Birk is Ronja's friend in "Ronia, the Robber's daughter". But I'm not sure if Astrid made this up or if it is an old forgotten name. Birk sound like it means "birch". But though Ronja is popular as a girl's name the same is not true for Birk as a boy's name.
"You sought a flower and found a fruit. You sought a spring and found a sea. You sought a woman and found a soul. You are disappointed." "It does not become me to make myself smaller than I am." (Edith Södergran 1891-1923)