Effects of northern pike on patterns of nest use and resproductive behavior of male fathead minnows in a boreal lake

We conducted a two-part study to assets predator avoidance by reproductive male fathead minnows (Pimephates prxmelas) subjected to predation threat from northern pike (Esox hicxus). First, we determined if patterns of nest use by egg-guarding male minnows in a boreal lake were related to pike densities. We sampled northern pike and identified four areas of pike-density and three areas of pike-density. We censused natural nests and placed nest boards in these areas. We found eggs on natural nests more frequently in areas with low densities of pike than in areas with high densities of pike. However, we could not fuDy explain the distribution of nests by predation risk. Second, we evaluated the behavioral response of egg-guarding males to a control stimulus (a piece of wood) or a live pike in a wire cage. We used time to return to the nest after a stimulus as a measure of risk taking. Males took different amounts of risk based on predation threat; males in the predator treatment took longer to return to their nests than control males. Risk taking was not related to the number or age of the eggs but to distance to nearest egg-guarding neighbor; males with close neighbors returned sooner than more isolated males. Males in the predator treatment had lower total activity and egg rubbing than control males after they returned to their nests. We conclude that male fathead minnows altered their reproductive behavior in ways that reduced predation risk, but the cost of predator avoidance might include egg predation, lost mating opportunities, or usurpation of nests. Kty words: egg-guarding, encounter rate, Esox hichis, Pimephalts promelas, predation. [Behav Ecol 8:655-662 (1997)]