This small, canopy-foraging insectivore breeds locally in mature and older deciduous forests with broken canopies across much of the eastern United States, and spends the nonbreeding season also locally in a number of forested habitats in the northern Andes of South America. Sky blue, sky high in the canopy, the Cerulean Warbler is remarkably difficult to study in the field. Among Setophaga, this species forages and nests higher in the canopy, and migrates farther and earlier, than most others. Still, its social system remains poorly understood, and a variety of interesting questions about biology and management await investigation.
Although the Cerulean Warbler was formerly among the most abundant breeding warblers in the Ohio and Mississippi river valleys, its numbers plummeted in the late 1900s. Concern for the future of this species is warranted. Yet even in the face of these steep declines, populations continue to occur across the breadth of the nonbreeding range, and are currently expanding in the northeastern portion of the breeding range.
Spurred by declining populations and concern for the species, several independent teams have recently investigated this warbler on its breeding grounds: in southern Illinois, by the Illinois Natural History Survey, principally Scott Robinson (Vanderah and Robinson 1995); in the Cumberland Plateau, Tennessee, by David Buehler and his students at the University of Tennessee (Nicholson 2004, Beachy 2007, Boves 2011); in southern Ontario by Raleigh Robertson at Queen's University and his students (Oliarnyk 1996, Veit 1999, Jones 2000, Barg 2002, Girvan 2003); in West Virginia, by Petra Wood with the U. S. Geological Survey and her students at West Virginia University (Weakland 2000, Bosworth 2003, Perkins 2006, McDermott 2007, George 2009); in Ohio by Amanda Rodewald and her students at the Ohio State University (Bakermans 2008, Newell 2010); in Kentucky on the Daniel Boone National Forest by Jeff Larkin at his students at the University of Kentucky and Indiana University of Pennsylvania (Hartman 2006, White 2008, Evans 2012); in Indiana by Kamal Islam and his students at Ball State University (Roth 2004, Jones 2006c, Register 2007, MacNeil 2010); and in the lower Mississippi Alluvial Valley, by scientists at the USDA Forest Service, Southern Hardwoods Lab, principally Paul Hamel.
Interest in the little sky blue princess has grown enormously since Hamel (2000), both scientifically and in the popular press (Franzen 2010, Fallon 2011, Universal Studios 2011). As documented population declines continue, a coordinated effort to address urgent unanswered questions of breeding and nonbreeding habitat management coalesced as the Cerulean Warbler Technical Group in 2001. Capitalizing on the existing work of several independent teams (Vanderah and Robinson 1995, Nicholson and Buehler 1998, Oliarnyk 1996; Oliarnyk and Robertson 1996; Jones and Robertson Jones and Robertson 1997, Jones and Robertson 1998, Hamel 1998a, Hamel et al. 1998a ), the collaboration became stronger and more inclusive as the decade progressed (Hamel et al. 2004). This effort has become a model for species conservation efforts that bring conflicting interests into a common process: as stand-alone meetings, or summits, of the group occurred in Shepherdstown, West Virginia in 2002; Quito, Ecuador in 2005 (http://www.srs.fs.usda.gov/egc/events/conf2005/conf2005.html); Morgantown, West Virginia in 2007 (http://www.srs.fs.usda.gov/egc/events/Summit2_2007/summit2.html); and Bogotá and San Vicente de Chucurí, Colombia in 2008 (http://www.srs.fs.usda.gov/egc/events/Summit3_2008/summit3.html).
Symposia have been organized by members of the group at international and national ornithological meetings in the US: North American Ornithological Conference, Veracruz, Mexico 2006 (http://www.srs.fs.usda.gov/egc/events/NAOC2006/NAOC2006.php); the Neotropical Ornithological Congress in Maturin, Venezuela, in 2007 (http://www.srs.fs.usda.gov/egc/events/NOC2007/NOC2007.html); the combined meeting of the Association of Field Ornithologists, Cooper Ornithological Society, and Wilson Ornithological Society in Kearney, Nebraska in 2011 (http://www.srs.fs.usda.gov/egc/events/Kearney2011/Kearney2011.html); and the Neotropical Ornithological Congress in Cuzco, Peru in 2011 (http://www.srs.fs.usda.gov/egc/events/NOC2011/NOC2011.html), and elsewhere.
Supported by grants from the National Fish and Wildlife Foundation, the efforts of independent groups extant in the 1990s have coordinated into a substantial evaluation of land management practices in the breeding season, and a rigorously constructed and validated predictive model of non-breeding distribution (Barker et al. 2006, Colorado et al. 2008). Results of these studies exist in report form at this time. The effect of the efforts can be seen in the evaluation process conducted by U.S. Fish & Wildlife Service in response to a petition to list the species as Threatened under the Endangered Species Act.Upon publication of Hamel (2000), a number of environmental groups, concerned about declining numbers of the Cerulean Warbler, filed a petition to list the species as Threatened (Southern Environmental Law Center 2000), which the U. S. Fish and Wildlife Service acknowledged (USFWS 2002). After lengthy delay, a Cerulean Warbler risk assessment and conservation planning workshop was convened in Shepherdstown, West Virginia in 2006 (http://www.fws.gov/midwest/es/soc/birds/cerw/cerw06ra.html) to respond to the issues raised in the petition. Cerulean Warbler Technical Group members constituted the bulk of the participation in that workshop. Results of the workshop formed the basis of the decision not to list the species as Threatened (U.S. Fish and Wildlife Service 2006). Petitioning groups were not pleased with this decision (http://www.birdlife.org/news/news/2006/12/cerulean_warbler.html). The uncertainties involved in the process of arriving at the decision were itemized by Woods and Morey (2008). Conservation actions outlined in two planning documents resulted from the efforts of the Cerulean Warbler Technical Group (U.S. Fish and Wildlife Service Division of Migratory Bird Management Focal Species Program 2007, Fundacion ProAves et al. 2010).