Com­mon pes­ti­cide can make mi­grat­ing birds lose their way, re­search shows

The Guardian Australia - - The Guardian View/Environment - Damian Car­ring­ton En­vi­ron­ment edi­tor

The world’s most widely used in­sec­ti­cide may cause mi­grat­ing song­birds to lose their sense of di­rec­tion and suf­fer dras­tic weight loss, ac­cord­ing to new re­search.

The work is sig­nif­i­cant be­cause it is the first direct ev­i­dence that neon­i­coti­noids can harm song­birds and their mi­gra­tion, and it adds to small but grow­ing re­search sug­gest­ing the pes­ti­cides may dam­age wildlife far be­yond bees and other in­sects.

Farm­land birds have de­clined dras­ti­cally in North Amer­ica and Europe in re­cent decades and pes­ti­cides have long been sus­pected as play­ing a role. The first ev­i­dence for a link came in 2014 when a study in the Nether­lands found that bird pop­u­la­tions fell most sharply in the ar­eas where neon­i­coti­noid pol­lu­tion was high­est, with star­lings, tree spar­rows and swal­lows among the most af­fected.

“The rea­son our new study is spe­cial is this is not a cor­re­la­tion – it is ac­tual ex­per­i­men­tal ev­i­dence,” said Prof Christy Mor­ris­sey, at the Univer­sity of Saskatchewan in Canada, who said the re­sults shocked her. “The ef­fects were really dra­matic. We didn’t an­tic­i­pate the acute tox­i­c­ity, be­cause the lev­els [of neon­i­coti­noid] we gave them were so low.”

Three neon­i­coti­noids were banned from use on flow­er­ing crops in the Euro­pean Union in 2013 due to un­ac­cept­able risks to bees and other pol­li­na­tors and a to­tal out­door ban is be­ing con­sid­ered. Canada is also con­sid­er­ing a to­tal ban. Neon­i­coti­noids now pol­lute the en­vi­ron­ment across the world and pres­sure is grow­ing to slash pes­ti­cide use, which re­search shows would not re­duce food pro­duc­tion on al­most all farms.

The new re­search, pub­lished in the peer-re­viewed jour­nal Sci­en­tific Re­ports, an­a­lysed the ef­fect of the neon­i­coti­noid im­i­da­clo­prid on white-crowned spar­rows that mi­grate from the south­ern US and Mex­ico to north­ern Canada in sum­mer.

Birds were given doses equiv­a­lent to less than a sin­gle corn seed and within hours be­came weak, de­vel­oped stom­ach prob­lems and stopped eat­ing. They quickly lost 17-25% of their weight, de­pend­ing on the dose, and were un­able to iden­tify the north­ward di­rec­tion of their mi­gra­tion. “Ba­si­cally, th­ese birds be­came lost,” said Mor­ris­sey. Con­trol birds that were not ex­posed to the in­sec­ti­cide were un­af­fected.

The birds re­cov­ered their weight and sense of di­rec­tion when tested af­ter 14 days, but Mor­ris­sey said: “We know from other stud­ies on many dif­fer­ent species of mi­gra­tory birds that if you are de­layed by even a few days get­ting to your breed­ing ground, or you are in poor con­di­tion when you ar­rive, you have lower re­pro­duc­tive suc­cess. We know th­ese ef­fects are really im­por­tant for pop­u­la­tion level changes.”

Neon­i­coti­noids are usu­ally ap­plied to seeds, so they can per­me­ate the en­tire plant, and an­other new study shows that birds and other an­i­mals do eat spilled seeds. Char­lotte Roy, in the Min­nesota Depart­ment of Nat­u­ral Re­sources in the US, found seed spills were com­mon and eaten by many crea­tures.

“Every­thing from pheas­ant to black­birds, house spar­rows, deer, rac­coons, bun­nies, mice, squir­rels. Lots of dif­fer­ent an­i­mals are com­ing to the spills,” said Roy. Her col­league Ju­lia Pon­der, at the Univer­sity of Min­nesota, said their work was in its early stages but is go­ing to have “sig­nif­i­cant ram­i­fi­ca­tions”.

Mor­ris­sey said seed sow­ing co­in­cides per­fectly with when birds are mi­grat­ing north, ex­pos­ing them to harm: “They [the pes­ti­cides] are ap­plied in spring which ex­actly over­laps the time when they are mov­ing through th­ese ar­eas and many are stop­ping in agri­cul­tural fields to re­fuel along the jour­ney.”

A spokesman for Bayer, which makes im­i­da­clo­prid, said: “Sci­en­tific ev­i­dence shows that im­i­da­clo­prid has min­i­mal en­vi­ron­men­tal im­pact when used ac­cord­ing to the la­bel, in­clud­ing in­ges­tion by seed-eat­ing song­birds. We take the safety and en­vi­ron­men­tal im­pact of our prod­ucts se­ri­ously.”

He said that song­birds typ­i­cally re­move the seed hull, which is where the in­sec­ti­cide is ap­plied, and sug­gested that birds would there­fore be un­likely to reach the dose lev­els tested. He added that stud­ies of caged birds in­di­cated a lack of in­ter­est in treated seeds if other food sources were avail­able.

Mor­ris­sey’s team are now mea­sur­ing lev­els of the in­sec­ti­cide in the birds’ blood, to mea­sure the level of con­tam­i­na­tion. They are also analysing data from ra­dio-tagged birds given even smaller doses of neon­i­coti­noid, but even this ap­pears to af­fect their mi­gra­tion.

Mor­ris­sey said sci­en­tists were only just be­gin­ning to un­der­stand the harm neon­i­coti­noids cause birds: “Pes­ti­cides have long been spec­u­lated as be­ing one of the driv­ers of farm­land bird de­clines, but we are only just barely touch­ing the edge of that and un­der­stand­ing how pes­ti­cides can af­fect birds.”

The new re­search an­a­lysed the ef­fect of the neon­i­coti­noid im­i­da­clo­prid on white­crowned spar­rows that mi­grate from the south­ern US and Mex­ico to north­ern Canada in sum­mer. Pho­to­graph: Danita De­limont/Alamy

Neon­i­coti­noids are usu­ally ap­plied to seeds, which can be eaten by many dif­fer­ent an­i­mals. Pho­to­graph: Daniel Acker/Bloomberg via Getty Images

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