Great Crested Flycatcher

The Great Crested Flycatcher is the only cavity-nesting flycatcher in eastern North America — a distinction that shapes almost every aspect of its breeding biology. Both sexes inspect potential cavities, but nest construction is performed almost entirely by the female while the male guards her closely. Natural cavities in live or dead trees and old woodpecker holes are preferred, but the species readily uses nest boxes, hollow fence posts, drainpipes, buckets, and even mailboxes. Cavities are typically 2–6 m above the ground, though heights range from 1 to 23 m. If a cavity is much deeper than 30 cm, the female first backfills it with debris — leaves, bark, and other loose material — before building the nest cup on top. This backfilling behaviour is rarely mentioned in popular accounts but is a consistent and practical adaptation to the variable dimensions of natural cavities.

Nest materials include grasses, leaves, twigs, bark strips, moss, feathers, animal fur, snail shells, and eggshells. The inner cup measures 7–9 cm in diameter and 4–5 cm deep. Most famously, shed snakeskin is almost always woven into the nest — a behaviour that has been scientifically validated as an anti-predator strategy (see Did You Know). Where real snakeskin is scarce, birds substitute crinkly synthetic materials such as cellophane, onion skins, and plastic wrappers, suggesting they are specifically seeking the texture and visual appearance of shed skin rather than using whatever is available.

Nest building begins as early as mid-April in southern populations and as late as June in Manitoba. A single clutch of 4–8 eggs (typically 5) is laid per season. Eggs are creamy white to pinkish buff, heavily splotched and streaked with brown, purple, or lavender markings; they measure approximately 2.1–2.4 cm long by 1.5–1.8 cm wide. Incubation is performed by the female alone and lasts 13–15 days. Hatchlings are altricial — helpless, sightless, and initially naked, developing a grey down within days. Both parents feed the nestlings, though the female makes more frequent visits. Nestlings fledge at 13–15 days. The family group then remains together for up to three weeks post-fledging, with both parents continuing to feed and defend the young. There is only one brood per season.

The typical lifespan of a Great Crested Flycatcher in the wild is estimated at 2–10 years, with most individuals in the lower part of that range due to the high mortality rates common in the first year of life. The maximum recorded lifespan is 14 years and 11 months — a bird banded in New Jersey in 1953 and recovered in Vermont in 1967, making it one of the longest-lived small flycatchers on record for North America.

Survival rates improve significantly after the first breeding season. Adults show strong site fidelity, returning to the same breeding territories year after year, which likely contributes to their longevity by reducing the risks associated with finding new habitat. Natal dispersal, however, is high — nestlings rarely return to breed near where they were born, which is one reason why long-term banding recaptures are uncommon despite the species' potential longevity.

The main mortality factors are predation (particularly of eggs and nestlings by snakes and squirrels), collisions with man-made structures during nocturnal migration, and exposure to pesticides that reduce insect prey availability. Compared to open-cup nesters of similar size, the cavity nest provides meaningful protection against nest predation, likely contributing to higher adult survival rates. Within the genus Myiarchus, lifespan data are limited for most species, but the Great Crested Flycatcher's 14-year record is consistent with the upper range seen in other medium-sized tyrant flycatchers.

The Great Crested Flycatcher is listed as Least Concern by the IUCN, with an estimated global population of approximately 8.8 million mature individuals (Partners in Flight / BirdLife International). North American Breeding Bird Survey data from 1966 to 2019 show populations have remained stable across the breeding range. Partners in Flight rates the species 8 out of 20 on the Continental Concern Score, indicating low conservation concern. Local population increases have been recorded in areas of increased forest fragmentation, which expands the edge habitats the species favours — a paradox in conservation terms, since fragmentation harms many other woodland species.

The primary potential threats are loss of forest habitat and the reduction of suitable nesting cavities. 'Clean' forestry practices that remove dead snags from managed forests directly reduce the availability of natural nest holes. Competition for cavities from European Starlings, Tree Swallows, House Wrens, Eastern Bluebirds, and squirrels can cause local breeding failures. Collisions with buildings, vehicles, and communication towers during nocturnal migration are an additional mortality factor, as is exposure to pesticides that reduce insect prey availability. Brood parasitism by Brown-headed Cowbirds is infrequent, likely because the cavity nest and the species' aggressive nest defence make successful parasitism difficult.

The species is resilient and benefits from its tolerance of human-modified habitats. Its willingness to adopt nest boxes makes it a straightforward target for active conservation support — erecting nest boxes in suitable woodland edge habitat is one of the most effective ways to support local populations where natural cavities are scarce. Climate change is projected to affect the species' range over the longer term, though current populations show no sign of decline.

Within eastern North America, the Great Crested Flycatcher has no close lookalikes — the combination of bright lemon-yellow belly, grey breast, and rufous-orange tail is unique among the region's flycatchers. The challenge arises when comparing it to its western relatives in the genus Myiarchus. The Ash-throated Flycatcher (Myiarchus cinerascens), which breeds across the western US and occasionally strays east, is the most similar in structure but is noticeably paler overall: the belly is a very pale yellow (almost white in some individuals), the grey of the breast is lighter, and the rufous in the tail is less saturated. The Brown-crested Flycatcher (Myiarchus tyrannulus) of the southwestern US and Texas is larger than the Ash-throated but still shows a paler yellow belly than the Great Crested.

In the limited overlap zones along the Gulf Coast and in southern Texas, careful attention to belly colour saturation and the depth of rufous in the tail is the most reliable field mark. Vocalisation is also diagnostic: the Great Crested's wee-eep is distinctly buzzy and up-slurred, while the Ash-throated gives a rougher, more burry ka-brick or prrit. In the hand, wing formula and bill dimensions separate the species reliably, but in the field, the Great Crested's richer, more saturated colours and louder, buzzier calls are the key features to focus on.

Courtship in the Great Crested Flycatcher is closely tied to cavity inspection, with the male leading the female on tours of potential nest sites as a central part of pair formation. Males arrive on the breeding grounds before females — typically by one to two weeks — and begin establishing territories and prospecting cavities immediately. When a female arrives, the male pursues her through the canopy in rapid, twisting chases, calling persistently with the emphatic wee-eep contact call.

Once a pair bond forms, the male guards the female closely throughout the nest-building period, following her on foraging trips and returning with her to the nest cavity. This mate-guarding behaviour is thought to reduce the risk of extra-pair copulations, which have been documented in the species. The male does not assist with nest construction but remains in close attendance, calling frequently and chasing away rival males from the territory.

Display behaviours during territorial confrontations — hunching low over the perch, erecting the crest, fanning the rufous tail, and snapping the bill — are also used in a modified form during courtship, with the male performing these postures towards the female in a less aggressive context. The pair is socially monogamous, and some pairs are known to reform in subsequent breeding seasons, suggesting a degree of mate fidelity beyond a single year.