Rab­bit pop­u­la­tion den­sity can vary through­out year

Bray People - - LIFESTYLE - JIM HURLEY’S Na­ture Trail

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.

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