I just want to second what /u/linuxpaul said, I have now strapped a 220uF cap across 3.3v and Gnd and it works fine. no more brownouts.

I have exactly the same problem on my two new hornbills. When powered from USB, the 5v line measures about 3.5v and triggers the brownout detector. I've tried with many different cables and USB chargers (some rated as high as 3.2A) but nothing makes a difference.I've contacted the manufacturer to se...