Jan 1 =
YearDay1, Feb 29 adds an extra day in Leap years so that March 1 is YearDay
60 in non Leap years but is YearDay 61 in a Leap year.
females arrive 14 days later than males. The males have already set up
territory and the females sneak in. They are much more difficult to net than
the males, hence the apparently lower numbers.