untitled

be reinoculated on an annual basis. This means that the technique is limited to

animals that are easy to capture and from small populations. This problem has been

overcome partly through the use of PZP proteins encapsulated in liposomes allow-

ing the proteins to be released gradually over a long time span. Thus, 10 years of

contraception was achieved in gray seals (Halichoerus grypus) with a single dose of

encapsulated PZP (Brown et al. 1996, 1997), while Fraker et al. (2002) report 3 years

of contraception in fallow deer (Dama dama). Some of the problems are being over-

come, but this technique remains limited to small populations where a significant

proportion of the females can be captured for inoculation.

Genetic engineering

Tyndale-Biscoe (1994) suggested using a pathogen of low virulence to vector a

foreign gene that would disrupt reproduction. He suggested particularly that the Myxoma

virus could be used to carry an inserted gene that would reduce the birth rate of the

European rabbit (Oryctolagus cuniculus) in Australia. Similar approaches are being

used for red foxes and house mice (Shellam 1994; Pech 2000).

Exclusion

The most obvious way of reducing the deleterious effect of wildlife is to exclude

animals from the area. That can be achieved by fencing, by chemical repellents, or

by deterrents of one sort or another. Often exclusion is necessary for only part of

the time. For example, damage by deer to regenerating pines may be limited to only

the first few years after establishment.

Exclosures can be as small as a hectare or of mind-boggling proportions. The first

of the latter was the Great Wall of China erected at the instigation of Shih Huang

Ti, the first Emperor of the Ch’in Dynasty, between 228 BCand 210 BC. It protected

his northern and western frontiers, the direction from which he was most frequently

attacked. The wall traverses about 2400 km of rough country.

Another big one is the Australian barrier fence built to keep dingoes out of sheep

country. It runs from the south coast, divides South Australia into two, skirts around

the top inland corner of New South Wales, and then loops to enclose all of central

Queensland. It was started in 1914 and built in sections, often as an upgrading

of previous state border fences and rabbit fences. At its greatest extent it spanned

8614 km, 3.5 times longer than the Great Wall of China. In 1980 the loop up

through inland Queensland was fenced off about half-way up and the upper fence

abandoned. The present exclosure has a perimeter of 5614 km. In contrast to the

numerous rabbit fences that have been built in Australia, the dingo barrier fence has

been relatively successful in reducing the spread of a pest species.

The difficulty in reducing populations of introduced predators in New Zealand,

Australia, and other islands has promoted the use of fences in those countries with

some success. Although only relatively small areas can be protected, fence mainten-

ance is high, and some predators get through occasionally, this method has worked

better than any other so far (Long and Robley 2004).

Sonic deterrents

The modern forms of the scarecrow comprising sonic devices (bangers, clangers,

alarm calls, ultrasonics) have been reviewed by Bomford and O’Brien (1990), who

suggested that, at best, these achieve only short-term reduction in damage. They were

WILDLIFE CONTROL 363

20.6.3Control by
indirect methods