snell@utzoo.uucp (snell) (11/12/88)
Recently, mjm@oliven.olivetti.com (Michael Mammoser) and gpasq@picuxa.UUCP (Greg Pasquariello X1190) having been having an interesting discussion of "Thayer's Gulls", and characteristics which might be used to identify these birds. For the past four years I have been working on a PhD at utzoo which deals with hybridization and genetic differentiation between Herring, Glaucous, Iceland and "Thayers" gulls. I have collected large numbers of specimens of all these "taxa", on their breeding grounds, including colonies on Baffin Island, Iceland, Spitzbergen, Norway, southern Europe and the Canadian maritimes. I have been impressed by the variability in plumage and eye-colouration in these birds. These gulls are far more variable, morphologically, than one would assume from reading field-guide descriptions, and more variable than than one might assume even from reading P. Grants book on gull identification. Unfortunately, the more northern forms (especially Iceland and "Thayer's") breed in colonies which are difficult to reach; not a great deal is known about them. Certainly, their systematic relationships have been hotly debated, and are not yet fully resolved. As well, these birds are only a portion of a much wider complex of white-headed gulls which frequently hybridize with each other. A problem with published descriptions of "Thayer's Gull" is that they are inconsistent and largely based on winter collected specimens. Few people have ever seen "Thayer's Gull" on their breeding colonies. Virtually none have ever been banded on their high arctic colonies, either as chicks or adults. As far as I am aware, not a single such banded bird (if any ever existed) has ever been recovered. As well, not even one "Thayer's Gull" has ever been banded in the south and later recovered at an arctic breeding colony. Perhaps those 1st and 2nd year birds sighted in the south really are "Thayer's Gull" but there is no particular reason to believe it. There is no evidence that the various 1st and 2nd year "Thayer's Gulls" in museum collections (the birds on which descriptions are based) actually were hatched in cliff colonies in the Canadian high arctic. It is generally assumed that that was their origin, but descriptions based on such assumptions tend to become self-fulfilling prophecies. It may be that many of those small young birds are merely youthful variants of the more southerly Herring Gull. I would argue that there is little evidence to reject that idea. So, what is a "Thayer's Gull"? Almost certainly it is merely a plumage variant of a group of northern gulls (the Iceland Gull complex) which preferentially breed together. Call it hybridization if you like, but "Thayer's Gull" as well as "Kumlien's Gull" are but variants of Iceland Gulls. This complex varies clinally from east to west, with lighter birds more common in the east, and darker ones more common in the west. There are colonies where the very light and very dark winged ones breed together (especially on Baffin Island), and at those colonies there is considerable interbreeding between birds of the various plumages (see E. Godfrey's discussion of this in the revised Birds_of_Canada, 1986). The plumages of breeding birds (and presumably wintering ones too) are so variable that each of these groups blends into the other. There is no good evidence that "Thayer's Gull" is a `good' species. When people see a gull which they might want to call "Thayer's Gull" they compare that bird to pictures in books and to the self-perpetuating descriptions of this supposed species which accompany them. The birder finds a pigeon-hole, and stuffs it. Tick! I am not intending this to be a diatribe against tickers, nor against anyone who has ticked "Thayer's Gull" on their list. However, the process of ticking presupposes that one can assign a bird to a specific group which is clearly defined, and biologically meaningful (the pigeon-hole). Usually, the pigeon-holes are thought to be `species'. Not always. I am quite happy to tick different morphs of birds (e.g., I have ticked the three morphs of Parasitic Jaegers). However, whereas the borders around the pigeon-holes for the plumage morphs of Parasitic Jaegers are clear, they are extremely fuzzy for the plumage variants of the Iceland Gull. There was a time when I too had ticked "Thayer's Gull"; I had seen a `typical' bird, so I thought, sitting at a garbage dump up at Churchill, Manitoba, a long way from the breeding range. Since then, I have also seen classic "Thayer's Gulls" at their breeding colonies on Baffin Island. I have also seen, at those colonies, the range in plumage from the "Thayer" bird right through the classic "Kumlien" to the classic "Iceland". -- Name: Richard Snell Mail: Dept. Zoology, Univ. Toronto, Toronto, Ontario, Canada M5S 1A1 UUCP: uunet!attcan!utzoo!snell BITNET: snell@zoo.toronto.edu
mjm@oliven.olivetti.com (Michael Mammoser) (11/16/88)
In article <1988Nov11.185810.22941@utzoo.uucp>, snell@utzoo.uucp (snell) writes: > Recently, mjm@oliven.olivetti.com (Michael Mammoser) and > gpasq@picuxa.UUCP (Greg Pasquariello X1190) having been having an > interesting discussion of "Thayer's Gulls", and characteristics which > might be used to identify these birds. For the past four years I have > been working on a PhD at utzoo which deals with hybridization and > genetic differentiation between Herring, Glaucous, Iceland and > "Thayers" gulls. The controversy over Thayer's Gull has gone on for years, with the bird being classified as a subspecies of Herring Gull, a subspecies of Iceland Gull, a hybrid between the two, and a full species in its own right. I would not be surprised if the status of this bird changed at any time. > Unfortunately, the more northern forms (especially Iceland and "Thayer's") > breed in colonies which are difficult to reach; not a great deal is known > about them. Certainly, their systematic relationships have been hotly > debated, and are not yet fully resolved. > > So, what is a "Thayer's Gull"? Almost certainly it is merely a > plumage variant of a group of northern gulls (the Iceland Gull complex) > which preferentially breed together. Call it hybridization if you > like, but "Thayer's Gull" as well as "Kumlien's Gull" are but > variants of Iceland Gulls. Are you claiming to have fully resolved the issue, or are you just claiming your allegiance to one side of the hot debate? > When people see a gull which they might want to call "Thayer's Gull" > they compare that bird to pictures in books and to the self-perpetuating > descriptions of this supposed species which accompany them. > The birder finds a pigeon-hole, and stuffs it. Tick! Bear in mind that the pictures in books, the self-perpetuating descriptions, and the pigeon-holes are all defined by you scientists, not by us birders. Note that the American Ornithologists Union currently ranks the Thayer's Gull as a full species. IF, and WHEN, they demote the bird to some lesser status, it will be duly noted on the lists of birders. However, this will not invalidate the desire of birders to identify the bird in the field (regardless of its status), nor does it invalidate a discussion of the characteristics by which this identification can be accomplished. If you want to lend your knowledge and experience to this discussion, it would be greatly appreciated. However, if you just want to rant about the difference of opinion that you have with your peers at the A.O.U., then I suggest that you are "barking up the wrong tree". > I am not intending this to be a diatribe against tickers, nor against > anyone who has ticked "Thayer's Gull" on their list. Who are you trying to kid, I know a diatribe when I see one. Mike
dmark@cs.Buffalo.EDU (David Mark) (11/20/88)
> Bear in mind that the pictures in books, the self-perpetuating >descriptions, and the pigeon-holes are all defined by you scientists, not >by us birders. Field guides are rarely written by 'scientists', and especially not by systemmatists (sp?). They are usually written by birders, by 'naturalists', and/or by nature artists. The point may be: If Thayer's-Kumlein's-Iceland is a single species, and forms a cline darkening to the west, with a continuum of phenotypes, then a search for reliable field characteristics may be misguided, since there probarably *are* no gaps between them!
mjm@oliven.olivetti.com (Michael Mammoser) (11/23/88)
In article <2775@cs.Buffalo.EDU>, dmark@cs.Buffalo.EDU (David Mark) writes: > > > Bear in mind that the pictures in books, the self-perpetuating > >descriptions, and the pigeon-holes are all defined by you scientists, not > >by us birders. > > Field guides are rarely written by 'scientists', and especially not by > systemmatists (sp?). They are usually written by birders, by 'naturalists', > and/or by nature artists. The source of information for the field guides with which I am familiar is the American Ornithologist's Union checklist and the scientific data upon which the checklist is based. Regardless of who performs the "task" of writing the guide, the definitions ultimately come from the scientific community. Also, many field guides have as authors, or employ as consultants, professional scientists in the field of ornithology or wildlife biology. Mike