Responses of invasive birds to control: the case of common mynas in Australia

Wildlife harvesting is one of the first ways in which humans have influenced their environment. Effects of harvesting through hunting and fishing on target populations are now well recognised. However little attention has been directed at effects of other modalities of harvesting such as control of problem species. Using a predator-prey framework, I looked at what behavioural responses could be expected from controlling a population of invasive birds. The main predictions that arose were that control should lead to increased risk aversion and larger groups in target species. To verify these predictions, I used the common myna (Acridotheres tristis), a very successful alien invasive species worldwide. Mynas were introduced in Australia at the end of the 19th century and have been spreading across the country. Due to concerns about effects on native wildlife, a number of control programs have appeared in the last two decades. Using questionnaires, I was able to localise trapping efforts, which allowed me to perform surveys of myna populations undergoing high and low control pressure. This showed that mynas undergoing trapping tended to be more risk- averse, less conspicuous and form smaller groups. This in turn raised the question of what mechanism may be responsible for these changes. A captive study provided little support for the implication of selective removal of certain personalities through trapping. However a field study revealed the important impact of learning on responses towards stimuli related to trapping. I suggest responses to control practices are divided into responses specific to the method in use, and general responses to the increased risk in the environment. I discuss theoretical and management-related implications of these two categories of responses. Additionally, based on integrated pest management theory and on information collected from questionnaires to the public and to organisations involved in control, I make recommendations for improving current myna control practices.