A study of the role odour plays in risk of nest predation in birds.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Nest predation is the most important source of reproductive failure in many bird species, and thus acts as a powerful selection pressure influencing the evolution of their life history traits. A number of studies have found that birds use a variety of visual and auditory cues to assess nest predation risk and alter their behaviour in ways that appear to minimise this risk. However, few studies have examined the relationship between odour cues and nest predation risk. In this thesis, I use several species of native and introduced bird species in New Zealand to examine the role that odour cues might play in mediating nest predation risk. The birds in New Zealand provide an ideal opportunity to study the evolution of odours and nest predation risk as they are comprised of both native and introduced continental species which differ in their evolutionary history with predatory mammals. The odour of a bird might be expected to affect nest predation because mammalian predators use a well developed sense of smell to locate prey items. Given this difference, I examined three ways in which birds may lower predation risk in regards to odour cues. First, I compared the ability of two native New Zealand, and two introduced bird species to respond to the presence of a rat (Rattus norvegicus) at the nest. I found some evidence to support my prediction that the native birds do not respond to a predator scent at their nest, perhaps due to their lack of co-evolutionary history with mammalian predators, while some introduced birds responded with anti-predator behaviours. I then looked at the differences in the detectability of preen waxes, a source of odour in both New Zealand and introduced birds, and found evidence to support that rats were more likely to detect the preen wax of bellbirds (Anthornis melanura), a native species, than at least one introduced bird species. Finally, I investigated the possibility that European starlings (Sturnus vulgaris) use the ammonia-like odour associated with active nests as a predator deterrent. I found that rats avoided nest material taken from active starling nests, but did not avoid the raw materials similar to those used by starlings in nest building. Although future work involving field trials are needed, my results suggest that the odour associated with active starling nests may function as a predator deterrent. Overall, my findings suggest that at least some New Zealand native birds differ from introduced birds in both the way they “smell” and the way they use “smell.” However, there is now a need for field studies to test the generalities of this pattern in real world situations, and whether such information can be used to devise novel methods for reducing the risk of nest predation of native birds threatened by introduced predatory mammals.