Rabbit population density can vary throughout year
THERE are plenty of young Rabbits out and about at the moment in my neck of the woods. Passing a gateway in the late evening, it is not at all unusual to see three or more youngsters making a dash for cover, their white tails bobbing as they bolt for the safety of their burrows.
Rabbits are such a feature of the Irish countryside that we tend to forget that they are invasive aliens. The Normans introduced them and farmed them for their meat and their fur. Since the Normans did not have the benefit of chicken wire, walled enclosures had to be built to contain the stock. Otherwise they were farmed on islands or in other isolated places where they were naturally confined.
Needless to say, Rabbits escaped from captivity and the Mediterranean natives made themselves at home in the Irish countryside. The species is native to the region comprising Spain and Portugal in the south west of Europe and Morocco and Algeria in the north west of Africa.
In 2013, the Waterford-based National Biodiversity Data Centre carried out a prioritization risk assessment of invasive species. Forty-eight non-native species were ranked as at risk of having a ‘High Impact’ and 78 species, including the European Rabbit, were ranked as at risk of having a ‘Medium Impact’.
Rabbits are voracious feeders, they breed very rapidly and they burrow extensively all of which add up to make them agricultural pests.
Studies show that when Rabbits are thriving, population density can rise as high as 40 animals per hectare in summer falling back to 15 animals per hectare in winter. Population size normally peaks in September and October and drops back with the onset of winter.
The Rabbit population is kept in check by predation by foxes, stoats, badgers and mink, by disease, by shortage of food in autumn and by bad weather in winter. However, the combined impact of all of these factors falls short of the animals’ potential for reproduction.
Breeding females produce three to seven litters a year with five kittens being the average litter size. Kittens born early in the year are able to breed late in that same year so the population can rise quite quickly.
While myxomatosis is now endemic in Irish Rabbits, the strains of the myxoma virus that have evolved in recent years are less virulent than the original disease that wiped out 99% of Rabbits in the early 1950s. Rabbits are also co-evolving greater resistance.
Rabbit population size normally peaks in September and October and drops back with the onset of winter.