[R] fitdistr question

[Antje Niederlein]

Hello,

I tried to fit a poisson distribution but looking at the function
fitdistr() it does not optimize lambda but simply estimates the mean
of the data and returns it as lambda. I'm a bit confused because I was
expecting an optimization of this parameter to gain a good fit...
If I would use mle() of stats4 package or mle2() of bbmle package, I
would have to write the function by myself which should be optimized.
But what shall I return?

-sum((y_observed - y_fitted)^2)

?

Any other suggestions or comments on my solution?

Antje