North American Birds

VOLUME 66 NO3 2013

A Quarterly Journal of Ornithological Record Published by the American Birding Association. The mission of the journal is to provide a complete overview of the changing panorama of our continent’s birdlife.

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spring and fall migrations of kirtland���s warbler from very detailed notes to vague descriptions such as ���yard��� or ���trees.��� Dawson (1903) noted Kirtland���s Warblers were found ���frequenting the lower levels of bushes and trees.��� In Illinois, Kirtland���s Warblers were found in low edge vegetation or on the ground (Graber et al. 1983). Mayfeld (1960) describes spring migration habitat preferences as ���low elevations and brushy situations.��� In the records summarized here, most habitats used by migrant Kirtland���s Warblers are best described as shrub/ scrub, similar in structure to that on the breeding and wintering grounds. Standardized scientifc annual surveys of singing male Kirtland���s Warblers show an increasing population since 1987, and records of migrants have increased since that time as well. Although the increasing number of records Table 10. Accepted reports of migrant Kirtland���s Warblers by decade. Decade Spring Fall Total 1851-1860 4 0 4 1861-1870 0 0 0 1871-1880 8 0 8 1881-1890 9 4 13 1891-1900 13 0 13 1901-1910 28 5 33 1911-1920 13 7 20 1921-1930 10 4 14 1931-1940 11 12 23 1941-1950 9 14 23 1951-1960 14 7 21 1961-1970 24 11 35 1971-1980 13 15 28 1981-1990 16 8 24 1991-2000 40 12 52 2001-2011 99 13 112 of migrant Kirtland���s Warblers can potentially be explained by many factors���including the increasing number of birders, the increasing number of reporting venues, increasing quality of feld identifcation information, and improvements in optics���the strong correlation with the standardized survey results indicates that at least some of the increase in records is attributable to the increase in population. Despite the diffculties in vetting and analyzing sight records, whether in citizen-science contexts or from individuals outside the context of such projects, the advantages of using carefully vetted sight records are manifest. In the case of Kirtland���s Warbler, records analyzed in this paper show a much broader geographic and longer temporal span of migration than do earlier efforts to assess migration in the species. To acquire data on migrant Kirtland���s Warblers using an array of standardized surveys dispersed throughout eastern North America would be costly and logistically prohibitive. Our understanding of Kirtland���s Warblers��� migratory routes���and of the value of shrub/scrub habitats for migrants���is richer and more robust because of the contributions of birders to the literature on this endangered species. Acknowledgments Many people working on state and provincial bird records committees, and others with expertise in their respective regions, were most helpful, as were hundreds of observers connected to records, and we extend our gratitude to all of them, too many to list here. In particular, we thank Paul Aird (Ontario), Bruce Anderson (Florida), Steve Bailey (Illinois), Phil Davis (Maryland), Sam Droege (PWRC), Lynda Garrett (PWRC), Janet Hinshaw (University of Michigan Museum of Zoology), Chandler S. Robbins (PWRC), Bill Whan (Ohio), Alan Wormington (Ontario), and Jessica Zelt (PWRC) for their assistance in locationg hardto-fnd reference materials and records. We Table 11. Linear correlation coefcients among spring reports, fall reports, total reports, and the annual census data on breeding grounds. Values closer to 1 signify stronger relationships, and values closer to 0 signify weaker relationships. Year Spring reports Fall reports Total reports Year 1.00 Spring reports 0.77 1.00 Fall reports -0.06 0.13 1.00 Total reports 0.72 0.98 0.32 1.00 Annual census of males 0.80 0.86 0.08 0.84 Annual census of males 392 1.00 thank Bonnie F Kepler (Athens Field Station, . PWRC) for typing the manuscript through the various revisions. We also express appreciation to those who reviewed the manuscript at different stages: Bruce Anderson, Carol I. Bocetti, David N. Ewert, Cameron B. Kepler, Bruce Peterjohn, Jerry Weinrich, and Alan Wormington. The fndings and conclusions in this article are those of the authors and do not necessarily represent the views of the United States Fish and Wildlife Service or Department of the Interior. Literature cited and consulted Abbott, J. M. 1979. report to Maryland/District of Columbia Bird Records Committee. Adams, C. C. 1904. The migration route of Kirtland���s Warbler. Bulletin of the Michigan Ornithological Club 5: 14-21. American Ornithologists��� Union [A.O.U.]. 2011. Fifty-second Supplement to the American Ornithologists��� Union Check-list of North American Birds. American Ornithologists��� Union���s Committee on Classifcation and Nomenclature���North and Middle America. Auk 128: 600-613. Anderson, B. H. 2005. The spring migration: Florida region. North American Birds 59: 426-429. Anderson, M., and T. Kemp. 1989. The spring season 1989: 1 March���31 May. Ohio Cardinal 12: 1-14. Anderson, R. M. 1907. The birds of Iowa. Proceedings of the Davenport Academy of Sciences 11: 125-417. Atherton, L. 2006. Kirtland���s Warbler, Polk County, Lake Kissimmee State Park, Florida 29 October 2006. . Accessed 2 November 2006. Atherton, L. S., and B. H. Atherton. 1982. The fall migration: Florida region. American Birds 36: 168-171. Aune, V. 2003. By the wayside. Passenger Pigeon 65: 93-105. Baerg, W. J. 1951. Birds of Arkansas. Arkansas Experimental Station Bulletin 258. University of Arkansas, College of Agriculture, Fayetteville, Arkansas. Baillie, J. L. 1953. The spring migration: Ontario���Western New York region. Audubon Field Notes 7: 270-272. Bain, M. J. C. 1992. Ontario Bird Records Committee report for 1991. Ontario Birds 10: 43-62. ���. 2002. 29 August, report to Ontario Bird Records Committee. ���. 2003. The fall migration: Ontario region. North American Birds 57: 49-52. Baird, S. F. 1852. Description of a new species n o rt h a m e r i c a n b i r d s

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