|dc.description.abstract||Poisonous baits are successfully deployed over large areas of New Zealand to control mammalian pests such as brushtail possums (Trichosurus vulpecula) and rats (Rattus spp.). While poison-based control leads to positive ecological and disease control outcomes, non-target native birds, such as robins (Petroica australis) and tomtits (Petroica macrocephala), are sometimes killed after eating bait. In this thesis, I investigated the use of primary and secondary repellents to prevent non-target birds from feeding on baits. Primary repellents invoke instantaneous rejection responses through unpleasant visual, olfactory, taste or irritant cues. Secondary repellents act via an illness-induced learned avoidance and require some ingestion of treated food before learning can occur. I determined the efficacy of several primary repellents (neem oil, agricultural lime and d-pulegone) and a secondary repellent (Avex; an anthraquinone-based product) for deterring a model avian species, the house sparrow (Passer domesticus), from feeding, prior to testing the efficacy of the repellents with two native birds: robins and tomtits.
In Chapter 2, I measured the responses of free-ranging house sparrows to wheat treated with primary and secondary repellents over four day periods. Eight sparrow populations were trained to eat plain wheat from food trays on feed tables and were presented, in choice tests, with plain wheat and wheat coated with low, medium or high concentrations of repellent. Wheat treated with either lime or neem oil was consumed by sparrows at the same rate as plain wheat on all days; this suggested that neither compound was an effective sparrow repellent, so I did not evaluate these repellents further. D-pulegone significantly reduced wheat consumption on Day 1, with birds continuing to eat less d-pulegone-treated wheat than plain wheat throughout the four days. Avex did not reduce wheat consumption on Day 1 of exposure, but sparrows ate progressively less Avex-treated wheat over each of the following days. I combined d-pulegone (the primary repellent) and Avex (the secondary repellent) and compared the efficacy of the combination to the efficacy of Avex alone for preventing feeding. The combination of 2% d-pulegone + 2% Avex reduced wheat consumption significantly more than 2% Avex alone, with the effect lasting over a 10-day test period. The results demonstrated the potential of combined repellents for modifying avian feeding behaviour, and provided evidence for the enhanced efficacy gained by combining primary and secondary repellents.
In Chapter 3, I evaluated the efficacy of the combination of d-pulegone + Avex for deterring native robins from feeding on baits. I identified a preferred dough bait, which I used to offer robins repellent-treated (green and surface coated with a combination of 2% d-pulegone + 2% Avex) and "standard" dough (green and coated with cinnamon oil; the bait formulation currently used for pest control operations in New Zealand). Free-ranging robins were presented baits over four consecutive days on an "arena" of cleared leaf litter, on the forest floor within their home territory. Robins pecked at and removed standard dough more frequently than repellent dough, with the frequency of pecking at repellent dough declining over days. These results demonstrated that the combination of 2% d-pulegone + 2% Avex effectively deterred robins from feeding, but that green dye and cinnamon oil may not be effective deterrents.
As the combination of d-pulegone + Avex had effectively deterred sparrows (Chapter 2) and robins (Chapter 3), I compared this combination with other combinations of repellents and cues in Chapter 4. I presented sparrows with wheat treated with the secondary repellent Avex, paired with either a novel visual cue (blue colour), cinnamon oil (containing primarily olfactory cues), or d-pulegone (containing olfactory, taste and irritant cues). Avex alone significantly reduced wheat consumption, but cinnamon oil + 2% Avex was no more effective than 2% Avex alone. Blue colour + 2% Avex and 2% d-pulegone + 2% Avex elicited the most effective avoidance responses, reducing food consumption by at least 85%, and substantially more than 2% Avex alone or cinnamon oil + 2% Avex. When I compared the combination of blue colour + 2% Avex to colour alone (blue or green), sparrows initially avoided all three treated wheat types. However, sparrows progressively consumed more green and blue wheat each day, eating significantly more of these "colour only" treatments than blue colour + 2% Avex by Day 5. Colour alone did not provide a long-lasting avoidance response. These data clearly demonstrated that combinations of Avex with additional visual or olfactory/taste cues were effective repellents, but that certain primary cues were more effective than others.
In Chapter 5, I evaluated the efficacy of the blue colour + 2% Avex repellent combination for deterring robins from feeding in comparison to standard baits. Robins pecked at and removed standard baits more frequently than repellent baits, with the frequency of pecking at repellent bait declining over the four days. They pecked more frequently at both bait types in the winter than summer, and juvenile robins tended to peck at repellent bait more frequently than adult males or females. The pecking responses of robins towards both bait types were similar in choice and no-choice tests. The combination of blue colour + 2% Avex effectively deterred most robins from feeding and is likely to reduce their propensity to eat baits during pest control operations.
I compared the feeding behaviour of free-ranging robins and tomtits towards blue colour + 2% Avex baits and standard baits in Chapter 6. Robins pecked at and removed standard baits more frequently than repellent baits, with the pecking frequency for repellent baits remaining very low. Tomtits never pecked at or removed either bait type and they spent less time on the test area than robins. Using an alternative test method in which baits were thrown to birds, robins investigated > 90% of baits thrown to them by an observer, but pecked at significantly fewer repellent baits. Tomtits ignored over 89% of thrown baits. They investigated more standard baits than repellent baits, but never pecked at either bait type. These results clearly indicated a difference in the feeding behaviour of robins and tomtits with respect to the baits, suggesting that tomtits may be less likely than robins to eat bait in some circumstances.
The experiments I conducted in my thesis have demonstrated that combining a secondary repellent with an appropriate primary repellent is a highly effective way of deterring the birds I tested from feeding. Two combinations of repellents (2% d-pulegone + 2% Avex or blue colour + 2% Avex) reduced food consumption more than any single repellent used alone. Not all combinations of cues, however, elicited the same level of repellency and care should be taken to select repellent combinations that effectively deter birds from feeding. I found that a secondary repellent paired with either a novel aversive colour and/or an innately aversive odour or taste reliably repelled birds. For pest control baits in New Zealand, a combination of blue colour and/or d-pulegone + 2% Avex may offer good potential for preventing non-target bird poisoning. Further research with additional avian species and field testing will now be required to demonstrate the value of these repellents for protecting native birds during normal pest control operations. This additional research should be conducted immediately, so that these findings may be implemented to provide greater protection during pest control to valued native wildlife.
Keywords: agricultural lime, anthraquinone, Avex, bird repellent, brushtail possum (Trichosurus vulpecula), colour, cue, d-pulegone, feeding behavior, house sparrow (Passer domesticus), neem oil, non-target species, North Island robin (Petroica australis), North Island tomtit (Petroica macrocephala), odour, pest control, poison baits.||