Cats kill bil­lions of birds, mam­mals yearly, study finds

Feral an­i­mals, pets a much greater threat than pre­vi­ously thought

The Washington Post Sunday - - POLITICS & THE NATION - BY JULIET EILPERIN eilper­inj@wash­post.com

Out­door cats are the lead­ing cause of death among both birds and mam­mals in the United States, ac­cord­ing to a new study, killing 1.4 bil­lion to 3.7 bil­lion birds each year.

The mam­malian toll is even higher, con­cluded re­searchers from the Smith­so­nian Con­ser­va­tion Bi­ol­ogy In­sti­tute and the U.S. Fish and Wildlife Ser­vice, rang­ing from 6.9 bil­lion to 20.7 bil­lion an­nu­ally.

The anal­y­sis, pub­lished Tues­day in the jour­nal Na­ture Com­mu­ni­ca­tions, sug­gests that feral and owned cats pose a far greater threat than pre­vi­ously thought. One study in 2011 es­ti­mated that cats in the United States kill roughly half a bil­lion birds an­nu­ally.

Peter P. Marra, the pa­per’s se­nior au­thor and a re­search sci­en­tist at the Smith­so­nian in­sti­tute, said he and his col­leagues “pulled to­gether all the best es­ti­mates” from 90 stud­ies to reach their es­ti­mate, tak­ing into ac­count the dif­fer­ence in be­hav­ior be­tween owned and un­owned cats.

“I don’t think there’s ever been an at­tempt like this,” Marra said in a tele­phone in­ter­view, adding that the new es­ti­mate is “con­ser­va­tive.”

Re­searchers es­ti­mate that one pet cat kills one to 34 birds a year, while a feral cat kills 23 to 46 birds an­nu­ally. As a re­sult, the new study pro­vides a wide range of the to­tal bird death count. “It’s not a sin­gle num­ber,” Marra said.

Ge­orge H. Fen­wick, pres­i­dent of Amer­i­can Bird Con­ser­vancy, said in a state­ment that the find­ings should serve as “a wakeup call for cat own­ers and com­mu­ni­ties to get se­ri­ous about this prob­lem be­fore even more eco­log­i­cal dam­age oc­curs.”

“The very high cred­i­bil­ity of this study should fi­nally put to rest the mis­guided no­tions that out­door cats rep­re­sent some harm­less new com­po­nent to the nat­u­ral en­vi­ron­ment,” Fen­wick said. “The car­nage that out­door cats in­flict is stag­ger­ing and can no longer be ig­nored or dis­missed.”

Cats pose the great­est dan­ger to birds and mam­mals liv­ing on is­lands be­cause there are fewer op­por­tu­ni­ties for th­ese an­i­mals to es­cape. Cats are re­spon­si­ble for help­ing drive 33 species of birds, mam­mals and rep­tiles to ex­tinc­tion on is­lands, in­clud­ing the Stephens Is­land wren in New Zealand in the late 1800s, ac­cord­ing to the In­ter­na­tional Union for Con­ser­va­tion of Na­ture.

Sci­en­tists have a hard time mea­sur­ing the ef­fect of cats on small mam­mals in the United States be­cause they lack pre­cise pop­u­la­tion counts for th­ese species, Marra said.

“We don’t know how many East­ern cot­ton­tail rab­bits are out there, and we don’t know how many chip­munks are out there,” he said.

By con­trast, re­searchers es­ti­mate that the United States is home to at least 15 bil­lion adult land birds. Cats kill about 10 per­cent of them each year, ac­cord­ing to the anal­y­sis.

Marra and two other sci­en­tists, the Smith­so­nian in­sti­tute’s Scott R. Loss and Tom Will from Fish and Wildlife, con­ducted their anal­y­sis as part of a broader study of hu­mans’ im­pact on bird mor­tal­ity. Roughly 150,000 to 400,000 birds in the United States die an­nu­ally in wind tur­bines, ac­cord­ing to re­cent es­ti­mates, while 10 mil­lion to 1 bil­lon birds die af­ter col­lid­ing with glass.

The fact that hu­mans can take ac­tion to pre­vent some of th­ese deaths — such as adopt­ing poli­cies to re­duce feral cat pop­u­la­tions and al­ter­ing how wind tur­bines are de­signed — should pro­vide hope, Marra said.

“Th­ese are things that are re­versible once we un­der­stand them,” he said. “That’s the im­por­tant thing here.”

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