Already at risk of extinction, the monarch butterflies that flutter through Texas on their way to Central Mexico face yet another formidable predator: deadly traffic.
Millions of monarchs die on the state's highways as they collide with vehicles while flying low. A grant from the Texas Department of Transportation's Research and Technology Implementation division is hoped to help Texas A&M University researchers identify the location and extent of so-called roadkill hot spots to better understand why it happens and find ways to mitigate it, the Houston Chronicle reported.
"The population that is moving through Texas, however large or small, that population is going to determine what the spring migration population looks like," said Robert Coulson, professor in the Department of Entomology at Texas A&M. "So any mortality variation that affects that fall population, particularly at this stage of the migration, is extremely important."
The population of the iconic orange and black insect with white spots along the edges, described by some as American as apple pie, has declined more than 80% in the last two decades. Part of it is due to the use of pesticides, development and global climate change, which undermines stable weather conditions and predictable flowering seasons the butterflies need to complete their migration, according to researchers.
But road mortality is also contributing to that decline. In previous investigations, Texas A&M researchers found that road mortality of autumn-migrating monarchs from Oklahoma to Mexico depleted up to 4% of the population that would typically arrive at Mexican overwintering sites.
Since 2014, the U.S. Fish and Wildlife Service has been looking into whether the monarch butterfly needs protection under the Endangered Species Act, and as it makes that decision, many, including Texas A&M's Department of Entomology, have been working to understand why the monarch population is so diminished and to find solutions, the university said in a news release.
"What is at stake is whether or not that population will continue to decline and eventually disappear or whether or not there are various factors that could be implemented to help preserve that population," Coulson said.
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Generations of the monarch butterfly, adopted as Texas' insect in 1995, travel 3,000 miles from Canada to Mexico in the autumn, then return another 1,000 miles back to Texas and Oklahoma in the spring to lay eggs, according to a Texas A&M news release.
On the return journey south during the autumn, as the migration corridor narrows when approaching Mexico, populations of monarchs become more concentrated and road mortality is expected to increase, researchers have found. Coulson said they are also working with colleagues on the Mexican side to examine what's happening across the border.
Over the next two years, Texas A&M researchers will conduct four seasonal surveys of dozens of 100-meter transects for road-killed monarchs along stretches of roadways, timed to follow the passage of the butterflies southward migration.
The data will be used to assess the impact of roadkill on the overwintering population in Mexico, define the location and extent of roadkill hot spots, and provide TxDOT mitigation options that could be implemented to reduce mortality, Coulson said.
"Part of the problem is that most of the literature on mitigation deals with mammals and birds," he said, but he hopes that by identifying not only where the hot spots are occurring but why, they will be able to provide better guidance to TxDOT as it weighs its options.
