There is a bridge called the Overtoun Bridge, near Dumbarton in Scotland, where dogs jump to their death.
That's the one purely factual statement I am able to make about this story, because all other details are either disputed or conjecture. Some say the first "dog suicide*" occurred in 1950. But other articles trace the weird occurrences back to the bridge's construction a century earlier. Some say 50 dogs have leaped to their death from the bridge. Some put that number closer to 600. Some blame paranormal phenomena, some blame human emotions of depression or despair that dogs are able to sense and react to, and some blame the repeated deaths on the local mink population.
The only thing the majority of articles agree upon is that this site, over the centuries, has witnessed a great deal of human tragedy. A number of articles also cite reports of unexplained phenomena occurring on or around the bridge. And, in Celtic mythology, Overtoun is known as a "thin" place, or place where the divide separating Earth and the spiritual realm is thinner and more easily penetrable.
I do not know why dogs are jumping over the Overtoun Bridge. I don't really believe dogs are mentally capable of premeditating their own deaths in a way that could label what these dogs have done "suicide." [Note - I have a dachshund, the most depressed, evolutionarily-challenged breed in existence. If dogs were capable of suicide, mine would have found a way]. But something is causing these pets to leap over the bridge. Is it paranormal or scientific? What do you think? Personally, I can't wait for resident veterinarian Helena to chime in.