Born in 1926, Eyles spent his early years living with his family at the Wairau Bar near Blenheim where, in 1939 as a schoolboy, he discovered early human skeletons and associated artefacts including necklaces, stone tools and moa egg. Eyles discovered several more burials on the bar, and assisted with the excavations carried out by Roger Duff from the Canterbury Museum. The site is regarded as one of the oldest and most important archaeological sites in New Zealand.
Eyles continued his association with Duff during the excavations of Pyramid Valley Swamp in the 1940s. Duff recognised his contribution by naming an extinct hawk found in the swamp the Eyles' harrier.