Posted by: atowhee | May 6, 2008

Traffic noise and birdsong, which shall prevail?

The Bewick’s Wrens, the whistling Wilson’s Warblers, the chattering Bullock’s Orioles–all seem far louder than usual in downtown Medford where they breed along the Bear Creek Greenway.  That Greenway’s in fact only a thirty-yard wide zone of cottonwood, willows, creek and berry brambles surrounded by asphalt, bordered on the east by I-5, the busiest freeway in Oregon.

I could find only one journal article relating to noise pollution and its effects on wild birds: “A Technique for Dorsal Subcutaneous Implantation of Heart Rate Biotelemetry Transmitters in Black Ducks: Application in an Aircraft Noise Response Study”(Condor: Vol. 99, No. 1, January-February, 1997) .  This study concluded that birds very quickly adjusted to the noise and were physiologically unaffected.  It’d be interesting to measure the loudness of birdsong for those nesting along Bear Creek Greenway and those in a quieter, more natural setting.  Perhaps the birds’ hearing is so acutely tuned that what we take for background noise and interference doesn’t even register for them.  Are they that attuned to the tones and pitch of their own species’ sound?

Certainly the noise has not deterred a number of riparian-loving species from spring song and nesting behavior.  At one point I stood less than six feet from a female Lesser Goldfinch working on her tiny grass cup, a nest with a smaller diameter than a tennis ball.  And the presence of competing female Brown-headed Cowbirds indicated I was not the only one appraising nest activity along Bear Creek.  Once I interfered and threw a stick at a female who was clearly looking for the Lesser Goldfinch nest I’d been observing.  That Cowbird was prorbably right back there the moment I walked away.

Lesser Goldfinch are abundant here in all seasons though we’re not far from the northern limit of their range.  They’re not found much to the east of the Rogue and Bear Valleys, nor are they are found often along the Oregon Coast.  Noise or not, they cling to the I-5 corridor.  In Medford some of them seemed to fly up from the creek bottom to nest nthe ornamental trees scattered around the parking lot of the nioeghboring Rogue Valley Mall.

LEAFBIRDS

The canopy was leafed out, pale green and yellowish with a bright blue, sunlit sky beyond.  Small birds, especially yellowish birds, were devilishly hard to discern.

 

 

 

 

A typical ground-up view of the Bear Creek canopy on a sunny day.

Just try picking out a yellow bird:

 

 

 

 

This was definitely a male Bullock’s Oriole.  Females have pale chests.  Note the color progression: Black chin, orangish throat, yellow chest and belly and undertail coverts, black tail feathers on both bottom and top, which you can’t see here.  There were frequent outbursts of the orioles’ paradiddle chatter calls. 

 

And now check this out:

 

 

 

 

 

I took this to be a female Western Tanager.  They were numerous along the creek.  One male provided calm, easy viewing though myc amera had dead batteries at the time.  This bird leaves me with mystery unsolved: why are the tail feathers so apparently light colored?  It was not a Summer Tanager, but apparently a Western.  All my books show dark undertails for both genders?

 I was grateful for the presence of the Mourning Doves, posing, observable even in deep shade and dense foliage.  I thank their placid demeanor.  I have noted in our garden they often frighten the other birds off the platform feeder, even the larger, more aggressive jays will flap away. Could it be the doves’s wing-whirring sound is an adpatation to make them sound ferocious or at least defensive?  Is that why the jays flea?

 

 

 

 

 

 

There were nesting Wrentits along the Greenway.  They huddle in the dense blackberry brambles so detested by the native plant purists.  If such folks succeed in getting all the Himalayan berry brambles pulled out I fear for the future of the local Wrentits, already confined to narrow strips of habitat along the creeks and rivers here.  One pair of Wrentits took exception to my presence.  They scolded me with a repetitive sound that reminded me of the a playing card hitting the spokes of a bicycle.  When we were kids that was considered way cool: the playing card was jammed into the bar connecting the axle to the bike’s frame, then the turning wheel would snap the playing card against each passing spoke.  “Thwak, thwak, thwak…”  No doubt the Wrentit evolved his scold before there were bicycles on the Greenway path.

My own pishing efforts were largely pointless, less audible than the whine of passing eighteen-wheelers.  But once I did bring a single White-crowned Sparrow to the peak of a berry mound.  Otherwise I found standing and waiting the best birding technique here.  A Red-tailed Hawk flew onto a utility pole. Red-tailed and tailed by a Scrub-jay.  A couple minutes later, exit stage right followed by a Brewer’s Blackbird. 

One male Black-headed Grosbeak seemed to be sunning himself on his leafy porch.  I have watched my garden’s male bird do the same thing.  Perch on a willow branch, close his eyes to the sun and absorb the solar energy through his black feathers.  The Grosbeaks were in song as well.  As I was writing this before dawn, my home male began singing at exactly 5:14 AM.  He continued for several minutes before taking a breather.  So far this is my favorite picture of my garden Grosbeaks:

Both genders of the grosbeaks are capable of song.  And both have that seed-crusher beak.  They seem to easily share the feeders with other birds, even the much larger Flicker.  They’re not easily frightened and do not fear the jays it seems.  The beak speaks.

The best performance of my hour along the greenway: a singing Bewick’s Wren.  He perched on top of a small cottonwood limb, threw back his head, raising his beak to the heavens.  With each crystalline note, each deft trill, every complex chord his tail would vibrate, his whole tiny body shake.  There perched just over a third of an ounce of musical energy, songs from across the eons all encoded on tiny brain cells.  The iPod has so far to evolve to even begin to compete.

My Greenway bird list:  Canada Goose, Red-tailed Hawk, Mourning Dove, Rock Dove, Downy Woodpecker, Warbling Vireo, Tree Swallow, Cliff Swallow, Raven, Scrub-jay, Eurasian Starling, Black-capped Chickadee, American Robin, Wrentit, Bewick’s Wren, Western Tanager, Wilson’s Warbler, White-crowned Sparrow, Brewer’s Blackbird, Bullock’s Oriole, House Finch, Lesser Goldfinch.

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Responses

  1. First what I’d like to say what a great setting it looks like you live in. It was a long time ago now but we used own a pair of bullocks Oriole birds they were beautiful things. Interesting photo of the Western tanager, I am sorry I am not able to help with the colour issues that you’ve mentioned, did you ever find out why the colours were different?


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