Brothers on a Hotel Bed

I’m a few days late on this one, but it’s never the wrong time to learn about the fascinating mating habits of turkeys. They don’t call them wild turkeys for nothin’.

You know that saying “It takes two to tango”? Well, in their case it takes three, four, or five.

File:Male north american turkey supersaturated.jpg

Male north american turkey (Meleagris gallopavo) – Wiki Commons

No, no, no – not in that sense.

Mating systems where males form large groups to attract females are called leks, which means ‘play’ in Swedish . Many bird species form leks, in which the males competitively display their stuff to get female attention. Meanwhile, the female wanders from male to male to judge them before making her final pick.

The thing about leks is that they are competitive. Males of most organisms engage in competition of some kind to win the girl. Which is why something like this rhinoceros beetle is equipped with such fabulous weaponry.

But in turkeys, within the larger, competitive leks, are smaller coalitions of two to four males that cooperate with one another. These unique display partnerships in which males cooperatively court females are found in only a few species of birds.

What’s even weirder is that only one of the males (the dominant) actually gets to mate with the female that the group attracts. The other male or males, the subordinates, get no reproduction at all. Nothing. Zilch. Nada. This is akin to Batman getting all the ladies and Robin helping for no other reason than to help Batman get all the ladies. Rather strange, isn’t it?

So why would these subordinate males engage in such altruism, benefiting another at a cost to itself?

Further investigation by Alan Krakauer (then a PhD student) revealed that these duos or groups are formed by close relatives, often brothers. So while it seems that the subordinates are getting nothing for their efforts, they are actually indirectly benefiting by helping out a close relative.

Both of them gain by cooperating. The dominant does better with the subordinate’s help. Likewise, the subordinate does better as a back-up strutter rather than trying to strut his stuff all by himself. Most important of all is that the benefits for helping outweigh the costs.

This famous saying by J.B.S. Haldane gets at the heart of the matter: “Would I lay down my life to save my brother? No, but I would to save two brothers or eight cousins.”

In other words, you share roughly 50% of your genes with your siblings, so saving two of them is equal to saving yourself, who you are 100% related to. Similarly, you share roughly 12.5% of your genes with your cousins, so eight of them equals 100% of you. All this to say, the number of genes you share with your relatives matters.

And in the case of the turkeys, subordinate males gain no direct benefit (i.e. having offspring of their own) by helping, but they do gain indirect benefits by helping their close relatives have offspring. This is called kin selection, and it provides us with an explanation for such altruistic acts as cooperative male display in turkeys.

Now, if we could just figure out what’s in it for Robin.

You can read the original work on turkey courtship displays here and a popular press story about it here.

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Combat Baby

Let’s return to the brood parasitism story.

Last time I left off wondering if it’s possible for hosts to defend themselves against their brood parasites or if they’re damned for eternity. If you’ll recall, cuckoo parasites have evolved incredible visual mimicry of their eggs, which makes it ever easier for them to deceive their hosts.

Eggs laid by different host-races of the Common Cuckoo are on the top row, with eggs laid by their target hosts shown directly below. Photos by M. C. Stoddard and copyright the Natural History Museum.

Eggs laid by different host-races of the Common Cuckoo are on the top row, with eggs laid by their target hosts shown directly below. Photos by M. C. Stoddard and copyright the Natural History Museum.

If you look closely, you’ll notice that these eggs are nearly matched, but not perfectly. Could these imperfections contain information that the host species can use to its benefit?

Some theoretical work done by Cassie Stoddard, a post-doctoral researcher in the Harvard Society of Fellows, indicates that hosts can fight back by developing highly elaborate but recognizable eggs. By developing a tool that mimics a bird’s visual perception capabilities and analyzing the complex patterns on eggs, she uncovered something quite remarkable – host species that have been subjected to the best cuckoo egg mimicry have evolved the most distinguishing and easy to recognize egg patterns. Pretty nifty, huh? You can read the original work here.

This is a fantastic system for exploring the evolution of visual signals. What’s more, it provides a classic example of a coevolutionary arms race. The cuckoo evolves a trait that will benefit it but cost the host (i.e. egg mimicry), and the host species in turn evolves a trait that allows it to overcome the cuckoo (i.e. egg pattern discrimination abilities). And so on and so on.

It’s almost hard to imagine the incredible pressure these brood parasites have put on their hosts for millions of years. And it appears that, given enough time, hosts can evolve strategies that help them fight back. But what of species that have not had adequate time to coevolve with a brood parasite?

Human activities are changing the environment at an alarming rate, and this is causing species that have never interacted with one another before to do so. This is precisely what is happening with brood parasites and new, unsuspecting victims due to shrinking habitat. In the short term, it’s unlikely that these new hosts can adapt quickly enough to evolve strategies that will allow them to overcome their brood parasites. Why should we care? Because many songbird populations are in decline due to brood parasitism. And we are a catalyst.

So not only can brood parasitism be an interesting area of study behaviorally, it can also provide us with a better understanding of how hosts overcome their brood parasites. Knowing this will allow us to predict how their new victims will fare, which will in turn provide us with a new framework for where and how we focus our future conservation efforts.

Now put yourself in the boots of a behavioral ecologist. To better understand this system, where would you start? And what would you do if I told you that some brood parasites actually target the nests of members of their own species?

Next time on The Birds.

Colors and the Kids

I’ve been addicted to Serial as of late, and if you are also following along with it, I want you to now cue in your head the theme song.

Except that this post will not resolve the mystery surrounding the murder of a teenage girl. Rather, the crime in question here involves the questionably mixed contents of a bird’s nest.

Recently, I told you about brood parasites, birds that will drop their eggs into the nests of others to have other individuals, even from other species entirely, raise their offspring.

However, this is not your typical babysitting service. Hosts are receiving nothing in return for their dutiful parental care. In fact, because raising baby birds requires a lot of energy and time, these hosts are paying hefty costs by caring for parasitic offspring. Because what they provide these parasitic young necessarily takes away from what they provide to their own young.

So what is a parasitized host species to do?

One obvious solution to the problem is to evolve a more discriminatory egg. Some kind of signal that is a secret code that will allow you to tell the difference between your egg and that of a parasite.

So let’s have a look, shall we?

Eggs laid by different host-races of the Common Cuckoo are on the top row, with eggs laid by their target hosts shown directly below. Photos by M. C. Stoddard and copyright the Natural History Museum.

Photos by M. C. Stoddard and copyright the Natural History Museum.

What you’re looking at are the eggs of parasitic cuckoos and their hosts. The top row are the eggs of different Common Cuckoo host-races, while shown directly below them are the eggs of their target hosts.

It appears that over time cuckoos have evolved eggs that look more and more like the patterned eggs of their hosts. Those that did a better job mimicking their host eggs were the ones that stayed and passed on their genes to future generations. Those that did not do such a good job duping their host may have been tossed over the nest. Over time, you get cuckoo eggs like those above. Save the first pair of eggs, aren’t these cuckoos’ eggs amazingly convincing!?!

Clearly these hosts have no chance in hell of outdoing their cuckoo parasites. Or do they?

Before you think that these hosts have been defeated, take a closer look at those egg pairs. The cuckoos have made pretty good replicas, but are they perfect? Might the hosts have recognizable patterns in their eggs that they have learned and that allow them to better discriminate eggs in their nest?

Next time on The Birds.

What Bird Is That

My favorite book as a child was this.

Ever read it? It’s about a young bird that hatches in the nest and its mother is no where to be found. It goes up to anything and everything asking “Are you my mother?” (fantastically original title here). In the end, it does meet its mother and discovers that she had been out collecting food for it all the while. Totally sweet, right?

I don’t study birds, though I am in a department that is immersed in bird research and that is highly interconnected with the Lab of Ornithology. Oddly juxtaposed with this sweet little bird story, there is a behavior found in some birds that gives me pause. A behavior so horrific it’s hard to believe it exists in nature.

Photo Credit: Harald Olsen

Photo Credit: Harald Olsen

‘Are you my mother,’ this large cuckoo is asking? Certainly not. But the reed warbler photographed here is none the wiser.

This is not normal behavior, by the way. Birds don’t go out of their way to forage and collect food for someone else’s kids. Yet, that’s exactly what has happened here to this reed warbler. It has been parasitized by a cuckoo, which has laid its egg in her nest to avoid the costs of a) making its own nest and b) taking care of its own young. This, my friends, is brood parasitism.

There are many different flavors of brood parasitism. One key distinction is who these brood parasites target. Most of them are specialists – they dump their egg or eggs in one or a few host species’ nests. Some of these brood parasites, however, are generalists – they dump their egg or eggs in just about any nest they can find. The brown-headed cowbird has over 200 known hosts. I think this this alone should classify it as the world’s biggest asshole bird.

But I would be wrong. THIS is the world’s biggest asshole bird.

You may wonder why this is EVEN ALLOWED!?! Who are these ‘dumb’ birds that can’t even recognize their own offspring?

I want you to put yourself in the talons of a host bird. You’ve seen the enemy flying around your home. Maybe you suspect they’ve dumped an egg or two in your nest. What are you options? Will you do nothing or get rid of suspect eggs? Think about this problem in terms of the costs and benefits for your behavioral choice.

What costs might you pay if you do nothing? Raising the young of others, likely at the expense of your own offspring. What are the costs if you destroy some eggs? If you make a mistake, you may be getting rid of your own kids!

Similarly, the benefit of doing nothing is to avoid the mistake of killing off your own. And if you decide to destroy an egg and it happens to be the parasitic egg, then you reduce your chances of raising young that are not your own AND maintain your offspring and future lineage.

Such are the behavioral decisions of a brood parasite host. May you never think of the sound of a cuckoo clock the same way again.

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