A BIRD’S EYE VIEW OF THE FOREST:
HOW DOES CANOPY OPENNESS AFFECT CANOPY SONGBIRDS?
A Thesis
Presented in Partial Fulfillment of the Requirements for
the Degree Master of Science in the
Graduate School of The Ohio State University
By
Felicity L. Newell
Graduate Program in Natural Resources
*****
The Ohio State University
2010
Master’s Committee:
Dr. Amanda Rodewald, Advisor
Dr. Roger Williams
Dr. Paul Rodewald
Copyright
Felicity L. Newell
2010
ABSTRACT
Today, the majority of eastern deciduous forests in North America are closed canopy mature second growth. In contrast, an open forest canopy is thought to have been important in presettlement forest ecosystems. Changes in forest structure are of special concern given that oaks ( Quercus spp.) cannot regenerate effectively in closed canopy stands. Although oaks have historically dominated many eastern forests, forest composition is changing due to anthropogenic impacts on disturbance regimes.
Consequently, many forest management efforts now aim to promote oak regeneration and restore forest structure, which ultimately will require a more complete understanding of the ecological processes associated with canopy disturbance. Partial harvesting (e.g. shelterwoods) provides one way to examine the importance of canopy openness. My research examined the link between canopy openness and birds that nest and forage in the forest canopy. Specifically I examined the extent to which (1) canopy songbirds select particular canopy features and (2) canopy structure affects reproductive success. I compared measures of preference (abundance, settlement patterns, site fidelity, and age distributions) and fitness (e.g. nesting success) between recent shelterwood harvests and unharvested second growth stands in mixed oak forests of southern Ohio. I studied a guild of sensitive canopy nesting species, including Cerulean Warbler (Dendroica cerulea ), Eastern Wood pewee (Contopus virens ), Scarlet Tanager (Piranga olivacea ),
ii Yellow throated Vireo (Vireo flavifrons ), and Blue gray Gnatcatcher (Polioptila caerulea ).
My research was conducted at four state forests in southern Ohio from 2007–
2009. I compared shelterwoods recently harvested to 50% stocking and reference closed canopy forest in the same landscape context. Distance based line transect surveys ( n = 56 in 18 stands at 4 state forests from 2007–2008) were used to examine changes in the bird community associated with shelterwood harvesting. Several midstory and ground nesting species were 26–67% less abundant in shelterwood stands compared to reference mature forest. Shrub nesting species increased >100% several years post harvesting while overall canopy nesting species were 46% more abundant in shelterwood stands.
Intensive research focused on canopy songbirds as one late successional group that might benefit from partial harvesting. Five species were studied intensively at 12 sites in three state forests from 2007–2009. Canopy species generally showed a weak positive association with partial harvesting with abundance of four species 31–98% higher in shelterwood stands compared to unharvested reference stands. For Cerulean
Warblers associations with partial harvesting were significant only when controlling for slope and aspect, and abundance was >200% higher in shelterwood stands in one state forest. Similar settlement patterns and site fidelity in shelterwood and unharvested stands suggested limited preferences for stand type. A higher proportion of first time breeders in shelterwood stands compared to reference stands for the Cerulean Warbler and Scarlet
Tanager may have been a post disturbance response of young birds colonizing newly created (or improved) habitat. For all five canopy species, nesting success was comparable in shelterwood and unharvested reference stands. Partial harvesting did not iii appear to negatively affect canopy songbirds, although reproductive success was generally low (15–36%) even in a predominantly forested landscape.
An information theoretic approach was used to compare different models to explain nest site selection and nesting success of canopy songbirds. Point sampling using a prism and variable radius plot was used to collect data on forest structure for nest and random plots in July and August each year. I identified basal area (m 2 ha 1) as the variable most strongly associated with harvesting. Examination of nest site selection and nesting success indicated that factors such as topography, canopy structure, and floristics may be important in habitat selection for canopy songbirds. Only the Eastern Wood pewee selected for canopy openness created by partial harvesting, but overall the canopy nesting guild selected areas with fewer medium sized trees (23–38 cm dbh). Cerulean
Warblers favored productive northeast facing slopes with abundant grapevine. Eastern
Wood pewees and Yellow throated Vireos nested in areas with 20% more white and red oaks, while Blue gray Gnatcatchers nested in bottomland areas avoiding areas with red oaks. The type of oak appeared to be important and four species nested in Quercus alba twice as much as available while three species avoided Quercus rubra. For the canopy nesting guild and several individual species, nesting success was negatively associated with red oaks around the nest. Concealment and size of the support branch were important for the Scarlet Tanager, which has a relatively large obvious nest. Tanager nests were more likely to be depredated early in the nesting cycle, whereas Cerulean
Warbler nests were more likely to be depredated later in the nesting cycle when feeding young. Nest success was 20% higher late in the season for Eastern Wood pewees.
iv Results from this study help to inform current management efforts designed to restore and maintain natural processes in forest ecosystems. Management implications from this study include prioritization of areas for protection, and recommendations on size and species of trees retained in partial harvests. Partial harvesting shifts the bird community from midstory and ground nesting species to shrub and canopy nesting species and can provide habitat for a mix of species as part of a balance of disturbance levels on the landscape. Results suggest shelterwood harvests provide at least short term breeding habitat suitable for canopy songbirds, although managers should carefully consider long term management of shelterwoods. Strong association between birds and oaks in this study demonstrates the value of current management efforts to promote oak regeneration. My work provides new insight that the species of oak may be important.
Patterns of habitat preferences and nesting success suggest that white oaks are more valuable than red oaks for canopy birds. Managers should make special effort to retain
Quercus alba in partial harvests and other restoration projects. In addition, harvesting of medium sized trees (23–38 cm dbh) may be preferable to harvesting large trees (> 38 cm dbh). My results also suggest that older forests with canopy gaps and/or those on northeast facing slopes should be protected for conservation of the severely declining
Cerulean Warbler. In areas lacking steep slopes, creation of canopy gaps could benefit ceruleans, but further work is needed.
v
ACKNOWLEDGMENTS
I would like to thank my advisor, Amanda Rodewald, for her encouragement and support during this research, and the inspiration and vision to make things happen. I value her guidance in maintaining a view of the big picture for science, research and conservation. I would also like to thank my committee for advice and comments throughout this study, Roger Williams for providing his expertise on forestry and always cheerfully answering my questions, and Paul Rodewald for a wealth of practical knowledge and experience working with birds. I would like to thank my fellow graduate students in the Terrestrial Wildlife Ecology Lab for feedback, advice, comments, and support throughout this project, as well as helping me remember that life is fun and sanity is important. Special thanks to Marja Bakermans and Andrew Vitz for first helping me to find cerulean nests and bringing me to southern Ohio, as well as assistance learning
Programs MARK and DISTANCE.
I would like to thank the funding sources for this research including the Ohio
Division of Wildlife, US Fish and Wildlife Service, National Fish and Wildlife
Foundation, the National Council for Air and Stream Improvement, and Mead Westvaco; funding for field technicians was in part from the Cooperative Cerulean Warbler
Silviculture Experiment. Thank you to the forest managers for providing information on site selection, including Daniel Yaussy, David Hosack, Robert Boyles, and Richard Lusk.
I am grateful to Lisa Rudy and Kevin Mark for working with us on housing field crews vi each year. Special thanks to Lisa for taking care of us and making summer in southern
Ohio finally enjoyable. I would also like to thank the Borror Lab of Bioacoustics for use of song recordings.
Much of the credit for this work belongs to several fantastic field crews who showed that we could actually do this research. Thank you for all the hard work which made it possible to study challenging canopy songbirds. Research is only as good as the data collected in the field. I appreciate the help of some great people including Richard
Aracil, Evelyng Astudillo Sanchez, Edwin Blaha, Grace Cochran, Gabriel Colorado,
Michael Gerringer, Michael Gill, Aaron Haiman, Samuel Holcomb, Tennille Johnson,
Linda Daily Leonhard, Julie Means, Desirée Narango, Angela Johnson, Jennifer
Philhower Gillen, Lauren Pulliam, and Ryan Trimbath.
I would like to thank my family for their constant love and support, and always being there for me no matter what. In the end I am not sure that one should try the impossibly possible, but you can’t go back and you don’t want to. Perhaps the only point is to experience one moment of the mystery which still remains, standing reaching for the sky. In memoriam: time stands still that instant in the sunshine and the shadow and a breathing beating human heart stands still in awe, that we are still created to rise as yet we fall.
vii
DEDICATION to the forest that grows and changes
viii
VITA
2007–present……………Graduate Research Associate, Ohio State University
2005–2006………………Biological Technician, Ohio State University
2005……………………. Bird Bander, University of Southern Mississippi
2004–2006………………Research Assistant, Powdermill Avian Research Center
2004……………………. B.S. Biology and English, Chatham College, Pittsburgh, PA.
2000……………………. Apprentice Louisville Ballet
1999……………………. Apprentice Colorado Ballet
PUBLICATIONS
Newell, F.L. (in press). Wood Thrush species account. In: M. A. Steele, M. C.
Brittingham, T. Maret, and J. F. Merritt (Eds.), Terrestrial Vertebrates of Concern
in Pennsylvania: A Guide to Conservation, Management, and Research . John
Hopkins University Press, Baltimore, MD, USA.
Mulvihill, R. S., S. C. Latta, and F. L. Newell. 2009. Temporal constraints on the
incidence of double brooding in the Louisiana Waterthrush ( Seiurus motacilla ).
Condor 111:341–348.
Mulvihill, R. S., F. L. Newell, and S. C. Latta. 2008. Effects of acidification on a stream
dependent songbird, the Louisiana Waterthrush ( Seiurus motacilla ). Freshwater
Biology 53:2158–2169.
ix Newell, F. L., S. L. Glowinski Matamoras, and M. E. Eastwood. 2007. Juvenal plumage
in the Green breasted Mountain gem ( Lampornis sybillae ) with observations on
timing of breeding and molt. Wilson Journal of Ornithology 119:733 –736.
Newell, F. L and M. S. Kostalos. 2007. Low Wood Thrush nests in dense understory may
be vulnerable to predators. Wilson Journal of Ornithology 119:603–702.
Newell, F. L. 2005. Wood Thrush, Hylocichla mustelina . Pennsylvania Comprehensive
Wildlife Conservation Strategy Species Assessment, Appendix 3, 12 pp.
FIELDS OF STUDY
Major Field: Natural Resources
x
TABLE OF CONTENTS
Page Abstract…….…………………………………………………………………………... ii
Acknowledgements…….………………………………………………………………. vi
Vita…….………………………………………………………………………………. viii
List of Tables………….……………………………………………………………….. xiv
List of Figures………….………………………………………………………………. xv
Chapters: Chapter 1……………………………………………………………………………….. 1 Introduction…………………………………………………………………….. 1 Thesis layout………………………………………………………………….... 5 Background…………………………………………………………………….. 6 Literature cited…………………………………………………………………. 29
Chapter 2: Short term changes in the bird community and suitability of shelterwood harvests for canopy songbirds………………………………………………………….. 60 Abstract………………………………………………………………………… 60 Introduction…………………………………………………………………….. 63 Study system…………………………………………………………………… 65 Methods………………………………………………………………………... 67 Results………………………………………………………………………….. 75 Discussion……………………………………………………………………… 80 Management implications……………………………………………………… 84 Literature cited…………………………………………………………………. 84
Chapter 3: Role of topography, canopy structure, and floristics in nest site selection and nesting success of canopy songbirds……………………………………………………108
Abstract………………………………………………………………………… 108 Introduction…………………………………………………………………….. 110 Methods………………………………………………………………………... 112 Results………………………………………………………………………….. 119 Discussion……………………………………………………………………… 122 Management implications……………………………………………………… 127 Literatures cited……………………………………………………………...... 128 xi
APPENDICES
Appendix A. Map of study region in southern Ohio………………………...... 155
Appendix B. Maps of state forests in southern Ohio…………...………...... ….. 156
Appendix C. Summary of stands studied in southern Ohio…………………..... 161
Appendix D. Comparison of abundance estimates from distance and non distance
based methods, and spot mapping……………...…..………………….………. 163
Appendix E. Relative abundance of non distance species in shelterwood and
unharvested forest……………………………………………………………… 164
Appendix F. Abundance of canopy nesting species by stand……………...... 166
Appendix G. Abundance of midstory nesting species, avian predators and brood
parasites by stand …………….…………………………………….……….…. 167
Appendix H. Abundance of shrub nesting species by stand …………………...168
Appendix I. Abundance of ground and cavity nesting species by stand…...... 169
Appendix J. Nesting success of Scarlet Tanagers by stand……………………. 170
Appendix K. Nesting success of Eastern Wood pewees by stand…..……….... 171
Appendix L. Nesting success of Cerulean Warblers by stand……...………….. 172
Appendix M. Nesting success of Blue gray Gnatcatchers by stand…….…….. 173
Appendix N. Nesting success of Yellow throated Vireos by stand….….…….. 174
Appendix O. Morphometric measurements of canopy songbirds……….…….. 175
Appendix P. Canopy structure in shelterwoods and unharvested forest...…….. 176
Appendix Q. Correlation matrix of canopy structure variables………….…….. 177
Appendix R. Boxplots of basal area and canopy closure…………………….…178
xii Appendix S. Available habitat versus nest sites of canopy songbirds...………..179
Appendix T. Selection of nesting substrate size by canopy songbirds…..…….. 180
Appendix U. Tree species groups by size classes………..……………...…….. 180
Appendix V. Regeneration of tree species groups 1–3 years post harvesting..... 181
Appendix W. Regeneration of tree species groups by stand……..…….……… 183
Appendix X. Importance values of tree species by aspect…………………..…. 185
Bibliography…………………………………………………………………………… 186
xiii
LIST OF TABLES
Page
2.1 Forest descriptions in southern Ohio………………………………...……..….. 93
2.2 Avian abundance estimates in shelterwoods and unharvested forest....……….. 94
2.3 Coefficients of Cerulean Warbler abundance model..….…………………..….. 97
2.4 Percent first time breeders and site fidelity of canopy songbirds in shelterwoods
and unharvested forest…………………………………………………………. 98
2.5 Nesting success of canopy songbirds in shelterwoods and unharvested forest... 99
2.6 Nest placement of canopy songbirds in shelterwoods and unharvested forest…100
2.7 Review of avian responses to partial harvesting………...…………………….. 101
3.1 Site descriptions in southern Ohio………………………………………...…… 136
3.2 Candidate habitat and nest placement models……...…..……………………… 137
3.3 Correlation matrix of habitat variables………………………………………… 138
3.4 Habitat models explaining nest site selection of canopy songbirds…...….…… 139
3.5 Coefficients of models explaining nest site selection of canopy songbirds….... 141
3.6 Non habitat models explaining daily survival of canopy nests...... 143
3.7 Habitat models explaining daily survival of canopy nests…………….……….. 146
3.8 Coefficients of models explaining daily survival of canopy nests...…...……… 149
xiv
LIST OF FIGURES
Page
2.1 RDA biplot of the bird community and forest structure………...…………….. 103
2.2 Abundance of canopy songbirds by state forest………...……………………... 106
2.3 Frequency distributions of territory settlement for canopy songbirds in
shelterwoods and unharvested forest……………...... …………….…………... 107
3.1 Nest substrate selection by canopy songbirds………………..………………… 151
3.2 Relationship between red oaks and daily survival of canopy nests…….………152
3.3 Habitat and nest placement variables associated with daily survival of Cerulean
Warbler and Scarlet Tanager nests………….…..……………………………... 153
3.4 Time dependent models of daily survival for nests of three species…...……… 154
xv
CHAPTER 1
Introduction
Because deforestation remains a global threat to forests around the world, the dominant paradigm in forest conservation has been to protect and retain forest cover.
Although this strategy is one essential component of effective forest conservation, it fails to explicitly recognize that quantity does not necessarily equal quality. An excellent example of the disconnect between quantity and quality of forest occurs in the central hardwood region of eastern North America where <1% of the original old growth forest that existed prior to European settlement remains (Parker 1989). This region was largely cleared for agriculture with the westward expansion of early settlers (Williams 1992).
The shift from an agrarian based society allowed some forested areas to regenerate, increasing forest cover in states such as Ohio from a low of 12% in the 1940s to a current estimate of 30% (ODNR 2007). Most of these current forests are even aged, mature second growth (Smith et al. 2004).
Evidence suggests that eastern deciduous forests as we know them today may not be representative of presettlement forest conditions. One argument has been that current forests lack canopy gaps and the structural diversity typical of old growth forest (Parker
1989, Martin 1992, Dahir and Lorimer 1996). In many old growth forests 10–20% of the forest may occur as canopy gaps (Runkle 1982, Cho and Boerner 1991), but studies have 1 found similar levels of canopy gaps in mature second growth (Keller and Hix 1999).
Direct comparisons between old growth and second growth oak hickory forest failed to detect any difference in canopy openness in Ohio (Goebel and Hix 1996). A second line of evidence suggests that presettlement forests may have been open woodlands or savannas, typically defined as ≤70% canopy closure (Anderson et al. 1999). Consistent with this idea is the fact that oaks ( Quercus spp.) have been an important component of eastern forests since the last ice age (Davis 1983, Webb 1988). Oak seedlings tend to be shade intolerant and require an open canopy to grow. Canopy openings are created by disturbance which is an integral part of forest ecosystems (Pickett and White 1985).
Small canopy gaps are created by small scale disturbance events such as mortality of individual trees (Runkle 1982), while oak is thought to be maintained by disturbance regimes such as regular low intensity wildfires (Abrams 1992). Although the scale and timing of disturbance events that shaped presettlement forest ecosystems are not completely understood, the poor oak regeneration documented throughout the central hardwoods suggests important changes to disturbance regimes (Lorimer 1984, Abrams
1998). Additionally in eastern forests, the largest avian population decline has occurred for the Cerulean Warbler ( Dendroica cerulea ), a species associated with canopy gaps
(Hamel 2000, Jones and Robertson 2001, Link and Sauer 2002, Hamel et al. 2004,
Weakland and Wood 2005, Perkins 2006, Sauer et al. 2008).
Restoring the structure and function of presettlement forest conditions (Fule et al.
1997) is an important component of ecosystem management, which seeks to maintain the integrity of forests (Grumbine 1994, Christensen et al. 1996). Consistent with the goals of ecosystem management, some forest management organizations have increased rotation 2 age in conjunction with harvesting to develop the large trees associated with old growth forest, for example Ouachita National Forest, Arkansas (Hedrick et al. 2007). Others recommend management to increase the structural heterogeneity of second growth forests and promote old growth characteristics (Mitchell et al. 2005). Management options using prescribed fire to promote oak regeneration are being examined (e.g.
Sutherland and Hutchinson 2003) and have been implemented in some areas along the edge of the prairie to restore open oak savannas and woodland (Hedrick et al. 2007).
However, the temporal scale of ecological processes operating within forests exceeds human management plans. Because many species depend on forest ecosystems, understanding how different species will respond to various silvicultural approaches is an essential component of ecosystem management. Moreover, understanding the dynamics of ecosystem processes may provide further insight into some of the important structural characteristics of eastern forests as they once existed.
Partial harvesting is one common approach to manipulate canopy openness and forest structure. The shelterwood method, designed to promote oak regeneration, typically removes 40–60% of the stand basal area (Loftis 1990, Brose and Van Lear
1998, Brose et al. 1999a, b). Clearing of dense understory and midstory vegetation allows sunlight to reach the forest floor. While many ground and midstory nesting forest birds tend to decline with partial harvesting (e.g. Annand and Thompson 1997), habitat conditions are thought to remain suitable for avian canopy nesting species because some overstory trees are retained (Probst 1979, Thompson et al. 1995). Indeed, most canopy songbirds have been detected in partial harvests in Ohio (Dennis 2002). Abundance of
Cerulean Warblers in older two age stands was comparable to unharvested mature 3 second growth in West Virginia (Wood et al. 2005). Many studies have found that
Eastern Wood pewees (Contopus virens ) increase with an open canopy (Annand and
Thompson 1997, Rodewald and Smith 1998, Guénette and Villard 2005, Helzel and
Leberg 2006, Campbell et al. 2007) and overall abundance of canopy nesting species could increase with canopy openness (Rodewald and Smith 1998). Despite some evidence for associations of canopy songbirds with an open forest canopy, few studies have examined how canopy structure might impact reproductive success. Identifying the importance and consequences of canopy openings to bird communities is one critical component of understanding the disturbance dynamics that shape forest ecosystems and learning ways to apply that knowledge in forest restoration efforts.
Goals and Objectives
The purpose of this study was to understand the influence of canopy openness on birds that breed in the forest canopy. Partial harvesting removes some of the full sized trees and opens the forest canopy, in the short term creating an open woodland. Specifically I compared open shelterwood stands and closed canopy mature second growth to examine the relationship between avian canopy nesting species and an open forest structure. I examined both avian responses to canopy openness and the effects of canopy openness on reproductive success for a guild of five canopy nesting species. My research focused on the following questions: (1) Do canopy songbirds exhibit any preference for an open or closed forest canopy? (2) Does canopy structure influence reproductive success, and how does this relate to habitat preferences?
4 Significance
Canopy openness may have been important in presettlement forest ecosystems, although whether this occurred as canopy gaps or open park like woodland remains unclear. Today deciduous forests of eastern North America are almost all closed canopy mature second growth. Partial harvesting provides the opportunity to examine how avian canopy nesting species respond to opening of the forest canopy and whether this influences reproductive success for different species. The quality of breeding habitat is thought to be an important driver of avian population dynamics, and studies suggest that forest structure is one of the key attributes determining habitat quality. Behavioral and demographic consequences of changes in forest structure on canopy nesting birds remain poorly understood; my research aims to fill this knowledge gap.
Thesis Layout
This chapter provides general background information on the research and includes an introduction, goals and objectives, study questions, and significance of the work. The remaining chapters have been written in publication format. Chapter 2, which is formatted for Journal of Wildlife Management, examines community and population level consequences of shelterwood harvesting for forest songbirds, with special emphasis on canopy nesting species. Chapter 3 examines factors affecting nest site selection and nesting success of canopy songbirds and has been prepared for submission to Forest
Ecology and Management .
5 Background
Canopy openness. Evidence suggests that canopy openness may have been important in presettlement forest ecosystems (Bartram 1791, Denevan 1992, Bonnicksen
2000). Openings in the forest canopy are generally created by disturbance, which is defined as “any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment” (Pickett and White 1985). Forest disturbance events can range from large scale stand replacing fires or wind storms to small scale disturbance events when individual trees die and leave canopy gaps. The disturbance agent opens up the forest canopy and allows sunlight to reach the forest floor. Successional regeneration of the forest begins subsequent to a disturbance. During early initiation stages a dense patch or stand of shrubs and saplings develops which eventually continues through the self thinning phase until finally a closed canopy of full sized trees has replaced the original opening created by disturbance (Oliver and Larson 1990).
The type, intensity, and extent of the disturbance can profoundly affect forest structure. Stand replacing disturbances tend to create an even aged forest because overstory trees are established at the same time. Mature second growth forests that exist today were established after abandonment of forested land cleared for agriculture or other industrial uses (Smith et al. 2004). Because trees are generally within a single age class, the canopy remains closed (≥90%). Some canopy gaps occur in forests of any age when trees die through competition, disease, wind storms, or fire. However, canopy gaps are an integral part of the shifting mosaic phase of old growth forests. Evidence from tree rings suggests that openings in the forest canopy may have competitively released trees and 6 stimulated growth every 20–30 years in presettlement forest ecosystems (Abrams et al.
1995). Openings are colonized by new regeneration and over time create an uneven aged stand (Runkle 1982). In some earlier classifications, late successional stages of forest were simply defined as old growth (Oliver and Larson 1990). Even in these older forests, gap formation processes may continue to occur that oftentimes increase vertical and horizontal diversification eventually resulting in replacement of the pioneer cohort
(Franklin et al. 2002). Forests maintained through small scale disturbance events tend to be characterized by a diverse range of age classes, old trees, and multiple foliage layers.
Fire is considered to be an important component of historic disturbance regimes in some eastern deciduous forests. Over time regular low intensity surface fires open the forest canopy as some of the overstory trees are killed by fire (White 1983, Faber
Langendoen and Davis 1995, Huddle and Pallardy 1996, Rebertus and Burns 1997,
Anderson et al. 1999, Peterson and Reich 2001). Fire is needed to maintain open savannas and woodlands on the edge of the prairie. These ecosystems are classified as
10–70% canopy cover (Anderson et al. 1999). Regular disturbance from low intensity surface fires creates an open forest structure without the dense regeneration that would naturally occur with opening of the forest canopy. Many early explorers describe the original forests they found as open and park like (overview in Hutchinson et al. 2003).
But because of the long time frames over which forest structure develops and changes, complex disturbance regimes that maintained presettlement forests are not fully understood.
There are three basic patterns of disturbance that different forest management options emulate (described in Lanham et al. 2002): 1) Infrequent large scale disturbances 7 create regeneration and eventually even aged stands such as mature second growth; clearcut harvesting is designed to regenerate forest stands in this way, 2) Frequent small scale disturbances from the death of individual overstory trees creates a mosaic of canopy gaps with patches of regeneration as in old growth forests; this might be represented by two age or uneven age stands with dense understory regeneration over time, and 3)
Regular low intensity wildfires create an open forest structure with an open canopy; prescribed fire is being used to manage for open savannas and woodlands. Forest management also can combine these options, such as with the shelterwood burn method which combines prescribed fire with opening of the forest canopy but regenerates as an even aged stand. Although management options may attempt to replicate natural forest conditions, the temporal scale of ecosystem responses as well as the associated uncertainty require that adaptive management approaches be used and include continued monitoring and evaluation over time.
Oak forests . Although oaks were historically dominant in many eastern forests, forest composition is shifting due to anthropogenic changes to disturbance regimes
(Abrams 1992). This shift is of concern to a variety of stakeholders given that oaks have both high commercial and ecological value (McShea and Healy 2002, Rodewald and
Abrams 2002). In the eastern United States oak forest types currently cover more than 80 million hectares (Smith et al. 2004). Pollen studies indicate that the abundance of oaks increased ten thousand years ago during the warming of the post glacial period (Davis
1983, Webb 1988), and evidence from witness trees suggest that oaks were likely dominant in many areas prior to European settlement (Abrams 2005). The oak hickory forest type occurs throughout the central and southern regions of the eastern deciduous 8 forest biome (Braun 1950). However, the understory layer of mature oak hickory forests now tends to be dominated by saplings of red maple ( Acer rubrum ). Without recruitment of oak into the forest overstory, replacement of this disturbance dependent forest type with later climax, mixed mesophytic succession is expected to occur (Lorimer 1984,
Abrams 1998).
Oak is considered a disturbance dependent climax community. Oak seedlings tend to be shade intolerant and initiate in canopy openings. Regeneration of oak into the forest overstory is thought to depend on fire (Brose and Van Lear 1998). Oak species are generally considered fire tolerant and as full sized trees tend to survive low intensity surface fires, in part because of thick bark (Hengst and Dawson 1994). Thus, fire kills other competitor species, allowing oak to rapidly regenerate new vegetative sprouts from underground roots that remain undamaged by fire (Van Lear and Watt 1993, Wade et al.
2000). Without the advantage of fire, oak saplings tend to be out competed by faster growing competitors. In this way, the historic dominance of oaks in many forest ecosystems is thought to have been maintained by a combination of both openings in the forest canopy and fire.
Historically fire was an important component of oak forest ecosystems (Abrams
1992). Paleolithic charcoal studies of presettlement forests have found oak pollen associated with evidence of regularly occurring forest fires (overview in Abrams 2002).
Lightning strikes igniting wildfires could be one possible cause (Petersen and Drewa
2006). Native Americans may also have used fire management for thousands of years, perhaps to promote growth of berries and nuts (Delcourt and Delcourt 1997). During the period of European settlement, records show that the occurrence of forest fires remained 9 common, especially in areas used for production of wood charcoal (overview in
Hutchinson et al. 2003). Study of old growth forests has found regularly occurring fire scars on 400 year old oak trees (Shumway et al. 2001). However, the understory in many old growth oak forests has become dominated by shade tolerant species and lacks oak regeneration (McCarthy et al. 2001 and others). Some argue that the remaining old growth oak forests that exist today are as much influenced by human alterations as other forests (Foster et al. 1996). Recent fire suppression efforts since the early 1900s appear to be altering structure and species composition of forests (Lorimer 1984, Abrams 1992).
Many current forest management strategies applied in the central hardwoods are intended to promote oak regeneration. In particular, the shelterwood burn method is used to stimulate regeneration of oaks (Loftis 1990, Brose and Van Lear 1998, Brose et al.
1999a, b). Shelterwood harvesting initially opens the forest canopy typically removing a range from 40–60% of the stand basal area (Loftis 1990, Brose et al. 1999a, b). Shade intolerant oak seedlings also benefit from removal of a dense understory and midstory which allows light to reach the forest floor. Once the regeneration of oak seedlings has taken hold (generally in 3–5 years) additional prescribed fire (Brose et al. 1999a, b) and more recently herbicide treatments are implemented to reduce oak competitors (Franklin et al. 2003). Generally the term “shelterwood” has been used to describe moderate levels of tree removal. This is one type of partial harvest in which some of the overstory trees are removed while others are retained. Partial harvesting can involve a wide range of tree removal from single tree selection, often called thinning, to retention of a few residual seed trees in modified clearcuts. Tree removal can occur in a generally uniform pattern or clumps of trees can be removed, such as in group selection, or retained, such as in 10 variable retention systems. Shelterwood harvesting can also be uniform, irregular, or grouped. In a typical uniform shelterwood harvest the overstory trees are later removed to create an even aged regeneration stand similar to clearcutting. Sometimes, though, canopy trees can be left either for aesthetic reasons or as reserve trees in a two aged stand
(Thompson et al. 1995).
Forest structure and avian community composition. Understanding the role of forest structure in avian habitat selection has important implications for bird use of modified environments associated with harvesting (Franzreb 1983). Forest structure is a broad term that incorporates the three dimensional nature of forests which can be important in plant and animal diversity. Forest structure is a product of some ecosystem processes such as disturbance and a driver of other processes such as plant and animal food chains, microclimate, and cover (Hansen et al 1991, Spies 1998). Important components of forest structure include vertical foliage distribution, horizontal variation in canopy cover, tree size, and coarse wood debris (Spies 1998), all of which can affect avian species abundance and distribution. Classic early research found that forest bird diversity increases with vertical foliage complexity and horizontal patchiness (MacArthur and MacArthur 1961, Willson 1974). Different species occupy unique niches within each foliage strata of the forest. Based on species specific habitat preferences, the presence of certain species can be predicted by habitat characteristics (Anderson and Shugart 1974).
These initial studies suggested that birds select habitat based on the availability of food within different foraging substrates. However, re evaluation of bird habitat relationships suggest that nesting substrates may be more important than foraging substrates, although
11 selection for both nesting and foraging substrates are probably occurring simultaneously
(Martin 1993).
Many studies have examined changes in avian abundance associated with different levels and types of partial harvesting. Both avian species diversity and overall abundance have been found to increase in shelterwoods (Annand and Thompson 1997,
Baker and Lacki 1997). One study recorded highest breeding bird density with 50% stocking (Lesak et al. 2004). Generally the short term response to partial harvesting has been that mature forest species nesting in ground and midstory layers use partially harvested stands but may decrease in abundance (Annand and Thompson 1997,
Rodewald and Smith 1998, King and DeGraaf 2000, Rodewald and Yahner 2000).
Removal of midstory layers probably impacts some species while regeneration that fills in the forest floor and eliminates leaf litter impacts others. Forest species that respond negatively to harvesting tend to show a 25–50% reduction in density with moderate levels of tree removal (Vanderwel et al. 2007). Patterns of decline vary with some being gradual while other species show a threshold response to the level of harvesting
(Guénette and Villard 2005). A recent meta analysis of partial harvesting demonstrated that only one forest species, the Ovenbird ( Seiurus aurocapillus ), consistently responded negatively to any level of partial harvesting (Vanderwel et al. 2007); this species of eastern deciduous forest depends on leaf litter for both foraging and nesting. Early successional and edge species colonize partially harvested stands after several years as the open canopy encourages dense regeneration of shrubs and saplings. Still many of these successional species are less abundant than in clearcuts (Annand and Thompson
1997). 12 Partially harvested stands change over time as regeneration occurs. In the absence of fire regeneration creates a dense shrub and sapling layer. Less extensive study has been conducted within two age or uneven aged stands which may provide improved habitat for some species, and shrub nesters have been found to increase in abundance in two age compared to unharvested stands (Duguay et al. 2000, Heltzel and Leberg 2006).
Effects of partial harvesting on midstory nesting species remain unclear. One study detected equal numbers of several midstory nesting species in two age stands fifteen years post harvesting compared to unharvested stands (Duguay et al. 2000) while another study showed lower abundance of some species in two age stands of similar age (Heltzel and Leberg 2006). As regeneration occurs early successional species also disappear approximately eight years post harvesting (Campbell et al. 2007).
Changes in forest structure created by low intensity surface fires could be similar to immediate effects of some types of partial harvesting because of loss of understory and leaf litter. The initial re introduction of fire into forest ecosystems appears to negatively affect abundance of some ground and shrub nesting species while disturbance dependent species increase (Wilson et al. 1995, Artman et al. 2001). Regular prescribed fire opens up the canopy and some early successional and grassland species increase in oak savannas and woodlands, although others associated with dense successional regeneration may not (Brawn 2006). For example, the Red headed Woodpecker ( Melanerpes erythrocephalus ) has been associated with oak woodlands and savannas (Davis et al.
2001, Brawn 2006, Grundel and Pavlovic 2007). Midstory nesting species such as the
Wood Thrush ( Hylocichla mustelina ) have not shown a negative response to initial re introduction of prescribed fire (Artman and Downhower 2003), although regular use of 13 fire may result in lower abundance of some midstory nesting species (Grundel and
Pavlovic 2007). Studies have consistently demonstrated that numbers of American
Robins ( Turdus migratorius ) increase with prescribed fire, perhaps because of increased areas of bare soil for foraging (Artman et al 2001, Davis et al. 2001, Grundel and
Pavlovic 2007).
Extensive research has focused on changes in avian abundance associated with different harvesting methods, but the association between avian abundance and forest structure is not always straightforward. Some research has found either no effect or different effects on the same species. Species abundance can change within their geographic range (Brown 1984) while effects of forest fragmentation occur at the landscape scale (e.g. Stephens, et al. 2003, Lampila et al. 2005, Lloyd et al. 2005). Bird habitat selection is hierarchical and occurs across multiple spatial and temporal scales
(Johnson 1980). Changes in forest structure associated with forest management will influence habitat at the stand level in the context of the regional landscape (Thompson et al. 2000). Although many studies have examined effects of forest management on birds, most research has been short term and conducted at small scales. Criticisms of current studies cite lack of experimental manipulation and minimal replication. Specifically, the majority of studies have examined the effects of clearcutting which has been the most common method of timber harvesting (Sallabanks et al. 2000, Thompson et al. 2000).
Most studies tend to measure density alone as a correlate of habitat preferences.
According to the ideal free or ideal despotic model, birds will saturate preferred habitat before occupying less preferred areas (Fretwell and Lucas1970, Fretwell 1972).
However, other factors can influence density, and additional correlated measures of 14 habitat preferences are needed such as settlement patterns, site fidelity and dominance hierarchy, e.g. age class distributions (Robertson and Hutto 2007). Earlier settlement may be associated with increased breeding density (Chalfoun and Martin 2007) or reproductive success (Smith and Moore 2005). Specific habitat preferences are part of a complex species specific evolution of morphology, physiology, and innate and learned behavior in response to a given environment (Block and Brennan 1993). While species select characteristics that promote fitness over evolutionary time (Martin 1998), a variety of factors can influence apparent habitat use and not all preferences are adaptive (Jones
2001).
The link between preference and fitness can be broken if habitat alteration negatively influences fitness without altering the habitat characteristics that birds are using as settlement cues. This can lead to what has been termed the ecological trap in which a mismatch occurs between preferences and fitness (Donovan and Thompson
2001, Schaepfer et al. 2002, Robertson and Hutto 2006). Recent study suggests that in the western North America selectively harvested forest may be serving as an ecological trap for the Olive Sided Flycatcher ( Contopus cooperi ) because of increased predator abundance (Robertson and Hutto 2007). However, abundance may not reflect fitness, and additional measures including reproductive success and adult survival are needed
(Robertson and Hutto 2006, Johnson 2007, Kristan 2007). Few studies have examined effects of harvesting on avian population dynamics (Sallabanks and Arnett 2005) which limits our understanding of the mechanisms by which forest structure, and hence different management strategies, influence birds. It is especially important to try to understand
15 ultimate causes such as changes in food availability or predator abundance (Marzluff et al. 2000).
Effects of silviculture on reproductive success . The direct impacts on nest success of an open forest structure associated with partial harvesting remain unclear. In West
Virginia no increase in nest predation was detected across a range of species in two age stands 10–15 years post harvesting compared to unharvested stands (Duguay et al. 2001).
Again in New Hampshire, no differences in nest success were detected for both natural and artificial nests in 3–5 year old shelterwood harvests compared to unharvested stands, perhaps because predator abundance did not change with harvesting (King and DeGraaf
2000). In Arkansas increased nest predation occurred in young, thinned pine plantations compared to single tree selection pine hardwoods suggesting that an open forest structure could lead to increased predation (Barber et al. 2000). On the other hand, in Illinois nesting success was higher for some species nesting in open oak savannas managed with fire compared to closed canopy forest (Brawn 2006). In Missouri early successional species were also documented nesting in shelterwood harvests as well as regenerating clearcuts although effects on success are unclear (Annand and Thompson 1997). These limited studies of natural nests are generally based on extremely small sample sizes for individual species which may respond differently based on behavior and life history strategies.
Some intensive work on reproductive success associated with harvesting has focused on individual species or guilds of species. A study in Canada found increased nest predation for the ground nesting Ovenbird in young (<5 year old) selection harvests compared to unharvested stands, but there was no change in reproductive success for low 16 shrub nesting Black throated Blue Warblers ( Dendroica caerulescens ), although this species increased in abundance with harvesting due to increased development of understory (Bourque and Villard 2001). In Ontario Rose breasted Grosbeaks ( Pheucticus ludovicianus ) also showed no change in nesting success, nest initiation dates, age structure or number of young fledged from a successful nest in partially harvested compared to unharvested stands, although a higher percentage of nests were parasitized by the Brown headed Cowbird ( Molothrus ater ) (Smith et al. 2006). When compared to unharvested stands in a fragmented landscape in Illinois, partial harvests had comparable rates of nest predation for Acadian Flycatchers ( Empidonax virescens ), Northern
Cardinals ( Cardinalis cardinalis ), Wood Thrush and Kentucky Warblers ( Oporornis formosus ), although again brood parasitism increased for some species (Robinson and
Robinson 2001). In Missouri with several types of partial harvesting, there were no significant differences in nest predation pre and post harvesting for a number of ground and midstory nesting forest species (Gram et al. 2003). In West Virginia nest success in partial harvests compared to unharvested stands varied by species for thrushes (Dellinger et al. 2007). Conversely in Mississippi, both canopy and midstory nesting species, especially the Acadian Flycatcher, experienced increased nest predation in recent group selection harvests compared to unharvested stands while ground and shrub nesting species were not affected (Twedt et al. 2001). In western coniferous forests the canopy nesting Olive sided Flycatcher (Contopus cooperi ) also experienced increased nest predation in selectively harvested stands compared to unharvested stands (Robertson and
Hutto 2007). In West Virginia Wood Thrush experience increased predation in two age
17 stands compared to unharvested forest which could have been related to changes in invertebrate biomass (Duguay et al. 2000).
Limited apparent effects on nest success from harvesting might be related to predator and brood parasite abundance. Many studies have detected no change in the number of Blue Jays ( Cyanocitta cristata ) associated with partial harvesting (Annand and
Thompson 1997, Rodewald and Smith 1998, King and DeGraaf 2000) although others have (Robinson and Robinson 1999). In several regions abundance of a number of different predators remained similar in harvested and unharvested areas (Annand and
Thompson 1997, King and Degraaf 2000). However, snake abundance was found to increase marginally in natural canopy gaps (Greenberg 2001). In western coniferous forest abundances of several predators was greater in partially harvested compared to unharvested stands (Robertson and Hutto 2007). Some studies have demonstrated increased abundance of Brown headed Cowbirds (Molothrus ater ) associated with partial harvesting (Annand and Thompson 1997, Baker and Lacki 1997) while others have not
(Rodewald and Smith 1998). The Brown headed Cowbird is often associated with open areas and increased parasitism has been documented in a number of studies (Robinson and Robinson 2001, Smith et al. 2006)
The abundance of predators and brood parasites can be influenced by both edge and landscape effects (Donovan et al. 1997, Chalfoun et al. 2002). Edges are defined as a discontinuity between two adjacent habitat types. Edges created by partial harvesting have been described as “feathered” edges and have not been found to increase predation, at least on artificial nests (Ratti and Reese 1988). Managed forest landscapes may not show edge effects (Hanski et al. 1996). However, whether changes in forest structure 18 increase predation on natural nests remains unclear. If trees are harvested in a relatively uniform pattern (evenly spaced) large open areas generally are not created as in clearcutting, but rather partial harvesting creates numerous gaps in the canopy. There is a change from unharvested closed canopy forest to open canopy woodland where some of the trees have been removed. Initially there is also a break in understory and midstory cover, although over time regeneration will lead to a denser shrub and sapling layer than the surrounding forest. Plant species composition does not change in the same way as on agricultural land. In general silviculture does not appear to influence predators in the same way as agriculture. Landscapes fragmented by silviculture have been found to have a lower abundance of avian and other nest predators than those fragmented by agriculture
(Rodewald and Yahner 2001a, Chalfoun et al. 2002) perhaps because agricultural areas provide additional food sources (Dijak and Thompson 2000). Nesting success may also be higher for canopy nesting species in silvicultural as opposed to agricultural landscapes
(Rodewald and Yahner 2001b).
As well as nest predation, food availability is an important factor that influences avian reproduction (Clinchy et al. 2004, Nagy and Holmes 2004, Zanette et al. 2004).
Experimental manipulations of food availability suggest birds may respond in a number of ways to increased food including earlier initiation of breeding, larger clutch size and increased breeding attempts, either renesting after predation or multiple broods (Arcese and Smith 1988, Simons and Martin 1990, Svensson and Nilsson 1995, Nagy and Holmes
2005). Food reduction experiments using insecticides have detected less effect of prey resources on reproduction (e.g. Rodenhouse and Holmes 1992, Marshall et al. 2002). In several studies nestling provisioning rates decline with reduced prey resources, indicative 19 of lower quality habitat. Parents compensate with large prey items but young are still in poorer condition than when prey are abundant (Zanette et al. 2000, Tremblay et al. 2005).
Birds may have to forage farther from the nest when food is less available (Adams et al.
1994, Tremblay et al. 2005). When food is experimentally increased females have been documented spending more time loafing near the nest and less time foraging (Nagy and
Holmes 2005). In western coniferous forest the Olive sided Flycatcher increased nestling provisioning rates in selectively harvested stands compared to unharvested stands presumably related to food (Robertson and Hutto 2007).
Changes in forest structure associated with partial harvesting might influence birds by modifying microclimate, chemical environment, and foraging substrate of their arthropod prey. Birds change their foraging behavior in response to natural changes in forest structure (Maurer and Whitmore 1981) and changes associated with harvesting
(Franzreb 1984, Hartung and Braun 2005, George 2009) which may reflect changing prey resources. Creation of canopy gaps can trigger changes in species composition of arthropods in ways that favor Homoptera (Gorham et al. 2002) as well as flying arthropods in general (Greenberg and Forrest 2003, Ulyshen 2005 but see Moorman et al.
2007). Birds may use canopy gaps because of increased prey availability (Blake and
Hoppes 1986), although recent work showed continued use of gaps even when arthropods were experimentally reduced with insecticide (Champlin 2007). Attack rates of Hooded
Warblers, although positively related to arthropod abundance, were also lower near gap edges (Kilgo 2005). On the other hand, harvesting might reduce foliage volume in ways that affect herbivorous prey such as Lepidoptera (Marshall and Cooper 2004). Reductions in this favored prey can result in dietary shifts with negative consequences in reduced 20 body fat for a number of forest species (Sample et al. 1993, Whitmore et al. 1993).
However, changes in microclimate may mediate this effect. High levels of sunlight in harvests stimulate growth rates in herbivorous insects (Scriber and Slansky 1981).
Temperature can affect caterpillar abundance, and indeed, long warm summers have been correlated with annual variation in caterpillar abundance the following year (Reynolds et al. 2007). In turn, increased consumption from herbivorous insects can promote plant defense compounds, such as oak phenolics, which may increase after thinning and partly explain lower insect abundance (Forkner and Marquis 2004). Arthropods may also depend on tree species composition. Oaks are known to support higher abundance of
Lepidoptera compared to other trees (Holmes and Schultz 1988, Butler and Strazanac
2000, Summerville et al. 2003). Some evidence suggests that abundance of breeding birds could be higher in oak forests for this reason (Rodewald and Abrams 2002). Oak dwelling arthropods may be resilient to disturbance caused by harvesting as Lepidoptera density on oaks did not change with harvesting, although only oak saplings were sampled
(Forkner et al. 2006).
Habitat mediates interactions among predators and prey. Changes in food availability and distribution might prompt behavioral responses from birds that affect nesting success. For example, locating sufficient food to feed hungry nestlings may force parents to spend increased time foraging and/or parents may forage farther from the nest resulting in less time spent watching and defending the nest (Rytkoenen et al. 1995,
Rastogi et al. 2006). Although difficult to quantify, nest defense has been directly observed in multiple species and may be related to success, perhaps associated with body size (Best and Stauffer 1980) or maneuverability (Fontaine and Martin 2006). Natural 21 nests tend to be more successful than similarly placed artificial nests which suggests that parental behavior, presumably nest defense, can increase success (Wilson and
Brittingham 1998). Weidinger (2002) demonstrated that nest defense may be more important than concealment for some species. Aggression towards Blue Jay (Cynocitta cristata ) models has been positively related to nest success during incubation (Olendorf and Robinson 2000), and male nest attendance promoted success when Blue Jays were the main nest predator (Schmidt and Whelan 2005).
On the other hand, behavioral plasticity allows birds to adjust to environmental conditions. An open canopy might increase vulnerability to predation if nests are more visible, although direct evidence for this remains unclear (Jones et al. 2001). Nest concealment may be especially important if predators are visually oriented (Johnson
1997) as with Blue Jays which have been observed depredating canopy nests in this study system (M. H. Bakermans and F. L. Newell, personal observation). Birds can adopt different nest sites that benefit fitness in a new environment (Yeh et al. 2007) or modify nest placement based on availability of substrates without any apparent effect on reproductive success (Artman and Downhower 2003). However, there may be trade offs between concealment and the ability of a parent to scan and detect predators in the nest area (Göttmark et al. 1995). When predators are detected, birds can adjust their behavior to reduce the risk of predation such as by making fewer visits to the nest (Ghalambor and
Martin 2002, F. L. Newell, personal observation) or attacking a predator (Weidinger
2002, F. L. Newell, personal observation). Indeed, risk of depredation rises with parental activity during the nestling stage (Martin et al. 2000, Stake et al. 2005). In conclusion, birds may be using multiple behavioral strategies to balance predation risks associated 22 with an open canopy in harvest areas, including concealment, watchful observation, and nest defense.
Canopy nesting songbirds. Canopy songbirds nest and forage predominantly in the forest canopy and, therefore, might be expected to be influenced by canopy openness.
However, studies of the effects of forest structure on canopy nesting species have been equivocal. Maintenance of a mature tree component with partial harvesting has been thought to provide habitat for canopy dwelling birds, although negative effects on insectivores have been suggested because of a reduced number of trees (Probst 1979,
Thompson et al. 1995). Flycatchers, in particular, may be favored by an open forest structure. For instance numbers of Eastern Wood pewees are consistently higher in open versus closed canopy forest (Annand and Thompson 1997, Guénette and Villard 2005,
Campbell et al. 2007). Pewees may also respond positively to understory removal
(Rodewald and Smith 1998) but decline with dense regeneration in two age stands
(Campbell et al. 2007). In western coniferous forest the canopy nesting Olive sided
Flycatcher also increased in abundance in partially harvested stands but nest success was negatively affected (Robertson and Hutto 2007). Evidence suggests that a number of insectivorous canopy species may not decline with moderate levels of tree removal.
Abundance of Cerulean Warblers was similar in two age compared to unharvested stands
(Wood et al. 2005, Register and Islam 2008) and Cerulean Warblers could be attracted to canopy openings created by timber harvesting (Rodewald 2004). In Arkansas canopy nesting species overall increased in abundance with canopy opening and understory removal (Rodewald and Smith 1998). However, only one study found that Scarlet
Tanagers increased with partial harvesting (Jobes et al. 2004) compared to others that 23 reported tanagers declined (King and DeGraaf 2000) or disappeared (Porter 1996) from harvests in the northern part of their range while studies have not detected any effect in the center of their range (Annand and Thompson 1997, Rodewald and Smith 1998). In general, habitat associations of canopy songbirds remain inconclusive and poorly documented for individual species.
Traditionally the Cerulean Warbler has been associated with forested landscapes and mature or old growth forest with large trees (Hamel 2000). Canopy gaps and a diverse foliage structure appear to be important in the microhabitat selected by Cerulean
Warblers, which nest at average heights of 11–15 m (Hamel 2000, Jones and Robertson
2001, Jones et al. 2001, Weakland and Wood 2005, Perkins 2006). Foraging height of
Cerulean Warblers is similarly high, though it can range from 2 to >45 m (Hamel 2000).
Cerulean Warblers glean insects from leaves and Homoptera and Lepidoptera may be especially important (Sample et al. 1993). This species has been documented to preferentially forage in hickory and avoid red maple (Gabbe et al. 2002). Territories tend to be clustered, especially in areas with increased vertical foliage structure (Roth and
Islam 2007). Recent interest has focused on the Cerulean Warbler because of extensive large scale population declines apparent in the Breeding Bird Survey (Hamel et al. 2004) and populations have been declining at – 4% although declines are lower in the Ohio
Hills region at – 2.3% (Link and Sauer 2002, Sauer et al. 2008). Cerulean Warblers are considered area sensitive and require large tracts of forest (Robbins et al. 1989, Wood et al. 2006). In some cases Ceruleans have been demonstrated to respond negatively to forest edge (Wood et al. 2006) although this may not occur along internal edges in more forested landscapes (Bakermans and Rodewald 2009). Nesting success in Ohio ranged 24 from 15–55% and success may be higher in areas with large trees and grapevines
(Bakermans and Rodewald 2009). In Ontario nest success ranges from 10–76% with 0.4–
2.2 young fledged per pair (Jones et al. 2001). Annual survival has been found to be approximately 50% with highest mortality occurring during the non breeding season, probably on migration (Jones et al. 2004). Cerulean Warblers remained at sites after ice damage opened the forest structure, but this disturbance appeared to have an immediate negative effect on nesting success (Jones et al. 2001).
The Eastern Wood pewee is typically associated with forest clearings and edges throughout eastern North America. Intermediate age forests with little understory may be important (Stauffer and Best 1980, Crawford et al. 1981). Nest heights average 9 m
(range: 2–21 m). Pewees fly catch from feeding perches often on dead branches averaging 10–11 m in the subcanopy or canopy. Flying insects are the main prey and
Diptera may be important with some Lepidoptera (McCarty 1996). Size of forest fragments does not appear to be important in habitat selection (Blake and Karr 1987,
Stauffer and Best 1980) although more recent work has found pewees to be area sensitive
(Keller and Yahner 2007). One study suggested that high densities of White tailed Deer
(Odocoileus virginianus ) may have negative effects, although reasons for this remain unclear (DeCalesta 1994). The Eastern Wood pewee has declined over much of its range including in the Ohio Hills region at –3.7% (Sauer et al. 2008). Causes of population decline are unknown. Nest success in the Midwest was 43% (Knutson et al. 2004). In some areas the Eastern Wood pewee may experience low levels of brood parasitism because of asynchrony in nesting compared to other bird species (Underwood et al.
25 2004). Using a model, mean annual productivity was predicted at 1.8–2.7 fledglings per female (Knutson et al. 2006).
The Scarlet Tanager tends to be associated with closed canopy mature forest and appears sensitive to forest fragmentation (Mowbray 1999). Large trees with fewer small trees may be important and oaks may be especially preferred (Anderson and Shugart
1974, Porter 1996). Nest height averages 7–12 m (range: 2–21 m) and foraging height averages 12–15 m with females tending to forage higher (Holmes 1986). Leaves are the most frequent foraging substrate and Lepidoptera may be important during breeding (in
Mowbray 1999). Oak and hickory species have been documented to be preferentially selected for foraging (Gabbe et al. 2002). Populations are relatively stable having declined in some regions but not in others including the Ohio Hills at 0.7% (Sauer et al.
2008). Considered an area sensitive species, occurrence of Scarlet Tanagers has been negatively related to forest fragmentation (Rosenberg et al. 1999) and small patch size
(Hames et al. 2001). In forest fragments males tend to be unpaired first time breeders, while paired males in fragments shift territories during the breeding season (Fraser and
Stutchbury 2004). These unpaired males moved more than paired males and adopted either a mobile or sedentary strategy. However, in contiguous forest pairing success can be as high as 100% (Roberts and Norment 1999). Roberts and Norment also documented effects of patch size on reproduction with 22% of pairs fledging young in small forest patches compared to 64% in contiguous forest, although productivity was low at 0.3–0.8 young per male. Using a model, mean annual productivity was predicted to be higher at
1.8 fledglings per female (Knutson et al. 2006). In the Midwest where nest success also
26 decreased with fragmentation, brood parasitism was high at >80% (Robinson et al. 1995).
Success in the Midwest ranged from 22–35% (Robinson et al. 1995, Knutson et al. 2004).
The Yellow throated Vireo breeds in both bottomland and upland forests in eastern North America and may often occur along edges and around forest canopy gaps
(Rodewald and James 1996). Nest height ranges from 1–24 m and foraging height averages 7–16 m depending on the height of the forest, and males have been shown to forage higher. Vireos glean prey from live branches and trunks; Lepidotera may be important (in Rodewald and James 1996). Tree foraging preferences are not apparent
(Gabbe et al. 2002). This vireo has been documented to occupy forest with 30–90% canopy cover (James 1976) and numbers may increase with partial harvesting (in
Rodewald and James 1996). Large trees with fewer shrubs may be important and oaks may be especially preferred (Ambuel and Temple 1983). Apparent nest success from
Cornell Nest Records was 55% (in Rodewald and James 1996) but other published data are not available. Yellow throated Vireos may be sensitive to forest fragmentation and have been found to decrease in small forest reserves < 100 ha (Robins 1979, Askin et al.
1990). In Texas, Yellow throated Vireos required forest widths > 70 m along streams
(Conner et al. 2004). Still population trends appear to be increasing at 1.2% although they have not changed in the Ohio Hills region at 0.3% (Sauer et al. 2008).
Blue gray Gnatcatchers are thought to be associated with forest edges across a wide range of habitat throughout the United States and Mexico. Densities are highest in riparian areas and lowest at upland sites (Ellison 1992). In the south central United States this species generally occurs in riparian woodland and upland deciduous forest. Nests are often placed in oaks and average 8–11 m (range: 1–26 m). Foraging is predominantly in 27 the forest canopy but the midstory may be used when feeding young. Gnatcatchers forage in foliage at the tips of branches and Lepidoptera may be important (in Ellison 1992).
Tree foraging preferences are not apparent (Gabbe et al. 2002). Populations have increased and are expanding northward although populations in the Ohio Hills region have declined – 2.5% (Sauer et al. 2008). Gnatcatchers experience high levels of brood parasitism (50–75%) but high abandonment rates compensate in part for parasitized nests fledging only cowbirds (Goguen and Mathews 1996, Kershner et al. 2001). In residential forests in Illinois, gnatcatcher nest success was low at only 11% and persistent renesting was important; pairs were recorded renesting up to seven times (Kershner et al. 2001).
Kershner et al. found gnatcatchers placed nests in areas with higher leaf density than available at random and successful nests were placed higher and farther from habitat edges. Blue gray Gnatcatchers may decline in abundance with increased housing density
(Burhans and Thompson 2006). Gnatcatchers were found to be less successful at 13% with partial harvesting compared to 34% in cottonwood plantations (Twedt et al. 2001).
However, in the Midwest gnatcatcher nest success was higher at 34% and success for a range of canopy species was not related to forest core area in the surrounding landscape
(Knutson et al. 2004). Using a model, mean annual productivity for gnatcatchers was predicted at 1.3–1.5 fledglings per female (Knutson et al. 2006).
Relatively few studies have examined effects of partial harvesting on avian reproductive success and other demographic processes, and none focus on canopy nesting species. Canopy gaps or canopy openness created by partial harvesting might be important to a range of forest species during both breeding and migration (Kilgo et al.
1999, Greenberg and Lanham 2001, Moorman and Guynn 2001, Bowen et al. 2007, 28 Moorman et al. 2007). However, it remains unclear whether changes in prey resources or predation risk occur with canopy openness. In addition, associations with oak forests of many canopy nesting species (in Ellison 1992, McCarty 1996, Rodewald and James
1996, Mowbray 1999, Hamel 2000) and other Nearctic Neotropical migrants (Rodewald and Abrams 1992) need to be further understood, especially because oaks depend on both an open forest canopy and fire to regenerate. The relative importance of canopy structure as opposed to floristics remains unclear. Management decisions need to be informed of both the short term effects of canopy disturbance (and also fire) and the long term consequences of changing forest composition. Restoration of eastern deciduous forests to presettlement conditions will require a complete understanding of complex disturbances regimes over time in forest ecosystems; research and monitoring is part of an adaptive management approach.
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59
CHAPTER 2
SHORT TERM CHANGES IN THE BIRD COMMUNITY AND SUITABILITY OF
SHELTERWOOD HARVESTS FOR CANOPY SONGBIRDS
Running head: Shelterwood harvesting and birds
ABSTRACT Interest in regenerating oaks ( Quercus spp.) has promoted use of partial harvesting techniques (shelterwoods) that create an open forest structure by removing some canopy trees and most understory and midstory vegetation. Shelterwood harvests are thought to simulate part of the historic disturbance regimes of many eastern deciduous forests of North America, and may provide habitat to a variety of disturbance dependent wildlife, including several declining forest songbirds. My research examined forest songbirds in shelterwoods recently harvested to 50% stocking in upland mixed oak forests in southern Ohio, USA. From 2007–2008 birds were surveyed using distance based line transects in shelterwood harvests and nearby mature second growth ( n = 56 in
18 stands at 4 state forests). Because partial harvesting could improve habitat for canopy songbirds, I further evaluated suitability of shelterwoods for five sensitive canopy nesting species by studying settlement patterns, age distributions, site fidelity, and nesting success in 12 stands at three state forests from 2007–2009. Several midstory and ground nesting species were 26–67% less abundant in shelterwood than unharvested stands
60 whereas shrub nesting birds increased > 100% several years post harvesting. Overall canopy nesting species tended to be more abundant in shelterwoods, but responses varied among forests. In particular, abundance of cerulean warblers ( Dendroica cerulea ) was
>200% higher in shelterwoods compared to unharvested stands in only one forest; differences appeared to be related to slope and aspect. Patterns in settlement and site fidelity were similar among stands, suggesting no strong preferences for stand type.
Shelterwood harvests had greater proportions of first time breeders (second year birds) of cerulean warblers and scarlet tanagers ( Piranga olivacea) and across the canopy nesting guild, which might have been a consequence of young birds colonizing newly created (or improved) habitat. Even within this predominantly forested landscape, nesting success
(>700 nests) was low, ranging from 15–19% for yellow throated vireos ( Vireo flavifrons ) and cerulean warblers, to 27–36% for scarlet tanagers, blue gray gnatcatchers ( Polioptila caerulea ) and eastern wood pewees ( Contopus virens ). However, nest survival did not differ between shelterwood and unharvested stands, possibly because numbers of avian predators did not change with harvesting. Despite increased abundance of brown headed cowbirds ( Molothrus ater ) in shelterwoods, only 2% of nests in which young could be identified were parasitized. Birds nested higher and in sites more concealed by leaves in shelterwoods than in unharvested stands. While these results suggest shelterwood harvests containing abundant overstory trees can provide suitable short term breeding habitat for canopy songbirds, complex interactions between topography, forest structure and floristics need to be better understood. Moreover, long term responses of birds to partial harvesting may differ from those documented here depending on different management options employed. For example, the shelterwood burn method for oak 61 regeneration will typically remove all overstory trees later in the cutting cycle initially resulting in loss of nesting substrates and hence breeding habitat for canopy songbirds.
KEY WORDS forest, shelterwood, bird community, distance methods, nest success, blue gray gnatcatcher, cerulean warbler, scarlet tanager, eastern wood pewee, yellow throated vireo,
62 I TRODUCTIO
Ecosystem management seeks to emulate natural disturbances that shape the structure and function of forests (e.g. Attiwill 1994, Long 2009). Although mature forest ecosystems have traditionally been managed to limit disturbances, such as through fire suppression, complex disturbances may play a critical role in maintaining late successional forest ecosystems. In eastern North America changes in historic disturbance regimes are currently shifting forests from a disturbance dependent climax community dominated by oaks ( Quercus spp.) to a mesophytic climax community dominated by shade tolerant species (Abrams 1992, Nowacki and Abrams 2008). Dominant for >10,000 years (Webb 1988), oaks are integral to many forest ecosystems with mast production providing food for a variety of wildlife species (McShea and Healy 2002). From a human perspective oaks provide commercially valuable hardwoods. Sound forest management requires maintaining ecological integrity that supports diverse plant and animal species while simultaneously balancing the interests of multiple stakeholders, and oak regeneration has become a priority for management (Yaussy et al. 2008, Nowacki et al.
2009).
In presettlement forests oaks appear to be associated with canopy disturbances and fire (e.g. Abrams et al. 1995, Nowacki and Abrams 1997, Delcourt and Delcourt
1997, Fesenmyer and Christensen 2010). In the mature closed canopy second growth stands typical today, oaks are not regenerating effectively because seedlings require sunlight to grow while recruitment into the overstory depends on fire (Lorimer et al.
1994, Brose and Van Lear 1998). Collectively this has stimulated interest in management
63 strategies that replicate complex disturbances regimes such as the shelterwood burn method (Loftis 1990, Brose et al. 1999a, b). Attempting to mimic multiple or repeated disturbances, this method first applies a partial harvest to open the forest canopy and allow light to reach the forest floor while retaining a shelterwood of large oaks for seed trees. Harvesting to 50% stocking is generally recommended for oak regeneration although a range of 40–60% or other stocking levels may be termed shelterwoods. After
3–5 years partial harvesting is followed by prescribed fire to remove fast growing fire intolerant competitors such as red maple ( Acer rubrum ). Typically once oaks are well established all overstory trees will be removed to allow regeneration as an even aged stand (Loftis 1990, Brose and Van Lear 1998, Brose et al. 1999a, b).
From a wildlife perspective, shelterwood harvests are known to provide habitat for a diverse and abundant assemblage of early and late successional songbirds (Annand and Thompson 1997, Baker and Lacki 1997, King and DeGraaf 2000, Hanowski et al.
2003), though individual species may be less abundant compared to similar alternative habitats (e.g. clearcuts or mature forest) (Annand and Thompson 1997, McDermott and
Wood 2009). Canopy nesting species may be one late successional group that responds positively to moderate levels of partial harvesting (Rodewald and Smith 1998). Cerulean warblers ( Dendroica cerulea ) are an example of a forest species thought to benefit from small scale natural disturbances (Jones et al. 2001) and partial harvesting has been suggested to improve habitat for this species of high conservation concern (Hamel 2000).
However, associations between canopy songbirds and canopy openness are poorly understood and effects of partial harvesting on nesting success remain virtually unknown.
Shelterwood harvesting may be a viable silvicultural option for songbird conservation 64 that provides timber resources and promotes oak regeneration (Lanham et al. 2002).
However, managers need a better understanding of the population and community level consequences of partial harvesting on birds.
The objectives of this study were to identify short term changes in the bird community associated with shelterwood harvesting and examine whether partial harvesting can improve habitat for canopy songbirds. Specifically I evaluated preferences of canopy songbirds for an open forest canopy created through partial harvesting by comparing abundance, settlement patterns, age distributions, and site fidelity in shelterwood stands and unharvested mature second growth forest. In addition, I examined the reproductive consequences of partial harvesting for canopy nesting species. I focused on five sensitive species: scarlet tanager ( Piranga olivacea ), eastern wood pewee
(Contopus virens ), cerulean warbler, blue gray gnatcatcher ( Polioptila caerulea ), and yellow throated vireo ( Vireo olivacea ).
STUDY AREA
Research was conducted in southern Ohio in Vinton, Jackson and Ross Counties from
2007–2009. Study areas were located in four landscapes comprised of different state forests separated by 15–30 km, Zaleski (ZSF), Vinton Furnace Experimental Forest
(VFEF) formerly Raccoon Ecological Management Area, Richland Furnace (RFSF) and
Tar Hollow (THSF). The landscape was predominantly forested with 75–83% forest in a
10 km radius centered on the study sites (Table 2.1). Forest cover was calculated from the National Land Cover Dataset for the state of Ohio (Homer et al. 2004). Elevation ranged from 240–340 m. Stands were characterized by 80–130 year old upland mixed
65 oak forest. Dominant oaks in the overstory included white oak ( Quercus alba ), northern red oak ( Quercus rubra ), chestnut oak ( Quercus montana ), black oak ( Quercus velutina ), and scarlet oak ( Quercus coccinea ). Hickory species included bitternut ( Carya cordiformis ), mockernut ( Carya tomentosa ), pignut ( Carya glabra ), shagbark ( Carya ovata ) and shellbark hickory ( Carya laciniosa ). Yellow poplar ( Liriodendron tulipfera ) was common in some areas along with some sugar maple ( Acer saccharum ), red maple
(Acer rubrum ), basswood ( Tilia americana ) and American beech ( Fagus grandifolia ).
Oaks were not regenerating effectively and replacement by maples was apparent in the small tree size class (Appendix U). Other shrubs and saplings included hornbeam
(Carpinus caroliniana ), hop hornbeam ( Ostrya virginiana ), black gum ( yssa sylvatica ), sourwood ( Oxydendrum arboreum ), downy serviceberry ( Amelanchier arborea), and redbud ( Cercis canadensis ). Ground cover included greenbrier ( Smilax spp.), low bush blueberry ( Vaccinium spp.), and maple leaf viburnum ( Vibernum acerifolium ).
I was not able to collect pre harvest data, and instead used a reference treatment study design comparing recent partially harvested stands and similar unharvested forest within the same landscape. Shelterwood stands were harvested to approximately 50% stocking from 2005–2007 as part of other research and forest management in the area.
Riparian buffers approximately 30 m wide were retained along streams within harvests and areas cut ranged in size from 10–30 ha. Mature second growth stands were selected in nearby forest with generally similar characteristics, no recent management activity
(forest at RFSF had a few decaying stumps while there was no evidence of harvesting in other forests), and without immediate plans for harvesting during the study. Canopy cover in the second growth stands was ≥ 90% with some heterogeneity in forest structure 66 (Table 2.1). Shelterwood and mature forest stands were clustered within a 2–7 km area in each state forest. Stands were relatively uniform in tree species composition, age, structure, and site quality, despite reflecting internal heterogeneity such as tree fall gaps and microtopography typical for the study area. Because forest bird populations are frequently spatially autocorrelated within distances < 1 km (Lichstein et al. 2002), I examined variation within forest structure at the stand level and by forested landscape where responses were independent.
METHODS
Avian Community Composition
Line transect surveys.–Distance based methods were used to estimate avian abundance . A total of 56 line transects were established in 18 stands across 4 state forests in southern Ohio. Within each landscape 4–5 stands were surveyed with 1–5 transects per stand depending on size for a total of 6–8 transects per group in each of the state forests.
Line transects are considered to be more efficient (hence cost effective) than point counts for detecting species occurring at low or variable abundances such as some canopy songbirds (Buckland et al. 2001). Also because a larger area is surveyed than point counts, line transects may be more robust to bird movement (Buckland et al. 2001,
Buckland 2006). For bird surveys I considered line length to be important because error due to individual movement during a survey is difficult to quantify, and I used transects of the same length to maintain similar survey duration between stand types. Shelterwood harvests tended to be ≥ 300 m wide, and I used 200 m as the best line length to sample this area. Transects were ≥ 200 m apart and ≥ 50 m from an edge with flags at 20 m 67 intervals. Lines were located to maximize the number per site. Whenever possible, lines were oriented along fixed compass directions, but because of irregular edges (especially in shelterwood stands) orientation had to fit available habitat. I do not believe this resulted in sampling bias as lines sampled across habitat gradients such as ridges and ravines. Generally line placement maintained a systematic sampling approach with random start point and uniform coverage probability (Buckland et al. 2001).
Bird surveys were conducted in 2007 and 2008; THSF was not harvested until
2007 and surveys were conducted only in 2008. Each line transect was surveyed three times per season from May through mid June using unlimited distance sampling
(Buckland 2001, Buckland et al. 2004). Morning surveys were conducted during peak bird activity, generally between sunrise and 1030 am on days without inclement weather.
One experienced surveyor conducted all surveys in 2007. With additional transects in
2008 two surveyors were needed, and to control for any observer bias, one observer conducted the first visit to each transect and the other observer conducted the second and third visits. Initial training of surveyors included double observer comparisons of species detection and distance estimation using range finders. Observers walked line transects at a rate of approx 10 m min 1 (generally 20 min although surveys were not timed) recording data on all birds seen or heard to an unlimited distance including species, type of detection (singing, calling, view, or flyover in that order), estimated distance, angle from the line, and location of the observer along the line to the nearest 20 m grid flag.
The order and direction of each survey was varied among visits.
Habitat measurements.–Data describing forest structure were collected along line transects in July and August each year. For each transect a point was randomly selected 68 along 100 m sections of the line (two plots per transect per year) and plot measurements were later averaged for each transect. I used point sampling with a variable radius plot and at each plot trees (≥ 10 cm dbh) were counted using a 2.3x metric prism (10x
English). Trees were identified to species and dbh was measured to the nearest centimeter. Using dbh and the prism factor I calculated the number of trees per ha in small (10–23 cm), medium (23–38 cm) and large (>38 cm) size classes. Canopy closure was measured using a densiometer and averaged over four readings, one in each compass direction centered on the plot. Foliage hits by height class were counted on two 11.3 m perpendicular transects oriented on fixed compass directions. Percent foliage was calculated for understory (0.5–6 m), midstory (6–18 m) and overstory (>18 m) by dividing the number of hits by the maximum possible number for the stratum. Woody stems (≥10 cm in height) were counted by species within a 3 m fixed radius plot, classifying shrubs as <1.5 m and saplings as ≥ 1.5 m. Slope (angle in degrees using a clinometer) and aspect (compass angle in degrees) were recorded for each plot.
Preferences and Reproductive Success of Canopy Songbirds
Arrival surveys.– Twelve sites approximately 12 ha each were studied intensively in three forested landscapes at ZSF, VFEF, and RFSF with two shelterwood and two unharvested sites in each forest plus additional areas at VFEF as part of the Cooperative
Cerulean Warbler Silviculture Experiment (CCSE). Sites were marked with grid flags at
50 m intervals for navigation and orientation on maps. We searched the 12 intensive sites for arrival and settlement patterns of canopy nesting and other Nearctic Neotropical migrant songbirds from 2007–2009. Logistical constraints and harvesting at one site
69 prevented inclusion of RFSF in 2009. Sites were surveyed at 2–3 day intervals by 1–2 trained observers during a four week period from mid April to mid May (about 12 visits per site) to encompass the range of settlement dates for all canopy species. Differences in settlement of about a week (Remes et al. 2003, Shustack 2008) would have been captured by this schedule. Start dates were adjusted annually based on first reports of the earliest migrants in Ohio from birdwatching list servers. Sites within a given landscape were surveyed on the same day. Using methods similar to spot mapping, trained observers walked within 50 m of every point and mapped locations of any birds seen or heard relative to grid flags (Bibby et al. 1992). Territories were later identified based on observations of nests, color banded birds, counter singing and observations of pairs throughout the season. As with spot mapping, identification of territories can be somewhat subjective. The first observation of a singing bird in an area was defined as the arrival date for that territory. If a bird was not detected later in the breeding season, observations were assumed to be floaters and excluded. Several territories were excluded from analysis because no clear arrival date could be identified. Initiation dates of first nesting attempts were used in combination with arrival dates. Timing of bud break on different trees species was scored during arrival surveys.
Color banding and resighting.–Males (and some females) were captured throughout the breeding season using target mist nets and song playback at the 12 intensive study sites plus additional areas at VFEF as part of the CCSE study. Birds were aged when possible as second year or after second year individuals using wing molt limits (Mulvihill 1993, Pyle 1997), and morphological measurements and feather samples were collected. Unflattened wing chord was measured to the nearest 0.5 mm; tarsus and 70 exposed culmen were measured to the nearest 0.1 mm; mass was measured using a digital scale to the nearest 0.1 mm. Individuals were uniquely color banded and resighted throughout the breeding season. Returning individuals were resighted in subsequent years. Song playback was used along with territory searching to locate previously banded birds or determine the territory was occupied by an unbanded bird. Birds encountered during arrival surveys, nest searching and nest monitoring were checked for bands.
Whenever possible, color band combinations of returning individuals were confirmed by at least two observers.
est monitoring. –Nest searching and monitoring was conducted at the 12 intensive sites with additional areas at VFEF as part of the CCSE study. All sites were studied from 2007–2008; in 2009 half of the sites were studied. We focused on finding the first nesting attempts while birds were building and later in the season we searched for renests in the territory within a few days after a nest failed. Two thirds of nests were found during building. Nests were searched for from the earliest blue gray gnatcatchers at the end of April until the last eastern wood pewee nests at the end August; in 2009 field work was ended at the end of July. Nests were checked every 2–3 days until failure or fledging. If there was no activity, we watched for 20 min (or 40 min if the female could not be seen on the nest) and checked again subsequently. A nest was considered to have failed if it was inactive prior to the earliest possible fledging dates estimated from known initiation dates for nests found during building plus additional behavioral observations including absence of active provisioning and immediate renesting without any sign of young for nests later in the nesting cycle. Once birds were actively feeding young, 30 min provisioning observations were used to estimate age of young and count brood size. 71 Visits to the nest were recorded and prey size relative to the bill, as well as prey items, were identified when possible. I erred on the side of caution counting only nests certain to have failed. Four nests that fledged only cowbirds were considered to be nest failures.
Data Analysis
Program DISTANCE 6.0 was used to estimate avian abundance for species with > 60 detections (Buckland et al. 2001, 2004). Detection probability is modeled as a function of distance with birds farther away less likely to be detected. Variance was estimated empirically from >20 line transects per group as well as by resampling lines (Buckland et al. 2001). I used multiple covariate distance sampling (MCDS) with group (unharvested or shelterwood) and year (differences between observers) as detection covariates
(Buckland et al. 2004), and a hazard rate model with a cosine key function as the most robust model to any violations of assumptions (Buckland et al. 2001). The hazard rate model helps to deal with observer avoidance or other issues of model fit by flattening the peak of the detection curve so that all individuals can be assumed to be detected across a wider area. Observations that fell beyond the end of transects were excluded from the analysis and for all species data was truncated at 5% to remove outliers (Buckland et al.
2001). I estimated abundance as territories ha 1 using only detections by song, the most common cue for the majority of species. Several species were most commonly detected by call and for these I divided abundance estimates by two for the number of territories; all other detection types were excluded. For predators and brood parasites I used all vocalizations and report the number of individuals. Examination of model fit using χ 2 goodness of fit tests (Buckland et al. 2001) showed models did not fit well for nine
72 species, including scarlet tanagers and eastern wood pewees. Several species showed detection peaks up to 50 m from the line possibly related to observer avoidance. Poor model fit may also be related to the probability that a bird vocalized during the survey
(Farnsworth and Simons 2002) while singing males can easily be detected up to 100 m.
For further analysis I output density per transect per year (corrected for detection probability).
I used CANOCO 4.5 to examine associations between avian abundance and habitat characteristics. This multivariate approach permitted consideration of multiple bird species in relation to multiple correlated habitat variables. A constrained ordination approach was used to examine the response of the bird community (species matrix) to changes in forest structure associated with shelterwood harvesting (environmental matrix) (Leps and Smilauer 2003). Only common species included in the DISTANCE analysis were included in the species matrix and I used the output per transect.
Ecologically meaningful variables representing forest structure were selected as the environment matrix. Because an initial Detrended Canonical Correspondence Analysis
(DCCA) showed a short gradient < 3, I used Redundancy Analysis (RDA) with a linear relationship (Leps and Smilauer 2003). I tested significance of the ordination axes using
Monte Carlo permutation tests.
I used the nest survival model in Program MARK 5.0 to estimate daily survival rates (DSR) and standard errors (SE) for each species in unharvested and shelterwood stands; this program applies maximum likelihood methods and considers exposures days
(Mayfield 1975). For the analysis I used year and site as covariates. I estimated nesting success by raising DSR to the power of the total length of the nesting cycle for each 73 species (Mayfield 1975). I excluded laying days because it was not always possible to observe activity at the nest during this period. Based on our data I used an incubation period of 12 days for all species except for yellow throated vireos, which had a 13 day incubation period. I used a nestling period of 9 days for scarlet tanagers, 11 days for cerulean warblers, 12 days for blue gray gnatcatchers, and 17 days for eastern wood pewees. Program CONTRAST 2.0 (Hines and Sauer 2002) with a χ 2 based test was used to compare stand types. Analyses were conducted both for individual species and for guilds. The guild concept has been applied in studies of nesting success (e.g. Rodewald and Yahner 2001, Knutson et al. 2004), which are labor intensive and either tend to monitor nests of many species with limited sample size or focus on one or a few species of conservation concern because of the limitations on data collection; both can be useful but problematic if species respond in different ways depending on their ecology and behavior.
Program R 2.1 (R Development Core Team 2009) was used for all other statistical analysis. Box plots and residual plots were examined for normality and homogeneity of variance. For abundance estimates I used mixed effects models with the nlme package
(Pinheiro et al. 2009) and restricted maximum likelihood methods (REML) (Zur et al.
2009). Group was the fixed effect of interest and I used a nested design with random effects including landscape, stand, transect and year, allowing for correlation within landscapes and stands and repeat surveys of line transects each year. For shrub nesting species, I examined effects of harvest age using HSD Tukey post hoc tests. Fisher’s Exact tests were used for small or unequal sample sizes to test differences in age distributions and site fidelity. I used a two way ANOVA to test differences in nest placement between 74 unharvested and shelterwood stands. A nonparametric Wilcox test was to test for differences in brood size. Statistical results were considered significant at P ≤ 0.05.
RESULTS
Avian Community Composition
Abundance estimates.–Over two years 8,838 birds of 87 species were detected on line transect surveys and abundance was estimated for 24 breeding species with > 60 detections (Table 2.2). Abundance of the canopy nesting guild as a whole was 46% higher in shelterwood stands compared to unharvested reference second growth forest.
For common species the scarlet tanager and eastern wood pewee, abundance was 31–
42% higher while for less common species the blue gray gnatcatcher and yellow throated vireo, abundance was 77–98% in shelterwood harvests compared to reference stands
(Table 2.2). Abundance of cerulean warblers was highly variable among stands with only a few territories at RFSF. Although abundance of ceruleans was >200% higher in shelterwoods at ZSF compared to unharvested reference stands (Figure 2.3), overall abundance was not consistently higher in shelterwood stands (Table 2.2). Differences may have been related to slope and aspect as ceruleans were positively associated with northeast facing slopes. When controlling for slope and aspect abundance of cerulean warblers was negatively associated with basal area (Table 2.3).
In contrast, late successional midstory and ground nesting species were negatively related to changes in forest structure associated with shelterwood harvesting.
Midstory removal and regeneration with canopy openness resulted in 33% and 46% lower abundance respectively for these groups in shelterwood harvests compared to 75 reference stands. At the level of individual species, red eyed vireos ( Vireo olivaceus ), wood thrush ( Hylocichla mustelina ), and worm eating warblers ( Helmitheros vermivorum ) were 26–38% less abundant while ovenbirds ( Seiurus aurocapilla ) and
Acadian flycatchers ( Empidonax virescens ) were 67% less abundant in shelterwoods compared to reference stands (Table 2.2). Although abundance of black and white warblers ( Mniotilta varia ) was 60% higher in stands one year post harvesting compared to reference mature forest ( t40 = 2.636, P = 0.011), overall abundance was not significantly different between stand types for this species and the American redstart
(Setophaga ruticilla ) (Table 2.2). Perhaps because similar numbers of snags remained in harvest areas, abundance of cavity nesting species also did not differ between shelterwood and unharvested stands (Table 2.2).
Shrub nesting species were all positively associated with dense shrub and sapling regeneration that occurred post disturbance after opening of the forest canopy, and overall abundance was 155% higher in shelterwood compared to unharvested stands. A common species in late successional forest at our upland sites, the hooded warbler
(Wilsonia citrina ) was 26% more abundant in shelterwoods (Table 2.2) and tended to increase two ( t40 = 2.242, P = 0.030) and three years ( t40 = 1.702, P = 0.096) post harvesting compared to reference stands. Abundance of other shrub species was >100% higher in partially harvested compared to unharvested stands. Although present in reference stands, abundance of eastern towhees ( Pipilo erythrophthalmus ) was 300% higher in shelterwoods three years post harvesting ( t40 = 6.140, P = <0.001). Kentucky warblers ( Oporornis formosus ), indigo buntings ( Passerina cyanea ), and prairie warblers
(Dendroica discolor ) all began breeding in shelterwood stands two and three years post 76 harvesting (all P values >0.001). Occupying a range of nest sites, the Carolina wren
(Thryothorus ludovicianus ) was 300% more abundant in shelterwood compared to reference stands one year post harvest ( t40 = 4.527, P = <0.001), but by three years post harvesting abundance was similar to mature forest levels ( t40 = 0.209, P = 0.835). Other less common species associated with shrubs were also more numerous in shelterwoods
(Appendix E) including the yellow breasted chat ( Icteria virens ), blue winged warbler
(Vermivora pinus ), common yellowthroat ( Geothlypis trichas ), and northern cardinal
(Cardinalis cardinalis ). Less common generalist or open canopy species moved into and were confirmed nesting in shelterwood stands, including mourning dove ( Zenaida macroura ), Baltimore oriole ( Icterus galbula ), cedar waxing ( Bombycilla cedrorum ), and chipping sparrow ( Spizella passerina ). Controlling for landscape effects between shelterwood and reference stands with the study design, I found no difference in abundance of common diurnal avian predators, the blue jay ( Cyanocitta cristata ) and
American crow ( Corvus brachyrhynchos ). Abundance of a brood parasite, the brown headed cowbird ( Molothrus ater ), was > 100% higher in shelterwood than unharvested stands at all forests.
Preferences and Reproductive Success of Canopy Songbirds
Territory settlement.–Birds arrived on territory and initiated their first nesting attempt over a 2–3 week period. Initially males appeared to spend a couple days in the territory before actively singing. Generally females arrived a few days after males, although both blue gray gnatcatchers and yellow throated vireos were sometimes paired when first observed; males and females of these species are known to arrive at the same
77 time (Ellison 1992, Rodewald and James 1996). Nest building began a few days to more than a week after the male first arrived on the territory. Settlement patterns were generally similar between unharvested and shelterwood stands (Figure 2.1). First arrival dates varied among years, and after a late frost in 2007 early species such as the blue gray gnatcatcher and yellow throated vireo arrived > 5 days later than in 2008 when there was warm spring weather with earlier emergence. Temperature differences tended to disappear by May and first arrival dates for pewees were similar between years.
Settlement was generally similar among forests (Figure 2.1).
Age distributions and site fidelity. A total of 318 adult birds of four canopy nesting species were color banded with 39–138 individuals per species; blue gray gnatcatchers did not respond to either song or call playback, and we were unable to capture this species. The majority of individuals captured were males, and we only captured male yellow throated vireos. Of the three other species 36 females with 7–16 females per species plus 10 cerulean warbler fledglings were captured. Males and females were pooled in the analysis due to small sample size. A total of 63 individuals were resighted in one or more subsequent years. Return rates were low < 30% and across all species return rates of second years males was 16% compared to 30% for after second year males. Birds were re sighted in 2009 that were not seen in 2008 for three species, and annual survival may be higher when including detection probability.
Returning birds were considered experienced breeders in age distributions for a total of
394 birds of known age pooled across years. There were > 2x as many first time breeders in shelterwood harvests for both cerulean warblers and scarlet tanagers, and a similar pattern for the canopy guild overall (Table 2.4). Site fidelity was similar in unharvested 78 and shelterwood stands for 74 returning individuals (Table 2.4), although for three species half of the birds changed territories between years, sometimes moving > 400 m.
Site fidelity for male eastern wood pewees was 100%, and only one female was found in a nearby territory.
Reproductive success. Over three years a total of 722 nests of the five canopy species were monitored with 75–236 nests per species. I calculated daily survival rates
(DSR) using the nest survival model in Program MARK 5.0 and compared shelterwood and reference second growth stands using Program CONTRAST 2.0. Although DSR varied among species, nesting success was similar between shelterwood and reference stands for all species and the canopy nesting guild (Table 2.5). Eastern wood pewees were the most successful despite having a nesting cycle up to one week longer than the other study species.
Nest placement changed with shelterwood harvesting and across the canopy guild nests averaged >1 m higher in harvest areas and were more concealed by leaves (Table
2.6). Chicks were counted at a total of 212 nests. Although parasitism was difficult to detect for high nests, only 2% of nests in which chicks could be identified contained cowbirds. Mean brood size ranged from 2.2 ± 0.1 SE for eastern wood pewees ( n = 104),
2.4 ± 0.1 SE for scarlet tanagers ( n = 27), cerulean warblers ( n = 40), and yellow throated vireos ( n = 19) to 2.8 ± 0.2 SE for blue gray gnatcatchers ( n = 22). For cerulean warblers mean brood size was larger in mature forest at 2.6 ± 0.1 SE ( n = 11) compared to 2.0 ±
0.2 SE in shelterwoods ( n = 29) ( W = 227, P = 0.019), whereas for scarlet tanagers mean brood size tended to be larger in shelterwoods at 2.7 ± 0.2 SE ( n = 9) compared to 2.3 ±
0.1 SE in mature forest ( n = 18) ( W = 50 P = 0.061); however sample sizes in harvest 79 areas were small. There was no difference in brood size for other canopy species (all P values > 0.10).
DISCUSSIO
Compared to mature forest stands, bird communities in shelterwood harvests were dominated by shrub and canopy nesting species, and generally had lower numbers of midstory and ground nesting species. For canopy nesting species, I found no strong preferences for an open forest canopy created through partial harvesting. However, harvesting did not appear to negatively affect this group of late successional forest songbirds, and I found no evidence of demographic consequences from harvesting. Thus, results from this research suggest that while partial harvesting does not necessarily improve habitat for canopy nesting species, shelterwoods can provide suitable breeding habitat in the short term.
In southern Ohio changes in the bird community associated with shelterwood harvesting were generally consistent with studies of partial harvesting in other regions
(Table 2.7). Generally shrub nesters respond most positively increasing several years post harvesting with shrub and sapling regeneration after opening of the forest canopy; however, abundance may still be lower than in clearcuts (Annand and Thompson 1997,
McDermott and Wood 2009). Negative responses of midstory and ground nesting species may be less consistent depending on the level of midstory removal and foraging behavior of ground nesting species (Table 2.7). Species that respond negatively to harvesting oftentimes show a 25–50% reduction in abundance with moderate levels of tree removal
(Vanderwel et al. 2007). Some declines may be gradual while other species exhibit a
80 threshold occurrence in response to the level of harvesting (Guénette and Villard 2005).
Similar to our study, responses of cavity nesters have been limited or inconsistent presumably dependent upon the number of snags retained post harvesting (Table 2.7).
Not surprisingly, as vegetation regenerates and succession proceeds, avian community responses to initial harvesting tend to attenuate (Campbell et al. 2007, Norris et al. 2008,
McDermott and Wood 2009).
In this study canopy species showed a weak positive association with partial harvesting, and four species were generally more abundant in shelterwood harvests compared to reference mature forest. Variation in cerulean warbler abundance appeared related to slope and aspect with a strong response to partial harvesting in only one of four forests. Others have found similar limited or variable short term responses of canopy songbirds to partial harvesting (Table 2.7). Weak and variable responses suggest other factors such as topography, existing forest structure or floristics mediate the response of canopy songbirds to harvesting. Further work is needed to examine more complex interactions of partial harvesting with other attributes of the forest landscape.
Interactions among slope and canopy openness suggest a possible common feature for Cerulean Warblers and perhaps other canopy species. Although difficult to quantify, from a bird’s perspective canopy openness may represent sunlight reaching the tree crown, not sunlight reaching the forest floor as typically measured by researchers. A similar effect of sunlight on the tree crown would be created by slopes stratifying trees, or possibly by a diversity of tree sizes allowing sunlight to reach crowns of the dominant trees. One hypothesis, primary association of Cerulean Warblers with northeast facing slopes in this and other studies could be selection for morning sunlight reaching the 81 crown of trees. Secondary associations with partial harvesting could be the same factor, but on a reduced number of trees. Presumably this would in some way be related to prey resources. Herbivorous insects feeding on plants with direct sunlight may have increased growth rates (Scriber and Slansky 1981) while temperature can affect caterpillar abundance (Reynolds et al. 2007).
Despite annual and interspecific variation in arrival dates in this study, there were no consistent differences in settlement patterns or nest initiation dates between shelterwood and unharvested stands. Birds moved territories between years and return rates were low, but similar site fidelity suggests that settlement patterns were not driven by stand type. The finding of greater numbers of first time breeders in shelterwoods compared to mature forest for two species found could suggest lower preference.
However, differences in age distributions in combination with higher abundance in recent harvests suggests an initial post disturbance effect of newly created (or improved) habitat available to young birds. Earlier arrival and territory settlement (or nest initiation dates for resident species) are reported in preferred habitat in several studies of forest birds
(Remes 2003, Rodewald and Shustack 2008, Mulvihill et al. 2009, Shustack and
Rodewald 2010). In my study system, the same territories tended to be settled first each year while several stands were consistently settled later suggesting preferences unrelated to harvesting. For several bird species earlier settlement was associated with earlier emergence of exotic plants among other possible reasons (Remes 2003, Rodewald and
Shustack 2008, Shustack and Rodewald 2010). At our study sites leaf emergence differed among tree species with oaks leafing out later than yellow poplar and maples, and also
82 among years with trees leafing out earlier in 2008 during warm spring weather, but there were no apparent differences in emergence with stand type.
Controlling for the landscape context, nesting success of canopy songbirds was similar in shelterwood and unharvested stands. Similar abundance of diurnal avian predators in the two stand types could explain absence of any effect of partial harvesting on nest survival. Changes in the landscape context surrounding harvests could produce different results as the landscape context can alter predator communities and affect nest success (Donovan et al. 1997, Rodewald and Yahner 2002). In addition, although results suggest that reproductive success of canopy songbirds is not strongly affected by shelterwood harvesting, in this system any effect would have been difficult to detect because of low success rates. In Tennessee where nest success was high, success was
20% higher for overstory species in thinned stands compared to control stands (Thatcher
2007). Nest success was also positively associated with canopy openness in unharvested forest (Bakermans and Rodewald 2009), although in the same study region I found no apparent relationship between success and canopy openness as created by shelterwood harvesting. A number of studies have found limited effects of partial harvesting on nesting success (Duguay et al. 2001, Robinson and Robinson 2001, Gram et al. 2003,
Smith et al. 2006, Thatcher 2007). Others, including this study, have found high numbers of cowbirds in partial harvests (Table 2.7), and parasitism rates have been linked to partial harvesting elsewhere (Thatcher 2007, Robinson and Robinson 2001, but see
Duguay et al. 2001, Gram et al. 2003, Smith et al. 2006). Although few cases of parasitism of canopy nests were observed in this study, high numbers of cowbirds in shelterwoods could pose a threat to other bird species breeding in shelterwood stands. 83 The effect of higher numbers of cowbirds on groups such as shrub nesters warrants additional study.
MA AGEME T IMPLICATIO S
From the perspective of bird conservation, partial harvests can provide habitat for a mix of species as part of a balance of disturbance levels on the landscape. This study supports that in the short term partial harvesting negatively affects midstory and some ground nesting late successional forest species, but benefits shrub nesting species. Results suggest shelterwood harvests can provide at least short term breeding habitat suitable for canopy nesting songbirds, including the severely declining cerulean warbler. However, northeast facing slopes already occupied by cerulean warblers should be protected. In areas lacking steep slopes, creation of canopy gaps could benefit ceruleans, but further work is needed. Managers should carefully consider the long term management of shelterwoods. Shelterwood harvesting is one part of a multi staged technique, and the complete removal of canopy trees later in the cutting cycle will initially result in almost complete species turn over from late to early successional songbirds (Annand and
Thompson 1997, Brawn et al. 2001, Lanham et al. 2002). Management decisions need to consider the importance of oak regeneration while maintaining the structural complexity of both open and closed canopy forest on the landscape.
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92 Table 2.1
Shelterwood harvests and unharvested upland mixed oak forest surveyed in southern Ohio, 2007–2008. Shelterwoods were 1–3 years
post harvesting. Means (± SE) are for random plots on line transect surveys.
Location (forest 10 km radius) Group Woody Basal area Canopy
Latitude/Longitude (transects, stands) Slope stems ha 1 (m 2 ha 1) closure (%) n
Zaleski State Forest (83%) Unharvested (8,3) 19 ± 2 4,125 ± 841 24.4 ± 1.3 94 ± 1 32
82° 18’ / 39° 19' Shelterwood (8,2) 13 ± 1 13,241 ± 3,301 11.6 ± 0.7 46 ± 4 32 93 Vinton Furnace Experimental Forest (75%) Unharvested (8,2) 19 ± 2 5,862 ± 1,190 25.1 ± 1.1 92 ± 1 32
82° 22’ / 39° 11' Shelterwood (8,3) 15 ± 2 3,590 ± 521 9.2 ± 0.7 45 ± 4 30
Richland Furnace State Forest (77%) Unharvested (6,2) 19 ± 2 4,409 ± 642 23.2 ± 1.1 94 ± 1 24
82° 36’ / 39° 10' Shelterwood (6,2) 17 ± 2 11,531 ± 1,754 9.6 ± 0.7 40 ± 6 24
Tar Hollow State Forest 1 (83%) Unharvested (6,2) 16 ± 1 7,196 ± 1,303 33.0 ± 2.4 95 ± 1 12
82° 45’ / 39° 21' Shelterwood (6,2) 15 ± 2 7,520 ± 305 16.5 ± 3.2 44 ± 9 12
1harvested in 2007 and only line transect surveys in 2008.
93 Table 2.2
Short term changes in the bird community in recent partial harvests with 50% stocking (shelterwoods) compared to reference
unharvested forest from line transect surveys ( n = 56 in 18 stands at 4 state forests) in southern Ohio, 2007–2008. Mean abundance
(± SE) was calculated using Program DISTANCE 6.0. Significance from mixed effects models in Program R using the nlme package.
Species Code n Unharvested Shelterwood F1,13 P
1
94 Breeding territories ha
Scarlet tanager ( Piranga olivacea ) SCTA 244 0.24 ± 0.02 0.31 ± 0.03 4.980 0.043
Eastern wood pewee ( Contopus virens ) EAWP 189 0.13 ± 0.02 0.19 ± 0.02 4.710 0.049
Cerulean warbler ( Dendroica cerulea ) CERW 104 0.11 ± 0.03 0.15 ± 0.04 0.711 0.414
Blue gray gnatcatcher ( Polioptila caerulea )1 BGGN 104 0.06 ± 0.01 0.11 ± 0.02 4.707 0.049
Yellow throated vireo ( Vireo flavifrons ) YTVI 73 0.06 ± 0.02 0.11 ± 0.02 5.705 0.032
Canopy nesting 711 0.66 ± 0.05 0.96 ± 0.07 6.336 0.025
continued
94 Tables 2.2 (continued)
Red eyed vireo ( Vireo olivaceus ) REVI 496 0.75 ± 0.04 0.56 ± 0.04 11.826 0.004
Wood thrush ( Hylocichla mustelina ) WOTH 268 0.33 ± 0.03 0.21 ± 0.02 11.794 0.004
American redstart ( Setophaga ruticilla ) AMRE 71 0.09 ± 0.03 0.12 ± 0.03 0.031 0.861
Acadian flycatcher ( Empidonax virescens )1 ACFL 96 0.10 ± 0.01 0.03 ± 0.01 14.434 0.002
Midstory nesting 930 1.41 ± 0.04 0.94 ± 0.05 20.436 <0.001
Hooded warbler ( Wilsonia citrina ) HOWA 367 0.44 ± 0.04 0.55 ± 0.04 2.992 0.107
Eastern towhee ( Pipilo erythrophthalmus ) EATO 114 0.10 ± 0.02 0.23 ± 0.03 17.813 0.001 95 Carolina wren ( Thryothorus ludovicianus ) CARW 69 0.04 ± 0.02 0.11 ± 0.02 8.153 0.013
Kentucky warbler ( Oporornis formosus ) KEWA 62 0.01 ± 0.01 0.14 ± 0.03 15.867 0.001
Indigo bunting ( Passerina cyanea ) INBU 91 0.00 ± 0.00 0.24 ± 0.04 47.621 <0.001
Prairie warbler ( Dendroica discolor ) PRAW 92 0.00 ± 0.00 0.21 ± 0.04 12.442 0.003
Shrub nesting 795 0.57 ± 0.05 1.44 ± 0.11 32.646 <0.001
Ovenbird ( Seiurus aurocapillus ) OVEN 420 0.81 ± 0.05 0.27 ± 0.03 45.954 <0.001
continued
95 Table 2.2 (continued) Black and white warbler ( Mniotilta varia ) BAWW 178 0.23 ± 0.03 0.28 ± 0.03 1.255 0.282
Worm eating warbler ( Helmitheros vermivorum ) WEWA 130 0.22 ± 0.03 0.14 ± 0.02 5.025 0.043
Ground nesting 728 1.29 ± 0.06 0.69 ± 0.06 23.845 <0.001
Eastern tufted titmouse ( Baeolophus bicolor ) TUTI 60 0.07 ± 0.01 0.08 ± 0.02 0.048 0.830
White breasted nuthatch ( Sitta carolinensis )1 WBNU 64 0.04 ± 0.01 0.04 ± 0.01 0.012 0.913
Red bellied woodpecker ( Melanerpes carolinus )1 RBWO 77 0.03 ± 0.01 0.04 ± 0.01 1.149 0.303
Cavity nesting 200 0.2 ± 0.02 0.23 ± 0.03 0.432 0.522 96
Predators and brood parasites individuals ha 1
Brown headed cowbird ( Molothrus ater ) BHCO 154 0.14 ± 0.02 0.33 ± 0.03 14.619 0.002
Blue jay ( Cyanocitta cristata ) BLJA 142 0.13 ± 0.02 0.14 ± 0.02 0.031 0.862
American crow ( Corvus brachyrhynchos ) AMCR 63 0.03 ± 0.01 0.04 ± 0.01 1.059 0.322
Avian predators 204 0.17 ± 0.02 0.18 ± 0.03 0.234 0.636
1 species for which calls were used; density was divided by two for number of territories.
96
Table 2.3
Abundance of Cerulean Warblers was negatively associated with basal area when controlling for slope and aspect on line transect surveys in southern Ohio, 2007–2008 (n
= 56 in 18 stands at 4 state forests). Significance from mixed effects models in Program
R using the nlme package..
Parameter Estimate SE t35 P
Intercept 0.255 0.130 1.957 0.057
Basal area (m 2 ha 1) 0.009 0.004 2.185 0.036
Slope (degrees) 0.010 0.004 2.604 0.013
Aspect (SW to NE) 0.184 0.046 3.983 <0.001
97
Table 2.4
Age distributions and site fidelity of color banded birds in southern Ohio, 2007–2009 (12 stands in 3 state forests). Shelterwood stands had a higher percentage of second year cerulean warblers and scarlet tanagers, but site fidelity was not related to partial harvesting for any species. Significance from Fisher’s Exact tests.
Species Unharvested Shelterwood P
Percent second year birds
Scarlet tanager 18% (9/49) 43% (15/35) 0.026
Eastern wood pewee 18% (10/56) 26% (12/47) 0.470
Cerulean warbler 16% (14/90) 35% (21/60) 0.010
Yellow throated vireo 34% (11/32) 26% (5/19) 0.756
Canopy nesting 19% (44/227) 33% (53/161) 0.003
Percent site fidelity
Scarlet tanager 50% (4/8) 50% (2/4) 1.000
Eastern wood pewee 94% (17/18) 100% (9/9) 1.000
Cerulean warbler 62% (8/13) 44% (4/9) 0.727
Yellow throated vireo 56% (5/9) 50% (2/4) 1.000
Canopy nesting 71% (34/48) 65% (17/26) 0.850
98 Table 2.5
Daily survival rates (DSR ± SE) of nests for a guild of five canopy songbirds in unharvested and shelterwood stands in southern Ohio,
2007–2009 (12 stands in 3 state forests). Nesting success did not change with harvesting but differed among species with eastern
wood pewees nearly twice as successful as cerulean warblers and yellow throated vireos. DSR calculated using Program MARK 5.0
and significance from χ 2 tests using Program CONTRAST 2.0.
Unharvested Shelterwood
1 2
99 Species n DSR Success n DSR Success χ P
Scarlet tanager 99 0.942 ± 0.009 28% 74 0.939 ± 0.008 27% 0.062 0.803
Eastern wood pewee 127 0.969 ± 0.005 40% 109 0.963 ± 0.004 34% 0.878 0.349
Cerulean warbler 90 0.929 ± 0.013 18% 43 0.932 ± 0.008 20% 0.038 0.844
Blue gray gnatcatcher 57 0.954 ± 0.013 32% 48 0.954 ± 0.006 32% 0.000 0.999
Yellow throated vireo 39 0.930 ± 0.013 15% 36 0.928 ± 0.009 14% 0.016 0.899
Canopy nesting 412 0.953 ± 0.004 35% 310 0.951 ± 0.003 33% 0.160 0.689
1success was calculated using a nest phase length of 21, 29, 23, 24, and 26 days for each species based on our data.
99
Table 2.6
Canopy species nested higher in sites more concealed by leaves in shelterwood stands than in unharvested mature forest in southern
Ohio, 2007–2009 (14 stands at 3 state forests). Cerulean warblers and blue gray gnatcatchers nested higher than scarlet tanagers and
eastern wood pewees. Cerulean warblers and scarlet tanagers nested in sites more concealed by leaves than blue gray gnatcatchers and
yellow throated vireos which were more concealed by leaves than pewees. Significance from two tailed t tests.
Unharvested Shelterwood P
100 Species n Hgt (m) Leaves n Hgt (m) Leaves Hgt Leaves
Scarlet tanager 99 17.7 ± 0.5 5.6 ± 0.4 74 19.0 ± 0.6 6.9 ± 0.5 0.106 0.029
Eastern wood pewee 127 17.3 ± 0.4 1.0 ± 0.2 109 18.7 ± 0.4 1.0 ± 0.1 0.019 0.861
Cerulean warbler 90 19.8 ± 0.5 5.1 ± 0.3 43 20.1 ± 0.7 6.7 ± 0.6 0.740 0.013
Blue gray gnatcatcher 57 19.5 ± 0.7 3.2 ± 0.4 48 21.7 ± 0.7 4.5 ± 0.7 0.027 0.107
Yellow throated vireo 39 18.6 ± 0.9 3.1 ± 0.5 36 20.6 ± 0.8 4.9 ± 0.7 0.088 0.036
Canopy nesting 412 18.4 ± 0.3 3.5 ± 0.2 310 19.7 ± 0.3 4.2 ± 0.2 0.000 0.021
100 Table 2.7 Summary of species responses by nesting guild to different types of recent partial harvesting from a review of other studies. Shrub
nesting species showed strong positive responses while midstory nesting and one ground nesting species, the ovenbird, showed
consistent negative responses to partial harvesting. Eastern wood pewees showed a positive response in almost all studies, while other
canopy species showed less consistent responses.
Canopy Midstory Shrub Ground Cavity Predators
Study WEWA TUTI WB U RBWO BHCO BLJA AMCR SCTA SCTA EAWP CERW BGG YTVI REVI WOTH AMRE ACFL HOWA EATO CARW KEWA I BU PRAW OVE BAWW 101 Annand & Thompson(1997) = = + = = + + + + = = = = = + = = Baker & Lacki (1997) + + + Rodewald & Smith (1998) = + = = = = = = = + = + = = = Robinson & Robinson (1999) = + + + = = + + + + = = = = + + King & DeGraaf (2000) + = = = = = + = = Gram et al. (2003) = = + + + Hanowski et al. (2003) continued
101 Table 2.7 (continued)
Jobes et al. (2004) + = = + Guénette & Villard (2005) = + + + = = Heltzel &Leberg (2006) + = = = + + = + + = = + + = = Campbell et al. (2007) = + = = + Thatcher (2007) + + + + + = = Norris et al. (2008) + + + + + + + + + + + Register & Islam (2008) = 102 Goodale et al. (2009) = = = + + = = = = = This study + + = + + = + + + + + + = = = = + = =
102
12 Unharvested Scarlet tanager 10 Shelterwood
8
6
4 Territoriessettled
2
0 8 May 2 May 2 May 5 May 2 May 5 May 17 Apr 20 Apr 23 Apr 26 Apr 29 Apr 12 Apr 17 Apr 20 Apr 23 Apr 26 Apr 20 Apr 23 Apr 26 Apr 29 Apr 17 Apr 20 Apr 23 Apr 26 Apr 29 Apr 20 Apr 23 Apr 26 Apr 20 Apr 23 Apr 26 Apr 29 Apr 14 Apr 17 Apr 20 Apr 23 Apr 26 Apr 20 Apr 23 Apr 26 Apr 29 Apr 2007 2008 2009 2007 2008 2009 2007 2008 ZSF VFEF RFSF continued 103 Figure 2.1
Frequency distributions of territory settlement by date for canopy songbirds in southern Ohio, 2007–2009 (12 stands at 3 state forests). Settlement patterns did not differ with partial harvesting, but first arrival dates varied among years with some species arriving as much as six days earlier with warm spring weather and earlier leaf emergence in 2008.
103 Figure 2.1 (continued)
7 Unharvested Eastern wood pewee 6 Shelterwood 5
4
3
Territoriessettled 2
1
0 2 May 5 May 8 May 5 May 8 May 2 May 8 May 2 May 5 May 8 May 2 May 5 May 8 May 2 May 5 May 8 May 2 May 5 May 8 May 2 May 5 May 8 May 29 Apr 26 Apr 29 Apr 29 Apr 29 Apr 29 Apr 29 Apr 11 May 14 May 11 May 14 May 11 May 14 May 2007 2008 2009 2007 2008 2009 2007 2008 ZSF VFEF RFSF
104 7 Unharvested Cerulean warbler 6 Shelterwood 5
4
3
Territoriessettled 2
1
0 8 May 2 May 2 May 5 May 8 May 2 May 8 May 5 May 8 May 23 Apr 26 Apr 20 Apr 23 Apr 26 Apr 20 Apr 23 Apr 26 Apr 29 Apr 20 Apr 23 Apr 26 Apr 17 Apr 20 Apr 23 Apr 29 Apr 23 Apr 26 Apr 29 Apr 29 Apr 23 Apr 2007 2008 2009 2007 2008 2009 2007 2008 ZSF VFEF RFSF continued
104 Figure 2.1 (continued)
7 Unharvested Blue gray gnatcatcher 6 Shelterwood
5
4
3
Territoriessettled 2
1
0 20 Apr 23 Apr 26 Apr 5 May 14 Apr 17 Apr 20 Apr 14 Apr 17 Apr 20 Apr 23 Apr 12 Apr 20 Apr 23 Apr 29 Apr 17 Apr 20 Apr 12 Apr 17 Apr 23 Apr 23 Apr 8 May 14 Apr 17 Apr 20 Apr 23 Apr 26 Apr 29 Apr
2007 2008 2009 2007 2008 2009 2007 2008
105 ZSF VFEF RFSF 7 Unharvested Yellow throated vireo 6 Shelterwood 5
4
3
Territoriessettled 2
1
0 5 May 2 May 5 May 2 May 2 May 2 May 23 Apr 29 Apr 14 Apr 17 Apr 20 Apr 23 Apr 26 Apr 20 Apr 23 Apr 26 Apr 20 Apr 23 Apr 14 Apr 17 Apr 20 Apr 23 Apr 26 Apr 29 Apr 17 Apr 23 Apr 23 Apr 26 Apr 17 Apr 20 Apr 23 Apr 29 Apr 2007 2008 2009 2007 2008 2009 2007 2008 ZSF VFEF RFSF
105 106
Figure 2.2 RDA bi plot of the bird community and forest structure variables from line transect surveys in southern Ohio, 2007–2008 ( n = 56 in
18 stands at 4 state forests). The primary axis represents a gradient from closed canopy forest to an open canopy with shrub
regeneration in shelterwoods (see Table 2.2 for species codes).
106 0.5 a.) Scarlet tanager 1 0.4 0.3
Territories ha Territories 0.2 0.1 0.0
0.5 b.) Eastern wood pewee 1 0.4 0.3
Territories ha Territories 0.2 0.1 0.0
0.5 c.) Cerulean warbler 1 0.4 0.3
Territories ha Territories 0.2 0.1 0.0
0.5 d.) Blue gray gnatcatcher 1 0.4 0.3
Territories ha Territories 0.2 0.1 0.0
0.5 e.) Yellow throated vireo 1 Unharvested 0.4 Shelterwood 0.3
Territories ha Territories 0.2 0.1 0.0 ZSF VFEF RFSF THSF Figure 2.3 Abundance of canopy songbirds in 4 state forests in southern Ohio, 2007–2008. Cerulean warblers were more abundant in shelterwood stands at ZSF, but abundance varied at other forests. Means for 6–8 line transects per forest; error bars indicate standard error.
107
CHAPTER 3
ROLE OF TOPOGRAPY, CANOPY STRUCTURE, AND FLORISTICS IN NEST
SITE SELECTION AND NESTING SUCCESS OF CANOPY SONGBIRDS
Running head: Canopy songbird nest site selection and nesting success
ABSTRACT During presettlement times, many eastern deciduous forests in North
America are thought to have been open park like woodlands rather than the closed canopy, even aged forests encountered today. As such, agencies have begun to apply a variety of silvicultural practices, including partial harvesting, to simulate historic disturbance regimes and, thereby, restore a more open forest structure. However, effective forest restoration requires a better understanding of specific habitat requirements for plant and animal species. The knowledge gap is especially large for canopy songbirds, which have been the focus of few studies. From 2007–2009 my research examined nest site selection and nesting success of a guild of five sensitive canopy songbirds in upland mixed oak forests in southern Ohio, USA. Over 700 nests were monitored at 12 sites in three state forests with half in open canopy stands created through partial harvesting (shelterwoods with 50% stocking) and half in closed canopy mature forest. Habitat attributes, including topography, canopy structure, and floristics, were measured at nest sites and random plots ≤ 100 m from nests representing habitat
108 available within the territory. The best ranked models indicate that canopy structure was important in nest site selection, as canopy openness or tree size was among the top models for all species. Cerulean Warblers ( Dendroica cerulea ) especially favored northeast facing slopes (315–135 degrees). Of the five focal species, four species selected white oak ( Quercus alba ) as the nest substrate twice as much as available at random, and three species avoided red oaks ( Quercus rubra ). Daily survival rates of nests were negatively associated with red oaks for two species and across the entire canopy nesting guild. Canopy openness and tree size also explained nest survival for Cerulean Warblers while predation was higher late in the nesting cycle when adults were feeding young.
Concealmen and size of the support branch were associated with success for Scarlet
Tanagers ( Piranga olivacea ) while Eastern Wood pewee ( Contopus virens ) were more successful late in the season. Results of this study suggest that canopy songbirds are sensitive to forest structure and seem to favor open canopies with fewer medium sized trees and white oaks.
Keywords canopy structure, forest, oak, shelterwood, nest site selection, nesting success, Scarlet
Tanager, Eastern Wood pewee, Cerulean Warbler, Blue gray Gnatcatcher, Yellow throated Vireo
109 1. Introduction
Because deforestation remains a global threat to forests around the world, the dominant paradigm in forest conservation has been to protect and retain forest cover.
Although this strategy is one essential component of effective forest conservation, it fails to explicitly recognize that quantity does not necessarily equal quality. An excellent example of this disconnect between quantity and quality of forest occurs in the central hardwood region of eastern North America where <1% of the original old growth forest that existed prior to European settlement remains (Parker 1989). During European settlement this region was largely cleared for agriculture or industrial uses such as the charcoal industry (Williams 1992). The shift from an agrarian based society allowed some forested areas to regenerate, increasing forest cover in states such as Ohio from a low of 12% in the 1940s to a current estimate of 30% (ODNR 2007). Most of these current forests are even aged, mature second growth (Smith et al. 2004). Because trees are generally within a single age class, the canopy remains closed (≥90%).
Second growth forests of today may not be representative of presettlement forests, which were described by early explorers as open park like woodlands (Bartram
1791, Denevan 1992, Bonnicksen 2000). Evidence from tree rings suggests that openings in the forest canopy may have competitively released trees and stimulated growth every
20–30 years in presettlement forest ecosystems (Abrams et al. 1995). Canopy openings are generally created by disturbance which is an integral part of forest ecosystems
(Pickett and White 1985). The type, intensity, and extent of the disturbance affect the structure of the forest that develops. Oaks ( Quercus spp.) are thought to be maintained by
110 disturbance regimes that include regular low intensity wildfires (Abrams 1992). A disturbance dependent climax community, oaks have been dominant in eastern deciduous forest for the past 10,000 years (Davis 1983, Webb 1988). Presettlement forests dominated by oaks may have been open woodlands or savannas, generally defined as
≤70% canopy closure (Anderson et al. 1999). Although the scale and timing of disturbance events that shaped presettlement forest ecosystems are not completely understood, poor oak regeneration documented throughout the central hardwoods suggests canopy openness as well as fire may have been important (Lorimer 1984,
Abrams 1992).
Restoring the structure and function of presettlement forest conditions (Fule et al.
1997) is an important component of ecosystem management, which seeks to maintain the integrity of forests (Grumbine 1994, Christensen et al. 1996). Forest restoration efforts that aim to replicate historic disturbance regimes and promote oak regeneration are becoming widespread. Partial harvesting can be one management technique used to restore a more open forest structure, such as shelterwood harvesting (Loftis 1990, Brose and Van Lear 1998, Brose et al. 1999a, b). However, forest restoration requires a more complete understanding of specific habitat requirements for plant and animal species.
Canopy songbirds have typically been associated with canopy gaps or canopy openness, though limited study of breeding ecology makes these associations unclear. In eastern forests, the largest avian population decline have occurred for the Cerulean Warbler, a species typically associated with canopy gaps (Hamel 2000, Jones and Robertson 2001,
Link and Sauer 2002, Hamel et al. 2004, Weakland and Wood 2005, Perkins 2006, Sauer et al. 2008, Bakermans and Rodewald 2009). The objective of this study was to identify 111 important habitat features for conservation of canopy songbirds, such as the declining
Cerulean Warbler. I developed alternate (and possibly complimentary) habitat models to explain both nest site selection and nesting success. Using an information theoretic approach, different models were compared to understand the relative importance of topography, canopy structure, and floristics for individual species and the canopy nesting guild.
2. Methods
2.1 Study system
Research was conducted in southern Ohio in Vinton and Jackson Counties from
2007–2009. Study sites were located in three landscapes comprised of different state forests separated by 15–30 km, Zaleski (ZSF), Vinton Furnace Experimental Forest
(VFEF) formerly Raccoon Ecological Management Area, and Richland Furnace (RFSF).
The landscape was predominantly forested with 75–83% forest in a 10 km radius centered on the study sites (Table 3.1). Forest cover was calculated from the National
Land Cover Dataset for the state of Ohio (Homer et al. 2004). Elevation ranged from
240–340 m. Stands were characterized by 80–130 year old upland mixed oak forest.
Dominant oaks in the overstory included white oak (Quercus alba ), northern red oak
(Quercus rubra ), chestnut oak ( Quercus montana ), black oak ( Quercus velutina ), and scarlet oak ( Quercus coccinea ). Hickory species included bitternut ( Carya cordiformis ), mockernut ( Carya tomentosa ), pignut ( Carya glabra ), shagbark ( Carya ovata ) and shellbark hickory ( Carya laciniosa ). Yellow poplar ( Liriodendron tulipfera ) was common in some areas along with some sugar maple ( Acer saccharum ), red maple ( Acer
112 rubrum ), basswood ( Tilia americana ) and American beech ( Fagus grandifolia ). Oaks were not regenerating effectively and replacement by maples was apparent in the small tree size class (Appendix U). Other shrubs and saplings included hornbeam ( Carpinus caroliniana ), hop hornbeam ( Ostrya virginiana ), black gum ( yssa sylvatica ), sourwood
(Oxydendrum arboreum ), downy serviceberry ( Amelanchier arborea), and redbud
(Cercis canadensis ). Ground cover included greenbrier ( Smilax spp.), low bush blueberry
(Vaccinium spp.), and maple leaf viburnum ( Vibernum acerifolium ).
Twelve sites approximately 12 ha each were studied with two shelterwood and two unharvested sites in each forest plus additional areas at VFEF as part of the
Cooperative Cerulean Warbler Silviculture Experiment (CCSE). Sites were clustered within a 2–7 km area in each state forest. Shelterwoods were harvested to approximately
50% stocking from 2005–2006 as part of other research and forest management in the region. Harvest areas ranged in size from 10–30 ha. Oaks tended to be retained as residual seed trees and riparian buffers about 30 m wide were retained along streams within harvests. Mature second growth sites were selected in nearby forest with generally similar characteristics, no recent management activity (forest at RFSF had a few decaying stumps while there was no evidence of harvesting in other forests), and without immediate plans for harvesting during the study. Canopy cover in the second growth stands was ≥ 90% with some heterogeneity in forest structure (Table 3.1). Sites were marked with grid flags at 50 m intervals for navigation and orientation on maps.
2.2 Study species
Study focused on a guild of five sensitive canopy songbirds that typically breed in southern Ohio: Scarlet Tanager ( Piranga olivacea ), Eastern Wood pewee ( Contopus 113 virens ), Cerulean Warbler ( Dendroica cerulea ), Blue gray Gnatcatcher ( Polioptila caerulea ), and Yellow throated Vireo ( Vireo flavifrons ). These species all nest in the forest canopy but have different nest placement, foraging behavior, and body size, and belong to different families (warbler, tanager, flycatcher, vireo, and gnatcatcher).
Studying a guild of species allowed examination of habitat selection and nesting success among different species using similar resources to better understand guild level responses. Species were selected based on previous experience of their presence and nesting behavior in the area. American Redstart was the only other possible candidate species breeding in the area but generally nests and forage lower (Sherry and Holmes
1997, George 2009).
2.3 est monitoring
Nest searching and monitoring was conducted at all sites plus additional areas at
VFEF from 2007–2008; in 2009 half of the sites were studied. We focused on finding the first nesting attempts while birds were building and later in the season we searched for renests in the territory within a few days after a nest failed. Two thirds of nests were found during building. We searched for and monitored nests from the earliest Blue gray
Gnatcatchers at the end of April until the last Eastern Wood pewee nests at the end
August; in 2009 field work was ended at the end of July. Nests were checked every 2–3 days until failure or fledging. If there was no activity, we watched for 20 min (or 40 min if the female could not be seen on the nest) and checked again subsequently. A nest was considered to have failed if it was inactive prior to the earliest possible fledging dates estimated from known initiation dates for nests found during building plus additional behavioral observations including absence of active provisioning and immediate 114 renesting without any sign of young for nests later in the nesting cycle. Age of young and brood size were estimated from 30 min provisioning observations once birds were actively feeding young. We recorded number of visits to the nest and identified size of prey relative to the bill when possible. I erred on the side of caution counting only nests certain to have failed. Four nests that fledged only cowbirds were considered to be nest failures.
2.4 Measurements of habitat characteristics
Habitat data were collected in July and August at random and nest plots each year. Random plots were placed using a stratified random approach with generally one plot per hectare per year for a total of >20 random plots per site. In 2009 random plots were only sampled at CCSE study sites where the most intensive nest searching was conducted. Point sampling was used with a variable radius plot and at each plot trees (≥
10 cm dbh) were counted using a 2.3x metric prism (10x English). Trees were identified to species and dbh was measured to the nearest centimeter. Using dbh and the prism factor, I calculated the number of trees per ha in small (10–23 cm dbh), medium (23–38 cm dbh) and large (>38 cm dbh) size classes to examine the effect of tree size. Canopy closure was measured using a densitometer, taking an average of four readings one in each compass direction centered on the plot. We counted foliage hits by height class on two 11.3 m perpendicular transects oriented on fixed compass directions. We estimated percent foliage in understory (0.5–6 m), midstory (6–18 m) and overstory (>18 m) as the number of hits out of a maximum number. We counted woody stems (≥10 cm in height) by species in a 3 m fixed radius plot classifying shrubs as <1.5 m and saplings as ≥ 1.5 m. We measured slope (angle in degrees using a clinometer) and aspect (compass angle 115 in degrees). We grouped compass angles into two categories for analysis, xeric southwest
(135–315 degrees) and mesic northeast (315–135 degrees) facing aspects. Mesic northeast facing slopes are generally more productive than xeric southwest facing slopes
(Lipscomb and Nilsen 1990, Stephenson 1998). Although multiple measures of canopy structure were examined, I identified basal area as the best measure of canopy openness associated with partial harvesting (Appendix Q, R). With training trees can generally be counted consistently across observers while measuring diameter allowed examination of the effects of tree size. Other measures of foliage cover or light gaps may be more subjective and less sensitive to variation.
Habitat data were collected at all nests monitored each year. At each nest we collected the same data as at random plots plus additional nest site data. We measured the height of the nest to the nearest meter (range finder or clinometer). To examine three dimensional placement of the nest within the substrate, we estimated or measured the vertical distance of the nest from the top of the canopy above the nest, the horizontal distance of the nest from the bole of the tree, and the horizontal distance of the nest from the edge of the crown of the tree. Concealment can be difficult to measure objectively especially for high nests, but leaves provide the main substrate hiding the nest, and we counted or estimated the number of leaves concealing the nest (within 10 cm).
Importance values of different tree species were calculated based on relative frequency, relative density, and relative basal area from 447 random plots ≤ 100 m from a nest of any canopy species (importance values were the same ≤ 100 m from nests of individual species, and we pooled random plots). I used percent importance values and focused on trees with importance values > 2%; hickory species were pooled due to small 116 numbers of individual species and difficult identification. Percents were multiplied by the total number of nests for each species for expected values and Fisher’s Exact tests were used for small sample sizes. Differences were considered significant at P < 0.01 because of repeated tests.
2.5 Model selection
An information theoretic approach was used to compare different habitat models to explain nest site selection and nesting success of canopy songbirds. I developed a set of five a priori candidate models including topography, forest structure, and floristics based on previous information in the literature (Table 3.2). I identified two models of canopy structure, one associated with opening of the forest canopy by partial harvesting, the other associated with structural characteristics of tree size. Both because I was most interested in identifying relationships with particular habitat attributes rather than treatment per se, and the related wide variation of canopy openness even within the same treatment, I used basal area as the primary indicator of canopy openness. Basal area and canopy closure were highly correlated, and both variables were strongly correlated with partial harvesting ( r >0.7) (Appendix Q). I used the variable basal area because of unequal variance in canopy closure between mature forest and shelterwood harvests
(Appendix R). In the canopy openness model I controlled for slope, because slopes stratify trees in ways that could create a similar effect to canopy openness allowing sunlight to reach the tree crown. Also slope appeared to contribute to the variable responses of Cerulean Warblers to partial harvesting (Chapter 2). The second model of canopy structure examined tree size and a more diverse canopy structure created as forests age. In this model I examined the number of medium (23–38 cm dbh) and large 117 (>38 cm dbh) trees. Oaks were dominant in the overstory in my study system, and I focused on white (Quercus alba and Quercus montana ) and red ( Quercus rubra , Quercus velutina , and Quercus coccinea ) oak groups because of differences in tannin levels in the model examining floristics. Variation in other groups or individual species was too limited to examine separately. As location of the nest can be related to success (Beachy
2008, Newell and Kostalos 2007, Johnson 1997), I considered two models of nest placement (nest height, distance to the bole, and diameter of the support branch) and concealment (number of leaves around the nest). Prior to analysis of habitat factors associated with nesting success, I compared models including shelterwood harvesting, forest, and year as well as additional factors that may influence success including nest age (number of days since the start of laying) and time of season. The best ranked model from these analyses was used as the null model in the subsequent habitat analysis. Forest and site were dropped from these null models to avoid controlling for habitat differences among forests and sites.
I used binomial generalized linear models with a logit link in Program R 2.1
(logistic regression) for the nest site selection analysis. To characterize habitat available within a territory (Jones 2001), a subset of random plots ≤ 100 m from a nest were selected for each species using ArcGis join functions. Territories for my focal species are generally 1–2 ha (Ellison 1992, McCarty 1996, Rodewald and James 1996, Mowbray
1999, Hamel 2000). Thus selecting random plots ≤ 100 m from the nest likely represented habitat available within the territory. Moreover the maximum distance between renests was 100 m. To examine factors associated with nesting success, I used the nest survival model in Program MARK 5.0 which allows for examination of 118 covariates and a model selection approach (Dinsmore et al. 2002); variables were not standardized for analysis. Akaike’s information criterion adjusted for small sample size
(AIC c) was used to rank models based on variance and the number of parameters. Models with ∆ AIC c < 2 were considered equivalent to the best ranked model while models with
∆ AIC c < 10 were considered to have some support. Model support was examined using
Akaike weights (Burnham and Anderson 2002). Variables in the top models were considered important with P values < 0.05 based on z tests in Program R or if confidence intervals did not overlap zero in Program MARK.
3. Results
3.1 est site selection
Nest site selection was complex and all the models examined were included in the best ranked model for at least one species (Table 3.4). However, the best ranked models were well supported with ∆ AIC c >2 and Akaike weights > 0.8 compared to the next best model or the null model, with the exception of scarlet tanagers. Nest site selection was directly associated with canopy structure created through partial harvesting (as measured by basal area) for only one species, the Eastern Wood pewee (Table 3.5). The four other canopy species selected nest sites in areas with 20–40% fewer medium sized trees (Table
3.5, Appendix S). Nest sites averaged 1–3 fewer medium sized trees (equivalent to a canopy gap) counted in prism plots than random plots in both harvested and unharvested forest. Strength of the association with tree size varied among species. For example, only
Cerulean Warblers directly selected for areas with large trees (Table 3.5, Appendix S), and tree size did not explain nest site selection better than the null model for Scarlet
119 Tanagers. Across the canopy guild, nests were placed in large trees (Appendix T), and areas with fewer medium sized trees were selected (Table 3.5), although medium and large trees were not correlated (Table 3.3).
Selection of nest site characteristics varied among species. Cerulean Warblers favored slopes with a northeast facing aspect. Both Eastern Wood pewees and Yellow throated Vireos nested in areas with 20% more white and red oak than available at random (Table 3.5, Appendix S). Eastern Wood pewees and Blue gray Gnatcatchers avoided steep slopes, but gnatcatchers nested in areas with 50% less red oak than available (Table 3.5, Appendix S). Across all species, nests were placed in areas with more white oak than available (Table 3.5). Four canopy species selected Quercus alba as the nest substrate more than twice as much as available at random, but avoided Acer rubrum (Figure 3.1). Scarlet Tanagers, Cerulean Warblers, and Blue gray Gnatcatchers avoided Quercus rubra as nest substrates and Eastern Wood pewees avoided Tulipfera liriodendron (Figure 3.1). The Yellow throated Vireo was the only species that showed no apparent selection of substrates and used tree species in proportion to availability for nest sites (Figure 3.1); two nests were even found in snags.
Typical in this region (McCarthy et al. 1984), importance values of different tree species changed with aspect at unharvested mature forest sites in our study system. Oak species were more important on southwest facing slopes, whereas yellow poplar and sugar maple were more important on northeast facing slopes (Appendix X). Although aspect was not a significant predictor for individual oak species, basal area of red oaks
(t12 = 3.055, P = 0.002) and white oaks ( t12 =2.427, P = 0.015) was higher on southwest facing aspects while basal area of yellow poplar was higher with northeast facing aspects 120 (t12 = 2.026, P = 0.015). Interestingly, grapevines were also more abundant on northeast facing slopes with 4.6 ± 0.9 SE vines ha 1 compared to 3.2 ± 0.7 SE vines ha 1 on southwest facing slopes ( W = 30970, P = 0.008), a pattern that may explain why the northeast favoring Cerulean Warbler tended to nest in areas with more grapevines at 5.4
± 0.9 S.E. vines ha 1 around nests compared to 3.3 ± 1.0 S.E. vines ha 1 available at random within the territory ( W = 18064, P = 0.104). On the other hand, Eastern Wood pewees avoided areas with grapevine with 1.6 ± 0.7 S.E. vines ha 1 at nest sites ( W =
45592, P = 0.083). Other canopy species showed no association with grapevine.
3.2 esting success
Nest success of canopy species was low with daily survival rates (DSR) of 0.951
± 0.002 S.E. translating to a 29% success rate. DSR of individual species ranged from
0.929 ± 0.008 S.E. for Yellow throated Vireos to 0.965 ± 0.002 S.E. for Eastern Wood pewees (15–36%). Initial model selection analysis showed variation in nesting success among forests and sites for Eastern Wood pewees and Ceruleans Warblers with success
49% at RFSF compared to 30% at the other forests for pewees while cerulean success ranged from 8–34% in mature forest for sites with sufficient numbers of nests (Appendix
K, L). During (different) single years nest success of Scarlet Tanagers and Yellow throated Vireos was half that of other years. Success decreased with age of the nest
(number of days since the start of laying) for Cerulean Warblers, but increased with nest age for Scarlet Tanagers, perhaps because more obvious nests were depredated early in the nesting cycle. For relatively large and conspicuous nests of the Scarlet Tanagers success was positively related to the size of the nest support branch and concealment around the nest (Table 3.6, Figure 3.3b). Eastern Wood pewees began nesting three 121 weeks after the other species and continued to renest through the end of July. Success improved across the season (Figure 3.4c) with DSR of 0.978 ± 0.008 S.E or 56% success
(n = 87) for late season nests compared to 0.958 ± 0.005 S.E. or a 32% ( n = 169) success for nests initiated before the third week of June when species such as the Cerulean
Warbler and Blue gray Gnatcatcher generally stopped nesting (Scarlet Tanagers and
Yellow throated Vireos continued to nest through the first week of July).
Habitat models failed to explain nesting success for three species (Table 3.7). For
Cerulean Warblers three models were equally well supported with ∆ AIC c < 2 including tree size, canopy structure and oak species. Collectively these three models had 70% of the weight and performed better than the null model. Daily survival rates of Cerulean
Warblers were either negatively associated with number of large trees, basal area or basal area of the red oak groups. Oak species was also the best ranked model for Eastern
Wood pewees, although not better than the null model. Across all canopy nests, oak species was the best ranked model with 80% of the weight. Daily survival rates were negatively associated with basal area of the red oak group around the nest (Figure 3.2).
4. Discussion
Topography, canopy structure and floristics were all important in nest site selection of canopy songbirds, but only floristics was related to nesting success. The declining Cerulean Warbler was the only canopy species to favor northeast facing slopes, as previously observed by others (Weakland and Wood 2005, Wood et al. 2006, Hartman et al. 2009). Generally, canopy structure appeared to be important in nest site selection and most species selected areas with fewer medium sized trees (23–38 cm dbh) than
122 available at random. In addition approximately 70% of nests were in large trees
(Appendix T). This could suggest that canopy openness in association with forest age is important, perhaps describing presettlement conditions. Results suggest that floristics, especially the type or species of oak, are important. Specifically white oak was preferred for nesting and red oak was negatively associated with nest success. From a management perspective partial harvesting may create some of the features favored by canopy nesting species. However, my results suggest that habitat preferences may be more nuanced and further work is needed to examine whether removing medium sized trees and preferentially leaving large trees (>38 cm dbh) of species such as Quercus alba improves habitat for this group.
Although canopy nesting species seemed to consider canopy structure when selecting nest sites, the key attributes did not parallel stocking levels as typically considered by forest managers. Most notably nest site selection of canopy songbirds was not explained by basal area, which is a measure of the cross sectional area of tree trunks
(or area occupied by living trees), accounting for both the number of trees and their size in a single measurement. In mixed oak forest, both basal area and canopy closure are similar in second growth and old growth stands while old (and generally large trees) are indicative of old growth conditions (Goebel and Hix 1996, F. L. Newell, unpublished data). Rather, number of medium sized trees (23–38 cm dbh), an attribute that reflects canopy structure, was among the top models explaining nest site selection. Preferences of canopy birds for areas with fewer medium sized trees might indicate the importance of an open canopy in older forests matching descriptions of presettlement open park like woodland with large trees (Nowacki and Abrams 2008). Associations of canopy 123 songbirds with large trees have been documented previously (Ellison 1992, McCarty
1996, Rodewald and James 1996, Mowbray 1999, Hamel 2000), and further work is needed to examine the relationship of canopy songbirds with tree size (and age). One explanation for associations of canopy songbirds with large trees could be that insects on white oaks change with age (Jeffries et al. 2006). Large trees could also provide substrates of suitable nesting height (average nest height in my study system was 19 m).
The Eastern Wood pewee was the only species selecting nest sites with lower basal area, the habitat measure most directly associated with partial harvesting. Tree size was not an important model for pewees. Of the canopy species studied, abundance of
Eastern Wood pewees has most consistently been higher with partial harvesting (Chap 2) suggesting canopy openness created through partial harvesting could be beneficial for this flycatcher. Flying insects may be more visible and active in sunny areas, or more abundant ( Blake and Hoppes 1986, Smith and Dallman 1996, Gorham et al. 2002 ) and several species have shown increased use of aerial maneuvers in harvest areas (George
2009).
Results highlight the role of forest composition in nest site selection and nesting success of canopy songbirds. Counter to the tendency to generalize about the importance of oak, not all oak species were equal for canopy birds. Almost all canopy species favored Quercus alba for nest sites and nested in areas with an abundance of white oaks.
Bakermans (2008) also reported that Cerulean Warblers preferentially selected Quercus alba as nest substrates. The extent to which preference for white oak reflects tree morphology (e.g. rough bark for nest attachment), or other plant animal interactions (e.g. arthropods associated with different tree species) remains unclear. Interestingly, the 124 Yellow throated Vireo, the only species not selecting Quercus alba for nest sites (or any tree species) weaves a hanging basket nest attached to a fork. Not only does this study demonstrate a preference for white oak, but my data also suggest that most canopy birds avoided red oak as a nest substrate which was negatively associated with nesting success.
Others have found that a number of forest species including the Cerulean Warbler and
Scarlet Tanager avoided red oaks for foraging as well (George 2009). Additionally, birds avoided red maple for foraging (George 2009), while in my study birds avoided red maple as a nesting substrate.
Tree species preferences may be a consequence of leaf architecture or arthropod communities (Gabbe et al. 2002, McShea and Healy 2002, Rodewald and Abrams 2002).
Although abundance of Lepidotera appears similar on red oak compared to other tree species, Lepidotera may specialize on specific host trees (Butler and Strazanac 2000) and may be sensitive to high levels of tannin (Feeny 1970, Schultz and Baldwin 1982,
Rossiter et al. 1988). In some oak species levels of tannins may be higher on a southwest facing compared to a northeast facing aspect (Forkner and Marquis 2004). Tree species preferences reflect presettlement conditions, and Quercus alba is thought to have been more abundant in presettlement forests than today(Abrams 2003, Nowacki and Abrams
2008), with importance values up to 40% in Ohio (Dyer 2001). On the other hand, the distribution of Quercus rubra has increased post settlement due to an increase in large scale disturbances (Abrams 2003). An important caveat to my findings is that separating the effects of tree species from other factors is difficult. For example, red oak and red maple were often found on more xeric ridges in my study system. Red maple was also in
125 the smaller size classes and bird generally used medium and large trees as nest substrates
(Appendix A).
To my knowledge, this study is the first to document that they type of oak may differentially affect nesting success. If prey resources differ on red oaks, perhaps because of high tannin levels, birds might have to leave the nest unattended for longer periods to spend time foraging as they cover a larger area. Reproductive success has been related to prey resources (Nagy and Smith 1997, Zanette et al. 2006). Interestingly the two canopy species that did not avoid red oaks for nest sites were either a flycatcher (Eastern Wood pewee) or a less consistent foliage gleaner (Yellow throated Vireo). Yellow throated
Vireos primarily forage on trunks and bare or dead limbs and obtain only about 30% of prey from foliage (Rodewald and James 1996). We observed Yellow throated Vireos pulling a variety of large insect prey from bark and small twigs, including spiders, grubs, and small brown caterpillars. In contrast, red oak avoiding Cerulean Warblers and Scarlet
Tanagers were foliage gleaners and most often observed bringing small (and sometimes large) green caterpillars to young at the nest.
Topography may play an important role in habitat associations of canopy songbirds which could be explained by the fact that slope and aspect tend to be good indicators of microhabitat and tree species composition. For example, xeric ridge tops that were favored by Eastern Wood pewees in my study and elsewhere (McCarty 1996,
Dettmers and Bart 1999) are generally dominated by oaks and have fewer mesic tree species. In fact, abundance of pewees was higher in partial harvests in ravines, but not on ridges where pewees were already abundant (Robinson and Robinson 1999). On the other hand, Blue gray gnatcatchers selected for bottomland or riparian areas, avoiding red oaks 126 and slope. Abundance of this species may reach its highest level in riparian areas (Ellison
1992). While Yellow throated Vireos can be abundant in bottomland hardwoods in some areas (Norris et al. 2008), in our study system they selected upland areas with oaks.
Yellow throated Vireos could be somewhat of a generalist, in this study showing no selection for nest substrates and in another study showing no foraging preferences (Gabbe et al. 2002), perhaps because the majority of insects are gleaned from bark and twigs.
Topography seemed to be most important for Cerulean Warblers which clearly favored productive northeast facing slopes in this and other regions (Weakland and Wood 2005,
Wood et al. 2006, Beachy 2008, Hartman et al. 2009). Slope may be an important habitat attribute because it can influence canopy structure, and steep slopes have more heterogeneous canopies. Aspect may be related to microhabitat features. At our study sites grapevines were more abundant on northeast facing slopes. Associations with grapevine and use for nest construction (Bakermans and Rodewald 2009) could be part of an evolutionary adaptation of this species to a particular forest microclimate.
5. Management implications
The strong association between birds and oaks in this study further reinforces the value of current management efforts to promote oak regeneration. My work provides new insight that the species of oak may be important. Patterns of habitat preferences and nesting success suggest that white oaks are more valuable than red oaks for canopy birds.
Managers should make special effort to retain Quercus alba in partial harvests and other restoration projects. In addition, harvesting of medium sized trees (23–38 cm dbh) may be preferable to harvesting large trees (>38 cm dbh). My results also suggest that older
127 forests with canopy gaps and/or those on northeast facing slopes may be valuable for conservation of the severely declining Cerulean Warbler.
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.
135 Table 3.1 Means (± SE) for recent shelterwood harvests and unharvested upland mixed oak forest studied in southern Ohio, 2007 2009. Location (% forest 1) Slope Basal area Trees 23–38 Trees >38 White oak Red oak
Latitude/Longitude Site Harvest? (degrees) (m 2 ha 1) cm dbh ha 1 cm dbh ha 1 (m 2 ha 1) (m 2 ha 1) n
ZSF (83%) KH no 15 ± 2 21.6 ± 4.2 65 ± 12 68 ± 6 7.4 ± 1.5 7.4 ± 1.2 26
82° 18’ / 39° 19' LR no 18 ± 2 24.5 ± 4.9 94 ± 12 68 ± 6 6.2 ± 0.7 7.0 ± 1.3 25
SS yes 12 ± 1 9.6 ± 1.5 23 ± 5 37 ± 3 4.6 ± 0.9 4.0 ± 0.6 39
MH yes 16 ± 1 13.6 ± 2.8 71 ± 15 42 ± 5 6.9 ± 1.1 4.0 ± 1.0 24
VFEF (75%) R2 no 17 ± 1 24.6 ± 3.2 100 ± 9 64 ± 4 8.7 ± 0.5 5.7 ± 0.7 61
136 82° 22’ / 39° 11' AR no 13 ± 2 23.9 ± 5.0 101 ± 14 74 ± 6 13.7 ± 0.4 4.3 ± 1.0 23
R3 yes 16 ± 2 12.3 ± 2.3 59 ± 10 43 ± 4 2.8 ± 1.3 5.0 ± 0.9 26
WO yes 17 ± 2 9.3 ± 1.8 14 ± 5 40 ± 3 4.6 ± 1.5 4.3 ± 0.7 27
RFSF (77%) GS no 17 ± 1 24.5 ± 4.9 148 ± 14 56 ± 6 8.7 ± 0.6 3.9 ± 0.9 25
82° 36’ / 39° 10' ON no 18 ± 2 23.4 ± 4.8 110 ± 13 69 ± 6 12.9 ± 1.1 1.9 ± 0.6 24
FP yes 17 ± 2 9.3 ± 1.7 25 ± 6 32 ± 4 4.2 ± 1.0 4.0 ± 0.7 31
WS yes 13 ± 1 11.5 ± 2.1 22 ± 7 47 ± 3 6.2 ± 1.1 3.9 ± 0.5 30
1 measured in 10 km radius centered on the study sites.
136
Table 3.2
Candidate models developed for analysis of nest site selection and nesting success of canopy songbirds.
Model Variables References
Topography slope (degrees) and aspect (NE to SW) Dettmers and Bart 1999, Hartman 2009, etc
Canopy structure basal area (m 2 ha 1) and slope (degrees) Rodewald and Smith 1998, Hamel et al. 2000
Tree size trees 23–38 cm dbh and > 38 cm dbh ha 1 Hamel et al. 2000, Bakermans and Rodewald 2009
Oaks basal area (m 2 ha 1) of white and red oak groups George 2009, Bakermans and Rodewald 2009 137
Nest placement nest height and distance to bole (m), support diameter (cm) Beachy 2008, Bakermans and Rodewald 2009
Concealment number of leaves around nest Johnson 1997, Best and Stauffer 1980
137
Table 3.3
Spearman rank order correlations for variables used in nest site selection and nesting success analysis. Correlations are from
447 random plots included in the analysis.
Slope Aspect Basal area Trees 23–38 Trees >38 White oak Red oak
(degrees) (NE to SW) (m 2 ha 1) cm dbh ha 1 cm dbh ha 1 (m 2 ha 1) (m 2 ha 1)
Slope (degrees) 1.00
Aspect (NE to SW) 0.01 1.00 138 Basal area (m 2 ha 1) 0.03 0.10 1.00
Trees 23–38 cm dbh ha 1 0.07 0.02 0.60 1.00
Trees > 38 cm dbh ha 1 0.05 0.02 0.62 0.04 1.00
White oak (m 2 ha 1) 0.00 0.02 0.43 0.18 0.40 1.00
Red oak (m 2 ha 1) 0.00 0.18 0.17 0.01 0.27 0.09 1.00
138
Table 3.4
Comparison of candidate habitat models to explain nest site selection of canopy songbirds in southern Ohio, 2007 2009. Models with strong support are highlighted in bold. For Scarlet
Tanagers none of the models explained nest site selection better than the null model.
Model k AIC c ∆ AIC c Akaike weights
Scarlet Tanager (173 nests and 348 random plots) Tree size 3 665.74 0.00 0.52 Null 1 666.60 0.86 0.34 Oaks 3 670.19 4.44 0.06 Canopy structure 3 670.84 5.10 0.04 Topography 3 671.00 5.26 0.04 Eastern Wood pewee (236 nests and 369 random plots) Topography + Canopy Structure + Oaks 6 777.03 0.00 1.00 Oaks 3 794.07 17.04 0.00 Topography 3 795.88 18.85 0.00 Canopy structure 3 801.66 24.63 0.00 Null 1 811.31 34.28 0.00 Tree size 3 812.21 35.18 0.00 Cerulean Warbler (133 nests and 238 random plots) Topography + Tree size 5 525.49 0.00 0.95 Tree size 3 531.59 6.09 0.05 Topography 3 537.06 11.56 0.00 Null 1 542.83 17.34 0.00 Canopy structure 3 545.70 20.20 0.00 continued
139 Table 3.4 (continued) Oaks 3 546.93 21.44 0.00 Blue gray Gnatcatcher (105 nests and 213 random plots) Global 8 372.32 0.00 0.91 Oaks 3 376.92 4.60 0.09 Canopy structure 3 399.15 26.83 0.00 Topography 3 401.77 29.45 0.00 Tree size 3 402.90 30.58 0.00 Null 1 405.51 33.19 0.00 Yellow throated Vireo (75 nests and 221 random plots) Tree size + Oaks 5 329.33 0.00 0.88 Oaks 3 334.84 5.51 0.06 Tree size 3 336.26 6.93 0.03 Null 1 336.58 7.25 0.02 Topography 3 339.22 9.89 0.01 Canopy structure 3 339.36 10.04 0.01 Canopy nesting guild (722 nests and 447 random plots) Global 8 1596.08 0.00 0.96 Tree size 3 1602.94 6.86 0.03 Canopy structure 3 1608.32 12.23 0.00 Topography 3 1608.53 12.44 0.00 Oaks 3 1612.86 16.77 0.00 Null 1 1614.12 18.03 0.00
140
Table 3.5
Coefficients of the best ranked models for nest site selection of canopy songbirds in southern Ohio, 2007–2009. Important variables in each model are highlighted in bold.
Parameter Estimate SE z P
Scarlet Tanager (173 nests and 348 random plots) Intercept 0.704 0.223 3.154 0.002 Trees 23–38 cm dbh ha 1 0.002 0.001 1.887 0.059 Trees > 38 cm dbh ha 1 0.003 0.003 1.169 0.243 Eastern Wood pewee (236 nests and 369 random plots) Intercept 0.402 0.283 1.420 0.156 Slope (degrees) 0.035 0.011 3.334 0.001 Aspect (NE to SW) 0.244 0.181 1.350 0.177 Basal area (m 2 ha 1) 0.042 0.015 2.788 0.005 White oak (m 2 ha 1) 0.084 0.018 4.564 <0.001 Red oak (m 2 ha 1) 0.077 0.022 3.566 <0.001 Cerulean Warbler (133 nests and 238 random plots) Intercept 0.124 0.328 0.378 0.706 Slope (degrees) 0.021 0.012 1.762 0.078 Aspect ( E to SW) 0.621 0.216 2.876 0.004 Trees 23–38 cm dbh ha 1 0.005 0.002 3.055 0.002 Trees > 38 cm dbh ha 1 0.008 0.003 2.377 0.017 Blue gray Gnatcatcher (105 nests and 213 random plots) Intercept 0.419 0.423 0.990 0.322 Slope (degrees) 0.039 0.015 2.599 0.009 continued
141 Table 3.5 (continued) Aspect ( E to SW) 0.558 0.284 1.965 0.049 Basal area (m 2 ha 1) 0.059 0.039 1.519 0.129 Trees 23–38 cm dbh ha 1 0.009 0.004 2.437 0.015 Trees >38 cm dbh ha 1 0.003 0.008 0.372 0.710 White oak (m 2 ha 1) 0.048 0.026 1.852 0.064 Red oak (m 2 ha 1) 0.224 0.043 5.192 <0.001 Yellow throated Vireo (75 nests and 221 random plots) Intercept 1.358 0.333 4.079 <0.001 Trees 23–38 cm dbh ha 1 0.008 0.003 2.954 0.003 Trees > 38 cm dbh ha 1 0.007 0.006 1.113 0.266 White oak (m 2 ha 1) 0.088 0.031 2.826 0.005 Red oak (m 2 ha 1) 0.096 0.035 2.727 0.006 Canopy nesting guild (722 nests and 461 random plots) Intercept 0.770 0.203 3.798 <0.001 Slope (degrees) 0.023 0.007 3.324 0.001 Aspect (NE to SW) 0.002 0.126 0.017 0.986 Basal area (m 2 ha 1) 0.001 0.017 0.031 0.975 Trees 23–38 cm dbh ha 1 0.004 0.001 2.511 0.012 Trees > 38 cm dbh ha 1 0.000 0.004 0.049 0.961 White oak (m 2 ha 1) 0.028 0.011 2.578 0.010 Red oak (m 2 ha 1) 0.025 0.014 1.787 0.074
142
Table 3.6 Comparison of candidate non habitat models to explain daily survival of canopy nests in southern Ohio, 2007 2009. Models with strong support are highlighted in bold. Partial harvesting was not related to nesting success for any species. Factors related to success included nest age, time of season, year and forest.
Model k AICc Delta AICc Akaike weights
Scarlet Tanager (173 nests) est age + Season + Year 4 542.22 0.00 0.90 Year 2 547.56 5.35 0.06 Nest age 2 549.37 7.16 0.03 Season 2 552.04 9.82 0.01 Null 1 552.84 10.62 0.00 Forest 2 554.25 12.03 0.00 Site 2 554.73 12.51 0.00 Shelterwood 2 554.84 12.62 0.00 Eastern Wood pewee (236 nests) Season + Forest 3 842.83 0.00 0.83 Season 2 846.12 3.29 0.16 Forest 2 852.88 10.05 0.01 Null 1 857.09 14.27 0.00 Nest age 2 857.57 14.75 0.00 Shelterwood 2 858.42 15.59 0.00 Site 2 858.92 16.09 0.00 Year 2 858.96 16.14 0.00 continued
143 Table 3.6 (continued) Cerulean Warbler (133 nests) est age + Site 3 485.46 0.00 0.38 est age 2 486.73 1.26 0.20 Season 2 487.55 2.09 0.13 Site 2 487.93 2.47 0.11 Forest 2 488.97 3.51 0.07 Null 1 489.26 3.80 0.06 Year 2 491.13 5.67 0.02 Shelterwood 2 491.24 5.78 0.02 Blue gray Gnatcatcher (105 nests) Null 1 396.32 0.00 0.23 Year 2 396.62 0.31 0.20 Forest 2 397.15 0.83 0.15 Season 2 397.32 1.00 0.14 Site 2 397.66 1.34 0.12 Shelterwood 2 398.25 1.93 0.09 Nest age 2 398.31 1.99 0.08 Yellow throated Vireo (75 nests) Year 2 290.95 0.00 0.29 Null 1 291.43 0.47 0.23 Nest age 2 292.19 1.23 0.15 Site 2 293.38 2.43 0.08 Shelterwood 2 293.41 2.45 0.08 Forest 2 293.41 2.45 0.08 Season 2 293.43 2.48 0.08 Canopy nesting guild (722 nests) Species + est age + Season + Forest + Year 6 2609.63 0.00 0.67 est age 2 2611.04 1.41 0.33 continued
144
Table 3.6 (continued) Forest 2 2622.19 12.56 0.00 Season 2 2622.67 13.04 0.00 Year 2 2624.77 15.15 0.00 Species 2 2626.83 17.20 0.00 Site 2 2628.15 18.52 0.00 Null 1 2629.42 19.79 0.00 Shelterwood 2 2631.25 21.62 0.00
145
Table 3.7
Comparison of candidate habitat and nest placement models to explain daily survival of canopy nests in southern Ohio, 2007 2009. Models with strong support are highlighted in bold. For three species none of the models explained nesting success better than the null model while for Cerulean Warblers several models were equally well supported.
Model k AIC c ∆ AIC c Akaike weights
Scarlet Tanager (173 nests) est placement + Concealment 8 532.80 0.00 0.73 Concealment 5 535.14 2.35 0.23 Nest placement 7 539.30 6.50 0.03 Null 4 542.22 9.42 0.01 Oaks 6 543.09 10.29 0.00 Topography 6 545.09 12.29 0.00 Tree size 6 545.44 12.64 0.00 Canopy structure 6 545.89 13.10 0.00 Eastern Wood pewee (236 nests) Oaks 4 844.87 0.00 0.42 Null 2 846.12 1.25 0.23 Topography 4 847.22 2.35 0.13 Concealment 3 847.55 2.68 0.11 Canopy structure 4 848.73 3.86 0.06 Tree size 4 849.85 4.97 0.04 Nest placement 5 851.40 6.53 0.02 continued
146 Table 3.7 (continued) Cerulean Warbler (133 nests) Tree size 4 484.08 0.00 0.26 Canopy structure 4 484.14 0.05 0.25 Oaks 4 484.69 0.60 0.19 Canopy structure + Oaks + Tree size 8 486.08 2.00 0.10 Null 2 486.73 2.64 0.07 Concealment 5 487.51 3.43 0.05 Nest placement 4 487.59 3.51 0.05 Topography 3 488.00 3.92 0.04 Blue gray Gnatcatcher (105 nests) Null 1 396.32 0.00 0.31 Canopy structure 3 397.43 1.11 0.18 Tree size 3 397.87 1.55 0.14 Concealment 2 398.24 1.93 0.12 Nest placement 4 398.52 2.20 0.10 Topography 3 398.57 2.25 0.10 Oaks 3 399.71 3.40 0.06 Yellow throated Vireo (75 nests) Null 2 290.95 0.00 0.35 Tree size 4 292.50 1.55 0.16 Concealment 3 292.88 1.93 0.13 Canopy structure 4 293.05 2.09 0.12 Oaks 4 293.21 2.25 0.11 Topography 4 294.12 3.17 0.07 Nest placement 5 295.03 4.07 0.05 Canopy nesting guild (722 nests) Oaks 7 2606.55 0.00 0.79 Nest placement 8 2611.18 4.62 0.08 continued
147 Table 3.7 (continued) Null 5 2612.03 5.48 0.05 Tree size 7 2613.07 6.52 0.03 Concealment 6 2613.53 6.98 0.02 Canopy structure 7 2613.82 7.27 0.02 Topography 7 2615.83 9.28 0.01
148
Table 3.8
Coefficients of the best ranked models explaining daily survival of canopy nests in southern Ohio, 2007–2009. Important variables in each model are highlighted in bold.
Parameter Beta SE 95% CI
Scarlet Tanager (173 nests) Intercept 1.705 0.479 0.766 2.644 est age 0.027 0.017 0.006 0.061 Season 0.010 0.005 0.020 0.000 Year 0.248 0.156 0.553 0.058 Nest height 0.006 0.021 0.047 0.036 Distance to bole 0.067 0.062 0.055 0.190 Support diameter 0.146 0.061 0.026 0.266 Leaves 0.106 0.039 0.031 0.182 Eastern Wood pewee (236 nests) Intercept 2.864 0.256 2.363 3.365 Season 0.017 0.005 0.007 0.026 White oak (m 2 ha 1) 0.003 0.013 0.024 0.029 Red oak (m 2 ha 1) 0.035 0.015 0.065 0.005 Cerulean Warbler (133 nests) Intercept 3.718 0.381 2.970 4.466 est age 0.041 0.016 0.073 0.008 Trees 23–38 cm dbh ha 1 0.001 0.002 0.004 0.003 Trees > 38 cm dbh ha 1 0.009 0.004 0.017 0.002 Intercept 3.269 0.380 2.524 4.014 est age 0.040 0.016 0.072 0.008 continued
149 Table 3.8 (continued) Basal area 0.028 0.014 0.055 0.001 Slope 0.025 0.013 0.000 0.051 Intercept 3.438 0.305 2.840 4.035 est age 0.038 0.016 0.070 0.006 White oak (m 2 ha 1) 0.020 0.018 0.056 0.016 Red oak (m 2 ha 1) 0.046 0.021 0.088 0.005 Blue gray Gnatcatcher (105 nests) Intercept 3.552 0.360 2.846 4.258 Slope (degrees) 0.017 0.013 0.042 0.008 Basal area (m 2 ha 1) 0.019 0.017 0.052 0.015 Yellow throated Vireo (75 nests) Intercept 2.652 0.323 2.018 3.286 Year 0.420 0.210 0.008 0.832 Trees 23–38 cm dbh ha 1 0.004 0.003 0.009 0.001
Trees > 38 cm dbh ha 1 0.002 0.005 0.008 0.011 Canopy nesting guild(722 nests) Intercept 2.820 0.150 2.527 3.114 Season 0.000 0.003 0.005 0.005 est age 0.019 0.006 0.008 0.030 Species 0.031 0.038 0.106 0.044 Year 0.094 0.069 0.229 0.042 White oak (m 2 ha 1) 0.002 0.008 0.013 0.017 Red oak (m 2 ha 1) 0.030 0.010 0.049 0.011
150 60% * * Random plots (447) Scarlet Tanager (173) 50% Eastern Wood pewee (236) * Cerulean Warbler (133) Blue gray Gnatcatcher (105) Yellow throated Vireo (75) 40% *
30%
Percent importance value value importanceimportance PercentPercent 20%
10% 151 * * * ** * ** 0% Que Q Q Q Q Tulipfer Carya spp. Acer A Fagus ue ue u ue cer rc rcu rcus ercus vel rcus cocci us rubr um saccharum gr s a alba m rubr l andi ont ut irio ana a ina ne d fol Figure 3.1 a endron ia
Tree species used by canopy songbirds for nest sites versus availability. Percent importance values based on relative frequency,
relative density, and relative basal area were calculated from random plots ≤ 100 m from any nest. Asterisks indicate significant
differences from Fisher’s Exact tests ( P < 0.01).
151 1 . 0 0 1 . 0 0 0 . 9 5 0 . 9 5 0 . 9 0 0 . 9 0 0 . 8 5 0 . 8 5 0 . 8 0 0 . 8 0
Daily survival rate rate rate Daily Daily Daily survival survival survival 0 . 7 5 0 . 7 5 a) Scarlet Tanager ( n = 173) b) Eastern Wood pewee ( n = 236) 0 . 7 0 0 . 7 0 0 5 10 15 20 25 0 5 10 15 20 25 1 .0 0 1 .0 0 0 .9 5 0 .9 5 0 .9 0 0 .9 0 0 .8 5 0 .8 5 0 .8 0 0 .8 0
Daily survival rate rate rate Daily Daily Daily survival survival survival 0 .7 5 0 .7 5 c) Cerulean Warbler ( n = 133) d) Blue gray Gnatcatcher ( n = 105) 0 .7 0 0 .7 0 0 5 10 15 20 25 0 5 10 15 20 25 1 .0 0 1 . 0 0 0 .9 5 0 . 9 5
152 0 .9 0 0 . 9 0 0 .8 5 0 . 8 5 0 .8 0 0 . 8 0
Daily survival rate rate Daily Daily survival survival 0 .7 5 0 . 7 5 e) Yello w throated V ireo ( n = 105) f) Canopy nesting guild ( n = 722) 0 .7 0 0 . 7 0 0 5 10 15 20 25 0 5 10 15 20 25 B asal area red oak (m 2 ha 1 ) B asal area red oak (m 2 h a 1) Figure 3.2 Relationships between daily survival rates of nests for canopy songbirds and basal area of red oaks at study sites in southern Ohio,
2007–2009. Red oaks were an important model for Eastern Wood pewees, Cerulean Warblers, and the canopy nesting guild.
152 a) Cerulean Warbler (n = 133) b) Scarlet Tanager ( n = 173) 1. 00 1. 00
0. 95 0. 95 0. 90 0. 90 0. 85 0. 85
0. 80 0. 80 0. 75 0. 75 0. 70 0. 70 0 10 20 30 40 50 60 70 80 90 100 110 0 3 6 9 12 Trees >38 cm dbh ha 1 Leaves around the nest
1.00 1. 00 0.95 0. 95 0.90 0. 90
0.85 0. 85
153 0.80 0. 80
Daily survival raterate Daily Daily survival survival 0.75 rate rate Daily Daily survival survival 0. 75
0.70 0. 70 0 5 10 15 20 25 30 0 1 2 3 4 5 6 7 8 Basal area (m 2 ha 1) Support diameter (cm)
Figure 3.3
Variables explaining daily survival rates of nests for Cerulean Warblers and Scarlet Tanagers. The model of red oaks around the nest (Figure 3.2) was equally well supported as the number of large trees and basal area for Cerulean Warblers.
153 a) Cerulean Warbler ( n = 133) 1. 00 0. 95 0. 90 0. 85 0. 80
rate Daily survival 0. 75 0. 70 Nest age b) Scarlet Tanager ( n = 173) 1 .0 0 0 .9 5 0 .9 0 0 .8 5 0 .8 0
rate Daily survival 0 .7 5 rate Daily survival
0 .7 0 Nest age
c) Eastern Wood pewee ( n = 236) 1 .0 0 0 .9 5 0 .9 0
0 .8 5
0 .8 0 Daily survival rate Daily survival 0 .7 5
0 .7 0 Season d ate Figure 3.4
Time dependent models of daily survival rates of nests in southern Ohio, 2007–2009. Predation increased during the nestling phase for Cerulean Warblers, but predation was higher during early incubation for Scarlet Tanagers. Eastern Wood pewees were more successful late in the season.
154
Appendix A.
Map of study region in southern Ohio.
THSF ZSF
VFEF RFSF
155
Appendix B.
Stands studied in shelterwoods and unharvested reference mature forest in 4 state forests in southern Ohio, 2007–2009. Black lines indicate intensive sites, gray lines indicate line transects, and dashed lines indicate shelterwood harvests.
156 Appendix B (continued)
a) Zaleski State Forest (ZSF)
LH
MH
SS
KH LR
continued
157 Appendix B (continued)
b) Vinton Furnace Experimental Forest (VFEF)
EF
R2
RO R3
AR WO
R1
continued
158 Appendix B (continued)
c) Richland Furnace State Forest (RFSF)
GS FP WS
ON
continued
159 Appendix B (continued)
d) Tar Hollow State Forest (THSF)
WC BR
LT LC
160 Appendix C. Summary of stands studied in southern Ohio, 2007–2009. Surveys were conducted at 18 stands in 4 state forests, intensive
monitoring was conducted at 12 stands in 3 state forests plus additional areas as part of the CCSE.
Stocking Harvest Arrival Transect Nest Banding/ UTM
Forest Stand Harvest? (%) area (ha) surveys surveys monitoring resighting (NAD 83)
ZSF KH no 2007 09 2007 08 2007 09 2007 09 386671 4354099
LR no 2007 09 2007 08 2007 08 2007 09 387673 4354043
LH no 2007 08 384460 4357439 161 SS 2006 50 30 2007 09 2007 08 2007 09 2007 09 387172 4354645
MH 2005 50 20 2007 09 2007 08 2007 09 2007 09 386460 4355696
VFEF R2 no 2007 09 2007 08 2007 09 2007 09 380815 4339835
AR no 2007 09 2007 08 2007 08 2007 09 380961 4338292
R1 1 2006 75 10 2007 09 2007 09 379705 4335556
EF 1 2006 25 10 2007 09 2007 09 381720 4340553
continued
161 Appendix C (continued)
R3 1 2006 50 10 2007 09 2007 08 2007 09 2007 09 381380 4339018
WO 2006 50 30 2007 09 2007 08 2007 08 2007 09 379863 4337386
RO 2005 50 20 2007 08 377944 4338467
RFSF GS no 2007 08 2007 08 2007 08 2007 09 360137 4336888
ON no 2007 08 2007 08 2007 08 2007 09 361938 4336335
FP 2005 50 20 2007 08 2007 08 2007 08 2007 09 360921 4336928
WS 2005 50 20 2007 08 2007 08 2007 08 2007 09 361704 4336873 162 THSF BR no 2008 347642 4362032
LC no 2008 349283 4355561
WC 2007 50 20 2008 346606 4362178
LT 2007 50 10 2008 349593 4356074
1mature forest around harvest studied as part of the CCSE; no banding or nest monitoring in harvest at EF.
162
Appendix D.
Comparison of different survey methods for 10 species in southern Ohio. Distance based methods increased abundance on average 0.1 territories ha 1 compared to 50 m fixed width line transects for the same dataset ( n = 56 in 18 stands at 4 state forests, 2007–
2008). Estimates from spot mapping (14 stands) in the same region, although not at the same sites (M. H. Bakermans, unpublished data 2004–2006 and/or CCSE study 2007–
2009) tended to be 0.1 territories ha 1 higher than line transects. Some differences may have been related to habitat (e.g. Hooded Warblers in upland mixed oak forest).
0.8
fixed width 0.7 distance based
0.6 spot map
0.5 1
0.4
Territories ha Territories 0.3
0.2
0.1
0 SCTA EAWP CERW YTVI BGGN WOTH HOWA KEWA OVEN WEWA
163
Appendix E. Relative abundance of additional bird species with >10 detections in unharvested and shelterwood stands in southern Ohio, 2007–2008 ( n = 56 at 18 stands in 4 state forests).
Unharvested Shelterwood
Species Mean SE Mean SE
American Goldfinch ( Spinus tristis ) 0.00 0.00 0.04 0.02
American Robin ( Turdus migratorius ) 0.23 0.06 0.30 0.07
Baltimore Oriole ( Icterus galbula ) 0.02 0.01 0.63 0.10
Blue winged Warbler ( Vermivora pinus ) 0.01 0.01 0.21 0.06
Carolina Chickadee ( Poecile carolinensis ) 0.19 0.04 0.23 0.04
Cedar Waxwing ( Bombycilla cedrorum ) 0.12 0.03 0.43 0.13
Chipping Sparrow ( Spizella passerina ) 0.01 0.01 0.30 0.08
Common Yellowthroat ( Geothlypis trichas ) 0.02 0.01 0.21 0.05
Chestnut sided Warbler ( Dendroica pensylvanica ) 0.02 0.01 0.04 0.02
Downy Woodpecker ( Picoides pubescens ) 0.13 0.03 0.17 0.03
Eastern Phoebe ( Sayornis phoebe ) 0.11 0.03 0.06 0.02
Field Sparrow ( Spizella pusilla ) 0.00 0.00 0.06 0.03
Great Crested Flycatcher ( Myiarchus crinitus ) 0.11 0.04 0.23 0.05
Hairy Woodpecker ( Picoides villosus ) 0.06 0.02 0.07 0.03
continued
164 Appendix E (continued)
Louisiana Waterthrush ( Seiurus motacilla ) 0.29 0.05 0.14 0.04
Mourning Dove ( Zenaida macroura ) 0.11 0.03 0.55 0.10
Northern Cardinal ( Cardinalis cardinalis ) 0.15 0.03 0.34 0.05
Northern Flicker ( Colaptes auratus ) 0.07 0.02 0.19 0.05
Pileated Woodpecker ( Dryocopus pileatus ) 0.30 0.05 0.29 0.06
Rose breasted Grosbeak ( Pheucticus ludovicianus ) 0.07 0.02 0.14 0.04
Red headed Woodpecker ( Melanerpes erythrocephalus ) 0.10 0.03 0.27 0.05
Ruby throated Hummingbird ( Archilochus colubris ) 0.09 0.02 0.09 0.03
Summer Tanager ( Piranga rubra ) 0.04 0.02 0.14 0.04
Wild Turkey ( Meleagris gallopavo ) 0.02 0.01 0.04 0.02
Yellow breasted Chat ( Icteria virens ) 0.00 0.00 0.21 0.09
Yellow billed Cuckoo ( Coccyzus americanus ) 0.17 0.04 0.21 0.04
Yellow throated Warbler ( Dendroica dominica ) 0.07 0.03 0.04 0.02
165
Appendix F.
Territories ha 1 of canopy nesting species by stand in southern Ohio, 2007–2008. See habitat summaries by forest (Table 2.1) and by stand (Table 3.1).
Stand ( n) SCTA EAWP CERW BGGN YTVI
KH (3) 0.33 0.06 0.17 0.03 0.05 LR (2) 0.37 0.11 0.04 0.12 0.00 LH (3) 0.20 0.12 0.07 0.03 0.02 SS (5) 0.46 0.27 0.35 0.15 0.20 MH (3) 0.35 0.23 0.22 0.16 0.14 AR (2) 0.28 0.27 0.11 0.10 0.04 R2 (6) 0.21 0.20 0.28 0.08 0.16 WO (4) 0.37 0.13 0.00 0.07 0.10 R3 (1) 0.31 0.27 0.87 0.15 0.21 RO (3) 0.27 0.24 0.12 0.19 0.19 GS (3) 0.29 0.14 0.00 0.13 0.05 ON (3) 0.24 0.15 0.00 0.03 0.00 FP (3) 0.35 0.14 0.05 0.10 0.14 WS (3) 0.26 0.17 0.00 0.16 0.05 BR (3) 0.33 0.06 0.00 0.03 0.00 LC (3) 0.20 0.06 0.39 0.13 0.19 WC (4) 0.21 0.20 0.18 0.00 0.18 LT (2) 0.37 0.18 0.15 0.19 0.00
166
Appendix G.
Territories ha 1 of midstory nesting species, predators and a brood parasite by stand in southern Ohio, 2007–2008.
Stand ( n) REVI WOTH AMRE ACFL BHCO BLJA AMCR
KH (3) 0.78 0.25 0.23 0.10 0.16 0.06 0.02 LR (2) 0.56 0.28 0.22 0.03 0.49 0.15 0.02 LH (3) 0.61 0.62 0.00 0.08 0.41 0.29 0.02 SS (5) 0.71 0.25 0.39 0.03 0.44 0.12 0.03 MH (3) 0.98 0.40 0.04 0.06 0.04 0.32 0.02 AR (2) 0.54 0.26 0.00 0.01 0.21 0.23 0.08 R2 (6) 0.90 0.47 0.04 0.12 0.16 0.18 0.04 WO (4) 0.53 0.37 0.16 0.04 0.65 0.29 0.06 R3 (1) 0.86 0.54 0.05 0.21 0.08 0.15 0.03 RO (3) 0.48 0.23 0.03 0.06 0.35 0.08 0.03 GS (3) 0.86 0.37 0.05 0.09 0.25 0.17 0.06 ON (3) 0.63 0.29 0.10 0.03 0.33 0.33 0.04 FP (3) 0.98 0.33 0.08 0.13 0.08 0.15 0.06 WS (3) 0.58 0.14 0.03 0.05 0.35 0.19 0.12 BR (3) 0.71 0.37 0.26 0.10 0.05 0.04 0.00 LC (3) 1.16 0.25 0.36 0.03 0.11 0.04 0.02 WC (4) 0.95 0.28 0.04 0.10 0.08 0.03 0.00 LT (2) 1.44 0.31 0.08 0.00 0.33 0.12 0.03
167
Appendix H. Territories ha 1 of shrub nesting species by stand in southern Ohio, 2007–2008.
Stand ( n) HOWA EATO CARW INBU KEWA PRAW
KH (3) 0.55 0.17 0.05 0.00 0.00 0.00 LR (2) 0.45 0.25 0.12 0.22 0.08 0.13 LH (3) 0.66 0.12 0.00 0.00 0.00 0.00 SS (5) 0.61 0.39 0.05 0.17 0.24 0.04 MH (3) 0.56 0.12 0.07 0.00 0.00 0.00 AR (2) 0.51 0.35 0.19 0.21 0.08 0.31 R2 (6) 0.30 0.10 0.10 0.01 0.00 0.00 WO (4) 0.40 0.25 0.14 0.14 0.00 0.00 R3 (1) 0.31 0.06 0.02 0.00 0.02 0.00 RO (3) 0.64 0.22 0.16 0.38 0.24 0.43 GS (3) 0.57 0.06 0.00 0.00 0.04 0.00 ON (3) 0.79 0.33 0.14 0.43 0.31 0.45 FP (3) 0.44 0.11 0.05 0.00 0.00 0.00 WS (3) 0.46 0.19 0.09 0.36 0.18 0.47 BR (3) 0.26 0.22 0.00 0.00 0.04 0.00 LC (3) 0.40 0.17 0.18 0.00 0.09 0.00 WC (4) 0.43 0.17 0.31 0.14 0.03 0.00 LT (2) 0.59 0.17 0.00 0.22 0.07 0.00
168
Appendix I.
Territories ha 1 of ground and cavity nesting species by stand in southern Ohio, 2007–
2008.
Stand ( n) BAWW OVEN WEWA RBWO TUTI WBNU
KH (3) 0.54 0.86 0.33 0.04 0.02 0.01 LR (2) 0.47 0.24 0.12 0.06 0.06 0.04 LH (3) 0.41 1.08 0.19 0.05 0.04 0.06 SS (5) 0.41 0.50 0.25 0.04 0.08 0.04 MH (3) 0.29 0.93 0.19 0.03 0.04 0.06 AR (2) 0.26 0.27 0.17 0.04 0.02 0.03 R2 (6) 0.27 0.85 0.28 0.07 0.05 0.06 WO (4) 0.24 0.50 0.15 0.03 0.00 0.06 R3 (1) 0.11 1.15 0.20 0.01 0.02 0.02 RO (3) 0.35 0.33 0.20 0.03 0.00 0.04 GS (3) 0.27 1.24 0.18 0.04 0.01 0.05 ON (3) 0.24 0.14 0.18 0.10 0.09 0.04 FP (3) 0.08 0.67 0.10 0.02 0.04 0.03 WS (3) 0.14 0.41 0.05 0.04 0.06 0.02 BR (3) 0.11 0.53 0.51 0.00 0.12 0.04 LC (3) 0.22 0.72 0.36 0.00 0.07 0.00 WC (4) 0.29 0.07 0.04 0.04 0.00 0.06 LT (2) 0.49 0.43 0.23 0.03 0.04 0.03
169
Appendix J.
Number of nests and nesting success of Scarlet Tanagers by stand in southern Ohio,
2007–2009.
Stand Nests Days DSR SE Mayfield
KH 15 133 0.925 0.023 19%
LR 8 87 0.942 0.025 29%
SS 21 231 0.939 0.016 27%
MH 8 65 0.922 0.033 18%
AR 13 174 0.948 0.017 33%
EF
R2 18 151 0.934 0.02 24%
WO 12 76 0.884 0.039 8%
R3 26 244 0.943 0.015 29%
R1 7 69 0.947 0.026 32%
GS 11 124 0.944 0.021 30%
ON 6 68 0.956 0.025 39%
FP 14 177 0.955 0.016 38%
WS 14 115 0.930 0.024 22%
170
Appendix K.
Number of nests and nesting success of Eastern Wood pewees by stand in southern Ohio,
2007–2009.
Stand Nests Days DSR SE Mayfield
KH 20 329 0.982 0.007 59%
LR 17 178 0.933 0.019 13%
SS 23 386 0.961 0.010 32%
MH 12 96 0.896 0.031 4%
AR 14 230 0.969 0.011 41%
R2 17 245 0.955 0.013 26%
EF
WO 20 370 0.946 0.014 20%
R3 25 351 0.949 0.012 22%
R1 18 259 0.984 0.007 62%
GS 12 203 0.970 0.012 42%
ON 7 163 1.000 0.000 100%
FP 29 542 0.978 0.006 52%
WS 22 370 0.965 0.010 35%
171
Appendix L.
Number of nests and nesting success of Cerulean Warblers by stand in southern Ohio,
2007–2009.
Stand Nests Days DSR SE Mayfield
KH 18 135 0.896 0.026 8%
LR - - - - -
SS 28 280 0.932 0.015 20%
MH 12 105 0.905 0.029 10%
AR - - - - -
R2 18 197 0.954 0.015 34%
EF 6 50 0.9 0.042 9%
WO - - - - -
R3 26 39 0.936 0.014 22%
R1 23 216 0.921 0.018 15%
GS - - - - -
ON - - - - -
FP 2 299 0.974 0.026 55%
WS - - - - -
172
Appendix M.
Number of nests and nesting success of Blue gray Gnatcatchers by stand in southern
Ohio, 2007–2009
Stand Nests Days DSR SE Mayfield
KH 5 71 0.944 0.027 25%
LR 2 18 0.889 0.074 6%
SS 15 259 0.965 0.011 43%
MH 13 198 0.965 0.013 42%
AR 1 31 1 0 100%
R2 5 82 0.976 0.017 55%
EF
WO 3 21 0.854 0.078 2%
R3 15 183 0.945 0.017 26%
R1 30 401 0.95 0.011 29%
GS 2 27 0.962 0.037 40%
ON 3 36 0.917 0.046 12%
FP 7 95 0.947 0.023 27%
WS 4 32 0.938 0.043 21%
173
Appendix .
Number of nests and nesting success of Yellow throated Vireos by stand in southern
Ohio, 2007–2009
Stand Nests Days DSR SE Mayfield
KH 11 92 0.913 0.03 9%
LR 1 5 0.778 0.196 0%
SS 12 189 0.963 0.014 37%
MH 6 20 0.744 0.099 0%
AR 5 80 0.975 0.017 52%
R2 7 98 0.959 0.02 34%
EF 2 33 0.969 0.03 44%
WO 3 115 0.957 0.03 31%
R3 11 131 0.931 0.022 16%
R1 8 46 0.939 0.022 20%
GS 1 5 0.778 0.196 0%
ON 4 29 0.862 0.064 2%
FP 3 46 0.957 0.03 31%
WS 1 20 0.949 0.05 25%
174 Appendix O.
Morphometric measurements of canopy songbirds in southern Ohio, 2007–2009.
Body mass Wing length Exposed culmen Tarsus
n Mean SE Mean SE Mean SE Mean SE
Scarlet Tanager Male 66 28.6 0.2 95.4 0.3 14.4 0.1 19.4 0.1
Female 5 29.2 1.1 92.1 0.8 14.4 0.2 19.3 0.2
Eastern Wood pewee Male 58 14.2 0.1 84.5 0.3 12.1 0.1 13.9 0.1
175 Female 16 14.3 0.3 79.5 0.5 11.7 0.2 13.6 0.1
Cerulean Warbler Male 90 9.5 0.0 65.9 0.2 9.7 0.1 16.7 0.1
Female 13 9.1 0.2 62.2 0.4 9.5 0.1 16.2 0.1
Nestling 10 8.3 0.2
Yellow throated Vireo Male 37 16.6 0.1 75.1 0.3 11.5 0.3 19.2 0.1
175
Appendix P.
Canopy structure variables in shelterwood and unharvested reference stands in southern
Ohio, 2007–2009.
Unharvested Shelterwood
(n = 276) (n = 195)
Mean SE Mean SE
Basal area (m 2 ha 1) 23.6 0.4 11.5 0.4
Canopy closure (%) 1 92% 0% 50% 2%
Overstory foliage (%) 2 70% 1% 48% 2%
Crown volume (%) 3 26% 1% 14% 1%
Trees 23–38 cm dbh ha 1 104 4 42 4
Trees >38 cm dbh ha 1 64 2 39 2
1 measured using a densiometer
2 percent of foliage hits ≥ 18 m according to the CCSE
3 crown volume ≥ 18 m measured according to Avina et al. (2006)
176 Appendix Q.
Spearman rank correlation coeficients for canopy structure variables at random plots in southern, Ohio 2007–2009 ( n = 447). Basal
area and canopy closure were both highly correlated with partial harvesting.
Partial Basal area Canopy Overstory Crown Trees 23–38 Trees >38 cm
harvesting (m 2 ha 1) closure (%) foliage (%) volume (%) cm dbh ha 1 dbh ha 1
Partial harvesting 1.00
Basal area (m 2 ha 1) 0.75 1.00
177 Canopy closure (%) 0.81 0.71 1.00
Overstory foliage (%) 0.47 0.50 0.55 1.00
Crown volume (%) 0.37 0.44 0.40 0.40 1.00
Trees 23–38 cm dbh ha 1 0.47 0.61 0.49 0.23 0.09 1.00
Trees >38 cm dbh ha 1 0.42 0.63 0.39 0.40 0.49 0.01 1.00
177
Appendix R.
Boxplots of basal area and canopy closure from random plots in unharvested (n = 276) and shelterwood stands ( n = 195) in southern Ohio, 2007–2009. Basal area was used as the best measure because of limited variance in canopy closure in closed canopy forest
. ) 1 ha 2 Canopy closure Canopy Basalarea (m 10 20 30 40 0.2 0.4 0.6 0.8 1.0
Unharvested0 Shelterwood 1 Unharvested0 Shelterwood 1
178
Appendix S.
Variables used in habitat models for random and nest plots of canopy songbirds in southern Ohio, 2007–2009.
Available 1 SCTA EAWP CERW BGGN YTVI
(n = 447) (n = 174) (n = 236) (n = 163) (n = 105) (n = 75)
Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE
Slope (degrees) 15.8 0.4 15.8 0.7 12.9 0.5 14.7 0.7 13.4 0.9 13.9 0.9
Basal area (m 2 ha 1) 19.1 0.4 19.3 0.6 19.3 0.6 20.5 0.6 16.5 0.7 18.9 0.9 179
Trees 23–38 cm dbh ha 1 81 3 70 5 80 5 69 5 62 6 69 6
Trees >38 cm dbh ha 1 55 1 60 2 57 2 66 3 50 3 59 3
White oak (m 2 ha 1) 7.5 0.3 8.3 0.5 9.4 0.5 7.6 0.5 6.8 0.6 8.7 0.7
Red oak (m 2 ha 1) 4.6 0.2 4.7 0.3 5.7 0.3 4.8 0.4 2.3 0.3 6.2 0.5
1 plots ≤ 100 m from any canopy nest; for analysis species were compared with plots ≤ 100 m from nests of that species, representing
habitat available with the territory.
179
Appendix T.
Canopy songbirds selected nest sites in large trees and avoided small trees for nesting substrates in southern Ohio, 2007–2009.
100% Large trees (>38 cm) 90% Medium trees (23 38 cm) Small trees (10 23 cm) 80%
70% 1 60%
50%
40% Percent trees Percent ha trees
30%
20%
10%
0% Available SCTA EAWP CERW BGGN YTVI (447 plots) (174 nests) (236 nests) (133 nests) (105 nests) (75 nests)
180
Appendix U.
Distribution of tree species groups by size class from random plots at unharvested forest in southern Ohio, 2007–2009 ( n = 277). Oaks were dominant in the large and medium size classes, but maples were dominant in the small size class.
50% Large trees (>38 cm) Medium trees (23 38 cm) 45% Small trees (10 23 cm) 40%
35% 1 30%
25%
20% Percent ha trees
15%
10%
5%
0% White oak spp. Red oak spp. Hickory spp. Yellow poplar Maple spp. Am beech
181
Appendix V.
Regeneration 1–3 years post harvesting from random plots in shelterwood stands in southern Ohio, 2007–2009 ( n = 202). The number of woody stems (< 10 cm dbh and height > 0.5 m) increased for all tree species groups, including oaks.
2500
One year post harvesting
2000 Two years post harvesting Three years post harvesting
1500
(<10 dbh(<10 cm m) and > 0.5 height 1000 1
500 Woody stems Woody ha stems
0 White oak spp. Red oak spp. Hickory spp. Yellow poplar Maple spp. Am beech
182 Appendix W.
Number of woody stems ha 1 (< 10 cm dbh and > 0.5 m tall) by stand in southern Ohio, 2007–2009.
Stand White oak spp. Red oak spp. Yellow poplar Hickory spp. Maple spp. Am Beech n
KH 27 14 231 82 858 245 26
LR 42 99 0 14 595 198 25
LH 0 0 0 383 177 207 12
SS 261 177 317 84 717 28 39
183 MH 1426 552 458 541 1530 281 34
AR 154 477 0 1231 662 169 23
R2 262 319 64 541 711 577 100
WO 708 615 139 246 1292 0 27
R3 77 232 199 431 232 343 32
RO 118 59 30 207 148 0 12
GS 57 99 99 467 1317 127 25
continued
183 Appendix Z (continued)
ON 59 133 133 74 841 59 24
FP 525 457 468 183 2112 57 31
WS 448 201 1180 224 1180 0 30
BR 0 0 767 0 1593 59 6
LC 0 0 295 177 531 0 6
WC 44 0 0 44 929 266 8
184 LT 0 0 177 443 2301 0 4
184 Appendix X.
Importance values of tree species changed with aspect in mature forest in southern Ohio, 2007–2009. Importance of oaks increased on
southwest facing slopes while mesophytic species were more important on northeast facing slopes.
25% Northeast facing 315–135 degrees (144 plots) Southwest facing 135 315 degrees (133 plots)
20%
15% 185
10%
Percent importance values values Percent Percent importance importance 5%
0%
Q Que Q Que Qu T C A A F u u uli a c c a er e e ry er rubru er g c r r rcus vel rcus co pfe a us u cu cus sa g s s ra spp. cc r a m ru a lba lir a n on b u c i m ru d tana ra ti cine o m if n den oli a a a dr on
185
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