| UID |
|
| Digital Object Type |
Rare birds documentation form |
| Content DM Link |
https://n2t.net/ark:/87292/w9fx74169 |
| Type |
Text |
| Description |
Records Committee review for a Thayer's Gull at Red Rock Reservoir Dam in Marion County, IA on December 10, 1985. Includes a record review document with votes, an article in Iowa Bird Life, and six documentation forms submitted to the committee. |
| Related Genres |
Administrative records Clippings (information artifacts) Field notes |
| Sort Date |
1985-12-10 - 1993-09-03 |
| People / Organizations |
|
| Time |
2:15 PM |
| Rights |
This complex item has mixed rights protection. Portions in which Iowa State University is the copyright holder are made available for non-commercial use, including sharing and adapting the work. No permission is required for non-commercial use to these portions so long as attribution is provided. All other uses of these portions, including commercial, require permission from the Iowa State University Library Special Collections and University Archives (archives@iastate.edu). (CC BY-NC 4.0 International). Portions in which Iowa State University is not the copyright holder are believed to be under copyright, but either (a) no rights-holder(s) have been identified or (b) one or more rights-holder(s) have been identified but none have been located. If you have any information that can contribute to identifying or locating the rights-holder(s) please notify the Iowa State University Library Digital Initiatives Program (digital@iastate.edu). (Rightsstatements.org InC-RUU 1.0). The original object is available at the Iowa State University Library Special Collections and University Archives (archives@iastate.edu). |
| Data Access Rights |
http://vertnet.org/resources/norms.html |
| Data License |
http://creativecommons.org/publicdomain/zero/1.0 |
| Collection |
Iowa Ornithologists' Union | MS 166 |
| Box |
11 |
| Folder |
3 |
| Contributing Institution |
Iowa State University Library Special Collections and University Archives |
| Creator / Author |
Bendorf, Carl J. |
| Contributors |
Kent, Thomas H. (Thomas Hugh), 1934- Moore, Francis L. Myers, Robert K. Proescholdt, Beth Proescholdt, Mark Thompson, Dennis Iowa Ornithologists' Union Records Committee |
| Topics |
Bird watching Ornithology Ornithology--Societies, etc |
| Birds |
Thayer's Gull |
| Locations |
Red Rock Dam |
| Map |
|
| Verbatim Locality |
Red Rock Res. Tailwater |
| Location Remarks |
The documentation forms do not include georeferences |
| Habitat |
|
| Extent |
16 pages |
| Language(s) |
eng |
| Bibliographic Citation |
|
| Information Withheld |
|
| Individual Count |
1 |
| Occurrence Remarks |
The documentation form by Carl J. Bendorf forms the basis of this record. Other documentation forms by Thomas H. Kent, Francis L. Moore, Bob Myers, Beth Proescholdt and Mark Proescholdt, and Dennis Thompson were submitted. Other observers include Joe Schaufenbuel, Darwin Koenig, Steve Dinsmore, Eugene Armstrong, Eloise Armstrong, and many unidentified observers. | Elimination of similar species: Thayer's Gull is a difficult bird to identify. In researching this problem, I have found several helpful sources in addition to the standard field guides and I have tried to understand what it takes to know a Thayer's Gull when you see one. Nearly every reference makes it clear that Thayer's cannot be identified on the basis of one or two positive field marks. It takes a combination of characters to come to a conclusion of any certainty. In discussing this particular observation, I will examine each of the fieldmarks and compare and contrast to similar species with liberal reference to the literature, especially Lehman (1980). The most likely similar gulls in this case are 1st winter Herring and 1st winter Iceland (Kumlien's). The Kumlien's form is the darker form of the Iceland Gull and is the form that breeds in the Baffin Island area and winters mainly on the Atlantic coast. Lehman's article deals mainly with Kumlien's. Several similarly sized and possible but unlikely candidates can be eliminated rather quickly. A 1st winter California should not have an all dark bill and would show much darkening in the primaries in flight. Lesser Black-backed Gull could be about the right size, but in flight a 1st winter bird should show darker primary and secondary coverts, more extensively dark primaries, even compared to Herring Gull. A 1st summer Slaty-backed Gull is also light uniform brown with an all dark bill, but it should exhibit extensive darkening in the primaries on the upper wing. A 1st winter Glaucous-winged Gull would be very similar to Thayer's but should be larger, with a larger bill, and less mottling to the body color. Except for the first two, one would probably not consider the likelihood of their occurrence in Iowa to be very great. One hybrid, Glaucous-winged X Western, might be similar but should have a quite heavy bill. [...] Summary: Of the most likely similar species, 1st winter Herring Gull and 1st winter Kumlien's Iceland Gull, each is eliminated by one or more of the features discussed above. The wing pattern is especially damaging to the possibility of Herring, along with the bill shape and size. Iceland is ruled out by the presence of the noticeable tail band and by the darker secondaries on the upper wing. To identify a Thayer's Gull, one must see a combination of field marks. I feel that the bird I saw at Red Rock is consistent on every point.| The original documentation form event lasted from 14:15:00/14:45:00. |
| Occurrence Status |
present |
| Field Number |
1985-22 |
| Event Remarks |
Viewing Conditions: [...] I studied it with my 20-45X scope and noted the following details at about 75 yards. [...] After about 15 minutes, I flushed the resting gull flock and followed this bird with 7X binoculars as it circled about at approximately 50 to 150 yards. [...] The light was that of a medium bright but solid gray overcast winter day, without any shadow being cast by the su. It was beginning to snow at the end of the observation time. |
| Supporting Documentation |
Gosselin M & David N. Field identification of Thayer's gull (Larus thayeri) in eastern North America. American Birds. December 1975; 29;1059-1064. | Lehman, P. The Identification of Thayer's gulls in the field. Birding. 1980;12(6);198-210. | Eckert KR. A Birder's guide to Minnesota. 2nd Edition. Duluth: Gavian Guides; 1983. | Farrand J. The Audubon society master guide to birding, vol. 2, gulls to dippers. New York: Alfred A. Knopf, Inc; 1983. | Harrison P. Seabirds: an identification guide. New York: Houghton Mifflin Harcourt. | National Geographic Society. National geographic field guide to the birds of North America. Washington D.C.: National Geographic Society. |
| Date Digital |
30 May 2017 |
| File Type |
image/jpeg |
| Hardware / Software |
Epson - sheet feed |
