Bird-proofing poison bait stations

Forest and Bird, Issue 296, 1 May 2000, Page 48

Bird-proofing poison bait stations

Landcare Research project has produced useful advice for people involved in the control of possums by poisoning. The research assesses the risk of poisoning other animals, including weka and kiwi, by mistake. Working from Lincoln in Canterbury, G.A. Morriss and E.B. Spurr assessed the risk to other animals, and evaluated the safest way to set bait stations to avoid accidental kills. In some operations against possums, using 1080 or brodifacoum in cereal baits, there are further desirable kills; of predators such as rats, and secondary kills of the stoats which eat them. Risks to valued animals, such as rare and endangered birds, and farm livestock, are unacceptable, however. Baits stations were originally developed as an alternative to aerial or ground-laid bait. In the last decade the ‘bait station’ -akind of feeder — has proved increasingly popular because of its effectiveness in attracting possums, and growing concern about the effects of scattered poison on other animals. Many different kinds of bait station are used for dispensing poisons to possums, but all are designed to contain toxic baits in various forms. For example, Feral Control produces a bait station specifically for dispensing Feratox pellets and pre-feed. Others, such as KK stations, are designed for paste baits. The Landcare Research project tested the four most commonly used stations for dispensing cereal bait — Pelifeed, Philproof, Sentry and Kilmore (as illustrated). For each, the scientists assessed the risk to weka from eating bait directly from the stations, and from eat-

ing bait spilled by feeding possums. Using 12 weka as experimental birds, the scientists set their bait stations, (containing nontoxic baits) at different heights. Weka fed from all four stations when they were set with the opening 30 centimetres above the ground. Bait stations with the openings 70 centimetres above the ground could not be reached by weka. This reinforces previous research by Landcare Research, and also reflects the minimum height at which traps are set by the Department of Conservation, to avoid accidental capture of ground-dwelling birds. Regional councils also recommend that bait stations should be placed high up in areas where livestock may have access. The problem of bait spillage was tested with 40 captive possums. Ten of each type of bait station were set with their openings 30 centimetres or 70 centimetres above ground to see if the height of the station had any impact on the possums’ consumption of bait. Spillage in relation to set-height was also recorded. Possums feeding from Pelifeed bait stations spilt significantly more bait than from any of the other bait station types: there was no significant difference in bait spill from the other three types. Also there was no significant difference in the amount of bait spilt at the two heights. The scientists say caution needs to be exercised when examining the results. At first glance it seems that if weka are present all you need to do is place the stations above 70 centimetres. However, if pellets are spilt, they could still potentially kill weka who could take them on the ground. Also, by placing

baits higher up other animals could be at risk — for example, kaka may be more likely to investigate bait stations set higher in trees. Other studies by Landcare Research suggest that possums may not encounter higher-set stations as often as low-set stations. Thus higher stations may not be as effective as low ones. For optimal possum control, and least risk to other species, the less bait spilt the better. Once bait is on the ground in damp conditions it quickly loses its palatability, or the toxin leaches out. Any possums feeding on damp bait lying on the ground may not eat enough and receive only a sub-lethal dose, thereby becoming bait shy. Landcare Research recommends that before people start using cereal bait stations for possum control, they stop to consider what other non-target species may be in the area. If ground birds, such as weka or kiwi are present, choose the type of bait station that is likely to result in the least spillage of bait. Source: G.A. Morriss and E.B. Spurr, Landcare Research, Lincoln. Bait stations tested, from top to bottom, Pelifeed, Philproof, Sentry, Kilmore.