New Zealand Journal of Ecology (2007) 31(2): 261- 262

How many possums make a cow?

Short Communication
Phil Cowan  
  1. Landcare Research, Private Bag 11052, Palmerston North, New Zealand

The importance of possums as competitors with livestock for pasture is sometimes used as justification for possum control. Unfortunately a confusion of wet and dry weight values of pasture and daily consumption by possums appears to have resulted in a significant overestimate of the economic costs of possums as pasture pests. A correctly estimated daily dry matter intake of pasture by possums is 0.0144 kg pasture dry matter per possum per day. For a possum density of 1 ha-1, this amounts to a reduction of about 1% of a stock unit ha-1 year-1. At higher possum densities, which often occur on farms adjacent to forest or scrub, losses would be correspondingly higher. A more direct way to measure possum impact on pasture production would be to use exclosures.