The Basel ex­pe­ri­ence

Down to Earth - - WILDLIFE -

feral. In Au­gust 2014, the coun­try’s Depart­ment of En­vi­ron­men­tal Af­fairs listed the feral pi­geon as an in­va­sive species. “Ac­tiv­i­ties in­clud­ing im­port­ing, breed­ing, trad­ing and translo­ca­tion of pi­geons are now listed as pro­hib­ited,” ac­cord­ing to a press re­lease of the depart­ment.

Daniel Haag Wack­er­nagel, a bi­ol­o­gist based in Basel,Switzer­land,who has stud­ied pi­geons for more than 20 years,says that sev­eral other coun­tries, in­clud­ing the US, have de­clared the feral pi­geon as a pest and their men­ace has earned them the de­ri­sive moniker,“fly­ing rats”, in many parts of the world. “Feral pi­geons are free-roam­ing descen­dants of once-do­mes­ti­cated birds.The pi­geon was one of the first bird species do­mes­ti­cated by man, more than 5,000 years ago. Mil­lions were raised in an­cient and me­dieval Asia and Europe. They ar­rived in Africa and the Amer­i­cas with the Euro­peans in the 17th cen­tury. An­other batch ap­peared in Africa with the Asians two cen­turies later,” the bi­ol­o­gist ex­plains.

Wack­er­nagel as­cribes the men­ace from the birds to sev­eral fac­tors.“The ideal habi­tat and nest­ing sites for pi­geons are sea-cliffs, prefer­ably those af­ford­ing caves and crevices. But the pi­geon is a highly adapt­able bird. High build­ings that bor­der streets form gorges re­sem­bling rocky cliffs, their orig­i­nal habi­tat. Pi­geons, thus, adapt eas­ily to the struc­ture of our towns.Vast food sources are avail­able nearby through ac­cu­mu­la­tion of rub­bish, ac­ci­den­tal spillage and de­lib­er­ate feed­ing by peo­ple,”he ex­plains.

Wack­er­nagel adds that in most parts of Europe, Asia, North Amer­ica and Africa there is one pi­geon for ev­ery 20 hu­man be­ings.“The ex­plo­sion of the pi­geon pop­u­la­tion in many parts of the world is, in some mea­sure,due to the large food sup­ply. Af­ter World War II,food be­came cheap in re­la­tion to in­come.This was ini­tially so in parts of Europe and Amer­ica,where so­ci­ety pro­duced abun­dant pi­geon food through waste­ful prac­tices. Pi­geons living in ur­ban ar­eas have ex­panded their orig­i­nally graniv­o­rous diet to eat all kinds of filth,to the ex­tent that town pi­geons are now om­niv­o­rous,” says the bi­ol­o­gist. Be­sides, in most parts of the world, feed­ing pi­geons is re­garded as a won­der­ful ex­pe­ri­ence.“Feed­ing an­i­mals is prob­a­bly an in­nate IN 1961, Basel in Switzer­land be­gan ra­pa­ciously culling a pop­u­la­tion of what the mu­nic­i­pal au­thor­i­ties be­lieved were 20,000 pi­geons. Trap­pers and marks­men de­pleted some flocks by 80 per cent, only to watch them re­turn, some­times in greater num­bers, within weeks. The shoot­ing spree went on for 25 years. The city fi­nally stood down, hav­ing killed 100,000 pi­geons. There were still 20,000 pi­geons in Basel!

In 1988, bi­ol­o­gist Daniel Haag Wack­er­nagel em­barked on a pro­gramme to check the city's pi­geon pop­u­la­tion. "Our in­ten­tion was to re­verse at­ti­tudes to­wards pi­geon­feed­ing, con­vinc­ing the public that feed­ing ul­ti­mately harms the pi­geons and is coun­ter­pro­duc­tive. We demon­strated the neg­a­tive ef­fects of feed­ing with pam­phlets and posters and tried to ex­plain the com­pli­cated re­la­tion­ship be­tween feed­ing and over­crowd­ing by pi­geons," he says.

Wack­er­nagel's team built su­per­vised pi­geon lofts to house a small but healthy pop­u­la­tion of pi­geon. "Th­ese lofts prove that we do not in­tend to ex­ter­mi­nate the pi­geons at all; we want to de­velop a small but healthy pi­geon stock," the bi­ol­o­gist notes. hu­man in­stinct.Chil­dren in par­tic­u­lar en­joy feed­ing pi­geons,”he adds.

Chan­dran agrees,rem­i­nisc­ing days when he would hud­dle with his grand­par­ents feed­ing grains to pi­geons.Wack­er­nagel says this is not nec­es­sar­ily a healthy prac­tice (see “The Basel ex­pe­ri­ence”). “Pi­geons are ex­tremely fast learn­ers and im­me­di­ately get used to a re­li­able food source. Know­ing quickly the habits of their fanciers, the birds ar­rive in good time for a ren­dezvous with the food provider. Pi­geons can eat their daily food re­quire­ments of 20-50 gram within a few min­utes. And as they are fed, they no longer have to look for food by for­ag­ing for hours and can spend their gained ‘spare time’ in breed­ing in­stead,”he ex­plains.

Curt Vo­gel,a Ger­man bi­ol­o­gist who has stud­ied the feed­ing habits of pi­geons, says, “Pi­geon milk is pro­duced un­der the in­flu­ence of the hor­mone pro­lactin,by cells in the wall of the crop of both par­ents. It is ex­tremely nour­ish­ing since it con­sists mainly of pro­teins and fats, to­gether with wa­ter.” This con­cen­trated,rich nu­tri­ent en­ables nestlings to dou­ble their weight within 34 hours af­ter hatch­ing.That is why pi­geons are one of the fastest-grow­ing ver­te­brates. Crop milk makes the par­ent pi­geons in­de­pen­dent of spe­cial foods dur­ing the breed­ing sea­son, while an in­sect-eat­ing bird like the great tit, and even seed-eat­ing birds like finches,have to search dili­gently for ad­e­quate nu­tri­tious food—small in­sects—to of­fer to their nestlings. “So par­ent pi­geons can sim­ply en­joy choco­late, sausage or what­ever they find to eat and trans­form it into ‘all-round baby milk,’”Vo­gel adds.

Pi­geons also trans­mit dis­eases and par­a­sites that can attack man, says Wack­er­nagel. “They pass in­fec­tions like or­nitho­sis,cryp­to­coc­co­sis and tox­o­plas­mo­sis to peo­ple. Soft ticks like Argas re­flexus, fleas and red mites that dis­perse from pi­geon-breed­ing places can attack peo­ple,”he adds.

The ex­pan­sion of the bird pop­u­la­tion, be­sides be­ing in­im­i­cal to hu­mans,is not good for the pi­geons them­selves.“As the den­sity of nest­ing and roost­ing pi­geons in­creases, the qual­ity of life of a pop­u­la­tion de­te­ri­o­rates, just as in hu­man pop­u­la­tions,” says Wack­er­nagel. Ex­ces­sive pop­u­la­tion den­sity ex­poses the bird to dis­eases and at­tacks from par­a­sites. Crowded breed­ing places make pi­geons be­have more ag­gres­sively, which mostly af­fects nestlings and ju­ve­niles that are the weak­est mem­bers of the pop­u­la­tion. “Pi­geons would prob­a­bly never be­have this way in their nat­u­ral en­vi­ron­ments.Ter­ri­to­rial be­hav­iour as well as other reg­u­la­tory mech­a­nisms,in­clud­ing pre­da­tion by birds of prey, would keep pi­geon pop­u­la­tion at lev­els where they lead less stress­ful lives,”he adds.

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