By Prof Phil Seddon, University of Otago.
The newly released report from the Parliamentary Commissioner for the Environment (Taonga of an island nation) highlights the precarious state of our native avifauna, with one in five of our 168 native bird species at risk of extinction.
Birds are highly visible but also highly vulnerable indicators of habitat change, not just in New Zealand, but also globally. The IUCN Red List assessment lists more than 1,300 species of birds globally, one in eight, as threatened with extinction with habitat loss to agriculture and habitat change due to alien invasive species the principal threats to birds.
One intensive conservation intervention to rescue species from the brink of extinction involves population restorations through conservation translocation to reintroduce wild populations. Reintroduction is the intentional movement of an organism into part of its native range from which it has disappeared. The number of reintroduction projects is increasing and New Zealand has been a world leader in restoring populations of birds through translocation. Evaluation of reintroduction outcomes across a large number of projects has highlighted the importance of releases into appropriate habitat.
Traditionally translocations have had a focus on relatively intact habitat, but habitat modification by agricultural and urban expansion, and the presence of invasive pests has become an increasingly important threat to birds globally. This means that that the area of natural, relatively intact habitat available in which to undertake restorations is shrinking. It is worth considering, therefore, the possibility of restoring wild bird populations within habitats that have been substantially altered. Some native species will be more adaptable than we assume, and for some the cause of original declines could be addressed, for example through eradication or suppression of predators, without restoring habitat to near pristine conditions.
There are international examples of viable reintroductions taking place within highly modified habitats. These examples offer a glimpse of the future where reintroduction practitioners explore increased opportunities to reintroduce bird species into modified habitats rather than assuming an overriding need for near-pristine habitat conditions.
Wings over Manhattan
Following a rapid decline in population throughout the continental United States, in 1969 the Peregrine Falcon was placed on the U.S. Endangered Species list. The primary cause of the population crash was widespread use of the pesticide DDT, and following the ban on DDT use in 1970, projects were started to reintroduce Peregrines. Between 1974 and 1999 over 5,000 Peregrines were released, with some of the most successful releases taking place in cities, where tall buildings effectively mimicked the bird’s cliff nesting habitat and common pigeons stand in for the falcon’s native prey. New York city now has one of the highest concentrations of peregrine falcons in the world, and peregrine falcons are increasingly a feature in many UK cities.
Growing rice for birds
Both the Oriental White Stork (OWS) and Japanese Crested Ibis (Toki) were extinct in the wild in Japan by 1971 and 1981, respectively, the decline of both species being due to the combined effects of increased use of agricultural pesticides and changes in the management of the rice paddy field systems in which the species used to forage for fish, frogs, and a wide variety of invertebrates. Reintroduction projects for OWS and Toki started with pilot releases in 2005 in the Toyo-oka Basin of Hyogo Prefecture, and in 2008 on Sado Island in the Niigata Prefecture, respectively.
For both species the key to future success lies in the restoration of traditional paddy field agriculture, entailing the forging of strong links with the farming community in order to reduce the use of pesticides, to resume winter flooding of paddy fields, to maintain peripheral water channels to support diverse invertebrate communities, and to install fish ladders to facilitate natural fish dispersal and migration pathways. The most fascinating aspect of these reintroduction projects is the almost total reliance of the birds on a highly modified agricultural landscape. The first paddy fields in Japan date to the Yayoi period, 1500-2000 years ago, and before that time it can be assumed that OWS and Toki foraged in much less modified wetland sites. Under traditional rice paddy management systems, with no artificial sprays and with winter flooding , the birds presumably regarded paddy fields as just another wetland, albeit with more human disturbance.
It is perhaps unique to have to go back more than 2000 years to locate the original habitat type of a species, but clearly the long intervening history of use of paddy fields by both species indicates that up until recently, self-sustaining populations could be sustained in this highly modified environment. However, populations of neither OWS nor Toki can persist in the face of increased mechanisation necessitating changes in water flow regimes, or with the increased use of pesticide sprays. The restoration of OWS and Toki on mainland Japan will depend on strong support for the project from farmers and local communities and a willingness to restore traditional paddy field management systems in the face of economic incentives to modernise.
It is possible, for at least some threatened bird species, to consider restoration of viable wild populations within habitats that have been substantially altered by agriculture or urbanisation. The challenge will be to determine the factors, for example exotic predators such as cats and rats, that may limit the establishment, growth and persistence of a reintroduced population and to address these specifically. The physical appearance of habitat within a reintroduction target area might be a poor guide to habitat suitability, particularly if we consider habitat to encompass more than just landscape and vegetative elements. For example, the presence of rats and stoats in areas of native forest in New Zealand might not be very obvious, and might not radically alter the appearance of the forest itself, but would significantly reduce the suitability of the site as a potential reintroduction area.
This is not to say that we give up on the protection and restoration of functional natural ecosystems; relatively intact habitats will always be needed to sustain sensitive habitat specialists. However, it seems likely that some native species will be more adaptable than we might assume, and that for many species the cause of any original decline could be addressed without having to restore habitat to near pristine conditions.
We already have kārearea (the NZ falcon) in vineyards, what about some pāteke (brown teal) in the Avon?
Featured image: Pāteke/Brown Teal, Zealandia. Credit: Chris / Flickr.