Tree swallows are common songbirds of North and Central America. Compact, streamlined, and highly agile, Tree swallows are often spotted skillfully catching flying insects. This is a guide to female Tree swallows and how to identify them from males.
By their second year, female Tree swallows are similar to males, with paler undersides and dark, iridescent blue upper parts. However, they are typically duller overall and sometimes retain a brown patch on their heads.
At the start of the breeding season, males tend to arrive at territories around a week before the females. They select a nesting cavity and await the females to return, who’ll choose a male based on their nest cavity as well as their courtship displays and appearance.
Female Tree swallows proceed to line the cavity nest while males perch and watch from a nearby branch. The female usually handles incubation, but both parents feed the young birds.
There are a few other ways to identify female Tree swallows from males - read on to find out!
First year female Tree Swallows are easy to differentiate from males, as they are mostly brown
The easiest way to tell if a Tree swallow is male or female is by the color of its feathers - but the difference is only obvious for first-year birds. 1st-year male Tree swallows have bright blue upperparts with a white underbelly, while female Tree swallows have dull brownish gray upperparts with a grayish white underbelly.
In addition, the male’s blue plumage can be a strike iridescent blue, whereas the female only has a small blue section across her upper wings.
As you might expect, the color difference allows males to stand out by having brighter, contrasting colors. Studies have found that brighter male Tree swallows were likelier to pair with more than one mate.
As mentioned, however, this color difference is only reliable for first-year females. In their second year, female Tree swallows look very similar to males, with darker blue plumage, although some remain duller overall. Females may also retain some brown plumage on their heads, which the male lacks.
Female Tree Swallow
Male Tree Swallow
An adult female Tree swallow is relatively dark blue with a white to gray-white underside, similar to the male. However, females are browner overall, though the difference is often exaggerated.
First-year females are much duller than first-year males, though some develop light blue iridescent feathers across their upper wings and upper body, but lack the dark blue iridescent plumage of the male.
Female Tree Swallows look more like males after the first year, but are generally duller
Male Tree swallows are slightly bigger than females, but the difference is negligible in most cases. Precise measurements of wings, bodies, and bills reveal males as slightly larger.
There’s little significant difference between songs and calls by male and female Tree swallows.
However, analysis reveals that males have greater song complexity and variation. Females call primarily for communication, whereas males sing to advertise for a mate and establish territories.
Intriguingly, both males and females sing throughout the day - it’s often only the male that sings gratuitously. This is probably because both males and females are capable of aggression due to high competitiveness over nesting cavities.
Interestingly, males sing at night in the breeding season, probably to maintain their territory and prevent other males from attempting to seize their mate.
Breeding pair of Tree Swallows - male left, female right
Males arrive at territories first and secure nesting cavities prior to females returning. The male will then advertise his cavity and display to the female with an upright posture and call. Female Tree swallows bear most of the burden of building the nest and incubating eggs. Male Tree swallows often assist with sourcing materials, but the female transports most material to the nesting cavity.
The male Tree swallow often takes a more active role in foraging for food and bringing it to the nestlings. The female usually incubates, but when it’s cold, the male also crams himself into the nest and sits on eggs to maintain their warmth.
Males can be highly aggressive and may even kill other nestlings if they find a widowed female.
Females can also be competitive over nesting cavities, but their behavior is usually self-limiting, while males are prepared to kill young birds. However, there have been rare cases of two females nesting in the same hollow, probably due to the extremely low availability of valid cavities.
Female Tree Swallow perched on a wire
Female Tree swallows can most likely raise young alone if the male dies or abandons at some point. This may occur if the male forms an extra-pair bond, though it’s a rare occurrence since male and female Tree swallows share parental responsibility, and in ideal scenarios, they’ll mate for life.
Although Tree swallows are typically socially monogamous, some males tend to be polygamous (around 8% in one study). So, it’s possible to find a male Tree swallow mating with more than one partner, particularly if there is a shortage of males.
Also, even though Tree swallows mate for life, male Tree swallows can be quite unforgiving if they determine their partner is engaging in extra-pair copulation. Often, they’ll abandon the female and the nest and search for a new partner.
Nesting pair of Tree Swallows - female right, male left
1st-year female Tree swallows are relatively pale with a white to gray-white underside, but they turn darker in their second year to appear almost identical to the males. However, their plumage may remain duller with a brown tinge, though this isn’t always obvious.
Female Tree swallows have virtually the same repertoire of calls as males.
Tree Swallow pair nesting - female left, male right
Like their male counterparts, female Tree swallows sing mostly during courtship and copulation. The songs can be classified as a gurgle, whine, or chirp. Females sing throughout the day the same as males.
However, male Tree swallows are capable of complex songs, and females have a slightly smaller repertoire.
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