Comparison of Circadian Changes in the Retinas of Migrating and Non-migrating Blackcaps, Sylvia atricapilla
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The retinas of birds and other vertebrates undergo morphological and physiological changes throughout the day, which help regulate daily changes in visual sensitivity. One particular change is the contraction and elongation of photoreceptor outer segments, which is regulated by an endogenous circadian clock. Normally, Blackcaps (Sylvia atricapilla) are diurnal, but they migrate at night. In the current experiment, outer segment lengths of migrating and non-migrating Blackcaps were measured throughout the day and analyzed, and they show a trend toward circadian rhythmicity across the day. There also appears to be an advance in the phase of the rhythm in retinomotor movements when birds are migrating. These results indicate that circadian-controlled retinomotor movements could be modifications within the retina to accommodate the nocturnal lifestyle of migratory Blackcaps. We hypothesize that a change in retinal physiology and morphology may allow the formation of a migratory “night-vision” to accommodate the migrating Blackcap’s nocturnal lifestyle.
Shockley, Ross (2006). Comparison of Circadian Changes in the Retinas of Migrating and Non-migrating Blackcaps, Sylvia atricapilla. Available electronically from