Amass mortality event (MME), also known as amass die-off (or simplydie-off),[1][2] is an incident that kills a vast number of individuals of a single species in a short period of time.[3] The event may put a species at risk ofextinction or upset anecosystem.[4] This is distinct from the mass die-off associated with short lived and synchronous emergent insecttaxa which is a regular and non-catastrophic occurrence.[5]
Causes of MME's include disease and human-related activities such as pollution. Climatic extremes and other environmental influences such as oxygen stress in aquatic environments play a role, as does starvation. In many MME's there are multiple stressors.[4] An analysis of such events from 1940 to 2012 found that these events have become more common for birds, fish and marine invertebrates, but have declined for amphibians and reptiles and not changed for mammals.[6]
In March 1904, 1.5 million migrating birds died in Minnesota and Iowa during a strong snowstorm.[7] According toThe Guardian, this was the largest avian mortality event on record in the region.[7] Records of MMEs have been kept since the 1880s.[7] MMEs of this size are rare, however, and few before or since have been as big as the 1904 event. According to the records, MMEs "are always associated with extreme weather events such as a drop in temperature, snowstorm or hailstorm".[7]
In 1984, about 10,000caribou of the George River caribou herd—one of Canada'smigratory woodland caribou herds—drowned during their bi-annual crossing of theCaniapiscau River when theJames Bay Hydro Project flooded the region.[8]
In 1988, the deaths of 20,000harbour seals in theNorth Sea were found to be caused byphocine distemper virus.[9]
Ten years later, two strains of bacteria were implicated in the deaths of approximately 1,600New Zealand sea lions.[9]
OnMarion Island in 2007, some 250–300 adult malesubantarctic fur seals died in a two-week period. It was suggested, though not proven, that this gender-biased mortality was caused byStreptococcus sanguinis, a bacterium carried by thehouse mouse, an alien species accidentally introduced to the island in the 1800s.[9]
In 2003, a rain-on-snow event encased the ground in ice, resulting in the starvation of 20,000muskoxen onBanks Island in the Canadian Arctic.[10][11]
Shortly before midnight on New Year's Eve 2010, between 3,000 and 5,000red-winged blackbirds fell from the sky in Beebe, Arkansas. Most died upon hitting the ground, but some were living but dazed. Laboratory tests were performed and the Arkansas Livestock and Poultry Commission, theNational Wildlife Health Center in Madison, Wisconsin, and theUniversity of Georgia's wildlife disease study group procured specimens of the dead birds. In addition to the blackbirds, a fewgrackles andstarlings also fell from the sky in the same incident. A test report from the state poultry lab concluded that the birds had died fromblunt trauma, with an unlicensed fireworks discharge being the likely cause.[12][13]
The months-longDeepwater Horizon oil spill that began in April 2010 in the coastal waters of theGulf of Mexico resulted in about 600,000 to 800,000 bird mortalities.[14]Dolphins and other species of marine life continued to die in record numbers into 2013.[15]
The Beebe, Arkansas bird deaths were repeated again on New Year's Eve of the following year, 2011, with the reported number of dead birds being 5,000.[16]
On 3 January 2011, more than five hundred starlings, red-winged blackbirds, andsparrows fell dead inPointe Coupee Parish, Louisiana.[17]
On 5 January, "hundreds" of deadturtle doves were found atFaenza, Italy.[18] According to Italian news agencies, a huge number of the birds were found to have blue stains on their beaks that may have been caused by paint orhypoxia.[19]
Over the weekend of 8–9 January, "over a hundred" dead birds were found clustered together on a California highway, while "thousands of deadgizzard shad" (a species of fish) turned up in the harbors of Chicago.[20][21]
Between 28 December 2010 and 3 January 2011, 100 tons of dead fish washed ashore on theBrazilian coast.[22]
On 3 January, an estimated two million dead fish were found floating in theChesapeake Bay inMaryland.[23]
On 7 March, millions of small fish, including anchovies, sardines, and mackerel, were found dead in the area of King Harbor atRedondo Beach, California. An investigation by the authorities within the area concluded that the sardines had become trapped within the harbor and depleted the ambient oxygen, which resulted in the deaths. The authorities stated that the event was "unusual, but not unexplainable".[24]
On 14 January, approximately two hundred cows were found dead in a field inStockton, Wisconsin. The owner of the cattle has told deputies that he suspected the animals died ofinfectious bovine rhinotracheitis (IBR), orbovine virus diarrhea (BVD). Authorities in Wisconsin sent samples from thecarcasses to labs inMadison in order to determine cause of death.[25]
On 5 August, around 100 tonnes of dead fish, primarilymullets, were found floating inKarachi Port Trust waters, includingKarachi harbour, Manora channel, andChinna Creek.[26]
In 2015, some 200,000saiga antelope died within a period of one week in a 20 km2 (7.7 sq mi) area of theBetpak-Dala desert region ofKazakhstan. They had gathered in large groups for their annual calving. It was determined that warm and humid temperatures had causedPasteurella multocida, a strain of bacteria that normally lives harmlessly in their tonsils, to cross into their bloodstream and causehemorrhagic septicemia. This event wiped out 60% of the population of thiscritically endangered species.
Mass mortality events are not uncommon for saiga. In 1981, 70,000 died; in 1988 there were 200,000 deaths; and more recently, in 2010, 12,000 died.[27][4]
Starting in the summer of 2015 and continuing into the spring of 2016, about 62,000 dead or dying birds were found on Pacific Ocean beaches from California to Alaska. Some researchers believe that as many as one millioncommon murres may have died in the massive die-off.[28]
In May 2016, theLos Angeles Times reported that millions of fish had washed ashore along the coast of north-centralVietnam, stretching over 201 kilometres (125 mi) of beaches.[29] This included the shoreline in the Phu Loc district, in Thua Thien Hue province.[29] Possible causes include industrial pollution, as government researchers had found that "toxic elements" had caused the "unprecedented" fish mortalities.[29] Concerns were raised about a "massive Taiwanese-owned steel plant" that was allegedly "pumping untreatedwastewater" into the ocean.[29]
In theInyo National Forest in California, there are several records of large numbers of migratingmule deer falling to their deaths by slipping on ice while crossing mountain passes. This has occurred when heavy snowfalls have persisted until fall, and have been turned to ice by frequent thawing and refreezing.[30]
In 2019, an extremeheatwave with temperatures exceeding 42 °C (108 °F) in centralAustralia lead to the death of approximately 40brumbies.[31]
In 2014 and 2018, heatwaves in Australia killed significant portions of local bat populations.
In August 2020, observers reported that hundreds of dead migratory birds heading south for the winter had been found at theWhite Sands Missile Range inNew Mexico.[7] By September, the number had increased to tens of thousands, and the die-off had spread across at least New Mexico, Colorado, Texas, Arizona, and farther north into Nebraska.[7][32] The birds were migrating species, including "owls, warblers, hummingbirds, loons, flycatchers, and woodpeckers".[32] They seemed to be emaciated, as if they had just kept on flying until they dropped.[32] Possible causes of the deaths include climate crisis and wildfires, according toThe Guardian.[7]
In 2022, a mass die-off of fish,beaver and other wildlife occurred in theOder river, betweenPoland andGermany.[33]
In March 2023, millions of fish were reported dead along theDarling River atMenindee, following a heatwave.[34] Initially, police attributed the cause to (naturally occurring)hypoxicblackwater.[35] Subsequently it was announced that the New South Wales government will treat the deaths as a "pollution incident", thus giving the Environmental Protection Authority (EPA) greater investigative powers.[36]
In April 2023, an explosion and subsequent fire at South Fork Dairy, nearDimmitt, Texas resulted in the deaths of an estimated 18,000dairy cattle.[37]
According to most scientists, massive die-offs of animals are not necessarily unusual in nature and may happen for any of a wide variety of reasons, both preventable and unpreventable. Natural causes often includesevere weather, volcanic eruptions, disease outbreaks, and accidental poisonings,[38] while human-caused die-offs are typically due to pollution (especially major oil and chemical spills) andclimate change adding to the stresses on wildlife.[39] The U.S. Geological Survey's website listed about 90 mass deaths of birds and other wildlife from June through 12 December 2010;[40] Louisiana's State Wildlife Veterinarian Jim LaCour stated that there had been 16 similar mass blackbird deaths in the previous 30 years.[41] Sudden or short-term die-offs must also be distinguished from much longer-termextinction events, which have occurred naturally for countless species throughout the Earth's history and for many extant species are often demonstrated to be ongoing, if gradually, in the modern era.
On the other hand, some mass die-offs appear to be unique because there are no previous records of similar occurrences, or because the likely cause of death can be pinpointed to a novel man-made event that has never previously existed; human technologies of a type or scale unknown at any prior point in history are frequently implicated in catastrophic mortality events. These types of mass die-offs are, then, unusual by definition. According to Italy'sWWF president Giorgio Tramonti, mass dove deaths like the ones that occurred in Italy had never happened before 2010.[42] The event in Arkansas was attributed primarily to an unexpected temperature change causing atmosphericturbulence (visible onNEXRADDoppler weather radar images) above the birds' roosting areas, which likely disoriented them.[43]
Some Christians[which?] asserted that the cluster of cow deaths in 2011 was a sign of theApocalypse.[44] They reference a passage in theBook of Hosea[44] in theHebrew Bible which reads: "By swearing, and lying, and killing, and stealing, and committing adultery, they break out, and blood toucheth blood," and the prophecy continues "Therefore shall the land mourn, and every one that dwelleth therein shall languish, with the beasts of the field, and with the fowls of heaven; yea, the fishes of the sea also shall be taken away."[44]
The termaflockalypse was adopted by some media commentators in reference to the 2010–2011 bird deaths.[45][42][46]Aflockalypse is aportmanteau of the words "flock" and "apocalypse".
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