The Done-Up Bird Gets the Worm

Starling chick with open mouth and a cotton swab with yellowish oil
Spotless
starling
chicks
use
a
bright
yellow
oil
to
enhance
the
color
of
their
mouth,
which
scientists
verified
by
rubbing
a
cotton
swab
over
the
area.

Juan
José
Soler

Spotless
starling
chicks
make
quite
a
sight
when
they’re
hungry.
Tucked
inside
their
nest,
the
gray
baby
birds
stretch
their
necks,
stick
their
little
faces
up
in
the
air,
open
their
beaks
wide
and
cry
out
insistently.
Like
many
bird
parents,
all
the
adult
starlings
see
when
they
look
down
at
their
chicks
is
a
cluster
of
circular
yellow
mouths,
each
vying
for
a
larger
share
of
food.
Now
scientists
know
the
color
of
those
mouths
results
from
a
surprising
trick
that
helps
the
chicks
catch
their
parents’
attention:
they
make
a
bright
yellow
lipstick
that
shows
off
their
immune
health.

A
team
of
ecologists
in
Spain
found
that
the
color
of
the
chicks’
preen
oil,
which
they
take
from
a
gland
and
apply
to
the
edges
of
their
beaks,
influences
how
much
food
their
parents
give
them.
The
birds
with
the
most
intense
yellow
and
ultraviolet-colored
mouths—an
indicator
of
good
immune
health—get
more
worms.
This
finding,
published
in
a
recent

study

in

Behavioral
Ecology,

represents
one
of
the
first
known
examples
of
birds
using
cosmetics
to
communicate
between
parents
and
offspring.

“Cosmetic
coloration
in
birds
mostly
has
been
studied
and
understood
or
interpreted
as
serving
as
a
signaling
function,
a
sexual
signaling
function,
like
something
that
birds
would
do
to
attract
other
mates,”
says

Liliana
D’Alba
,
an
evolutionary
biologist
at
the
Naturalis
Biodiversity
Center
who
was
not
involved
in
this
study.
This
research
“provides
good
evidence
that
this
can
also
be
a
very
important
part
of
the
communication
between
parents
and
their
offspring.”


Juan
José
Soler
,
lead
author
of
the
study
and
evolutionary
ecologist
at
the

Estación
Experimental
de
Zonas
Áridas
,
explains
in
an
email
that
this
research
was
actually
kicked
off
by
an
accidental
discovery.
Birds
have
a
specialized
gland
that
secretes
the
oil
they
use
for
preening
their
feathers,
and
Soler’s
team
suspected
that
the
oil
might
also
have
beneficial
bacteria
living
in
it.
His
team
had
been
working
with
spotless
starlings
for
years,
but
it
was
only
when
they
started
collecting
samples
for
their
microbe
study
that
they
noticed
the
conspicuous
yellow
color
of
the
chicks’
preen
oil.
The
researchers
found
that
the
bright
yellow
preen
oil
produced
by
baby
starlings
eventually
pales
to
a
light
beige
by
adulthood.
Because
only
chicks
have
this
yellow
oil,
they
wondered
if
the
youngsters
use
it
to
catch
their
parents’
attention.

The
scientists
suspected
that
the
yellow
color
of
the
oil
might
be
due
to

carotenoid
pigments
.
In
addition
to
providing
color,
carotenoids
also

function
as
antioxidants
.
Soler
writes
that
having
lots
of
carotenoid
pigments
indicates
that
a
bird
has
a
generally
healthy
immune
system.
Since
adult
birds
will
often

give
more
food

to
their
healthiest
offspring
when
resources
are
limited,
the
researchers
thought
that
chicks
with
yellower
mouths
might
get
fed
more
by
their
parents.

To
test
this
hypothesis,
the
scientists
monitored
the
94
nest
boxes
at
their
field
site
in
southern
Spain
at
the
beginning
of
the
starling
breeding
season
in
March
2019.
They
placed
video
cameras
inside
the
nest
boxes
to
verify
that
nestlings
actually
spread
their
preen
oil
on
their
mouth.
They
then
tracked
how
much
food
the
parents
gave
the
chicks.
At
ten
days
old,
the
researchers
took
color
measurements
of
the
chicks’
mouth
and
preen
oil.
At
14
days,
the
scientists
measured
the
carotenoid
levels
in
the
chicks’
blood.

The
video
recordings
verified
that
spotless
starling
chicks
actively
collect
oil
from
their
preen
gland
and
spread
it
over
their
body.
When
the
researchers
rubbed
cotton
swabs
over
the
chicks’
mouths,
the
cotton
turned
a
bright
yellow
from
the
oils.
The
scientists
also
found
that
parents
gave
more
food
to
chicks
whose
preen
oil
was
warmer-colored
overall
and
whose
mouths
had
more
yellow,
orange,
or
red
and
more
ultraviolet
coloration—a
wavelength
beyond
the
visible
spectrum
for
humans.
Chicks
with
more
ultraviolet
preen
oil
also
tended
to
have
higher
carotenoid
levels
in
their
blood.
The
oil’s
yellow
color
was
not
directly
associated
with
carotenoid
levels,
but
the
researchers
note
that
the
complex
associations
between
the
various
color
traits
made
it
difficult
to
untangle
how
each
one
related
to
the
chicks’
health.

In
another
part
of
the
experiment,
the
researchers
switched
two
chicks
between
different
nests
so
they
would
be
raised
by
different
parents.
At
ten
days
old,
the
warm
colors
as
well
as
the
hue
of
the
preen
oil
were
more
similar
among
biological
siblings,
even
if
they
were
raised
by
different
parents,
than
among
unrelated
nestmates,
which
suggests
that
these
characteristics
have
a
genetic
basis.
But
other
color
characteristics
were
more
influenced
by
where
the
chicks
grew
up,
so
the
coloration
of
the
preen
oil
seems
to
be
due
to
both
nature
and
nurture.

Based
on
all
these
findings,
the
scientists
concluded
that
spotless
starling
chicks
use
their
preen
oil
to
alter
the
coloration
of
their
mouth,
which
advertises
their
health
to
their
parents.
The
adults
then
feed
the
chicks
with
yellower
and
more
ultraviolet-colored
mouths
more
often,
possibly
because
those
chicks
have
the
healthiest
immune
systems.

Open mouths of five starling chicks
A
spotless
starling
nest
as
seen
from
above,
with
five
hungry
chicks
begging
for
food.

Juan
José
Soler

D’Alba
suspects
that
this
use
of
natural
cosmetics
by
chicks
may
be
found
in
other
bird
species
as
well.
“I
think
it
might
be
very
common,
especially
in
those
birds
that
have
what
we
call
altricial
chicks,
those
chicks
that
when
they
come
out
of
their
eggs
are
completely
naked,
and
they
have
to
spend
a
long
time
in
their
nest,”
she
says.
“There
has
to
be
something
about
this
individual
chick
that
makes
the
parent
feed
them
more.
So
I
think,
in
any
of
these
species
where
we
see
this
case,
then
I
think
it’s
very
likely
that
cosmetic
coloration
could
be
important.”

More
research
is
needed
to
fully
understand
how
and
why
the
spotless
starling
chicks
use
their
preen
oil
as
makeup.

Philipp
Heeb
,
a
behavioral
ecologist
at
the
Université
Paul
Sabatier
who
was
not
involved
in
this
study,
asks
“why
would
the
birds
put
coloration
in
the
preen
gland
instead
of
placing
it
directly
in
the
mouth
and
the
gapes?
You
know,
why
would
they
evolve
this
new
system?”

Soler
says
that
his
team
is
excited
to
study
these
birds
more
so
they
can
piece
together
a
clearer
picture
of
the
evolutionary
origin
and
function
of
this
fascinating
behavior.

Artikel ini diambil dari https://www.smithsonianmag.com/science-nature/the-done-up-bird-gets-the-worm-180980490/

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