Six geese are laying

Graihagh Jackson and Chris Smith are celebrating 12 scientific days of Christmas with the help of Hugh Hunt, Alan Calverd and Eleanor Drinkwater.

Graihagh - Are we ready for the 6th day of Christmas? Our voices should be really warmed up by now...

Everyone sings: on the sixth day of Christmas my true love gave to me, six geese a laying, five gold rings, four calling birds, three French hens, two turtle doves, and a partridge in a pear tree.

Graihagh - So we are back to birds again. But this time not bird calls but bird eggs. Our producer this week, Caroline Steel, has put raw and uncooked chicken eggs in some vinegar for a few days and the results are interesting to say the least! We’ve got a couple here. It’s changed colour! There’s no shell on it anymore. It’s kind of squishy, a bit bouncy, I would say naked. Hugh - can you explain why it has gone all naked and bouncy?

Hugh - Well, the vinegar, it’s an acid; and the egg shell is made of calcium carbonate. And I remember learning at school that "acid plus carbonate gives salt, carbon dioxide and water". And as these eggs were sitting in the vinegar, there were bubbles of what must have been carbon dioxide on the outside. Now, all of that carbonate - all of that shell - has now gone, and it’s very "squidgy".

Graihagh - It is isn’t it? You're "squidging" it and I’m rather nervous you're going to break it.

Hugh - What’s left is that membrane. You know when you have a hard boiled egg, and you peel the hard boiled egg, there’s this membrane that’s between the shell and the egg itself. That’s the only thing that’s left.

Graihagh - That’s the only thing that’s holding it together. Rather delicate. What is that membrane for?

Hugh - Well it’s a seal, an air seal, a water seal, because the shell, the calcium carbonate is fairly porous, so without that seal the egg inside would dry out.

Graihagh - Ah, I see then. And before the programme you mentioned to me about this is relevant to climate change and the oceans. And I thought no -  because eggs aren’t found in the sea. So what were you getting at there?

Hugh - Well, this shell has dissolved in the acid of vinegar and we know that the oceans are becoming more acidic because carbon dioxide levels in the atmosphere are rising. So the acidity of the oceans is rising and that’s making it more difficult for shellfish to create the shells. So one of the real worries for ocean acidification is the threat on the marine life, particularly shellfish.

Graihagh - Um, you get things like this. I’m going to pass it round so that everyone can have a feel. Don’t break it - please be careful!  Your hand will smell very vinegary afterwards, I warn you.

Graihagh - Eleanor - do we know why birds lay eggs instead of live young like mammals?

Eleanor - Well, that is actually a fantastic question. Except for lamprey and hagfish, birds are actually the only vertebrate group that don’t have any live young and people don’t have a definitive answer as to why this is. There’s lots and lots and lots of suggestions, one of which is it might make it difficult to fly but, then again, we have lots of flightless birds. Other people have suggested it might be to do with immune function. Still others have suggested that it might be to do with lung formation or the eggshell itself.

My personal favourite, however, is the idea that birds have quite complex caring behaviours. So you will have two parents who will tend to care for the young and the females tend to be adapted to lay one egg at a time. So, from the female’s perspective, it seems like a good idea to try and get the egg out of you as quickly as possible because then the male can also invest lots of time and energy looking after the offspring rather than the entire burden being on her.

Chris - You mentioned things that do or don’t lay eggs. What about platypuses and echidnas - the duckbilled platypus because they lay eggs don’t they but they’re not birds and they’re not fish?

Eleanor - Yes, they’re just strange. we don’t talk to them.

Chris - Did they evolve to do that independently - how did they get that skill?

Eleanor - I don’t know. They’re also very odd. They’re one of the only poisonous mammally type things. Even though we call them monotremes, they don’t really fit neatly into anywhere.

Alan - I often wondered about - what about snake eggs? That’s a wholly different species and they’re very similar eggs.

Eleanor - Well, yes. But snakes also have instances where they have live young, so unlike birds where you only have egg laying. You do have some snakes who give birth to live young.

Hugh - But this is proof of which came first - the chicken or the egg. Because we know that dinosaurs laid eggs so, therefore, the egg came before the chicken.

Graihagh - Ahh. Glad we got that sorted!

So do birds serenade their eggs? You talked about birds practicing their singing and you often think of them stereotypically in a tree with their nests and their eggs. Is there any reason why they might be doing that?

Eleanor - Yes. Well, in fact, there was an amazing study that’s only recently been done that showed that zebra finches, when it’s over 26 degrees they have a particular call which they make to their eggs. Now what scientist did, they took a group of these eggs; half of them they played the song two, half of them they didn’t. And then they looked to see what happened when the birds started developing. And what they found was very strange in that those that had been played the call would develop slower and would end up smaller at higher temperatures than those that hadn’t been played the call. So the call from the mother caused changes to their physiological development after hatching, which is quite extraordinary.

Graihagh - Yes, I was going to say absolutely amazing.

Chris - Why. Why is it good to do that?

Eleanor - They put it down to the smaller size being better adapted to hotter environments so it was easier for the chicks to regulate their heat. And also, interestingly, when these chicks grew up they found that they were much more successful as smaller adults, producing more babies in higher temperatures than the ones who weren’t.

Graihagh - Aw, absolutely fascinating. I know Hugh, you’re playing with the egg here and I know you really want to pop it.

Hugh - That would be great!

Graihagh - So, do you want to do the honours and pop it?

Hugh - Alright.

Graihagh - Let's get a photo of it and we can put it up on facebook live.

Hugh - Well, I used to say the scissors that we’ve been using to make snowflakes...

Graihagh - I feel like you’re a bit close to me still!  They do smell really bad actually.

Hugh - Yeah. Okay, well are we ready?

Graihagh - Okay, are we ready? And pop…

Hugh - Awww. Urgh!

Graihagh - What’s interesting is the membrane looks like saggy skin, doesn’t it, around the thing? Hugh - I can’t believe you're touching it. Why are you touching it?

Hugh - Actually that membrane is just like the skin of a grape and it’s just this thin. Amazing, isn’t it?

Graihagh - Yeah. Keep it away from me!