Male frigatebirds are the ones with the inflatable red chest. I like to imagine this as a male in drag, inflating his chest as faux breasts.

I am unsure how such traits of sexual dimorphism affect tagging when no genitals are visible. I've seen the rule go both ways. Though I am sure most people searching for female avians wouldn't be disappointed to see this in their search results, as this comes off as very much female.