Horicon Marsh is about 50 miles northeast of Madison and is comprised of a national (Horicon National Wildlife Refuge) and state wildlife refuge (Horicon Marsh Wildlife Area). It covers 32,000 acres and consists of open water and marsh vegetation, separated by embankments to control water levels.
The northern federal section is bisected by State Highway 49 (about 2.3 miles in road length). This two-lane highway connects Waupun and U.S. Highway 151 (on the west) to Brownsville and I-41 (on the east) and has daily traffic volume of about 4,100 vehicles (2008) and a posted speed limit of 55 m.p.h. Average vehicle speed is about 59 m.p.h. and trucks comprise about 22-26% of the traffic.
The U.S. Fish & Wildlife Service as well as other stakeholders (e.g. naturalists, including bird watchers) have been concerned about the high number of animals, including birds, being killed along the section of Highway 49 that bisects Horicon Marsh for well over a decade.
In response, U.S. Fish & Wildlife Service employees initiated a road-kill monitoring program. The species groups that are hit include amphibians, reptiles, birds, and mammals; 10,648 road-killed animals have been recorded from 2001-2013 by Horicon National Wildlife Refuge staff (see graphic).
The most commonly recorded mammal species found dead were muskrat and raccoon (82.8% and 5.8% of all mammals respectively).
Amphibian roadkills are typically severely underestimated, especially when counting from a moving vehicle. However, frogs accounted for 97% of all observed amphibian roadkill.
The most frequently observed roadkilled bird species were Canada Goose, American Coot, Red-winged Blackbird, and Tree Swallow (20.9%, 14.6%, 12.1%, 9.0%, 6.7%, and 5.1% of all bird species respectively). Painted turtle and common snapping turtle were the most frequently observed roadkilled reptile species (66.5% and 29.3% of all reptile species respectively).
While one can argue that any road-killed animal should be a concern, only one federally listed threatened or endangered species has been reported as road-kill between 2001 and 2013; Piping Plover. However, an experimental population of Whooping Cranes is nearby, a few Whooping Cranes are now also residing at Horicon Marsh, and a low flying Whooping Crane had several narrow escapes with vehicles along 49 in spring 2014.
While the road-kill data show that bird mortality is substantial, the recorded mammal and amphibian mortality were higher than that for birds. This is despite the fact that amphibian mortality is likely to have been severely underreported.
Amphibians and reptiles appear particularly vulnerable to direct road mortality and about half of all federally listed species for which direct road mortality is among their primary threats are amphibians or reptiles. In this context, the high mortality of painted turtles and common snapping turtles may be of particular concern.
Mature female turtles are typically attracted to roadsides to lay eggs; it is above the water level and the slope of the roadbed allows for higher temperatures. Natural mortality among adult turtles is very low, and the persistance of turtles in the landscape depends on that.
This means that whenever large numbers of adult turtles, especially females, are dying of unnatural causes, there is reason for substantial concern. Direct road mortality of turtles has led to substantial mitigation projects elsewhere such as Jackson Lake and Payne's Prairie in Florida and the Mobile Causeway in Alabama.
Previous suggestions for mitigation measures emphasized measures that can reduce collisions with low-flying birds. These include poles placed along the roadway that act as a visual barrier and encourage birds to fly higher. This measure has reduced strikes with Royal Terns on a high bridge in Florida by 64%. However, poles do not address road mortality of amphibians, reptiles, and mammals, and they may also not reduce mortality of bird species that primarily walk on or alongside the road, including the most frequently hit bird species (Canada Goose and American Coot).
Furthermore, all stakeholder groups, including natural resource management agencies, transportation agencies, and NGOs are concerned about the effect that poles will have on landscape aesthetics and wildlife viewing opportunities.
Re-routing 49 north of the marsh is likely the best option to avoid the negative effects of the highway and traffic on the birds. It also elimates the human safety risk of having people on and along 49 who may be viewing wildlife in the midst of high speed and high volume traffic. However, re-routing is also an option that comes with its own set of problems
The "next best" option would be to elevate the highway for the road section that cuts through Horicon Marsh. It appears birdwatchers prefer the elevated highway to be on the north side of the current embankment, which needs to stay in place for current water management.
The existing road could serve as a recreational, low volume, low speed route with one-way traffic, ample parking or large pull-outs. The new elevated road could have poles to reduce collisions with low-flying birds. This package would improve human safety, reduce mass bird mortality by 80% or more, and reduce mass amphibian and reptile mortality on the current embankment by 80% or more and eliminate it entirely on the elevated Highway 49.
An alternative-- but less preferred-- option would be to keep Highway 49 on its current embankment but create a limited number of pull-outs so that people who want to watch wildlife can safely pull off the road. In the immediate future, retaining walls could be installed (about 2-4 feet high) on both sides of the highway.
Whenever the barrier effect of a road and traffic is increased, it is considered good practice to also install safe crossing opportunities for wildlife. Underpasses may be installed with an open roof structure so that air and soil temperature and humidity are similar to the surroundings. Over the long term, consider raising the height of the embankment so that taller barrier walls (5 feet) and taller underpasses can be constructed. This option does not include the installation of poles along the current embankment because of the effects on landscape aesthetics and hindering the view for wildlife watchers.
If poles are installed along the current emankment they would likely not have the support of natural resource agencies and birdwatchers, and therefore the project would risk losing their support altogether.
This option would improve human safety by providing safe pull-outs, reduce bird-mortality as the most frequently recorded road-killed species would no longer access the actual travel lanes, and reduce mass amphibian and reptile mortality by perhaps 95%.
This option would not or only partially address human safety concerns with vehicles pulling off and on Highway 49 and people on and alongside the road, or reduce mass mortality further for flying birds as there are no measures that encourage birds to fly higher over Highway 49.
The least preferred alternative is not to implement any measures that would address these problems. Choosing to do nothing implies that the current human safety issues and the current or likely future effects on the highway and traffic on wildlife are characterized as acceptable.
The Western Transportation Institute at Montana State University consists of an excellent group of scientists specializing in highway vs. wildlife issues and road ecology. They have worked on projects on several continents. Their complete report was finished in February, and appeared in the summer issue of The Passenger Pigeon and is now downloadable from the internet here: Horicon Marsh Final Report.