PLASTICITY IN FORAGING BEHAVIOR OF A LOTIC MINNOW (RHINICHTHYS-CATARACTAE) IN RESPONSE TO DIFFERENT LIGHT INTENSITIES

Longnose dace forages primarily at night in streams in S Alberta. All measures of foraging ability were superior under twilight conditions. Although search times in starlight were double those in twilight, this increase was much smaller than was predicted using a hemispherical search volume model. The daces' ability to offset small nocturnal search volumes was accomplished by changing their pattern of search behaviour. In particular, use of a benthic rooting behaviour increased, behaviour apparently associated with location of prey by olfaction. Although the nocturnal foraging strategy of dace does not appear to maximize net energy gain, this strategy may be a response to other constraints, such as high predation risk during diel periods with increased illumination. -from Authors