ceases in August once the young have fledged and adults begin molting (Elliott 1969).
Red Warbler is socially monogamous and most often found in mated pairs. Courtship chasing, which can include both short flights as well as extended chases through the understory, starts in mid-March. After such chases, both birds sit close to one another while the male sings as the female utters "soft calls". Sometimes males perform a courtship display where they sing in flight and then enact a "redstart-like wing-and-tail fanning performance" (Elliott, 1969).
Social and interspecific behavior
Red Warbler occasionally associates with mixed species flocks in the winter, but are most commonly found foraging in pairs (Elliott 1969). Elliott once observed a pair forage alongside a pair of Slate-throated Redstarts (Myioborus miniatus) during March, yet on another occasion he also saw one male and two female Red Warblers chase off an Empidonax flycatcher that entered their territory.
Elliott (1969) observed a male Red Warbler give alarm calls in response to a nearby Sharp-shinned Hawk (Accipiter striatus); Accipiter are predators of small birds, presumably including Red Warbler. He also reports another male chasing a Troglodytes wren from the nest, as well as an instance of nest predation, so it is also reasonable to assume Red Warblers are susceptible to nest predators such as wrens, rodents, raccoons, feral cats, and snakes. It has not been described whether nest parasites like cowbirds (Molothrus) parasitize Red Warbler nests.