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 (Chapter 6, this unpublished data of which nearly all represent volume). Quantifying diet across the entire distri- the Appalachian Mountains region (A. M. Roth bution and throughout the breeding season, and et al., unpubl. plan), and little data represent the developing methods for sampling prey abundance other 95% of the global breeding population of and phenology, is necessary precursors for future Golden-winged Warblers. The precipitous decline work regarding potential range shifts, preda- of the Appalachian population segment necessi- tor–prey mismatches, and inter- and intraspecific tates intensive monitoring and research designed resource competition. to identify the causes of the decline and develop Many remaining gaps in knowledge of the strategies and plans to reverse it. However, there is breeding ecology of Golden-winged Warblers are an inherent risk of bias when deriving most of the related to the question of transferability or the knowledge about a species from small and declin- geographic range of inference from observations ing populations, especially if that knowledge is made at only one or a few locations. For example, intended to inform management and conservation are the radiotelemetry-based observations that for the species as a whole. Until recently, relatively song territories are considerably larger than those little research had focused on Golden-winged based on spot mapping (Streby et al. 2012), that Warblers in the western Great Lakes region where breeding adults forage in later successional forest a majority of the species breeds (Streby et al. 2012, (Streby et al. 2012; Chapter 5, this volume), and Roth et al. 2014; Chapters 9 and 10, this volume). that a considerable proportion of females nest in More information is needed on breeding-grounds later successional forest adjacent to early succes- ecology in this core, with respect to population sional stands (Streby et al. 2014a; Chapter 10, this density, of the Golden-winged Warbler breeding volume) consistent in other portions of the breed- distribution, where population numbers are rela- ing distribution? How widespread is the problem tively stable (Chapter 1, this volume), or appar- of misidentifying nest fates based on traditional ently recently populated and increasing, such as monitoring methods (Streby and Andersen parts of Manitoba (Sauer et al. 2012). Currently, 2013b), and what impact does that bias have on the only information available about postfledg- local and regional productivity estimates? What ing ecology of Golden-winged Warblers is from are the factors underlying female mate choice, as the western Great Lakes region. Considering the song variation (Harper et al. 2010) and plumage importance of fledgling survival to full-season phenotype of social mates (Vallender et al. 2007a) productivity and population growth of songbirds do not appear to be important? Are the positive (Anders et al. 1997, Faaborg et al. 2010a, Streby and
Research on Golden-winged Warblers 219 Andersen 2011), and of Golden-winged Warblers foraging, and raising young. Adult Golden-winged in particular (Streby et al. 2014a; Chapter 8, Warblers usually include later successional forest this volume), research on postfledging ecology in territories and home ranges (Streby et al. 2012; is a pressing need in the Appalachian Mountains Chapter 5, this volume), especially later in the day breeding-distribution segment. when territorial defense subsides (Streby et al. 2012). The use of later successional forest by terri- torial males goes undetected when forest edges are Rapidly Changing Knowledge of Breeding- assumed to be study-site boundaries (Streby et al. Grounds Cover-Type Associations 2012). In addition, tracking radio-marked females In a special section of The Wildlife Society Bulletin to nest sites reveals that some females nest in later summarizing research on Golden-cheeked successional forest ≤100 m away from early suc- Warblers (Setophaga chrysoparia), Morrison et al. cessional areas (Streby et al. 2014a; Chapter 9, this (2012) made a unique and valuable contribution volume). It is not possible to locate nests in areas not that also rings true with Golden-winged Warblers. searched in traditional nest-finding protocols, and Morrison et al. (2012) described how a prevailing the prevailing paradigm results in study designs paradigm can hinder progress in current research that only consider early successional shrublands, and conservation. In Golden-cheeked Warblers, a which can result in a biased distribution of nest limited and biased understanding of the distribu- sites and a biased estimate of nest success (S. M. tion, habitat associations, and status of the species Peterson, unpubl. data). Golden-winged Warbler led to research unconsciously designed to per- nests in later successional forest can be found dur- petuate the prevailing paradigm, which reduced ing standard nest-finding methods if search areas the efficacy of conservation efforts (Morrison are expanded to include later successional forest et al. 2012). Similar biased paradigm perpetuation (H. M. Streby, unpubl. data). is evident in Golden-winged Warbler breeding- It remains to be seen if the nesting and post- grounds research. Golden-winged Warblers are fledging use of later successional forest by commonly described as an early successional Golden-winged Warblers in the western Great shrubland specialist throughout the published Lakes region is also common in the Appalachian literature (Confer and Knapp 1981, Confer et al. breeding-distribution segment. However, the 2011). The current paradigm acknowledges that recent observations that Golden-winged Warblers early successional stands or patches must be use at least some later successional forest dur- within a later successional forested matrix to host ing the nesting season in two areas in the cen- breeding Golden-winged Warblers, and a positive tral Appalachians (Chapter 5, this volume), and a association between Golden-winged Warblers and radiomarked adult male that traveled into forest primarily forested landscapes has been demon- with fledglings in West Virginia (Chapter 5, this strated (Thogmartin 2010). However, the degree volume), suggest the early successional special- to which later successional forest is used by ist description is likely inappropriate across the Golden-winged Warblers throughout the breed- breeding distribution. A more appropriate cat- ing season is only starting to be appreciated. egorization for Golden-winged Warblers might be The early successional specialist paradigm is so diverse-forest obligate or dynamic-forest special- entrenched in Golden-winged Warbler research ist. Incorporating full-season habitat associations that early successional or open shrubby areas are in breeding-grounds management and conserva- commonly described as “study sites” bounded by tion planning will be crucial to the success of con- the edges of later successional forest (Ficken and servation plans for Golden-winged Warblers and Ficken 1968; Confer et al. 2011; Roth et al. 2014; likely other forest-associated songbirds. Chapter 7, this volume). Early successional areas are certainly a critical component of breeding Hybridization of Golden-winged habitat, and Golden-winged Warblers are usu- Warbler × Blue-winged Warbler ally not observed breeding in landscapes that lack at least some forest openings. However, recent Hybridization between Golden-winged and Blue- research published in this volume and elsewhere winged Warblers (Vermivora cyanoptera) is thought demonstrates that later successional forest is used to be one of the principal drivers behind wide- throughout the breeding season for nesting, spread population declines in Golden-winged
220 STUDIES IN AVIAN BIOLOGY NO. 49 Streby, Andersen, and Buehler Warblers. Indeed, a typical pattern of replace- Warblers will inform conservation plans for both ment of the Golden-winged Warbler phenotype species. Some have suggested that Golden-winged by the Blue-winged Warbler phenotype has been Warblers may become very rare or even extinct documented in several regions throughout the by 2080 (Gill 1980). Continuing to document the breeding distribution, and replacement tends to progression and impact of hybridization is para- occur within 50 years of contact between the two mount for determining where genetically pure species. The hybridization system has interested populations of Golden-winged Warblers remain researchers for many years (Gill and Murray 1972; and for applying appropriate on-the-ground con- Gill 1980, 1987) but has only been quantitatively servation measures. examined since the application of genetic mark- Chapter 3 (this volume) reported that land- ers in several studies since the late 1990s (Gill scape-scale settlement patterns of Golden-winged 1997; Shapiro et al. 2004; Dabrowski et al. 2005; Warblers in the Appalachian Mountains region are Vallender et al. 2007a,b, 2009). There is varia- positively associated with increasing percent for- tion across the breeding distribution—perhaps est and high elevations, and negatively correlated dependent on the length of time that the two spe- with increasing agriculture and human develop- cies have been in contact with one another in a ment, whereas Blue-winged Warblers showed the given region—with a well-established pattern opposite relationship with these covariates. In fact, of bidirectional gene flow between Blue-winged Blue-winged Warblers were positively associated Warblers and Golden-winged Warblers. To date, with agriculture. The findings may be important patterns in gene flow have been established using to better understanding the land-use patterns that genetic markers derived from the mitochon- are driving spatial interactions between Golden- drial genome, as attempts to quantify hybrid- winged and Blue-winged Warblers and in describ- ization using markers from the nuclear genome ing potential distribution shifts for both species. have been largely uninformative (Vallender et al. More work, however, is needed to understand 2007b). The lack of data from the nuclear genome how landscape-scale changes in distribution and is the most significant challenge to elucidating the abundance of cover types used by Golden-winged true impact of hybridization on Golden-winged Warblers are related to population trends in both Warblers and to enabling researchers to make pre- species and if these changes have a role in mediat- dictions about the future of this species pair. ing hybridization. The most immediate short-term research need with respect to hybridization between Golden- Breeding-Grounds Research Needs winged and Blue-winged Warblers is the devel- opment of informative genetic markers from the In addition to the needs discussed above about nuclear genome for each species. Once available, broad inference from local studies, research is genetic markers can be applied to the large num- needed on habitat characteristics associated with ber of samples already collected from across the Golden-winged Warbler breeding density and breeding distributions of both species. As detailed population productivity throughout the west- in the chapter on hybridization of these spe- ern Great Lakes region, especially in northern cies (Chapter 4, this volume), next-generation Minnesota where populations are dense and sequencing likely provides the most promise in highly productive, and in south-central Canada this regard. A second short-term need is a bet- where the breeding distribution is expanding ter understanding of the ecology of Blue-winged northward. In the Appalachian Mountains region, Warblers and the impact of hybridization on allo- research is needed to determine the efficacy of patric populations of this poorly studied species, current conservation and management actions and a better understanding of the mate-choice intended to benefit Golden-winged Warblers, dynamics within this hybrid complex (Vallender and to identify additional forested landscapes or et al. 2007a, Hartman et al. 2012). Over the long landscapes that could be converted to forest where term, the continued application of genetic tech- management efforts will have the greatest impact. niques using markers derived from both the mito- Research on habitat associations and survival dur- chondrial and nuclear genomes to better reveal ing the postfledging period is an immediate need patterns and extent of hybridization between in the Appalachian Mountains region; results Golden-winged Warblers and Blue-winged from that research will be important for adapting
Research on Golden-winged Warblers 221 management actions already underway and plans reproductive success, and blood-parasite load to be implemented in the near future. (Hartman et al. 2012; Vallender et al. 2007a,b, 2012). An important first step will be additional genetic sampling and purity analyses of Blue- Future Research on Golden-winged winged Warblers, especially from regions where Warblers and Blue-winged Warblers they have been poorly sampled to date, such as Over at least the past two decades, Vermivora con- Missouri and both peninsulas of Michigan. servation attention and action has primarily been driven by the decline and vulnerability of Golden-winged Warblers. Hybridization with NONBREEDING ECOLOGY Blue-winged Warblers has been viewed primarily Key Findings and Knowledge Gaps as a threat to the continued persistence of Golden- winged Warblers, and as such the research agenda Until recently, little was known about the status, has largely focused on Golden-winged Warblers. distribution, or ecology of Golden-winged Warblers We are not aware of any research that has focused on their nonbreeding grounds, and much of what on Blue-winged Warblers in the core of their has been observed is reported in the gray litera- breeding distribution where Golden-winged ture (Chavarría and Duriaux 2009, Chandler 2013). Warblers are rare or absent. In addition, no stud- Chapters 1, 2, and 11 (this volume) are among the ies have considered the Vermivora complex as an first peer-reviewed publications focused on Golden- adaptive evolutionary system in its own right. winged Warblers during the nonbreeding period. However, given their propensity to hybridize We know from the work reported herein that whenever sympatric, attempts to unravel indi- wintering Golden-winged Warblers are concen- vidual life histories for Golden-winged and Blue- trated in the highlands and Caribbean slopes from winged Warblers in isolation are unlikely to be Guatemala and Belize to northwestern Nicaragua, successful. at middle elevations of both Caribbean and Pacific Several studies have examined the genetics of slopes in Costa Rica and western Panama, and in an hybridization between Golden-winged and Blue- arc of the northern Andes from central Colombia winged Warblers with the goal of understanding to northern Venezuela. Little is known about pat- the impact and implications of their intermixing terns of habitat use across the full nonbreeding dis- (Gill 1997; Shapiro et al. 2004; Dabrowski et al. tribution (Chapter 2, this volume), but abundance 2005; Vallender et al. 2007b, 2009). However, appears to be greatest in mid-elevation primary and most genetic sampling to date has been done secondary forest (Bennett 2013, Chandler 2013). either in the zone of breeding distribution over- Golden-winged Warblers on the nonbreeding lap between Golden-winged and Blue-winged grounds select microhabitat features associated with Warblers or in regions where phenotypic Golden- intermediate forest disturbance, likely due to their winged Warblers are more common (Vallender use of hanging dead leaves as foraging substrates et al. 2009). Our understanding of the genetic and (Chandler and King 2011). Golden-winged Warbler ecological effects of hybridization and introgres- use of agricultural cover types, such as shade cof- sion on Golden-winged Warblers is growing, but fee, appears to be contingent on adjacency of those far less is known about the impact on Blue-winged cover types to intact primary or secondary forest Warbler populations. Moreover, basic informa- (Chavarría and Duriaux 2009, Chandler 2010). tion is lacking about breeding, mate choice, In Costa Rica and Nicaragua, Golden-winged wintering-ground ecology, migration, and many Warblers maintain larger nonbreeding territories other aspects of Blue-winged Warbler ecology. and home ranges, and may have larger area require- It has therefore been recommended that general ments than other Neotropical migrants. They dis- research be conducted on life history character- play a high propensity to join mixed-species flocks istics of Blue-winged Warblers, particularly in where they forage by probing dead-leaf clusters and the distribution of phenotypically “pure” Blue- epiphytes (Chapter 11, this volume). A high degree winged Warblers (Chapter 4, this volume). Such of sociality may have important conservation work could include behavioral and genetic analy- implications. For example, territoriality and group ses of mate choice in allopatry and sympatry with size can clearly affect population density, which is Golden-winged Warblers and hybrids, realized a primary determinant of carrying capacity, and
222 STUDIES IN AVIAN BIOLOGY NO. 49 Streby, Andersen, and Buehler dependence upon mixed-species flocks may be a resource selection and demography would permit liability because forest fragmentation can disrupt the identification of the factors that limit popula- cohesion within mixed-species flocks (Rappole and tion growth during the annual cycle, which can Morton 1985, Stouffer and Bierregaard 1995). enable conservationists to target resources most efficiently and effectively. Non-Breeding-Grounds Research Needs The first, and primary, hurdle in non-breeding- MIGRATORY CONNECTIVITY grounds research is gaining a better understanding AND MIGRATION ROUTES of Golden-winged Warbler nonbreeding distribu- Key Findings and Knowledge Gaps tion. Even more so than on the breeding grounds, knowledge of non-breeding-grounds ecology in The most difficult challenge for informing full Golden-winged Warblers is limited geographically, life-cycle conservation plans for small migratory with the published research coming from a few songbirds is connecting geographically distinct sites in the northwestern region of the nonbreeding areas in the absence of adequate tools to track indi- distribution. Analyses of distribution-wide survey vidual birds (e.g., GPS tags). Chapter 12 (this vol- data yielded a coarse-scale indication of Golden- ume) used stable-isotope analysis to take a first step winged Warbler nonbreeding distribution and in understanding migratory connectivity across general cover-type associations (Chandler 2013); Golden-winged Warbler breeding and nonbreed- however, sampling intensity was modest relative ing distributions and made reasonable speculation to the area covered and was not evenly dispersed about likely migration routes. The authors used across the nonbreeding distribution. Therefore, a stable isotopes in tissues generated on the breeding primary wintering-ecology research need is addi- grounds and collected on the nonbreeding grounds tional surveys in poorly sampled portions of the to create a coarse, but informative map linking distribution, such as Belize, and in a greater range Golden-winged Warblers from the Appalachian of land-use and cover-type associations. population segment to more southern wintering Knowledge of the regions and cover types grounds, and Golden-winged Warblers from the occupied by Golden-winged Warblers on the Great Lakes breeding-distribution segment gener- nonbreeding grounds is important to their con- ally to more northwestern wintering grounds. It is servation; however, despotic interactions among possible that Chapter 12 (this volume) has provided conspecifics may cause individuals to be forced an explanation, aside from insufficient non-breed- into marginal sites where survival or other ele- ing-ground sampling effort, for why thousands of ments of overwinter performance can be com- Golden-winged Warblers banded on the breed- promised. The relationship between land use and ing grounds have yielded no recaptures on the cover-type-specific survival and body condition nonbreeding grounds. The majority of breeding- in Golden-winged Warblers is poorly understood. grounds research that involved banding was in the Therefore, broad-scale surveys of geographic Appalachian breeding-distribution segment and and cover-type distribution should be followed the majority of non-breeding-grounds research up with detailed studies of demographic param- was in northwestern Central America, which are eters. Last, replication of previous studies on space likely two, largely unconnected populations. requirements and behavioral ecology should be undertaken in unstudied areas of the nonbreeding Migratory Connectivity and distribution. Better knowledge of the nonbreeding distribution, variation in cover-type associations, Migration Research Needs behavioral ecology throughout that distribution, Establishing fine-resolution, distribution-wide and cover-type-specific survival will facilitate migratory connectivity is a research challenge additional needed studies on correlations between in Golden-winged Warblers and in many other nonbreeding habitat associations and subsequent migratory species (Hobson 2003; Faaborg et al. survival and reproductive success, migratory con- 2010a,b). Building upon the framework established nectivity between wintering and breeding loca- by Chapter 12 (this volume) is necessary to allow tions, and winter-range shifts owing to climate conservation efforts to target individual popula- change or other factors. A better understanding of tions on their breeding and wintering grounds
Research on Golden-winged Warblers 223 and along their migration routes. Until recently, Migratory connectivity and cover-type-specific the only feasible step toward that goal was to survival on the wintering grounds are likely the increase the geographic coverage of non-breeding- most urgent problems to address with respect grounds sampling locations and to increase the to full life-cycle research in Golden-winged number of birds sampled across the nonbreeding Warblers. Until individual populations can be distribution to improve accuracy of stable-isotope- studied throughout their annual cycle, and fac- based connectivity maps (Chapter 12, this vol- tors most limiting growth for a population of ume). However, light-level geolocators have now interest can be identified, conservation plans been carried by Golden-winged Warblers with will be limited to focusing on the apparent needs no deleterious effects (Peterson et al. 2015; Streby of different populations during different times et al. 2015b,c) and preliminary results suggest geo- of the year. locator tags will considerably improve knowledge While acknowledging that many substantial of Golden-winged Warbler migratory connectivity research gaps remain and that some previously held in the next few years (H. M. Streby, unpubl. data). truths about Golden-winged Warblers are being The only information available about Golden- revised, the current information must be translated winged Warbler migration routes is speculation into conservation and management actions within in this volume based on coarse migratory con- areas of appropriate geographic inference sooner nectivity (Chapter 12, this volume) and incidental rather than later. Otherwise, we risk current reports from eBird (www.ebird.org) or banding knowledge being useful only for describing even- stations (Chapter 1, this volume). Chapters 1 and tual extinction events (Lindenmayer et al. 2013), 12 (this volume) referenced eBird records, which especially for the Appalachian breeding-distribu- suggest that Golden-winged Warblers use a trans- tion segment if long-term trends continue. Forest Gulf of Mexico migration pathway during spring management efforts designed to benefit Golden- and fall migrations. However, eBird observations winged Warblers and other disturbance-depen- of Golden-winged Warblers during migration are dent species are underway in many areas across sparse (<0.5% of checklists) and the distribution the Golden-winged Warbler breeding distribu- of detections is likely biased by highly nonrepre- tion, and some progress is being made in reversing sentative spatial sampling of perceived migration deforestation in areas of their nonbreeding distri- hotspots such as the Gulf of Mexico Coast of North bution (Chapter 2, this volume). New research is America. Current research using light-level geolo- needed not only to address remaining information cation has provided promising preliminary data gaps, but also to study the effects of conservation about Golden-winged Warbler migration routes and management actions and to inform the adap- and stopover locations and duration (H. M. Streby, tive nature of long-term management plans. Our unpubl. data). Questions about when and where volume of Studies in Avian Biology provides a solid Golden-winged Warblers rest and refuel dur- foundation on which future research in Golden- ing migration, and about their diet, habitat asso- winged Warblers can be built, but the recent ciations, and survival along migration routes, acceleration in knowledge about Golden-winged and about how these factors affect their ability to Warblers indicates above all else that there is still reproduce, remain urgent research needs. much to be learned.
CONCLUSIONS LITERATURE CITED A common limiting factor in conservation of Aldinger, K. R., and P. B. Wood. 2014. Reproductive migratory birds is a lack of adequate knowledge success and habitat characteristics of Golden- from all stages of the annual cycle to inform full winged Warblers in high-elevation pasturelands. life-cycle models and identify conservation pri- Wilson Journal of Ornithology 127:279–287. orities for individual populations (Faaborg et al. Anders, A. D., D. C. Dearborn, J. Faaborg, and F. R. 2010a). Despite the recent increase in knowledge Thompson III. 1997. Juvenile survival in a population about Golden-winged Warblers, their ecology of migrant birds. Conservation Biology 11:698–707. during most of the annual cycle, especially dur- Anders, A. D., J. Faaborg, and F. R. Thompson III. 1998. ing spring and fall migration, has not been stud- Postfledging dispersal, habitat use, and home-range ied thoroughly enough to inform such models. size of juvenile Wood Thrushes. Auk 115:349–358.
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