Amazon preening his mate

[parrotpainter]

Hi,
I just adopted a pair of red-lored amazons a few days ago. They have been together for 16 years. I was told they have never been breeders, and I do not intend on breeding them, however I have a question regarding their mutual preening habits. The male (Fred) seems to have "over-preened" the female's (Ethyl) facial area. Her feathers are sparse around her beak and nose area to the point where her red patch is pale in hue, almost pinkish. Is this behavior a seasonal issue, or will he continue to over preen her face year round? They are in a large 6x6 cage with a divider in the center, but they preen each other through the bars. Anyone have pairs who do this? Thanks!