A sea lion crawled out of a Delta waterway in January, across a field and into a farm near Tracy.

A 19-foot bottlenose whale achieved a British first last summer when it swam up the River Thames in London past Big Ben and Parliament, before dying.

A manatee, a creature found in warm Florida waters, made its way up the coast and followed a river last year to New York City and then swam off.

It's not just the two humpback whales that swam upriver to Sacramento and international fame last month that have fascinated and puzzled people with travel out of the ordinary.

"There are many species that end up in places we don't expect," said Jay Holcomb, director of the International Bird Rescue and Research Center in Cordelia. "I think sometimes they just make mistakes."

Or, Holcomb said, "The animals may be simply curious. Each species has its own story."

Some scientists, environmentalists and animal rescue experts say the unusual travel may be linked to storms, food shortages, sickness or injuries. In some cases, they said, global warming or sonar testing may disrupt habitat and confuse the animals.

Scientist say they may never know what motivated Delta and Dawn, the humpback whales that visited the Delta for two weeks before returning to the Pacific Ocean last week.

After all, whales can't talk, or at least they can't in a way people can understand.

Under one theory, the mama whale sought out calm waters to safely rest and recuperate from suspected boat propeller wounds to both whales. The mom may have sensed she and her calf would be vulnerable to killer whales known to prowl the Northern California coast.

The humpbacks' tale has some parallels with the plight of an endangered North Atlantic right whale and her injured calf that were out of place this winter.

The two whales -- the calf with an apparent propeller wound like the two humpbacks in the Delta -- were spotted in January along the Gulf of Mexico more than 1,200 miles away from their normal wintering habitat.

The Coast Guard issued alerts to shippers and boaters to steer clear of the two whales.

Some environmentalists suggested Navy testing of long-range sonar may have confused the whales. Navy officials say there is no proof.

Injured or sick animals are known to land in strange places.

A green heron too young or sick to fly boarded a San Francisco-bound BART train in August last year, causing a stir among passengers.

One rider brought the heron to the bird rescue center in Cordelia, where it was nursed to health and later released in the Suisun Marsh.

Birders are still cooing over the 2001 sighting in Marin County of a Central Asian bird that had never been seen before in North America.

The greater sand plover, a small wading bird with a thick bill, is believed to have flown over the Pacific Ocean and landed in Bolinas Lagoon.

"Birders traveled from other states to see the plover," recalled Steve Glover, a bird-watching trip leader with the Audubon Society's Mount Diablo chapter. "Sometimes, birds turn left when they should have turned right."

Young birds and animals sometimes end up in odd places as they learn how and where to survive.

Albatross, big birds that live at sea, occasionally mistake barges or tankers at sea for their island breeding habitat.

"We get calls from ships docked in the Bay asking us to rescue this big bird that's been on board for days or weeks, and it won't leave," said Susan Heckly, rehabilitation director at the Lindsay Wildlife Museum in Walnut Creek.

Food shortages can pressure animals to change travel patterns.

The Marine Mammal Center in Sausalito this past winter rescued 34 beached young northern fur seals, a species that lives at sea, breeds on islands and rarely comes to the mainland The center usually gets no more than one or two of this type of seals in a year.

"We're not sure what happened, but we think something may have affected their food supply," said Doreen Moser Gurrola, assistant education director of the Center.

A bumper crop of northern fur seals born on the Farallon Islands also may have played a role in the high number of fur seals coming to shore, where they are rarely seen, Gurrola said .

Holcomb of the bird rescue center in Cordelia said he is pleased when he hears wildlife experts admit they don't understand the strange travels of wildlife, like the two whales that just left the Delta.

"I think these animals in unexpected places puts us in our place," Holcomb said. "It shows us there's a lot we don't know. Maybe the animals know a lot more than we give them credit for."

Reach Denis Cuff at 925-943-8267 or dcuff@cctimes.com. News researcher Beverly Hunt and Associated Press contributed to this story.

UNEXPECTED CREATURE TRAVEL

A 19-foot-long bottlenose whale swam up the River Thames in London in January 2006. Scientists suspect the whale took a wrong turn near Scotland. The whale died during rescue attempts.

Bottlenose whales, which normally swim in colder waters in the North Atlantic, were seen off the East Coast last summer.

Caspian terns, which breed on islands in very few places, built nests on two Long Beach barges last year. Three individuals face animal cruelty charges for allegedly washing off and drowning the chicks and eggs.

A single snowy owl made an usual winter stop in Suisun Marsh last year. Food shortages in its habitat to the north may have motivated its travel plan.

A sea lion emerged in January from a Delta waterway near Tracy, crawled across a farm field and into a barn. The sick animal died after it was rescued.

Salmon are showing up in larger numbers in the Arctic Ocean off upper Alaska, far north of the rivers that support a commercial salmon industry. Some suspect global warming is making cold rivers more attractive to salmon.

A rare yellow-billed cuckoo was found near a Richmond house about eight years ago in its only confirmed sighting in Contra Costa County. The bird lives in the Central Valley.

A Layson albatross, a bird that lives at sea, was found walking down Third Street in San Mateo in November 2003, a year after the same bird had hitchhiked a ride on a ship from far out at sea to docks in Benicia.

In 1985, Humphrey the humpback whale became a celebrity with its visit to the Delta before swimming back to sea.