I'm pretty much a "casual" birder but recently I've been wondering about something that maybe you more "scientific-types" can answer for me. Here's the background behind my asking. We have a large flock of Redpolls this year and have been carefully watching them for Arctics. (thank you David and Fjord for suggesting Sibley's website for help with this!) The difference between the two kinds of Redpolls seem rather minor and yet they are listed as different species. A few years ago we had an Oregon Junco at our feeders here in NE Pennsylvania, but when I went to add it to my life list, I discovered that it is not considered a separate species from the Dark-eyed Junco... of which it is very much different in appearance. In checking some of my older field guides, it was in the past listed as Junco oreganus. We were pretty excited to have this rare-for-our-neck-of-the-woods bird, and now I can't even list it! (Is that whining? I was trying not to do that!)
I'm not very qualified to answer this, but here are some thoughts.
This is an extremely complicated topic because life is extremely complicated.
There are various "species concepts" -- ways of defining species. Ornithologists have tended to use the more traditional biological species concept (BSC), more or less, often with modifications. To read about that that means, start with this page on Defining a Species and follow the links at the bottom to read about the various species concepts.
So the question is, do two populations interbreed, or not? Are they isolated by actual physical and/or genetic incompatibility, by geographic or ecological separations, by rituals like songs or displays (so that they can't recognize each other as potential mates), etc.?
If we think the answer is yes to one or more of those questions, then the populations will probably be defined as different species. But there are still enormous gaps in our knowledge, and many populations that are currently classified as one species may represent more than one (i.e., Eastern and Western Marsh Wrens; the Red Crossbill complex -- and won't that be a headache if they're ever split apart!). And of course the reverse is also true, but the general ornithological trend these days (it does go in cycles) is toward "splitting", not "lumping."
There is also the problem of determining how different or separated populations should be before they are treated as separate species. In the case of titmice, for example, there is an intergrade zone in Texas where the titmice show characteristics intermediate between Black-crested and Tufted. There isn't a sharp distinction between the two forms. So are they separate species or not?
In the case of juncos, many scientists believe that the different populations of juncos form an continuum, with birds from different subspecies interbreeding in the overlap areas. In fact, the whole situation is still rather poorly understood. See this juncos discussion for more.
And even redpolls aren't fully understood; did you see Sibley's latest post on the breeding range and ecology of different populations, and the poorly understood intergrade population?
These days, genetics are playing a larger role in taxonomic decisions, and genes can yield surprising results too.
In some ways, it's like trying to slice a rainbow into different colors. You can identify red, green, etc., but what about the fuzzy edges? We are seeing a continuum of frequencies, so where exactly do you draw the line between blue and purple?
Thank you for your answer, David - I found it very interesting. After reading your reply and the websites you included in it, I think you really summed it up with your first statement, "this is an extremely complicated subject because life is extremely complicated" - but that just makes the study of it all the more interesting, don't you think? And another applicable quote from the Defining a Species link, "the idea of a species is something that we humans invented for our own convenience"! Since you mention that the ornithologists' thinking tends to cycle, between "lumping" and "splitting"- I'll just have to keep checking and maybe someday they'll split those Juncos up again! :-)
I have found this site interesting enough to spend many hours fixing up my list to upload it and several more hours trying to figure out what names are now okay for the birds I saw and identified 28 years ago. I really ran into trouble with the vireos. For some reason I just can't remember the bird I saw back then. :( My old book says Solitary vireo: Vireo solitarius. My list says Solitary (Plumbeous)and I have sitings in 3 different countries. The scientific name that I noted down has been assigned to Blue-headed. Now I don't know if I have seen Blue-headed, Cassin's, Plumbeous or all three. For this site, I finally just picked one. And I agree about the juncos. I have seen oregon, pink-sided, slate-colored, and gray-headed. If they ever lump them together again I'll be able to add 3 more birds to my list!
I just read the sites you recommend, David, and found them very interesting. I like the simplicity of the species explanation. It sounds very much like the problem we are having deciding what determines a separate language group. No easy solution. And after looking at the junco discussion and pictures, I'll be happy with Dark-eyed for now and quit complaining about the changes back and forth. ;)
Nancy said:
I'm pretty much a "casual" birder but recently I've been wondering about something that maybe you more "scientific-types" can answer for me. Here's the background behind my asking. We have a large flock of Redpolls this year and have been carefully watching them for Arctics. (thank you David and Fjord for suggesting Sibley's website for help with this!) The difference between the two kinds of Redpolls seem rather minor and yet they are listed as different species. A few years ago we had an Oregon Junco at our feeders here in NE Pennsylvania, but when I went to add it to my life list, I discovered that it is not considered a separate species from the Dark-eyed Junco... of which it is very much different in appearance. In checking some of my older field guides, it was in the past listed as Junco oreganus. We were pretty excited to have this rare-for-our-neck-of-the-woods bird, and now I can't even list it! (Is that whining? I was trying not to do that!)
Posted Thursday, 24 January 2008, 13:58
djringer said:
Hi Nancy,
I'm not very qualified to answer this, but here are some thoughts.
This is an extremely complicated topic because life is extremely complicated.
There are various "species concepts" -- ways of defining species. Ornithologists have tended to use the more traditional biological species concept (BSC), more or less, often with modifications. To read about that that means, start with this page on Defining a Species and follow the links at the bottom to read about the various species concepts.
So the question is, do two populations interbreed, or not? Are they isolated by actual physical and/or genetic incompatibility, by geographic or ecological separations, by rituals like songs or displays (so that they can't recognize each other as potential mates), etc.?
If we think the answer is yes to one or more of those questions, then the populations will probably be defined as different species. But there are still enormous gaps in our knowledge, and many populations that are currently classified as one species may represent more than one (i.e., Eastern and Western Marsh Wrens; the Red Crossbill complex -- and won't that be a headache if they're ever split apart!). And of course the reverse is also true, but the general ornithological trend these days (it does go in cycles) is toward "splitting", not "lumping."
There is also the problem of determining how different or separated populations should be before they are treated as separate species. In the case of titmice, for example, there is an intergrade zone in Texas where the titmice show characteristics intermediate between Black-crested and Tufted. There isn't a sharp distinction between the two forms. So are they separate species or not?
In the case of juncos, many scientists believe that the different populations of juncos form an continuum, with birds from different subspecies interbreeding in the overlap areas. In fact, the whole situation is still rather poorly understood. See this juncos discussion for more.
And even redpolls aren't fully understood; did you see Sibley's latest post on the breeding range and ecology of different populations, and the poorly understood intergrade population?
These days, genetics are playing a larger role in taxonomic decisions, and genes can yield surprising results too.
In some ways, it's like trying to slice a rainbow into different colors. You can identify red, green, etc., but what about the fuzzy edges? We are seeing a continuum of frequencies, so where exactly do you draw the line between blue and purple?
There are very few neat and tidy answers.
David J. Ringer
http://djringer.com/birding
http://birdstack.com
Posted Thursday, 24 January 2008, 20:26
Nancy said:
Thank you for your answer, David - I found it very interesting. After reading your reply and the websites you included in it, I think you really summed it up with your first statement, "this is an extremely complicated subject because life is extremely complicated" - but that just makes the study of it all the more interesting, don't you think? And another applicable quote from the Defining a Species link, "the idea of a species is something that we humans invented for our own convenience"! Since you mention that the ornithologists' thinking tends to cycle, between "lumping" and "splitting"- I'll just have to keep checking and maybe someday they'll split those Juncos up again! :-)
Posted Friday, 25 January 2008, 13:32
Chivis said:
I have found this site interesting enough to spend many hours fixing up my list to upload it and several more hours trying to figure out what names are now okay for the birds I saw and identified 28 years ago. I really ran into trouble with the vireos. For some reason I just can't remember the bird I saw back then. :( My old book says Solitary vireo: Vireo solitarius. My list says Solitary (Plumbeous)and I have sitings in 3 different countries. The scientific name that I noted down has been assigned to Blue-headed. Now I don't know if I have seen Blue-headed, Cassin's, Plumbeous or all three. For this site, I finally just picked one. And I agree about the juncos. I have seen oregon, pink-sided, slate-colored, and gray-headed. If they ever lump them together again I'll be able to add 3 more birds to my list!
Posted Thursday, 28 February 2008, 00:01
Chivis said:
I just read the sites you recommend, David, and found them very interesting. I like the simplicity of the species explanation. It sounds very much like the problem we are having deciding what determines a separate language group. No easy solution. And after looking at the junco discussion and pictures, I'll be happy with Dark-eyed for now and quit complaining about the changes back and forth. ;)
Posted Thursday, 28 February 2008, 00:57