I believe these are two males, as they were both huge and alternating each other on doing their very intricate display call. Definitely look up their sound if you've never heard it before (and that of other oropendolas - some chestnut-headed oropendola calls almost sound like a stream of water!).
I made a recording myself (the Montezuma oropendola sound starts at 0:02) but I'm sure better ones have to be available online. There was a group of about 8 of these right next to the hotel we were staying at, so it was quite crazy to hear these wonderful sounds every morning!
