Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences
at the University of Oxford, and we're right in the middle of this very serious corona virus crisis right
now. And my students are all stuck at home and we want to keep them in touch with biology
and keep in touch with us. And so we're going to make a new series of videos and they're going to be called back garden
biology.
Hello, welcome to this episode of Golden Biology, and it's an incredibly hot, sunny day in
a very, very dry month of May, and I'm sure you're finding the same in your garden, having to do a lot of watering
and so on. For the first time, this episode is going to be centred on birds.
I've kind of avoided that because it's very difficult to take good footage of birds unless you've really got a good camera,
which I don't really have. But I was able through the very kind agreement of some of my
colleagues to borrow some footage. So you're gonna see a mixture of footage. Some of it is sort of fairly poor
quality. And that's my footage taken in my garden, but also some much better. Close-Up shots
may have been taken by colleagues in the zoology department who work up at White Wighton Woods
and White and Woods is really famous for the study of great [INAUDIBLE] and bleated. So
they've been monitoring both great [INAUDIBLE] and blue [INAUDIBLE] at Weitzen for about 60
years. And that makes it one of the longest running ecological studies in the country, possibly
in the world. Now, I was inspired by that because I put up a nest box in my garden, as I'm
sure many of you have done. If we just pan over behind me, we can hopefully see it. So that is a
brand new nest box that I was given for as a Christmas present. And we decided
to put that up just the day after lockdown. And to be honest, we thought we're probably going to be too late
to have anything use it this year. But within 24 hours of putting that
nest box up, a pair of blue [INAUDIBLE] arrived and started checking it out because we were really delighted about
and in fact, they've just finished and all left has nothing, no sound coming from there anymore.
So I want to just talk you through what is the nesting behaviour of the blue [INAUDIBLE]? How long does
it take? What do they do? How many eggs do they lay? And they're going to look at some of that and a bit more detail.
So it begins in about February for blue [INAUDIBLE]. They start looking for nest sites.
Obviously, our two have not been very successful, haven't really found anywhere that they like that much. And that's
why they had to wait a bit late and as soon as they saw that they were in there. Now the female alone
will first start to build the nest. She's not going just layer actions to the bottom of that box and she collects
Moss to do that. So we saw her actually in the lawn pulling up moss and bringing it
back and polluted make, you know, as all animals are sort of individuals. They didn't all make
an identical nest. Some of them build a thick layer of moss that just a few feathers on the top.
Some of them have a thin layer of loss with a great big carpet of feathers on the top. But Bluett is very
fond of feathers for the tops of their nests. And those examples were from Wighton,
where the researchers are going in and having to monitor the nest very closely. And that takes
the female bullshit about two weeks. And she probably won't get any help from the male in doing it.
And once she's happy with that and she's got it built, she starts to lay her eggs and she will lay
one egg every day until she has her clutch. And only then will she start to
incubate the eggs. And to do that, she'll actually still strip off some of the feathers from her
belly so she can press her bare skin against the eggs and transfer warmth to them.
And she has to incubate them for around two weeks. And when that's processes finished out will
emerge these tiny sorts of pink, helpless chicks that look a bit ugly, to be honest, like a little newborn
mouse or something very helpless, obviously needing a lot of help from the parents. And that's
when we really started to notice them, because then we realised that the two parents have to work like crazy.
Each one of those chicks can eat up to 100 caterpillars a day
in order to grow as fast as they need to. So both parents are backwards and forwards in and out
of the box to the point where sometimes one parent would arrive as the other are leaving and have to sort of bounce
off in mid-air before it could even get in and feed them. So you see how hard they are working.
And in fact, it's been estimated that birds who are rearing chicks are working
as hard as a Tour de France cyclist. So it's the equivalent of doing the Tour de France as a human. If you're a
bird trying to to raise offspring, it's hugely energetically demanding. And what
you may have noticed, irrespective of whether you actually have a nest box in your garden, is there's a period of time
for about a week when Blue Tech seemed to be launching themselves at the windows of your house. And I managed
to film this one in the front of my house when I was actually staking out the sparrows last week.
And you can see them going all around the windows and behind the drainpipes and they are looking for spiders.
And people have always noticed this about its blue [INAUDIBLE]. And great is that they start feeding chicks spiders
at a critical period. And they wondered why. And someone did a really nice study to investigate
it. So proteins, which are the molecules that are the building blocks of all organisms, are made
up of things called amino acids. And there were 20 different ones. And some of them are harder to obtain
than others. And spiders are peculiarly rich in a particular amino
acid. And so somebody did a study where they gave bluechip chicks a supplement which contained
this amino acid to see what impact did it have. And it affected their behaviour as the chick wants
the chicks fledge and were older. So it made them bolder and more inquisitive and investigative.
So that behaviour of looking for spiders is really kind of to protect the mental
developments, if you like, off their chicks. Now, once the chicks, about 14 weeks old, they
looked like they're sorry, 14 days old, just two weeks later, they look like this. You can see they've got
lots of feathers on the man nearly ready to go. And then the parents change their behaviour about it.
And when they arrive at the box, as you can see here, they start shaking quite a lot
like this. And that's that kind of aggressive shouting, get out of that box. You know, you need
to head. We need to get out of here so I can start feeding you properly. And they
will keep feeding the chicks. The parents will stay with them. I don't know quite where they've gone. I don't see them around the garden. No,
but they will continue to look after them for another few weeks. That's the pinch point for bleated
chicks, the young ones. Are they going to make it? They've got to fatten up. They've got to make it through the winter.
Of course, most of them won't, because a lot of chicks are born every year. So the bleated
average klatsch size is about seven, but it can be a lot more. And that's the thing that we're going to look at
in a lot more detail today. Why is it that different birds have different
sizes of clutch? And what factors determines that?
So I got through a made. Three little helpers here, but great. It's not. It's because more of the
work that I'm going to talk about has actually been done with great [INAUDIBLE] rather than blue [INAUDIBLE]. There wasn't I
didn't have any. They played I honestly. Going to think about a life history
trait and a life history trait is a characteristic of a species that's
not a physical characteristic. So a physical characteristic might be something like wing length
or beak length, but a life history trait is something to do with the way
the bird lives its life. So it might be how long it lives. Lifespan is a life history trait,
or it might be the number of eggs that it lays. Or it might be. How much care it then gives to those
chicks when they hatch. Those are all examples of life history traits and whether traits are physical
or whether their life history traits. We believe as ecologists and evolutionary biologists that
all those traits are under natural selection and natural selection is a force
that shapes organisms. And it doesn't just shake the way they look, but it also shapes the way they behave.
I can also understand that a little bit better what natural selection is and how it works.
We're going to hear a little bit from Professor Stuart West, who is a professor of evolutionary biology
in the Department of Zoology here in Oxford. The theory of natural selection
is Darwin's greatest contribution to science, and it follows him just three simple ingredients.
First of those is variation. And all that means is that within a population of
something, you see variation. So, for example, if you're looking at giraffes, some might have
longer names. Some might have shorter legs. The second ingredient needs is
heritability. And what that means is the offspring are like parents. So to go back to
the giraffe example, giraffes with longer necks have offspring, belongingness,
leks, their babies are bigger things. Now, the third thing is slightly more
complicated thing is that you need differential success or differential fitness
limited to the linked variation. And what that means
is the individuals that are different, that have vary in their ability
to survive and reproduce. So again, if we go back to the giraffe example we
might find is the giraffes. Longer necks are better reaching out for trees.
They get more food. They're able to have offspring more successfully. So they end up having more offspring,
then draws shorter necks and evolutionary biology. We sort of lump all these things,
link your ability to survive and reproduce into a term called fitness. So this might be your ability
to cut food, aid, predators, anything like that. Okay,
so now we found out a little bit more about natural selection and how it tends to maximise
something called fitness, which we can say is probably best approximated by the number
of grandchildren that an organism has. Now, let's have a look at Harper's,
because something exciting has happened to them since we last saw them. All three of them have dealt log
and they've all got five eggs in them. I want you to imagine that five is the standard
number of eggs. That's a great tip. I don't think it is. In reality, it's more like seven. But I couldn't fit seven eggs
into my little nest. And what we're going to do is to try to understand if five
is the average that we observe, is that actually the clutch size that will maximise
their fitness. And one way we can test that is to change the number of eggs
that the birds have. By adding extra ones. So I could go to another bird's nest and I
could give this bird one extra egg. And similarly for this bird, I could perhaps
give it two extra eggs and then I could allow it to reach those extra eggs
and see how many chicks does it successfully rear. And when people do things
like this with birds, they tend to find that they are able to reia more chicks
than they would have tonight. They are able to reach those extra chicks. So it looks like their fitness
could actually be higher if they laid more eggs, which of course raises the question then why don't
they lay more eggs on? One of the criticisms of those studies is that it hasn't taken
into account properly of all of the costs of egg laying. So if you just
give a bird an egg that some offer bird has laid and they haven't paid the full costs of
it because they didn't have to manufacture the egg and perhaps they an incubator for quite as long.
The other thing that we haven't taken account of is that birds don't just live for one year. The
females might survive the winter. They have a reasonable chance of doing that. And they might have a higher
chance of doing that if they didn't have a very large number of eggs. Because the bigger the clutch,
the more food they have to find, the more tired they're going to be, the more rundown they're going to get.
So we have to think about the future offspring as well and whether they're being compromised.
So one way of doing this is a really nice study that did this instead. So they again started off.
With three different treatments, so they have their control birds, which would be laying exactly five eggs.
Then they found other birds who had clutches of five and they manipulated them in the following way.
So to some of them, they simply gave them to free eggs. So this one gets free,
actually didn't have to lay them. But she has got to incubate them and rear them
for another one. They decide, well, maybe a lot of the costs come from the actual incubation.
That's after all, it's quite costly for the bird. So they like this one. They didn't get free eggs. They actually
got free chicks. So they waited for the eggs to actually hatch and then transfer to
newborn chicks. I'm going to sort of put them on the side there. So she's also going to have two extra,
but she got them as chicks rather than as eggs. And then finally, this one is going
to have the toughest treatment. So what they actually did was to remove some eggs from
the nest. And if you remove eggs from a great titmice, they will lay more.
So she lays a couple of extra eggs and then we put these ones back.
Right. And now this one has the same class size as this one or
would have done in my cabinet rolled off. I just try and replace it. All right. So she's got the same as that
one. But those ones came for free. And this one had to pay the full cost
of those eggs because she had to actually leave them. And when they then calculated
the number of surviving offspring, how well all these birds did. These ones definitely
had lower fitness. That means that if you if they're really forced to pay the full
cost of all of those extra eggs, then it really does have fitness consequences.
And those fitness consequences came in part because the females didn't survive as well
till the following year. But also in part because if you give great, it's extra chicks,
they don't actually survive as well, because the larger the breed size, the smaller the chicks
are. So it looks like they've got more chicks, but actually they don't actually survive quite
as well. So some pretty clever stuff. It's all done very carefully by trained
researchers who know how to handle the birds and the eggs and know how much stress the birds
can manage. Don't try anything like this at home, for goodness sake. Right. Well,
let's end this where we began at the back of the garden, looking at my empty nest,
empty nest box anyway. So my blue [INAUDIBLE] have gone off and I hope that
those young are still alive out there and being fed by their parents. I hope this doesn't
happen to them. This was footage taken by my uncle. A sparrow hawk arrived in
his garden just literally a few days ago, found the Black Bird's Nest and came back
and at one blackbird nestling after another. I'm afraid that is what Raptors do once they find the
nest. They're not going to leave any of them behind. However, we can at least say that the
Sparrowhawk is a natural predator and it does have its own chicks to feed. I would plead with
you if you have a cat to think about the damage that cats cause. They are the source
of water. The biggest source of mortality for a lot of blue and greater chicks in gardens.
And of course, people want to keep cats and they are lovely animals. But there are things you can do to limit the damage they cause,
like making sure that they have a bell and also actually not letting them wander around at night
where upset. That's not when they tend to eat looters. But they do cause a lot of damage to frogs and small mammals at that
time. Well, I hope in your garden this week, you can maybe see some of these newly
fledged blue turtles and great chicks feeding and and moving around the garden and finding
food for themselves. And we'll see you next time on that garbology.