ONE TO WATCH
Cerulean Warbler: a bolt from the blue
e often forget how rare the
colour blue is in the animal
world. Mammals, for instance,
can only create the pigment
melanin, which restricts their coats to
brown, black and reddish tones. But birds
are different. They are able to capture
pigments from the food they eat or, in
the case of blue colouration, refract
light using the internal structure of the
feathers themselves. Nowhere is this
more captivating than in the Cerulean
Warbler Setophaga cerulea, whose
delicately-patterned plumage glimmers
like a sapphire between the trees.
Every year, this tiny songbird makes an
intrepid journey between two different
types of forest within the Americas,
breeding in the USA and southern Canada
before migrating as far south as Bolivia.
80% of its population breeds in the
Appalachian Mountains in the Eastern
USA, where its high-pitched, musical
call compliments (and probably inspired)
the bluegrass music so famous in the
region. However, the idyllic atmosphere
is disturbed by mining companies
removing the entire tops of mountains to
access the coal reserves beneath – in the
process, destroying tens of thousands of
hectares of prime deciduous forest.
The freshly opened-up land also
attracts the Brown-headed Cowbird
Molothrus ater – a notorious brood
parasite, whose cuckoo-like habit of
dumping its eggs in Cerulean Warbler
nests for them to raise takes a heavy
toll on the population. In fact, its forest
W
homes are shrinking at both ends due to
logging, mining and the encroachment
of agriculture. The precipitous decline
in Cerulean Warblers (more than 70%
reduction in numbers in the past 44
years) means it qualified as Vulnerable on
the IUCN Red List of threatened species
in 2004.
However, since 2008, the rate of
decline seems to have slowed down.
The science world is not quite sure of
the reason behind this much-needed
respite, but they have a few theories.
Firstly, forest loss may also have
slowed in recent years. In the USA, land
protection and forest management
initiatives are beginning to take notice
of the species’ plight, and over a million
acres of forest have been replanted with
native hardwoods. Meanwhile, in South
America, the first ever Cerulean Warbler
Bird Reserve in Colombia is championing
‘bird-friendly’ shade-grown coffee, which
allows woodland birds to thrive within
plantations.
Another theory is that the warbler’s
breeding range is now expanding towards
the northeast and into southern Canada,
which may be a consequence of climate
change. Put simply, warmer temperatures
may be opening up new habitat into
which the species can move.
Regardless of the reason, it looks like,
for now, the species is starting to recover.
We’re even considering re-classifying it
as Near Threatened. But that won’t stop
us keeping an eye on it, watching for that
familiar flash of blue between the trees.
CERULEAN WARBLER Setophaga cerulea
Photo Ray Hennessy/Shutterstock