Migratory Songbirds Have a Specialized Night-vision Brain Area
Durham, N.C. -- Neurobiologists have discovered a specialized
night-vision brain area in night-migratory songbirds. They believe the area
might enable the birds to navigate by the stars, and to visually detect the
earth's magnetic field through photoreceptor molecules, whose
light-sensitivity is modulated by the field.
The researchers published their findings May 23, 2005, in the early
online edition of the Proceedings of the National Academy of Sciences. The
collaboration was led by Henrik Mouritsen of the University of Oldenberg in
Germany and Erich Jarvis of the Duke University Medical Center. Other
co-authors were Gesa Feenders and Miriam Liedvogel in Mouritsen's laboratory
and Kazuhiro Wada in Jarvis's laboratory. The research was supported by the
VolkswagenStiftung to Mouritsen and the National Science Foundation's
Waterman Award to Jarvis.
To migrate successfully over thousands of miles at night, night-migratory
birds need to see where they fly, as well as navigate by stars and the
earth's magnetic field. Surprisingly, Jarvis said, recent scientific
evidence has suggested that birds have specialized molecules in their visual
system that translate magnetic compass information into visual patterns.
Thus, , the researchers hypothesized that night migratory birds would need a
specialized night-vision brain area.
"There was no evidence of such a specialized region in night migratory
birds before we began this research," Jarvis said.
In their study, the researchers compared two species of night-migratory
songbirds -- garden warblers and European robins -- with two non-migratory
songbirds -- zebra finches and canaries.
Using a transparent cylindrical cage in Mouritsen's laboratory, they
first accustomed the birds to the illumination equivalent of moonlight. They
waited until the birds were sitting quietly to eliminate brain activity from
movement. The researchers then quickly preserved the birds' brains, and in
Jarvis's laboratory analyzed the brain structures for the active expression
of two genes called ZENK and c-fos that signal activity in a particular
The researchers found that the night-migratory species showed strikingly
high activity in a particular cluster of cells located adjacent to a known
visual pathway. According to Jarvis, what excited the researchers was that
the area, which they named Cluster N, was not active in the migratory birds
during the daytime. Furthermore, non-migratory songbirds did not show strong
activation in the Cluster N even under moonlight conditions.
To determine whether the brain cluster is really specialized for
night-vision, the researchers performed the same gene expression analysis on
the night-migratory songbird species with the birds' eyes covered. The
researchers found that blocking night-time vision dramatically reduced gene
activity in cluster N.
"This result confirmed that night-migratory birds seem to have a brain
area specifically adapted for seeing during their night-time flight," Jarvis
said. The researchers suspect that the newly discovered brain region could
be involved in processing and integrating light-dependent magnetic compass
information and star compass information; and thus may be responsible for
the impressive navigational abilities of birds migrating during the night.
In future studies, Jarvis, Mouritsen and their colleagues plan to test this
hypothesis in more detail, they said.