I am basing the sexing of these two birds on my observations over the last two years -

The dark head stripes, aspecially the one under the beak, are much bolder on the male in image 1. They also have a more clean-cut look as though the male has spent more time preening himself. The stripes on the female, on the other hand have a softer edge to them and become less distinct behind the eyes and near the 'neck band' (images 3 and 4).

In image 2, the darker area at the top of the picture is produced by a neutral density filter, positioned in front of the camera lens to reduce the effect on the image of bright light at the box entrance.