Jump to content

Mass mortality event

From Wikipedia, the free encyclopedia

A mass mortality event (MME) is an incident that kills a vast number of individuals of a single species in a short period of time.[1] The event may put a species at risk of extinction or upset an ecosystem.[2] This is distinct from the mass die-off associated with short lived and synchronous emergent insect taxa which is a regular and non-catastrophic occurrence.[3]

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.[2] 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.[4]

Known mass mortality events[edit]

Migratory birds (1904), Minnesota and Iowa[edit]

In March 1904, 1.5 million migrating birds died in Minnesota and Iowa during a strong snowstorm.[5] According to The Guardian, this was the largest avian mortality event on record in the region.[5] Records of MMEs have been kept since the 1880s.[5] 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".[5]

George River caribou (1984), Canada[edit]

In 1984, about 10,000 caribou of the George River caribou herd—one of Canada's migratory woodland caribou herds—drowned during their bi-annual crossing of the Caniapiscau River when the James Bay Hydro Project flooded the region.[6]

Harbour seals (1988), North Sea[edit]

In 1988, the deaths of 20,000 harbour seals in the North Sea were found to be caused by phocine distemper virus.[7]

Sea lions (1998), New Zealand[edit]

Ten years later, two strains of bacteria were implicated in the deaths of approximately 1,600 New Zealand sea lions.[7]

Fur seals (2007), Prince Edward Islands[edit]

On Marion Island in 2007, some 250–300 adult male subantarctic fur seals died in a two-week period. It was suggested, though not proven, that this gender-biased mortality was caused by Streptococcus sanguinis, a bacterium carried by the house mouse, an alien species accidentally introduced to the island in the 1800s.[7]

Muskoxen (2003), Canada[edit]

In 2003, a rain-on-snow event encased the ground in ice, resulting in the starvation of 20,000 muskoxen on Banks Island in the Canadian Arctic.[8][9]

Birds (2010), Arkansas[edit]

Shortly before midnight on New Year's Eve 2010, between 3,000 and 5,000 red-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, the National Wildlife Health Center in Madison, Wisconsin, and the University of Georgia's wildlife disease study group procured specimens of the dead birds. In addition to the blackbirds, a few grackles and starlings also fell from the sky in the same incident. A test report from the state poultry lab concluded that the birds had died from blunt trauma, with an unlicensed fireworks discharge being the likely cause.[10][11]

Seabirds and marine life (2010–2013), Gulf of Mexico[edit]

The months-long Deepwater Horizon oil spill that began in April 2010 in the coastal waters of the Gulf of Mexico resulted in about 600,000 to 800,000 bird mortalities.[12] Dolphins and other species of marine life continued to die in record numbers into 2013.[13]

Birds (2011), Arkansas[edit]

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.[14]

On 3 January 2011, more than five hundred starlings, red-winged blackbirds, and sparrows fell dead in Pointe Coupee Parish, Louisiana.[15]

On 5 January, "hundreds" of dead turtle doves were found at Faenza, Italy.[16] 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 or hypoxia.[17]

Over the weekend of 8–9 January, "over a hundred" dead birds were found clustered together on a California highway, while "thousands of dead gizzard shad" (a species of fish) turned up in the harbors of Chicago.[18][19]

Fish (2011), Brazil[edit]

Between 28 December 2010 and 3 January 2011, 100 tons of dead fish washed ashore on the Brazilian coast.[20]

On 3 January, an estimated two million dead fish were found floating in the Chesapeake Bay in Maryland.[21]

On 7 March, millions of small fish, including anchovies, sardines, and mackerel, were found dead in the area of King Harbor at Redondo 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".[22]

Cows (2011), Wisconsin[edit]

On 14 January, approximately two hundred cows were found dead in a field in Stockton, Wisconsin. The owner of the cattle has told deputies that he suspected the animals died of infectious bovine rhinotracheitis (IBR), or bovine virus diarrhea (BVD). Authorities in Wisconsin sent samples from the carcasses to labs in Madison in order to determine cause of death.[23]

Saiga antelope (2015), Kazakhstan[edit]

In 2015, some 200,000 saiga antelope died within a period of one week in a 20 km2 (7.7 sq mi) area of the Betpak-Dala desert region of Kazakhstan. They had gathered in large groups for their annual calving. It was determined that warm and humid temperatures had caused Pasteurella multocida, a strain of bacteria that normally lives harmlessly in their tonsils, to cross into their bloodstream and cause hemorrhagic septicemia. This event wiped out 60% of the population of this critically 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.[24][2]

Seabirds (2015–2016), Pacific Ocean beaches[edit]

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 million common murres may have died in the massive die-off.[25]

Fish (2016), Vietnam[edit]

In May 2016, the Los Angeles Times reported that millions of fish had washed ashore along the coast of north-central Vietnam, stretching over 201 kilometres (125 mi) of beaches.[26] This included the shoreline in the Phu Loc district, in Thua Thien Hue province.[26] Possible causes include industrial pollution, as government researchers had found that "toxic elements" had caused the "unprecedented" fish mortalities.[26] Concerns were raised about a "massive Taiwanese-owned steel plant" that was allegedly "pumping untreated wastewater" into the ocean.[26]

Mule deer (2017), California[edit]

In the Inyo National Forest in California, there are several records of large numbers of migrating mule 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.[27]

Brumby (2019), Australia[edit]

In 2019, an extreme heatwave with temperatures exceeding 42 °C (108 °F) in central Australia lead to the death of approximately 40 brumbies.[28]

Bats (2014, 2018), Australia[edit]

In 2014 and 2018, heatwaves in Australia killed significant portions of local bat populations.

Migratory birds (2020) New Mexico[edit]

In August 2020, observers reported that hundreds of dead migratory birds heading south for the winter had been found at the White Sands Missile Range in New Mexico.[5] 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.[5][29] The birds were migrating species, including "owls, warblers, hummingbirds, loons, flycatchers, and woodpeckers".[29] They seemed to be emaciated, as if they had just kept on flying until they dropped.[29] Possible causes of the deaths include climate crisis and wildfires, according to The Guardian.[5]

Fish (2022), River Oder[edit]

In 2022, a mass die-off of fish, beaver and other wildlife occurred in the Oder river, between Poland and Germany.[30]

Fish (2023), Darling River[edit]

In March 2023, millions of fish were reported dead along the Darling River at Menindee, following a heatwave.[31] Initially, police attributed the cause to (naturally occurring) hypoxic blackwater.[32] 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.[33]

Dairy cattle (2023), Texas explosion[edit]

In April 2023, an explosion and subsequent fire at South Fork Dairy, near Dimmitt, Texas resulted in the deaths of an estimated 18,000 dairy cattle.[34]


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 include severe weather, volcanic eruptions, disease outbreaks, and accidental poisonings,[35] while human-caused die-offs are typically due to pollution (especially major oil and chemical spills) and climate change adding to the stresses on wildlife.[36] The U.S. Geological Survey's website listed about 90 mass deaths of birds and other wildlife from June through 12 December 2010;[37] Louisiana's State Wildlife Veterinarian Jim LaCour stated that there had been 16 similar mass blackbird deaths in the previous 30 years.[38] Sudden or short-term die-offs must also be distinguished from much longer-term extinction 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's WWF president Giorgio Tramonti, mass dove deaths like the ones that occurred in Italy had never happened before 2010.[39] The event in Arkansas was attributed primarily to an unexpected temperature change causing atmospheric turbulence (visible on NEXRAD Doppler weather radar images) above the birds' roosting areas, which likely disoriented them.[40]


Some Christians [which?] asserted that the cluster of cow deaths in 2011 was a sign of the Apocalypse.[41] They reference a passage in the Book of Hosea[41] in the Hebrew 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."[41]

The term aflockalypse was adopted by some media commentators in reference to the 2010–2011 bird deaths.[42][39][43] Aflockalypse is a portmanteau of the words "flock" and "apocalypse".

See also[edit]


  1. ^ Fey, Samuel B.; Siepielski, Adam M.; Nusslé, Sébastien; Cervantes-Yoshida, Kristina; Hwan, Jason L.; Huber, Eric R.; Fey, Maxfield J.; Catenazzi, Alessandro; Carlson, Stephanie M. (27 January 2015). "Recent shifts in the occurrence, cause, and magnitude of animal mass mortality events". Proceedings of the National Academy of Sciences. 112 (4): 1083–1088. Bibcode:2015PNAS..112.1083F. doi:10.1073/pnas.1414894112. PMC 4313809. PMID 25583498.
  2. ^ a b c Derbyshire, David (25 February 2018). "The terrifying phenomenon that is pushing species towards extinction". The Guardian. Retrieved 25 February 2018.
  3. ^ Rasnitsyn, Alexandr P., ed. (2002). History of insects (Reprint. ed.). Dordrecht, The Netherlands: Springer. p. 28. ISBN 9781402000263. Retrieved 26 February 2018.
  4. ^ Lee, Jane J. (14 January 2015). "Mass Animal Die-Offs Are on the Rise, Killing Billions and Raising Questions". National Geographic. Archived from the original on 19 January 2015. Retrieved 25 February 2018.
  5. ^ a b c d e f g Weston, Phoebe (16 September 2020). "Birds 'falling out of the sky' in mass die-off in south-western US". The Guardian. ISSN 0261-3077. Retrieved 26 December 2020.
  6. ^ Berkes, F. (1988), "The intrinsic difficulty of predicting impacts: Lessons from the James Bay hydro project", Environmental Impact Assessment Review, 8 (3): 201–220, doi:10.1016/0195-9255(88)90067-4
  7. ^ a b c de Bruyn, P. J. Nico; Bastos, Armanda D. S.; Eadie, Candice; Tosh, Cheryl A.; Bester, Marthán N.; Hansen, Dennis Marinus (19 November 2008). "Mass Mortality of Adult Male Subantarctic Fur Seals: Are Alien Mice the Culprits?". PLOS ONE. 3 (11): e3757. Bibcode:2008PLoSO...3.3757D. doi:10.1371/journal.pone.0003757. PMC 2582944. PMID 19018284.
  8. ^ Putkonen, Jaakko; Grenfell, Thomas C.; Rennert, Kevin; Bitz, Cecilia; Jacobson, Paul; Russell, Don (30 June 2009). "Rain on Snow: Little Understood Killer in the North". Eos. 90 (26): 221–222. Bibcode:2009EOSTr..90..221P. doi:10.1029/2009EO260002.
  9. ^ Berger, J.; Hartway, C.; Gruzdev, A.; Johnson, M. (18 January 2018). "Climate Degradation and Extreme Icing Events Constrain Life in Cold-Adapted Mammals". Scientific Reports. 8 (1): 1156. Bibcode:2018NatSR...8.1156B. doi:10.1038/s41598-018-19416-9. PMC 5773676. PMID 29348632.
  10. ^ Weise, Elizabeth (5 January 2011). "Fireworks likely cause of massive Ark. bird kill". USA Today. Retrieved 19 January 2011.
  11. ^ "911 Tapes Released from Beebe Bird Scare". KATV. 7 January 2011. Retrieved 19 January 2011.
  12. ^ Haney, J.; Geiger, Hal; Short, Jeffrey (22 October 2014). "Bird mortality from the Deepwater Horizon oil spill. II. Carcass sampling and exposure probability in the coastal Gulf of Mexico". Marine Ecology Progress Series. 513: 239–252. Bibcode:2014MEPS..513..239H. doi:10.3354/meps10839. Retrieved 26 December 2020.
  13. ^ Viegas, Jen (2 April 2013). "Record Dolphin, Sea Turtle Deaths Since Gulf Spill". Archived from the original on 30 January 2016. Retrieved 26 December 2020.
  14. ^ "Dead blackbirds fall again in Arkansas town". The Boston Globe. Associated Press. 31 December 2011. Retrieved 1 January 2012.
  15. ^ Addo, Koran (4 January 2011). "Mass La. bird deaths puzzle investigators". 2theadvocate. Archived from the original on 15 January 2011. Retrieved 23 January 2011.
  16. ^ "Birds Dying in Italy: Thousands of Turtle Doves Fall Dead From Sky". HuffPost. 6 January 2011. Archived from the original on 9 January 2011. Retrieved 16 January 2011.
  17. ^ "Dead Birds Fall From Sky in Italy: Mass Animal Death Mystery Solved?". HuffPost. 10 January 2011. Retrieved 16 January 2011.
  18. ^ Donovan, Travis Walter (11 January 2011). "Birds Fall From Sky in California, Thousands of Dead Fish Found in Chicago". HuffPost. Archived from the original on 12 January 2011. Retrieved 23 January 2011.
  19. ^ "Thousands of Dead Fish Along Lakefront". NBC Chicago. 12 January 2011. Archived from the original on 13 January 2011. Retrieved 23 January 2011.
  20. ^ Coleto, Leonardo (4 January 2011). "Mortandade misteriosa de peixes no litoral" (in Portuguese). Parana Online. Retrieved 23 January 2011.
  21. ^ "Two Million Dead Fish Appear in Chesapeake Bay". CBS. 5 January 2011.
  22. ^ "Millions of dead fish at King Harbor in Redondo Beach, CA". Archived from the original on 12 March 2011. Retrieved 9 March 2011.
  23. ^ Adams, William Lee (18 January 2011). "Does the Death of 200 Cows in Wisconsin Confirm Biblical Prophecy?". Time. Archived from the original on 23 February 2011. Retrieved 19 January 2011.
  24. ^ "Catastrophic Collapse of Saiga Antelopes in Central Asia". UN Environment. 5 October 2017. Retrieved 25 February 2018.
  25. ^ Mogensen, Jackie Flynn (15 January 2020). "A new study about the death of 1 million seabirds should scare the crap out of you". Mother Jones. Retrieved 26 December 2020.
  26. ^ a b c d Harris, Scott Duke (4 May 2016). "Millions of dead fish on Vietnam's shores raise industrial pollution fears". Los Angeles Times. Retrieved 26 December 2020.
  27. ^ Rea, Sarah (22 November 2017). "A Slippery Slope". The Sheet. Retrieved 25 February 2018.
  28. ^ Cox, Lisa (23 January 2019). "Shocking pictures show dead horses at dried-up waterhole in central Australia". The Guardian. ISSN 0261-3077. Retrieved 26 July 2019.
  29. ^ a b c Fox, Alex (17 September 2020). "Thousands of Migrating Birds Drop Dead Across Southwestern U.S." Smithsonian Magazine. Retrieved 26 December 2020.
  30. ^ Strzelecki, Marek (12 August 2022). "Dead fish in River Oder on Polish-German border spur contamination probe". Reuters. Retrieved 14 August 2022.
  31. ^ Radford, Antoinette (18 March 2023). "Menindee: Millions of dead fish wash up near Australian town". BBC. Retrieved 20 March 2023.
  32. ^ Housden, Tom (20 March 2023). "Menindee: Australia begins mass fish death clean-up". BBC. Retrieved 20 March 2023.
  33. ^ "NSW to investigate Menindee mass fish kill as 'pollution incident'". www.theguardian.com. 19 April 2023. Retrieved 21 April 2023.
  34. ^ Bernd Debusmann Jr (13 April 2023). "18,000 cows killed in Texas dairy farm explosion". BBC News. Retrieved 13 April 2023.
  35. ^ Sohn, Emily (6 January 2011). "Birds Falling From the Sky Not Unusual". Discovery News. Archived from the original on 26 January 2011. Retrieved 19 January 2011.
  36. ^ Doyle, Alister (6 January 2011). "SCIENCE NEWS Mass bird deaths rare, not apocalyptic: experts". NewsDaily.Com. Reuters. Retrieved 19 January 2011.
  37. ^ McConnaughey, Janet (4 January 2011). "La. has mass bird kill just days after Ark". HuffPost. Retrieved 19 January 2011.
  38. ^ "Fact Sheet: The Arkansas blackbirds and 8 other mysterious mass animal deaths". The Week. 5 January 2011. Archived from the original on 19 January 2011. Retrieved 19 January 2011.
  39. ^ a b Taylor, Lesley Ciarula (7 January 2011). "'Aflockalypse' now: Hundreds of turtle doves die in Italy". Toronto Star. Retrieved 19 January 2011.
  40. ^ Jackson, Rachel (3 June 2011). "Mark Johnson helps solve bird death mystery". The News-Herald. Retrieved 3 June 2011.
  41. ^ a b c Adams, William Lee (18 January 2011). "Does the Death of 200 Cows in Wisconsin Confirm Biblical Prophecy?". Time. Archived from the original on 23 February 2011. Retrieved 19 January 2011.
  42. ^ Walsh, Brian (5 January 2011). "Why the Aflockalypse Is Business As Usual For Biodiversity—And Why That's Not Good". Time. Archived from the original on 10 January 2011. Retrieved 23 January 2011.
  43. ^ Bell, Melissa (5 January 2011). "Dead birds, dead fish, dead crabs turn up all over the world: Signs of the Aflockalypse?". The Washington Post. Retrieved 23 January 2011.