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= Feral Cats as an Invasive Species =

Introduction
Domestic Cats (Felis silvestris Catus) have been introduced to many islands and have proven to have immense ecological impacts. The domestic cat has grown in population to approximately 148 to 188 million individuals. There are three types of cats. The house cat which has been domesticated. The stray cat which lives in multiple houses but usually prey on mostly wild animals. The feral cat which is independent of humans. The undomesticated cats that live on the island have had substantial negative impacts on the native wildlife. The population of feral cats is responsible for 14% of birds, mammals, and reptile extinctions, while currently affecting 8% of the critically endangered species.

Physical Characteristics of Domesticated and Feral Cats
There are 40 different distinct breeds of cats. These different breeds vary in looks, coat lengths, and other characteristics, but they vary little in size. The domestic cat ranges in weight between 5 to 10 pounds. Cats, likes humans, have five senses, but they tend to be more developed than humans. Domestic and feral cat utilize the same senses, but feral cats for hunting more than domestic cat.

Cats also have keen vision. Cat eyes contain cones that are responsible for color and binocular vision, the ability to judge speed and distance to enable better hunting skills. Cat eyes are better at seeing in the dark than humans. Although they cannot see in total darkness, they can see with 1/6 of the illumination we need. The muscles surrounding their pupil are able to narrow to a vertical slit in bright light and then open fully in dim lights which allows for maximum illumination. This characteristic may have developed for survival, as wild cats are nocturnal and most often hunt at night.

Hearing is an essential sense that allows cats to be effective killers. They are able to hear frequencies above that which the human ear can perceive. They use this ability to pinpoint sound locations, aid in balance, and be fast and agile.

The other two senses that go hand in hand are smell and taste. Cats have a less developed sense of smell which can affect their eating. This is because in the wild smell alerts the cat of what may be dangerous to eat. The taste of an item can do this for the cat as well, but if the feral cat ingests the substance without knowing the scent, then it may be at risk.

Competition
The negative impact that feral cats are causing is mainly due to their wide consumption of over 248 species, on 40 different islands. The break down of species affected are two fish, three amphibians, 27 mammals, 34 reptiles, 69 invertebrates and 113 birds. The three different types of cats have different effects on these numbers. The indoor cat will have little to no impact because they are kept inside away from prey. The stray cat can be considered an indoor/ outdoor cat that hunts only at certain times of the day. This may be because they seek shelter or have food provided to them that day. The last type of cat that creates the most damage is the feral cat. A feral cat has no permanent home, so its instincts help it to provide for itself at all times. In just the U.S. alone it is estimated that free-ranging cats kill 1.3-4.0 billion birds and 6.3-22.3 billion mammals annually. The majority of these animals are killed by the feral cats that hunt for a living. Based on these number this lists cats in the top 100 worst nonnative species in the world

Effects on ecological processes
Feral Cats can cause severe disturbances on islands, which is because islands have unique ecosystems because most of the animals evolved in isolation. Feral cats have had effects on seed dispersal and bird migration patterns. During migration birds complete stopovers. Birds choose their site specifically due to their refueling rate, foraging intensity, or predation risk. This meaning with a higher risk of predation in some areas due to cat presence than it will affect birds survival during migration because they are unlikely to stop and refuel if they are at risk for predation. Another process that feral cats have a severe effect on is seed dispersal. Cats prey on many different species on the islands, on the Canary Islands specifically cats prey on the giant lizards. This causes an effect on seed dispersal because the seeds on the islands are dispersed by lizards. The different sizes of lizards disperse different sizes of seeds, meaning the smaller seeds are dispersed a lot heavier because the smallest endemic lizards are less preyed on than giant lizards.

Control Factors
There are two types of control factors that have and are currently being used. These are trap and kill, and trap-neuter-return. Trap and kill as it sounds is just catching large amounts of feral cats and euthanizing them to create total eradication. This is done by capturing the animals and killing them by using carbon monoxide poisoning. Carbon monoxide poisoning is not used often because it is a slow and painful death that continues until the animal suffocates to death. As well another euthanizing method is lethal injection with sodium pentobarbital. This method is more humane and tends to be more widely used. Although, many choose to avoid the trap and kill method if possible due to the cruel nature.

The second method that is used is the trap-neuter-return. This treatment is completed by capturing feral cats and spaying or neutering, and vaccinating against rabies and distemper. In order to keep track of the feral cats that have been TNRed the left tip of the ear is clipped off. This method is more widely used because it is more humane, and if cats are removed from the environment it could disrupt the food chain.