Bald eagles and peregrine falcons, quite visible in such national parks as Grand Teton and Acadia, are readily recognized as species that have been able to reverse their slide towards extinction thanks in large part to the Endangered Species Act.

And across the National Park System there are a good number of success stories where species, be they plant, animal, bird, fish, or invertebrate, have been helped by the ESA. Some stories are substantial:

* Grizzly bears, at least in the greater Yellowstone ecosystem, seem to be rebounding in number;

* Gray wolves have successfully been returned to Yellowstone National Park and removed, albeit controversially, from the Endangered Species List in some parts of their range in the Northern Rockies, and;

* Channel Island foxes, listed as endangered in 2004, have approached biological recovery on Santa Cruz, Santa Rosa, and San Miguel Islands within Channel Islands National Park, according to the Park Service. Four of the six subspecies of island fox declined by more than 90 percent by the late 1990s due to predation by golden eagles. Since 1999, 44 golden eagles have been live-captured and relocated to the mainland and the foxes have rebounded. Today, there are about 2,800 island foxes in the wild.  

Others stories, however, are more subtle. Red-cockaded woodpeckers, found in Big Cypress National Preserve and Everglades National Park, just to name two parks, did not go extinct as was predicted in the 1960s but the species also isn't about to be removed from the Endangered Species List.

Indeed, across the National Park System today, the fifth annual Endangered Species Day, there seems to be more stories whose happy endings have yet to be written than those with happy endings.

The Florida panther in Big Cypress and Everglades continues to want for more habitat, and the Kemp's ridley sea turtles that nest on the sandy beaches of Padre Island National Seashore still wear the tag of the "most-endangered" sea turtle. (Although, this year's nesting season on Padre Island so far seems to be particularly robust.)

In Glacier National Park, if not in Yellowstone and Grand Teton as well, there are concerns that climate change could melt the snowfields that wolverines, a candidate species for listing under the Endangered Species Act, rely on for denning. Cape Hatteras National Seashore has turned into a legal battleground over the future of piping plovers, a threatened species along the Atlantic Coast. In Yellowstone, crews bombard critical habitat for the Canada lynx, a threatened species, with 105mm howitzer rounds as part of their avalanche control work.

And, of course, the search for the Ivory-billed woodpecker continues -- in 2010 the Park Service spent $10,000 on this effort -- in the Southeast.

According to the National Park Service, there currently are 1,969 threatened and endangered species listed worldwide. A recent report in Science said, "On average, 50 species of mammal, bird, and amphibian move closer to extinction each year..."

NatureServe, the non-profit organization that maintains what is said to be the most complete list of imperiled species in the United States, has said that the "actual number of known species threatened with extinction is at least ten times greater than the number protected under the Endangered Species Act."

Many units of the National Park System, their landscapes left largely in their natural conditions, are vital to the recovery of threatened and endangered species.  Sometimes, though, even those protective boundaries can't produce miracles, as the futile efforts to bring the red wolf back to Great Smoky Mountains National Park demonstrate.

As of 2010, there were 421 species of federally listed plants and animals that occur or have historically occurred in the park system. The Park Service maintains a helpful web portal that allows you to search by park or species to pinpoint threatened and endangered species in the park system.

Some species that historically have been native to a park unit but are no longer found there still show up on lists of endangered and threatened species in the park as long as they haven't entirely vanished from the Earth. For instance, while brown (aka grizzly) bears once roamed Arches National Park, according to the Park Service, they no longer can be found in this unit of the park system but nevertheless show up listed as a threatened species in the park.

This website also lets you find out how much the
Park Service spent on a particular threatened or endangered species
during Fiscal 2010.

Here's a look at some of the ESA cases in the National Park System:

* Amistad National Recreation Area. This NRA shows six species that either are threatened or endangered, and one candidate species.

* Arches National Park. Four species -- two of which are not currently found in the park -- are listed as either threatened or endangered, one species is a candidate for listing, and two have been delisted.

* Apostle Islands National Lakeshore. Piping plovers, the same species as those causing problems at Cape Hatteras, are considered an endangered species at the lakeshore, which also is home to bald eagles and has even recorded presence of a gray wolf.

* Big Cypress National Preserve. The preserve is the heart of the population of Florida panthers, a population thought to number 100-130 or so adults. Listed as an endangered species since the arrival of the ESA, the big cats are struggling to cope with dwindling habitat and genetic issues. Nine other species -- American alligator, American crocodile, Cape Sable seaside sparrow, eastern indigo snake, Everglade snail kite, red-cockaded woodpecker, West Indian manatee, and wood stork -- are listed either as threatened or endangered.

* Biscayne National Park. Seventeen species -- including five sea turtle species and the West Indian manatee -- are listed as either threatened or endangered, and there is one candidate species in the park.

* Buffalo National River. Five species -- three varieties of bat and and two clam species -- are listed as endangered in this unit.

* Cape Lookout National Seashore. Seven species are listed as either threatened or endangered, including the American alligator, four sea turtle species, the piping plover, and seabeach amaranth.

* Chesapeake and Ohio Canal National Historic Park. Four species are listed as either endangered or threatened, including the shortnose sturgeon and Indiana bat.

* Delaware Water Gap National Recreation Area. There are three species considered either threatened or endangered here: the Indiana bat, bog turtle, and dwarf wedgemussel, a clam.

* Dinosaur National Monument. There are nine species considered either threatened or endangered at Dinosaur, including the brown bear, gray wolf, Mexican owl, and black-footed ferret, all of which are no longer found in the monument but which once were.

* Everglades National Park. There are 21 species -- among them the Florida panther, American crocodile and American alligator, and five sea turtle species -- listed as either threatened or endangered, and six candidate species.

* Gauley River National Recreation Area. Two species -- the Indiana bat and the Virginia spiraea, a flowering plant -- are either endangered or threatened.

* Glacier Bay National Park. The humpback whale and stellar sea lion are both considered endangered in this park.

* Grand Canyon National Park. There are 14 species listed as either endangered or threatened here, including the humpback chub, desert tortoise, and southwestern willow flycatcher.

* Grand Teton National Park. Two species -- the brown bear and Canada lynx -- are listed as threatened in the park, while the wolverine is a candidate for listing and as such treated as threatened by the Park Service.

* Great Sand Dunes National Park. Five species are listed as either endangered or threatened, including the Canada lynx, gray wolf, and brown bear, and there's one candidate species.

* Guadalupe Mountains National Park. There are three species listed as either endangered or threatened: Mexican spotted owl, gray wolf, and brown bear.

* Haleakala National Park. Thirty-six species -- including the Maui parrotbill, Pacific Hawaiian damselfly, Hawaiin monk seal, and Haleakala silversword -- are listed as either threatened or endangered, and there are 14 candidate species.

* Hot Springs National Park. Two species no longer found here -- the red wolf and piping plover -- nevertheless are listed as endangered at this park.

* Isle Royale National Park. There are three species listed as either endangered or threatened: the gray wolf, the woodland caribou, and the Canada lynx.

* Katmai National Park and Preserve. There are two species listed as either endangered or threatened for this park, the Stellar sea lion and the Steller's eider.

* Lake Mead National Recreation Area. This unit lists seven species as either endangered or threatened, including the desert tortoise and the razorback sucker.

* Lassen Volcanic National Park. The gray wolf is listed as endangered, although it hasn't been seen in the park in quite some time.

* Little River Canyon National Preserve. There are five species either threatened or endangered, including the blue shiner (a fish), gray bat, and Kral's water-plantain.

* Mesa Verde National Park. Six species are listed as either threatened or endangered, including the gray wolf, brown bear, and Mexican spotted owl.

* Mount Rainier National Park. There are nine species listed as threatened or endangered, including the gray wolf, bull trout, northern spotted owl, and Canada lynx.

* North Cascades National Park. There are eight threatened species in the park, none that are endangered.

* Ozark National Scenic Riverways. There are five species listed as either threatened or endangered, including the gray wolf, red wolf, and red-cockaded woodpecker. The Ozark hellbender, a large salamander, is listed as a candidate species.

* Point Reyes National Seashore. Twenty-seven species are listed as either threatened or endangered, including the southern sea otter, tidewater goby, and short-tailed albatross.

* Redwood National Park. There are 21 species listed as either threatened or endangered, including the blue whale, two salmon species, the finback whale, and western snowy plover.

* Saguaro National Park. Six species are listed as either endangered or threatened, including the jaguar, Mexican spotted owl, and lesser long-nosed bat.

* Sequoia and Kings Canyon national parks. Five species are listed as threatened or endangered, including the brown bear and California condor, and there are two candidate species.

* Tallgrass Prairie National Preserve. The Topeka shiner, a fish, and the Eskimo curlew, a bird, are both listed as endangered.

* Virgin Islands National Park. Ten species are listed as either threatened or endangered, including three sea turtle species, the humpback whale, and West Indian manatee.

* Zion National Park. There are six threatened or endangered species listed, including the gray wolf, brown bear, southerwestern willow flycatcher, and desert tortoise.

You can explore what threatened and/or endangered species can be found in your favorite park unit at this site.