Life
Keays says he’s not challenging the
idea that birds can detect Earth’s mag-
netic field, and he hopes researchers will
keep looking for the detector cells.
Magnetic effects
seen in bird brain
Source of signal in pigeons’
nerve cells still mysterious
By Susan Milius and Rachel Ehrenberg
For navigating birds, the X that marks the
spot for processing information about the
Earth’s magnetic field has been uncovered in the brain stem. Scientists have
pinpointed a set of nerve cells in pigeons’
brain stems that fire at different strengths
depending on the direction and strength
of the surrounding magnetic field.
The discovery, published online April
26 in Science, fills in a piece of the navigation puzzle, which has flummoxed scientists for years. But it doesn’t resolve
how birds sense the field to begin with.
The researchers, from Baylor College of
Medicine in Houston, suspect the field-sensing cells may be in the birds’ ears.
Previous research has implicated eye
and beak cells, but in the April 19 Nature ,
other researchers challenged the identification of proposed sensors in the beak.
In the Science study, the research-
ers used coils to cancel out the Earth’s
magnetic field. Then they created a new
magnetic field and exposed
pigeons to it while manipulating
the field’s strength and direction. This
revealed a cluster of 53 cells in the birds’
vestibular brain stem — an area already
implicated in bird navigation — that
process information about a magnetic
field’s strength and direction. Where
these cells get the information and how
it is integrated with a bird’s mental map
remains a mystery.
Earlier work identified six clusters of
iron-containing cells in the bird’s beak
that appeared to serve as biological
compass needles. That identification
turns out to be “totally wrong,” says neu-
roscientist David Keays of the Research
Institute of Molecular Pathology in
Vienna. Keays and colleagues looked for
these cells in about 250,000 thin slices of
tissue from beaks of almost 200 pigeons
collected across Europe.
But one pigeon had 108,000 cells con-
taining iron, while another of the same
age and sex had only about 200, Keays
and colleagues report. Another pigeon
had tens of thousands of iron-containing
cells clustering at the site of a beak infec-
tion, suggesting that they were from the
immune system.
x
A new study challenges whether
some cells in pigeons’ beaks
sense magnetic fields. Yellow
shows bone (imaged by
CT scans) and purple soft
tissue (from MRI scans).
l
o
tissue (from MRI scans).
