Birds
Tree Swallow
Tachycineta bicolor · also called tree swallows
Arriving back north while a late cold snap still lingers, a tree swallow switches to feeding on berries rather than the flying insects a sudden freeze has wiped out, a dietary backup plan most other aerial insect hunters simply do not have.
Overview
The tree swallow, Tachycineta bicolor, is an iridescent blue-green songbird native to open habitat near water across a broad range of North America, nesting in tree cavities and nest boxes near lakes, marshes, and fields. Its unusual ability to fall back on fruit during cold weather, strong reliance on nest boxes, and habit of forming enormous pre-migration flocks make it one of the more adaptable and behaviourally flexible aerial insectivores in North America.
A backup meal plan other insect hunters lack
While a sudden cold snap can be disastrous for birds that depend entirely on flying insects, the tree swallow’s willingness to switch to berries gives it a genuine safety net most of its aerial-hunting relatives never developed.
Status
Least Concern, though showing a decreasing trend in parts of its range linked to declining flying insect abundance and nest cavity competition.
Tree Swallow: common questions
Why can the tree swallow survive cold snaps that other insectivores cannot?
This species can switch to eating berries and other fruit when cold weather temporarily wipes out the flying insects it normally depends on, a dietary flexibility that most other aerial insect-hunting birds lack, allowing tree swallows to survive short cold periods and even arrive earlier in spring than insect-dependent relatives that have no comparable backup food source.
Does the tree swallow use nest boxes?
Yes, this species readily nests in artificial nest boxes in addition to natural tree cavities and old woodpecker holes, making it one of the most commonly encountered species in bluebird trail and other nest box monitoring programs across its range.
Why do tree swallows gather in such huge flocks before migration?
This species forms enormous pre-migration flocks, sometimes numbering in the tens of thousands, often roosting communally in marshes at night, a social behaviour that may help individuals share information about food sources and provide some protection from predators before the flock disperses southward.
How can you identify a tree swallow?
Look for iridescent blue-green upperparts contrasting sharply with clean white underparts, a striking two-tone pattern visible especially in good light, combined with the species' habit of nesting in tree cavities or boxes near open water.