As the debate over the U.S.-Mexico border fence continues to roll on, a group of biologists claim that besides keeping undocumented immigrants from crossing between the two countries the fence also blocks black bears in Arizona from migrating to Mexico and back.

Already under stress from urban build-up, the black bear migration in southern Arizona's Sky Island mountain ranges is further threatened by the border fence, a study in Biological Conservation concluded.

“In the U.S.–Mexico borderland, urbanization and construction of the border fence have the potential to increase genetic subdivision and vulnerability to isolation in large mammal populations by bisecting movement corridors that have enabled dispersal between adjacent Sky Island mountain ranges,” the study stated.

The study looked at the Sky Island mountain ranges along Arizona’s southern border with Mexico in an effort to assess the genetic link between black bears in Sonora, Mexico, and the main population segment in east-central Arizona as well as to identify potential corridors linking black bear habitats in the border mountain ranges.

“The expanding human footprint near Tucson and other urban areas in southeastern Arizona, and the US–Mexico border fence represent contemporary impediments to movement and function to hasten genetic isolation of black bears in the border region,” the report stated. “Because rapid urbanization and border security activities threaten to alter the spatial structure of trans-border wildlife populations, it is important to identify opportunities to maintain or restore borderland connectivity.”

The report only studied bears on the Arizona side of the U.S. border, noted Dr. Todd C. Atwood of the National Wildlife Research Center

The report comes as the state of Arizona is soliciting private donations to build a border fence. The amount of money collected so far by the website is over $191,000.

The first barriers along the U.S.-Mexico border were constructed in 1990 in an effort to stem the tide of undocumented immigrants and drugs entering the U.S. Today about one-third of the 2,000-mile U.S.-Mexico border is plastered with these barriers, with nearly half of them in Arizona, according to the Colorado Independent.

While black bears and other wildlife are not hindered by vehicle fencing set-up along the border,pedestrian barriers –such as the 15-foot high chain link fencing- is impenetrable to bears, Atwood said.

“Where the fence is impenetrable, the potential to prohibit movement is very high,” Atwood added.

Pedestrian fencing made up 140 of the miles of the border fencing completed by October of 2008 and cost between$400,000 to $15.1 million per mile for an average of $3.9 million per mile, according to the Government Accountability Office.

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