Brood parasitism is so heart breaking. Twice in front of my eyes I have seen sunbirds being parasited by cuckoos. Having no understanding of this natural mechanism, all I could do was watch in vain the sunbirds feeding the cuckoo 100s of times each day working hard to make it grow. Do they know they are growing their own potential enemy? I wonder how many more years or centuries will this process last. What if the cuckoos lost all their hosts due to decreasing population? Are they on the brink of endangering their own existence along with their hosts? How this evolutionary process works? Great and very informative video! ✌🏼
"Mimicry - When Animals Copy Other Animals" by "Deep Dive" is a superb documentary covering this. Cuckoos have a lineage of female per host, remembering that host's nest and evolving to mimic its eggs. Hosts evolve to reject the intrusion, eventually extincting that lineage. Occasionally a female cuckoo gets the "wrong" nest, parasites a new hosts that has little to no rejection, starting a new lineage.
Brilliant video! It won't be long before one of these goes viral I'm sure. It boggles my mind how something like brood parasitism evolved. Thanks for sharing
I had a juvenile cuckoo brought into the vet when I started vet nursing many years ago. It was a horrific monstrosity, very creepy looking. Crawling with parasites as well. It wasn't until another staff member ID'd it that I even knew they were in Western Australia
The destruction of rejector nests makes sense from an evolutionary standpoint. If they make sure those who can recognize the parasitic eggs can't breed, those adaptations can't take hold. As such the target species becomes basically selectively bred to not recognize the parasitic eggs. This would only work if the "vengeful" behavior is widespread, and/or the behavior is cheap fitness-wise.
Just incredible they have the built in instinct to push out the other eggs as a baby.... It seems so evil and manipulative to mess with the young like this but im guessing only very healthy populations of common birds get parasitized? Otherwise if they were too successfully, that would just wipe out their host species. It makes me wonder if you could engineer an extinction by somehow introducing a brood parasite to say a pest bird. Also are there species that does this but also make their own nests as a backup or last resort? Interesting to see if birds still have the ability or instinct to do it
I'm so curious as to how innate this really goes. When you think about it, the parasitic eggs that go on to fledge never end up making contact with their biological mothers. So it's not as if the act of brood parasitism is physically taught to them. Cuckoo chicks ejecting rival eggs and other hatchlings too, they come into the world blind and featherless, yet still with that survival instinct. I wonder if they would eject fellow cuckoo eggs, if they could even tell. The thought of this behaviour being passed down the generations through genetic code alone is fascinating, it also makes me view brood parasites in a more sympathetic light. It's almost as if it's a compulsion, born from a mix of evolution and adaptation. It can't be an easy thing to break. I do think anthropomorphising these creatures plays a large role in how we as humans seem to hold these parasites in such contempt. Our brains are built and sized differently, we operate on a much higher level. It's not fair to expect or impose our morals, or expect a change, when this behaviour is so engrained into who they are as a being.
No human value judgement in cowbird behavior or evolution, I admire the females spatial memory, finding the host nests! Big hippocampus, for sure. They are my common feeder bird, living between stables, and farms! We have many passerines, and many cowbirds!
In stating that the costs of recognition error is greater than the costs of parasitism, is it assumed that producing a parasitic offspring is nevertheless a production of the host's offspring? Accepting a parasitic offspring results in all of the host's own eggs being ousted. Thus, if the definition of "production of offspring" is limited to the host's own eggs, then the cost of recognition error would be equal to the costs of parasitism - i.e., a total annihilation of the host's own eggs.
These Parasites should hunted by Owls and Eagles and the baby cuckoo do need to get pecked back at by the Mom bird that's not really it's mom since it's self defense.
At 6:24, the narrator says, "This mafia-like tactic may be an act of punishment or an attempt to force them to produce a new clutch." I would argue that it's neither, in the sense that I don't think the cowbirds ransack the host's nest out of anger or with the aim of teaching the host a lesson. That would be an example of anthropomorphism, i.e., attributing human emotions and motivations to these birds. From a biological perspective, the most objective and accurate we can be when discussing the reasons behind this "mafia-like" behavior is that it exists in modern cowbirds because their cowbird ancestors that exhibited this behavior produced more viable offspring that survived to reproductive age. We have no way to know, and no reason to believe, that the cowbird ransacks the host nest with some intention or goal in mind. We just know that when the cowbird mother goes to check on her egg, if it's not there, this automatically triggers the ransacking behavior. One might make a comparison to a possum "playing dead" when there is a threat. The possum is not "trying" to play dead because it "thinks" this will fool a predator; rather, when triggered by the presence of a threat, the possum involuntarily enters a coma-like state in which it can stay for hours until it "wakes up." In this state, its body also releases a chemical that smells like rotten flesh, which may help to fool predators. However, it can't be said that the possum is doing any of that with volition; it's an automatic, stereotypical response to a particular stimulus that tends to aid in survival. The cowbird's "mafia-like" behavior is likely the same type of involuntary behavior that persists in the species because the cowbirds that exhibit that behavior are, in the long-term, more successful at reproduction.
