BLUEGILL SUNFISH (LEPOMIS-MACROCHIRUS) FORAGING BEHAVIOR UNDER TEMPORALLY VARYING FOOD CONDITIONS

Risk sensitivity (foraging responses to variances in food availability ) has been observed in numerous taxa, including fish, under conditions of extreme temporal variance (i.e., between patch visits, no matter h ow short the visit or the time between visits). Because fish can gener ally survive for weeks without food, they are expected to and have bee n observed to be risk-averse (i.e., prefer patches with low variance i n food availability). We conducted patch choice experiments with indiv idual bluegill sunfish, using an automated shuttlebox system, to test their sensitivity to variance in food availability under temporal vari ation that was less extreme and perhaps more realistic (i.e., 40-min f eeding periods) than previous risk-sensitivity experiments. Because we expected bluegills to be risk-averse, we offered one patch with no va riance in food availability whereas the other patch exhibited variable food as sampled from a normal distribution of food availability-mean food availability was equal between patches. Simultaneously, we explor ed food availability/temperature combinations above and below expected maintenance ration to determine whether fish response depended on ene rgy balance (i.e., growth potential) as estimated from a bioenergetics model for bluegill. Even when energy balance was negative, bluegills appeared risk-neutral (i.e., they did not respond to variance). In the second set of experiments, bluegills were tested for risk sensitivity with more extreme variance in food availability; the temporal distrib ution again was based on a 40-min period. Bluegills were again risk-ne utral. Bluegills were able to effectively sample and track changing re sources at least over 40-min periods. Overall variance in food availab ility over IO-min feeding periods appears not to be a major factor in patch choice for bluegills. Bluegill patch use depends on encounter ra tes with food items within a patch resulting in a foraging pattern bas ed on mean food availability within a patch.