The names cormorant and shag are used almost interchangeably. If fact, which you prefer might be more a function of where you live than the species you are referring to. That said, if a species has a crest, that raises the odds of it being termed a shag.

There is not agreement about how many genera there should be for the cormorants. This presentation has used only two: Microcarbo for the smaller cormorants and Phalacrocorax for everything else. The cormorants with blue eye-rings, commonly referred to as blue-eyed shags, are often split into genus Leucocarbo.

Every species of cormorant swims underwater to catch fish for eating. They have thus evolved certain characteristics to aid their aquatic hunting. Webbed feet are an obvious must for efficient swimming; all ducks have them too. But not all ducks swim underwater, many are so buoyant that it is physically impossible for them get their entire body under the surface of the water.

Cormorants have evolved to be dense birds so that when they are underwater, they have about the same density as their surroundings. They have to spend little energy fighting buoyancy. In order that their feathers do not retain lots of air when they submerge, they do not produce as much water repellant oil as do ducks. The saying is “like water off a duck”, not “like water off a cormorant”. As a result, a characteristic posture for cormorants is standing facing the sun with their wing outspread to dry.

Cormorants pay a price for their underwater efficient design. They have to work harder than most birds at flying. Take off is particularly challenging. To help get into flight mode, cormorants typically use their webbed feet to run along the surface as their wings beat energetically. And after liftoff is successful, their initial flight is close to the water so that the downward beat of the wings will get some lifting pressure reflected from the water surface.

While they are graceful underwater, on land they are clumsy walkers because their feet have been optimized for swimming, not walking. As a result, they walk as little as possible. When is the last time you saw a cormorant walk?

Cormorants catch their prey by pursuing it – swimming rapidly after it. Some species try to limit the escape route of the potential meal by hunting close to the sea bottom. And of course there are not just fish in the sea: worms, eels, mollusks, crustaceans, octopus, said and more are on their menu.

When is a cormorant not a cormorant? When it is an anhinga! Anhingas look and act like cormorants, but they are distinctive enough to merit their own family Anhingidae. There is just one genus anhinga and four species. Contrasted with cormorants, anhingas have wider tails and thinner, more pointed bills.

To learn more about cormorants in general, see Cormorants – The Master Divers by Raeesah Chandlay.

These are the smallest of the cormorants. They are found in Europe, Asia, Africa, Australasia.

Description: The Reed cormorant has a relatively long tail, and for that reason it is also known as the long-tailed cormorant. It has black legs and a yellow bill with red or yellow skin at the bill’s base and also the lores. During breeding season it has glossy black plumage and a short crest. In the rest of the year the long-tailed cormorant has blackish-brown upperparts and whitish underparts. Southern races may retain their head crest after the breeding season.

Range: sub-Saharan Africa.

Habitat: Prefers freshwater ponds, rivers, marshes, protected coasts. Usually hunts in shallow water; can dive deep.

Diet: Slow moving fish; also frogs, aquatic invertebrates, small birds.

Conservation status: Least concern.

Description: The crowned cormorant has a small crest at the front of its crown. It has all black plumage, but red eyes and red facial skin around the lores. Juveniles have dark brown upperparts, paler brown underparts, and no crest. The red eyes of the crowned cormorant are unique among small African cormorants. It was previously considered conspecific with reed cormorant, which has a longer tail.

Range: southwest Africa, from Angola to southwest South Africa.

Habitat: Mainly marine, going perhaps only 100 m inshore to roost or breed. Keeps within 10 km of shore. The population appears to be stable, but there may be less than 10,000 birds.

Diet: Fish, small crustaceans.

Conservation status: Near threatened.

Image By Ryanvanhuyssteen

Description: The little pied cormorant, also known as the little shag, is a black and white bird: black above and white below. The contrasting black and white plumage is sufficient to identify this species. It has dark lores, a short yellow bill, and black feet. In New Zealand some little pied cormorants have mostly black underparts with a white throat.

Range: Australia, New Guinea, New Zealand.

Habitat: Lives near bodies of water such as swamps, lakes, lagoons, estuaries, the coast.

Diet: Mainly fish, crustaceans; also eels, insect larvae.

Description: The little cormorant is slightly smaller than the Indian cormorant. It has a shorter bill than the Indian cormorant, while the latter has a relatively peaked head. The little cormorant has black plumage, black feet, and black eyes. When not in the breeding season, the plumage has a brown tinge to the black and there is often a white patch on the throat. During breeding season there may be some white facial spots.

Range: Indian Subcontinent and east to Java.

Habitat: Lives near freshwater: small ponds, large lakes, streams; sometimes coastal estuaries.

Diet: Fish; maybe sea urchins.

Image By MV Bhaktha

Description: The nonbreeding pygmy cormorant has brown plumage which is darker on the back. It has a pale greyish bill. During breeding season it has black plumage, a black bill, and a short erectile crest. The pygmy cormorant is very like the little cormorant, but the crest is often more noticeable in the pygmy cormorant.

Range: Southern Europe; southwest Asia. About 3/4 population lives in Europe.

Habitat: Prefers waterbodies with vegetation; especially rice fields. During winter, estuaries make the list.

Diet: Fish.

Some species in this genus are termed blue-eyed shags, which refers to eye-rings, not eye color. They are the Antarctic shag, imperial shag, Kerguelen shag, Macquarie shag, South Georgia shag, and white-bellied shag. Some consider them all as subspecies of the imperial shag. The blue-eyed shags and others with similar plumage are often put in a separate genus Leucocarbo. Note: the terms shag and cormorant are used indiscriminately with these species.

The White-bellied shag is also considered to be a subspecies of the the imperial shag. In that case its scientific name is Phalacrocorax atriceps albiventer.

Description: The white-bellied shag has black upperparts and white underparts. Since it is only found on the Falkland Islands, the white belly of this cormorant is sufficient to identify it.

Range: Falkland Islands.

Habitat: Primarily rocky coastal regions.

Diet: Fish, crustaceans, octopus.

Description: The European shag, also known as the common shag, is a medium sized cormorant which has black plumage and a yellow gape. It has a long thin tail. In the breeding season there is a greenish sheen to the plumage. The great cormorant is larger than the European shag and has a thicker bill.

Range: Iceland, Europe (coastal Scandinavia to Mediterranean), southeast corner of Asia, northwest Africa.

Habitat: Coastal, rare inland.

Diet: Fish, eels.

Image By Andreas Trepte

Description: The imperial cormorant (shag) has blue eye-rings and may be referred to as a “blue-eyed shag”. It has black upperparts including the nape. The underparts including the fore-neck are white. The imperial cormorant has an orange-yellow nasal knob, pinkish legs, and pinkish feet. In breeding season there is a black erectile crest. The rock shag is similar, but has an entirely black neck. However, some shag species with blue-eye rings are difficult to distinguish from the imperial cormorant. Identification is often based on location and may not be accurate.

Range: southern Argentina and Chile.

Habitat: Primarily rocky coastal regions; also large inland lakes.

Diet: Fish, crustaceans, octopus, worms.

Description: The double-crested cormorant is the most numerous and widespread of the 6 North American cormorant species. It has black plumage and a bare patch of orange-yellow facial skin. There is a small black-and-white crest during the breeding season. Juveniles have lighter upperparts and whitish underparts. The great cormorant is larger and bulkier than double-crested cormorant while the double-crested cormorant has more yellow on its throat and bill. The neotropic cormorant is smaller than double-crested cormorant and usually has a longer tail.

Range: Mainly North America, also Central America.

Habitat: Near coasts, rivers, lakes. Dives down to 8 meters (25 ft).

Diet: Mainly fish; also amphibians, crustaceans.

Breeding P. A. Albociliatus (Image By Mike Baird)

Description: The guanay cormorant is a major producer of guano deposits, hence its name. It has black upperparts, head, and neck. The underparts are white. There is red facial skin, a grey bill with some red at base, and red feet. The guanay cormorant has similar coloration as the rock cormorant, but the former is larger.

Range: Pacific coast South America; mainly Chile, Peru.

Habitat: Mainly located off shore islands.

Diet: Mainly Peruvian anchoveta, a small plentiful fish.

Description: The Antarctic shag (cormorant) has blue eye-rings and sometimes be referred to as a “blue-eyed shag”. It has black upperparts including the head. Its black wings have white wing-bars. There is a yellow fleshy patch above the bill, a white patch on the back, and pink feet. During the breeding season there is a crest on head.

Range: Antarctic Peninsular and nearby islands.

Habitat: Marine. Inhabits coasts and island.

Diet: Fish, crustaceans, octopus, squid.

Description: The neotropic cormorant mainly has black plumage and a yellow-brown throat porch. In the breeding season there are white tufts on the sides of the head and the throat patch has white edges. Juveniles have brownish plumage. The neotropic cormorant is small and slender compared to the larger, double-crested cormorant.

Range: Extreme south US to tip of South America. A very large range for a cormorant.

Habitat: Coastal and inland waters. Adapts to diverse habitats; which explains its large range.

Diet: Fish, frogs, insects.

Breeding (Image By Dario Sanches)

Description: The Campbell Islands shag, which is also called the Campbell shag, has blue eye-rings and is sometimes referred to as a “blue-eyed shag”. It has black upperparts, neck, and head. The underparts are white and some of these shags have white wing-bars.

Range: Cambell Island (south of New Zealand).

Habitat: Stays within 10 km of Campbell Island; also its rocky shores.

Conservation status: The Campbell Island shag is listed as vulnerable because it breeds only on one island. However, the population seems to be doing quite well has rats and cats on Campbell Island seem have been eliminated.

Description: The cape cormorant has glossy black plumage with a purplish tinge during the breeding season. It does not have a crest, but it does have orange-yellow facial skin. Unusual for cormorants, a flock of cape cormorants will fly above the water searching for fish. When found, they will then swim after the fish in pursuit.

Range: coastal Angola, Namibia, South Africa.

Habitat: Often found at open sea, within 10 km of shore.

Diet: Fish, crustaceans, mussels.

Conservation status: The cape cormorant is listed as endangered as it periodically suffers great losses due to disease or prey moving due to environmental changes. There still may be over 100,000 individuals, but their future is in doubt.

Description: The Japanese cormorant, also known as Temminck’s cormorant, has been domesticated for centuries by Japanese fisherman as helpers. It has a black body, white cheeks and throat, and a white patch on the flanks. The bill is partially yellow. The Japanese cormorant and great cormorant are very similar: “Japanese” has greenish upper-wing coverts while “great” has brownish.

Range: coastal east China and Russia; Korea, Japan, Taiwan.

Habitat: Located along the coast (not far inland) or the adjacent sea.

Diet: Mainly fish which they catch by pursuit swimming.

Description: Except for the subspecies white-breasted cormorant, the great cormorant has mainly black plumage. It has a long tail, a yellow throat patch, and white near its bill. During the breeding season there is white on its head. The white-breasted cormorant (Phalacrocorax c. lucidus) has white on its neck that extends to the upper-breast.

Range: East coast North America, Europe, Asia, Africa, Australia, New Zealand.

Habitat: Found at the coast, freshwater lakes and ponds.

Diet: Mainly fish. Most fish caught near bottom, some at higher levels. Dives to 6 meters (20 ft); stays under for up to 30 seconds.

Similar species:

P. C. Lucidus (Image: Dick Daniels)

Description: The New Zealand king shag, also known as the rough-faced shag or king shag, has yellow-orange caruncles (wart-like swelling) near the bill. Its scientific name carunculatus refers to that feature. It has black upperparts and a black tuft on the head. The underparts are white and the feet are pink. The grey gular pouch is reddish in the breeding season. With its blue eye-ring it is one of the “blue-eyed shags”.

Range: New Zealand.

Habitat: They hunt in coastal waters and nest on rocky islands.

Diet: Fish and crustaceans.

Conservation status: The king shag is classified as vulnerable due to egg and feather collection. It is now protected and the population has stabilized.

The Foveaux shag (P. stewarti) and the Otago shag (P. chalconotus) were both previous considered to be conspecific as the Stewart Island shag.

Description: The Otago shag has two morphs. The bronze morph has dark bronze plumage. The pied morph has bronze upperparts with a white patch on the folded wing and white underparts. It has blue eye-rings and is one of the “blue-eyed shags”. The Foveaux shag can be identified by the bright orange caruncles they have during breeding season which are lacking in the Otago shag.

Range: New Zealand (islets off Otago Peninsular on eastern coast of the South Island).

Habitat: Forages mainly along the coast, but also 10 or more km offshore. Roosts and nests on rocky shores.

Diet: Mainly fish; also crustaceans, squid, octopus.

Conservation status: The Stewart Island shag is now considered vulnerable. They were plentiful before New Zealand became populated with people. Now there may be about 5000, and the population may be still declining.

Description: The Auckland Islands shag has black upperparts and sometimes a white wing-bar. It has white underparts and a white throat. The Auckland Island shag has blue eye-rings and is one of the “blue-eyed shags”.

Range: Auckland Islands which are south of New Zealand.

Habitat: At sea or along the coast. Nests in rock areas and also flat ground.

Diet: Crustaceans and fish.

Conservation status: Considered vulnerable because there are less than 2000 birds and they do not have geographical diversity.

Image By Su Yin Khoo

Description: During the breeding season, the Pitt Island shag has black with bluish-gloss upperparts and neck, green facial skin, and two black crests on the head, one forward and the other aft. At other seasons the upperparts tend towards dull brown, facial skin dull yellow, and the crests become less prominent and may disappear. The underparts are white and the feet yellow.

Range: Chatham islands of New Zealand.

Habitat: The sea and coasts for foraging and rocky shores for roosting and breeding.

Diet: Mainly fish; also crustaceans.

Conservation status: The Pitt Island shag is endangered because of its small number, less than 1500. Population seems to still be declining, perhaps due to changing environment affecting its prey.

Description: The black-faced cormorant has black upperparts, bill, and facial skin. It has a black cap which extends below its eyes leading to its name. The underparts are white. The black-faced cormorant can be differentiated from the similar little pied cormorants and pied cormorants by the black that extends below their eyes. Juveniles have brownish-black upperparts with brownish-white face and neck.

Range: southern Australia.

Habitat: Mainly coastal and marine; also river estuaries.

Diet: Mainly fish; also squid and octopus.

Description: The Indian cormorant has a mainly dark appearance with bronzed wings. It has blue eyes, a small and slightly peaked head, and a long narrow bill that ends in a hook. During the breeding season the plumage becomes mainly glossy black versus brownish-black at other time. The similar little cormorant is lightly smaller than the Indian cormorant and has a considerably smaller bill.

Range: southern Asia.

Habitat: River inlets, mangroves, estuaries; not the open coast.

Diet: Mainly fish.

Description: As expected, the red-legged cormorant does have bright red legs and feet. It has mainly grey plumage with white spots on the wings and a white patch on the neck. The tail is black, the eyes are green, and the bill yellow.

Range: South America, mainly on the west coast.

Habitat: Near the shore and relatively close to its nest. It avoids freshwater.

Diet: Fish, especially anchovies, and eels.

Conservation status: The red-legged cormorant is considered near threaded because, even though its range is wide, it population density is small; and probably getting smaller.

Description: The South Georgia shag has black upperparts including the nape. It has a white wing-bar. The underparts are white, including the underside of its neck. During breeding season the South Georgia shag has an erectile crest and orange warty flesh (caruncle) above the bill’s base. With its blue eye-ring it is one of the “blue-eyed shags”.

Range: Islands between South America and Antarctica. Specifically South Georgia, South Sandwich Islands, and South Orkney Islands.

Habitat: Marine and inshore.

Conservation status: Not globally threatened.

Description: The flightless cormorant is the only nonflying cormorant. The wings are about 1/3 the size of what is necessary for flight. It has blackish upperparts, brown underparts, and turquoise eyes.

Range: Galapagos Islands.

Habitat: No more than 200 meters off shore. Nests on rocky shores.

Diet: Fish, octopus, squid, eels.

Conservation status: The flightless cormorant is listed as vulnerable. It evolved as flightless as it had no predators it needed to escape. Along with humans came dogs and cats which they cannot escape by flying. The population seems to be stable at about 1000.

Description: The Magellanic Cormorant, also known as the rock shag, has black upperparts, head, and neck. It has white underparts; red facial skin, and pinkish legs. During breeding season there is a small blackish crest and a white ear patch.

Range: South America (Patagonia, Argentina).

Habitat: It forages close to shore and does not dive much deeper than 10 meters. It nests on steep rocky cliffs.

Diet: Marine worms, fish, octopus, squid.

Similar to:

Description: The bank cormorant, also known as Wahlberg’s cormorant, has mainly black plumage with dark brown wings. It is glossy with a bronze sheen. The bank cormorant has a blackish bill, black legs, and yellow eyes.

Range: African west coast (Namibia and South Africa).

Habitat: Found coastal and up to 10 km offshore. Prefers kelp beds that house lobster. Mainly breeds on islands and rocky shores.

Diet: Fish, crustaceans, squid, octopus, mollusks.

Conservation status: This cormorant is endangered with a population that is declining due to fishing reducing their prey and more kelp gulls that eat their eggs and chicks. There are about 1000 birds left.

Description: The Socotra Cormorant has blackish plumage and blackish legs. During the breeding season it has greyish-green tinged upperparts and glossy purple-tinged fore-crown. It is found in the Persian Gulf and the southeast coast of the Arabian Peninsula.

Range: Persian Gulf of Asia.

Habitat: Very much a marine bird which nests on isolated islands.

Conservation status: The Socotra cormorant is listed as vulnerable, even though there are thought to be over a quarter million of birds. There is concern because of coastal development and pollution near its breeding sites.

Description: The Heard Island shag has mainly black upperparts with wide white wing-bars and white underparts. The cheeks and ear-coverts are also white, the bill is dark, and the feet are pink. During breeding season there is a crest on the head and orange fleshy patches (caruncles) above the bill’s base. The Heard Island shag has blue eye-rings and is one of the “blue-eyed shags”. It usually has more white on the upperparts than other shags in its range.

Range: Heard and McDonald Islands (Antarctic islands southwest of Perth, Australia).

Habitat: Prefers shallow coastal waters around their islands for hunting. They roost and nest mainly on cliffs, but also on beaches.

Conservation status: The Heard Island shag is vulnerable because of its small population which is around 1000. Any increase in commercial fishing could threaten their existence.

Description: The Chatham Islands shag has black upperparts including the head which is black. It has white underparts, a dark grey bill, and dull pink legs. The Chatham Islands shag has blue eye-rings and is one of the “blue-eyed shags”.

Range: Chatham Islands of New Zealand.

Habitat: Breeds along the coast, hunts within a few km of shore in sheltered areas.

Conservation status: The Chatham Islands shag is critically endangered because of humans disturbing their nesting areas and introduced predators such as feral cats.

Image By Biodiversity Heritage Library

Description: The pelagic cormorant has iridescent black plumage. It has black feet, a long thin black bill, and green eyes. During breeding season it has white flanks and one or two short black crests on the head. The patch of dark naked skin below the eyes turns red in the breeding season.

Range: Pacific Coast of North America and Asia.

Habitat: Sheltered bays and inlets, but also far out to sea. They nest on rocky coasts.

Diet: Mainly fish, also crustaceans.

Image By Blake Matheson

Description: The Brandt’s Cormorant has mainly black plumage, but it does have a white cheek patch. During breeding season there are white plumes on the neck and back; there is also at this time a blue throat patch. The Brandt’s cormorant can be differentiated from the similar pelagic cormorant by its white check and also its blue throat patch while breeding.

Range: Pacific coast of North America.

Habitat: Coastal environments such as estuaries and lagoons. Dives to 60 meters (200 ft).

Diet: Herring, rockfish and other readily available fish. Also shrimp, crabs.

Image By Becky Matsubara

Description: The Spotted Shag has brown upperparts with small dark spots. The underparts are mainly white, but the lower belly is black. The sides of the neck and the face are white. The crown and the throat are blue-green. The legs of the spotted shag vary from bright yellow to dull yellowish-brown. During the mating season the spotted shag has a black crest.

Range: New Zealand, mainly the South Island.

Habitat: Coastal and offshore up to 15 km. Does not frequent fresh water. They nest in on rock shores and cliffs.

Description: The Macquarie shag, named after its favorite island, has mainly black upperparts including the crown and nape. It has white wing-bars. The underparts, fore-neck and face are white. During breeding season there are orange fleshy growths (caruncle) above the bill’s base The Macquarie shag has blue eye-rings and is one of the “blue-eyed shags”.

Range: Macquarie Island and closely islets (between New Zealand and Antarctica).

Habitat: Breeds and roost on islands, other than that it is a marine bird.

Conservation status: The Macquarie shag is vulnerable because there are less than a 1000 birds and they live in a localized region. Severe weather or food shortage can be problematic and introduced rats add to their problems.

Description: The Bounty Islands shag, also known as the Bounty shag, has black upperparts and nape with a blue metallic sheen. The underparts are white and there is a white patch on the wings that appears as a wing-bar when folded. The feet are pink. The Bounty Islands shag has blue eye-rings and is one of the “blue-eyed shags”.

Range: Bounty Islands – which are southeast of New Zealand.

Habitat: Open seas and rocky shores.

Conservation status: The Bounty Islands shag is considered vulnerable because there are less than 1000 birds, plus it has have a small breeding range. The population does seem stable.

Description: The Foveaux shag has two morphs. The bronze morph has dark bronze plumage. The pied morph has bronze upperparts with a white patch on the folded wing and white underparts. It has blue eye-rings and is one of the “blue-eyed shags”. The Foveaux shag can be identified by the bright orange caruncles they have during breeding season which are lacking in the Otago shag.

Range: New Zealand (Stewart Island and Foveaux Strait).

Conservation status: The Stewart Island shag is now considered vulnerable. They were plentiful before New Zealand became populated with people. Now there may be about 2500, and the population may be still declining.

Image By Jim Scarff

Description: The little black cormorant has black plumage and black legs. Its long and slender bill is grey. The eyes are blue-green. Juveniles have brown and black plumage plus brown eyes. The little black cormorant is more brownish when it is not the breeding season.

Range: Australia, northern New Zealand.

Habitat: Mainly freshwater, occasionally coastal.

Image By Birdsaspoetry

Description: The red-face cormorant has glossy black plumage with greenish-blue iridescence. While in the breeding season it has orange or red facial skin and a double crest. The orange / red facial skin is slightly visible when not in the breeding season.

Range: Asia, Alaskan coast.

Habitat: Almost exclusively marine. Ventures a few meters onshore to roost and nest.

Similar to: Pelagic cormorant. The ranges of these two species are very similar and they often share the same breeding grounds. Breeding red-faced cormorants have extensive red on their face while the red of breeding pelagic cormorants is restricted to below their eyes. Nonbreeding red-faced cormorants still have some red on their face while Pelagic Cormorants don’t.

Description: The pied cormorant, also known as the Australian pied cormorant, has black upperparts and also black legs and feet. The black on the head stays above the eyes, below is white. The pied cormorant has white underparts and orange lores.

Range: Australia, New Zealand.

Habitat: Mainly marine, also ponds and lakes. Forages usually less than 10 meters deep (30 ft).

Diet: Mainly fish; also crustaceans, octopus, squid.

Description: The Kerguelen shag has black upperparts, tail, and thighs. It has blackish facial skin and a dark blue forehead. Some have white patches on the wings and back; The underparts and throat are white. There are orange fleshy bumps (caruncles) above base of bill. In breeding season they have brighter plumage and there is a small erectile crest. The Kerguelen shag has dull blue eye-rings and is the smallest blue-eyed shag. Juveniles are mainly dark brown, they lack caruncles, and have brown feet.

Range: Kerguelen Islands in southern Indian Ocean.

Habitat: The Kerguelen shag forages at sea, but usually within 6 km (4 mi) of shore.

Diet: Fish, crustaceans, worms. Hunt alone in summer; large group otherwise.

Similar to: Heard Island shags range rarely overlaps. “Heard” has white cheeks, “Kerguelen” doesn’t.

Image By Gazelle

Most cormorant population numbers are stable. However, several species are listed as vulnerable or endangered. The Chatham shag, which is endemic to the Chatham Islands, New Zealand is critically endangered due to human-induced disturbances at breeding colonies as well as the introduction of predators like wekas, possums, and feral cats.

Several other New Zealand species are also at risk, such as the Otago shag, the New Zealand king shag, the Campbell shag, the Auckland shag, and the endangeredPitt shag.

Other vulnerable insular species include the Socotra cormorant endemic to the Socotra Islands, the Macquarie shag endemic to the Macquarie Islands, the bounty shag of the Bounty Islands, and the black cormorant endemic to south-western coasts of Africa. Meanwhile, the Cape cormorant of the same region is listed as endangered.

What is the theme common to most of these species whose survival is challenged? They occupy a small piece of real estate, often breeding on just one island. To understand why an isolated species could be endangered, consider the following. Perhaps a hundred thousand years ago, a pair of Antarctic shags visited an island hundreds of kilometers further north from their traditional home and found the warmer climate to their liking. Their offspring proliferated and over the millennia developed features that enhanced their ability to survive in their new environment. They became a new species (Darwinism at work!)

They adapted so well they that they became content to limited their breeding to just that one relatively little island and forage close to it. Then a hundred years ago a wrecked ship inadvertently deposits rats on the island. Or maybe instead the world started warming so their favorite fish moved further south. Either way, that species would probably have a hard time adapting to their changing world. Its population could decline, and their survival could become “endangered”.

As small populations become endangered because of a world that we are causing to change, some of these species will not survive. Hopefully before that happens, we can save some of these threatened species by undoing the harm we have done and / or introducing those species to more promising locations. But introduction of a threatened species into a new location could create its own problems – it could become an invasive species!