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A Growing Conspiracy: Recolonization of Common Ravens (Corvus corax) in Central and Southern Appalachia, USA
Zachary J. Hackworth, John J. Cox, Joshua M. Felch, and Mitch D. Weegman

Southeastern Naturalist, Volume 18, Issue 2 (2019): 281–296

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Southeastern Naturalist 281 Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 22001199 SOUTHEASTERN NATURALIST 1V8o(2l.) :1288,1 N–2o9. 62 A Growing Conspiracy: Recolonization of Common Ravens (Corvus corax) in Central and Southern Appalachia, USA Zachary J. Hackworth1,*, John J. Cox1, Joshua M. Felch1, and Mitch D. Weegman2 Abstract - Corvus corax (Common Raven, hereafter Raven) was historically ubiquitous throughout much of North America, but persecution and habitat loss after European settlement resulted in range reduction and population decline across much of the eastern US. Increasing numbers of confirmed sightings of Ravens in the eastern US over the past 70 years suggest rapid regional recolonization, particularly in central and southern Appalachia where, in many states, Ravens were thought to be extirpated or at least highly range-restricted. We compiled 64,611 Raven observations from multiple public and private sources across Appalachia between 1950 and 2016 and performed spatial analyses to characterize regional recolonization trends. The Appalachian Mountain range has served as both a refugium for Ravens during the late 19th and early 20th centuries and a regional source population for range expansion between 1950 and 2016. Ravens are now common in the mountainous areas of Appalachia and have recently expanded their range into lower elevations, including the successful recolonization of 4 states: Alabama, Kentucky, Ohio, and Tennessee. Spatial analyses demonstrated a 40% increase in the Raven’s apparent geographic range in central and southern Appalachia, which now spans at least 470,380 km2. We present an updated map detailing current Raven distributions in central and southern Appalachia and review potential habitat, interspecific, and trophic factors aiding range expansion for Ravens. Introduction Modern techniques for monitoring species distributions require spatial and temporal survey replication for precise estimation of trends (Dennis et al. 2010, Kéry et al. 2009). However, elucidating distributional patterns over extended time periods is challenging given the absence of robust occupancy data in prior decades when the need for formal monitoring was not yet fully recognized. In recent years, development of rigorous methods employing presence-only data has provided useful alternatives for evaluating population and distributional changes (Elith et al. 2006, Kéry et al. 2010). The increasing assimilation and recognition of citizen-science databases, often of presence-only data, in the conservation of a host of species has bolstered the general public’s interest and participation in data collection. Historical accounts afford a unique repository of citizen-science data, as they comprise the observations of citizens of former time periods and offer a plethora of anecdotal revelations of species occupancy that can augment modern data collection, particularly for species with histories of frequent human interaction. 1Department of Forestry and Natural Resources, University of Kentucky, Lexington, KY 40546. 2School of Natural Resources, University of Missouri, Columbia, MO 65211. *Corresponding author - zachary.hackworth@uky.edu. Manuscript Editor: Jason Davis Southeastern Naturalist Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 282 Corvus corax L. (Common Raven; hereafter Raven) is the largest and historically most widespread passerine inhabiting the Holarctic (BirdLife International 2017, Boarman and Heinrich 1999). As a species whose foraging strategies and portentous appearance have fostered strife with humans, Ravens often appear in ancient lore and historical accounts (Archibald 1996, Foufopoulos and Litinas 2005, Johns 1948), affording researchers supplementary information to further ecological understanding of this charismatic corvid. While discovery of skeletal remains (Majkić et al. 2017, Serjeanston and Morris 2011) and genetic phylogeography (Omland et al. 2006) have provided some information on Raven distributions, history presents a collection of presence-only (and at times, presence–absence) data for evidence of the species’ former distributions. Prior to European settlement, Ravens were likely ubiquitous across North America, as manifested by archaeological and historical evidence. A search of the Paleobiology Database (Paleobiodb.org), an online catalogue of flora and fauna fossil records maintained by the University of Wisconsin-Madison, WI, revealed 13 occurrences of Raven remains in archaeological sites distributed across the US, including Alabama (Parmalee and Graham 2002), California (Guthrie 1992, Hoffman et al. 1927, Howard 1936), Colorado (Emsile 2004), Georgia (Martin and Sneed 1989), New Mexico (Harris 1987, Howard 1971), Oregon (Elftman 1931), and Wyoming (Long 1971). Documented oral history and the discovery of Raven effigies reveal the focal role of Ravens in the totems of numerous Native American tribes distributed across North America (Bogoras 1902, Heinrich 1989, Mooney 1900, Oosten and Laugrand 2006, Romain 2009). Later writings of the American West further disclose the presence of Ravens in the Great Plains, as they followed Bison bison L. (American Bison) herds and Canis lupus L. (Gray Wolf) packs, commensally scavenging carcasses (Boarman and Heinrich 1999, Mead 1986). Therefore, historical evidence indicates that Ravens were likely cosmopolitan in pre-European Nearctic landscapes. Raven populations in the eastern US declined rapidly after European settlement. Anthropomorphized Ravens figured prominently in the mythology of European people-groups, although, unlike Native American lore, Ravens in Anglo-Saxon, Norse, and Celtic legends often personified witchcraft and the macabre, creating a connotation of fear and distrust around this species (Archibald 1996, Johns 1948, Saxby 1893). With imported negative attitudes toward Ravens, European settlers in America persecuted Ravens through poisoning, shooting, and nest destruction, often implicating them for livestock mortality (Heinrich 1989, Nicholson 1997). Incidental kills from predator-control poisonings further quelled Raven numbers (Mead 1986). Concomitant with persecution, forest-clearing for agriculture and new settlements (Harlow 1922) and eradication of large mammals (Cox et al. 2003, Mead 1986) aided the decline of eastern US Raven populations. Although the species has persisted across much of the western US, by the early-20th century, Raven distribution and numbers in most of the eastern US had experienced dramatic declines, with remaining populations restricted to remote, rugged mountainous refuges (hereafter core areas) in New England and central Appalachia (Barrows 1912, Hooper 1977, Nuttall 1903). Southeastern Naturalist 283 Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 During the early years of North American wildlife conservation, mandates, such as the Migratory Bird Treaty Act of 1918 and Federal Aid in Wildlife Restoration Act of 1937 (Pittman-Robertson Act), benefited many animal species, including Ravens, and the forests they inhabited. Raven sightings in the eastern US noticeably increased outside of traditional core areas after 1950 (Buckelew and Hall 1994, Heinrich 1989, Kilham 1989, Palmer-Ball 2015). However, aside from anecdotal information on local population recovery, range expansion and regional recovery of Raven populations in lower Appalachia has received little attention. We compiled sightings from several sources to characterize the apparent spread of the Raven from refugia in central Appalachia into portions of its historical range across the central and southern Appalachian Region of the eastern US between 1950 and 2016. We hypothesized that recolonization would be slow in the early years, as is typical of small remnant or founding populations, but would accelerate as populations grew and forests matured, thereby providing more abundant habitat. Study-Area Description The Appalachian Region is characterized by steep mountains, rolling hills, and geologically weathered and hydrologically dissected plateaus, interspersed with occasional wide valleys, historically covered by biodiverse mixed-mesophytic forests (Braun 1950, Martin 1992). Agriculture and exploitation of the region’s vast forest resources (i.e. commercial forestry and harvest of non-timber forest products, e.g., Panax quinquefolius L. [American Ginseng]) have pervaded Appalachian land-use history (Yarnell 1998). Expansive region-wide timber harvest and introduction of Cryphonectria parasitica (Murrill) Barr (Chestnut Blight) eliminated much of Appalachia’s old-growth Castanea dentata (Marsh.) Borkh. (American Chestnut)-dominated forests during the late-19th and early-20th centuries (Yarnell 1998), and maturation of second- and third-growth forests have produced species compositions which include Quercus spp. (oaks), Carya spp. (hickories), Acer spp. (maples), Pinus spp. (pines), Liriodendron tulipifera L. (Tulip-poplar) and a mixture of other overstory, midstory, and understory woody and herbaceous species (Braun 1950). Mineral extraction, predominantly of coal via surface-mining techniques, has produced widespread forest fragmentation and compacted soils that hinder forest succession across more than 600,000 ha of mined lands in Appalachia (Pericak et al. 2018, USDOI-OSMRE 2012). As a mosaic of varying forest types and ages fragmented by surface mines and interspersed with agricultural land and urban areas, Appalachia has become a novel landscape starkly different from conditions at the time of European settlement (Yarnell 1998), when Ravens were likely regionally abundant (Heinrich 1989). Although Appalachia is defined geographically by the presence of the Appalachian Mountain range stretching southward from Maine to northern Alabama, we restricted our analyses to include only the states in central and southern Appalachia where Ravens were either thought to be extirpated (i.e., Alabama [Boarman and Heinrich 1999], Kentucky [Mengel 1965], Ohio [Peterjohn 2001], and Tennessee [Nicholson 1997]) or highly range-restricted (i.e., Georgia [Schneider et Southeastern Naturalist Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 284 al. 2010], Maryland [Robbins 1997], North Carolina [Pearson et al. 1942], Pennsylvania [Harlow 1922], South Carolina [Sprunt and Chamberlain 1949], Virginia [Rottenborn and Brinkley 2007], and West Virginia [Smith 2008]) during the early 20th century (hereafter referred to as the Appalachian survey area). Methods Sighting data We conducted a comprehensive search of public- and private-access sources for mention of confirmed Raven sightings prior to and during 2016. Sources examined include databases of peer-reviewed journals, library sources (e.g., breeding-bird atlases), long-term monitoring programs (e.g., Breeding Bird Survey [Pardieck et al. 2018] and Christmas Bird Count [National Audubon Society 2010]), online citizen-science initiatives (e.g., eBird [eBIRD Basic Dataset 2016]), sighting records from Appalachian state ornithological societies, museum specimens, and observations recorded by Felch (2018) during a Raven occupancy study conducted in central Appalachia in 2009–2011 (see full list of data sources in Table 1 and Acknowledgments). Geographic coordinates were supplied with many of the sightings; however, where missing, we georeferenced points given the geographic detail provided with the sighting record. Descriptions of certain sightings directed us to exact geographic or topographic locations, while other descriptions were vague and required coordinates to be placed at a coarser scale. For example, if the county was the smallest geographic scale provided in the original sighting narrative, coordinates for the sighting were placed in the geometric center of the county. The county was the broadest scale permitted in the analysis, and sightings at greater scales Table 1. Peer-reviewed and published text sources from which sightings were compiled for spatial analysis of Common Raven range expansion in central and southern Appalachia, USA, 1950–2016. Source Reporting area Barbour et al. 1979 KY, TN, VA Buckelew and Hall 1994 WV Burleigh 1958 GA Conner 1974 VA Felch 2018 KY, NC, WV, VA Hall 1983 WV Hooper 1977 VA Imhof 1962 AL Lacki and Baker 1998 KY Mengel 1965 KY Nicholson 1997 TN Palmer-Ball 2015 KY Peterjohn 2001 OH Post and Gauthreaux 1989 SC Potter et al. 2006 NC, SC Robbins 1997 MD Schneider et al. 2010 GA Watts 2006 KY, WV, VA Southeastern Naturalist 285 Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 (e.g., at the state-level) were discarded. We discarded sightings with the same geographic coordinates on the same calendar day to avoid record duplication. Spatial analysis We employed fixed-kernel density estimation to spatially assess the expansion of the Raven's range (Worton 1989). With preliminary analyses revealing continued range reductions and the presence of disputed observations in decades prior to 1950, we restricted the scope of our analysis to sightings between 1950 and 2016. We temporally divided pooled data from states in the Appalachian survey area into 7 decadal categories (i.e., 1950–1959, 1960–1969, ... 2010–2016). For sighting locations in each decade, we used the Geospatial Modelling Environment software (Beyer 2015) in association with ArcMap 10.3 (ESRI, Redlands, CA) and Program R 3.4 (R Core Team 2017) to calculate 50% (core range), 95% (expansion range), and 99% (maximum range) kernel density isopleths via the quartic kernel function (Silverman 1986) with a 160.9-km user-defined bandwidth. We calculated isopleth areas to evaluate overall (1950–2016) and decadal range expansion. We mapped the geometric centroid of the core range (50% isopleth) for each decade and examined their spatial distribution for evidence of general directional shifts in the Raven’s core range during this period. Furthermore, we measured the linear decadal extension of the maximum range (99% isopleth) along each major colonization front (i.e. north, northwest, west, southwest, south, southeast, east, and northeast) to elucidate directional patterns in recolonization. Results We amassed 64,611 individual Raven sightings in the Appalachian survey area between 1950 and 2016. Observations recorded in 2000–2016 comprised 93.7% of all sightings (Table 2). However, we documented an increase in the number of sightings in each successive decade. Sightings reported with only anecdotal location information (i.e., without geographic coordinates) comprised only 5.2% of all locations and were distributed relatively evenly among all decades. Isopleth areas Density isopleth areas demonstrated near-continual range expansion from 1950 to 2016 (Fig. 1). With the exception of small area reductions in 1960–1969 and 2010–2016, core ranges expanded with each successive decade, increasing 95% in area from 54,332 km2 in 1950–1959 to 105,936 km2 in 2010–2016 (Table 2); the largest core-range estimate was observed in 2000–2009 (107,980 km2). The expansion range increased 48% from 245,676 km2 in 1950–1959 to 364,021 km2 in 2010–2016. We observed the largest expansion range during 2000–2009 (390,038 km2), with subsequent area reductions of 26,017 km2 between the 2000–2009 and 2010–2016 periods. Maximum ranges exhibited trends similar to those of expansion ranges: overall area increased 40% from 335,726 km2 in 1950–1959 to 470,380 km2 in 2010–2016, including area reductions during 2010–2016. The largest maximum range area was observed in 2000–2009 (540,162 km2), as in core and expansion ranges. Mean decadal growth of core, expansion, and maximum ranges Southeastern Naturalist Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 286 between 1950 and 2016 was 8601 km2, 19,724 km2, and 22,442 km2, respectively. Aside from an initial reduction between 1950–1959 and 1960–1969, the largest core range growth was observed in initial decades, with growth rate decreasing over time. Expansion ranges demonstrated similar growth trends to those of core ranges; however, the largest decadal growth rate in the expansion range was between 1990–1999 and 2000–2009 (47,469 km2). Maximum range growth rates increased between 1950–1959 and 1970–1979, decreased between 1970–1979 and 1980–1989, and increased between 1980–1989 and 2000–2009. As in expansion ranges, the largest maximum range growth was observed between 1990–1999 and 2000–2009 (88,894 km2). Core-range centroid distribution Core-range centroids in 1960–1969 and 1970–1979 were distributed within a 30-km radius of the 1950–1959 centroid, indicating little change in core range centrality during early decades. Beginning in 1980, core-area centroids demonstrated a near-continual northern shift in each successive decade, with the 2010–2016 centroid located 196 km northeast of the 1950–1959 centroid. Geographically, the centroid of the Raven’s core range shifted from northwestern Virginia in 1950 to the Maryland panhandle in 2016. Notably, there was only an 18-km difference between the 1990–1999 and 2000–2009 decadal centroids, suggesting that the geometric center of the Raven’s apparent core range changed little despite large areal growth and directional range extensions during this period. Table 2. Decadal sightings, kernel density isopleth areas (km2), and net and periodic areal growth of Common Raven geographic range in central and southern Appalachia, USA, 1950–2016. Area growth denotes isopleth change in successive periods since the 1950-1959 decade. Density isopleth Period Sightings 50% 95% 99% Isopleth areas 1950–1959 115 54,332 245,676 335,726 1960–1969 182 49,013 276,935 365,820 1970–1979 631 77,857 305,611 411,260 1980–1989 1110 90,365 329,252 421,720 1990–1999 2040 101,022 342,569 451,268 2000–2009 10,731 107,980 390,038 540,162 2010–2016 49,802 105,936 364,021 470,380 Area growth 1960–1969 - -5319 31,259 30,094 1970–1979 - 28,844 28,676 45,440 1980–1989 - 12,508 23,641 10,460 1990–1999 - 10,657 13,317 29,548 2000–2009 - 6958 47,469 88,894 2010–2016 - -2044 -26,017 -69,782 Net increase, 1950–2009 - 53,648 144,362 204,436 Net increase, 1950–2016 - 51,604 118,345 134,654 Mean decadal increase, 1950–2009 - 10,730 28,872 40,887 Mean decadal increase, 1950–2016 - 8601 19,724 22,442 Southeastern Naturalist 287 Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 Figure 1. (A) Decadal kernel density isopleth ranges of Common Ravens in central and southern Appalachia, USA, 1950–2016. (B) Decadal Raven sightings in central and southern Appalachia, USA, 1950–2016. Southeastern Naturalist Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 288 Directional maximum range expansion Directional patterns in decadal maximum range expansion indicated positive extension along all colonization fronts, with the exception of the eastern front (where maximum range extended to the directional edge in 1950 and thus no expansion occurred; Table 3), although directional expansion rates were highly variable over the study period. Directional expansion was greatest toward the northwest (189.9 km) and south (160.6 km); expansion toward the west (26.0 km), southwest (57.9 km), and southeast (87.6 km) was considerably lower. Northern and northeastern directional expansion reached the edge of the survey area in 1960–1969 and 1980–1989, respectively. We observed large range extensions toward the northwest (134.6 km) between 1970–1979 and 1980–1989 and toward the southwest (119.3 km) between 1990–1999 and 2000–2009. Between 2000–2009 and 2010–2016, range contraction resulted in considerable negative range extension for the western, southwestern, southern, and southeastern directions. Since maximum range contractions between the 2000–2009 and 2010–2016 periods greatly diminished net directional expansion on several colonization fronts, we calculated net directional expansion from 1950 to 2009 to present the species’ maximum range extent prior to range contraction. Between 1950 and 2009, maximum range expansion was greatest toward the south (193.4 km) but was similar to expansion along the northwest (176.5 km), southwest (173.0 km), and southeast (145.3 km) fronts; western expansion (71.1 km) also increased but at a lower rate. Discussion Observational data indicate range expansion of Ravens since 1950 and suggest that Ravens are now common in many areas of Maryland, Pennsylvania, Virginia, and West Virginia, as well as in the mountainous regions of southern Appalachia. Overall, core ranges have nearly doubled, and expansion and maximum ranges have increased 48% and 40%, respectively. Range expansion was greatest in the Table 3. Decadal directional expansion (km) of Common Raven maximum range (99% kernel density isopleth) in central and southern Appalachia, USA, 1950–2016. Directional expansion indicates periodic linear extension of isopleths along major colonization fronts in successive periods since the 1950–1959 decade. All decadal maximum ranges extended to the eastern edge of the survey area for all periods, reached the northeren edge in the 1950–1959 and remained extended to it for all subsequent decades, and also reached and then extended to the northeastern edge for 1970–1989. Maximum range directional expansion (km) Period North NW West SW South SE East NE 1960–1969 2.8 28.6 -15.1 20.2 -12.7 31.3 0.0 67.0 1970–1979 0.0 1.5 14.5 1.2 96.7 3.0 0.0 16.9 1980–1989 0.0 134.6 46.7 3.5 26.4 12.4 0.0 5.8 1990–1999 0.0 -9.8 7.3 28.8 29.2 2.5 0.0 0.0 2000–2009 0.0 21.6 17.7 119.3 53.8 96.1 0.0 0.0 2010–2016 0.0 13.4 -45.1 -115.1 -32.8 -57.7 0.0 0.0 Net increase, 1950–2009 2.8 176.5 71.1 173.0 193.4 145.3 0.0 89.7 Net increase, 1950–2016 2.8 189.9 26.0 57.9 160.6 87.6 0.0 89.7 Southeastern Naturalist 289 Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 northwestern direction, although southern, southwestern, and southeastern ranges have increased at similar rates in recent decades. Although maximum ranges have expanded substantially toward the southwest, south, and southeast, the core range has shifted toward the northeast, indicating substantial population increase in northcentral Appalachia relative to southern Appalachia and/or immigration of Ravens to this area from established populations in northern Appalachia. Despite range restrictions in the early-20th century, Ravens remained more abundant in the northeast US, which, currently, sustains higher densities of Ravens compared with central Appalachia (Boarman and Heinrich 1999). Range isopleths encompassed the northern and northeastern edges of the central Appalachian survey area in 1950–1959 and 1980–1989, respectively, demonstrating connectivity of established northeastern populations and the growing populations in north-central Appalachia. Comparison of species distributions over time is key to understanding range colonization and extinction patterns, which is often important for single-species management and conservation efforts, but can be hindered by insufficient information on historic distributions. Cox et al. (2002) and Moore (2002) demonstrated that toponyms (place-names) often reflect the historical presence of locally important wildlife species and can be used as a coarse approximation of former distributions. However, unverified, unempirical source material, such as historical accounts from non-scientists, has been criticized as lacking credibility (Rackham 1986). Our use of general sighting data in kernel density estimation of geographic range (and subsequent results) are subject to potential bias due to the nature of unstandardized, multiple-observer citizen-science data. We make the foundational assumption that sighting densities reported and portrayed across a coarse regional spatial scale are representative of the best estimate of Raven distribution in central and southern Appalachia during this period. However, our data are likely patterned according to accessibility and density of Raven-occupied lands: areas commonly visited by birders (e.g., forested natural areas) may possess a greater frequency of Raven detections. Additionally, it is plausible that a single bird or breeding pair occupying an easily accessible location (e.g., roadside cliff) may be observed by many individuals, producing a hotspot of activity that could skew kernel density estimates (Paul et al. 2014). With the advancement of general-use, handheld global positioning systems (GPS) and online database accessibility in recent decades, the large number of sightings not only provides researchers with an abundance of otherwise unattainable data but also introduces the potential for inaccuracies in kernel estimation. In recent decades, analyses of citizen-science data have become important conservation tools for monitoring ecological trends. Established in 2002, the eBird database comprises information on global avian sightings reported by birders of all experience levels. eBird sourced several thousand Raven locations in our analysis between 2000 and 2016, and we speculate that the observed range contraction in all isopleths during the 2010–2016 decade may be attributed to the relative weight of points within and closer to the core area relative to those on the periphery, leading to a reduction of kernel density estimates near the margins of the Raven’s maximum range (Millspaugh and Marzluff 2001). Recently available electronic mechanisms Southeastern Naturalist Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 290 for submitting bird observations may provide more accurate descriptions of relative abundance compared to prior time-periods when submission of sightings was more cumbersome and a “novelty-of-sighting” bias may have prevailed, whereby observations outside or on the periphery of a species’ range were deemed more novel and, thus, more likely to be reported. Similarly, range contraction in 2010– 2016 caused by the relative weight of core versus peripheral locations may also be explained ecologically by a slowed colonization front as Ravens reached portions of the outer fringes of western Appalachia. In this scenario, further movement of Ravens westward would be impeded by habitat limitations and possible Allee effects, while areas within inner portions of a newly colonized range experienced population increase and range infill (and, therefore, more repor ted observations). Evidence of range expansion presupposes underlying factors aiding successful recolonization. In recent decades, successful Raven reintroductions and conservation efforts have bolstered Raven populations in Europe (Gibbons et al. 1995, Ratcliffe 1997), with numbers more than doubling in areas of the United Kingdom (Amar et al. 2010). It appears that similar forest and wildlife conservation efforts have encouraged Raven recolonization in portions of its former range in central and southern Appalachia, including states where the species was considered extirpated. As a species preferring mature forests, Appalachian Ravens likely owe their recovery, in part, to the maturation of forests that were clearcut in the late-19th and early 20th centuries. While habitat-driven increases in small-mammal activity in recently regenerating clearcuts can provide Ravens with foraging opportunities, the denseness of early-successional forests after canopy closure inhibits foraging and nesting of birds of prey, including Ravens, until stem densities are reduced to residuals that permit sub-canopy flight (Marquiss et al. 1978, Vanderwel et al. 2009). European habitat-use studies concluded that Ravens occupied and foraged within large mature-forest patches preferentially over agricultural land, small forest patches, and wetlands (Andrén 1992). Reclaimed surface mines composed of early-successional forest, shrub-scrub, and grasslands are widespread across the fragmented Appalachian landscape. Although the vegetation structure is seemingly unconducive to Raven occupancy, mined lands in eastern Kentucky harbor breeding pairs of Ravens (Cox et al. 2003, Felch 2018). Creation of exposed rock-faces and highwalls during the surface-mining process may increase nesting habitat not only for Ravens but also for other cliff-nesting obligates (e.g., Falco peregrinus Tunstall [Peregrine Falcon]). Marquiss et al. (1978) linked afforestation of traditional Ovis aries L. (Sheep)-grazing meadows with Raven population declines in Scotland and northern England, not only providing corroborating evidence of the Raven’s use of grassland habitats and avoidance of dense forests but also highlighting the importance of scavenging in the Raven’s diet. Range reductions for Ravens in the eastern US during the late-19th and early- 20th centuries have been attributed to the decline and extinction of large-mammal populations (Cox et al. 2003, Mead 1986). Carcasses of Odocoileus virginianus Zimmermann (White-tailed Deer; hereafter Deer), American Bison, and the nowextinct Cervus canadensis canadensis Erxleben (Eastern Elk) provided abundant Southeastern Naturalist 291 Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 scavenging opportunities for Ravens, as carnivores (e.g., Gray Wolf and Puma concolor L. [Cougar] ) opened carcasses that Ravens could not easily access, a role which the naturalized Canis latrans Say (Coyote) likely now fulfills to some extent in the eastern US. Notably, Raven recolonization in recent decades has been accompanied by rapid Deer population growth and range expansion into habitat considered less favorable (Vercauteren et al. 2011). Considered overpopulated in many areas of the eastern US, Deer are now common throughout Appalachia, with the highest densities occurring in Pennsylvania and northern Appalachia (Boulanger and Curtis 2016), which now comprises much of the Raven’s current core range. Although deer are somewhat less abundant in higher-elevation areas of southern Appalachia (Kilgo et al. 2014), the introduction of Cervus canadensis nelsoni Erxleben (Rocky Mountain Elk; hereafter Elk) in many central and southern Appalachian states (Cox 2011, Kindall et al. 2011, Larkin et al. 2002,) has created an additional source for Raven scavenging, which will continue to increase as state wildlife agencies prioritize growth of Elk populations. Ravens have repeatedly been sighted scavenging Elk carcasses in eastern Kentucky (J.J. Cox, pers. observ.). Competitive release is another hypothesized factor aiding Raven recolonization. Sympatric corvids (i.e. crows, Ravens, and Corvus frugilegus L. [Rook]) demonstrate high phenotypic similarity, which often results in interspecific resource overlap and competition (Laiolo 2017). Corvus brachyrhynchos Brehm (American Crow, hereafter Crow) is often implicated in the damage of agricultural crops, prompting state agencies to sanction regulated hunting of the species. During the Great Depression, the US Department of Agriculture provided ammunition to farmers to control depredation of crops by Crows. While some suggest that incidental take of Ravens by hunters seeking Crows may be partially responsible for Raven declines and may impact their future recovery (Cox et al. 2003), the popularity of hunting Crows during the 20th century may have reduced resource competition and facilitated population growth and range expansion of Ravens. Bodey et al. (2009) demonstrated that the culling of Corvus cornix L. (Hooded Crow), a European species similar in its ecological niche to American Crows, produced a competitive release of co-occurring Ravens, promoting home-range expansion and the creation of new territories. Based on reported observations in written accounts and, more recently, in electronic citizen-science and standardized monitoring databases, our findings suggest that the Common Raven has rapidly expanded its range from high-elevation refugia in central Appalachia, along the Appalachian Mountain range, and is now common in nearly all mountainous regions of Appalachia. Records also demonstrated expansion into lower elevations across Appalachia, as well as the coastal plains of states in this region, but our analyses indicate that the colonization front of Ravens based on the frequency of reported sightings currently appears to be weighted predominantly southward and westward where features such as cliffs, mountains, and forests would be more conducive to species occupancy. Since 1950, the Common Raven has recolonized 4 states where it was considered absent for decades, and our findings suggest that it will perhaps continue to recolonize other unoccupied Southeastern Naturalist Z.J. Hackworth, J.J. Cox, J.M. Felch, and M.D. Weegman 2019 Vol. 18, No. 2 292 portions of its historical range across Appalachia and the eastern US; however, given observed contractions in range during recent years, recolonization may wane in the coming decades, as unoccupied, preferred raven habitat is depleted. Acknowledgments We extend our gratitude to the agencies and organizations throughout Appalachia who offered us access to their avian sighting databases and to the many professionals and private individuals who offered their time to communicate sighting information. We are thankful for the diligent work of the state ornithological societies of Georgia, Kentucky, Maryland, Ohio, Pennsylvania, Tennessee, and Virginia and of the American Birding Association, Brooks Birding Club, and Carolina Birding Club in documenting sightings in regional publications. Christmas Bird Count and Great Backyard Bird Count data were provided by the National Audubon Society and through the generous efforts of Bird Studies Canada and countless volunteers across the western hemisphere. We are also grateful to the thousands of participants who annually perform and coordinate the US and Canadian Breeding Bird Survey. For making information regarding Raven museum specimens publicly available via VertNet, we thank the Academy of Natural Sciences of Philadelphia, Carnegie Museum of Natural Sciences, Florida Museum of Natural History, Macaulay Library, National Museum of Natural History at the Smithsonian Institute, New York State Museum, North Carolina Museum of Natural Sciences, and Western Foundation of Vertebrate Zoology. We are further grateful to the proprietors of the online databases Avian Knowledge Network and Birding on the Net. We thank E. Hackworth for technical assistance with database management. 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