Data from: Fast visual adaptation to dim light in a cavity-nesting bird

Many birds move fast into dark nest cavities forcing the visual system to
adapt to low light intensities. Their visual system takes between 15 and
60 minutes for complete dark adaptation, but little is known about the
visual performance of birds during the first seconds in low light
intensities.  In a forced two-choice behavioural experiment we
studied how well budgerigars can discriminate stimuli of different
luminance directly after entering a darker environment. The birds made
their choices within about one second and did not wait to adapt their
visual system to the low light intensities. When moving from a bright
facility into an environment with 0.5 log unit lower illuminance, the
budgerigars detected targets with a luminance of 0.825 cd/m2 on a black
background. When moving into an environment with 1.7 or 3.5 log units
lower illuminance, they detected targets with luminances between 0.106 and
0.136 cd/m2. In tests with two simultaneously displayed targets, the birds
discriminated similar luminance differences between the targets (Weber
fraction of 0.41-0.54) in all light levels. Our results support the notion
that partial adaptation of bird eyes to the lower illumination occurring
within one second allows them to safely detect and feed their chicks.