Response of New Zealand birds to the presence of novel predators
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Predation is the highest cause of mortality for birds and can place intense selection pressures on their behavioural traits. A number of studies have shown that some animals have innate predator recognition, while others which are predator-naïve have been unable to adapt to the introduction of exotic predators. For my thesis, I firstly studied how eight species of introduced and native birds respond to model predators at their nests. This enabled me to determine whether the native birds have been able to adapt to introduced mammalian predators and have developed recognition of them being a threat. In most species, the reaction to the stoat (Mustela erminea) (an introduced predator) was similar to that of a model morepork (Ninox novaeseelandiae) (a native predator). This suggests these species can successfully recognise introduced mammals as a risk. It also allowed me to test whether recently introduced birds have any innate recognition of snakes, which are a significant nest predator in their native ranges but do not exist in New Zealand. I found that introduced birds did not appear to have any recognition of snakes as being a threat. These losses and gains of recognition may have been caused by evolutionary changes or they may be influenced by learning and experience. Secondly, I examined how South Island robins (Petroica australis) on a predator-free island responded to predator models and compared this to the responses of robins on the mainland (where they co-occur with mammalian predators). The island birds were assumed to show the ancestral reactions to mammalian predators, while any differences in response shown by the mainland robins would indicate they had acquired these behaviours in response to increased predation risk. I found that the island robins did not appear to recognise or react to a taxidermic mount of a stoat while mainland robins did respond to the stoat, confirming that at least some native birds can develop recognition of novel predators. Finally, I compared the personalities of South Island robins on a predator-free island and on the mainland (where mammalian predators are present). I tested where individuals placed on the ‘bold-shy’ continuum by observing their willingness and speed to approach a risky situation in order to collect food. Studies have shown that average personality between populations can differ where predation risk differs. I found that the island robins were on average bolder than mainland robins. They came nearer to the observer and were faster to approach and remove a food item, while mainland robins were less likely to approach, and those that did approach took a longer time. It is likely that these differences were due to selection pressures by mammalian predators favouring shy individuals on the mainland while other pressures such as interspecific competition favours bold individuals on the island. Personality has been shown to be genetic and heritable, however, learning and experience cannot be ruled out and may also play a part in influencing how personality is expressed. Together, my results support the importance of historical and ontogenetic factors in influencing how predator recognition and personality traits are expressed.