The birds and the bees, part one

Okay, so you have been told about the birds and the bees. But do you really know how the birds are doing it? (Sorry, bees, we'll talk about you another time. Okay?) Because when you begin to think about it, there often are at least two points at which you begin to wonder: How do birds actually do it?

Passerine penisless passion

The first thing that may puzzle you is that most birds don't have a penis... (Oh boy, and we'll definitely have to talk about those that do at some point!) So how do you get sperm into a female cloaca without a penis? Of course, if you are female you immediately know the solution for ejecting fluid into something: Simply sit down! And that's more or less it. The act is called cloacal kiss and usually is really quick. And if you want to see that in a little movie, just go here. The actual act takes place at second 36 in case you missed it the first, second, or third time! Aaaaand in case you wondered: the picking of the cloaca probably is to remove sperm from the last guy.

So overall, bird sex is a bit like the movie cliche of a high-school ball date: The guy tries to impress her by his dancing, then does some clumsy foreplay and just as she is willing to mate and allows him to get really close, the very moment their genitals touch, everything is over already...

Okay, but now for the real puzzle, the one students actually ask almost every semester in our developmental biology course: How does a sperm fertilize a bird egg? I mean - it cannot go through the shell, right? Well, to cut a short story, even shorter: It doesn't. The actual ovum (the egg cell) is produced in the ovary and then filled with yolk, from which the chick is later fed. Then the ovum is fertilized, the egg white is added as a kind of aquarium for the embryo to grow into and finally the shell is added - with colorful sprinkles in the outer layer in some species and with a bubble of air for gas exchange. So the next time you enjoy a breakfast egg (most of which are not fertilized actually), take a moment to marvel at the miracle of the bird egg.

Simplified origin of a bird egg

Dance as if someone important is watching!

Let's imagine you're a little male spider. One day you may feel a little - let's say: romantic. So you begin to look for a female. But when you find one you get a little scared. She is bigger than you, so what if she assumes that you are an enemy or worse - a snack? So you hesitate, torn between fear and desire, twitching forward and back just at the edge of her field of view.

Trying to look cute - for a spider...

And she just watches. Her instincts don't label you as a rival and you're not behaving like food either. So the two of you mate successfully, while many of the non-twitchers got eaten or chased away.
Fast forward a few hundred or thousand generations - which are the same number of years for little spiders. Now all male spiders twitch, as they out bred the non-twitchers, and the females have learned that a twitching object is a mate.
But not all twitchers are the same! Some are more colorful and some move more elegantly. And both catch the female's eyes more easily. So now these will out breed the regular twitchers.
Fast forward another few thousand or million generations and the little shy spiders have become beautiful dancers! Some of them may get eaten by birds, as they are easier to spot. And that is why they may not get more flamboyant but overall the success with the ladies outweighs the risk by far!
Now you may think that this story is absurd. It might work for big, complex animals like birds, but spiders? And you are partially right, as most spiders have bad sight. However, jumping spiders don't. It pays off to have good eyes when you jump at your prey! And actually, among these tiny creatures there are some great dancers!
You still have doubts? Well, have a look at the mating dance of Saitis barbipes - a little Mediterranean spider that makes at least a great "twitcher".
And when that does not impress you properly, take a look of the Australian peacock spiders of the genus Maratus, some of which actually make peacocks look clumsy and bland, like this one or this, where the female also dances, or actually anything from this YouTube channel!
So the next time you are on the dance floor or admire a dancer, remember: There are little spiders in Australia, that might do it much better!