Visual sensitivity in the black-bellied tree duck (Dendrocygna autumnalis), a crepuscular species.

Produced visual adaptation curves for 3 black-bellied tree ducks using D. S. Blough's (1955) psychophysical tracking procedure. 2 scotopic curves from different preexposure light intensities and 1 photopic curve were generated. Nonlinear regression curves were then fit to the raw data. The mean scotopic thresholds did not differ significantly, but as expected, they were significantly lower than the mean photopic threshold. Time to the curves' asymptotes correlated with preexposure light intensity. Although the adaptation curves showed no distinct rod-cone "break," retinal histology revealed a duplex retina with a preponderance of rods, which reflects this species' crepuscular habits. Results are discussed in relation to the ecology of the species. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)