30 December 2015

Freeze. Thaw. Freeze. Thaw.  In this non-winter of 2015 we’ve had days and weeks of warmth punctuated by occasional frosts.  Eventually the freeze-thaw cycle produces fermented fruit and that leads to drunken birds.

Fruit ferments outdoors when freezing temperatures break down the hard starches into sugars and then a thaw allows yeast to get into the softened fruit and begin the fermentation process.

The sweet, soft fruit is particularly tempting to birds.  After a good frost the ornamental trees in my neighborhood, like the one above, are swamped with hungry starlings and robins.  When they swallow a fermented berry it has a fizzy zing, but so what?  It tastes good.

But some birds don’t know when to stop.  They eat so much fermented fruit that they walk with a wobble and can’t fly straight.  When they’re falling-down drunk, they end up in “detox” at a wildlife center until they sleep it off.  Bohemian waxwings are famous for this.

Back in 2014 National Geographic reported on an incident in Whitehorse, Yukon when a bumper crop of fermented rowan (mountain ash) berries were the waxwings’ undoing.  The birds were in such bad shape that they ended up in Meghan Larivee’s “drunk tank” at Environment Yukon.

It turns out climate change is increasing the likelihood of these episodes up north.  National Geographic explains:

Larivee’s recent waxwing patients were admitted to her Yukon animal unit following several frosts and thaws due to warmer temperatures. … While fermentation is most pronounced in winter, “we also likely have longer autumns, which gives more time for berries to ferment, but still have early frost that allow sugars to be produced in berries early in the fall,” she said.

The waxwings were drunk on climate change.

Read more here in National Geographic.

(photo by Kate St. John)