I’m pretty sure the answer is no, or else we would be seeing mutt birds everywhere. But why is this? Why can’t a robin and a blue jay mate and produce a mix between the two? Why not a duck and a goose or an eagle and a hawk? Why are birds unable to cross-breed?
For the same reason you can’t cross-breed with a baboon (I’m assuming).
More distantly related birds, such as jays and robins, can’t crossbreed because of genetic incompatablity. The developmental programs are sufficiently different that even if they mated no viable embryo would be produced.
Other, more closely related species, such as many species of ducks (usually those in the same genus), are quite capable of producing fertile hybrids in captivity, but don’t do so in the wild because of differences in courtship behavior. If the male doesn’t go through the courtship rituals in precisely the right way for the species, the female will reject him.
In fact, that’s what most bird song is about - it enables a female to recognize a male of the correct species. If a male doesn’t sing right, he won’t be able to mate. (However, song also often does have a territorial function in warning off other males of the same species.)
What about a species like the Mallard, whose males will copulate with damn-near anything, alive or dead?
I read that a lot of birds have mating rituals (sometimes very subtle ones) that other types of birds wouldn’t understand and would not respond properly to.
Well, yeah, you do get a lot of funny looking ducks where mallards are around. 
Seriously, while male Mallards do often resort to rape, they mostly end up mating with other Mallards.
However, in the northeastern US, the American Black Duck is declining in part due to hybridization with Mallards.
Correct. Some rituals are very elaborate and spectacular, others are so subtle you would hardly recognize them unless you knew what to look fot.
Many macaws have been cross bred, forming hybrids with cutesy names.
Serious bird breeders are against this practice, BTW.
Examples:
Blue & Gold and a Scarlet = Catalina
Blue & Gold and a Greenwing = Harliquin
Blue & Gold and a Hyacinth = Caloshua
Scarlet and a Greenwing =Ruby
Scarlet and a Military = Shamrock
Scarlet and a Buffons = Verde
Catalina and a Scarlet =Camelot
Camelot and a Scarlet =Capri
Greenwing and a Military = Calico
Military and a Blue & Gold = Miligold
etc.
Many humans have a sort of warped sense of taxonomy. We’ll put “humans” in one category, “dogs” in another (both of those being species), “cats” in another (including the Great Cats like lions and tigers, which makes that one a full family), another category each for “birds” and “fish” (both of which are classes), and a category for “invertebrates” (which is all of the animal kingdom except for one phylum). Plus several other categories, of course. So, while nobody would ask whether humans and dogs can cross-breed, people will ask things like whether different birds can cross-breed, despite the fact that birds can show as much variation as between humans and dogs.
I understand that birds (aves) and mammals (mammalia) are two classes of vertebrates. But is there as much genetic diversity among birds as there is among mammals? I don’t mean regarding physical characteristics, but genetically. Is the difference between, say, a penguin and a hummingbird comparable to that between a human and a dolphin?
Very roughly speaking, yes. At least some of the present orders of birds apparently go back to the Cretaceous. Most mammalian orders probably originated in the early Tertiary, but the splits between monotremes, marsupials, and placentals took place in the Cretaceous or maybe earlier. Perhaps monotremes might be more distinct from other mammals than the differences found within birds, but by and large the genetic differences between orders of birds and mammals are going to be roughly comparable. This is not so for “reptiles” (in the non-technical sense), whose origins go back much more deeply in time.
Apologies for reviving a very old thread but this question came to me and it was a Google top hit.
The further thought now comes to me, how then did the duck billed platypus come into existence?
The bill of the platypus is not the same structure as the bill of a duck or any other bird. It is superficially similar but not related, being made of a flexible, leathery substance instead of the keratin of bird’s beaks.
Platypusses have been around for just a little short of forever so they cannot be considered as a cross between any two modern creatures.
Unless you were trying to make a joke.
See post #4.
Linkee no workee, and I gotta see it.
I believe the reference was probably to this article on homosexual necrophilia in mallards.
It resulted in an Ig Nobel prize.
One of my favorite ornithological articles is Avian Davian* Behavior, on a case of heterosexual necrophilia by five male mallards on a dead female.
*“Davian” refers to the limerick about an old hermit named Dave:
There was an old hermit named Dave,
Who kept a dead whore in his cave.
He did admit
the feeling was shit,
But think of the money he saved!
I had the exact question as the OP and never got around to asking it.
this quote makes me feel like I almost understand it - but I sure could use a visual aid. anyone know of a chart that shows species and classes and so forth?
I’d really appreciate it.
so far I’ve found this
so birds would be like mammals? but an eagle would be like…what?
You’re correct about “birds” being like “mammals” taxinomically – *Aves *and *Mammalia *are both Classes within the Phylum *Chordata *(vertebrates).
As for where the eagle falls … I chose the bald eagle for sake of an example. Here are the bald eagle’s classifications below the Class level:
Order: *Accipitriformes *(most diurnal birds of prey: hawks, eagles, vultures, ospreys, etc.)
Family: *Accipitridae *(hawks, eagles, kites, harriers, and Old World vultures)
Genus: *Haliaeetus *(the so-called “sea eagles”)
Species: Haliaeetus leucocephalus (the familiar bald eagle)
All eagles belong to the family Accipitridae, but there are several genera of eagle.
“Eagle” might be something like “antelope.” Eagle just refers (mainly) to larger species of day-hunting birds of prey in the family Accipitridae. But it has no real significance for classification. There are many species of “eagles,” and some belong to different genera and are not that closely related to one another. (Some are more closely related to species that are called “hawks.”
Likewise, “antelope” refers to a variety of species in the family Bovidae, mostly smaller ones (although some like the eland are very large).
Relationships between species are often plotted as phylogenies, which are conceptual “trees” that show how closely related different groups are. I managed to find this very nice phylogeny which compares mammalian and bird evolution, side by side. (It’s from this review of evolutionary biology, looking at whether there are really evolutionary “explosions”)
Crudely speaking, this phylogeny shows relatedness along vertical lines. So if you want to see how primates are related to whales or carnivores, you can trace back each branch until they meet, which happens about 100 million years ago. Among birds, there’s a similar level of relatedness between ducks and chickens (galliformes and anseriformes), and also between parrots and penguins.
Even within each group on that phylogeny there are a lot of species that are too distantly related to cross-breed.
I keep feeling like I alllllllmost have it…
so, Bald Eagle would like what?