Neuronal activation in the geomagnetic responsive region Cluster N covaries with nocturnal migratory restlessness in white-throated sparrows

Cluster N is a region of the visual forebrain of nocturnally migrating
songbirds that supports the geomagnetic compass of nocturnal migrants.
Cluster N expresses immediate-early genes (ZENK), indicating neuronal
activation. This neuronal activity has only been recorded at night during
the migratory season. Night-to-night variation in Cluster N activity in
relation to migratory behaviour has not been previously examined. We
tested whether Cluster N is activated only when birds are motivated to
migrate and presumably engage their magnetic compass. We measured
immediate-early gene activation in Cluster N of white-throated sparrows
(Zonotrichia albicollis) in three conditions: daytime, nighttime migratory
restless, and nighttime resting. Birds in the nighttime migratory
restlessness group had significantly greater numbers of ZENK-labelled
cells in Cluster N compared to both the daytime and the nighttime resting
groups. Additionally, the degree of migratory restlessness was positively
correlated with the number of ZENK-labelled cells in the nighttime
migratory restless group. Our study adds to the number of species observed
to have neural activation in Cluster N and demonstrates for the first time
that immediate early gene activation in Cluster N is correlated with the
amount of active migratory behaviour displayed across sampled individuals.
We conclude that Cluster N is facultatively regulated by the motivation to
migrate, together with nocturnal activity, rather than obligatorily active
during the migration season.