Avian Community and Microhabitat Associations of Cerulean Warblers in Alabama
نویسندگان
چکیده
—Cerulean Warblers (Dendroica cerulea) have experienced one of the highest population declines of any neotropical-Nearctic migratory species in North America. We performed point counts and habitat assessments in areas used and unused by Cerulean Warblers in northern Alabama during the 2005 and 2006 breeding seasons to examine their avian associations and identify microhabitat features that best explained their occurrence. We detected on average ,50 Cerulean Warbler males (total) in three disjunct populations during each breeding season. Areas used by Cerulean Warblers were characterized by avian communities with significantly higher species richness, diversity, and abundance compared to areas where they were not detected. Correspondence analysis related Cerulean Warblers to inhabitants of riparian, bottomland deciduous forests (e.g., Kentucky Warbler [Oporornis formosus], Acadian Flycatcher [Empidonax virescens], and Northern Parula [Parula americana]) and two edge specialists (Blue-winged Warbler [Vermivora cyanoptera] and Indigo Bunting [Passerina cyanea]) suggesting Cerulean Warblers in our study areas may be tolerant of some habitat disturbance within an otherwise largely forested landscape. Information theoretic criteria and canonical correspondence analysis indicated Cerulean Warblers preferred bottomland forests containing tall (. 29 m), large diameter, well-spaced (. 27 m/ha) deciduous trees with greater canopy cover ($ 90%), closer (, 20 m) canopy gaps, fewer snags (# 25/ha), and a moderately complex canopy structure. Received 5 March 2010. Accepted 22 December 2010. The Cerulean Warbler (Dendroica cerulea) has lost nearly 70% of its breeding population since 1966 (Rich et al. 2004) because of alterations in breeding, migratory, and wintering habitats compounded by the bird’s dependency on extensive tracts of large deciduous trees in many parts of its range (Hamel 2000a). Northern Alabama historically represented a portion of the Cerulean Warbler’s southern-most breeding range where they were described as common and even numerous in several counties throughout the state (Imhof 1976). This warbler is now rarely encountered in Alabama during the breeding season and was designated a Priority One species (highest conservation concern) by the Alabama Department of Conservation and Natural Resources (Mirarchi et al. 2004). Selection of breeding territories by landbirds is heavily influenced by structure and composition of the surrounding habitat and avian community (MacArthur and MacArthur 1961, Wiens 1989). Thus, effectiveness of management initiatives is dependent upon not only identifying the habitat requirements of the species under investigation, but also the avian community with which it associates. Recent studies of Cerulean Warblers emphasize breeding habitat requirements (Robbins et al. 1992, Jones and Robertson 2001, Weakland and Wood 2005, Barg et al. 2006b), nesting behavior (Oliarnyk and Roberston 1996, Barg et al. 2006a, Rogers 2006, Roth and Islam 2008), and habitat management (Hamel 2005, Hamel et al. 2005b, Hamel and Rosenberg 2007), while information regarding avian associations of Cerulean Warblers remains scarce (Jones et al. 2004) and anecdotal (Lynch 1981, Hamel 2000b). Recent discoveries of two small Cerulean Warbler populations in Alabama suggest habitat is available in this portion of the species range to support small breeding populations (Carpenter et al. 2005). This study was initiated in response to the Rosenberg et al. (2000) recommendation for additional Cerulean Warbler research in Alabama to provide more accurate population estimates and habitat requirements needed to effectively manage habitat for this species. Our objectives were to: (1) examine avian associations of the Cerulean Warbler to facilitate a better understanding of this species’ habitat use and the bird community in which it breeds, and (2) identify microhabitat features that best explain Cerulean Warbler occurrence in the southern portion of its range where populations are in serious decline (Buehler et al. 2008). 1 Department of Natural Resources and Environmental Sciences, Alabama A&M University, P. O. Box 1927, Normal, AL 35762, USA. 2 USDA, Forest Service, Southern Research Station, P. O. Box 1568, Normal, AL 35762, USA. 3 USDA, Forest Service, Center for Bottomland Hardwoods Research, P. O. Box 227, Stoneville, MS 38776, USA. 4 Current address: North Carolina Wildlife Resources Commission, 1751 Varsity Drive, Raleigh, NC 27606, USA. 5 Corresponding author; e-mail: [email protected] The Wilson Journal of Ornithology 123(2):206–217, 2011
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ADVANCING OUR UNDERSTANDING Of THE NON-BREEDING DISTRIBUTION Of CERULEAN WARBLER (sEtOphAGA CErulEA) IN THE ANDES
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