Bronzed Swallow
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Bronzed Swallow, Tachycineta aeneafrons
L 12-14 cm, WS 28-30 cm, Family: Hirundinidae
IUCN Conservation Status: Least concern (LC)
Description:
Small,
active songbird with cone-shaped body, long, tapered wings, and a short,
notched tail. Upperparts blue-green with coppery iridescence, undersides stark
white. Forehead appears more green than back or rump. Wings, tail, and legs
dark. Bill short and flat. Sexes similar, but females tend to be duller with
slight brownish spotting in throat. Only native swallow with noticeable
greenish coloration.
Voice:
Song
is a series of high-pitched, watery warbles, gurgles, and chirps. Sounds
watery, or slightly metallic. Both sexes sing. Calls include any single part of
the song, as well as chatters and harsh tinks. Will click bill when
threatened. Often quite vocal, especially in flocks.
Range and Habitat:
Summer
range encompasses the entirety of Novasola, including Kosatka and Francis
Islands, but less common in the interior steppe. Migrates to spend winter in California,
Arizona, and Mexico. Prefers open to semi-open woodlands or forests with nearby
water sources like lakes or rivers, especially mature woodlands with standing
deadwood and snags with cavities or woodpecker holes. Human development has
allowed them to expand their range into the prairie. Will readily use nest boxes.
Discussion:
Amazing
aerial acrobats, like most swallows, the Bronzed Swallow can become a dazzling display
of metallic greens and blues as it forages for insects above the water or among
the trees. When not foraging, they are most often seen sunbathing out in the
open. Their steely, iridescent plumage and active nature combine with their willingness
to nest in human structures and nest boxes to make them a well-known and
well-studied endemic bird.
Insectivores,
Bronzed Swallows eat mostly flying insects like flies, bees, mosquitoes,
beetles, butterflies and moths, and dragonflies, which they catch mid-flight. They
are extremely acrobatic fliers, able to make quick, sharp turns and dives, which
they use to aid in catching prey. Unlike Orchard Swallows, the other most
common endemic swallow, with which they are often confused, Bronzed Swallows
will forage at any height and often fly high above the ground. They will skim
water bodies and stay low to fields but may just as often forage well above the
canopy hundreds of feet in the air. They also swallow grit like gravel, sand,
or shells to aid in digestion, especially during the breeding season when they need
extra calcium. They will forage over water bodies like lakes and ponds as well
as over meadows or deep within forests, depending on insect numbers and food availability.
Gregarious, swallows will often forage in large flocks and will often be seen
in mixed flocks with other swallows and bird species, especially during large
insect hatches or in highly productive areas. Bronzed Swallow will occasionally
supplement their diets with plant matter, which is thought to be an adaptation
for cold weather.
Bronzed
Swallows prefer to breed in open woodlands of evergreen or deciduous canopy,
especially mature woodlands with lots of standing deadwood and natural
cavities. This may also include post-burn areas or places with nearby cliffs. They
may also breed near human development and use human structures, nest boxes or
birdhouses. Bronzed Swallows are secondary cavity nesters, meaning they build
their nests in pre-existing or naturally occurring holes, cavities, or crevices.
These may include woodpecker holes, dead or rotted areas in trees, craggy
cliffsides, and so on. Both sexes help build and protect the nest inside the
cavity, which is cup-shaped and made mostly of grasses and leaves. Bronzed
Swallows often nest alone but will nest in small colonies on occasion. Males defend their mates from other males
vigorously and aggressively until eggs are laid and he devotes more time to
defending the nest. As a result, losing the nest or hole to other birds is
common. Competition for nest holes can be fierce, not just against other
Bronzed Swallows but all other cavity nesting birds as well. There are multiple
accounts of Bronzed Swallows engaging in cooperative breeding behaviors where
they forgo laying eggs and instead help to raise the offspring of another pair,
and they do this not only with other swallows but other bird species as well.
Scientists believe this strategy has evolved as a way for the swallows to “inherit”
the nest hole after the parent birds either die or abandon the nest.
Like
many other swallows, Bronzed Swallows are long distance migrants which winter
in Central America and breed on Novasola. They typically arrive on Novasola in
mid-to-late May and leave by early or mid-July. Males typically arrive earlier
and establish nest sites and territories which they advertise to the females
through song and display flights. During migration they form large flocks,
which on rare occasions can number in the hundreds of thousands of individual
birds. At twilight they can be seen flocking in amazing, shifting forms like the
murmurations of European starlings. Compared to its close relative the
Violet-green Swallow, Bronzed Swallows have stronger flight muscles and other
adaptations which aid in their cross-pacific migration from Novasola to the
mainland.
Members
of the genus Tachycineta, or New World Tree Swallows, the Bronzed
Swallow is closely related to Violet-green Swallows (Tachycineta thalassina)
and Tree Swallows (Tachycineta bicolor) native to mainland North
America but also found infrequently on Novasola. Both species have been known to
hybridize with Bronzed Swallows, though this is more common with Violet-green
Swallows. There have been a few isolated cases of Bronzed Swallows hybridizing
with Orchard Swallows of the genus Hirundo. T. aeneafrons was first
described by William Bartram in 1782 based on a specimen sent to him by George
York Baker, the naturalist with Morgan Fairweather’s Cape George expedition. Though
new to science, the Bronzed Swallow was already a well-known animal to Novasola’s
indigenous tribes, as it had been for centuries. The Cishtaklun name for the
bird is agaluyaq.
With
a widespread distribution and large population, Bronzed Swallows are common and
their population is stable, especially compared to most endemic birds. However,
there has been a significant decrease in the overall population in the past
century. New management practices and bans on pesticides have helped, but climate
change and increased drought and fire severity will no doubt have profound
impacts on the population. Nonetheless, they were likely even more common to
Richard Reichwald, who encountered countless Bronzed Swallows during all three
NRC expeditions.
“This
bird is copiously dispersed throughout the Fastwaters, populating all the
wooded country wherein it might make home a tree hollow. They can be found in
the Castor and Pollux valleys with ease, and greater numbers of them can be counted
along the mighty Chidkayook and in the basin it drains. I have observed them flying
above Culver Bay and at the foothills of the Red Mountains. Small numbers of the
bird exist outside the well-wooded regions, clinging to the cottonwoods and
willows lining the prairie rivers and homesteads. At these homesteads, and
indeed in the towns of Charlotte Bay, the swallow abandons its ancient habit
and nests in the boxes set out for bluebirds and wrens, with which it must
contest, and do so it does with antagonism and guile. Springtime on many a farm
is punctuated with the back and forth business of swallows and wrens and
sparrows and bluebirds all rushing to claim the same box or jar or old boot for
a nest, and in most such instances the swallow emerges the victor.” – Birds of
Novasola, 1912
“In
the hand, the Bronzed Swallow has perhaps the most handsome of plumages among the swallows, with lustrous
copper-greens and oiled bronze above a deep, steel blue. In flight, however,
their color may go unseen and instead appear plainly dark. Their stark white
bellies and breast distinguishes them from the barn [Orchard] swallow, with
which it often shares company.” – Manual to Novasolan Birds, 1914
“Perhaps
there is no greater a relief to men so tired and so worn than the sudden and
unexpected arrival at their destination. This feeling I now share, as from the
days of miserable trekking our party has emerged, faced now with the oasis of
the Great Shadow. We have spent much of our energies hiking down from the
Uludacks to arrive here on the shores of the lake, so grand in scale I fail to
see across it.
…
Above
the waters swarm a multitude of swallows, flitting high and low before
vanishing into the forest behind me and reappearing over the water moments
later. I am happy to have the swallows here, as a great number of mosquitoes
has begun to burden us.” – Expedition log, September 5, 1904