The great majority of avian species is diurnal and thus endures variation in light intensities, associated with daily, seasonal or lunar cycles. These diurnal birds search their food in light abundant environment and raise their broods in dark cavities. However their visual performance in dim light conditions is largely unknown. Here, we compared light intensity threshold of activity in two groups of passerines, i.e. secondary cavity and non-cavity nesting. For this purpose, different species of secondary cavity and non-cavity nesting passerines were subjected to two phases of trials: in the first trial birds were released in an experimental cage and allowed them to accommodate themselves in darkness for 10 min. In the second trial we turned on the dimmer to a given luminance for 2 min. We found that activity threshold for secondary cavity nesting passerines ranged from 0.05 to 0.2 cdm-2 and non-cavity nesting passerines from 22.00 to 16.00 cdm-2. Our results shed light on the question about potential effect of luminance on visual performance by secondary cavity and non-cavity nesting passerines.
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