[Mnbird] White-breasted Nuthatch Question (Female)

[Stan - Molly Jo Miller Johnson]

I have a pair of White-breasted Nuthatches building a nest in the fascia of our house, the same place as the last two years. In addition, a pair built a nest three years ago in a tree in the same general area. The female in the previous years had a very dark gray cap. It was so dark that it could really only be detected if you saw her from the top so you could compare it to the black on her neck. The female this year has a very "normal" gray cap. 
Could this be the same female? Does anyone know if their caps can get darker or lighter throughout their lives?
Thanks,Molly Jo MillerInver Grove Hts, Dakota Co. 		 	   		  
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