 Mahalski was born in Dunedin, New Zealand, the only child of two academics; his father, Dr E. R. Nye, was a physician and researcher at Otago Medical School, and his mother Pauline Mahalski was a teacher of psychology.Both were collectors of biological curiosities and ephemera, and Mahalski credits them with inspiring his own collecting.From the age of eight he collected shells, fossils, insects, crabs, and bones, and the skins of small animals.