Sexual dimorphism is by iris colour.

See: Condor. 75 (1): 17–27. doi:10.2307/1366532

I hope this helps :-)

In F. Ciconiidae, generally speaking sexes are alike, but males tend to be a little  large than females: Handbook of the birds of the world (Del Hoyo et al. Ed)

According to a study, the researchers identified males from females in terms of size and plumage. Males tend to be slightly larger, and for C. episcopus, males have a bright color.

Reference: http://threatenedtaxa.org/index.php/JoTT/article/view/2904/3906