I used to wonder about how homing pigeons could, well,
find their way home.
I blame this on a young Alex who really
wanted to strap a note onto a little pigeon leg
and send it off into the distance.
And I read somewhere that homing pigeons navigated
using little iron oxide crystals in specialized
cells in their beaks that responded
to the Earth's magnetic field.
They would learn what the magnetism of their home loft
felt like, and then when they were released,
they could use the Earth's magnetic field
and their special cells to fly back to wherever
the magnetism felt like home.
Now I have been using this magnetic pigeon beak
story as a science fun fact for years
because obviously I am great at parties.
But it turns out that that might not have been the whole truth.
Now a 2007 German paper found some convincing evidence
that homing pigeons can indeed sense magnetic fields.
They trained groups of homing pigeons
to dig for buried food bowls in a sandy area.
And in one group with the homing pigeons,
they attached bar magnets to the bottom of the bowls
so that these birds would begin to associate
the magnetic fields with the food.
When released into an area with two hidden food bowls, one
with magnets and one without, the experimental birds
dug near the magnetized food 49% of the time
whereas control birds who had never before been
exposed to magnetize food only dug
near that bowl 11% of the time.
So these experimental birds did indeed
seem to be sensing the magnetism and associating it
with the food.
A similar paper published in Nature in 2004
put homing pigeons into a choice test
and anesthetized different parts of their beak.
And they found that the magnetic sensing was probably occurring
in the upper beak area.
Now that first German group also looked at the upper beak area
in homing pigeons and found delicate iron
containing structure in the skin on the upper beak.
"Histology has revealed various iron sights
within dendrites of the trigeminal nerve."
For real trigeminal nerve?
Are you just involved with everything cool?
The researchers found magnetite in these structures
and argued that they might be able to serve
as magneto receptors.
"The appropriate alignment between the Earth's
magnetic field and the magnetite bands
would induce a multiple attraction
of the magnetite bullets perpendicular to the membrane,
allowing birds to detect to their geographic position
by the magnetic vector."
In fact there have been quite a few studies
done on homing pigeons and magnetism including some where
they strapped magnets to the bird
and watched them get disoriented when released.
Oh.
There are some other common hypotheses, too,
including that the birds may use their sense of smell
or solar navigation to find their way home.
So this all seems great, but there's
a new hypothesis, which suggests that this may not
be the whole picture because sometimes the birds do
get lost.
Last week a study came out in the Journal
of Experimental Biology, which suggested that the birds may
actually be following ultra low frequency sounds back
to their lofts.
John Hagstrom of the USGS came up with this hypothesis
after hearing of occasions where birds would lose their ability
to navigate after being released from certain areas.
Hagstrom looked at data from areas
where Cornell University birds experienced
these navigational troubles.
From one area, all the released birds
would take the same wrong turn, and from another, the birds
would all fly off in different directions, and from a third,
young birds and old birds would fly in different directions.
But on some days, all the birds found their way back home
just fine.
Now Hagstrom knew that the birds could
hear at very low frequencies, infrasound,
and he wondered if the birds were finding their way
home by listening for the distinct low rumble
of their home loft.
He decided to study the topographic and atmospheric
conditions of the troublesome release sites
to see if they might be interfering
with this infrasound.
What he found is that in normal conditions, one of these
released sites was in a sound shadow where
the local topography and atmosphere would bounce
the infrasound up and over the area, meaning
that the distinctive low rumble of home
never reached the birds.
But in perfect conditions, which matched up with the days
when the birds were able to find their way home,
the infrasound was in fact reaching
the area aided by changing wind patterns in temperatures.
When he studied the two remaining areas,
he found similar atmospheric and topographic conditions,
which bounced the sound around and made
the birds think that it was coming
from a different direction than it was,
leading them off course.
So there's a new hypothesis on the homing pigeon playground.
And while there's still work to be done on it,
I think it deserves a little respect.
So the next time I tell my homing pigeon story,
I'll make sure I throw in a little infrasound.
Go forth, do science.