The Mangatepopo river, is situated in the Tongariro National Park, this the homen of The Whio (Blue Duck).
History. Past/Present
In early European times Blue Ducks were very widespread in New Zealand except in the Northland and the Chatham Islands, early naturalist refer to the whio presence in alpine rivers and tarns, as well as some lowland wetlands.
There are strong indications that the whio occurred in higher densities than today and that the species at one time might have been a flocking bird.
In these times large sections of New Zealand no longer support the whio or only support relic populations.
Habitat of the Whio
The Whio are river specialist, mostly confined to headwater catchments rivers over both North and South Islands. This does not indicate a preferred habitat but rather one of convenience due to, forest clearance for agriculture where poor riparian management resulted in reduced water quality and hydro-electric power generation or irrigation .
The river sections where the Whio are found have a high water quality, stable stream banks, low movements of sediment, standing native riparian shrubs and a wide diversity and abundance of aquatic invertebrates.
The Whio principally occupy a habitat in which food is available in adequate quantities all year round as well as having other essentials such as shelter, nesting sites.
Food
The main food of the Whio are freshwater invertebrates, principally the larvae of the caddis fly, mayfly and the stone fly. Freshwater snails and chironomid larvae .
Most feeding occurs by dabbing or up-ending in riffles and occasionally by diving in white water areas. They also feed for short periods at night.
However for the Whio living on the Mangatepopo river the Tricoptera larvae is a favourite .
Breeding
The females tend to begin breeding as young as 12 months while the majority of the males in their second year. The mating season commences as early as August, when the female feeds more avidly and for longer periods each day . If the previous chicks were successful, the same nesting area is used, these are often found in river-side caves, beneath clumps of flax, holes in the river bank and in hollow logs.
Usually five or six eggs are laid, although clutches of as large as nine have been found. Eggs weigh about 70g each, which is close to 10% of the females weight, there is often a delay of two days interval between laying of consecutive eggs. Only the female incubates throughout the 35 day incubation period, during this time the male positions himself not far from the nesting site and defends the territory from intruding birds. The female normally leaves the nest to feed with her mate during the early morning and late afternoon.
When the ducklings hatch they are immediately capable of battling strong currents and feeding themselves. Throughout the 70 – 82 days of development to fledging both parents are on guard and each have their designated roles, the female is always close to the young ducklings while he often trails behind the brood to watch for predators.
When the ducklings get closer to fledging the parents interest start to wane, also at this time the parents start to moult, during this time the pair take to hiding emerging to feed at night as they cannot fly and become vulnerable prey.
Demography
Territory-holding Whio are long lived with an average lifespan of 7-8 years although about a quarter of all birds will live longer than 10 years .
On the Mangatepopo, as many as 40% nesting attempts failed over a ten year period, because they were either flooded or invaded by predators.
Duckling survival rate is affected mostly by water flows and the weather, high floods and heavy rain can lead to brood fragmentation, ultimately death. However 50-60% of the ducklings survive to fledge .
Productivity is low and variable but generally about one fledgling per pair per annum . In some years total breeding failure may occur throughout the whole or part of the catchments, which means production from any one year may need to compensate for adult deaths over previous years.
Threats
Perceived known threats to the Whio populations are:
Ø Habitat Loss/ Disturbance – Past land development has resulted in the loss of the Whio habitat on the middle and lower reaches of major rivers.
Ø Human Impact – White-water recreational activities like, jet-boating, white-water rafting and canoeing. Disturbances by hunters and dogs, accidental or deliberate shootings and road kills.
Ø Competition for Food – Although not yet proven the caddisfly, stonefly and the mayfly nymphs are also food of the trout. This could be the answer to the decline in numbers of the Whio on the Tongariro River over the years.
Ø Predators – Known predators of the Whio include the rat who eats the eggs, stoats devours eggs, chicks and adults, whereas, the ferret, feral cats/dogs, gulls, hawks, eels, shags and falcons eats adults or chicks. Therefore the stoat is the bigger threat.
Ø Population Fragmentation – Population fragmentation and the gradual extinction of small and isolated populations has been a conspicuous feature in the process of decline of many native bird species over the past 150 years . The present known distribution of the blue duck that shows that the population is fragmented although the long-term viability of these isolates is uncertain. Henderson (1994), as part of his population viability analysis of the blue duck, calculated that an isolated population of 9 pairs with demographic characteristics of the birds inhabiting the Mangtepopo “ study area” has an 8% probability of surviving 100 years . However, the productivity of Mangatepopo study area birds are considerably higher that those from other sections of the same river or from any other blue duck population studies in new Zealand . Therefore, the long-term persistence of many populations isolates is doubtful.
Ø Volcano Eruptions/Lahar - Effects of volcanic events such as lahars from Mount Ruapehu. This is especially significant for ducks in the Tongariro and Manganui-a-te-ao catchments which contain major lahar pathways .
In 1997, the Department of Conservation in consultation with the new Central North Island Blue Duck Charitable Trust finalised the second specific strategy for the central North Island ‘Recovery Plan for Blue Duck’. These were
Ø Securing key populations
Ø Re-establishing the Mount Taranaki population
Ø Monitoring the outcomes of management, including increased water releases by Genesis Power on the Whanganui and Mangatepopo rivers
Ø Working closely with community groups and iwi. This approach will complement and enhance the priority work already being done on the Whio conservation nationally
Ø Monitor the eradication projects, ensuring they are on target.
The establishment of the Central North Island Blue Duck Charitable Trust provides an important opportunity to increase that knowledge further. While this will primarily benefit the species effected by the TPD in catchments running off the mountains of Tongariro National Park, it will also help the Whio throughout the country. Over the next few months, the Blue Duck Recovery Group will work with the Trust looking at options and priorities for that work. As a result, the recovery group are confident that the next decade will see continued progress in conserving this special river icon .
The Department of Conservation is charged with conserving our native wildlife in the Tongariro/Taupo Conservancy for all to enjoy now and in the future.
Ø Operation Nest Egg (O.N.E.) to protect and enhance the kiwi population of Tongariro Forest
Ø Ongoing Blue duck monitoring on the Tongariro, Mangatepopo and Whakapapa rivers.
Ø Short-tailed bat in Karioi Rahui, part of Rangataua Conservation Area
If we want to preserve any of our unique New Zealand plants and animals, then we must protect what we have left before it is completely gone. We need to respect not only conservation areas but the whenua all around us, if we all take a little care, we will be able to enjoy our whenua for all time.
Hope you enjoyed this article.