We hypothesized that hunters' use of approximate responses for participation and harvest survey questions was prompted by the cognitive complexity of giving an exact answer. Approximate responses we considered were: (1) rounding days of participation and harvest to numbers ending in zero or 5 (0–5 prototypes) and (2) multiplying days of participation by an integer to approximate harvest. Both types of survey responses result in response heaps (spikes in the data) that can introduce bias. Our analyses were based on the frequency of responses in heaps relative to all responses in a neighborhood (a set of responses close to each other). Data from the Illinois hunter harvest survey (1998–2000) showed that the relative frequency of using approximate responses in a neighborhood was statistically constant across years and species despite differences in day-harvest frequencies. Our results supported accepting the hypothesis that survey responses are influenced by the cognitive complexity of formulating a response. We discuss the following strategies for identifying, reducing, and correcting bias in estimates derived from surveys: (1) basic research to identify the extent to which respondents use prototypes when answering participation and harvest questions; (2) survey methodology modifications to increase the accuracy of answers; and (3) the development of bias correction factors.