Abstract

Magnetic compass orientation in a night-migratory songbird requires that Cluster N, a cluster of forebrain regions, is functional. Cluster N, which receives input from the eyes via the thalamofugal pathway, shows high neuronal activity in night-migrants performing magnetic compass-guided behaviour at night, whereas no activation is observed during the day, and covering up the birds’ eyes strongly reduces neuronal activation. These findings suggest that Cluster N processes light-dependent magnetic compass information in night-migrating songbirds. The aim of this study was to test if Cluster N is active during daytime migration. We used behavioural molecular mapping based on ZENK activation to investigate if Cluster N is active in the meadow pipit (Anthus pratensis), a day- and night-migratory species. We found that Cluster N of meadow pipits shows high neuronal activity under dim-light at night, but not under full room-light conditions during the day. These data suggest that, in day- and night-migratory meadow pipits, the light-dependent magnetic compass, which requires an active Cluster N, may only be used during night-time, whereas another magnetosensory mechanism and/or other reference system(s), like the sun or polarized light, may be used as primary orientation cues during the day.

Highlights

  • Twice each year, millions of migratory songbirds travel thousands of kilometres between their breeding grounds and overwintering sites and back, thereby using a geomagnetic compass and ⁄ or celestial cues to find their way

  • Relative to the day (Fig. 1A), meadow pipits tested during the night showed high ZENK expression in a distinct cluster of brain regions located in the hyperpallium and mesopallium (Fig. 1B) that is comparable with the neuroanatomical location of Cluster N in nightmigratory European robins and garden warblers (Mouritsen et al, 2005)

  • Nissl- and GluR1staining showed that the area active during night-time in meadow pipits corresponds to Cluster N in night-migrants: it includes parts of the H, interstitial region of the hyperpallium (IH), the dorsal mesopallium (MD), the dorsal nucleus of the hyperpallium (DNH), and a shelllike structure around the DNH (Fig. 1D–F)

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Summary

Introduction

Millions of migratory songbirds travel thousands of kilometres between their breeding grounds and overwintering sites and back, thereby using a geomagnetic compass and ⁄ or celestial cues to find their way (for a review see Wiltschko & Wiltschko, 1996). A forebrain region, Cluster N, was shown to be highly active in two night-migratory species, European robins (Erithacus rubecula) and garden warblers, at night but not in two non-migrating songbird species, zebra finches (Taeniopygia guttata) and canaries (Serinus canaria), tested under the same conditions (Mouritsen et al, 2005). This neuronal activation of Cluster N is movement independent (Feenders et al, 2008) and disappears when the eyes of the birds are covered (Mouritsen et al, 2005; Liedvogel et al, 2007a). Cluster N seems crucial for the processing of magnetic compass information in night-migrants, but is Cluster N used during the day?

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