At the Project:
Most Tree Swallow nests are empty now, although a few boxes where replacements or
takeovers occurred may still hold late young being tended by adults. Since some of
your former nestlings, now fully independent juveniles, may linger around the project
for a week or more if the foraging is good, this is the best time to observe them.
How can you tell juvenile Tree Swallows from adults?
- Juveniles that have recently fledged, like the ones above, have sooty gray-
brown upper bodies, wings, and tails, with no traces of blue or green.
- A few juvenile Tree Swallows may show a faint breast band (see below).
- Don't mistake these juvenile Tree Swallows for Bank Swallows, whose breast
band is much darker and more solid. Compare the well-defined band on the
Bank Swallow below left to the faint one on the Tree Swallow above. The bird
below right is a more typical, bandless juvenile Tree Swallow.
- Juveniles weigh about the same as adults but their shorter, rounder-tipped
wings and tails make them appear smaller and chunkier.
- Juvenile flight is a bit slower, weaker, and more "fluttery" than adult flight.
- If viewed up close some juveniles may still show traces of yellow flanges at the
corners of their mouths, as in the photo below by Len Blumin.
When will juveniles get their adult Tree Swallow plumage?
- Juvenile molt to adult plumage begins a few weeks after fledging.
- Molt in Tree Swallows is a gradual process, extending over several months.
- Surviving juveniles will complete feather replacement by late autumn.
- Juvenile males will acquire the blue-green iridescent upper body possessed by
all after-hatch-year (AHY) males.
- Juvenile females will acquire the brownish-green upper body plumage that
distinguishes second-year (SY) females from older ASY females.
Where have the adults that have finished nesting gone?
- Parent Tree Swallows tend to move to large wetlands soon after their nestlings
fledge, where they join other Tree Swallows to form large post-breeding
foraging and roosting flocks.
- A few scruffy adults may still hang around your project sunning and preening.
- Check these lingering adults for the beginning stages of molt, the replacement
of their feathers, which usually starts by early July.
- As they fly overhead look for notches in the trailing edges of adults' wings and
tails where their flight feathers have begun to be lost, and new ones, still short,
are growing in.
While juvenile Tree Swallows hang around, what are they doing?
- Juveniles may join remaining adults hunting for food over fields and wetlands.
- Some may beg at passing adults, trying to get a free meal.
- When not foraging they often perch with adults in groups on wires and trees,
resting and preening.
- They may land and sun themselves on roads, beaches, roofs and other warm
- Juveniles frequently approach nest boxes, fluttering around, perching on, and
even entering them, especially boxes that still contain living nestlings.
Why do juveniles congregate at boxes that still contain nestlings?
- We aren't sure.
- It's been suggested they're "scouting" potential nest sites for next year, but
there's no evidence supporting this.
- Some may be trying to mooch a free meal from resident adults.
- They are not "helping out." Their presence may actually interfere with parents
trying to feed nestlings in late nests.
- If you look closely at the photos above and below you'll see a juvenile blocking
the entrance hole, preventing an adult from delivering food to its own small
Question for the next Topic: Flocks, Migration, Molt and Wintering.
- What happens after nesting is complete?
- Where will your the swallows go next and what do they do?
Learn About Birds at Tree Swallow Nest Box Projects
|Life History and Nesting Guide, Spring Return, Songbird Behavior, Song and Calls,
Nest Site Competition, Pair Formation, Nest Building, Bird Flight, Mating,
Eggs and Egg Laying, Incubation, Nest Takeovers, Feather Care, Hatching and Begging,
Parental Care, Sexing and Aging, Nestling Growth, Mortality Causes, Older Nestlings,
Fledging, Ectoparasites, Juveniles, Flocks, Migration, Molt, and Winter,
Box Care and Project Assessment