But what awaits you at the bottom is both delightful and disgusting. The mud that oozes between your toes is teeming with tiny shrimp-like animals. And it is these plump, squirming mud shrimp that are the heart of one of Fundy's most celebrated natural events—the annual arrival of millions of migrating shorebirds.

Trans-Atlantic migration routes of Semipalmated Sandpipers

Shorebirds are a fascinating lot, entertaining audiences with their precise mid-air acrobatics. Thought to have evolved to confuse predators, their synchronized movements have inspired writers and poets alike. Writer and naturalist Harry Thurston describes these manoeuvres in his book, The Nature of Shorebirds:

"As they bank, the light is absorbed by their dark backs, then reflected by their bright bellies...Sandpipers flow and turn together with such uncanny precision as to make one think they are a single organism."

"Basically they come here to get fat," said Thurston in an interview. "They come to feed on the huge densities of Fundy mud shrimp, Corophium volutator.There are as many as 20,000-60,000 of these things per square metre!"

"If these birds are disturbed too much they experience migratory failure. Some of these birds just literally end up dropping out of the sky."

Indeed, when the shorebirds aren't around, life is good for the little amphipods. Feeding on the abundant algae, detritus and diatoms from nearby salt marshes, they burrow into the sand when the Fundy's incredible tides roll out. But come July, when the shorebirds begin to arrive en masse, the mud shrimps' luck changes dramatically. Feeding on as many as 20,000 of them per day, the shorebirds rapidly deplete mud shrimp populations in a bid to pack on as much fat as possible for the non-stop 72-hour trip to South America.

Because of this massive food reserve, the Bay of Fundy is one of a handful of global "critical links" for Shorebirds, as Thurston puts it. "Their survival depends on a few widely separated sites, and the Bay of Fundy is a very important part of that chain," he said.

Thurston explains that all of the critical links, from their breeding grounds in the arctic to their wintering areas in the south, need to be conserved. "Most of the continent is a barrens to shorebirds because most of it doesn't support what they need," he said. "We have to look at these critical links as oases. It's very important to conserve these areas."

Fundy mud shrimp, Corophium volutator

When birds are in such large numbers, stretching as far as the eye can see, it becomes far too easy to ignore that the future of shorebirds is in jeopardy.

As Thurston explains, there are three problems that could seriously affect the future of shorebird populations. "First of all there's a chronic threat. In the last 50 years tidal rivers have been dammed with tidal control structures for the purpose of protecting agricultural land and dykelands. What happens is we get this cumulative sedimentation in the bay that changes the nature of the mudflats, making them less amenable to mudshrimp.

"Then there's the acute problem that they face. There's a lot of oil transport to and from St. John, so an oil spill at the mouth of the bay could have serious toxic effects on shorebird habitat."

But far more immediate and real is the disturbance to the birds themselves. "As people become more aware of what's happening here, more people come to observe the birds," said Thurston. "What happens is people try and get too close, usually to take a picture. But anything that makes them get up and fly is putting them in jeopardy."

Observation platforms have been constructed in some areas around the bay, and Thurston advises people to stick to them. But where such measures have not been introduced, he suggests using a little common sense.

"If you're causing the bird to move, you're too close," said Thurston. "They're here to conserve calories. And if these birds are disturbed too much they experience migratory failure. Some of these birds just literally end up dropping out of the sky."

The Bay of Fundy sets the stage for so many incredible feats of nature—from 16-metre-tides to pods of leaping whales to the acrobatics of a million shorebirds. And fortunately, in light of this, many areas of the bay are now officially protected through national and international agreements. It is this kind of progress that will ensure, at least for a little while yet, that the mudflats will continue to teem with life, and the shorebirds will return to share Fundy's bounty.

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Shorebirds and Other Birds of Coastal Wetlands Part the Natural History of Nova Scotia, PDF required