flagging glm models with warnings

I'm attempting to run 250 permutations of a negative binomial GLM model for
data on fish counts. Many of the models are fit appropriately, but some
issue warnings such as "convergence not reached" or "step size truncated due
to divergence." 

I'd like to figure out a way to flag the models that have warnings and
output them into either a table or into R console. Then I could evaluate the
problems associated with these models and know not choose them as the best
models for fitting the data.