We focused on birds because they're familiar to most but their attraction to salt, like mammals, is unfamiliar to many. We didn't mean to suggest that de-icers of any kind don't have other negative impacts to other wildlife.
Research does indeed show that use of salt or sand on roadways with significant run-off into adjacent waterways or wetlands can hurt fish, amphibians and other aquatic fauna and flora. That's why the Washington Department of Transportation (WSDOT) tries to minimize its use, or use non-salt alternatives, in those situations, according to WSDOT wildlife biologist Kelly McAllister.
There is no perfect solution to both keeping our roads safe for winter motor vehicle traffic and avoiding impacts to fish and wildlife.
The use of sand for road traction instead of de-icers is not without problems. Our southcentral regional habitat manager Perry Harvester notes that sand application can have significant adverse impacts to fish life, particularly in-stream incubating eggs and alevins of salmonids.
"In areas of heavy sand application," Harvester said, "the sand builds up along the road shoulders adjacent to streams, and during the first big rain-on-snow event in the spring, this sand and grit is flushed into the streams. In smaller streams that are already at critical threshold for fine sediment loading, it doesn't take much additional sediment to result in a significant increase in mortality of eggs and alevins of salmon, trout, and steelhead. If silt or sand fills in the spaces between the spawning gravel, clean water cannot circulate and the eggs may die from lack of oxygen, accumulated waste products, or physical encasement."
Both McAllister and WDFW southcentral district wildlife biologist Jeff Bernatowicz also note that more recent use of Calcium chloride (CaCl) and Magnesium chloride (MgCl), instead of Sodium chloride, seems to attract some wildlife even more - despite some research that indicates it's the sodium part of de-icer that attracts animals.
"I wondered why we were seeing more animals on highways and suddenly licking clean our vehicles at winter feed sites," Bernatowicz said. Prior to the use of Magnesium chloride, we never had sheep on Highway 821 along the Yakima River between Ellensburg and Yakima. But now, if snow is forecast and that road is sprayed, and if the snow is light and melts, sheep will be on the highway in the morning."
Bernatowicz conducted an experiment at a bighorn sheep winter feeding site by setting up 55-gallon plastic drums at the site, some sprayed with a commercially available solution of MgCl and some with dissolved table salt (Sodium chloride). He ran three trials, rotating the location of the barrels, and in each trial the sheep licked the MgCl barrels clean first.
Because the commercially available formulations of MgCl include proprietary compounds that reduce the corrosiveness of the salt, it's unclear what element of the mixture is so attractive to sheep. While ingestion of the product may not hurt wildlife, it does seem to attract wildlife. And attracting large animals like bighorn sheep, elk or deer to roadways is highly hazardous, both for drivers and for the animals.