losing hair?!

[maxyzapfy]

my rabbit has been losing hair on the top of his head, he's 1 and a half and I don't know why this is happening, could it just a birth mark forming or should I be more concerned about this? there's a picture View attachment ImageUploadedByRabbit Forum1465394643.131827.jpg

 

[RavenousDragon]

From the picture it looks more like a "molt line" to me. Can you part some of the hair and look underneath? How does the skin look?