Predators

Feral Cat (Felis catus)/ roaming domestic cats

Feral cats are No.1 on the hit list. They are wild animals that have existed in New Zealand since the early days of colonisation. They arrived as pets with the first immigrants and by the 1840’s many had established themselves in the wild. By 1860’s many domestic cats had been released into the wild in the hope that they would keep the rapidly expanding rabbit population under control (Thomson 1922).

Rabbits were first imported from Australia in 1838 (Thomson 1922) and by 1842 large numbers of rabbits were being reared in captivity. By 1844 the first rabbits had been released into the wild had taken place, but it did in fact take close to twenty years before they were established in the wild. Another twenty years on they were plague proportions in the wild and an extensive rabbit industry, for meat and fur, had been established.

To a degree the release of cats to keep wild rabbit populations under control was successful, but as the rabbit population grew the feral cats failed to stem the growth and as the cats became completely wild and, in fear of man, they retreated to the wild bush areas where they found that New Zealand’s endemic bird life offered easy targets and a succulent diet.

As the cats failed to do their job on the rabbits many eyes turned towards mustelids as a means of combating the rabbit explosion.

In modern times most feral cats are derived from abandoned pets, others are strays gone wild, and many are born in the wild to existing ferals, or to strays. Kittens born in the wild, with no exposure to humans during the socialisation period (3-8 weeks) end up as wild animals.

Examples now exist which provide an insight into the feral cat problem and to the numbers of feral cats in New Zealand – 350 killed at Reporoa in five years, 100 killed on one small Wairarapa property in eight years and 100 killed on Great Barrier Island in one year.

Other examples confirm that the feral cat population is large and rampant, but as already mentioned, given impetuous and conviction needed to save Brown Teal, feral cats can be easily trapped and eliminated. Wherever serious predator control has been carried out the bird population has multiplied very rapidly and life expectancy has increased dramatically.
As mentioned earlier feral cats are known carriers of Bovine TB and many regional councils’ are now trapping/eliminating feral cats in their area.

Stoats (Mustela erminae)

Stoats in New Zealand appear to be slightly less in numbers than ferrets, but are just as widespread. The stoat diet is much the same as the ferret – they kill and eat, mice, rats, birds of every species, rabbits, invertebrates of all sorts, devour eggs at every opportunity, and, in many instance, will kill and devour mammals much larger than themselves.

With a rapidly increasing mouse and rat population the stoat population has also increased.
Mustelids in New Zealand are active during night and day and their movement can cover vast areas of land. Movements of over 60 kilometres in one month, by a female stoat, has been recorded (Yellow-eyed Penguin Trust 2002).

The lifespan of a stoat is much shorter than that of a ferret, but their productivity rate is higher.
Stoats mostly have a brown body and legs, a white undercarriage and distinctive black tip to their tail. Their average sizes are 280mm length and 325g in weight for a male, and 250mm in length and 205g in weight for a female.

Weasels (Mustela nivalis)

The weasel is by far the smallest of mustelids present in New Zealand and their numbers are considerably less than both the ferret and the stoat. They tend to prey on smaller animals – mice, lizards, frogs, and a vast array of small birds species. They are also eat eggs of all types.

Colouring of the weasel is very similar to the stoat – brown body and legs, white undercarriage, and a brown tail. The size and weight of a male weasel is 220mm and 125g, and for a female 180mm and 60g (Yellow-eyed Penguin Trust 2002).

Their impact on Brown Teal populations is not clear, but they are known to be a major predator of many NZ bird species.

Ferret (Mustela furo)

The ferret is by far the largest of the mustelid family of Brown Teal predators and their colour and size vary considerably. The average weight and length of an adult male is 1200g/420mm, and an adult female 600g/350mm (Yellow-eyed Penguin Trust 2002).

They were first brought to New Zealand in 1867 for the sole purpose of keeping rabbits under control. Gradual releases into the wild started in the 1870’s, with very large numbers being released in the early 1880’s and over 3,000 released in Marlborough alone (Thomson 1922).

A meeting of farmers at Masterton, in the Wairarapa, in 1886, a resolution was carried which stated:
‘That the introduction of ferrets, stoats and weasels in large numbers is, in the opinion of this meeting, the only means by which the rabbit pest can be successfully put to an end to, and that every landowner infested with rabbits should either turn out ferrets in proportion to his acreage, or contribute funds for the breeding and purchase of ferrets, stoats and wesels to be turned out in the district. That the land-owners present form themselves into an association for the purpose of providing the natural enemies. (Thomson 1922).

During the late 1970’s and 1980’s ferret farming, for their fur, became popular, but as these commercial activities failed – one after the other – large numbers of ferrets were released into the wild. The result being that New Zealand’s endemic birds have been unable to cope with a very large ferret population. And now large amounts of money and labour need to be applied to control, what is now, a very serious problem.

Contrary to what pet ferret lovers would have you believe, feral ferrets survive extremely well in New Zealand, they breed well, kill well and feed well on rats, mice, and on every type of bird. They also often appear to kill ‘for the sake of it’, but will also often leave a ‘kill’ for several weeks before coming back to eat it. In 2002 the Minister of Conservation, in a move which was a well supported and popular move, banned the keeping of ferrets in captivity.

No guesstimates have been recorded of the number of mustelids in New Zealand, but collectively they must total in the millions.

Mustelid Habits & Habitat

The New Zealand bush, native scrub, sand dunes, tussock country and farmlands are the preferred habitats for mustelids. All mustelids climb well, swim well and travel rapidly over long distances. Besides being a menace to native birds they also present a major threat to poultry farms.

RATS

There are three main kinds of rat in the wild in New Zealand
1. The Polynesian rat or Kiore (Rattus exulams)
2. The ships rat (Rattus rattus)
3. The Brown rat (Rattus norvegicus)

Kiore
Kiore first came to New Zealand with the first Polynesian migrants just over 2000 years ago. Although quite small – c 150g – they were an important food source for the early migrants.
In modern New Zealand Kiore are now largely extinct on the New Zealand mainland, where they have been mainly eradicated by the other two rat species.
Kiore are now only found on a few off-shore islands and are not thought to greatly impinge on Brown Teal populations, but on Tiritiri Matangi Island they have already been eradicated by extensive poisoning and elsewhere their possible influence of Brown Teal needs to be rigorously monitored.
The Brown Rat

The Brown or Norway rat was the second rat to arrive in New Zealand and is believed to have been brought here in 1769 by Captain Cook. Like all newly arrived animals they found New Zealand much to their liking and multiplied rapidly.
The Norway rat is the largest of rats present in the wild in New Zealand, with a males weighing an average of 450g. They thrive on New Zealand’s abundance of insects, on lizards, and on the eggs of all birds species. They are known to kill and eat Brown Teal ducklings. They swim well and often travel great distances over water and land.

The Ships Rat
The last rat to arrive in New Zealand was the ships rat, also often referred to as ‘the black rat’. Many researchers claim that this is the worst rat predator that there is conclusive evidence shows that it has created havoc amongst many endemic bird populations. Rattus rattus weighs only around 200g, but is an excellent climber and also swims well.
Both the Norway and Ships rat are widespread throughout the mainland, but major poisoning campaigns have already eradicated them from a number of off-shore islands.
Eliminating Rats

Eels
Large fresh water eels are known to take ducklings of all sizes and farm ponds where Brown Teal breed, such as at Mimiwhangata, other areas in Northland, release sites and on Great Barrier Island should have large eels removed at regular intervals. Commercial eel fishermen will be only too pleased to assist.

Pukeko
The abundant pukeko (Porphyrio porphyrio) is native to New Zealand, with the same species being spread throughout many coastal areas of Australia.
Pukeko have cannibalistic instincts and often reek havoc amongst broods of ducklings. They often kill ducklings for the sake of it.
They are a game bird throughout New Zealand, but are rarely hunted seriously by anyone, as they are not the most desirable table bird! However, even semi-serious hunting of pukeko would undoubtedly help keep the population under control.
In Brown Teal areas they must be kept under control and this can be easily done by shooting them – having obtained the necessary permit – either with a 22 rimfire rifle or with a shotgun.

Feral And Domestic Dogs
Only on Great Barrier Island have feral dogs impacted on Brown Teal; these mainly being dogs lost by pig hunters on the island. But also on Great Barrier and in Northland domestic dogs are known to have killed considerable numbers of Brown Teal at their flock sites.
“Education’ amongst dog owners living close to Brown Teal sites is essential, as is the need to totally eliminate the problem of rogue dogs.

Hedgehog (Erinaceus europeus)
The hedgehog first arrive in New Zealand in 1870 and over the next twenty years considerable numbers were imported.
It has been stated many times, that hedgehogs have absolutely no value in the New Zealand environment and no reasons for their importation appear to have been documented. But we can assume they were imported to control garden insects and to make those from ‘the old country’ feel at home again.
The hedgehog in now found throughout lowland areas of New Zealand and whilst their impact on ground nesting Brown Teal is not know, it is known that they are avid eaters of birds eggs and must be eliminated at critically important Brown Teal sites. Fortunately they are easily eliminated by the Fenn trap, although they are at time a nuisance to extract from a Fenn trap, and easily caught in cage trap.
Good numbers have also been killed in the Timms trap.
The sad thing is that it was a ludicrous move to import and release hedgehogs and that yet again there was no accountability whatsoever.

Paradise Shelduck (Tadorna varigata)
The endemic Paradise Shelduck is the only endemic species which, by a complete fluke, has benefited from man’s interference with nature in New Zealand. By chopping down native bush and creating grasslands the paradise population steadily expanded.
Historically, however, the species was killed for food in large numbers by the Maori and the species barely maintain itself in a few localized areas. The species was absent in many districts and eventually became protected – except during the hunting season.
During the 1970′ and 80’s the NZ Wildlife Service translocated paradise to areas where they were absent. The eventual result of this being that the paradise is now found throughout the country and the total population is estimated to be around 150,000 and is now a game bird in most areas, with around 20,000 being killed annually during the game bird hunting season.
Their impact on Brown Teal is not yet fully understood, but they are a very aggressive bird; they are known to frequent Brown Teal areas and to like farm ponds frequented by Brown Teal.
It is vital that their potential impact on Brown Teal is monitored and that if necessary they must be removed from Brown Teal areas, or eliminated on site.

Black Shag (Phalacrocorax carbo) “GIANT SHAG”
As we mentioned earlier, the black shag in known to be very partial to ducklings and whilst their impact on Brown Teal is unknown they should be eliminated at known Brown Teal sites.
Like the Australasian harrier, the black shag gained total, but dubious, protection (they are also known to devour large quantities of trout) and permits are needed to eliminate them.

Black-Backed Gull (Larus dominicanus)
One only needs to consider that farmers hate the black-backed gull at lambing time to appreciate what damage these large scavenging birds can do.
Almost nothing is known about their affect on Brown Teal ducklings, but it is believed that they do present a predation factor and should be actively discouraged from known Brown Teal sites.