sample size - poisson dist'n?

Hello,

I am designing a survey questionaire and need help estimating sample sizes.

The survey will ask the respondents about the number of a certain animal species seen in a given month. e.g., how many bears did you see?

Because this is count data (# of animals seen/person), I don't believe methods for normal distributions apply? (or do they?).

Can someone point me to an equation that will estimate the required sample size for these data?

(For the sake of an example, let's assume I want to estimate the mean with a margin of error of 5% and a 95% confidence interval. The population of people will vary, but lets use 200).

Thank you,

Shawn Morrison