Reproduction and potential rate of increase of the sika deer herd in Co. Wicklow.

  • David J. O'Brien Science Dept., Cathedral High School, 74 Union Park St., Boston, MA 02118,U.S.A.
  • Sean M. Rooney Coarse Fish Unit, Central Fisheries Board, Swords Business Campus, Swords, Co. Dublin, Ireland.
  • Thomas J. Hayden UCD School of Biology & Environmental Science, UCD Science Education and Research Centre - West, Belfield, Dublin 4, Ireland.
Keywords: Sika deer, reproduction, survival, rate of increase.


All three deer species in Ireland mainly inhabit forests, where they can cause significant economic and ecological damage through browsing and bark stripping of trees. Sika deer and sika x red hybrids are currently the most numerous deer. Their expansion through Co. Wicklow and beyond was associated with afforestation. Deer must be managed, and to do this effectively, knowledge of their reproductive potential is needed. We investigated the reproduction of female sika-like deer harvested in the Co. Wicklow area during the hunting seasons from 1995/1996 to 1997/1998. Fifteen percent of calves, 87% of yearlings and 84% of adult females were pregnant. One female was found with twin foetuses. Seventy-two percent of adults were lactating and 71% had a calf-at-foot. Eighty-five percent of calves survived to six months of age. The deer herd has a yearly potential rate of increase of 28%. Pregnancy and survival rates are very high for sika deer in Ireland and in line with other populations elsewhere. It is likely that our estimate of 15% of calves becoming pregnant and raising offspring is low. This high fertility is despite the high densities at which sika-like deer are found in Co. Wicklow. Deer are increasing in numbers because insufficient numbers arc harvested compared with their rate of increase. This trend could cause a serious increase in tree damage levels. We recommend that the harvest be increased to at least 30% of the female population and reproduction be continuously monitored, with an emphasis on assessing for pregnancy in calves and checking for twins.
How to Cite
O’Brien, D. J., Rooney, S. M. and Hayden, T. J. (2007) “Reproduction and potential rate of increase of the sika deer herd in Co. Wicklow.”, Irish Forestry. Available at: (Accessed: 25June2022).