Sika Deer in the British Isles

Since their introduction to the British Isles approximately 150 years ago, sika deer have expanded their distributional range and established many large free-ranging populations in Scotland, Ireland, and England. As such, they have become a significant resource, or pest, depending on various local, regional, or national objectives.

In Ireland, initial concern was their ability to hybridize with local populations of red deer (Cervus elaphus) (e.g., Harrington 1973, 1982). Examples of both complete admixture of species (Wicklow) and strong within-species breeding are found within Ireland. Explanations for these different outcomes have mostly centered on the genetic status of the original founders (Lowe and Gardiner 1975; Harrington 1982) rather than effects of the abundance of each species and differ ences in ecology that are equally likely to have contributed (Swanson 1999; Putman 2000). More recently, attention in Ireland as elsewhere within the United Kingdom has turned to their damage of habitats and commercial forestry (e.g., Lowe 1994).

The largest populations of sika deer within the United Kingdom are currently found in Scotland, partly due to the number and extent of introductions (Ratcliffe 1987a), but also because of the widespread availability of suitable habitat. Populations in Scotland have shown significant increase in number and steady expansion in distribution. As in southern Ireland, management has been focused primarily on concerns about hybridization with red deer and damage to tree crops and habitats. There is difference of opinion about the seriousness of hybridization and also whether it is now perhaps too late to achieve effective management. Culls of sika deer have increased steadily across Scotland recently, but there is little sign that these have affected their abundance or distribution.

In England, sika deer have remained essentially local to their introduction locations until recently. Patterns of expansion in Dorset and Hampshire in the south and Lancashire in the north suggest that populations may have to reach a critical density before expanding. Hybridization with red deer has been reported in Lancashire and Dorset/Devon and recent work has established the genetic origin of a number of English as well as Scottish populations.

In this chapter we review the general ecology of sika deer in the British Isles (habitat use, feeding ecology, population ecology), the impacts of sika deer on habitats and on native deer through competition and hybridization, and the management approaches applied.