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.
So welcome to this episode of Back Garden Biology. Why were once again going to look at some birds
at this time? The birds of choice are going to be pigeons. And I want to start with
the wood pigeon of the wood pigeon is very common in Britain. There are an estimated five
and a half million breeding pairs. So you're almost certainly see them in your garden. If you have a garden,
unless you live right in the middle of a city where you might have another kind of pigeon, that will be coming to later.
Now, the wood pigeon is a very familiar site. They can become quite tame if you feed birds
in this feed around on the ground like this one. There's also some very
familiar sounds associated with the wood pigeon. So the call of the wood pigeon is very distinctive.
It sounds like someone complaining about their feet. That's how my uncle described it. Someone saying my poor feet
but my poor feet. Here it is, in case you don't know what I'm talking about.
The other very familiar sound of the wood pigeon is the clapping of the wings. So if
you walk out into your garden and they're feeding somewhere, you might hear a noise like this
and lots of pigeons make that kind of clapping noise as they take off. And it's something to do with
him being able to generate a lot of lift because they're big birds. I mean, it's about a rocket off vertically.
All right. So those are some of the familiar sounds and sights. This is a sound that you may be a bit less keen to
hear in your garden.
That is the sound of a wood pigeon attacking a lilac tree in my case, so
they will often sit in the top of various trees in my garden and attack with foliage. So they're just eating
the mature leaves of things like lilac and plum trees and hawthorn. And you think really
those leaves are clearly not very nutritious as we have seen in the world is green episode leaves.
Mature leaves are not energy dense food that poor quality food. So how
can a large bird, a wood pigeon that weighs about as much of this bag of beans, about half a kilo
or a standard bag of pasta? That's how much they weigh. How can they get away with eating such rubbish
food? So we need to ask ourselves, how would Pageau, which is a big bird,
can survive when it only eats low quality food? Now, that argument doesn't just apply
to wood pigeons so that all people in the world who do not believe that animals like this ever
really existed. Now, this is a model of a Brachiosaurus and that is a species of sauropod.
And the sauropods were a type of dinosaur that were the largest land animals that have ever walked
the earth. And they were truly gargantuan, some of them. And we know that they only at low quality
food. They just browsed on the trees of the time. And some creationists have said, well, we don't
believe they exist because it's impossible to imagine an animal that large could possibly have existed,
if at all it was eating this low quality food. So how is that possible? Well, the truth is, if you think about
mammals today, the very largest mammals, things like elephants and rhinos, also eat
very low quality food. So it's a general pattern that we see. And actually it does make sense.
So the cells inside large animals are actually much more efficient and require
less energy than the cells inside a small animal. And that's something to do with scaling.
It's masses. But it is true that small animals require much more food per
unit mass than a large animal does. So actually, it's only large animals that
can survive on low quality food. Small animals simply can't. So a shrew
can die overnight if it gets stuck in a trap and it doesn't have food. There's no way that will happen to
a large animal. So actually, it's one of the selective pressures for getting large. As you
can then have access to all the plentiful, low quality plant food that's out
there. So I've got this wonderful diagram drawn by former student Pandora Jun.
And this is a pigeon. So the pigeon eat some food. It doesn't have any teeth to grind
up the food first. And it goes down the oesophagus into the crop. And this is like a storage place
where it can keep a lot of food that it eats rapidly. So it can then fly off and doesn't have to stay around
on the ground for a long time. And from the crop, the food is passed into a first stomach.
Has a horrible name. A proven track is to remember that. And that first stomach is a bit like our stomach
in that it secretes hydrochloric acid. And a key enzyme to help digest food. But
there's also a second stomach, and that's called the gizzard. And that's really muscular and
strangely in pigeons. It contains a lot of gravel and grit and sand. The
pigeon deliberately eats. And so the food is churned up here. And then it's often passed
back into this stomach to get some more acid and enzymes and the fuegos backwards and forwards and backwards and forwards
between these two stomachs until the food is ground up and digested. And then it can go
down the long the short small intestine where the good stuff's all absorbed. Now,
the problem. Okay, that's great for the pigeon. So it's able to digest and get nutrition
out of this low quality food. But what about the nestlings, the young birds? They
need proper food. They need lots of protein and lots of fat. And that's not going to come from this
low quality diet. And so pigeons got a really special and cool adaptation for that. So when
the chicks hatch, the adults stop feeding a couple of days beforehand, and then both parents
can regurgitate from the crop a special food called crop milk.
And it's basically sloughed off cells that are just full of protein and fat and they regurgitate those up.
And that's all squabs, which is what the young birds are called get for the first week or so of life.
And only after that to the adult birds start to feed a bit and start to give the young birds
a bit of ground up, solid food as well. And pigeon chicks grow really fast because this
crop meal is so nutritious. And it's also a reason why pigeons only ever
have two eggs. They never lay more than that. And that's probably because they simply couldn't manage
to provide that crop milk. So more than two chicks at a time. But they do have multiple
brood. So it's quite different to the bloater who just mass warmth has a very large brood. They only
have two chicks. But they can repeat breed all the way through the year and during
lockdown. One of my former students, Anna Du'a, noticed that a pair of weapons were nesting
in a tree just outside the window of her flat. And she managed to film them
nesting and feeding the chicks through her not. As with our mobile phone, which is a really great
achievement, and here we have a bit of footage, you can see the adults regurgitating that crop milk to
the chicks and then the chicks growing and finally stumbling around, leaving the nest
and they fleche successfully. Now what? Pigeons aren't the only kind of pigeon that you might see
in your garden. And I'm going to go down to the town now, talks to town centre to me, another kind
of pigeon that where even less well disposed towards. So I'm sitting in Bond
Square in the centre of Oxford, just outside the Westgate. It's the shopping centre.
It's all closed out. It's quite a lot of people down here. And the pigeons, of course, know this is somewhere
where people congregate. So there's a big group of feral pigeons here. And what you're struck
by is the diversity of them. They've got lots of different plumage, types and colours. And that's pretty
unusual. If you imagine to be looking at a flock of sparrows, you wouldn't see that kind of diversity.
I can also say that quite a lot of them have got rings on their legs. And I know them that my
ex student, he was an undergraduates of mine. His name is Will Smith, who's now doing a P
HD on feral pigeons and trying to understand their origins because they're all descended
from a bird called the Rock Dive. And he's going to tell us a little bit more about
feral pigeons and the rock star and what he's trying to do in a moment. But perhaps we can just pan out
and see if we can see one of these birds. There were some just close by with some of these. But, yeah,
it's quite interesting as well to see how people behave towards them. People sorts of love and hate them.
People can't resist giving them food. But I've also seen a child sort of kicking at them, and that's a pretty common thing
to see. When you think about it, it's quite odd because people generally are well disposed towards birds.
And I don't think they would kick out any other kind of bird, but they seem to feel it's okay to kick pigeons
or don't quite know what that's all about. Pigeons have
been really valuable to scientists for a very long time. So, for example, Darwin was completely fascinated
by other breeds of domestic pigeon and all of these were descended from a single type of bad could erupt.
And these usually lived in caves near to the sea and they were probably really common. Dadge throughout Europe, Asia and North
Africa. But nowadays we're way more familiar with the pigeons that we see in cities and towns.
These city pigeons are called feral pigeons and they're basically free living. Domestic pigeons that have escaped
and bred over the last few hundred years. They come in loads of different colours, but most
of what's called a chicken pattern. And that means that they have lots of black marks on their wings, like this one here.
So feral pigeons like this are really good at surviving not only in cities, but also in the same habitats
as their ancestors. And when they meet rock doves, they tend to hybridised with them.
And there are so many feral pigeons around that they can easily hybridised the rock doves completely out of existence
and fully replace them. So this process is called extinction by hybridisation.
And that's what I study. So Flamborough Head in Yorkshire was home to what was probably the last
colony of rock in England. And it was also probably one of the largest Rogov colonies in Europe. And
you can see why it's got massive cliffs with lots of open land above and lots of small caves
opening to the sea. So it's perfect rucked of habitat for a pigeon spike to mix with rucked
of that probably at the start of the last century. And if you visit today, there are thousands of feral pigeons
and no rectums. And the same things happened across almost all of Europe.
My research is looking at the extent to which rodef does still exist in anything close to a pure form,
because the differences between Bodos and feral pigeons are quite small. We don't really know whether there are any colonies
left that still represent the original form. We do know that there's a type of bed that
seems to be a wild rodef, which is found in certain places in Scotland, in Ireland. And looking
at plumage is sort of helpful in identifying it potential death. This is one
that I caught in a flower meadow in the West. Now they are temporaries. He's got a big white patch on its back
to blackbirds and its wings and then a general blue grey. However,
there's lots of feral pigeons. Probably about a fifth of them have plumage that's almost identical to this.
So another way of identifying more rodents is to study their morphology, their shape.
In this photo, we have a feral pigeon on the left and a potential rubbed off on the right.
So first of all, the set that's out see a and it's the white bit on the top with the beak
is larger in the feral pigeon. Secondly, the beak is much thinner in the rock.
As well as this, the orbital ring, which is the ring of skin surrounding the eye, is pale in the feral pigeon
and dark grey interruptive. The biggest difference, once you get your eye in, is the shape of the head
itself. If you look at the rough stuff has much more of a round full head than the feral
pigeon. And that in the field, that's really distinctive. When you look at them through binoculars.
Stuff like this can be really useful and explain what type of pigeon exists in a particular location.
We really need to morphology image and genetics in combination to find out if there are any populations left.
They're still a representative about death. So from my work, I get to go to the Hebrides and the Northern Ireland,
Scotland. And I work with citizen scientists all around these regions to collect data to help us figure out
where the poorest relatives are and where exactly feral pigeons are invading. So this
work will allow us to protect any job of colonies, but also the process of exploring how the rodents
gone extinct across its original range will give us a model system which is really useful in helping to understand
how the process of genetic extinction works. And this is super useful because it's a process that affects
lots of different species and it's a major contributing factor in the global US biodiversity.
Well, we wish well every success with that project. What he's hoping is that on remote Scottish
islands and possibly in remote parts of Ireland, there are populations of pure rock
dive still left. And he has an army of volunteers out helping him. Thank you
very much to all of them who are taking part with that important project. Why have
feral pigeons ended up looking so different from their ancestors? Well, one of the reasons
is that there was deliberate hybridisation. So people have been domesticating pigeons for around
5000 years and possibly even longer. And as part of that process,
they've also used some other species of pigeons, although they're derived from the rock dive.
They've also been some crosses, for example, with the speckled pigeon, which is a North African species.
Some of that chequered plumage has come in from that species. And in addition to that, pigeon
fanciers who like to specialise in different breeds, different types of it's all the same species,
but they concentrate on exaggerating particular features. And Pandora, Juhan
and Joy, looking at all those different types of pigeon that exist out there, the different breeds. And she's
drawn to some fantastic pictures as if they were kind of Tenzer profiles. So this is the frill back
which has been bred to have these extraordinary curly feathers all over its back. And
this one's called the pygmy poutre. And it's been bred to have an enormous sort of chest
full of feathers. So it's an extraordinary shape. And if you type in fancy pigeon into Google,
you will find some truly extraordinary pigeons. And through all that selective
breeding, you know, pigeon fanciers have been able to produce an incredible array
of different pigeons. Now, most of those are not going to be successful in feral flocks, which is why we don't
see quite the same level of variation in the feral pigeons as we do in the fancy breeds.
So perhaps it's time to re-examine our attitude to pigeons. It's absolutely clear
that we humans are not very tolerant of the species that have actually been very successful
in our wake. In other words, we're very sympathetic towards the species that we've kind of annihilated
or were causing enormous problems for and are becoming rare as a result of our actions. But we're all
the intolerance of the species that are actually doing very well and are able to take advantage of us.
So, you know, rats, we talk about pigeons being rats with wings. And that's really unfair
characterisation. They are just species that have been able to be successful around humans.
And perhaps we should learn to tolerate them a little bit more. Mean, especially as a gardener. Pigeons don't
really do a lot of damage in your garden. It's true of your growing brassicas and you definitely need
to put a net over them. But otherwise they're relatively innocuous, really.
So I would just urge you to think, you know, stop the pigeon. Never. Till next time.
Goodbye.