Individual study: Use of dipped repellents to deter North Island robin Petroica australis longipes from pest control baits on Tiritiri Matangi, Auckland, New Zealand
Day T.D., Matthews L.R. & Waas J.R. (2003) Repellents to deter New Zealand's North Island robin Petroica australis longipes from pest control baits. Biological Conservation, 114, 309-316
Non-target animals may be at risk during poisoning operations to eradicate introduced mammalian pests. Indeed, pest control operations to assist the recovery of bird populations can result in mortality of native birds and ground-dwelling species, such as North Island robin Petroica australis longipes (endemic to New Zealand), are at particular risk from poisoned baits. Despite a current lack of evidence of the effects of long-term poisoning on the populations of non-target species, non-target mortality remains a key issue in reducing public support for pest-poisoning operations.
In New Zealand, baits must be larger than 16 mm, making them difficult for smaller birds to manipulate, and dyed green, with cinnamon oil also often added, to act as an avain deterrent. Despite these measures, native birds sometimes still consume baits and die. Therefore, additional manipulations are required to effectively repel native birds, while maintaining bait attractiveness to mammalian pests. In this study, the rate that North Island robin's pecked dough balls treated normally (with green dye and cinnamon) and treated with repellents (a combination of green dye, d-pulegone, and AvexTM) was observed.
Study site: The study was undertaken on Tiritiri Matangi Island, lying in the Hauraki Gulf off mainland North Island.
Bait and treatment: Dough (flour, water, lard, sugar and green dye [0.01% Special Green V200A dye, Bayer NZ Ltd., Auckland] cooked for 15 min at 150°C) was used as the base material, having been identified as the preferred food base material (between cereal, carrot and dough) in a previous experiment (presented in the original paper).
In the experiment, wild North Island robin's Petroica australis longipes were offered standard dough (green dyed and containing 0.1% cinnamon) as the control and repellent dough (coated with a water solution containing a combination of 2% d-pulegone and 2% Avex). D-pulegone (85% tech., CAS No. 89-82-7; Aldrich Chemical Co., USA) is a primary repellent volatile peppermint Mentha compound that has been shown to repel several bird species by volatile cues (odour) and direct contact (taste). However, it alone is not sufficient to promote long-term avoidance. Avex is an anthraquinone-based secondary repellent, containing 9,10-anthraquinone (50% wt./wt.; CAS No. 84-65-1; Loveland Industries Inc., USA), which deters avian feeding. Both d-pulegone and Avex treated baits are readily eaten by wild possums and rodents. Dough was cut into 5 mm cubes which were treated by dipping them in the repellent mixture 36 hr before the experiment, allowing them to air-dry, and then storing them in airtight containers.
Bait testing: Twenty-one wild robins (four females, ten males, and seven of unknown gender) were used to test the efficacy of the two bait treatments, in June and July 2000. A test arena, consisting of a 0.75 x 0.50 m area scraped clear of leaf litter, was set up in woodland at the centre of each robin territory on each of four consecutive days. A teaspoon each of repellent dough and of standard green-dyed dough cubes was placed in plastic cups, which were positioned 25 cm apart in the arena, and presented for 25 min (between 07:00 and 16:00 hrs) each day. Robins were attracted by tapping on the plastic pots and tossing small twigs into the arena.
During each 25 min test, robin activity was recorded on video camera. The number of pecks directed at each food source was recorded. Additionally, if a robin removed one of the cubes from the test area, its type and fate (eaten, dropped, or taken from sight) was recorded.
Robins pecked at standard dough (green-dyed + 0.1% cinnamon) more frequently than repellent dough, and the frequency of pecks at repellent dough declined significantly over the four days, relative to the standard dough. Mean peck frequencies (estimated from figure in original paper) on days 1-4 were:
Day 1 - 6 for standard and 1.5 for repellent
Day 2 - 5 for standard and 0.5 for repellent
Day 3 - 3 for standard and 0.25 for repellent
Day 4 - 3.25 for standard and 0 for repellent
Male robins tended to peck at repellent dough more than females and birds of unknown sex.
Robins removed standard dough more frequently from the test arena than repellent dough (see Table 1, attached). Furthermore, robins ate standard dough, whereas they did not eat repellent dough when removed from the arena. Lastly, 50% of removals occurred on day 1.
Conclusions: Standard bait treatment (green-dyed + 0.1% cinnamon) does not seem sufficient to prevent non-target deaths, whereas dipping baits in a mixture of d-pulegone and Avex appears to act as an increasingly effective deterrent with time. This suggests that birds learned to avoid the repellent bait. Therefore, using these repellents on poisonless bait before any poisoning program commences might prove the most effective measure to prevent non-target deaths. The merit of spraying baits with the same repellent mixture was also evaluated (for a summary see: http://www.conservationevidence.com/ViewEntry.asp?ID=353), results suggest however, that dipping is the most effective method of repellent application.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at http://www.environmental-expert.com/magazine/elsevier/biocon/index.htm.