in the last 20,000 years or so, spread of human populations into new areas has resulted in waves of extinction

• arrival of humans in North and South America from northeastern Asia some 20-30,000 years ago was followed by extinction of many large vertebrates (giant beaver, camels, horses, ground sloths, giant bison, elephants, large birds)
• arrival of Polynesians in Hawaii and New Zealand (about 1000 years ago in each case) resulted in rapid extinction of large flightless birds (flightless ibis and goose on Hawaii, ostrich-like moas on New Zealand)
• spread of Europeans, firearms, and introduced species (species brought intentionally or unintentionally by humans to places where they did not occur previously) since 1500 has resulted in waves of extinction everywhere ... especially on islands

from 1600 through 1965, some 168 species of birds became extinct . . .

• 30 because of hunting (for various purposes, including intentional efforts to exterminate a species)
• 43 because of predation or habitat destruction by domestic animals (sheep, goats, rabbits, dogs, pigs, and especially cats -- 32 extinctions ascribed to cats alone)
• 24 because of mammals introduced by humans (rats, mongooses)
• 3 because of introduced diseases
• 68 because of habitat destruction by humans (including 28 because of destruction of forests)

of these 168 species, 101 are documented with preserved scientific specimens (Clements Checklist of the Birds of the World, sixth edition, 2007) -- these species thus do not include most extinctions before 1800 when preservation of scientific specimens began -- these species were last seen in the following periods ...

• 1600-1699 ... 1
• 1700-1799 ... 6
• 1800-1849 ... 11
• 1850-1899 ... 27
• 1900-1949 ... 40
• 1950-1999 ... 16

some extinctions (or near extinctions) are easily understood . . . Great Auk, a large flightless relative of the Puffin, was killed with sticks by sailors for food on its breeding islands off the coasts of Newfoundland and Iceland (last ones killed in 1844) ... probably occurred south to NC during winter

some are not . . . Carolina Parakeet extinct by 1925 after a prolonged and mysterious decline -- once a common bird in the Southeast . . . my hunch is they were overexploited by humans who raided their nests for young to be sold as pets (the problem facing a large fraction of the world's sveral hundred species of parrots) . . . farmers also shot them when they ate fruit in orchards but this activity does not seem likely to have resulted in their extinction

species on islands are particularly susceptible to extinction

Hawaiian honeycreepers are a good example -- they occur only on the Hawaiian islands isolated in the middle of the Pacific -- a common ancestor radiated into 47 known species -- a distinctive phylogenetic family (or subfamily) of finches (family Drepanidae) -- morphological and behavioral specializations covered every imaginable ecological niche for small birds (seeds, nectar, insects in foliage, insects in bark) -- including an alternative for woodpeckers (no woodpecker ever colonized the Hawaiian islands) -- a short lower half of the bill is used to chisel into bark and a long upper half of the bill is used to probe for beetle grubs (woodpeckers use the entire bill to chisel and a specialized tongue to probe)

15 of these species became extinct after Polynesians colonized Hawaii (about 1000 years ago) -- 16 more have become extinct since the first Europeans arrived (1778) -- including 2 species (one with multiple subspecies) since 1998 -- most of the remainder are now endangered

causes of extinction are not clear in any case -- all possibilities for human impacts have probably played a role (see more about Hawaiian honeycreepers)

Hawaiian honeycreepers are an extreme case of radiation and extinction on islands -- but similar (less extreme) patterns of evolution and extinction have occurred on oceanic islands everywhere in the world -- New Zealand, islands of the Indian Ocean, islands of the Caribbean . . .

Dodo was a giant flightless pigeon that evolved on Reunion, an isolated island in the Indian Ocean -- extinct within 100 years after its discovery in 1600's -- like the Great Auk they were clubbed to death by seaman who wanted meat to eat (so they would not die of scurvy)

because oceanic islands are remote, most of these extinctions have attracted little publicity -- the Dodo was the first vertebrate extinction that attracted attention in Europe -- but it was widely doubted until well into the 1800's over a century after the last Dodo had died

what finally convinced people to rethink the role of humans on earth were several extinctions and near-extinctions in North America . . .

American Bison provide a gruesome example of a species that came close to extinction -- once perhaps numbering 60 million from North Carolina through the Rockies -- by 1850, as result of increase in human populations, hunting, and destruction of forests, bison limited to about 40 million, mostly on the Great Plains -- in 1867 and 1868 treaties with Great Plains tribes gave verbal agreement to preserving their hunting grounds in certain areas -- in 1871 manufacturers in Europe and United States discovered a way to cure bison hides to make leather and thus hunting for hides became lucrative -- in 1872 Dodge City founded (originally Buffalo City) for outfitting "buffalo" hunters and shipping hides -- hunters learned to kill 50-100 animals at a time by stalking on foot and shooting old females first

by 1874 bison exterminated in Kansas, hunters moved into Texas, treaties ignored, bloddy skirmishes with natives (culminating in "Custer's Last Stand" in present-day Wyoming in 1876) -- in 1874 and 1876, attempts in Congress to outlaw killing of bison failed (pocket veto by President Grant in '74, failed in Senate in '76) -- winter of 1876-77, peak of Texas slaughter, some 1500 hunters at work -- 1879, end of hunting in Texas, northern herds discovered wintering in Montana -- 1881, hunting in Montana began on large scale -- 1883, only small remnants remained -- 1886, Smithsonian Institution organized an expedition to secure specimens for their collection before the species was extinct, collected about 25 animals after intensive search in Montana

surviving bison estimated not to exceed 1000 animals, including 500 that escaped notice for many years in northern Canada, 200 in Yellowstone National Park (established by Congress in 1872 without much publicity), and 300 in private ownership -- in 12 years (1871 through 1882) some 40 million bison killed (9,000/day! assuming even distribution of killing) -- bison were skinned, carcasses left to rot, in such numbers that years later many places still had piles of bleached "buffalo" bones -- after protection from hunting, bison populations recovered -- animals that eat grass (geese or bison, for example) do well if hunting is regulated

Passenger Pigeons provide another example of nearly unbelievable human rapacity -- unlike bison, they are now truly and forever extinct -- after this extinction (about 100 years ago) it became harder to argue that humans could not wipe out a species

four times the size of our familiar Mourning Doves, Passenger Pigeons depended for food primarily on nuts and acorns, which trees in any one area tend to produce in large quantities every 3-4 years -- the pigeons' name comes from their dramatic movements from one feeding ground to another -- such flocks involved almost unbelievable numbers of birds -- one in Kentucky about 1805 passed overhead for more than four hours and was at least a mile wide and a number of pigeons deep . . . assuming modest flight speed of 25 miles/hour, this flock exceeded 100 miles X 1 mile or 300 million square yards in area and perhaps 1 billion pigeons in all . . . and such reports were not unusual

these enormous flocks would roost in square miles of forest every night during winter and fly 50-100 miles each day to feed -- roar of their wings, rain of their droppings, cracking of breaking branches masked the sounds of hundreds of guns firing all night long to kill pigeons

Passenger Pigeons also nested in enormous aggregations, mostly in northern states where beech nuts or acorns were abundant -- one colony in Wisconsin covered 40 square miles of forest, with as many as 90 nests in one tree (perhaps 50 million nests, many other colonies this large were also reported)

these large aggregations attracted hunters (originally native Americans, later mostly market hunters) -- pigeon squabs were shipped to large cities for food -- feathers were used for bedding -- carcasses were fed to hogs

by 1800, numbers were drastically reduced east of the Appalachians, probably mostly a result of clearing the forests -- west of the mountains, the story is hard to follow, partly because large groups of pigeons moved around to find good feeding grounds (they were abundant in one area for a while then became scarce when they moved elsewhere) -- by 1870, still enormous numbers in the states around the Great Lakes -- even in 1880's, substantial aggregations nested in Wisconsin and Pennsylvania -- by 1870, however, slaughter was unmitigated -- every nesting colony and every winter roost was subjected to relentless killing -- after 1885, flocks became scarce -- in 1891, one hunter killed 2,000 -- in 1895, still reports of flocks of more than a hundred -- in 1900, last known wild Passenger Pigeon shot in Ohio -- in 1914, last bird died in Cincinnati zoo

New York passed a law protecting nesting colonies (no shooting within 1/4 mile) in 1856, Wisconsin in 1877 -- these laws evidently seldom enforced -- only state to give full protection to this species was Michigan in 1897 (!!) -- in 1909, ornithologists and conservationists could not believe the Passenger Pigeon was extinct -- offered a total of $2000 in rewards (worth 20X as much in present-day dollars) for information about nesting colonies -- with no takers!

why did this species become extinct? -- surely, not all (not even the last thousands) were killed by humans -- yet, unlike American Bison, Passenger Pigeons failed to outlast human slaughter . . .

Passenger Pigeons laid one egg a year -- low fecundity suggests high survival as adults -- populations of long-lived animals can be in danger of extinction from failure to reproduce long before the last ones die (other examples today include California Condor and Wandering Albatross) -- disruption of nesting colonies must have reduced production of young birds long before a decrease in the numbers of adults was noticed -- furthermore, the forests of eastern North America were fast disappearing and with them the supplies of beech nuts and acorns

unexpected demise of the Passenger Pigeon alerted people in the United States and in England to the possibilities when species are subjected to unregulated hunting -- stimulated more effective conservation efforts in the United States -- Lacey Act in 1894 prohibited poaching in national parks (especially elk and bison in Yellowstone)

demand for feathers for women's hats and feather boas nearly doomed egrets (white herons) and terns (relatives of gulls) between 1880 and 1920 -- National Audubon Society organized to protect these birds -- two NAS wardens guarding some of the last colonies of nesting egrets in Florida and SC were shot and killed by poachers

in response Congress finally passed the Migratory Bird Protection Act (1918) -- prohibited killing, capturing or possessing native birds except certain game species in hunting seasons -- today egrets are again common birds -- in early 1990's NAS changed its traditional logo (a Great Egret in flight) on grounds that the egret is no longer a suitable symbol for conservation(!!) -- but they have reversed this decision

pesticides were responsible for near extirpation of Ospreys, Bald Eagles, Peregrines, and Brown Pelicans in U.S. -- DDT (and other persistent chlorinated hydrocarbons like dieldrin and aldrin) became widely used in the 1950's -- DDT is not degraded or excreted by vertebrates (or invertebrates) -- accumulates in the bodies (dissolved in lipids) of long-lived predators that eat insectivorous birds or fish that injest DDT from the environment -- DDT interferes with estrogen metabolism -- in birds estrogen stimulates calcium deposition in bones prior to egg-laying for use in producing egg shells -- DDT also specifically inhibits carbonic anhydrase -- enzyme in females' oviducts necessary for deposition of calcium in the egg shell -- birds contaminated with DDT thus laid eggs with shells so thin that the birds broke them during incubation

by 1970, Ospreys, Bald Eagles, and Brown Pelicans had decreased to a few small remnants in the lower 48 states, Peregrines were extirpated in eastern North America -- the ban on use of DDT in the US in 1974, Ospreys and Brown Pelicans recovered dramatically -- Peregrine and Bald Eagle populations have been laboriously re-established with birds bred in captivity -- birds migrating to the tropics today still spend most of the year in habitats contaminated with DDT (American firms exported DDT to Latin America until about a decade ago!)

habitat destruction is the major cause of extinctions in second half of this century -- Ivory-billed Woodpeckers are now extinct (reports in 2004 that a few survive have yet to be confirmed) -- a victim of virtually complete destruction of the old-growth bottomland forests of the southeastern U.S. -- between 1937 and 1977, about 250,000 acres (400 square miles) of bottomland forest were cleared each year in the lower Mississippi valley -- only remaining big tracts of old-growth forest in the US are northwestern coniferous forests in northern CA, OR, WA and southeastern AK, the habitat of Spotted Owls -- most of this forest is already drastically fragmented -- what will happen to America's old-growth forests?

wetlands are another habitat disappearing fast in the U.S. -- and with them our populations of waterfowl -- many of the ducks that winter along the coast of North Carolina breed around small marshy lakes ("potholes") in the northern Great Plains of US and Canada -- intensive agriculture has resulted in losses of 50,000 acres of these wetlands each year in recent years -- loss of salt marshes along the Atlantic coast has occurred almost as fast -- continent-wide populations of Pintails (most abundant duck in North America) dropped from 10 to 2.5 million birds during 1960-1990 -- devastating floods in the Mississippi valley in the summer of 1993 also resulted in part from loss of wetlands in the northern Great Plains

some states passed laws restricted the draining of wetlands on the Great Plains -- Conservation Reserve Program (a result of the Farm Bills of 1985 and 1990) began large-scale reimbursements for farmers who preserved wetlands -- populations of ducks partly recovered -- in 2008 higher prices for corn (as a result of increased production of biofuels) once again increased conversion of wetlands to farmland -- what will happen to America's wetlands in the next decade?

there are some general lessons from these histories . . .