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Highway noise can block key fish mating calls

Animal Communication, Effects of Noise on Wildlife, Vehicles Comments Off on Highway noise can block key fish mating calls

AEI lay summary of:
Daniel E. Holt, Carol E. Johnston. Traffic noise masks acoustic signals of freshwater stream fish. Biological Conservation 187 (2015) 27-33 (ScienceDirect link)
Screen Shot 2015-05-13 at 1.35.59 PMWith each passing year, we learn more about the ways that animals use sound—and so also how human noise interferes with their lives.  A new paper looks at how traffic noise from bridges may impinge on the mating calls of freshwater fish; this is the first study to use some of the new metrics of “communication space” in these important and widespread habitats. The species studied was the blacktail shiner, a member of the largest family of fishes (including carps and minnows), with the study sites being small streams passing under bridges on I-85 in Alabama (image shows one of six sites).

Screen Shot 2015-05-13 at 2.06.36 PMMale shiners make two sounds during mating: loud “knocks” used to challenge other males who are intruding, and softer “growls” used to court females.  Streams are naturally loud environments, with noise from wind, rain, and turbulence; shiners take advantage of a relatively quiet “window” in the broadband noise, between 172 and 366Hz (like many other animals that vocalize in frequency ranges less cluttered by local sounds or other species).  While the traffic noise is not much louder than the natural stream sounds at frequencies above 700Hz, unfortunately for the shiners, in this key quiet window it is significantly louder than the stream noise—and also the seductive growls of male shiners.  The graph shows natural ambient noise (green), road noise (red), and growls (black dotted line).  The two peaks in the growl acoustic spectrum are particularly important; the lower peak in particular is dramatically drowned out by traffic noise.

blacktail_shiner2The bottom line for the fish is that their knocks, which can be heard above the natural sounds of the creek out to about a half meter, are just slightly masked—only within three meters of the bridge are they lost in road noise (3m is the mean; maximum modeled range of effect is 22m).  So these calls of challenge and defense among males, which may also show females who’s the most fit, can serve their purpose unless the action is taking place right under a bridge.  The subtler sounds of the growls, however, are much more impacted.  These sounds, being quieter, are meant to be heard at very close range (generally just a few inches from the nest sites); yet the lower peak in the growl sound spectrum will be effectively inaudible in areas out to 640m (almost a half mile) from a bridge, and the second peak will be similarly masked out to 40m (both distances are means; maximum ranges are, respectively, 12km/7 miles and 1600m/1 mile). Adding insult to injury, peak spawning time is morning, before water temperatures rise, which may coincide with peak morning traffic.  Of course, only a small portion of most spawning streams is near heavily travelled interstates or secondary roads; those near more sporadically-travelled local roads are likely to be less affected.  Still, if the effect extends a half mile or more, large stretches of many streams could have some degradation of their natural and necessary acoustic habitat.

The authors’ conclusion neatly sums up what all this means going forward:

The noisy environment in which C. venusta spawn has a convenient window in the noise spectrum, which is exploited by C. venusta for the purpose of communication with females during reproductive behaviors. Our results show that this quiet window is disrupted by road traffic noise. This discovery should be followed up by studies investigating the behavioral and stress responses of C. venusta, as well as other more imperiled fishes, to noise from bridge crossings. Future efforts should also be made to characterize noise from different bridge styles, daily temporal patterns of noise, and attenuation at longer distances.

 

 

Forest Service starts “minimal roads” planning

Effects of Noise on Wildlife, News, Vehicles, Wildlands Comments Off on Forest Service starts “minimal roads” planning

Unbeknownst to most of us, a long-term National Forest Service approach to managing roads on its millions of acres of non-wilderness lands has been waiting for activation since January 2001, when the Forest Service finalized a plan for the long-term management of their oversized and under-maintained road system. That plan basically directed the agency to identify an ecologically and fiscally sustainable minimum road system that would meet resource management and recreational access needs. The plan projected that the agency might reduce the overall road system by more than 30%, and that as a result “unroaded” acreage might increase by up to 15% nationally.  Wildlands CPR fills us in on the details with this web post and a real nice pdf version of their magazine feature on the story.

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A combination of political neglect and other factors has meant that even as the “minimum road system” goal remained on the books, and was part of the Travel Management Plan process that many forests engaged in over the past decade, implementation of the idea has never happened.

Now that has changed, with the release in late 2010 of a directive from the Forest Service Chief. The guidance memo directs all national forests to identify, through a science-based analysis, an ecologically and fiscally sustainable minimum road system by 2015.

In addition to the five years it will take to conduct this analysis nationally, it will likely take decades to actually implement the minimum system on-the-ground. But the plans developed through this process will, over the long-term, create a blueprint for future road maintenance and decommissioning investments, including Legacy Roads and Trails Remediation Initiative funding.

For those interested in large landscape connectivity for wildlife, this initiative presents an opportunity to reduce road densities as well as protect and restore linkages and core habitat. For those interested in clean water and fisheries, it is an opportunity to improve water quality and watershed health. And for those interested in fiscal responsibility, it is an opportunity to identify a road system that the Forest Service can afford to maintain.