Last updated at 23:28 17 October 2006

For Donna Cooper, the worst thing about watching her collie dog, Ben, leap to his death has been the effect it has had on her two-year-old son Callum.

'Nearly a year on, Callum still asks about Ben. He was very upset by the dog's death and wants to know if his leg has been fixed in heaven,' she says.

Just 12 months previously, Donna, her husband and son were walking their dog across the picturesque Overtoun Bridge in Milton, near Dumbarton, Scotland.

Without warning, Ben leapt over a parapet on the century-old granite bridge and fell 50ft to his death on the rocks below.

'His paw was broken, his jaw was broken and his back was broken and badly twisted. The vet decided it wasn't worth putting him through the pain, so we had to let him go,' recalls Donna.

Kenneth Meikle can sympathise with the Cooper family because he, too, has had to watch in horror as his golden retriever, Hendrix, leapt from the same bridge at virtually the same spot.

'I was out walking with my partner and children when suddenly the dog just jumped. My daughter screamed, and I ran down the bank to where the dog lay and carried her up to safety.

'As I did so, her hair started to fall out. It must have been shock because when we got her home, she shook all night.

'Next day, thank goodness, she was fine. We were lucky because she landed on a moss bed which broke her fall.'

50 dogs in the last 50 years



Other dogs have not been as fortunate. In the past half-century, some 50 dogs have leapt to their deaths from the same historic bridge.

During one six-month period last year, five dogs jumped to their deaths.

All of the deaths have occurred at virtually the same spot, between the final two parapets on the right-hand side of the bridge, and almost all have been on clear, sunny days.

Furthermore, the dogs which have perished have all-been long-nosed breeds: labradors, collies and retrievers.

Dorren Graham, of the Scottish Society for the Prevention of Cruelty to Animals calls the phenomenon a 'heartbreaking mystery'.

'There are lots of owners whose dogs have died and who are trying to find out why they jumped.'

Could dogs be deliberately committing suicide?



Built in 1895 by Calvinist Lord Overtoun, the ornate Victorian structure arches 50ft over Overtoun Burn, the stream which runs below.

Now, thanks to stories posted on the internet, doglovers from around the world are asking: could dogs be deliberately committing suicide on this particular bridge, and if so, why?

In an attempt to solve a problem which has left many local dog owners so concerned, they will no longer walk their pets on the doomed bridge, a host of specialists converged on the west Scotland town earlier this year to investigate - and finally solve the mystery.

Rumours have long circulated that the bridge and nearby Overtoun House are haunted. In 1994, local man Kevin Moy threw his baby son to his death from the bridge, claiming he thought the child was the anti-Christ.

Shortly after he tried to end his own life with an unsuccessful suicide attempt from the same bridge.

Donna Cooper says: 'Rumour has it that he was on drugs, but he insisted the place was haunted and it does seem to have a strange effect on people and dogs.'

The Thin Place



In Celtic mythology, Overtoun is known as 'the thin place' - an area in which heaven and earth are reputed to be close.

Certainly dogs have been shown in the past to be more sensitive than humans.

Were they 'spooked' by some supernatural or external force emanating from the bridge, and deliberately leaping to their deaths?

Psychic Mary Armour took her own labrador for a walk along the bridge to test the theory. However, she reported no unusual sensations.

'Animals are hyper-sensitive to the spirit world, but I didn't feel any adverse energy.'

In fact, Mary said she experienced a feeling of 'pure calmness and serenity' but admitted that her dog did pull her towards the right-hand side of the structure.

Suicidal or depressed feelings



If there is nothing supernatural propelling animals to their deaths, could they be picking up on suicidal or depressed feelings of their owners?

Kendal Shepherd, a veterinarian behavioural specialist, believes dogs can indeed suffer from psychosis, and anyone who has ever owned a dog would agree they can pine, look listless and go off their food when they are depressed.

As far back as ancient Egypt, dogs have been bred to do specific jobs on farms and in hunting.

Today, the need for working dogs has diminished, but we still breed them as surrogate friends and partners, a situation which has led some experts to believe we might be transferring our own negative emotions onto our pets.

A famous Austrian experiment has shown dogs can pick up on the thoughts and intentions of their owners from many miles away and don't just rely on physical clues to interpret what their owners want.

In the study, conducted by Dr Rupert Sheldrake, a dog and its owner were filmed simultaneously in separate environments.

Dog could sense its owner



The female owner went out for the day while the dog remained at home. The owner was instructed to return home at a time chosen by the researcher and to do so in a taxi so as not to provide any familiar car sounds.

Just 11 seconds after she was told to go home, the dog moved to the window, where it could look out and await her arrival.

It remained there the entire 15 minutes it took the woman to travel home, proving, says Dr Sheldrake, that thoughts and intentions can be transmitted to dogs.

So perhaps the dogs jumped to their deaths because they picked up on some human cues.

Dumbarton, near to where the bridge is situated, is a site of economic decline and regularly voted one of the most depressing places in Britain to live.

Suicide among the adult population has risen 200 per cent in the past three years, and it is now the leading cause of death among young men in the area - greater even than road accidents.

However, none of the owners whose dogs jumped from Overtoun Bridge reported any suicidal feelings and after careful analysis, Kendal Shepherd concluded: 'Human suicide is usually precipitated by a feeling that tomorrow will not be any better than today.

'But there is no evidence to suggest dogs have a sense of now and tomorrow.'

If not suicide then what?



So if the dog deaths cannot be attributed to suicide, what is causing them?

In a final bid to solve the mystery, canine psychologist Dr David Sands was dispatched to Dumbarton to try to view the bridge - and the sensation of crossing it - from an animal's point of view.

His first experiment was to recross the bridge with the only dog known to have survived the fall, to see how she reacted.

When he took 19-year-old Hendrix to the scene of her near-death experience, the dog walked happily across the bridge until towards the end on the right-hand side she suddenly tensed.

Because of her advanced age, Hendrix did not have the strength to jump, but something had clearly caught her attention, and Dr Sands concluded one of her three primary senses - sight, sound or smell - must have been so stimulated that she experienced an overwhelming urge to investigate.

Sight was quickly eliminated, as from a dog's eye view the only thing visible on the bridge is uninterrupted-granite.

Visit from an animal expert



To establish if either sound or smell was the culprit, specialists from a Glasgow acoustics company and the RSPB's David Sexton, an animal habitat expert, visited the spot.

Locals thought the nearby nuclear base at Faslane might be emitting some sound audible only to dogs, and there was also the possibility that nearby telephone pylons or the bridge structure itself might give off a sound only animals could hear.

However, after monitoring sound levels across the bridge, acoustic experts found nothing untoward that might explain the dog deaths.

Sexton, on the other hand, who laid bait in the undergrowth beneath the bridge, soon discovered that mice and mink resided there, while evidence of squirrel nests was also found in cannons embedded in the bridge's structure.

In order to narrow down which smell might be attracting the dogs, he distributed odour from all three species in a field and unleashed ten dogs - of the varieties which have died at the bridge - to see which one most interested them.

His findings were remarkable. Of the ten dogs tested, only two showed no interest in any of the scents while the overwhelming majority - 70 per cent - made straight for the mink.

Could a mink be the cause?



The mink's powerful anal glands leave marks wherever they go and the strong musty smell they emit is obviously proving irresistible to dogs.

It would also explain why the deaths have all occurred on sunny, dry days - relatively rare on the notoriously wet west coast - when the mink smell has not been diluted by the damp weather.

Furthermore, the theory fits with the timeline of the deaths - single minks were introduced to Scotland in the Twenties but only started to breed in large numbers in the Fifties - which is when the mysterious dog deaths began occurring.

But there are 26,000 mink in Scotland. Why are dogs in pursuit of them only jumping to their death from this particular bridge?

According to Dr Sands: 'When you get down to a dog's level, the solid granite of the bridge's 18-inch thick walls obscures their vision and blocks out all sound.

'As a result, the one sense not obscured, that of smell, goes into overdrive.'

For Donna Cooper, at last there is some explanation to offer her troubled son for the reason behind the death of their beloved family pet. Yet for others some questions still remain.

Why for example are all the deaths centred around the final two parapets on the right-handside?

Until a satisfactory answer is found how many dog lovers will feel brave enough to walk their animals over the mysterious ramparts of the dog suicide bridge?

Dog Suicide Bridge is on Channel Five on Wednesday night at 8pm