The Predators
rats on aotea, great barrier island
Rats have a major impact in any ecosystem because they are omnivores (eat both plants and animals), with a diet that varies depending on what habitat they are in. Rats prey on eggs, chicks, birds, lizards, frogs, invertebrates (i.e, skinks and weta) and plants (seeds, flowers and fruit) and are key ecosystem changers due to this predation. Two (of three) species of rats introduced to New Zealand are established on Aotea, Great Barrier Island; the ship rat, able to climb trees and Kiore or better known as the Pacific rat. We do not have Norway rats and hope to keep it that way.
Rats are rapid breeders, breeding 20-30 times faster than native birds. In suitable environments, a rat can reach sexual maturity at 5 weeks of age and will breed throughout the year, with a female producing three to six litters of up to 9 – 14 young. They generally live for two to three years and can form social groups of up to 60. Rats have a relatively small home range (about 1ha for ship rats) and this combined with their rapid breeding means that reinvasion of rats in a controlled area is generally very rapid.
Photo credit Predator Free NZ. In order from first preview: Rat Comparison, Ship Rat and then Kiore Rat
Ship rat
The ship rat (Rattus rattus) is the most commonly found rat in New Zealand.
Distinctive features: Beady eyes, dark tail much longer than body, grey-brown or black fur, rounded hairless ears, long whiskers. Unlike a Norway rat, a ship rat’s tail reaches its nose and the ears are big enough to cover its eyes. Females usually have 10 nipples on the belly. They are good climbers, so they can access many bird nests high in trees.
Droppings: Small cylindrical pellets on average 6.8 mm – 13.8 mm long, ends tapering to a point.
Footprints: Four-toed forefeet and five-toed hindfeet.
Kill signs: Shell fragments in predated nests, distinctive parallel double incisor marks in chewed flesh, neatly chewed holes in snail shells. Piles of insect legs near feeding areas. Food caches in trees or epiphytes.
Vegetation damage: Seeds with neatly chewed holes to access contents, larger fruit may show distinctive parallel double incisor marks about 2 mm wide, damage to growing tips of some species may occur.
Information Source: Pest Detectives www.pestdetective.org.nz
Photo credit Predator Free NZ.
kiore rat
Kiore is the Māori name for the Pacific or Polynesian rat (Rattus exulans). An adult kiore is approximately 4 cm shorter than an adult ship rat, but looks very similar and the two species are often confused. The tail of a kiore is shorter than the body
Distinctive features: Brown fur, white-tipped grey fur on belly, pale feet with dark mark on outer edge of hindfeet. Eight nipples on female belly. Ears cover eyes when pulled forward. Thin tail about the same length as body.
Size: Smaller than other rats in New Zealand, maximum body length is 180mm without tail, and they usually weigh 60g – 80g, maximum 180g.
Droppings: Small cylindrical pellets, 6.4mm -9.0mm long.
Footprints: Four-toed forefeet and five-toed hindfeet.
Kill signs: Similar to ship rats, including shell fragments in preyed-on nests, parallel double incisor marks in chewed flesh, neatly chewed holes in snail shells.
Vegetation damage: Similar to ship rats, such as seeds with neatly chewed holes to access contents, larger fruit may show parallel double incisor marks, damage to growing tips of some species may occur.
Information Source: Pest Detective www.pestdetective.org.nz
Photo credit Predator Free NZ.
FERAL CATS
Cats are unusual in that they are a predator of our native species as well as pets and companions for many people. A feral cats lives in the wild and differs from domestic cats as they have none of their needs provided for by humans.
Feral cats are generalist predators, with a diet that varies depending on what habitat they are in. They eat mostly birds, lizards and invertebrates, scavenge readily and can travel long distances. Ground nesting birds and bats are particularly vulnerable to feral cat predation. They are highly skilled apex hunters — apex means nothing preys on it.
Controlling feral cats needs to be done as humanely as possible and live capture traps are one of the best tools available. Live capture traps also allow users to confirm if the cat is an owned domestic cat or not. If you have a problem with unowned or feral cats we recommend you contact Auckland Council or the Department of Conservation.
History of Cat Introduction
New Zealand’s taonga (native wildlife) evolved over millions of years, isolated from the rest of the world, so they didn’t develop defences against mammalian predators such as cats. Cats were one of the first introduced species to establish in New Zealand, they arrived with European ships in 1769 as cats were carried onboard to keep rat numbers down. 50 years later there was an established feral cat population. Cats were then deliberately released in the 1870s in an attempt to control rabbit numbers.
Cats are highly skilled hunters and are known to kill all kinds of native wildlife including birds, bats, lizards and insects. Cats are an apex predator in New Zealand , this means nothing preys on them and therefore humans need to minimise their impact on our ecosystems as much as possible.
What you can do to help
Responsible cat ownership is important. It includes microchipping cats, desexing, limiting the number of cats per household and keeping cats inside as much as possible at night. Add bells to your cats collar, the more bells the better. Bells don’t completely stop hunting but they do minimise it.
Auckland Council supports neutering and micro chipping of domestic cats and provides funding to the local vet so that this service can be done at a discounted rate.
Video credit DOC
ARGENTINE ANTS
Argentine ants are one of the world’s most problematic ant species. They are aggressive and territorial, so while they are not poisonous, they can bite people.
Unlike other ants, Argentine ant nests cooperate with each other and can build ‘super-colonies’. They form these by connecting their nests through cooperation between worker ants, enabling a high density of nests which can grow to huge numbers.
The colonies have massive appetites, making them more aggressive and destructive because of their sheer numbers.
How to spot them
We know of Argentine ants in many parts of Auckland, Northland, Waikato, Bay of Plenty, Hawke’s Bay, Wellington, Nelson and Christchurch.
The best way to tell them from other ant species is by their colour and trails. They are:
- 2-3 mm long
- honey-brown (most other ants seen in New Zealand are black)
- often moving in large, distinctive trails of five or more ants wide and close together like a multi-lane motorway
- able to readily climb trees.How do they threaten native species?
Besides being a major household and garden pest, Argentine ants pose a serious threat to our natural areas and biodiversity because of their aggressiveness and appetite.
Argentine ants kill and displace native invertebrates that many indigenous species depend on. They will eat lizards, bird eggs and newly hatched chicks, potentially threatening endangered populations.
During spring and summer, when nests are expanding, they have an insatiable appetite for protein and sweet foods such as honeydew and nectar. Because their diet spans all food types from insects to nectar, they take food sources away from:
- kiwi
- nectar-eating birds such as tuis, bellbirds and silvereyes
- lizards like skinks and geckos
- native invertebrates.
Help stop the spread
It is important to report findings of Argentine ants. If you believe you have discovered Argentine ants in your home or garden, please contact pestfree@nullaucklandcouncil.govt.nz
Nests can be found in a variety of commodities, especially those associated with the ground and which can easily be moved from place to place. You can help to make sure that they are not moved around by checking the following before moving:- potted plants (these have the highest risk of spread)
- garden soil, bark, and building materials, especially in bags
- camping gear, especially when visiting in and around reserves
- inside kayak and dingy cavities.
Information courtesy of DOC https://www.doc.govt.nz/nature/pests-and-threats/animal-pests/argentine-ants/
Video credit Kurzgesagt
PEST fish
Prevention is key
Many of the waterways in mainland Auckland have been invaded by pest fish including Gambusia (also known as mosquitofish), koi carp, catfish, perch, rudd and tench.
Even goldfish can become pests when released into the wild. They breed quickly and degrade freshwater ecosystems.
These fish have either been accidentally or deliberately released and aquarium releases is an ongoing problem
There are no known freshwater pest fish on Aotea/Great Barrier Island, and it is a priority to keep it this way to preserve the outstanding natural values of the streams and wetlands on the island.
Pest fish cause degradation of our lakes and rivers through:
- Resuspension of sediment through feeding methods making the water murky
- Increasing nutrient levels and algal concentrations.
- Competition, with native fish species like whitebait species
- Predation of native invertebrates (koura) and fish species.
- Grazing of native aquatic plant communities
Once pest fish have become established it is very difficult to remove them, so prevention is key.
If pest fish became established in Aotea waterbodies it would be costly and logistically difficult to remove them.
Under the Auckland Council RPMP pest goldfish are listed as an exclusion species on Aotea. This means it is illegal to move goldfish to Aotea or breed and distribute them on the island. However, if you already own a goldfish you can still keep it on the island as long as it is securely contained in an aquarium or outdoor pond.
If you have pet goldfish in an outdoor pond make sure they are securely contained so they don’t get washed away into other waterbodies in a flood.
Never release pet fish into waterways.
If you are aware of any pest fish or observe any ‘different’ looking fish in the waterways around Aotea or for further information please contact the Auckland Council Service Centre 09 4290 258
Top to bottom: Goldfish and Catfish
Freshwater gold clam
The freshwater gold clam (Corbicula fluminea) is a small shellfish that reproduces rapidly and can clog water pipes and possibly overrun native species.
Please see link below:
CFW2023 Stop Gold Clam DL factsheet