A comparative analysis of nesting life-history traits and the risk of predation among island and continental birds.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Islands are home to one of the most endangered ecosystems today with high extinction rates, deteriorating biodiversity and high numbers of critically threatened species. Part of reason for the current situation is that island biotas are subject to different selective pressures compared to continental environments resulting in differences in life-history traits that may make island species especially susceptible to human-induced changes, especially the introduction of exotic predators. Although earlier studies have found a variety of behavioural and morphological differences between island and continental bird species, few studies have compared the reproductive life-history differences between insular and continental bird species. In this thesis, I compare how island passerines differ from continental passerines in some of their nesting life-histories. I focus my studies on New Zealand birds as this avifauna provides an excellent system to examine the nesting life-history traits of birds on islands that evolved without mammalian predators. At the same time, a large number of continental bird species have been introduced that evolved with mammalian predators, providing an opportunity to compare the two groups in a common environment. First, I compared predation rates of artificial nests baited with the preen waxes of New Zealand endemic birds and compared them to nests baited with continental preen waxes and control nests with no waxes. I expected that the artificial nests of the endemic species would be baited with more volatile (“smellier”) preen waxes and thus would depredated at a higher rate. The endemic nests were found to be predated in higher rates than the other nest treatments supporting the ‘olfactory crypsis’ theory. I then compared behavioural differences in flushing between endemic New Zealand species and continental species. I hypothesised that endemic New Zealand birds which evolved in a predator regime with avian predators but no mammalian predators would behave in ways that increase their vulnerability to mammalian predators compared to continental species. I found that New Zealand birds flushed from nests later or not at all compared to continental species, and returned earlier to the nests after flushing and did not alter their parental behaviours after flushing. All of these behaviours are likely to increase the vulnerability of endemic birds to introduced mammalian predators. Finally, I then took a broader perspective of island life history evolution and assessed evolutionary changes in the nest sizes of insular and continental bird species across a of islands. Island species were found to build larger nests with larger dimensions and overall ‘sizes’ than their continental relatives. The reasons for the changes in nest sizes may include the higher predation regimes encountered by continental birds, which puts a premium on minimising nest conspicuousness (and thus size). Overall, my findings confirm that life-history traits of island birds differ from those of continental species, and suggest that these differences arise from differences in the intensity of selection from predators. This highlights the unique features of island birds and identifies some of the attributes that may now make them vulnerable to introduced predators.