Chapter FOURTEEN Research on Golden-winged Warblers* RECENT PROGRESS AND CURRENT NEEDS Henry M. Streby, Ronald W. Rohrbaugh, David A. Buehler, David E. Andersen, Rachel Vallender, David I. King, and Tom Will Abstract. Considerable advances have been made related Blue-winged Warblers (Vermivora cyanoptera). in knowledge about Golden-winged Warblers Second, we discuss the much-less-studied, non- (Vermivora chrysoptera) in the past decade. Recent breeding-grounds ecology, including the first employment of molecular analysis, stable-isotope empirical studies of non-breeding-grounds cover- analysis, telemetry-based monitoring of survival type associations and spatial and social behavioral and behavior, and spatially explicit modeling ecology. Third, we address migratory connectivity techniques have added to, and revised, an already and migration ecology, for which little is known broad base of published knowledge. Here, we and research has only just begun. Last, we close synthesize findings primarily from recent peer- with cautious optimism that current knowledge is reviewed literature on Golden-winged Warblers, adequate to inform initial conservation and man- from this volume and elsewhere, and we iden- agement plans for Golden-winged Warblers, and tify some of the substantial remaining research with a sobering acknowledgement of the quantity needs. We have organized this synthesis by stages of research still needed. of the Golden-winged Warbler annual cycle. First, we discuss the relatively well-studied breeding- Key Words: annual cycle, breeding ecology, hybrid- grounds ecology including nesting and post- ization, migration, nonbreeding ecology, Vermivora fledging ecology and hybridization with closely cyanoptera. bREEDING-GROUNDS ECOLOGy prior to this volume of Studies in Avian Biology (Ficken and Ficken 1968, Klaus and Buehler 2001, Nesting-Habitat Associations Martin et al. 2007, Vallender et al. 2007a, Confer and Nesting Ecology et al. 2010) and within this volume (Chapters 7 and The nesting ecology of Golden-winged Warblers 9, this volume). Across their breeding distribution, has been the focus of most research on the species Golden-winged Warblers are typically associated * Streby, H. M., R. W. Rohrbaugh, D. A. Buehler, D. E. Andersen, R. Vallender, D. I. King, and T. Will. 2016. Research on Golden-winged Warblers: Recent progress and current needs. Pp. 217–227 in H. M. Streby, D. E. Andersen, and D. A. Buehler (editors). Golden-winged Warbler ecology, conservation, and habitat management. Studies in Avian Biology (no. 49), CRC Press, Boca Raton, FL. 217 with landscapes dominated by forest in later seral Postfledging Survival and Habitat Associations stages (hereafter, later successional forest) with For two decades, a growing body of literature has openings of shrub–sapling and herbaceous vegeta- demonstrated that postfledging survival and habitat tion that can be shrub-dominated uplands or wet- associations are critical components of breeding- lands or very young forest (hereafter, shrublands grounds ecology in migratory songbirds (Anders or early successional areas). However, beyond this et al. 1997, Streby and Andersen 2011). Several spe- broad-stroke description of the breeding landscape cies that nest in later successional forest use early structure, results reported here and elsewhere sug- successional areas during the postfledging period gest there is no one-size-fits-all breeding habitat (Anders et al. 1998, Pagen et al. 2000, Marshall description at the stand-level scale (Chapter 9, this et al. 2003, Vitz and Rodewald 2007, Streby et al. volume) or the territory or nest-site scale (Confer 2011) and in some species, a mid-season switch et al. 2003, Bulluck and Buehler 2008, Aldinger in cover-type associations can benefit body condi- and Wood 2014; Chapter 7, this volume) that is tion (Stoleson 2013) and fledgling survival (Streby consistently associated with nesting habitat selec- and Andersen 2013a, Vitz and Rodewald 2013). To tion and nest success of Golden-winged Warblers. our knowledge, recent postfledging research on Perhaps not surprising, considering the tremen- Golden-winged Warblers represents the first report dous variation in plant communities across the of the opposite pattern, in which a species most breeding distribution of Golden-winged Warblers, commonly associated with nesting in early succes- the relative importance of small-scale vegetation sional areas selects later successional forest for rais- characteristics such as percent ground cover by ing young (Streby et al. 2014a, 2015a; Chapters 8 certain species or vegetation types to nesting habi- through 10, this volume). tat selection and nest success is not generalizable In the western Great Lakes region, Golden- among regions or even among sites within a region winged Warblers choose later successional forest (Chapter 7, this volume). Studies incorporating over shrublands for raising recently fledged young data from many sites primarily in the Appalachian (Streby et al. 2014a; Chapter 8, this volume). Parents Mountains region support the results of previous of both sexes raise fledglings in later successional single-site studies (Confer et al. 2003, 2010; Bulluck forest, but adult females lead fledglings hundreds and Buehler 2008; Kubel and Yahner 2008; Roth of meters away from natal stands before young et al. 2014), indicating fine-scale vegetation asso- are independent from adult care (Chapter 10, this ciations of nesting Golden-winged Warblers are volume). In addition, fledglings choose later suc- mostly site-specific. Furthermore, spatially explicit cessional forest over all other cover types after models of full-season productivity, or young raised independence from adult care (Streby et al. 2015a). to independence from adult care, indicate that a Postfledging research is currently underway in single management action can affect productivity populations within the Appalachian Mountains differently depending on the cover-type composi- region (J. A. Lehman, unpubl. data), and those tion of the surrounding landscape (Chapter 10, this studies could provide at least a partial explana- volume). Therefore, it is unlikely there is any single tion for the substantial differences in population stand-level management action, such as increasing growth between regions with similar fledgling area of shrubland, that generally increases Golden- production from nests and apparently similar adult winged Warbler productivity, at least in the western annual survival. Indeed, pilot research in Tennessee Great Lakes region. In fact, Chapter 10 (this volume) suggests that fledgling survival there might be low demonstrated that in some areas that already host (J. A. Lehman, unpubl. data). highly productive populations, reducing the area of later successional forest can have a net negative impact on population productivity, even if breed- Limitations of Current Breeding-Grounds ing density increases. As frustrating as it might be Knowledge that there is no evidence for a single management prescription that can be applied broadly to benefit A tremendous amount of research has focused breeding Golden-winged Warblers, the knowledge on breeding Golden-winged Warblers in the that management and conservation plans must be past few decades and that research has provided flexible and locally informed is an equally impor- considerable new insights. However, many tant research outcome. important gaps remain in our understanding 218 STUDIES IN AVIAN BIOLOGY NO. 49 Streby, Andersen, and Buehler of the breeding-grounds ecology of Golden- relationships between residual tree retention winged Warblers. For example, attempts to relate after forest harvest and breeding-male density food availability to foraging habitat selection and pairing success observed in Wisconsin (Roth (Chapter 6, this volume) are complicated by lim- et al. 2014) also present in the Appalachian region ited available data on the diet of Golden-winged where breeding densities are relatively low, or in Warblers (Streby et al. 2014b). The published and areas of Minnesota where pairing success is near anecdotal descriptions of diet in Golden-winged 100%? Do patterns of postfledging cover-type Warblers (summarized in Confer et al. 2011, selection observed in the western Great Lakes Streby et al. 2014b) suggest their diet may be too region (Chapter 8, this volume) hold true in the specialized for food availability to be sampled rest of the Golden-winged Warbler breeding dis- with standard methods. Leaf-roller caterpillars tribution? If not, what are the cover types and (Archips spp.) constitute 89% of the diet of nest- habitat characteristics associated with high fledg- ling and fledgling Golden-winged Warblers in ling survival in populations outside the western Minnesota and Manitoba (Streby et al. 2014b), but Great Lakes region? initial attempts to develop efficient prey sampling The vast majority of research on breeding methods indicated the required sampling effort Golden-winged Warblers has focused on the nest- might be a prohibitive challenge (B. Vernasco, ing season in the Appalachian population seg- unpubl. data). Regardless, recent evidence sug- ment, which is declining and represents ~5% of gests patterns of differential arthropod abundance the global breeding population (Chapter 1, this and distribution among shrub and tree species volume). Current breeding-distribution-wide influence territory placement by Golden-winged conservation plans are based on published and Warblers in central Pennsylvania