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The news is all about birds this week!
Well, our news, at least. And really, what else do you need to know?
So first up, a review paper out this week in Trends in Ecology and Evolution
suggests that certain bird species, as well as other animals,
may be sort of shape-shifting to keep up with the climate crisis.
In particular, scientists were looking at a general pattern
naturalists have noticed called Allen’s rule.
Picture a bird, like a little sparrow or something,
sitting on a branch in a snowy forest, trying to keep warm.
Most of its body is covered in feathers, which it can poof up for insulation.
But not its beak, which is naked.
This makes the beak kind of a weak point, a little uninsulated spot where the poofy
sparrow will lose body heat, putting it at risk of bird hypothermia.
So you might imagine that, in this snowy forest, having a tiny beak
might be advantageous, because you’re minimizing heat loss.
On the other hand, take that little bird and put it in a desert,
where the bird is no longer at risk of hypothermia,
but instead birdy heat stroke.
There, maybe a big honking schnozz would be better,
since it can help heat escape. And that’s the logic behind Allen’s rule.
In short, warm-blooded animals tend to evolve to have
bigger heat-radiating appendages, like ears, tails, or beaks, in warmer areas
and smaller ones in colder areas.
And, indeed, we do generally see this play out in a lot of species, including birds.
What’s interesting here today is that, all around the world,
the average temperature of different regions is rising due to the climate crisis.
Which begs the question of whether we’ll see a corresponding
shift in the size of heat-radiating appendages, as predicted by Allen’s rule.
Like, if the average size of certain birds’ beaks
has increased over time in areas that are getting warmer.
To figure this out, the researchers in this study compiled and sifted through
studies of both old museum collections and living animals in the wild.
And lo and behold, it seems like this is, indeed,
happening to many animal populations around the world.
For example, it turns out that Australian parrots are getting bigger bills,
with changes lining up with the average summer high temperatures
in the five years before collection.
And in the North American dark-eyed junco, which is an extremely cute little bird,
bigger bill sizes were associated with episodes of unusually warm winter weather.
And the researchers saw this in mammals too,
such as increasingly large appendages in shrews and bats.
Now, it’s worth pointing out that this doesn’t mean
that individual animals are morphing their bodies.
Rather, it reflects an overall shift in the population
over time thanks to natural selection. So it’s the average appendage.
And it’s difficult to actually tie any one particular change to the climate crisis
specifically, since there are a lot of other factors,
like possible changes in food sources, that could be responsible.
Nevertheless, taken as a whole, there is enough there to argue
this is happening on a broad scale. Now, speaking of birds with big schnozzes,
let’s zoom in on the southern hemisphere for our second story.
Aotearoa New Zealand, if you didn’t know, is home to the kākāpō,
a large, flightless parrot that’s just, well, just look at it.
I think we can all just really enjoy the fact that this bird exists.
Unfortunately, like a lot of large flightless birds that live on islands,
while it used to be really common before people, today it’s pretty rare.
While their historic numbers may have been in the hundreds of thousands,
by 1995 they’d dropped to 51 individuals.
50 on an isolated island and just one, named Richard Henry, on the mainland.
Today their numbers have improved, up to about 200.
But going through such a sudden population drop
is rarely good news for a species.
Even if kākāpōs were to swell back up to previous numbers,
they still seem to have lost about 70-80% of their previous genetic diversity.
This kind of population bottleneck generally results in in-breeding,
which typically increases the number of harmful mutations
present in a population’s collective DNA.
But, remarkably, these parrots may actually be doing better than we’d expect.
Scientists publishing this week in Cell Genomics analyzed the genomes of 36
modern individuals and compared them to DNA from
13 130-year-old specimens from the mainland.
That is, before the bottleneck took place and the mainland population went extinct.
They found that the current population actually seems to have lower overall
numbers of potentially harmful mutations, counter to what we’d expect.
Now, this could be partly due to genetic drift,
which is basically just the random chance of a mutation disappearing.
But it could also be the result of something called purging.
See, in a large population, harmful variants of genes are more likely
to get spread around and paired with healthier versions,
so they don’t end up having much impact.
But in a small population, as happens with inbreeding, the mutations are more
likely to get concentrated in individuals, and then
natural selection kind of does its thing.
Basically, in smaller populations, the harmful mutations have a harder time hiding.
Unfortunately, kākāpōs still experience other problems
as a result of their small population.
For example, their eggs have a relatively low chance of hatching,
which may be a result of inbreeding.
But the good news is that these findings could be helpful in
protecting and growing the kākāpō population.
So, they’re still critically endangered, but it does give us a bit more hope
about keeping these birds around for a long time.
Thank you to Omaze for sponsoring this episode.
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