OTTAWA — Political defections in Canada go right back to 1869 in the very first Parliament, when Nova Scotia MP Stewart Campbell moved to the Liberal-Conservative party from the anti-confederate movement.

But for Campbell, and most MPs who followed his example over the years, jumping ship eventually became a political kiss of death.

MPs have changed parties for a variety of reasons. Some acted out of principle, others out of pique. Some were moved by opportunism and the glittering lure of a cabinet seat.

Paul Hellyer, a Liberal minister in the 1960s, lost the party leadership to Pierre Trudeau and ran as a Tory. He lost. He formed his own party. And lost again.

Jack Horner, a veteran, high-profile, rock-ribbed Alberta Conservative took a Liberal cabinet post in 1977 and was trounced in the 1979 election.

Hazen Argue, a prominent 1960s New Democrat lost a leadership bid in 1961. He promptly joined the Liberals, won re-election in 1962 and then lost his seat in 1963. He eventually ended up in the Senate.

Belinda Stronach, in moving from the Conservatives to the Liberals, is the latest politician to take this calculated risk, but she's doing it at a time when the political price of defection seems to have eased.

And at a time when more MPs seem willing to take the chance.

"There do seem to be more (defections) in the last few years but you could also say we have more MPs," says Nelson Wiseman, a political science professor from the University of Toronto.

"It might also reflect the fact that the elections now are more than ever controlled from the top down in national campaigns where the local factors mean less."

The present Liberal government now has three Conservative defectors in its ranks _ two of them in cabinet, including Stronach.

Public Works Minister Scott Brison was a front-bench Conservative when he jumped to the Liberals in December 2003, just as Prime Minister Paul Martin took office. Brison has gone from being a question period gadfly to a fly swatter as he leads the government's sponsorship defence.

Former Reform, Alliance and Tory MP Keith Martin ran and won as a Liberal last June, and now is a parliamentary secretary.

Martin's government also includes Transport Minister Jean Lapierre, who may be the reigning champion of ship-jumpers.

He began as a Liberal MP in 1979. He became an Independent for six months in 1990, then sat with the Bloc for two years. He left federal politics for a decade and returned as a Liberal last June.

That kind of flip-flop isn't unique. In Britain, Sir Winston Churchill twice changed parties, going from Tory to Liberal and back. After his second change, he noted: "Anyone can rat, but it takes a certain amount of ingenuity to re-rat."

Alberta MP David Kilgour is also well-travelled politically. After 11 years as a Tory, he joined the Liberals in 1991 and was re-elected four times, only to become an Independent last month.

Between 2000 and 2003 there was a rash of defections to the Liberals from the Conservatives, the NDP and the Bloc. There was also John Bryden, who jumped the other way, to the Conservatives from the Liberals for a three-month stint last year.

There are no simple explanations for this, says Wiseman.

"There are just too many factors," he said. "Maybe what's telling is that it speaks to the great volatility of politics in this country."

Allen Tupper, political scientist from the University of British Columbia, said "it's very difficult to say what's happening."

The biggest round of defections in modern history came in 1990, when Lucien Bouchard abandoned his great friend Brian Mulroney and led a clutch of Quebec Tories to found the Bloc Quebecois.

That was followed in 1993 by the collapse of the old Conservatives and the elevation of the Bloc to Official Opposition, developments that still echo politically.

"A lot of this, I think, is a function of the realignment of the parties that occurred in 1993," said Tupper.

He said the reconstituted Conservative party remains a frail vessel and "very susceptible to the sort of things that have happened."

There is also a lot of overlap between Liberal and Conservative policies.

"That's where I think the ease of transit is," he said.

Whether defectors hang onto the seats often depends more on personalities than politics. Brison, for instance, was a well-liked MP in a strongly Conservative riding and the voters stuck with the man over party.

Stronach may hope that applies to her as well.

Antonia Maioni, a political scientist at Montreal's McGill University, says Stronach has strength in her riding.

"As far as I can tell, she is someone who is very attuned to local needs."