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Deterring birds from baits by manipulating colour and odour

Poisonous baits are used extensively in New Zealand to control introduced mammalian pest species particularly brushtail possums (Trichosurus vulpecula) and rats (Rattus rattus, R. norvegicus, R. exulans). This thesis examined bait characteristics that could be manipulated to make poisonous baits less attractive to native birds. The first characteristic examined was colour as the appearance of foods was believed to be important to foraging birds. The target mammalian species may be more attentive when foraging to other aspects of food such as taste and smell. A six colour choice method for testing colour preference in birds was developed using chickens (Gallus domesticus). The procedure involved testing birds individually, on six occasions, with novel food of six different colours presented simultaneously. All three species of birds tested; captive New Zealand weka (Gallirallus australis), wild New Zealand robins (Petroica australis), and free range domestic chickens showed similar colour preferences. The red and yellow novel food was preferred to the blue novel food. Baits in New Zealand are currently dyed green to deter birds but this study suggested blue may be a more effective deterrent. There was considerable individual variability in colour preference suggesting one colour is not likely to deter all birds in a population from poisonous baits. Both weka and chickens showed a pattern of increasing consumption from test to test and the implications of this behaviour pattern are discussed in terms of poisonous bait consumption. Free range chickens were used to investigate whether chickens avoided some shades of blue more than others but no preferences were detected. The relative luminance of the colours offered to the chickens was calculated, however, and there was an indication that chickens preferred lighter rather than darker colours. I would suggest, therefore, that light coloured poisonous baits should not be used. It was suggested that natural predator-prey systems may provide useful concepts for the design of bird deterrents. Many toxic insects have a combination of several conspicuous characteristics, all of which assault different senses at the same time. I investigated combinations of colour, novelty and methyl pyrazine, an odour used by toxic insects to deter birds. Wild robins were not deterred from familiar food by methyl pyrazine odour and the addition of methyl pyrazine did not alter chickens’ colour preferences or their consumption of novel food. Pyrazine, however, was very effective in deterring captive weka from red and blue novel food. The weka ate very little of either colour when it was associated with pyrazine odour. The combination of pyrazine and blue, which was effective in captivity, was tested in the field using real (non toxic) baits. Consumption over six days was compared with that of the green-coloured, cinnamon-flavoured, baits commonly used in poisoning operations. Fewer of the blue-pyrazine baits were eaten on the first day and there was an indication that consumption of blue-pyrazine baits was lower overall. Methyl pyrazine may be useful in deterring birds from poisonous baits and is certainly worthy of more investigation.
Type of thesis
The University of Waikato
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