Deer Impact On Island Ecology


A feral population of Fallow deer have roamed free on Mayne Island for the past two decades. Their number is currently estimated at around 500 to 1,000 individuals. They compete for food with the native population of Black-tail deer whose numbers are believed to be about the same.

Wildlife biologists estimate that a normal, sustainable population of deer on an island the size of Mayne, in the presence of natural predators like wolves, cougar and bear, would be about 200 individuals. Mayne Island today has no predators at all.

This very large population of deer, all herbivores, has resulted in a number of significant changes to the island’s ecosystem. The dietary preferences of these deer are changing as favourite foods, such as Arbutus shoots, Snowberry, Oceanspray, Red Flowering Currant and many varieties of ornamental flowers, become more scarce. The range of palatable shrubs and herbaceous plants the deer will eat is increasing.
 Native Black-tailed deer, having different nutritional needs, are opportunistic browsers, taking what they need here, there and everywhere. The invasive Fallow deer, on the other hand, are grazers and if left alone will strip the ground bare.

Long time residents of Mayne Island report there used to be large numbers of wild flowers along road sides in summer. Not any more. Farmers, many of whom have lived and farmed on the island for decades, report that where in the past they used to enclose their fields with split rail fences, today it is necessary to construct deer-proof fences sometimes at a cost of tens of thousands of dollars. Fallow deer, who are particularly fond of grasses, can wipe out a hay crop in a matter of days.

Recent studies by island biologist Rob Underhill and others have shown a direct correlation between the condition of Oceanspray bushes and the presence of deer in areas of the island that are hunted, not hunted, and fenced.

As the growing population of deer compete for food, there has been a detrimental impact on the forest understory where trees are being stripped from ground level to a height of about five feet and in some cases plants and grasses are being pulled up and destroyed, leaving areas of exposed dirt and roots.

Among the effects of this heavy grazing is a threat to the diversity of native birds and insects due to loss of habitat. These effects are ongoing and cumulative.

The known abundance of deer on Mayne Island is far too high if we are to maintain anything like the historic plant and animal diversity. For these reasons the Mayne Island Deer Committee is currently engaged in negotiations with the provincial government with a view to obtaining assistance in dealing with this very serious threat to our island ecosystems.

For further information please contact Tom Masters masters9@telus.net.

posted March 2015

2 comments:

  1. I thank the Mayne Island Deer Committee for pursuing this problem, and hope that the province will help us to preserve the threatened plants and shrubs that have grown wild and cultivated on Mayne for many years.

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  2. This is very disheartening news. I attended the wonderfully facilitated "deer" meetings -- I think those were 2 years ago. It seems, from this report, that nothing has been done since then although the attendees were all in agreement on a number of solutions. What happened? I will attend the meeting on Saturday and look forward to more information.

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