Ireland has only one native deer species: the Red Deer.
Sika Deer were introduced to and kept in the Wicklow Mountains in 1859. They soon escaped and started to breed with the closely related Red Deer.
There are now very few pure Red Deer in Wicklow. Most look like Sika Deer which are smaller than the Red Deer. Probably all are hybrids.

Glendalough Monastic Site area, Wicklow Mountains National Park, Ireland, 9 June 2018