SNAG USE BY BREEDING BIRDS IN NORTHERN WISCONSIN CLEARCUTS
by
Tamara M. Ryan
A Thesis
submitted in partial fulfillment of the
requirements for the degree
MASTER OF SCIENCE
in
Natural Resources (Wildlife)
College of Natural Resources
UNNERSITY OF WISCONSIN
Stevens Point, WI
May, 1995 APPROVED BY THE GRADUATE COMMITTEE OF:
e E. Nauman, Committee Chairman Professor of Wildlife
Dr. James H. Hardin Professor of Wildlife
ii r ;/'J-t?_,::;, ': '.• .. s-.o ./G/~/ _:·;o (':r ✓<~93> ABSTRACT Bird use of snags in 10 clearcuts was studied on the Chequamegon National
Forest. Ninety-four snags were randomly selected for observation during the 1992 and
1993 breeding seasons. Treatment comparisons were conducted between snags retained
as single isolated stems or within clumps of live trees. Snag and vegetation
characteristics were measured in the effort to describe bird selectivity of snag habitat
through Logistic Regression analysis.
Overall, 32 snags were used by 31 bird species. Neotropical migrants comprised
39% of the bird species observed using snags whereas 32% were cavity-nesting species.
One-hundred and thirty-two individual activities, for 10 of 12 predetermined activity
types, were recorded. Snag visitation rates (birds/snag/hour) were highest for isolated
snags in clearcuts.
Chi square analysis indicated significant differences (P50.05) in bird use of snags
between treatments. Logistic Regression procedures identified 5 snag and habitat
variables that explain bird use with a likelihood ratio statistic of 100.08.
Recommendations are made for future snag management. These include re
evaluating the current guideline and selecting individual snags for retention.
iii ACKNOWLEDGMENTS
This project was funded by North Central Forest Experiment Station (NCFES), the Chequamegon National Forest (CNF), the University of Wisconsin - Stevens Point, the Zoological Society of Milwaukee County, and Wisconsin Society for Ornithology.
My advisor, Lyle Nauman, provided support and guidance throughout the project.
The other members of my committee, Jim Hardin and James Cook, gave additional advice and comments on this manuscript. Bob Rogers and Eric Anderson assisted in project design and statistical analysis. Bob Rosenfield provided equipment and advice.
Neil Payne supplied relevant literature.
Tom Nicholls (NCFES) secured substantial funding for this project and provided encouragement throughout the study. He continuously restored my confidence and desire to succeed. Norm Wieland and Linda Parker (CNF) arranged for further funding and supplied logisitic and morale support. Joanie Osterbrink, Marriah Sondreal, and Irene
Jorata provided invaluable field assistance. Jane Wiedenhaft volunteered and assisted in habitat sampling. Sherrie Zenk-Reed and Juliet Nachman provided true friendships upon which I could always depend.
My mother, Audrey Beck, exposed me to "the outdoors" and supported my educational endeavor with faith and love. I am especially grateful to my husband, Steve
Nadolny, for his never-ending patience, love, and support.
With sincere gratitude, I thank each of these individuals and organizations for contributing to the success of this project.
iv TABLE OF CONTENTS
ABSTRACT ...... iii
ACKNOWLEGMENTS ...... iv
LIST OF TABLES ...... vi
LIST OF APPENDICES ...... vii
INTRODUCTION ...... 1
STUDY AREA ...... 3
METHODS
Vegetation ...... 3
Bird Use ...... 7
Statistics ...... 7
RESULTS
Vegetation ...... 8 I' I ' Bird Use ...... 11
Statistics ...... 15
DISCUSSION ...... 20
MANAGEMENT IMPLICATIONS ...... 24
LITERATURE CITED ...... 29
APPENDICES ...... 35
V LIST OF TABLES
Table 1. Description of clearcuts studied in northern Wisconsin on the Chequamegon
National Forest during the 1992 and 1993 breeding sasons ...... 4
Table 2. Description of control areas studied in Northern Wisconsin on the Chequamegon
National Forest during the summers of 1992 and 1993 ...... 5
Table 3. Characteristics of snags windthrown after the 1992 field season on the Park Falls and Glidden Districts of the Chequamegon National Forest, Wisconsin ...... 9
Table 4. Number (Na) of bird observations on snags by treatment type for the 1992 and 1993 breeding seasons on the Park Falls and Glidden Districts of the Chequamegon National Forest,
Wisconsin ...... 12
Table 5. Number (Na) of bird observations by activity type for the 1992 and 1993 breeding seasons on the Park Falls and Glidden Districts of the Chequamegon National Forest,
Wisconsin ...... 13
Table 6. Visitation rate (birds/snag/hr) for each species observed by treatment type for the
1992 and 1993 breeding seasons on the Park Falls and Glidden Districts of the
Chequamegon National Forest, Wisconsin ...... 14
Table 7. Chi square values for testing independence between snag use and treatment type for the 1992 and 1993 breeding seasons on the Park Falls and Glidden Districts of the
Chequamegon National Forest, Wisconsin ...... 16
Table 8. Comparison of used vs. unused snags within each treatment through two-sample t- test analysis ...... 17
Table 9. Mean values of continuous independent variables by treatment type and use classification ...... 21
Table 10. Logistic regression model predictions for probablility (P) of snag use ...... 26
vi LIST OF APPENDICES
Appendix A. Control snag located in a mature forest stand on the Chequamegon National
Forest, northern Wisconsin ...... 35
Appendix B. Isolated snag located within a clearcut on the Chequamegon National Forest, northern Wisconsin...... 36
Appendix C. Reserve area located within a clearcut on the Chequamegon National Forest, northern Wisconsin ...... 37
Appendix D. Variables used in analysis for bird use of snag habitat on the Park Falls and
Glidden Districts of the Chequamegon National Forest, Wisconsin ...... 38
Appendix E. Number (Na of bird observations on snags by treatment type and percentage of yearly total for 1992 field season ...... 39
Appendix F. Number (Na) of bird observations on snags by treatment type and percentage of yearly total for 1993 field season...... 40
Appendix G. Observed visitation rate (birds/snag/hr) by species and treatment type for the
1992 and 1993 breeding seasons ...... 41
Appendix H. Importance values for tree/sapling species in habitat plots by treatment type ...... 42
Appendix I. Frequency(%) of dominant shrub species in habitat plots by treatment type.43
Appendix J. Frequency(%) of dominant ground cover species in habitat plots by treatment type ...... -- ...... 44
Appendix K. Common and scientific names for bird species observed during the 1992 and
1993 breeding seasons ...... 46
Appendix L. Incidental observations of bird species using snags not included in the study sample ...... 47
Appendix M. Incidental observations of bird species using reserve areas in clearcuts ...... 48
vii Appendix N. Visitation rates of isolated snags for 20 and 40 minute observation blind intervals ...... 49 I,I
Appendix 0. Results of 8 hour observation blind data by snag treatment ...... 50
Appendix P. Number (Na) of species observed during 20 and 40 minute observation blind intervals for the isolated treatment ...... 51
viii 1
INTRODUCTION
Snags are natural forest components that provide a portion of the life support system for many species of plants, invertebrates, reptiles, amphibians, mammals, and birds
(McClelland and Frissell 1975, Thomas et al. 1979, Evans and Conner 1979, Mannan et al.
1980, Goodwin and Balda 1983). While feeding and cavity-nesting are considered the most vital uses of snags by birds, they serve a variety of other purposes (Miller and Miller
1980). Some species use snags as singing perches when attracting mates and defending territories (Cunningham et al. 1980). Woodpeckers use snags as drumming sites for territorial announcements and feed on insects living in the dead wood (Scott et al. 1980).
Raptors and flycatching birds use snags for hunting, feeding, loafing, and roosting (Scott et al. 1980, Davis 1983, DeGraaf and Shigo 1985, Arbuckle 1986, Stribling et al. 1990).
Several factors influence the use of snags by birds, including individual snag characteristics and the successional stage of the surrounding plant community (Thomas et al. 1979, Brawn et al. 1984).
The importance of the species of snag with regard to use varies between forest communities (Nietro et al. 1985). Aspen (Populus spp.)_ is an important snag species in some areas due to its abundance (Minnesota Dept. of Natural Resources 1985). Runde and
Capen (1987) found quaking aspen (f,_ tremuloides) to be one of the most frequently used tree species for cavity nesting in a northern hardwood forest in Vermont. In the North
Central states the majority of aspen is located in Wisconsin, Minnesota, and Michigan where the recommended silvicultural system for growth and reproduction is clearcutting
(Perala 1977). The practice of clearcutting, just as with any specific forest management practice, benefits some wildlife species and not others (Thompson 1986).
Management for birds can be integrated into timber management by retaining snags in clearcuts (Dickson et al. 1983). Research on clearcuts in other states has documented greater use by cavity nesting birds in areas with snags retained than in those without 2
(Dickson et al. 1983, Marcot 1983, Zarnowitz and Manuwal 1985). Typically, snags in clearcuts benefit species that select open environments and are not used by many of the cavity nesters (Conner 1978, Brawn et al. 1984). However, snag use is not restricted to cavity nesting birds and few studies have investigated this.
Snags left standing alone in clearcuts are subject to windthrow (Scott et al. 1980).
Several studies have recommended leaving clumps of snags and/or live trees containing snags in clearcut units to reduce this problem, protect wildlife habitat, benefit cavity nesters, and provide future snags (Zeedyk and Evans 1975, Evans and Conner 1979,
Raphael and White 1984, Nietro et al. 1985, Arbuckle 1986, Lundquist and Mariani 1991).
Additional research is needed to evaluate this technique.
Planning snag management mandates the determination of species-specific requirements (Nietro et al. 1985). Monitoring is essential to assess the implementation and effectiveness of snag management programs (Lundquist and Mariani 1991). Because the use of snags in Lake States aspen forests may differ from other forest types in this region, or from other regions of the United States, forest managers need specific information to provide adequate snag habitat.
In accordance with the National Snag Policy of 1977, the USDA Forest Service established a snag management guideline to meet wildlife requirements on the
Chequamegon National Forest in northern Wisconsin. This guideline requires the
"maintenance of at least 1-2 snags per acre that are at least 12 inches in dbh". In addition, the retention of "reserve areas", or clumps oflive trees, has recently been incorporated into the planning of clearcut timber sale units. Currently, there are no quantitative data evaluating the guideline and identifying the characteristics of snags most important for birds', an important element of wildlife on the forest.
The objectives of this study were to: (1) document bird use of snags retained as single isolated stems, and within reserve areas in clearcuts, during the breeding season; 3
(2) quantify snag and surrounding habitat characteristics and identify any relationships that exist between them and bird use; and (3) determine if the current snag management guideline is being met; and (4) develop recommendations for future management.
STUDY AREA
Field work was conducted on the Park Falls and Glidden districts of the
Chequamegon National Forest in northern Wisconsin. These districts encompass 147,070 ha of publicly owned land in Price, Vilas, and Ashland counties. The dominant forest types on the 2 districts include quaking aspen, upland mixed hardwoods, sugar maple
(Acer saccharum), lowland brush, lowland black spruce (Picea mariana), and lowland mixed conifer.
Ten clearcuts, 9 reserve areas located within clearcut boundaries, and 3 unmanaged forest stands (controls) were chosen for study sites. Clearcuts (5 harvested in 1991, 5 in
1992) ranged from 3.6-17.2 ha in size (Table 1). Reserve areas ranged from 0.02-0.5 ha and the control stands ranged from 25.6-104.4 ha in size (Table 2).
Chequamegon Hardwoods, which is classified as a Research Natural Area (RNA), was selected as one of the control areas. This area has not been logged since the 1930's and is primarily a second-growth, mesic northern hardwood forest with an undisturbed understory. Memorial Grove Hemlocks, also an RNA, was the second control area selected. This is a remnant old growth hemlock forest exhibiting very little evidence of human disturbance. The third control area, Doering Tract, is a state Special Interest Area
(SIA) dominated by white cedar (Thuja occidentalis), black ash (Fraxinus nigra), and red maple (Acer rubrum). A 4 ha conifer swamp, composed of black spruce and tamarack
(Larix laricina), is also located within the area.
METHODS
Vegetation
Ninety-four snags were sampled. Snags were randomly selected within 3 treatment 4
Table 1. Description of clearcuts studied in northern Wisconsin on the Chequamegon
National Forest during the 1992 and 1993 breeding seasons.
Na Na Isolated Na Reserve Clearcut Size Harvest Reserve Density snags area snags Unit name District (ha) year areas (snags/ha) sampled sampled
Hogsback Salvage Park Falls 4.0 1991 10.0 4 6
Fireside aspen(PUl) Park Falls 8.8 1991 2 10.8 7 4
Fireside aspen(PU8) Park Falls 6.4 1992 2 8.5 3 5
Sunrise Park Falls 9.6 1992 9.0 0 2
Horsebarn Park Falls 6.8 1992 0 18.7 5 0
Junction Glidden 15.2 1991 0 1.5 7 0
Gates Combo Glidden 3.6 1992 7.0 0 8
Badger Glidden 6.8 1991 0 9.2 7 0
Cat Spruce Glidden 6.0 1991 2 8.8 0 5
East Twin Lake Glidden 17.2 1992 0 9.5 7 0 a denotes number 5
Table 2. Description of control areas studied in northern Wisconsin on the Chequamegon
National Forest during the summers of 1992 and 1993.
Density Na snags Unit name District Size(ha) (snags/ha) sampled
Doering Tract Park Falls 104.4 100.0 8
Memorial Grove Hemlocks Park Falls 25.6 62.5 8
Chequamegon Hardwoods Glidden 32.0 83.2 9 a denotes number 6
types including: (1) single isolated snags in clearcuts (N= 40); (2) snags located within reserve areas in clearcuts (N=29), and (3) control area snags (N=25) (Tables 1 and 2).
A grid overlay method, which identified random starting points within each stand, was used to select control area snags. Two north-south transects located at least 25 m apart
(Swallow et al. 1986) were walked in each clearcut. Isolated snags within 10 m on either side of the transects were flagged and numbered for later identification. All snags within reserve areas were mapped and numbered. Isolated and reserve area snags to be sampled were then selected from a generated random numbers list. Snags were defined as standing dead trees at least 7 .5 cm in diameter and were selected without regard to their height, condition, or use by birds.
Modification of a quantitative method of habitat description was used to characterize the habitat surrounding each snag (James and Shugart 1970). This involved establishing a 0.04 ha circular plot centered around each snag. This plot size is commonly used by researchers for this type of study (Raphael 1980, Cline et al. 1980, Mannan et al.
1980, McComb and Muller 1983, Moriarty and McComb 1983, Morrison et al. 1986,
Swallow et al. 1986, Sedgwick and Knopf 1990). Habitat characteristics measured within these plots included: number of standing live and dead trees by dbh class, number of saplings, shrub density, canopy cover, ground cover, mean canopy height, canopy depth, and dominant shrub and ground cover species. Importance values, indicating the prominence of a species in its community, were determined for tree/sapling species and frequency distributions(%) were calculated for dominant shrub and ground cover species.
Snag characteristics recorded were: snag type (hard or soft) - hard snags are defined as being in early stages of decay and soft snags are in advanced stages (Gale 1973,
Thomas et al. 1979, Cunningham et al. 1980), species, height, dbh, number of cavities, number of feeding holes, top condition (broken or intact), number of branches, percent bark cover, presence of stubs (branches<20 cm), presence of conks (fruiting bodies of 7
decay fungi), distance to nearest edge, distance to nearest snag, and size of area in which it was located (Mannan et al. 1980, Raphael 1980). Snag density measurements were obtained through complete counts in both the clearcuts (Mannan et al. 1980, Bull et al.
1990) and reserve areas. Extrapolation of habitat plot data was used to determine snag density in the control areas.
Bird Use
Data on bird use were collected during repeated 20 minute observation periods I 'I .I: (Morrison et al. 1986) for the 1992 and 1993 breeding seasons. Use was recorded as a presence or absence response during the 4 hours following sunrise (Dickson et al. 1983).
When a snag was used the following information was recorded: bird species and sex, height and position on snag, activity type (nesting, drumming, roosting, hunting, perching, preening, food caching, feeding, singing, calling, landing on, territorial defense), and duration of activity.
Statistics
Chi square analysis was used to identify significant differences (P50.05) in snag use by birds between treatment types. Two-sample t-tests were also conducted, within each treatment, to identify those variables significantly different (P50.05) between used and unused snags.
Determination of which snag and habitat variables best predict bird use/nonuse is frequentlrdone using stepwise discriminant analysis (Hicks 1983, Swallow et al. 1986).
However, it was determined that these data violate the analysis assumptions of multivariate normality and variance homogeneity. Logistic regression (Fienberg 1980, Hosmer and
Lemeshow 1989) provides an alternative method of assessing the importance of the habitat variables, and is designed to work well with both categorical and continuous explanatory variables. The analysis was done using LogXact-Turbo version 1.1 (Mehta and Patel
1993), which permitted adjusting the standard large-sample results for the relatively small 8
sample in the study. Logit, the primary analytical function, is defined as log{rr/l-1t} where
1t is the probability of success (i.e. snag use). The estimated probability that a snag will be
used, given that it has a particular set of characteristics, is 1t = elogit/(l+elogit).
The logistic regression analysis began with screening the variables based on their
simple effects. The data set consisted of all observations from the two field seasons. Each
of the snag habitat variables was discretized, then the variable was used in a simple logistic regression. If the P-value for the regression was less than 0.10, the variable was retained
for future consideration. The initial discretizing of the variables provided a flexible approach to determining the form of the relationship, in particular whether the form was linear. It was not necessarily expected that there would be linear relationships between the probability of use and the variables. For example, should the relationship between probability of bird use and snag height look like a line or a step function?
A second screening put the variables from the first step into a single model and used backward elimination to set aside weaker variables. The remaining variables were then worked with more intensively to estimate good functional forms, and thereby derive a candidate model. Once the candidate model was constructed, the excluded variables were given a final screening as part of the candidate model (P-to-remain = 0.05). This final model identified snag and habitat variables with significant effects on snag use by birds, and was used to determine if most of the variability in snag use induced by the three treatments-had been accounted for. RESULTS Vegetation
Seven snags (3 isolated, 2 reserve area, 2 control) were windthrown after the first field season (Table 3). Ten isolated snags were added in 1993 to increase the percentage of snags actually isolated (i.e. located within clearcuts void of reserve areas). Because no birds used the control snags in 1992, 15 were added to the sample in 1993. Clearcuts on ...... -----
9
Table 3. Characteristics of snags windthrown after the 1992 field season on the Park Falls
and Glidden Districts of the Chequamegon National Forest, Wisconsin.
SITE# DISTRICT TREATMENT SPECIES TYPE DBH(cm.) HEIGHT(m)
821 Glidden Isolated Quaking aspen Soft 27.2 16.8 816 Glidden Isolated Quaking aspen Soft 22.5 12.8 996 Park Falls Isolated Yellow birch Hard 999 Park Falls Reserve area Quaking aspen Hard 15.0 21.2 815 Glidden Reserve area unknown Soft 13.8 4.5 978 Park Falls Control Hemlock Hard 48.0 11.8 893 Glidden Control Sugar maple Hard 34.0 18.0 ►
the Park Falls District contained 1.36 to 10.72 snags/ha with an average of 2.5 snags/ha.
Glidden District clearcuts contained 1.12 to 1.52 snags/ha with an average of 1.36
snags/ha. Both districts combined averaged 2 snags/ha.
Reserve area snag densities ranged from 5.12 to 13.76 snags/ha with an average of
8.24 snags/ha on the Glidden District. Values for the Park Falls District ranged from 6.16
to 40 snags/ha with an average of 20.28 snags/ha. Both districts combined averaged 16.28
snags/ha.
The control areas had snag density values of 16 (Doering Tract), 10 (Memorial
Grove Hemlocks), and 13.32 (Chequamegon Hardwoods) snags/ha.
Sugar maple (66.3), yellow birch (Betula lutea) (37.3), eastern hemlock (Tsuga
canadensis) (28.9), and snags (27.6) were determined to have the highest importance
values in the control stands. In the isolated treatment, sugar maple (46.1), snags (41.7),
ironwood (Carpinus caroliniana) (35.7), and Prunus spp. (21.6) had the highest values.
Quaking aspen (50.8), sugar maple (28.5), snags (29.7), and balsam fir (Abies balsamea)
(35.7) had the highest importance values in the reserve areas. Species of snags within the
habitat plots surrounding the sample snags were not recorded.
Sugar maple (84%) was the dominant shrub in the control areas followed by white
ash (Fraxinus americanus) (20%), yellow birch (16%), and ironwood (16%). Most
frequent ground cover species included sugar maple (64%), lady fem (Athyrium filix
femina)(44%), shield fem (Dryopteris spinulosa) (44%), and long beech fem (Dryopteris
phegopteris) (28%). In the isolated snag habitat plots quaking aspen(55.2%), ironwood
( 44.8% ), and Prunus spp. (27 .6%) were the dominating shrub types. Large-leaved aster
(65.5%), Rubus spp. (62.1 %), quaking aspen (51.7%), and Graminae (37.9%) were the
most frequent ground cover vegetation. Ironwood (86.4%), quaking aspen (45.4%), and
sugar maple (36.4%) were the dominant shrub species in the reserve areas. Most frequent
ground cover vegetation included large-leaved aster (Aster macrophyllus) (63.2%), ...
11
Graminae (54.5% ), Rubus spp. (36.4% ), and northern-bush honeysuckle (Diervilla
lonicera) (36.4% ).
Bird Use
Snags were observed for 668, 20-minute observation periods (222.6 hours) and
each snag was sampled eight times. Thirty-two snags (34%) were used by birds during the
study [(3 control (9%), 22 isolated (69%), 7 reserve area (22%)]. Of these, 8 (25%) were
used both years and 24 (75%) were used only once. Sixty-two snags (66%) observed were
never used by birds.
One hundred and seventeen observations of 31 species using snags were recorded
(Table 4). Ten of the species are cavity-nesters (4 primary, 6 secondary) that reside in the
state year round, 12 are neotropical migrants, and the remaining 9 species breed and winter
in North America with some wintering south of the United States. The number of species
using isolated, reserve area, and control snags were 28, 9, and 3 respectively. One hundred
and thirty-two individual activities were observed for 10 of the 12 predetermined activity
types (Table 5). The percentage of bird activities recorded include: 27% landing on snags;
24% singing; 16% perching; 11 % calling; 8% feeding; 5% preening; 4% nesting; 2%
drumming; 2% territorial defense; and 1% roosting.
Visitation rates (birds/snag/hour) per species were calculated for each snag treatment. Use
of control snags was low with each bird species being observed only once (Table 6). Snag species
used included 1 sugar maple and 2 eastern hemlocks and all were hard snags (in early stages of
decay) averaging 33.25 cm in dbh and 10.8 min height. Control snags not used included 9 yellow
birch, 7 sugar maple, 5 eastern hemlock, and 1 black ash. Eighteen of these snags were hard and 4
were soft (in advanced stages of decay) and averaged 36.75 cm in dbh and 11.9 min height.
Visitation rates of isolated snags were greater for species associated with open woods,
clearings, brushy undergrowth and forest edges (Table 6). Some infrequent visitation was
observed by species associated with mature woods. Used snags included 19 quaking 12
Table 4. Number (Na) of bird observations on snags by treatment type for the 1992 arid 1993 breeding seasons on the Park Falls and Glidden Districts of the Chequamegon National Forest,
Wisconsin.
Na CONTROL ISOLATED RESERVE AREA SPECIES OBSERVATIONS (Nll::25) (Nll::37) (Nll::27)
Hairy woodpecker 5 (4.3) 0 0 5 Yellow-bellied sapsucker 5 (4.3) 1 1 3 Downy woodpecker 4 (3.4) 0 3 1 Common flicker 9 (7.7) 0 9 0 White-throated sparrow 8 (6.8) 0 7 1 Song sparrow 4 (3.4) 0 4 0 Ovenbird 2 (1.7) 1 1 0 Nashville warbler 1 (0.8) 0 0 1 Chestnut-sided warbler 18 (15.4) 0 17 1 Mourning warbler 4 (3.4) 0 4 0 Black-and-white warbler 3 (2.5) 0 3 0 Common yellowthroat 1 (0.8) 0 1 0 Hermit thrush 1 (0.8) 1 0 0 Veery 1 (0.8) 0 1 0 American robin 7 (5.9) 0 7 0 White-breasted nuthatch 1 (0.8) 0 1 0 Red-breasted nuthatch 1 (0.8) 0 1 0 Eastern bluebird 6 (5.1) 0 6 0 American goldfinch 6 (5.1) 0 6 0 Ruby-throated hummingbird 4 (3.4) 0 3 1 Indigo bunting 3 (2.5) 0 3 0 Bluejay 2 (1.7) 0 2 0 Great-crested flycatcher 2 (1.7) 0 2 0 American tree swallow 2 (1.7) 0 2 0 Dark-eyed junco 2 (1.7) 0 2 0 Black-capped chickadee 1 (0.8) 0 1 0 Rose-breasted grosbeak 1 (0.8) 0 1 0 Cedar waxwing 1 (0.8) 0 1 0 Red-eyed vireo 1 (0.8) 0 1 0 Red-winged blackbird 1 (0.8) 0 l 0 Common snipe 2 (1.7) 0 2 0 Unknown 8 (6.8) 0 8 0
TOTAL 117 3 101 13
( ) Indicates percentage of total observations 13
Table 5. Number (Na) of bird observations by activity type for the 1992 and 1993 breeding seasons on the Park Falls and Glidden Districts of the Chequamegon National
Forest, Wisconsin.
Na OBSERVATIONS Na OBSERVATIONS 1992 BREEDING 1993 BREEDING TOTAL ACTIVITY TYPE SEASON SEASON OBSERVATIONS
Landing 5 (13.8) 31 (32.3) 36 (27) Singing 13 (36.1) 19 (19.8) 32 (24) Perching 2 (5.5) 19 (19.8) 21 (16) Calling 4 (11.1) 11 (11.5) 15 (11) Feeding 3 (8.3) 8 (8.3) 11 (8) Preening 4 (11.1) 3 (3.1) 7 (5) Nesting 0 5 (5.2) 5 (4) Drumming 2 (5.5) 0 2 (2) Territorial defense 2 (5.5) 0 2 (2) Roosting 1 (2.7) 0 1 (1)
TOTAL 36 96 132
( ) Indicates percentage of yearly total ----
14
Table 6. Visitation rate (birds/snag/hr) for each species observed by treatment type for the
1992 and 1993 breeding seasons on the Park Falls and Glidden Districts of the
Chequamegon National Forest, Wisconsin.
SPECIES CONTROL ISOLATED RESERVE AREA
Hairy woodpecker 0.060 Yellow-bellied sapsucker 0.008 0.006 O.Q18 Downy woodpecker 0.016 0.006 Common flicker 0.046 White-throated sparrow 0.038 0.007 Song sparrow 0.021 Ovenbird 0.008 0.006 Nashville warbler 0.007 Chestnut-sided warbler 0.094 0.007 Mourning warbler 0.021 Black-and-white warbler 0.017 Common yellowthroat 0.006 Hermit thrush 0.008 Veery 0.004 American robin 0.039 White-breasted nuthatch 0.004 Red-breasted nuthatch 0.004 Eastern bluebird 0.030 American goldfinch 0.030 Ruby-throated hummingbird 0.015 0.006 Indigo bunting 0.015 0.006 Blue jay 0.015 0.006 Great-crested flycatcher -0.016 American tree swallow 0.016 Dark-eyed junco 0.016 Black-capped chickadee 0.004 Rose-breasted grosbeak 0.004 Cedar waxwing 0.004 Common snipe 0.016 Red-winged blackbird 0.006 Red-eyed vireo 0.006 Unknown 0.040 15 aspen, 1 ironwood, 1 tamarack, and 1 yellow birch. Fourteen snags were hard and 8 were soft with an average of 21.75 cm in dbh and 11.5 m tall. Eighteen isolated snags were not used including 13 quaking aspen, 3 ironwood, 1 yellow birch, and 1 unknown. Eleven of these were hard and 7 were soft with overall average dimensions of 22 cm in dbh and 10.1 min height.
Reserve area snags were more frequently used by woodland woodpeckers (Table
6). Some use was recorded by species more typically associated with the surrounding community. Six hard and 1 soft snag were used. Snag species were comprised of 6 quaking aspen and 1 yellow birch with overall average values of 28.75 cm dbh and 11 m tall. Nineteen hard and 3 soft reserve area snags were not used. Of these, 15 snags were quaking aspen, 4 red pine (Pinus resinosa), 2 paper birch, and 1 sugar maple. Unused snags averaged 17 .25 cm in dbh and 6.9 m in height.
Eighteen snags (5 control, 9 isolated, 4 reserve area) contained a total of 30 cavities. Direct use was observed for 2 (6.6%) cavities in isolated snags. Twelve control,
22 isolated, and 16 reserve area snags showed indirect evidence of use (cavities and feeding holes).
Statistics
Chi square analysis showed significant differences (P<0.001) in bird use of snags among treatments (Table 7). Control and reserve area snags did not differ (P>0.50); however, both control and reserve area snags differed from isolated snags (P<0.001 in each case). Two-sample t-tests further indicated significant differences (P.$0.05) in snag and habitat variables between used and unused snags (Table 8). Three habitat variables were significantly different between used and unused control snags. Twelve variables (6 of each type: snag and habitat) were significantly different between used and unused isolated and reserve area snags (although the variables were different for each treatment).
Initial screening of independent variables, through logistic regression, indicated 16
Table 7. Chi square values for testing independence between snag use and treatment type for the 1992 and 1993 breeding seasons on the Park Falls and Glidden Districts of the
Chequamegon National Forest, Wisconsin
CONTROL ISOLATED RESERVE AREA
USED 3.72 8.70 3.06
NOT USED 1.32 3.10 1.10
TOTAL 5.04 11.8 4.16
Overall chi square value= 21.02 P<0.001
! I 17
Table 8. Comparison of used vs. unused snags within each treatment through two-sample t-test analysis.
SNAG TREATMENT
Variable Control Isolated Reserve Area
Area(ha) NS NS NS Canopy depth(m) NS s NS Mean canopy height(m) NS s NS %Canopy Cover NS s NS %Ground Cover NS NS NS Snags/ha NS NS NS Deciduous trees/ha NS s s Coniferous trees/ha NS s s Saplings/ha NS s s Nearest snag(m) NS NS NS Nearest edge(m) NS NS NS Snag height(m) NS NS s Dbh(cm) NS NS s Snag type * NS NS Snag species NS NS s Deciduous shrubs/ha s s NS Coniferous shrubs/ha s s s Primary branches s NS NS %Bark cover NS NS NS Cavities * s s Stubs NS s s Topography NS NS s Conks NS ,NS s Feeding holes NS NS s Top condition NS s NS Fine branches NS s NS
* - Unable to perform function due to small sample size S - Indicates significant difference (P~0.05) between used and unused snags NS - Indicates non significant difference (P>0.05) between used and unused snags 18
that snag use was not significantly different in the control and reserve area treatments.
However, significant differences were indicated between the isolated and reserve area
treatments. As the percent bark cover increased the probability of snag use decreased.
Moreover, as the number of deciduous shrubs/ha increased, snag use also increased to a
certain point, and then decreased.
The final variables retained in the model for snag use by birds were snag species,
snag height, percent canopy cover, presence/absence of conks, and number of stubs:
logit =Bo+ B1[SP1] + B2[(1-SP1)(BTL0)]+ (1-SP1)(l-HTLo)[B3(CanCov) + B4(Conks) + B5(Ht) + B6(Stub)]
Bo= -0.7321
SP1 (P = 0.0117, B1 = -2.4899) = 1 if species= sugar maple, paper birch, red pine, black ash
0 = quaking aspen, yellow birch, hemlock, ironwood, tamarack
HTLo (P = 0.00001, B2 = -1.6375) = 1 ifheight5-5m
0 otherwise
CanCov (P = 0.0015, B3 = 1.6386) = 1 if canopy covers 10%
0 otherwise
Conks (P = .0002, B4 = -2.1667) = 1 if conks are present
0 otherwise
Ht (P = 0.0185, B5 = -0.8619) = 1 if 5m 2 if 7m 3 if 9m Stubs (P = 0.0157, B6 = 1.6392) = 1 ifnumber of stubs $10 0 otherwise Both percent canopy cover and snag height, despite being continuous variables, have a discrete representation in the model. The likelihood ratio statistic for this model is 100.08 with 7 degrees of freedom. This indicates that the model explains snag use beyond that 19 expected by chance. Dickson et al. (1983) reported an association between snag and bird densities in Texas clearcuts. The difference in snag definition between the guideline and this study has an impact on density measures (i.e. number of snags/ha and distance to nearest snag) and may account for their absence in the final model. Analysis of snag species effects, using contingency table methods, showed significant differences among the species in snag use (G2 = 25,36, df = 8, P<0.002). There was a fairly clear break into 2 groups based upon the lack of significant differences within a group (P=0.36 and P=0.46 respectively). The effects of snag height (m) on bird use were considered by breaking down the data into classes and testing for differences in use. This analysis indicated the [0,5] classes differed (P=0.077) but the following did not: (5,7] (P=0.43), (7,9] (P=0.29), (9,11] (P=0.13), (11,15] (P=0.35), (15,30] (P=0.54) after it had been established that (15,20] and (20,30] were not significantly different (P=0.28). Likelihood ratio tests showed that (5,7] and (15,30} and (7,9] and (11,15] were not significantly different (P>0.55 and P>0.70 respectively). This resulted in making very short snags, with a low probability of use, a special group(HTLQ) and the 3 separate categories for snags taller than Sm. It is worth noting that if each snag is tracked individually in each measurement year rather than pooled, and run through a simple forward-stepwise logistic regression routine, the variables that result without prior screening are (in order): canopy cover, number of primary branches, number of stubs, presence/absence of conks, and numbers of deciduous shrubs per hectare. The likelihood ratio statistic for this model is 87 .22 with 6 degrees of freedom. This indicates that the final model for this study explained more of the variability in the data set. However, it is somewhat reassuring to find such different modeling approaches focusing on 3 of the same variables. Using the average values of the model variables for each treatment, the average probabilities for snag use were determined. Using the model developed by the forward- 20 stepwise logistic regression procedure, the average probability for bird use was 2.1 %, 20.6%, and 2.1 % for control, isolated, and reserve area snags respectively. Thus, a control snag that was any other species but sugar maple, paper birch, red pine, or black ash, was at least 10.8 meters tall, had 88.3% canopy coverage within the plot, had conks and the number of stubs was 5 l 0, had a 2.1 % chance of being used. Isolated snags that were not any of the species described above, were at least 11.5 meters tall, had 5.3% of canopy coverage in the plots, had conks and the number of stubs was 510, had a 20.6% chance of being used. Finally, reserve area snags that were none of the species previously mentioned, were at least 11 meters tall, had a 53.7% canopy coverage in the plots, had conks and the number of stubs was 510, had a 2.1 % chance of being used. DISCUSSION For effective snag management, retention alone is not sufficient to provide for avian wildlife. Management consists of 2 main components: quality and quantity of selected snags and live trees retained to provide future snags (Bull et al. 1980, Nietro et al. 1985). This study provides baseline information on these components of snag management and their influence on bird use in aspen clearcuts. The results indicate that the current snag management guideline should be re-evaluted in aspen clearcuts on the Chequamegon National Forest. First, the guideline requires the "retention of 1-2 snags per acre". Overall, this aspect of the guideline is being exceeded in clearcuts on both districts (Table 9). However, there are no requirements in the guideline for snag height and some snags counted during density measures were quite short. Many of these snags would not meet the standards of other researchers who have identified minimum height values in defining snags (Bull and Meslow 1977, Scott et al. 1977, Thomas et al. 1979, Mannan et al. 1980, Cline et al. 1980, McComb et al. 1986, Runde and Capen 1987). Secondly, the guideline further emphasizes the retained snags be at least 30 cm in dbh. The diameters of snags retained in clearcuts were, Table 9. Mean values of continuous independent variables by treatment type and use · classification. TREATMENT CONTROL ISOLATED RESERVE AREA Independent variable Used Unused Used Unused Used Unused Snag height (m) 10.83 11.95 11.53 10.11 11.04 6.89 Dbh (cm) 33.25 36.77 21.85 22.20 28.67 17.42 Area (ha) 51.73 53.16 10.53 9.64 009 0.02 Canopy depth(m) 7.63 9.64 0.04 1.89 7.60 4.78 Mean canopy beight(m) 27.13 22.26 2.43 10.13 25.78 21.12 %Canopy cover 88.33 83.41 5.27 7.50 53.75 68.33 Snags/ha 83.33 53.41 20.83 31.25 56.25 90.28 Deciduous trees/ha 366.70 384.10 33.33 127.10 225.00 336.10 Coniferous trees/ha 183.30 110.20 2.77 0.00 18.75 138.90 Saplings/ha 75.00 356.80 87.50 125.00 806.30 556.90 Distance to nearest edge(m) 139.00 146.80 20.38 21.51 5.24 4.02 Distance to nearest snag(m) 5.56 6.51 11.09 10.48 6.23 3.81 Deciduous shrubs/ha 2072.00 10310.00 19660.00 13250.00 5931.00 14640.00 Coniferous shrubs/ha 180.00 12.32 90.00 22.50 675.00 135.00 Primary branches 9.33 4.95 7.23 3.22 9.43 7.09 %Bark cover 60.00 81.82 66.52 64.21 77.14 77.59 Cavities 0.00 0.45 0.27 0.36 0.20 0.57 Stubs 1.33 2.71 6.36 6.36 11.62 6.16 %Ground cover 36.67 44.77 63.89 60.00 63.89 50.00 Note: Values for snag type (hard or soft) and snag species can not be calculated due to their categorical nature. 22 average, less than the minimum requirement (22 cm for isolated treatment, 20.2 cm for reserve area treatment). The average height was greater for used isolated and reserve area snags compared to unused snags (Table 9). Although differences were not significant in the isolated treatment (Table 8), this variable was retained in the final logistic regression model because the analysis indicated a height limit (5 m) below which snags will not be used. Furthermore, as height increased, use increased to a point (11 m to 15 m) and then decreased. This information should be considered for the inclusion of a height requirement in snag management. Although clearcuts contained an adequate number of snags, it is not surprising that the minimum requirement for dbh is not being met. This can be attributed to the short rotation of many of these forests which generally does not allow trees to grow big enough to meet this standard. It is also possible that clearcut logging has reduced snag numbers or led to the retention of low-quality snags, resulting in an inadequate snag resource. The reserve area treatment appears to provide an environment in which this aspect of the guideline can be achieved (Table 9). Other studies have reported dbh to be an important factor in snag management (McClelland and Frissell 1975, Brawn et al. 1984, DeGraaf and Shigo 1985). However, this study does not reflect this due to the absence of diameter in the final logistic regression model. Logging alters the composition of bird populations (Resler 1972) and the remaining snags generally provide for those species associated with the resulting structure of the stand - namely species adapted to early successional stages. The birds observed using snags in this study were generally grassland or generalist species which typically are not dependent upon snags (Marzluff and Lyon 1983). Chestnut-sided warblers (Dendroica pensylvanica), common flickers (Colaptes auratus ), white-throated sparrows (Zonotrichia albicollis ), American robins (Turdus 23 migratorius). Eastern bluebirds (Sialia sialis), and American goldfinches (Carduelis tristas) were the species more commonly observed using isolated snags (Table 1). Species occasionally observed using snags included song sparrows (Melospiza melodia), mourning warblers (Oporornis formosus), and indigo buntings (Passerina cyanea). Similar to findings reported by others (Marcot 1983, Morrison and Meslow 1983, Nietro et al. 1985), most of the cavity-nesting species observed used isolated snags for perching posts or as feeding substrates. One nest each was observed for common flickers and Eastern bluebirds. Other snag-dependent/cavity-nesting species associated with open areas were not observed using isolated snags in clearcuts. Hairy woodpeckers (Picoides villosus) and yellow-bellied sapsuckers (Sphyrapicus varius) were the most frequently observed species using snags in reserve areas (Table 4). Both species typically are associated with mature forest stands. Other species observed using these snags were those typically associated with the surrounding clearcut community. Similar to the results of Niemi and Banowski (1984), this study has shown that the presence of any snag provides for some species' needs. Snags in this study were providing more for insectivorous passerines during the breeding season. In compliance with the National Snag Policy, the snag management guideline is intended to "provide habitat needed to maintain viable, self-sustaining populations of cavity-nesting and snag dependent wildlife species" (Scott et al. 1977). From these results it is evident that isolated snags are not adequately serving all the functions for which they were intended, perhaps indicating some inadequacy of retained snags. However, these snags do play an important role in the life support system of those species using them. Isolated snags served important breeding season functions (Cunningham et al. 1980) including the provision of feeding substrates, landing, perching, and drumming posts, in addition to providing locations from which birds sang and called while defending their territories or attracting mates (Table 5). The reserve area snags seem 24 to be reducing the negative impacts of clearcuts by attracting woodland snag dependent/cavity-nesting species. The dependency of a bird species on dead trees ranges from absolute to incidental (Nietro et al. 1985). Bird use of a snag does not mean that it is optimal or even sufficient, and use of smaller dbh trees may indicate that optimal trees are not available (Miller and Miller 1980). The absence of suitable snags can be the major limiting factor for some avian populations (Haapanen 1965, Balda 1975). Furthermore, forest communities differ in terms of number, species, and size of snags necessary to support those species associated with that community (Thomas et al. 1979). Snag requirements should be considered on a community-by-community basis. Applying one guideline to different timber types throughout a forest may be an inappropriate blanket approach. Because there are bird species adapted to nearly every habitat type, management should specify those bird species that are to benefit along with those that may be harmed (Zeedyk and Evans 1975). MANAGEMENT IMPLICATIONS Ecosystem management has recently been adopted by the USDA Forest Service, which, among other things, involves leaving residual forest structure (snags, trees, downed logs) as "biological legacies" (Swanson and Berg 1991). Some of the intentions include, although they are not limited to, the maintenance of future options and within-stand diversity for wildlife habitat. Therefore, knowledge of snag and surrounding habitat characteristics, which influence snag use by birds, is necessary for informed forest management decisions. This study reinforces this concept through the identification of 1 habitat and 4 snag variables influencing snag use by avian wildlife. Snag size and state of decay should also be considered in selecting snags to be retained (Nietro et al. 1985). The snag variables of the logistic regression model (presence/absence of conks, snag height, number of stubs) are all indications of decomposition. The fact that different stages of decay are preferred by 25 different species has been well documented (Thomas et al. 1979, Brawn et al. 1984, DeGraff and Shigo 1985, Nietro et al. 1985). The results of this study provide information that can assist in the development of future aspen clearcutting prescriptions in Lake States forests. Forest managers providing snag habitat for the species observed in this study, or a subset of them, should consider the 5 model variables identified as influencing snag use and an acceptable level of snag use probability (Table 10). However, due to the empirical nature of this model, extrapolation is limited to aspen snag management in aspen clearcuts. All model variables are easily measured and readers are again referred to James and Shugart (1970) for methodology on measuring canopy cover. The highest attainable probability for snag use with this model is 84.34% which is much higher than the average probabilities determined for snag use in all treatments of this study. Again, it should be noted that use observations in this study were greater for isolated snags. Therefore, it appears that this probability prediction, and the final logistic regression model, is biased toward this treatment type. This can be supported by the value of the canopy cover variable (i.e. <10%) which was only met in the isolated treatment (Table 9). When marking the stands prior to harvesting, time and effort should be spent to select isolated snags with the desired characteristics. The value for canopy cover is easily attainable by leaving enough trees to cover at least 10% of the area (rather than doing a complete clearcut). If management is to benefit snag-dependent, cavity-nesting species associated with mature forests, the reserve area treatment is recommended (Table 4). Two-sample t-test (Table 8) and logistic regression analyses indicate snag height as a significant factor in snag use in this treatment type. However, because dbh was not retained in the final logistic regression model there is an indication that birds are not selecting snags for this variable. This is further supported by the two-sample t-test results for the isolated treatment I Ii Ii II 26 Table 10. Logistic regression model predictions for probability (P) of snag use. Puse(%) Htlo(m)a Cancov(%) Conksb Ht(m)C Stubs(#) 2.05 >Sm >10 1 3 510 10.63 >Sm >10 1 l 510 4.85 >Sm >10 1 2 510 8.59 55m >10 1 0 510 9.91 >Sm 510 1 3 510 38.16 >Sm 510 1 l 510 20.69 >Sm 510 l 2 510 8.59 9m 510 l 0 510 15.75 >Sm >10 0 3 510 51.12 >Sm >10 0 l 510 30.65 >Sm >10 0 2 510 8.59 55m >10 0 0 <10 3.47 >Sm >10 0 3 >10 16.87 >Sm >10 0 1 >10 · 7.92 >Sm >10 0 2 >10 8.59 55m >10 0 0 >10 30.65 >Sm 510 0 2 >10 51.12 >Sm 510 0 1 >10 15.68 >Sm 510 0 3 >10 8.59 55m 510 0 0 >10 0.89 >Sm >10 1 2 >10 2.25 >Sm >10 1 l >10 0.39 >Sm >10 1 3 >10 8.59 55m >10 1 0 >10 84.34 >Sm 510 0 1 510 30.65 >Sm 510 0 2 >10 30.65 >Sm >10 0 2 510 Note: Snag species include quaking aspen, yellow birch, hemlock, ironwood, and tamarack (code=O). When snag species is coded "I "(i.e. sugar maple, paper birch, red pine, black ash) the probability of snag use, for all variable combinations, is 3.75. a Influential only when snag height is 5 5m (code=l) b 1= conks present, 0= conks absent c 1 = 5m (Table 8). Nonetheless, the isolated treatment is recommended to benefit those species associated with open areas (Table 4). However, if snag management is to be species specific then further research is needed to identify the requirements for these species. Based on the literature, further management considerations can be provided. Recommendations for snag management based upon average values of used snags, rather than minimum values, have been made (Raphael and White 1978, Evans and Conner 1979). Although dbh was absent in the final logistic regression model, this variable should not be ignored. Several studies have documented the importance of this characteristic in snag selection (McClelland and Frissell 1975, Scott 1978, Mannan et al. 1980). In this study, the average dbh values of used snags, in both the isolated and reserve area treatments, were lower than the 30 cm minimum requirement of the current guideline.This reflects the need to consider redefining and/or lowering the minimum requirement of the guideline by forest type and silvicultural treatment. Generally, taller snags, and their associated larger diameters, have been related to greater use (Mannan et al. 1980). Mean values for snag height have been recommended and incorporated in guidelines for other areas. On average, snags used in this study were taller than unused snags (Table 9). However, the current guideline has no provision for snag height. In this study, bird use increased with snag height and this trend continued up to 15 m after which snag use by birds decreased (snags between 9 m and 11 m were not used very often which may be partially attributed to their low representation (14.7%) in the • overall sample). It is recommended that forest managers incorporate this range of height values ( coded 1 for the Ht variable of the logistic regression model, Table 10) into their snag management strategy. This will meet the different preferences of avian species (Sedgewick and Knopf 1990). These values should be refined for species specific management. Guidelines specifying the retention of hard and soft snags have been made 28 on other forests to meet the requirements of snag dependent species. Generally, it is recommended that all soft snags be left in addition to a specific number of hard snags per hectare. Specific guidelines (number/ha) generally apply to hard snags. Therefore, it is recommended that snag management include the retention of all soft snags ( where safe and practical) with specific characteristics (i.e. dbh, height, etc.) applicable to the retention of hard snags. Consideration also needs to be made for future snags. Aspen snags remain standing for shorter periods than other species (Reynolds et al. 1985) and more high quality snags per hectare are needed to meet species requirements over time. Providing for the replacement of these snags by retaining live trees is critical to the conservation of snag dependent species (Gale 1973, Scott et al. 1980). All snags and future snags (i.e. live trees) should be marked for their identification and protection. Recommendations of this study are limited by several factors. First, the control area data provided no basis upon which to compare the use of snags in areas where no treatment had been applied. Furthermore, these stands were not of the same timber type as the clearcuts. Further research is needed to obtain this information. In addition, small sample sizes of snags and individual observations of bird species for general snag use provided the basis for recommendations. It was decided to survey a small sample of snags intensely rather than a large sample of snags occasionally. Furthermore, the 2 breeding seasons ofthis study are a very small window in time over the lifetime of snags. Snags are important during all seasons throughout the year. Further research should be conducted during each season in the effort to further evaluate and update the guideline. Although the implications of this research are limited, forest managers can benefit from the baseline information provided. Furthermore, rather than concentrating on single factors (i.e. cavity-nesting), an evaluation has been provided regarding the role of snags and the spectrum of uses which they supply for breeding birds in northern Wisconsin clearcuts. 29 LITERATURE CITED Arbuckle, J. 1986. Snags: widowmakers or wildlife habitat? Pages 149-157 in J. A. Bissonette, ed. Is good forestry good wildlife management? Maine Agr. Exp. Stn. Misc. Puhl. No. 689. Balda, R. P. 1975. The relationship of secondary cavity nesters to snag densities in western coniferous forests. USDA For. Serv., Southwest Regional Wildl. Habitat Tech. Bull. 1. Brawn, J. D., B. Tannenbaum, and K. E. Evans. 1984. Nest site characteristics of cavity nesting birds in central Missouri. USDA For. Serv. Res. Note NC-314. Bull, E. L., and E. C. Meslow. 1977. Habitat requirements of the pileated woodpecker in northeastern Oregon. J. For. 75:335-337. _, A. D. Twombly, and T. M. Quigley. 1980. Perpetuating snags in managed mixed conifer forests of the Blue Mountains, Oregon. Pages 325-336 in R. M. DeGraff, ed. Management of western forests and grassland for nongame birds. USDA For. Serv. Gen. Tech. Rep. INT-86. _, R. S. Holthausen, and D. B. Marx. 1990. How to determine snag density. W. J. Appl. For. 5:56-58. Cline, S. P., A. B. Berg, and H. M. Wight. 1980. Snag characteristics and dynamics in Douglas-fir forests, western Oregon. J. Wildl. Manage. 44:773-786. Conner, R. N. 1978. Snag management for cavity nesting birds. Pages 120-128 in Management of southern forests for nongame birds: Proceedings of the workshop. USDA For. Serv. Gen. Tech. Rep. SE-14. Cunningham, J.B., R. P. Balda, and W. S. Gaud. 1980. Selection and use of snags by cavity-nesting birds in the ponderosa pine forest. USDA For. Serv. Res. Pap. RM- 222. 30 Davis, J. W. 1983. Snags are for wildlife. Pages 4-9 in Snag habitat management: proceedings of a symposium. USDA For. Serv. Gen. Tech. Rep. RM-99. DeGraaf, R. M., and A. L. Shigo. 1985. Managing cavity trees for wildlife in the northeast. USDA For. Serv. Gen. Tech. Rep. NE-101. Dickson, J. G., R. N. Conner, and J. H. Williamson. 1983. Snag retention increases bird use of a clear-cut. J. Wildl. Manage. 47:799-804. Evans, K. E., and R. N. Conner. 1979. Snag management. 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Shugart, Jr. 1970. A quantitative method of habitat description. Aud. Field Notes 24:727-736. 31 Lundquist, R. W., and J.M. Mariani. 1991. Nesting habitat and abundance of snag dependent birds in the southern Washington Cascade Range. Pages 221-240 in Wildlife and vegetation of unmanaged douglas-fir forests. USDA For. Serv. Gen. Tech. Rep. PNW-285. Mannan, R. W., E. C. Meslow, and H. M. Wight. 1980. Use of snags by birds in Douglas-fir forests, western Oregon. J. Wildl. Manage. 44:787-797. Marcot, B. G. 1983. Snag use by birds in Douglas-fir clearcuts. Pages 134-139 in Snag habitat management: proceedings of a symposium. USDA For. Serv. Gen. Tech. Rep. RM-99. Marzluff, J.M., and L. J. Lyon. 1983. Snags as indicators of habitat suitability for open nesting birds. Pages 140-146 in Snag habitat management: proceedings of a symposium. USDA For. Serv. Gen. Tech. Rep. RM-99. McClelland, B. R., and S.S. Frissell. 1975. Identifying forest snags useful for hole nesting birds. J. For. 73:414-417. McComb, W. C., and R. N. Muller. 1983. Snag densities in old-growth and second growth Appalachian forests. J. Wildl. Manage. 47:376-382. _, S. A. Bonney, and R. M. Sheffield. 1986. Snag resources in Florida--are they sufficient for average populations of primary cavity-nesters? Wildl. Soc. Bull. 14:40-48. Mehta, C. and N. Patel. 1993. LoxXact-Turbo: Logistic regression software featuring exact methods. Cytel Software Corp. Cambridge, MA. 250pp. Miller, E. and D.R. Miller. 1980. Snag use by birds. Pages 337-356 in Management of western forests and grasslands for nongame birds. USDA For. Serv. Gen. Tech. Rep. INT-86. Minnesota Dept. of Natural Resources. 1985. Forestry-wildlife guidelines to habitat management. St. Paul, MN 137 pp. 32 Moriarty, J. J., and W. C. McComb. 1983. The long-term effect of timber stand improvement on snag and cavity densities in the central Appalachians. Pages 40-44 in Snag habitat management: proceedings of a symposium. USDA For. Serv. Gen. Tech. Rep. RM-99. Morrison, M. L., and E. C. Meslow. 1983. Avifauna associated with early growth vegetation on clearcuts in the Oregon Coast ranges. USDA For. Serv. Gen. Tech. Rep. PNW-305. Morrison, M. L., M. F. Dedon, M. G. Raphael, and M. P. Yoder-Williams. 1986. Snag requirements of cavity-nesting birds: are USDA Forest Service guidelines being met? West. J. Appl. For. 1:38-40. Niemi, G. J., and J.M. Banowski. 1984. Relationships of breeding birds to habitat characteristics in logged areas. J. Wildl. Manage. 48:438-443. Nietro, W. A., R. W. Mannan, D. Taylor, V. W. Binkley, B. G. Marcot, F. F. Wagner, and S. P. Cline. 1985. Snags (Wildlife Trees). Pages 129-169 in Management of wildlife and fish habitats in forests of western Oregon and Washington. USDA For. Serv., Pacific Northwest Region. Perala, D. A. 1977. Managers handbook for aspen in the north central states. USDA For. Serv. Gen. Tech. Rep. NC-36. Raphael, M. G., and M. White. 1978. Snags, wildlife, and forest management in the Sierra Nevada. Pages 23-41 in Cal-Neva Wildlife. Annual proceedings of West. Sect. Wildl. Soc. and Cal-Neva. Chpt. Am. Fish. Soc. 1980. Utilization of standing dead trees by breeding birds at Sagehen Creek, California. Ph.D. Thesis. Univ. Cal., Berkley. 195 pp. _, and M. White. 1984. Use of snags by cavity-nesting birds in the Sierra Nevada. Wildl. Monograph. 86: 1-66. 33 Resler, R. A. 1972. Clearcutting: beneficial aspects for wildlife resources. J. Soil and Water Cons. 6:250-254. Reynolds, R. T., B. D. Linkhart, and J. Jeanson. 1985. Characteristics of snags and trees containing cavities in a Colorado conifer forest. USDA For. Serv. Research Note RM-455. Runde, D. E., and D. E. Capen. 1987. Characteristics of northern hardwood trees used by cavity-nesting birds. J. Wildl. Manage. 51:217-223. Scott, V. E., K. E. Evans, D.R. Patton, and C. P. Stone. 1977. Cavity-nesting birds of North American forests. USDA Agr. Handbook No. 553. 112 pp. 1978. Characteristics of ponderosa pine snags used by cavity-nesting birds in Arizona. J. For. 76:26-28. _, J. A. Whelan, and P. L. Svoboda. 1980. Cavity-nesting birds and forest management. Pages 311-324 in Management of western forests and grasslands for nongame birds. USDA For. Serv. Gen. Tech. Rep. INT-86. Sedgwick, J. A., and F. L. Knopf. 1990. Habitat relationships and nest site characteristics of cavity-nesting birds in cottonwood bottomland. J. Wildl. Manage. 54:112-124. Stribling, H. L., H. R. Smith, and R. H. Yahner. 1990. Bird community response to timberstand improvement and snag retention. N. J. Appl. For. 7:35-38. Swallow, S. K., R. J. Gutierrez, and R. A. Howard, Jr. 1986. Primary cavity-site selection by birds. J. Wildl. Manage. 50:576-583. Swanson, F. and D. Berg. 1991. The ecological roots of new approaches to forestry. For. Perspect. 1 :6-8. Thomas, J. W., R. G. Anderson, C. Maser, and E. L. Bull. 1979. Snags. Pages 60-77 in J. W. Thomas, ed. Wildlife habitats in managed forests--the Blue Mountains of Oregon and Washington. USDA For. Serv. Agr. Handbook No. 553. 34 Thompson, F. R. III. 1986. Managing timber for people and wildlife. Missouri Cons. 47:26-29. Zamowitz, J.E., and D. A. Manuwal. 1985. The effects of forest management on cavity nesting birds in northwestern Washington. J. Wildl. Manage. 49:255-263. Zeedyk, W. D., and K. E. Evans. 1975. Silvicultural options and habitat values in deciduous forests. Pages 115-127 in Management of forest and range habitats for nongame birds. USDA For. Serv. Gen. Tech. Rep. WO-I. 35 Appendix A. Control snag located in a mature forest stand on the Chequamegon National Forest, northern Wisconsin. 36 Appendix B Isolated ,;nag located within :1 clearcut on ~he Chequarnegon Tbtional Forest northern Wisconsin. 37 , Appendix C. Reserve area located within a clearcut on the Chequamegon National Forest, northern Wisconsin. 38 Appendix D. Variables used in analysis for bird use of snag habitat on the Park Falls and Glidden Districts of the Chequamegon National Forest, Wisconsin. SNAG VARIABLES SITE VARIABLES CATEGORICAL CONTINUOUS CATEGORICAL CONTINUOUS Species Height(m) Topography Canopy depth (m) Top condition Dbh (inches) Treatment type Mean canopy height(m) Type Cavities %Canopy cover Conks % Bark cover %Ground cover Fine branches Stubs Snags/ha Feeding holes Primary branches Deciduous trees/ha Use Coniferous trees/ha Saplings/ha Nearest snag(m) Nearest edge(m) Deciduous shrubs/ha Coniferous shrubs/ha Area(ha) --- 39 Appendix E. Number (Na) of bird observations on snags by treatment type and percentage of yearly total for 1992 field season. CONTROL ISOLATED RA SPECIES Na OBSERVATIONS (Na= 25) (Na= 37) (Na= 27) Hairy woodpecker 3(9) 0 0 3 Yellow-bellied sapsucker 4(12) 0 1 3 Downy woodpecker 2(6) 0 1 1 Common flicker 1(3) 0 1 0 White-throated sparrow 3(9) 0 3 0 Song sparrow 1(3) 0 1 0 Ovenbird 1(3) 0 1 0 Chestnut-sided warbler 7(21) 0 7 0 Mourning warbler 1(3) 0 1 0 Black-and-white warbler 2(6) 0 2 0 Common yellowthroat 1(3) 0 1 0 American robin 3(9) 0 3 0 American goldfinch 2(6) 0 2 0 Red-winged blackbird 1(3) 0 1 0 Red eyed vireo 1(3) 0 1 0 TOTAL 33 0 26 7 ( ) Indicates percentage of yearly total RA = Reserve Area 40 Appendix F. Number (Na) of bird observations on snags by treatment type and percentage of yearly total for 1993 field season. CONTROL ISOLATED RA SPECIES Na OBSERVATIONS (Na=25) (Na= 37) (Na= 27) Hairy woodpecker 2(2.4) 0 0 2 Yellow-bellied sapsucker 1(1.2) 1 0 0 Downy woodpecker 2(2.4) 0 2 0 Common flicker 8(9.5) 0 8 0 White-throated sparrow 5(5.9) 0 4 1 Song sparrow 3(3.6) 0 3 0 Ovenbird 1(1.2) 1 0 0 Nashville warbler 1(1.2) 0 0 l Chestnut sided warbler 11(13.1) 0 10 1 Mourning warbler 3(3.6) 0 3 0 Black-and-white warbler 1(1.2) 0 1 0 Hermit thrush 1(1.2) 1 0 0 Veery 1(1.2) 0 1 0 American robin 4(4.7) 0 4 0 White-breasted nuthatch 1(1.2) 0 1 0 Red-breasted nuthatch 1(1.2) 0 1 0 Eastern bluebird 6(7.1) 0 6 0 American goldfinch 4(4.7) 0 4 0 Ruby-throated hummingbird 4(4.7) 0 3 1 Indigo bunting 3(3.6) 0 3 0 Bluejay 2(2.4) 0 2 0 Great-crested flycatcher 2(2.4) 0 2 0 American tree swallow 2(2.4) 0 2 0 Dark-eyed junco 2(2.4) o- 2 0 Black-capped chickadee 1(1.2) 0 1 0 Rose-breasted grosbeak 1(1.2) 0 1 0 Cedar waxwing 1(1.2) 0 1 0 Common snipe 2(2.4) 0 2 0 Unknown 8(9.5) 0 8 0 TOTAL 84 3 75 6 ( ) Indicates percentage of yearly total RA = Reserve Area 41 Appendix G. Observed visitation rate (birds/snag/hr) by species and treatment type for the 1992 and 1993 breeding seasons. CONTROL ISOLATED RESERVE AREA SPECIES 1992 1993 1992 1993 1992 1993 Hairy woodpecker 0.037 0.149 Yellow-bellied sapsucker 0.022 0.049 0.149 Downy woodpecker 0.049 0.027 0.049 Common flicker 0.049 0.108 White-throated sparrow 0.149 0.054 0.018 Song sparrow 0.049 0.040 Ovenbird 0.022 0.049 Nashville warbler 0.018 Chestnut-sided warbler 0.348 0.135 0.018 Mourning warbler 0.049 0.040 Black-and-white warbler 0.099 0.013 Common yellowthroat 0.049 Hermit thrush 0.022 Veery 0.013 American robin 0.149 0.054 White-breasted nuthatch 0.013 Red-breasted nuthatch 0.013 Eastern bluebird 0.081 American goldfinch 0.099 0.054 Ruby-throated hummingbird 0.040 0.018 Indigo bunting 0.040 Blue jay 0.027 Great-crested flycatcher 0.027 American tree swallow 0.027 Dark-eyed junco 0.027 Black-capped chickadee 0.013 Rose-breasted grosbeak 0.013 Cedar waxwing 0.013 Common snipe 0.027 Red-winged blackbird 0.049 Red-eyed vireo 0.049 Unknown 0.108 42 Appendix H. Importance values for tree/sapling species in habitat plots by treatment type. SPECIES CONTROL ISOLATED RESERVE AREA Sugar maple (Acer saccharum) 66.3 46.1 28.5 White ash ~ (Fraxinus americanus) 9.1 Ironwood {Cmpinus caroliniana) 13.6 35.7 2.8 Yellow birch {Betula lutea) 37.3 3.8 Salix spp. 1.1 American basswood {Tilia americana) 9.4 2.1 2.4 Black ash (Fraxinus nigra) 3.4 Eastern hemlock (Tsuga canadensis) 28.9 Quaking aspen (Populus tremuloides) 3.1 16.1 50.8 Mountain maple (Acer spicatum) 2.5 Prunus spp. 21.6 7.9 Bigtooth aspen {Populus grandidentata) 10.9 2.4 Paper birch {Betula papyrifera) 2.5 8.7 Balsam fir (Abies balsamea) 6.4 35.7 Black cherry {Prunus serotina) 2.1 2.2 Redmm>le (Acer rubrum) 2.1 Tamarack {Larix laricina) 2.1 Choke cherry {Prunus virginiana) 1.5 Pin cherry {Prunus pensylvanica) 3.1 Red pine {Pinus resinosa) 11.9 Snags 27.6 41.7 29.7 Unknown 1.1 -- 43 Appendix I. Frequency (%) of dominant shrub species in habitat plots by treatment type. SPECIES CONTROL ISOLATED RESERVE AREA Sugar maple fAcer saccharum) 84 13.8 36.4 Mountain maple (Acer spicatum) 8 3.4 13.6 Corylus spp"' 4 Whiteash (Fraxinus americanus) 20 13.6 Yellow birch {Betula lutea) 16 3.4 Ironwood (Ca.minus caroliniana) 16 44.8 86.4 Leatherwood (Dirca palustris) 4 3.4 22.7 American basswood (Tilia americana) 12 Quaking aspen (Populus tremuloides) 55.2 45.4 Prunus spp. 27.6 22.7 Bigtooth aspen 44 Appendix J. Frequency (%) of dominant ground cover species in habitat plots by treatment type. SPECIES CONTROL ISOLATED RESERVE AREA Sugar maple ~ saccharum) 64 10.3 Quaking aspen (Populus tremuloides) 51.7 Jack-in-the-pulpet (Arisamea atrorubens) 20 Lady fem (Atbyrium filix-femina) 44 3.4 Ground pine (Lycopodium obscurum) 8 3.4 4.5 Northern ground cedar Appendix J (continued). Fireweed (Epilobium angustifolium) 6.9 Vaccinium spp, 6.9 Cyperaceae spp. 4 27.6 Northern bush-honeysuckle {Diervilla lonicera) 31.0 36.4 Barren strawberry (Waldsteinia fragarioides) 3.4 Prunus spp 3.4 9.1 Ribes spp 4 6.9 Club moss {Lycopodium spp) 4 3.4 Bead lily (Clintonia borealis) 4 3.4 4.5 Wintergreen (Gaultheria procumbens) 9.1 Fragrant bedstraw (Galium triflorum) 6.9 9.1 Sweet fern (Comptonia peregrina) 4.5 Early meadow-rue (Thalictrum polygamum) 4 22.7 Common mullein (Verbascum thapus) 6.8 Salix spp. 3.4 Long beech fern (Dryopteris phegopteris) 28 Leatherwood (Dirca palustris) 16 American basswood (Tilia americana) 4 Cinnamon fern (Osmunda cinnamomea) 8 Impatiens spp. 4 Oak fern (Gymnocarpium dryopteris) 20 Partridge berry (Mitchella repens) 8 White baneberry (Actaea pachypoda) 4 Wood anenome (Anenome guinguefolia) 4 Round-lobed hepatica (Hepatica americana) 4 Common polypody (Polypodium vulgare) 4 Unknown 10.3 4.5 46 Appendix K. Common and scientific names for bird species observed during the 1992 and 1993 breeding seasons. COMMON NAME SCIENTIFIC NAME Hairy woodpecker Picoides villosus Yellow-bellied sapsucker Sphyrapicus varius Downy woodpecker Picoides pubescens Common flicker Colaptes auratus White-throated sparrow 'Zonotrichia albicollis Song sparrow Melospiza melodia Ovenbird Seiurus aurocapillus Nashville warbler Vermivora ruficapilla Chestnut-sided warbler Dendroica pensylvanica Mourning warbler Oporomis formosus Black and white warbler Mniotilta varia Common yellowthroat Geothylpis trichus Hermit thrush Cathrus guttatus Veery Catharus fuscescens American robin Turdus migratorius White-breasted nuthatch Sitta carolinensis Red-breasted nuthatch Sitta canadensis Eastern bluebird Sialia sialis American goldfinch Carduelis tristas Ruby-throated hummingbird Archilochus colubris Indigo bunting Passerina cyanea Blue jay Cyanocita cristata Great-crested flycatcher Myiarchus crinitus American tree swallow Tachycineta bicolor Dark-eyed junco Junco hyemalis Black-capped chickadee Parus atricapillus Rose-breasted grosbeak Pheucticus ludovicianus Cedar waxwing Bombycilla cedorum Common snipe Gaillinago gallinago Red-winged blackbird Agelaius phoeniceus Red-eyed vireo Vireo olivaceous 47 Appendix L. Incidental observations of bird species using snags not included in the study sample. COMMON NAME SCIENTIFIC NAME Downy woodpecker* Picoides pubescens Common flicker* Colaptes auratus Pileated woodpecker Dryocopus pileatus White-throated sparrow* 'Zonotrichia albicollis Song sparrow* Melospiza molodia Chipping sparrow Spizella passerina Rufous-sided towhee Piplo erythrophthalmus Bluejay* Cyanocitta cristata Gray jay Perisoreus canadensis Purple martin Progne subis American tree swallow* Tachycineta bicolor Common yellowthroat* Geothylpus trichas Yellow rumped warbler Dendroica coronata Chestnut-sided warbler* Dendroica pensylvanica Mourning warbler* Oporomis formosus Veery* Catharusfuscescens American robin* Turdus migratorius Eastern phoebe Sayomis phoebe Least flycatcher Empidonax minimus Great-crested flycatcher* Myiarchus crinitus Rose-breasted grosbeak* Pheucticus ludovicianus Scarlet tanager Piranga olivacea Cedar waxwing* Bombycilla cedorum Eastern bluebird* Sialia sialis American goldfinch* Carduelis tristas Black-capped chickadee* Parus atricapillus Indigo bunting* Passerina cyanea White-breasted nuthatch* Sitta carolinensis Belted kingfisher Ceryle alcyon Common snipe* Gallinago gallinago Turkey vulture Cathartes aura Wood duck Aixsponsa Mourning dove Zenaida macroura Brown-headed cowbird Molothrus ater Rusty blackbird Euphagus caolinus American crow Corvus cryptoleucus European starling Stumus vulgaris * Species in common with use observations of sample snags 48 Appendix M. Incidental observations of bird species using reserve areas in clearcuts. COMMONNAME SCIENTIFIC NAME Yellow-bellied sapsucker Sphyrapicus varius Hairy woodpecker Picoides villosus Common flicker Colaptes auratus Downy woodpecker Picoides pubescens Black-capped chickadee Parus atricapillus Nashville warbler Vermivora ruficapilla Chestnut-sided warbler Dendroica pensylvanica Mourning warbler Oporomis fomosus Common yellowthroat Geothylpis trichus Ovenbird Seiurus aurocapillus Black-throated green warbler Dendroica virens Black-and-white warbler Mniotilta varia Golden-winged warbler Vermivora chryosptera Palm warbler Dendroica palmarum Yellow-rumped warbler Dendroica coronata Pine warbler Dendroica pinus Rose-breasted grosbeak Pheucticus ludovicianus American robin Turd.us migratorius Swainson's thrush Catharus ustulatus Veery Catharus juscescens Gray-cheecked thrush Catharus minimus White-breasted nuthatch Sitta carolinensis Red-breasted nuthatch Sitta canadensis Solitary vireo Vireo solitarius Red-eyed vireo Vireo olivaceous White-throated sparrow 'Zonotrichia ,a[bicollis Song sparrow Melospiza melodia Great-crested flycatcher Myiarchus crinitus Eastern phoebe Sayomis phoebe Cedar waxwing Bombycilla cedorum Brown thrasher Toxostoma rufum Bluejay Cyanocita cristata American goldfinch Carduelis tristas Pine siskin Carduelis pinus Eastern bluebird Sialia sialis Dark-eyed junco Junco hyemalis Purple finch Carpodacus purpureus Scarlet tanager Piranga oivacea Golden-crowned kinglet Regulus satrapa Ruby-throated hummingbird Archilochus colubris American crow Corvus cryptoleucus Common grackle Quiscalus quiscula Brown-headed cowbird Molothrus ater 49 Appendix N. Visitation rates of isolated snags for 20 and 40 minute observation blind intervals. 20 minute interval Na Birds Visitation rate* 40 minute interval Na Birds Visitation rate* 0500-0520 4 6.06 0500-0540 13 9.7 0520-0540 9 13.64 0540-0620 4 2.98 0540-0600 3 4.54 0620-0700 3 2.24 0600-0620 1 1.51 0700-0740 2 1.49 0620-0640 0 0 0740-0820 0 2.98 0640-0700 3 4.54 0820-0900 4 3.03 0700-0720 1 1.51 0720-0740 1 1.51 0740-0800 0 0 0800-0820 0 0 0820-0840 3 4.54 0840-0900 1 1.51 a Denotes number * = Indicates birds/snag/hour Note: Paired t-test analysis identified no significant differences (P~0.05) in visitation rates between intervals (P=0.94) 50 Appendix 0. Results of 8 hour observation blind data by snag treatment. TIME INTERVAL CONTROL (Na) ISOLATED (Na) RESERVE AREA (Na) 0500-0520 NONE Chestnut-sided warbler (1) NONE Indigo bunting ( 1) Common flicker ( 1) Mourning warbler (1) 0520-0540 NONE Chestnut-sided warbler (3) NONE Cedar waxwing (5) Mourning warbler (1) 0540-0600 NONE Common flicker (2) NONE Mourning warbler (1) 0600-0620 NONE Mourning warbler (1) NONE 0620-0640 Least flycatcher NONE NONE 0640-0700 NONE Mourning warbler (1) White-breasted Eastern wood pewee (2) nuthatch (1) 0700-0720 NONE Blue jay (1) NONE 0720-0740 Least flycatcher ( 1) Chestnut-sided warbler (1) White-breasted nuthatch (1) 0740-0800 NONE NONE NONE 0800-0820 NONE NONE NONE 0820-0840 NONE Rose-breasted grosbeak (1) NONE Indigo bunting (1) Cedar waxwing (1) 0840-0900 White-breasted Cedar waxwing (3) NONE nuthatch (1) Indigo bunting (1) Chestnut-sided warbler (1) a Denotes number observed Note: Results are the compilation of 2, 4 hour observation periods for 2 different snags within each treatment. 51 Appendix P. Number (Na) of species observed during 20 and 40 minute observation blind intervals for the isolated treatment. 20 minute interval Na Bird Species 40 minute interval Na New Bird Species 0500-0520 4 0500-0540 3 0520-0540 3 0540-0620 1 0540-0600 2 0620-0700 2 0600-0620 1 0700-0740 2 0620-0640 0 0740-0820 0 0640-0700 2 0820-0900 4 0700-0720 1 0720-0740 1 0740-0800 0 0800-0820 0 0820-0840 3 0840-0900 1 Note: Wilcoxon Signed Rank Test identified no significant differences (P<0.05) in number of species observed between intervals (P=0.15)