Mass mortality event

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 eventsEdit

Harbour seals (1988)Edit

In 1988, the death of 20,000 harbour seals in the North Sea was found to be due to phocine distemper virus. Ten years later two bacteria were implicated in the death of 1600 New Zealand sea lions. On Marion Island in 2007, some 250–300 adult male Subantarctic fur seal died in a two-week period. It was suggested but not proven that this gender-biased mortality was caused by Streptococcus sanguinis which was carried by the house mouse, an alien species accidentally introduced in the 1800s.[5]

Mule deer (2003)Edit

In the Inyo National Forest 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 freezing.[6] 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.[7][8]

Drum fish (2010)Edit

In the final week of December, 83,000 dead and dying drum fish washed up along a 20-mile stretch of the Arkansas River, about 100 miles west of Beebe, Arkansas. The cause was speculated to be disease while full test results were expected after one month.[9]

Birds (2010)Edit

Shortly before midnight on New Year's Eve between 3,000 and 5,000 red-winged blackbirds fell from the sky in Beebe. Most were dead on the ground but some were living but dazed. Laboratory tests have been performed and the Arkansas Livestock and Poultry Commission, the National Wildlife Health Center in Madison, Wisconsin as well as the University of Georgia's wildlife disease study group have 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. An unlicensed fireworks discharge was the likely cause.[10][11]

Birds (2011)Edit

The Beebe 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.[12]

On January 3, 2011, more than five hundred starlings, red-winged blackbirds and sparrows fell dead in Pointe Coupee Parish, Louisiana, US.[13]

On January 5, "hundreds" of dead turtle doves were found at Faenza, Italy.[14] According to Italian news agencies, a huge number of the birds were found to have blue stains on their beaks that could be caused by paint or hypoxia.[15]

Over the weekend of January 8–9, "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.[16][17]

Fish (2011)Edit

Between December 28, 2010 and January 3, 2011, 100 tons of dead fish washed ashore on the Brazilian coast.[18]

On January 3, an estimated two million dead fish were found floating in the Chesapeake Bay in Maryland, US.[19]

On March 7, millions of small fish, including anchovies, sardines, and mackerel were found dead in the area of King Harbor at Redondo Beach, California, U.S. An investigation by the authorities within the area concluded that the sardines had become trapped within the harbor, depleted the ambient oxygen, which resulted in the deaths. The authorities stated that the event was "unusual, but not unexplainable."[20]

Cows (2011)Edit

On January 14, 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). The authorities in Wisconsin sent samples from the carcasses to labs in Madison, to determine cause of death.[21]

Saiga antelope (2015)Edit

In 2015, some 200,000 saiga antelope died within a period of one week in a 20 km2 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 bacteria that normally live 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.[22][2]

Brumby (2019)Edit

In 2019, an extreme heatwave with temperatures exceeding 42ºC in central Australia, lead to the death of approximately 40 brumbies.[23]


In 2014, and 2018, heatwaves in Australia have killed significant portion of bat population.


According to most scientists, massive die offs of animals are not unusual in nature and happen for a variety of reasons including bad weather, disease outbreaks and poisonings,[24] with pollution and climate change adding to the stresses on wildlife.[25] The U.S. Geological Service's website listed about 90 mass deaths of birds and other wildlife from June through December 12.[26] For instance, Louisiana's State Wildlife Veterinarian Jim LaCour has stated that there have been 16 similar mass blackbird deaths in the past 30 years.[27] According to Italy's WWF president Giorgio Tramonti, mass dove deaths like the ones that occurred in Italy have never happened before 2010.[28] The event in Arkansas was attributed primarily to an unexpected temperature change causing turbulence, visible on NEXRAD Doppler weather radar images, above their roosting areas which disoriented them.[29]


Some Christians assert that this particular cluster of animal mass deaths is a sign of the Apocalypse.[30] They reference a passage in the Book of Hosea[30] 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."[30]

The term aflockalypse was adopted by some media commentators in reference to the 2010–2011 bird deaths.[31][28][32] Aflockalypse is a portmanteau of the words "flock" and "apocalypse".

See alsoEdit


  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. 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. Retrieved 25 February 2018.
  5. ^ 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. doi:10.1371/journal.pone.0003757. PMC 2582944. PMID 19018284.
  6. ^ Rea, Sarah (22 Nov 2017). "A Slippery Slope". The Sheet. Retrieved 25 February 2018.
  7. ^ 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. doi:10.1029/2009EO260002.
  8. ^ 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. doi:10.1038/s41598-018-19416-9. PMC 5773676. PMID 29348632.
  9. ^ Nuss, Jeannie (January 4, 2011). "Wildlife Experts Probe Mass Death of Blackbirds in Arkansas". CNS. Archived from the original on January 9, 2011. Retrieved January 19, 2011.
  10. ^ Weise, Elizabeth (January 5, 2011). "Fireworks likely cause of massive Ark. bird kill". USA Today. Retrieved January 19, 2011.
  11. ^ "911 Tapes Released from Beebe Bird Scare". KATV. January 7, 2011. Retrieved January 19, 2011.
  12. ^ "Dead blackbirds fall again in Arkansas town". Boston Globe. AP. December 31, 2011. Retrieved January 1, 2012.
  13. ^ Addo, Koran (January 4, 2011). "Mass La. bird deaths puzzle investigators". 2theadvocate. Archived from the original on January 15, 2011. Retrieved January 23, 2011.
  14. ^ "Birds Dying In Italy: Thousands Of Turtle Doves Fall Dead From Sky". The Huffington Post. January 6, 2011. Archived from the original on January 9, 2011. Retrieved January 16, 2011.
  15. ^ "Dead Birds Fall From Sky In Italy: Mass Animal Death Mystery Solved?". The Huffington Post. January 10, 2011. Retrieved January 16, 2011.
  16. ^ Donovan, Travis Walter (January 11, 2011). "Birds Fall From Sky In California, Thousands Of Dead Fish Found In Chicago". The Huffington Post. Archived from the original on January 12, 2011. Retrieved January 23, 2011.
  17. ^ "Thousands of Dead Fish Along Lakefront". NBC Chicago. January 12, 2011. Archived from the original on January 13, 2011. Retrieved January 23, 2011.
  18. ^ Coleto, Leonardo (January 4, 2011). "Mortandade misteriosa de peixes no litoral" (in Portuguese). Parana Online. Retrieved January 23, 2011.
  19. ^ "Two Million Dead Fish Appear in Chesapeake Bay". CBS. January 5, 2011.
  20. ^ "Millions of dead fish at King Harbor in Redondo Beach, CA". Archived from the original on March 12, 2011. Retrieved March 9, 2011.
  21. ^ Adams, William Lee (January 18, 2011). "Does the Death of 200 Cows in Wisconsin Confirm Biblical Prophecy?". Time. Archived from the original on February 23, 2011. Retrieved January 19, 2011.
  22. ^ "Catastrophic Collapse of Saiga Antelopes in Central Asia". UN Environment. Retrieved 25 February 2018.
  23. ^ Cox, Lisa (2019-01-23). "Shocking pictures show dead horses at dried-up waterhole in central Australia". The Guardian. ISSN 0261-3077. Retrieved 2019-07-26.
  24. ^ Sohn, Emily (January 6, 2011). "Birds Falling From the Sky Not Unusual". Discovery News. Archived from the original on January 26, 2011. Retrieved January 19, 2011.
  25. ^ Doyle, Alister (January 6, 2011). "SCIENCE NEWS Mass bird deaths rare, not apocalyptic: experts". NewsDaily.Com. Reuters. Retrieved January 19, 2011.
  26. ^ McConnaughey, Janet (January 4, 2011). "La. has mass bird kill just days after Ark". Huffington Post. Retrieved January 19, 2011.
  27. ^ "Fact Sheet: The Arkansas blackbirds and 8 other mysterious mass animal deaths". The Week. January 5, 2011. Archived from the original on January 19, 2011. Retrieved January 19, 2011.
  28. ^ a b Taylor, Lesley Ciarula (January 7, 2011). "'Aflockalypse' now: Hundreds of turtle doves die in Italy". Toronto Star. Retrieved January 19, 2011.
  29. ^ Jackson, Rachel (June 3, 2011). "Mark Johnson helps solve bird death mystery". The News-Herald. Retrieved June 3, 2011.
  30. ^ a b c Adams, William Lee (January 18, 2011). "Does the Death of 200 Cows in Wisconsin Confirm Biblical Prophecy?". Time. Archived from the original on February 23, 2011. Retrieved January 19, 2011.
  31. ^ Walsh, Brian (January 5, 2011). "Why the Aflockalypse Is Business As Usual For Biodiversity—And Why That's Not Good". Time. Archived from the original on January 10, 2011. Retrieved January 23, 2011.
  32. ^ Bell, Melissa (January 5, 2011). "Dead birds, dead fish, dead crabs turn up all over the world: Signs of the Aflockalypse?". Washington Post. Retrieved January 23, 2011.

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