WHY DO SPECIES GET ENDANGERED ?

HABITAT LOSS

A habitat is the ecosystem a species needs to live in - a swamp, rainforest, g, loss of farmlands and the creation of farmlands (more likely outside of the U.S., as in the rainforest of South America) threatens many ecosystems large and small. 

POLLUTION

Pollution can take many forms. Water, air and ground pollution are all related. Toxic substances dumped in a wooded area will destroy the soil and the species that live in it (from bacteria, to insects and the birds & animals that eat them) but it will also get into the groundwater below it. that water may lead to the same source of water that comes out of your faucet!! 

COMPETITION FROM OTHER SPECIES

Sometimes there are just too many animals living in an area that compete for the space, water and food that is found there. For example, in NJ, a large population of raccoons (which turned out to have a parasitic disease) threatened the last remaining population of woodrats in NJ.  
DISEASE 

By our definition, diseases occur naturally. We are not talking about diseases that animals get because of pesticides or pollution. It is a part of nature that animals get diseases. But sometimes humans introduce diseases and problems into a species. The most publicized example is DDT. An insecticide that was used all over the U.S., it was found in water & soil and eventually worked its way up the food chain from small water feeders to the fish who ate the plant life in the water and the animals and humans who ate the fish! When DDT was left into the water it eventually broke down and became DDE. These toxic substances (along with others like PCB's) caused eagles and peregrine falcons to produce eggs that had shells so thin that they broke just from the mother sitting on them.
PREDATION

Predators are species that hunt other species as their way of getting food. For example, a peregrine falcon will kill small rodents (like mice & voles) and even kill other birds to get food. This is natural and expected. There are no predators that cause extinctions in NJ and none that we could find in our research - unless humans had changed the predators or introduced other predator species.

UNREGULATED OR ILLEGAL KILLING

People were once predators that hunted and killed to get their food. In some parts of the world people still need to do that. But, in most parts of the United States that is no longer true. For us in New Jersey, our food comes from a store. But many people still enjoy hunting or fishing, and when they are successful they will use it to supplement their food.
Hunting and fishing is strictly regulated in the United States. In New Jersey, the agency in charge of it is the Department of Environmental Protection. Their Division of Fish, Game and Wildlife makes the regulations that protect species from being over hunted. When people disobey those laws, the state's law enforcement officers' job is to arrest them and make sure they are prosecuted by the courts and forced to pay fines or go to jail. Sometimes this killing is due to ignorance about species - as in the case of bats and snakes. The bobolink's story is a good example of unregulated killing, as is the better publicized story of whale hunting.

INTRODUCED SPECIES

Plants and animals are sometimes introduced by people to areas where they never existed before. Sometimes it happens accidentally. Seeds may catch on people's clothing or on their car and then be carried to another area where they begin to grow. Birds may carry seeds in foods they eat. This process is very natural. But what happens if people introduce new animal species into an area? What is some fisherman decide it would be great to have largemouth bass in a lake in their area - so, they get a bunch of them and dump them in the lake, hoping they will grow for next season. That action upsets the balance of nature and changes that pond! The bass might eat the same food as another fish that already lives their - now they will compete for food. The bass might even eat another fish that lives in the pond. If the bass reproduce they could end up threatening other species. Sometimes people might but a pet, such as a snake or reptile, perhaps a bird that does not live in their area. After a while they get tired of caring for it, or it gets too big - for some reason, they decide to "release it into the wild." Again, they will upset the ecosystem that they put it into. That snake could easily threaten the existence of a native snake.
When the state of New Jersey RE-introduces a species, such as the wild turkey, bald eagle, or bobcat, they do so after careful scientific studies. They also will monitor that species to make sure it does not endanger other animals. The wild turkey is a good example of a species that NJ has successfully re-introduced into the state as a game species and the bald eagle is a good nongame species example.