The list of Liberal government members in Ontario and Quebec opting not to run again in this year's provincial elections is growing longer by the day.

And while it could be the result of a natural cycle that all long-standing governments face, it also could be a sign that the departing incumbents can see the writing on the wall.

CBC polls analyst Eric Grenier looks at the Liberal incumbents who aren't running for re-election in the Ontario and Quebec provincial races. 3:40

With the exception of a brief 19-month interregnum by the Parti Québécois between 2012 and 2014, the Liberals have governed both Ontario and Quebec since 2003.

And in both cases, the Liberals will be in tough spot to extend that streak beyond 2018.

In Ontario, the Liberals under Kathleen Wynne trail Doug Ford's Progressive Conservatives by about 17 points ahead of the June 7 election.

Philippe Couillard's Liberals in Quebec are behind François Legault's Coalition Avenir Québec by a smaller margin, but Couillard's low support among francophones makes his re-election odds in October look long.

Whether the exodus is due to the years in office or the sagging polls, both parties will have to campaign without a lot of familiar faces this year.

In Quebec, 12 Liberal MNAs have already announced they will not run for re-election, and rumours are swirling about a number of others — perhaps as many as a half-dozen more. The current list of those quitting the field includes cabinet ministers like Martin Coiteux, Jean-Marc Fournier, David Heurtel, Laurent Lessard and Stéphanie Vallée.

A similar number are heading for the exits in Ontario, or have left already. Glen Murray left cabinet last summer and Eric Hoskins followed in February. Former ministers Deb Matthews, Liz Sandals and Brad Duguid are also calling it quits, while Premier Wynne will have to replace Michael Chan and Tracy MacCharles in her current cabinet if she is re-elected in June.

It doesn't give the impression of a government confident in its chances.

Poor historical precedents for the Quebec Liberals

Though the polls aren't as bad for the Quebec Liberals as they are for their cousins in Ontario, the historical precedent on caucus departures is a bad sign for Couillard.

Just over a fifth of Couillard's Liberal caucus is not re-offering in October. The last two governments to see more of its members forego running for re-election were Daniel Johnson's Liberal government in 1994 (about 41 per cent of his caucus did not stand for re-election) and Bernard Landry's PQ government in 2003 (about 23 per cent).

Both were defeated.

In Quebec's elections of 1998, 2007, 2008 and 2012, only about 10 to 13 per cent of the governing party's caucus did not run for re-election. Only in 2012 was that governing party defeated.

The opposition Parti Québécois has also lost a significant portion of its caucus as polls suggest the party is on track for a third-place finish. It's a higher share than other opposition parties over the last two decades — though not abnormally high. Since 1994, between 10 and 20 per cent of opposition party MNAs did not run for re-election.

The CAQ, leading in the polls, has only one MNA not interested in a new mandate.

Highest rate of departures in Ontario in decades

In Ontario, no government since at least 1990 has seen as large a share of its caucus pass on running for re-election as Wynne's government did this year (that includes Hoskins and Murray, who have already bolted).

But the historical precedent isn't as dark for Wynne as it is for Couillard.

The Liberals in 2011 and the PCs in 1999 saw shares of the government caucus not running for re-election — 20 per cent and 18 per cent, respectively — that were similar to the 21 per cent departure rate the Liberals see in 2018. But both the PCs under Mike Harris in 1999 and the Liberals under Dalton McGuinty in 2011 were re-elected.

Nevertheless, these departure numbers are far higher than they were for the last three defeated Ontario governments. The rate of non-incumbency was 10 per cent or less for the Liberals in 1990, the NDP in 1995 and the PCs in 2003.

But recent federal history suggests Ontario may be an exception to the rule. Since 2004, the federal governments with the highest share of incumbents not running for re-election were those of Stephen Harper in 2015 (defeated) and Paul Martin in 2004 (reduced to a minority).

Chicken or egg

Asking why this happens invokes a bit of a chicken-or-egg dilemma. Do governments in office for over a decade face tougher re-election odds because more of their members retire? Or do more long-standing government members retire because re-election odds get worse the longer a party is in power?

Can a string of resignations and retirements due to an expected electoral defeat become a self-fulfilling prophecy?

Undoubtedly, time is a big factor in this equation. Politics can be a gruelling profession, so it's only natural that a government experiences more turnover the longer it's in power.

But there's another factor that could partly explain the higher rate of retirement in Quebec.

Golden parachute if you quit now, not later

In 2015, new rules were adopted in Quebec that limited when a "transition allowance" would be paid to retiring MNAs. Prior to the change, an MNA who retired in the middle of a mandate would still get the allowance — a sum that depends on how long an MNA has served, but is often in six figures.

After the change, an MNA who retires mid-mandate is not awarded the transition allowance. They must finish their term before retiring, or be defeated in an election, in order to get paid.

That undoubtedly is a factor in Quebec (Ontario MPPs get their allowance either way). Politicians can no longer try their chances and throw in the towel afterwards if their party fails to form government. They now need to be ready to serve a full four-year term — regardless of whether their time is spent in government or in opposition.

So while MNAs in Quebec have an extra incentive to stick it out, Liberals in both provinces are reading the tea leaves ahead of this year's provincial elections.

The polls aren't looking good for them and many are concluding they aren't up for another run.

But of course, it could be just a coincidence.