Detection Dogs: Learning to Pass the Sniff Test

With drug laws changing, there's a push to retrain and evaluate detection dogs. So how does a dog learn not to detect marijuana?

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A U.S. Customs and Border Protection officer uses a detection dog to sniff out cash hidden in cars heading to Mexico.

Anyone who's been through an airport, crossed national borders, or gone to a public school in the United States has seen detection dogs, noses diligently sniffing for illegal drugs or banned produce and invasive insects.

There are even dogs trained to detect wildlife or wildlife parts, like rhino horns and ivory, that smugglers try to sneak across borders. Just last week, the U.S Fish and Wildlife Service graduated their first class of dogs—four retrievers—trained to sniff out illegal wildlife.

But what happens when one of those drugs, fruits, or animals is taken off the list of contraband? The question has gotten new currency since Washington state and Colorado legalized marijuana through voter-approved referendums last fall.

At least 16 other states, meanwhile, have some form of legalized or decriminalized marijuana, whether for medical or recreational uses. And other states are taking steps toward legalization.

Some police departments in Washington have already announced plans to retrain their canines to stop indicating when they smell the plant. Other states may soon find themselves having to follow suit.

Mary Cablk, a scientist at the...

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