Outside of breeding season, it’s not unusual to find young Hooded Plovers
hanging out with non-related adults for a while. It’s a different story from
August onwards.
When the birds are banded and flagged, a small blood sample is taken along
with all the physical measurements. When the blood sample is sent off for
analysis, they can determine the sex along with all of the other data of
interest. There is no way to differentiate them by appearance.