Older native Aotearoa New Zealand birds may be more threatened with decline than younger species, a new report published in New Zealand Journal of Ecology suggests.
The report, conducted by Manaaki Whenua – Landcare Research, used new modelling and found that ‘deep endemic’ forest-bird species – ones that arrived in the country a long time ago – such as the famous kiwi and kokako are more vulnerable to decline than those that arrived later, like the fantail.
The team found that this may be because the early settler birds had three life-history traits that made them more vulnerable to deforestation and predation: they nest in tree cavities or burrows, they have large bodies, and they can’t travel very far.
“The results give us a new way to predict the future of different forest-bird species in different predator-free landscapes,” says Susan Walker of Manaaki Whenua – Landcare Research.
Read more: The mastery of convergent evolution
“The results give us a new way to predict the future of different forest-bird species in different predator-free landscapes,” says Susan Walker of Manaaki Whenua – Landcare Research.
“Our results support understanding that predation is the primary cause of forest-bird declines and limitation today, but they also suggest large tracts of native forest will be essential to restore some species, even without mammal predators.”
The research leads to three predictions about the restoration, if there were fewer predators.
Firstly, forest scarcity may impede recovery time of some of the larger deep endemic birds because they are less mobile and require certain tree cavities. Other, more mobile birds might not have the same restrictions.
Secondly, restoration will probably be more successful where there is more forest, but these forests won’t be equally successful. For example, cooler forests may not be the best environment for big-bodied birds that need to eat a lot because they contain less food.
Finally, instead of increased numbers of all species, the make-up of the bird community may change.
Currently, the larger, deep endemic birds are more vulnerable to predation and deforestation because they are less adaptable. However, in a hypothetical future without deforestation and predation, they might take over the sanctuary forest again. Newer endemic birds might then move to other, warmer places that are already deforested because they don’t need the burrows and tree cavities.
“This is the outcome we are starting to see in practice: that deeper endemic species in sanctuaries are replacing silvereye, grey warbler and fantail, which are from more recently arrived lineages and became common in warm and deforested landscapes since human settlement,” says Walker.