It waited on the west bank of the Humber River, coiled up beneath packed soil like buried treasure.

Then, one summer day in 2011, crews working with the Toronto and Region Conservation Authority were loosening the earth at King’s Mill Park, laying dark patio stones for sunbathing snakes in the area, when they discovered the prize.

A ring-necked snake — the first sighting in Toronto in more than 25 years.

“It was amazing,” Karen McDonald, a TRCA project manager, said of the find. She had believed, as others did, that this species of snake had disappeared from the city decades ago.

She was delighted to be wrong.

The ring-necked snake is not the only species benefitting from restoration projects in the city.

The common raven, extirpated from the waterfront “decades ago,” has also been making a comeback, McDonald said.

“As we've been bringing back a lot of habitat that has been historically lost ... I think that that is really making a difference,” she said of recent waterfront restoration efforts.

Over the past two winters, a pair of ravens has been spotted courting and taking care of their young in one of the towers at the Portlands Energy Centre near Tommy Thompson Park.

The mink population may be on the rise, too. When McDonald started working at TRCA 13 years ago, mink sightings were rare. But in the past five years, she said, they have become so common that she stopped keeping track of them.

In 2010, residents with backyard ponds on Toronto Island started noticing, too — they watched the minks with curiosity and a touch of wariness as pond goldfish disappeared.

A restoration of the city’s wetlands may be what’s attracting the minks, according to a City of Toronto report on mammals published in 2012.

The mink itself plays a role in maintaining healthy habitats in the city. It feeds on the pesky round goby, an invasive species in the Great Lakes that preys on bottom-dwelling fish, as well as others’ eggs and young.

Although a mink wouldn’t complain about the numbers of goby swimming in Lake Ontario, the invasive fish are upsetting the balance of the local ecosystem.

The goby is among the more than 185 invasive animal species identified in the Great Lakes region. Native to Eastern Europe, the round goby was thought to have been brought over as a stowaway on a trade ship in the 1980s. But in Toronto’s waters, the goby puts the survival of many other sport fish in jeopardy.

Before it broke for the summer, the Ontario government was studying a proposed law that would enable the province to act sooner to prevent the spread of potentially dangerous animal species, such as the round goby.

While some animal populations are on the rebound, others have vanished.

Here’s a look at Toronto’s native, invasive and extirpated species.

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NATIVE

Northern Mockingbird (Mimus polyglottos): While its grey, white and brown feathers might not look very interesting, according to Karen McDonald, a project manager with Toronto and Region Conservation Authority, these birds are “fascinating.” “They mock other noises — and I say noises, because they don’t just imitate other birds, but they can also imitate pretty much any sound.” The mockingbird can be found in Tommy Thompson Park and areas such as Humber Bay Park.

Red Fox: “They look very wild when you see them,” according to Justina Ray, president and senior scientist at Wildlife Conservation Society Canada, pointing out the agile red fox’s iconic feature: its usually red and orange coat, accompanied by a long bushy tail. According to a City of Toronto wildlife report published in 2012, the red fox (Vulpes vulpes) lives in the city’s “utility corridors, parks and golf courses,” using ravines to travel at night. Though they keep to themselves, they can be spotted near the Don Valley, Ray said.

Raccoon (Procyon lotor): These are intelligent and highly adaptive creatures. They are “opportunistic,” according to Ray, who said that raccoons are more “abundant” in urban areas such as Toronto than outside busy cities, in part because of the resources and food available. According to the City of Toronto’s wildlife report, raccoons have “amazing dexterity and use their front paws to pry things open.” Raccoons aren’t picky about shelter and can be found under decks and in roofs, nestled into the insulation.

INVASIVE

Zebra and quagga mussels: Thought to have come from the ballast water of European tankers in the late 1980s, these mussels (Dreissena polymorpha and Dreissena rostriformis bugensis) gobble up food particles, making the water clearer. While that may sound good, it’s problematic because it deprives plankton and fish of food. The mussels have also been found clustering around the raw water intake pipes of Toronto’s water treatment plants.

Round Goby: This pesky fish with a spotted dorsal fin was brought over from the Black and Caspian seas. It was first spotted in Ontario in the St. Clair River more than 25 years ago. Round gobies (Neogobius melanostomus) are thought to be spreading botulism E. from the mussels they eat to fish-eating birds. After they become infected, the gobies swim in “aberrant patterns” and become easy prey to loons, gulls and other birds, said Hugh MacIsaac, the invasive species research chair at the Department of Fisheries and Oceans. According to one recent estimate, up to 10,000 loons in Ontario die each year due to botulism. Round gobies also harass native fish and eat anglers’ bait.

Emerald Ash Borer: Native to eastern Asia, this destructive green beetle (Agrilus planipennis) was first detected in the GTA in 2007. It is thought to have come to North America via cargo ships carrying solid wood packing material. The city expects the bug to decimate Toronto’s 860,000 ash trees by 2017. An ash tree usually dies within two or three years of infestation.

EXTIRPATED

Wood turtle: Extirpated in Toronto, and endangered in Ontario, wood turtles (Glyptemys insculpta) are threatened by habitat loss and predators such as raccoons, foxes and skunks. The province tried to protect the turtles by making it illegal to collect them as pets. The omnivorous turtle has a special method for hunting bugs: it stomps to bring earthworms out of hiding.

Black bear: Black bear sightings might still make headlines in Northern Ontario towns, but the species was chased from Toronto a long time ago. According to the City of Toronto’s report on city mammals, animals such as the black bear (Ursus americanus) that require vast forested or natural areas disappeared due to the commotion in the area two centuries ago.

The bear lost its large habitat and amount of food it needs when the land was cleared for factories, businesses and homes in the 1800s, McDonald said.

Eastern ribbon snake: This snake (Thamnophis sauritus) likes to hang around forest fringes and at the water’s edge, where it hunts prey. But when factories started taking over, the snake suffered habitat loss in a city that was starting to boom. “We have fragmented many of the meadow and forest areas, so these small snakes (had) a hard time getting around,” McDonald explained, adding that snakes became more vulnerable to becoming road kill because they like to bask on pavement.