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Eggs! There are around 10,800 different species of birds, all which lay eggs that vary in size, color, shape, and parental care required. Dr. John Bates pulled some highlights from the Field Museum's egg collection to share these fragile, historically important and BEAUTIFUL specimens with us.

"The Book of Eggs" by Mark E. Hauber, Edited by John Bates & Barbara Becker:
Learn more about the Field Museum's work monitoring and supporting peregrine falcons in Chicago:

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Executive Producer, Creator, Host:
Emily Graslie

Producer, Director, Editor:
Sheheryar Ahsan

Production Assistant, Content Developer, Writer:
Raven Forrest

Special thanks:
Dr. John Bates, Ben Marks, John Weinstein & Lauren Bawiec!
This episode is filmed on location at the Field Museum in Chicago, Illinois.
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 parasitized 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.