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.
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.