In the “Pāteke survival guide”
The main and immediate threat to pāteke is from introduced mammalian predators, particularly mustelids (stoats, ferrets and weasels), cats and dogs. As a result of excessive predation, pāteke have vanished from many areas where the habitat is otherwise suitable for them. These and other localised threats are discussed below.
Mustelids—stoats, ferrets and weasels
On the mainland, mustelids are responsible for the majority of pāteke deaths. Ferrets are large (up to 1.5 kg) mustelids, usually with a dark facial mask and creamy-coloured body with dark guard hairs giving an overall darker appearance from a distance. Stoats and weasels are cinnamon-coloured with a white underbelly, with stoats being larger and with a black-tipped tail. Ferrets are strictly nocturnal but stoats and weasels often also hunt during the day.
Stoats are the most widespread and common mustelid in pāteke country and account for most pāteke deaths, even in some of the comprehensive trapping regimes.
Stoats are especially good climbers and swimmers. Young stoats disperse many kilometres from their birth site, beginning in early summer.
Those that survive can have a huge impact on pāteke in the autumn. Autumn is a particularly vulnerable time fo pāteke when adults (including some one-year olds) are increasingly moving between habitats as they prospect for nest sites. Unlike some other New Zealand birds (e.g. brown kiwi) pāteke are vulnerable to stoats throughout their lifetime, and predation can occur at any time of year.
Cats are one of the main predators of pāteke on Great Barrier Island, and they are also a threat at many mainland sites. As with mustelids they can kill pāteke at all life stages. Cats are active hunters during the day and night, and can cover long distances quickly.
Pāteke are at risk not only from feral cats, but also domestic cats around human settlements and/or where traps are limited to live-capture types.
Pāteke try to use camouflage (i.e. “freezing” instead of flying) to avoid predators. As a result, wandering and unsupervised dogs can have significant impacts on pāteke by catching and killing birds on nests and running them down and killing them in feeding areas. Single dogs have been responsible for multiple deaths in some areas.
Pigs, possums, rats and hedgehogs can destroy nests, and potentially compete with pāteke for food.
Bird competitors and predators
Several birds can impact on pāteke to various (usually small scale) degrees, including:
- Pukeko can prey on eggs and especially ducklings—this can be significant in areas where pukeko are common.
- Harriers (kahu) can prey on ducklings and adult pāteke, particularly weak or starving birds.
- Paradise shelduck and mallards can compete for nesting habitat, and paradise ducks can evict broods and resident pairs from ponds and other refuge areas.
- Mallards and grey duck which can hybridise with pāteke .
- Eels predate on ducklings, and other predators, such as morepork, possibly kill pāteke from time to time. However, their impacts are unlikely to be as significant as those of carnivorous mammals.
Habitat loss and degradation
The most chronic habitat loss has been the loss of lowland wetlands, e.g. swamps, slow-flowing streams and kahikatea forests, and their conversion to agricultural land and other development. Surviving wetlands have often been modified by the following:
- Excavation of deep, steepsided channels and the loss of backwashes and seepage areas causing the chronic drying out of lowlands in summer months and during droughts.
- The loss of riparian vegetation along margins of wetlands, ponds and streams which provide important areas in which to hide and nest.
- In poorly managed areas, kikuyu and other exotic grasses have proliferated, resulting in dense impenetrable swards of vegetation.
- The presence of rodents results in increased competition with pāteke for seeds, invertebrates and other foods.
Vehicles kill many pāteke; for example, in some locations 5–10% of birds can be killed on local roads annually, similar to mortality rates from predators. These sites are often where the flock site is slightly upstream of a preferred feeding area, e.g. intertidal pāteke often feed in drains and puddles at the edge of the road and are scared into the path of moving vehicles. At other sites, blocked culverts and artificial waterfalls force birds to cross roads rather than go under them. Fences and wires also account for some bird deaths.
Nets set for eels and mullet in streams and tidal areas are a risk to pāteke as they can become entangled and drown. These nets are especially dangerous when they extend above the surface of the water and are left unattended.