Friday, October 7, 2011
Sunday, February 27, 2011
“Our endemic braided river wildlife- survival in the balance”
“Our endemic braided river wildlife- survival in the balance”
-Wrybill a case study
Peter Langlands
Braided rivers are undoubtedly one of the most dynamic and changeable terrestrial environments in New Zealand and a challenge for the wildlife adapted to them. The changes that take place on braided rivers are dramatic as the river’s flow constantly changes and the gravels move. As arks of bio-diversity braided rivers rank highly for birds such as wrybills and black fronted terns. Braided Rivers are hotspots on the landscape for bio-diversity yet for many species their survival is fragile and threatened by the inter-play of threats such as reduced river flows, vegetation encroachment and predation. In this article I will look at these factors with the case study of the wrybill- our most specialised braided river bird. As pressures increase on our braided river birds we cannot take their long-term survival for granted.
Wrybill- the ultimate braided river specialist, survivors on islands
Braided rivers represent naturally made “arks” for our endemic birds to escape introduced predators such as ferrets, wild cats and hedgehogs which thrive on the margins of many of our braided rivers, in the form of the gravel islands created on their beds. The wrybill without a doubt epitomises adaptation to life on braided rivers. When the adult bird is sitting on its nest it blends in perfectly not just in colour, but in size with the surrounding greywacke stones.
Yet even when nesting on islands wrybills are still vulnerable. Cats will occasionally venture across side channels. Also as most wrybills nest on island sites new concerns are focussed the impact that other native birds may be having on wrybills. Both harriers and black-backed gulls a have increased dramatically in numbers over the last few decades benefiting from agricultural development along river margins.
With a population of only four thousand birds wrybills are one of our most vulnerable birds. Yet despite indications of a slight gradual decline, researchers are surprised that wrybills have managed to maintain a relatively stable population level. As time goes more and more data comes to hand evidence is now suggesting that it is the wrybill’s longevity that may be keeping the population going. Banding studies have now found that wrybills can live for over 20 years.
Yet if we have a series of years of floods in the spring, combined with an aging population of birds, we may see a crash in wrybills’ numbers. Seeking out island refuges has its cost, especially when the river floods. The 2008 breeding season for wrybills on the upper Rangitata was impacted on by two flood events at each one of the main egg laying stages for wrybills. From a total population of 450 birds only 15 fledglings survived. Climate change needs to be considered. At present the situation is looking tenuous for wrybills with the combination of wrybills being forced to use larger islands on rivers by predators and vegetation encroachment on the rivers margins. Under predicted climate change scenarios spring flooding is expected to increase (Mullan et al., 2008) and for braided river birds, especially wrybills this will result in recruitment failure threatening the birds’ survival.
Nationally it has been estimated that close to 65% of potential river bed nesting sites have been destroyed by encroachment of exotic vegetation. Broom, willows and lupins are the main species. There is no doubt that over the decades that wrybills have been pushed from the river’s edge onto islands in the braided river and that on certain braided rivers wrybills nest in clusters in flood prone areas, it is a trade off situation of which the benefits will only become apparent in the longer term.
Knowledge gaps and need for advocacy
Identifying knowledge gaps is also essential. For example there is no recent detailed monitoring of wrybills on the upper Rakaia, in a location for which water diversions are planned on the Wilberforce River, one of the Rakaia’s main tributaries. We are relying on historical data and more recent surveys are needed. While certain braided rivers are under active management such as the Tasman in the Mackenzie country ( Project River Recovery) and others are being monitored ( O Tu Wharekai – Upper Rangitata) there are large areas of braided river for which we have little information- especially the Rakaia. The Rakaia has fallen through the gaps in monitoring.
As researchers spend more time on braided rivers an increasing number of new threats are identified. Researcher John Dowding has found that the range of predators impacting on any one braided river varies markedly from river to river and the suite of predators at any one river is very specific. Therefore there is a need for detailed monitoring and predator control programs on each one of our main braided rivers. Other threats are being identified with collision events being significant s birds move up and down braided river beds at night hitting power cables. Gravel extraction and river works are also significant in displacing birds. The threats that braided rivers birds such as wrybills are suffering from are additive and increasing.
One of the main issues now is the increasing amount of recreational use on rivers. As peoples’ recreational activities become more regulated in many outdoor environments, braided rivers still represent a free for all in many areas for people with four wheel drives, dogs, and guns. Public education is a key factor, especially or the more remote braided rivers in the South Island.
Water abstraction and pressures on Canterbury’s wild rivers for irrigation
Proposals to divert water from many of Canterbury’s braided rivers are likely to impact significantly on braided river bed birds. Proposals to divert a significant flow from the Wilberforce River into Lake Coleridge and divert the water into a diversion scheme are likely to bypass flows from one of the wrybill’s most important breeding sites on the Rakaia River. Flow reductions are likely to allow increased access of predators onto the river bed. The fight to keep our braided rivers in good shape has been a relentless one, but one in which we should stay ever vigilant.
Braided rivers need large flows in the early spring to keep the gravels and spaces on rivers clear for our native birds. Broom, gorse and lupins all poise a constant threat and need to be actively controlled in key areas where wrybills, black-fronted terns and banded dotterels breed. In addition predator trapping needs to occur on the side channels and edges of braided rivers to give the bird such as wrybills a shot at breeding in locations that are not prone to large scale floods.
Like braided rivers themselves an integrated and dynamic approach will be needed to save our braided river birds and associated fauna. According to DOC scientists Dr Colin O’Donnell “for braided river ecosystems the sum of threats is truly greater than the individual danger. For example if water flow is reduced it might not only lead to an increase in weeds, but it also means feral cats, ferrets and rats and other predators are more easily able to get nests. To successfully protect our native species we need to be holistic in our conservation management actions”.
References
Mullan, B. et al (2008). Climate change and impacts assessment. A guidance manual for local government. Ministry for the Environment. Wellington
-Wrybill a case study
Peter Langlands
Braided rivers are undoubtedly one of the most dynamic and changeable terrestrial environments in New Zealand and a challenge for the wildlife adapted to them. The changes that take place on braided rivers are dramatic as the river’s flow constantly changes and the gravels move. As arks of bio-diversity braided rivers rank highly for birds such as wrybills and black fronted terns. Braided Rivers are hotspots on the landscape for bio-diversity yet for many species their survival is fragile and threatened by the inter-play of threats such as reduced river flows, vegetation encroachment and predation. In this article I will look at these factors with the case study of the wrybill- our most specialised braided river bird. As pressures increase on our braided river birds we cannot take their long-term survival for granted.
Wrybill- the ultimate braided river specialist, survivors on islands
Braided rivers represent naturally made “arks” for our endemic birds to escape introduced predators such as ferrets, wild cats and hedgehogs which thrive on the margins of many of our braided rivers, in the form of the gravel islands created on their beds. The wrybill without a doubt epitomises adaptation to life on braided rivers. When the adult bird is sitting on its nest it blends in perfectly not just in colour, but in size with the surrounding greywacke stones.
Yet even when nesting on islands wrybills are still vulnerable. Cats will occasionally venture across side channels. Also as most wrybills nest on island sites new concerns are focussed the impact that other native birds may be having on wrybills. Both harriers and black-backed gulls a have increased dramatically in numbers over the last few decades benefiting from agricultural development along river margins.
With a population of only four thousand birds wrybills are one of our most vulnerable birds. Yet despite indications of a slight gradual decline, researchers are surprised that wrybills have managed to maintain a relatively stable population level. As time goes more and more data comes to hand evidence is now suggesting that it is the wrybill’s longevity that may be keeping the population going. Banding studies have now found that wrybills can live for over 20 years.
Yet if we have a series of years of floods in the spring, combined with an aging population of birds, we may see a crash in wrybills’ numbers. Seeking out island refuges has its cost, especially when the river floods. The 2008 breeding season for wrybills on the upper Rangitata was impacted on by two flood events at each one of the main egg laying stages for wrybills. From a total population of 450 birds only 15 fledglings survived. Climate change needs to be considered. At present the situation is looking tenuous for wrybills with the combination of wrybills being forced to use larger islands on rivers by predators and vegetation encroachment on the rivers margins. Under predicted climate change scenarios spring flooding is expected to increase (Mullan et al., 2008) and for braided river birds, especially wrybills this will result in recruitment failure threatening the birds’ survival.
Nationally it has been estimated that close to 65% of potential river bed nesting sites have been destroyed by encroachment of exotic vegetation. Broom, willows and lupins are the main species. There is no doubt that over the decades that wrybills have been pushed from the river’s edge onto islands in the braided river and that on certain braided rivers wrybills nest in clusters in flood prone areas, it is a trade off situation of which the benefits will only become apparent in the longer term.
Knowledge gaps and need for advocacy
Identifying knowledge gaps is also essential. For example there is no recent detailed monitoring of wrybills on the upper Rakaia, in a location for which water diversions are planned on the Wilberforce River, one of the Rakaia’s main tributaries. We are relying on historical data and more recent surveys are needed. While certain braided rivers are under active management such as the Tasman in the Mackenzie country ( Project River Recovery) and others are being monitored ( O Tu Wharekai – Upper Rangitata) there are large areas of braided river for which we have little information- especially the Rakaia. The Rakaia has fallen through the gaps in monitoring.
As researchers spend more time on braided rivers an increasing number of new threats are identified. Researcher John Dowding has found that the range of predators impacting on any one braided river varies markedly from river to river and the suite of predators at any one river is very specific. Therefore there is a need for detailed monitoring and predator control programs on each one of our main braided rivers. Other threats are being identified with collision events being significant s birds move up and down braided river beds at night hitting power cables. Gravel extraction and river works are also significant in displacing birds. The threats that braided rivers birds such as wrybills are suffering from are additive and increasing.
One of the main issues now is the increasing amount of recreational use on rivers. As peoples’ recreational activities become more regulated in many outdoor environments, braided rivers still represent a free for all in many areas for people with four wheel drives, dogs, and guns. Public education is a key factor, especially or the more remote braided rivers in the South Island.
Water abstraction and pressures on Canterbury’s wild rivers for irrigation
Proposals to divert water from many of Canterbury’s braided rivers are likely to impact significantly on braided river bed birds. Proposals to divert a significant flow from the Wilberforce River into Lake Coleridge and divert the water into a diversion scheme are likely to bypass flows from one of the wrybill’s most important breeding sites on the Rakaia River. Flow reductions are likely to allow increased access of predators onto the river bed. The fight to keep our braided rivers in good shape has been a relentless one, but one in which we should stay ever vigilant.
Braided rivers need large flows in the early spring to keep the gravels and spaces on rivers clear for our native birds. Broom, gorse and lupins all poise a constant threat and need to be actively controlled in key areas where wrybills, black-fronted terns and banded dotterels breed. In addition predator trapping needs to occur on the side channels and edges of braided rivers to give the bird such as wrybills a shot at breeding in locations that are not prone to large scale floods.
Like braided rivers themselves an integrated and dynamic approach will be needed to save our braided river birds and associated fauna. According to DOC scientists Dr Colin O’Donnell “for braided river ecosystems the sum of threats is truly greater than the individual danger. For example if water flow is reduced it might not only lead to an increase in weeds, but it also means feral cats, ferrets and rats and other predators are more easily able to get nests. To successfully protect our native species we need to be holistic in our conservation management actions”.
References
Mullan, B. et al (2008). Climate change and impacts assessment. A guidance manual for local government. Ministry for the Environment. Wellington
Tuesday, February 8, 2011
Monday, January 3, 2011
Over a quarter of the world population of wrybills at Lake Ellesmere now
With recent floods wrybills have grouped up en masse at Lake Ellesmere with in excess of 1200 birds at the lake now- enforcing the importance of Lake Ellesmere as a Wetland of International Importance
Rangitata floods
River flows during the wrybill monitoring season 2010- fortunately about 70% of the breeding effort was completed prior to the floods
Friday, December 24, 2010
Wrybill female from Rangitata River at Greenpark today
An "exile" from the floods on the Rangitata River which reached close to 1000 cumecs earlier this week there.
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