Monitoring Rabbit Population Trends In New Zealand

Regional/District councils with semi-arid land (SAL) in their regions have carried out rabbit trend monitoring, principally using night-counting, since they were first established.

In some cases this was a continuation of the night-count routes that were set up during the time of Pest Destruction Boards or later during the RLMP.

Following the arrival of RHDV, the councils intensified their night-counting programmes in order to better track the changes that occurred in rabbit numbers. The night-count routes are very extensive but still only sample a portion of the land within each region.

However regional councils have all indicated that the data gathered support their observations on other properties. The other widely used method of assessing rabbit population density is to record ground sign using the Modified McLean Scale.

Night-counting:

Night-counting is a method used to determine rabbit trends and has been used in New Zealand since the late 1960s. Councils use a standard procedure for night-counting, so that all data collected in NZ is comparable (Rabbit Managers Fact Pack, 1992).

The method involves travelling along a set marked route on a motorcycle using a spotlight to count the rabbits seen in the light beam. The counts are repeated over the next two or three nights of good weather.

Count routes are selected so that the various levels of rabbit proneness, topography and vegetation found in the region are represented. Routes can be entirely within a single property but they often cover several.

It is important that various rabbit control programmes are represented in the surveillance work, from landholders with very effective programmes through to those with no human input. Councils use a number of count routes within a district so that a wide representation of the rabbit populations is obtained.

This also helps to avoid the risk of localised events unduly influencing the results of the monitoring programme. A typical ‘event’ is a winter  poison operation where poisoning occurs within a count route. As a result, rabbits counted subsequently drop off dramatically along that route but such a decline may not represent the area as a whole.

In Otago, night-counts have been carried out annually in the late winter – the period when rabbit numbers are most stable. This provides a good indication of the potential breeding population existing at the start of the main rabbit breeding season.

Information Sourced From: