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)
Summary
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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