In the bird world, there are plenty of male larks and wrens! I've never understood why so many nature names are automatically seen as girl names.
Neither name is common. Wren sounds like it could go either way. I've met a few males named Lark, usually short for Larkin.
I personally love both! I've met plenty male and female Robins. Why not a male Wren?
I know Wren
scores high among nameberry users as a female name but I don't know if anyone is actually being named that much?
I think male b/c of Christopher Wren, but I also think female for the WRENS. Certainly the sound of the word feels male, like REN in Lawrence. So I think it works.
Larkin is a male name too, right? Lark -- could go either way.
Ren sounds more masculine than Wren to me. Indeed, I've heard it as a nickname for Lawrence.
Personally I like Lark as a nn for Alaric, but I have a hard time seeing it as a stand alone masculine name. Wren feels very feminine to me, but I can see how it would work well as a nn for a boy.
They're so uncommon as names that I think it can work.
To me (personally) Lark sounds male and I like the pp's suggestion of it as a nn for Alaric. Wren sounds female.
However since your kid will be the only one with this name (I am sure), you will get to set the gender.