Great crested flycatcher

Males will sing a three-part song composed of two short whistles: a wheerreep followed by a higher-pitched whee, and a soft low churr. This song is meant to be heard by a mate at short distances, indicating periods of low disturbance and stress typically intensifying just before dawn. It is appropriately named "dawn song" (or twilight song).[7][8]

In addition to the dawn song, great crested flycatcher also produce various calls, a series of fast ascending huit, huit, huit is given in moments of stress or excitement during interactions of between neighbours.[8] The most characteristic sound is perhaps a single loud whee-eep, called out to communicate between mates or parents and young birds. A faster repetition of this call often signal predators in proximity to nests and young.[8] A rapid succession of harsh-sounds rasps signals alarm or stress often heard during territorial disputes between neighbouring birds[8][9]

The great crested flycatcher is primarily an insectivore, with insects and other invertebrates making up for the majority of its diet, but will also consume small portion of small fruits and berries. Despite the "flycatcher" of the bird's name, flies, along with spiders, make up only a small percentage of its diet; it prefers prey such as butterflies, moths, beetles, grasshoppers, crickets, and bees and wasps.[10]

Great crested flycatchers will use a variety of hunting tactics, although the most common method observed is a rather passive sit-and-wait strategy. Perched in high canopies, they search in all direction often accompanied by a characteristic head bobbing. Once they have spotted a potential prey, they swoop down and will pursue if they missed on the first dive.[5] They can also be seen abruptly braking and hovering, picking insects or small fruits off of leaves, trunks or other surfaces, sometimes crashing into the foliage in the process.[5][8]

Fruits and berries, when consumed are swallowed whole and the pits later regurgitated.[8]

Adult in Eastern Maryland with its catch for the nestlings

Nest building begins as early as mid April for populations of the southern distribution,[11] and as late as June for northern populations (i.e. Manitoba).[9]

Great crested flycatchers are socially monogamous[12] with chances of pairs reforming in following years, given that both members of the pair survive the winter.[6] Pairs have been observed to attempt copulation from the beginning of nest building all the way to the hatching of young, sometimes during the nest building process; this is thought to be a strategy developed by males in order to prevent female infidelity.[11] Mating ritual for the great crested flycatcher is described as males swooping down from a high perch in order to initiate mating with females, sometimes hovering near hideaway if female retreats, before returning to perch and repeating diving routine until mating is successful.[6]

Although both parents will inspect potential sites, building of the nest is done almost entirely by the female, while the male closely guards its mate.[12] Cavities that are large enough in size and opening are the preferred nesting sites, whether naturally occurring or excavated by other species (8) as well as use nesting boxes and other man-made structures.[12] Most chosen cavities are situated between 2m and 6m off the forest ground (11,15). The nest itself is built within 2 to 4 days and is composed mostly of vegetation and plant fibers, such as grasses, moss, leaves, but also pieces of animal fur and feathers, pieces of shed snakeskin, and artificial materials (ex: strings, tape, cloth, and plastic objects).[12] The inner diameter ranges from 7–9 cm.[12]

Great crested flycatchers lay a single clutch of 4-8 eggs, which are incubated on average for two weeks by the female only.[9][12][13] After hatching, nestlings will typically spend another two weeks in the nest before fledging. During this time, nestlings are fed an insect dominated diet by both parents, although females will make more frequent visits.[12][13]