Eggs- they're so much more than just a breakfast food. Each egg tells the story of a bird's ecology and behavior and the Field Museum
houses one of the largest egg collections in North America. Dr. John Bates isn't just any eggs-pert:
He's literally responsible for the book on the subject.
We met up with him in the egg collection to see what we can learn from
looking at different aspects of eggs like their size, the care they require, and their appearance and to hear about the egg research happening at
the Field Museum today.
Not a lot of people have spent a lot of time in the egg collection it's a collection
that's actually really amazing and yet at the same time
it hasn't had a lot of modern additions to it because people stopped collecting eggs back in about the
1920s or so for the most part and yet it's an incredibly important part of the biology of birds.
Oh, yeah, I mean all birds start as an egg, but there's a lot of variability in eggs themselves.
I guess to start with we can look at just the extreme differences in size.
Yeah, so we brought out some of the largest and smallest things so you can start small, let's do that.
These are long-tailed sylphs which are some hummingbirds from the Peruvian Andes. These are their eggs and they look like little Chiclets.
Yeah, they look like little breath mints or gum. They're like the size of a tic tac, pretty much.
Yeah, and you think about this basic biology of these birds and you know,
they're all hummingbirds, lay only two eggs, then you go up in size and you get to something like this.
This is an elephant bird. It's a real one, which is very rare. Actually these birds evolved on madagascar with no predators
and so they invested everything into one or two eggs.
They were easy pickings when a big predator like a human came along that was able to find them.
These are birds that were living in madagascar up until the time the first humans got there about 600 to 700 years ago,
and they went extinct pretty quickly after that.
Do you call it an elephant bird?
How big was this bird?
Compared to a modern ostrich, these things were taller and about twice as wide.
And as a comparison
This is an ostrich egg.
It is and so ostriches evolved in continental
situations with lots of predators around and they tend to lay very large clutches.
As a matter of fact more than one female will actually lay in the same nest
and so you'll often see clutch sizes of about 20 to 25 eggs.
And then you've got this little anomaly over here.
Kiwis are distant relatives of elephant birds
and in some ways they're sort of like them and in other words they involved in the island of New
Zealand and they have no predators
to speak of and so they could afford to invest
everything in this incredibly large egg and it takes upwards of 40% of the female's body cavity by the time they're ready to lay.
So that's like the equivalent of me
giving birth
to like a 50 pound baby.
Yeah, absolutely and it's and so it's you know
birds have figured out lots of different ways to do things and a lot of that's
related to the different pressures they have from the natural history of the area they're living in
There's a lot of energy that has to go into making an egg,
but then you also have to make sure that it hatches.
So clutch size and eggs
In birds it varies quite a bit and sometimes it varies for really bizarre reasons
so for instance, there are a ton of eggs in this
collection. These are smooth billed anis and this is a species of cuckoo
And actually that's again a nest where multiple females have put eggs and the same nest in the group
there'll be a hierarchy among the females and the oldest female will be the last female to lay. The
successively more dominant females will throw out eggs of other species or the other individuals up until the time they get to the final
incubation period for the eggs.
So how many eggs does one
smooth billed ani lay?
So
six to seven or so so.
Six to seven and then Bird A lays six or seven and then Bird B comes and is like
I'm gonna do away with four of these and you get eventually six or seven birds that are all laying?
Yeah, and because you've got to incubate the eggs and you got to get them to hatch
on time or in a situation where you can actually feed them.
So one bird is laying on all of these eggs at once trying to get them all to hatch?
Yes, and then the group will actually feed them. There's 25 eggs in here.
Yeah, you know they that old saying all your eggs in one basket,
well,
it basically came about because there are all these various strategies for how to do things with respect to how many eggs you should lay,
so this is a Laysan albatross and a bird just showed up on Laysan island where these albatrosses breed.
And it's 68 years old, laid an egg and hatched a chick
successfully and so it just goes to show you that birds can do this for a very long time.
I don't think I'll be doing that at 68.
I don't think I'll be no-
Well, I'm certainly not gonna be laying eggs when I'm 68,
if I am there's someone should write a study about that.
And then what about this clutch here?
because four of these eggs look similar, but one of the eggs is not like the other.
This is a species called brown-headed cowbird,
which is a member of the Oriole and Blackbird family so that black bird with a brown head is a male and then the females
Is the brown bird and she's what's called a brood parasite.
She's incredibly good at basically mating with the male and then going around and looking for places to lay her eggs.
And in this case, she laid her eggs in the clutch of a yellow warbler nest. The yellow warblers
most of the time will not recognize the egg. That egg will hatch, that chick will actually force the other
chicks out of the nest and the yellow Warbler will raise a
Brown-headed cowbird chick to adulthood which will then go off and actually find other brown-headed cowbird later.
Are they not at all confused? Like these tiny little
Warblers laying on this giant egg that hatches and looks nothing like what their babies should look like.
You don't think that they question it for a second?
Oh
I think they must but at the same time I think there's an innate
desire to feed your chicks that overcomes that and they just go ahead and and we'll feed that chick without even thinking about it and
when you see the fledglings, I mean
There's so much bigger a lot of times than the adults that are being parasitised that it's really something. Then we also, you
know, wanted to point out. There's a lot of role reversal in birds with respect to what happens.
So this is a wattled jacana which has got these very long toes-
they live on lily pads, and they're found throughout the the Neotropics and you'll notice this is a
bird that has some very big spurs on its wings and it's a female and in this bird
the females are bigger than the males they set up a territory and the males come and they mate with the males and they lay
these incredibly beautiful eggs, which are laid on wet vegetation, so they blend in perfectly.
So the males are actually doing the incubation and the females are actually out defending the territory
Yeah, they're yeah, these are the same kinds of things that show up and birds like chickens and in chickens
it's actually the males that have them
they have spurs on their ankles.
Mmm. I really wouldn't want that flying in my face.
Yeah, that would be that'd be dangerous.
So John how many birds are there.
So they're about ten thousand eight hundred species of birds.
And do they all have different eggs?
Yeah
They all do and some of them are actually pretty similar so you could make mistakes identifying,
some of them are just plain white, we
decided to go without plain white eggs today.
Here's a guira cuckoo and they live in these family groups in the open countries of
South America,
South of the Amazon basin. And the eggs start off powdery white and then the powder wears away and there's a blue-brown color
underneath so you get these spectacular looking eggs.
Then you look around and and you can see there are lots of birds that lay blue eggs.
This is a wren-like rush bird from South America.
Is there any explanation for why blue is such a popular egg color there?
There really isn't, you know, and all different families have blue eggs
and so it may just be that the
byproducts that are being used to make color and eggs are actually pretty easy to get.
But then you'll get something that's completely
different like this is a Cetti's Warbler from southern Europe.
I've never seen an egg that color.
Yeah, there's also this glossiness,
so this is a great tinamou
which is just part of this big family of South American birds that run around on the ground and eat fruit and insects and things.
They just have these
spectacularly glossy eggs of different colors.
What about an egg like this?
So this is from an emu and emus are
Australian birds distantly related to ostriches and elephant birds and Kiwis and they live in open country and why their eggs are dark is a
good question.
Wouldn't it just cook the embryo inside?
Sometimes that can actually be a good thing, right?
Because one of the things that has to happen is an egg has to be kept warm.
So maybe it's just a way that the female can like lay, and maybe not have to spend so much energy
She's like these are gonna be toasty.
Yeah, either way.
Yeah, that would be an interesting hypothesis.
My guess would be that you'd find that there would be less time spent on the nest than there would be say, for an ostrich
or a rhea some of these other groups of birds that lay white eggs instead of these dark ones.
What about these eggs
here, they have such an intricate sort of painterly looking pattern to them.
Yeah,
so these are belonged to a common grackle and one of the interesting things about the way eggs
form is they come out of the ovary into the oviduct,
the egg is actually twisting in the oviduct as it's coming down and that leads to these patterns and then there are shell glands that
put on the shell and in addition, there are other cells that can put on melanin and give color
It's been taken to extreme in something like a common murre.
So this is a bird that nests on cliffs
in the
North Atlantic and the North Pacific and they live in these big colonies and they lay one egg at a time and what they've evolved
the ability to do, is actually lay that egg and actually have it look unique relative to the other individuals around it
and then they can
fixate on it and know where it is when they come back and forth to the colony as they're incubating it.
So yeah, this is another aspect of eggs, which is shape.
These guys have what's called a piriform shaped egg. One of the
hypotheses for this is that these birds are nesting on cliffs and that this keeps the egg from actually rolling around on the cliff.
It's another one of those great mysteries that's hard to test.
So John in the beginning you sort of mentioned how egg collecting has gone out of fashion largely
because of increasing protections for birds. What are some of the ways in which this collection in particular have been significant from like a
historical perspective?
Yeah, well, it's easy to forget that
there's a tremendous amount of information in the historical egg collections.
Actually having representation of these in collections can be really useful for
documenting all kinds of things and these eggs are a perfect example of that. These are modern peregrine falcon eggs.
This is one of these stories that most people have heard which is that back in the 60s and 70s
peregrine falcons were laying eggs
and
none of them were hatching, the females would sit on the eggs and they would crack. The
Scientists came to realize that they thought this eggshell thinning was being caused by a pesticide called DDT,
which was percolating up through the food chain
into the things that peregrine falcons ate and leading to eggshell thinning and peregrines basically went extinct in the eastern part of the US and
by
1970 or so. Since then people have actually made a real concerted effort to establish
peregrine falcons in major
metropolitan areas across the Midwest. And so our own Mary Hennen who works in birds and as a assistant collection manager for the last 30
years has been monitoring the peregrine falcon eggs across Chicago. And we can also compare them to
historical eggs and look at what the changes have been since DDT has been banned.
Wasn't the field museum's bird collection sort of one of the collections that was consulted to go and measure
the eggshell thickness of birds
that
- peregrine falcons that laid eggs before the use of DDT
versus during the time of DDT.
It was and I always like to point out that one of the interesting things about egg
collections is ours is one of the largest in North America
but there are lots of other small collections and these guys had to go around in order to assemble a big enough database. They were
were able to narrow it down both within the species that were affected and in the regions that they were
affected, which is one of the reasons why DDT was banned.
That's pretty good science.
It was a really i-
I loved- it's a great example of scientific design.
Yeah, this is a pretty fragile collection that that needs a lot of good care.
Yeah, there's just things we don't know and again, I like to call it avian pediatrics because this is literally like-
we all go to doctors when were kids that specialize in young
people and these are young birds.
Yeah, so come here to the Field Museum and check out the egg collection, make some discoveries, do some science,
hang out with John.
See the eggs.
Yeah
It still has brains on it.