Backhoes are the number one cause of fiber cuts. But there are plenty of other culprits, including some you wouldn't expect. Fred Lawler. SVP of Global Field Services at Level 3, provides a highly entertaining review of The 10 Most Bizarre and Annoying Causes of Fiber Cuts (link via Slashdot).
One of the most unusual: In the aftermath of Hurricane Katrina, a Level 3 field manager was working to repair a fiber line about two miles inland, only to encounter a three-foot long shark in the fiber trench. Lawler also recounts in which a storm toppled a long chain of utility poles in Idaho, sparking a grass fire. Level 3 employees repaired the company's fiber even as airplanes flew overhead dumping fire retardant to battle the blazes. See Lawler's full post on the Beyond Bandwidth blog.