Why Don’t Cardinals Migrate?
For the last two videos, we’ve been focused on birds who migrate long distances every year: how they do it, and why they do it. This week, we turn our attention to the birds who don’t, like the Northern Cardinal. How do they survive the harsh winters that drives other birds thousands of kilometres south, and why do they choose to stay when so many others go?
EPISODE NOTES
Northern Cardinals are a fairly recent addition to Canada’s menagerie. As the climate has warmed (and bird feeders have gotten more popular) they’ve gradually moved into newly available territory and expanded their range north bit by bit where they can still weather the winters.
Case in point, a story I mentioned in the episode notes for part 2 of the Point Pelee series - when naturalist Dr. William Brodie visited in 1879 the locals told him about an ‘invasion of warbirds’ which he identified as Northern Cardinals. At the time, they would have been a surprising sight and not at all common in the area. That was at the start of what has been a century of cardinals’ expansion northwards.
TRANSCRIPT
4 billion birds leave Canada to migrate south every winter, to balmier weather and a smorgasbord of food.
This isn’t about them. This is about the ones who stay behind. Like Northern Cardinals, who stay in Canada all year but are often associated with winter when the bright red of males pops against the snow.
And since we spent the last two videos asking ‘how’ and ‘why’ birds migrate, today we’re asking ‘how’ and ‘why’ these birds… don’t.
As to the ‘how’. They start preparing for winter like migratory birds do, by gorging themselves on fatty foods. But cardinals are doing it to build a layer of insulation.
Once winter sets in, their first line of defense is feather fluffing. By puffing themselves up, cardinals actually create even more insulation. Pockets of warm air form, trapped between feathers, that slow the onset of cold.
But past a certain point that won’t be enough. That’s when cardinal biology picks up the slack. Their blood flows really quickly so it doesn’t lose a lot of heat as it circulates. And if they need to, cardinals can restrict their blood flow to favour their core over their extremities.
If that’s not enough, they can also shiver! But rather than outwardly shaking, they activate opposing muscle groups to create specific internal contractions that generate and retain heat more efficiently than human shivering.
And they can up their odds by huddling together for warmth and hiding in conifers to cut down on wind. So cardinals have an arsenal of tricks against the cold.
And that answers ‘how’ they stay north all winter. But we’re left with ‘why?’ Why go through a life-or-death struggle against freezing and starvation while so many others wait it out on a warm, abundant vacation? I mean, 78% of Canadian birds can’t be wrong, right?
Well, remember how migration evolved. It was a gradual response to increasing seasonality, multiplied by countless generations. So now, without any one bird choosing to fly thousands of kilometers a year, they’ve all just wound up accidentally doing it. Not because it’s necessarily the best solution - it’s just the one they ended up with.
Which is to say, sorry 78% of Canadian birds but… maybe you are wrong? Because when you think about it, long distance migration is… pretty insane. Yeah, it’s nice when you arrive, but getting there? And back? Means a brutally exhausting trip over endlessly unpredictable terrain. It is, in fact, a bit of a death trap.
Northern Cardinals don’t have a stellar mortality rate. The chances of an individual making it through a year are only about 65%.
And yet: for a bird making a long migration twice a year? That survival rate is a coin toss. 50%. In a study on migratory raptors, mortality was six times higher during migration than the rest of the year.
The Northern Cardinal happened to evolve differently, to withstand rather than retreat from winter. It’s not that they’re missing out on an easy season down south. The truth might be crazier: that the only thing more dangerous than spending months freezing and nearly starving… is migration.
And next week, to finish off this series, we’re going to take a look at the absolute poster-birds for migration… and ask why they’ve been slacking off lately.