In a previous video we counted down the top seven courtship displays in birds.
Now let's take a careful look at the science behind each of them and see why these amazing
displays exist at all.
Structures
Structures are often built by male birds and evaluated by females.
An example is the weavers, where males build one or more nests out of woven grasses.
If females approve of the nest they move in and lay eggs.
Bowerbird males do not assist with nest building, incubating eggs, or raising young.
The female is totally on her own for that.
But the males build structures called bowers for courtship.
There are several different styles of bower.
Some have decorative objects, some have food, some have walls and paths.
The structure has some functional uses, but it also tells the female something about the
male.
We don't know what exactly, but it could be his mental ability or his ability to collect
and arrange materials in the bower.
Dress to Impress
Ornaments on a bird also communicate something.
It might show their good nutrition, or their ability to escape predators.
Let's first talk about sensory bias.
In some species there is a preference for some type of color or shape.
If a bird develops a way to associate itself with that color or shape, it has an advantage
in courtship.
There was this great experiment where researchers went to a group of Least Auklets with some
decoys.
Some of the decoys had normal feathers, and others had feathery head crests.
The auklets tried to court the feathery crested decoys TEN TIMES more often than the normal
ones.
So if an auklet ever develops a new crest style it will be wildly popular.
Birds of paradise have an extensive array
of display feathers.
Each one could be tied to a sensory bias, or to some other form of consistent choice
among females.
Also, red marks on a bird can have a meaning.
The red pigments come from plants, not made by the bird itself.
So being very red means the bird has had access to a lot of food.
Plus, those same red pigments are used up in regulating the immune system, so a very
red bird is also doing well by not being sick.
This is called an honest signal because it's so expensive for the male to make a red patch
that he can't fake it.
There are lots of birds with red patches.
You'll start to see it more often now!
The giant, beautiful feathers of male pheasants and peacocks are possibly present due to female
choice, but another possible explanation is the handicap principle.
It says that male birds have giant, basically useless feathers.
If they survive despite this disadvantage, it shows females that their other traits must
be really good.
You would have to ask a bird to get the full story, because we can't ask them what they
think.
But this is our best guess of what is happening.
Be in the Right Place
Leks are interesting courtship displays in a few bird species.
In a lek, a group of males cluster together and start to do loud, energetic displays.
Females can then wander through and choose a male based on whatever criteria they have.
In lekking species the male is not involved in nest building or chick-rearing, so he provides
no benefit to the female that way.
Just for fun, let's cover the major theories as to why leks exist.
The predator protection hypothesis says that if you're doing a visible, loud display it
helps to have lots of other birds looking out for predators.
So this clustering is just a way to be safe.
The hotshot hypothesis says that there are some really, really attractive males called
hotshots, and a courtship display starts when they show up.
Females show up to see the hotshot.
Other males start displaying in hopes of distracting females before they get to the attractive
one.
The hotspot model says that males gather to display in places that females reside, like
a tree full of fruit.
Kin selection says that all the males in the group are in some degree related, so their
family benefits no matter which male is successful.
They all share some genes, so their genes get passed on even via a relative.
And my preferred theory as to why leks exist is a simple one, that it reduces the energy
needed by females to find and evaluate males.
It will be interesting to see if some, all, or none of these are supported by experiments
in the future!
Show Off Your Dance Moves
Elaborate displays increase along with the importance of female preference in courtship
success.
Or another way to say it is that the more choosy females are, the more males amp up
their displays.
So let's look at a few examples of dances and see how fancy those displays can get.
A Song Never Hurts
Bird singing is used to mark territory, but also to attract potential partners.
This could be achieved with two calls.
One in which the bird calls "Mine" and another where it calls "Look at me".
Like this Chiming Wedgebill is clearly doing the "Look at me" call.
But many birds have more complex songs than that.
An example is the sedge warbler, which has up to 100 different sounds it makes.
Males cycle through their sounds, and females are more likely to choose a male that knows
more different sounds.
The call has become an audio ornament, basically, which shows the male has some good quality.
Lyrebirds are another example of this effect, and their ability to mimic sounds is much
more amazing.
Listen to this lyrebird mimic a bunch of sounds.
Again, the birds that make the most different sounds are the ones that are most successful
in courtship.
The Palm Cockatoo has a pleasing call compared to other cockatoos,
but they have an additional signal.
They play music!
A palm cockatoo grabs a branch or other hard material and starts hitting a dead tree with
it.
It makes this loud sound that carries far.
This could be a courtship display, or a territorial marker.
Gifts
In most species the female has a bigger energy investment in producing offspring.
Eggs are expensive in terms of nutrients, and it takes a lot of work to find food for
the chicks.
So a male offering some nutrients is a way to offset the expense.
Even in a species like the Greater Roadrunner, where the parents raise chicks together, the
male still might offer some food.
This might just be a nutrient gift, or it might show how good he is at finding food.
Do a Synchronized Display
Some of the most amazing bird courtship displays fall in this category.
These displays tend to be in long-lived species that pair for life, where males and females
look similar.
They help the pair form and bond.
And let other birds know their status as a couple.
This may be an example where both males and females have a preference for partners that
can do this mutual display, so it is emphasized in both.
I split questions in science into three categories.
"What" questions like, "What kinds of birds live in this marsh?" are fairly easy to answer,
and you can figure out how good your answer is after the fact.
"How" questions like, "How do birds navigate over long distances during migration?" are
a little bit harder to answer and it takes a little bit more ingenuity to figure out
how to answer the question at all.
It's harder to know if your answer is complete also, like maybe you missed one of the senses
involved.
Finally, the "Why" questions.
These are really, really hard to answer.
Different "Why" theories take decades to evaluate and percolate through the science community
because it takes a lot of insight to design an experiment that tests why something happens.
And it's much harder to estimate if the answers you came up with in your models are what correspond
to actual reality.
And you'll notice this entire video was discussing "Why" questions.
Which means that the answers explained in this video are likely to be changed or disproven
in the future.
But it's accurate to say that these are our best guesses at explaining the amazing, complicated
world all around us.
Thanks for taking the time to learn about bird courtship.
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Thanks for taking the time this week to learn what makes Life awesome!