Birds raise their voices to be heard

Hu­man-gen­er­ated noise af­fects how birds com­mu­ni­cate.

Star Tribune - - VARIETY - By JIM WIL­LIAMS Con­tribut­ing writer

We make a lot of noise. Re­cent con­tin­ued dis­cus­sion of ex­panded air­port noise is one proof of that.

Flight pat­terns af­fect more than back­yard bar­be­cues, though; birds lose their most im­por­tant com­mu­ni­ca­tion tool.

It goes be­yond air­planes, of course. Birds suf­fer be­cause of many noises we make.

We are loud and out of tune with na­ture: planes, trains and au­to­mo­biles, leaf blow­ers, lawn mow­ers and chain saws.

“Hu­mans have dras­ti­cally changed much of the world’s acous­tic background with sounds [we pro­duce] that are markedly dif­fer­ent in pitch and am­pli­tude than sounds in most nat­u­ral habi­tats.”

I found that quote in an or­nitho­log­i­cal jour­nal ar­ti­cle that ex­plained one of dozens of stud­ies on adap­ta­tions — or not — by birds to hu­man sounds.

The din we cre­ate af­fects all phases of life for birds in ur­ban ar­eas. Some birds make ac­com­mo­da­tions, oth­ers don’t.

Birds sing to es­tab­lish nest­ing ter­ri­tory or to at­tract mates. They use soft chip­ping sounds to stay in touch with one an­other. Baby birds cheep when hun­gry. Preda­tor alerts are vo­cal.

Bird lives are built on sound. How do they cope with noisy us?

Black-capped chick­adees sing at higher fre­quen­cies when noise lev­els are high.

Robins, al­ready singers be­fore dawn, sing more of­ten at night in ar­eas with sig­nif­i­cant day­time noise. Other species, singing near air­ports, be­gin ear­lier in the morn­ing, when air traf­fic is lighter. One study showed fly­catch­ers singing longer songs in noisy ar­eas.

Finches in an­other study sim­ply stopped singing when air­port noise drowned them out. Around here, that pause might ex­tend as far from the run­ways as St. Louis Park.

Less fre­quent singing puts them at a mat­ing dis­ad­van­tage. Bonds be­tween male and fe­male birds are weak­ened by in­ter­fer­ence with singing. Noise lev­els can re­duce clutch sizes and the num­ber of young hatched and fledged, ac­cord­ing to re­search.

White-crowned spar­rows in San Fran­cisco re­sponded well to record­ings of songs mod­i­fied to be heard above traf­fic. The re­sponse was stronger than that for their usual songs. Like im­mi­grants adapt­ing to a new coun­try, the birds were us­ing a new lan­guage.

At a road­less Idaho stopover site for mi­grat­ing birds, a record­ing of ur­ban traf­fic noise was played, four days on, four days off.

Bird abun­dance in the test area de­clined by 25 per­cent when noise was present. Some species showed “al­most com­plete avoid­ance” of the ar­eas with traf­fic sound, ac­cord­ing to the re­search pa­per.

Mod­i­fi­ca­tions to bird sounds or sig­nals are made at a cost. Singing higher, lower, longer, louder burns en­ergy needed for other life func­tions. And some­times bird mes­sages sim­ply go un­heard.

Non­na­tive species like house spar­rows and Euro­pean star­lings do just fine, by the way. So do pi­geons, even those that choose to nest un­der free­way bridges.

Can we im­prove the noise sit­u­a­tion? Don’t we wish. The sound bar­ri­ers that line many of our free­ways help birds as well as peo­ple, re­search found. An­other study sug­gested clos­ing par­tic­u­larly busy roads in se­lected ar­eas dur­ing breed­ing sea­son. Take that to city hall.

Of all the prob­lems birds face, ur­ban noise seems in­tractable at best. This is not an en­dorse­ment of an 18th­cen­tury lifestyle. The world is what we’ve made it. Un­mak­ing is un­likely. Birds will cope or they won’t.

JIM WIL­LIAMS

Com­mon yel­lowthroat sings.

Pho­tos by JIM WIL­LIAMS • Special to the Star Tri­bune

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