The longevity of 1080 egg-baits in a regularly baited nature reserve in south-western Australia

Abstract

The longevity of 1080 in egg-baits (4.5 mg 1080 per egg) used for fox control was monitored at the Corackerup Nature Reserve, Western Australia. Irrespective of season, most egg-baits (94%) were found to retain sufficient 1080 to be theoretically lethal to all foxes for at least 42 days, and 75% of baits contained an LD50 of 1080 at Day 63. Exponential decay curves also predicted that these baits would remain toxic to most foxes for up to 32 weeks, depending upon environmental conditions. Sealing the injection hole with wax, or using sterile techniques to prepare some egg-baits, appeared to have little effect on the longevity of 1080 in these baits compared with that of unsealed eggs.

Bait take, and identification of those species taking bait, were monitored over 12 days at 216 permanent bait stations in the reserve. Track plots were present for 3–6 days on 83 of these stations in spring and summer but not in winter. In spring and summer, of those species likely to take bait, goannas were the most frequent visitors to the track plots and they were also responsible for most of the baits taken at this time (59% and 90% of baits taken). Foxes accounted for 27% (spring), 8% (summer) and 75% (winter) of the egg-baits taken. No egg-baits were taken by goannas in winter, but the overall bait take was also low at this time (28 of 211 baits laid; 13%). Overall bait take after 12 days in spring and summer was 64% (135 of 211) and 68% (145 of 212) of baits laid. Except for goannas, birds and other non-target species (e.g. bob-tail skink) took relatively few baits in any season. The implication of these findings for 1080-based predator-control programs are discussed.