Kristian Severin Nilsen - Vest-Agder to Liverpool

Hi, I'm trying to find out when and how Kristian Severin Nilsen left Norway. He was born on 17 March 1849 in Vanse, Vest-Agder and his parents were Nils Andreas Nilsen and Ane Kristine Petersdr. He was included in the 1865 census as a farmhand on Grimsby og Steensvold farm. The first record I have of him in Liverpool is on his son's (Rudolph) birth certificate in 1879. Any information would be greatly appreciated! Thanks [:)]