Yesterday, My Beautiful Wife and I were enjoying beers in our backyard when a stunning red cardinal appeared on our back fence. He was chirping and hopping and clearly was looking to score. Along came a finch or some other boring brown bird, and our hero was really trying to impress it. (I know female cardinals look different, but I’ve seen them and this was assuredly not a female cardinal.) The finch/whatever was unimpressed.
Given the vast number of different kinds of little birds, why don’t they interbreed? Are they really THAT genetically different? Would it not be evolutionarily advantageous for blue jays to be able to mate with canaries, or waxwings and chickadees to mate and bear waxachees?
Lots of animals that are different species can produce viable offspring. The key to biologists saying they are different species is that it’s relatively uncommon for it to happen. For example, all the species in the genus Canis are interfertile.
Birds have been around for 10s of millions of years, so there has been lots of time for them to be genetically different. Blue jays and canaries are not very closely related, but there are still bird species that are more closely related and that can interbreed. If the hybrids are fertile and have some evolutionary advantage over the purebreds, then yeah there will be an evolutionary advantage. But often the hybrids have some flaw that make them less evolutionarily advantaged. Either they are not as fertile as the purebreds, or they are not quite as good in either ecological niche as the purebreds.
They may all appear to be similar to you, but, to take your cardinal and finch, they’re not just genetically different enough to be different species, or different genera, they’re different families. If they could produce viable offspring, there would be some major re-categorising to do. Hybrids within a genera aren’t all that rare- though they’re often sterile, or almost so- but that would be kinda analogous to a cat mating with a dog. A dog may try and hump anything, but catdog was not a documentary.
You’re more familiar with the differences between cats and dogs, so that seems obvious, but the differences are still there with small birds, just less immediately obvious. I’m not expert, but I’d guess that with the restrictions for flight and perching, small bird body plans are less variable than mammal. Beaks change, feathers change, the rest of it doesn’t have much flexibility, however much the genetics have changed.
In the case of Blue jays, hybrids with the closely related Steller’s jay have been observed as their ranges have started overlapping. The above remarks apply, and also the observation that their ranges don’t overlap by all that much, so it doesn’t happen very often right now. I don’t know if the hybrid jay is fertile, or if hybrid males can succeed in attracting mates. If both are true, I suppose that at some distant date we might stop regarding them as separate species.
(Some grouse species can hybridize, too. Even if a male hybrid could reproduce, the different species have distinctly different mating displays to attract mates, and the hybrid male can wind up trying to do both half-assedly, attracting exactly zero females.)
I don’t think different species can successfully breed. I recently learned that African & Asian elephants can’t breed, because they are different species. There was one case of successful hybrid, but he died shortly after birth. If a cardinal could breed with a finch, they would have done it by now.
Hopefully Colibri will be here soon to post one of his excellent explanations of speciation/hybridization. As a birder, I’ll point out that hybrids do occur in nature. Notably, at least here in CA, within Anatidae (ducks) and Parulidae (warblers).
Define successfully. Is it a successful breeding when a donkey and a horse mate and produce a mule? Mules are viable but generally not fertile. An African elephant and an Asian elephant have bred and produced offspring that survived until it was born, though it died a few days after it was born. What has to happen for a breeding to be successful? Does the offspring have to survive to adulthood? Be able to reproduce?
The ranges of African and Asian elephants in the wild don’t overlap, so wild African and Asian elephants wouldn’t breed with each other. Humans would have to get involved for that to happen. African and Asian elephants are threatened species and reproduce slowly- people who are involved in breeding them are probably more interested in getting more African and Asian elephants, rather than hybrids that may or may not survive.
Macaw breeders create hybrids all the time. I used to be able to differentiate a Milligold (military X blue and gold) from a Catalina (I forget) from a whatever.
Birds evolve very specific mating behaviors/rituals also. Don’t dance the right way? Bye-bye birdie.
Coyotes and wolves successfully breed rather often. And interbreeding between polar bears and grizzles is also documented in the wild. Nature doesn’t “care” about our obsession with putting things into distinct boxes.
Hybrids between great tits and blue tits have been observed. Norwegian researchers swapped a number of eggs around so that blue tits grew up with great tit parents and vice versa. The blue tits grew up “normal” and went off to court their own species. The great tits grew up confused, trying to court blue tits and being rejected.
African and Asian elephants are not only classified as different species, they are put in different genera. But that is not always a barrier to hybridization. Witness the Cama, a hybrid of a camel (Camelus dromedarius) and a llama (Lama glama).
My personal definition of successful breeding would be production of offspring that can survive. So by my definition, a mule qualifies, even though they are sterile.
And yes, African & Asian elephants would never meet up in the wild. Motty (the only known hybrid to have survived to birth), was born at a zoo & died after a few hours. My theory is that if 2 animals can successfully breed & have access to each other, they will. If an expert comes along & tells me I’m wrong, I’ll change my position, but if a cardinal & a finch could breed, there would be a cardinch in my bird book.
Wow, I’ve never heard of a Cama & wonder why Wiki doesn’t include a picture. I googled it and saw pictures–very interesting hybrid!!
Oh they certainly can if they’re reasonably closely related. Just as a striking for example, this handsome fellow will readily reproduce with the females of this almost as good-looking gent. Helps that the females of those two species are virtually identical :). They are very, very close relatives, separated mostly by range. But they do overlap and hybrids do happen.
Seagulls can be a nightmare. Members of the genus Larus are happy to mix genes. In my area Western and Glaucous-Winged Gulls form a hybrid swarm. Go further south of the SF Bay Area( say Carmel )and suddenly all your Western Gulls look properly dark-backed, as opposed to the sorta washed-out locals.
The problem with species is that we are imposing a rather arbitrary human classification system on critters and they don’t always hew to our preferred notions. No matter which species concept you choose( and there are several ), you’re going to end up with problematic individuals eventually.
