Rabbit control in the Parwan Valley and its value for catchment

Plate 1 - Photograph taken in autumn 1989 illustrating effects of rabbit exclusion. Full details are given in the text.3.4 Rabbit number surveys in the ParwanValleyRabbit numbers in the Parwan Valley have beensurveyed by the Department (D. McPhan l ,unpublished data). Thirteen surveys were made indifferent seasons from 1985 to 1989. The data fromthese rabbit surveys have been used to find where therabbits are located on the landscape, and theirdensity.Surveys were made in the early evening, startingafter dusk. Rabbit numbers were observed byspotlight from a vehicle driving slowly along a 9 kmtransect in the Parwan valley. Estimated range of thespotlight is 50 metres. The location of the transect isshown in figure 3. Rabbits were counted on bothsides of the vehicle path. Counts were recorded at 0.5km intervals from a stationary vehicle. The meannumber of rabbits along the transect over the period1985 to 1989 is shown in figure 4. To illustrate theextreme situation, results are also shown of thesurvey on 18 January 1988, when rabbit numberswere high. Rabbit numbers tend to be higher nearpreferred habitat or where it is difficult to poison,e.g., at the foot of steep slopes.Valley. Results are shown in table 4.3.5 Measurements of biomassTwo sets of plots were studied to quantify thechanges in vegetation following rabbit exclusion. Thefirst set was in pastured land of the main catchment;the second on the ridge of the White Elephant Hill.The site in the pasture had a north-west aspect andwas near rabbit activity. Grasses present are mostlyDanthonia species. The site on the ridge had littlerabbit activity since 1986. Grasses are Danthoniaspecies, with a small amount of Poa labillardieri.The method was the same at both sites. An area of 1m 2 was harvested from the exclusion plot and fromthe adjacent area. Material was dried at 45°C for 4hours and weighed to determine biomass. Results aregiven in table 5. Because the vegetation is mostlynative grasses and mosses, the overall ground coverhas been subdivided to show their relativecontributions. These values are included in table 5.Science Officer, Department of Conservation andNatural Resources, Bacchus Marsh Numbers arelower where maintenance is done and conditions areharsher, e.g., near the road with the rabbit prooffence. Survey points 15 to 18 give the closestapproximation to the landscape within theexperimental area.Rabbit numbers have been averaged along the surveytransect for a given land use classification, as definedin Hexter et al. (1956). Results are shown in table 3.Simple arithmetic then gives the expected density ofrabbits for that land use class throughout the Parwan