AN ABSTRACT OF THE THESIS OF
Katherine Fortner Doerge for the degree of Master of Science in General Science (Biological Science) presented onMay 22, 1978
Title: ASPECTS OF THE GEOGRAPHIC ECOLOGY OF THE ACORN WOODPECKER
(Melanerpes formicivorus)
Abstract approved: Redacted for Privacy Dennis L. McDonald
Population and habitat characteristics of Acorn Woodpeckers
(Melanerpes formicivorus) were examined in oak stands (Quercus garryana) in Benton County, Oregon. Characteristics of eight oak stands not containing Acorn Woodpeckers were also examined. The data were used to determine which factors might be related to wood- pecker presence and abundance within the northern extension of the range of this species.
Population size varied from 2 to 8 individuals with a mean of
4.25 birds per group. All were resident populations with communal storage limbs for acorns which are used as a winter food. During winter months, birds were also observed flycatching and possibly ground-feeding and gleaning for food.
Neither the area of the home rance nor the number of trees in the home range were significantly correlated to the number of wood- peckers living in an area. Rather, the number of dead limbs in the home range was the best single indicator of woodpecker number. The number of storage limbs was related to the number of dead limbs in the home range. Trees in oak stands containing Acorn Woodpeckers were larger, in diameter and had more dead limbs than trees in oak stands not containing woodpeckers. The density of trees in stands occupied by woodpeckers was lower than the density of unoccupied stands. These three factors are important to the availability of resources on which the Acorn Woodpeckers depend: acorns for winter food and dead limbs for storage and nesting.
An hypothesis for the recent extension of the Acorn Woodpecker range into northern Oregon is that it is related to the development of oak forests in the Willamette Valley. Prior to settlement in the 1840's, oak savannas were maintained by periodic ground fires.
The control of these fires after settlement has allowed the development of mature oak forests which provide suitable habitat for Acorn Woodpeckers. Aspects of the Geographic Ecology of the Acorn Woodpecker (Melanerpes formicivorus)
by
Katherine Fortner Doerge
A THESIS
submitted to
Oregon State University
in partial fulfillment of the requirements for the degree of
Master of Science
June 1979 APPROVED:
Redacted for Privacy Assistant Professor of Biology in charge of major
Redacted for Privacy Chairman Department of General Science
Redacted for Privacy
Dean of Graduate School
Date thesis is presented May 22, 1978
Typed by Leona Nicholson for Katherine Fortner Doerge ACKNOWLEDGEMENTS
I wish to thank Dr. Dennis L. McDonald for serving as my major professor and for giving me support and encouragement during this study. I am especially grateful for the openness and enthusiasm he has shared for all things, from capacitors to country music.
I would also like to thank the following people and businesses that gave me access to their land for this study: C.S. Rondeau;
F. H. Watenpaugh; L. Brooks; L. J. Volmering; E. Radke; William L.
Finley National Wildlife Refuge; Tennis West; and Midwest
Fabrication. Carol Bickford, Nancy Lyford, and Susan Smith were very helpful in the collection of field data. I am appreciative of the time that Dr. John Lyford, Susan Fuller, Finn Pond, and Tom
Doerge gave for the discussion of various aspects of this study.
This research was aided by a Grant-in-Aid of Research from
Sigma Xi, The Scientific Research Society of North America. The
Oregon State University Computer Center provided funds for computer time for data analysis.
My special thanks to my husband, Ben, who freely gave his time and energy in data collection and discussion. I am grateful for his love and support. I also am thankful for David and Lucy
McCracken and the Seekers and the spirit of adventure that we share. TABLE OF CONTENTS
Page
I. INTRODUCTION 1
II. STATEMENT OF PURPOSE AND APPROACH 7
III. METHODS 9
Surveys 9 Acorn Woodpecker Characteristics 10 Characteristics of Oak Stands not Containing Acorn Woodpeckers 15 Statistical Analysis 18
IV. RESULTS 20
Surveys 20 Acorn Woodpecker Characteristics 20 Characteristics of Oak Stands not Containing Acorn Woodpeckers 32 Comparison of Characteristics of Stands Which Do and Do Not Contain 32 Acorn Woodpeckers Regression Models Predicting Acorn Woodpecker Number and Presence 35
V. DISCUSSION 45
REFERENCES CITED 54
APPENDIX I. Population and habitat characteristics of Acorn Woodpeckers in eight oak stands in Benton County, Oregon. 57
APPENDIX II. Correlation coefficients greater than .74 of variables measured in Acorn Woodpecker areas. 58
APPENDIX III. Shrub species recorded in sixteen oak stands in Benton County, Oregon. 59
APPENDIX IV. Characteristics of eight oak stands not containing Acorn Woodpeckers. 60 LIST OF ILLUSTRATIONS
Figure Page
1 Areas surveyed for Acorn Woodpeckers.. 11
2 Acorn Woodpecker groups located in Benton County, Oregon. 12
3 Eight oak stands in Benton County, Oregon not containing Acorn Woodpeckers. 16
4 The number of woodpeckers in the group as a function of the number of trees in the home range. 24
5 The number of woodpeckers in the group as a function of the mean number of dead limbs per tree. 25
6 The number of woodpeckers in the group as a function of the number of dead limbs in the home range. 27
The number of storage limbs as a function of the number of dead limbs in the home range. 28
8 The number of storage holes as a function of the number of dead limbs in the home range. 29
9 The number of woodpeckers in the group as a function of the number of storage holes. 30
10 The number of dead limbs as a function of tree DBH. 34
11 The mean number of dead limbs per tree as a function of the mean DBH of the stand. 36
12 Density measurements of sixteen oak stands. 37
13 Percent coverage determinations of sixteen oak stands. 38
14 Relationship between the number of woodpeckers in the group and the number predicted by the regression model containing the variables: density of stand and mean number of dead limbs per tree. 40
15 Christmas Bird Counts from 1963 to 1977 of the number of Acorn Woodpeckers seen in Corvallis and Salem, Oregon. 53 LIST OF TABLES
Table Page
1 Habitat characteristics of 32 oak stands containing Acorn Woodpeckers. 21
Correlation coefficients with probabilities less than .05 between population and habitat characteristics of Acorn Woodpeckers. 23
Land use characteristics of eight oak stands containing Acorn Woodpeckers. 31
4 Land use characteristics of eight oak stands not containing Acorn Woodpeckers. 33
5 Regression models predicting Acorn Woodpecker group size considering the number of dead limbs in the home range. 39
6 Regression models predicting Acorn Woodpecker groups size not considering the number of dead limbs in the home range. 42
Regression models predicting Acorn Woodpecker presence. 43
8 T2 values for combinations of variables measured in stands occupied by Acorn Woodpeckers and those not occupied. 44 Aspects of the Geographic Ecology of the Acorn Woodpecker (Melanerpes formicivorus)
I. INTRODUCTION
Recognition of the intimate relationship between an organism and its environment is basic to ecological understanding. It was not until the early part of the twentieth century and Adams' (1909) study of community succession that the importance of this relation- ship was recognized in the study of animal distributions. Adams emphasized the interrelationships of birds and vegetation in under- standing the distribution and evolution of birds (Pitelka, 1941).
Since that time, the study of animal distribution has, developed primarily along two lines. One stems from C. Hart
Merriam's (1894) life zone concept which proposed that temperature was the major factor controlling the distribution of living organisms (Grinnell, 1914). The life zone theory stated that the northern limits of distribution are determined by the total amount of heat during the season of growth and reproduction. The southern limits are determined by the "mean temperature of a brief period covering the hottest part of the year."The over-emphasis of temperature in determining distributional limits led to the develop- ment of the biome concept which proposed that the dominant life forms of biotic communities control the distribution of animals
(Clements and Shelford, 1939; Pitelka, 1941; Kendeigh, 1954).
The second line of development stems from Adams' (1909) study emphasizing the importance of ecological factors in animal distribu- tion. Grinnell (1914) characterized the composite factors controlling distribution as the availability of food, the presence of breeding places that meet the requirements of construction, defense, and concealment, and the availability of places of refuge during the day or night or while foraging.
Man's alteration of the natural environment has made the importance of these ecological factors increasingly evident.
Factors such as temperature or dominant life forms, although important in determining animal distribution, are not the factors that we must deal with in the conservation and management of species.
These factors that delineate the range of a species are as diverse as the organisms themselves. For example, Elton (1927) found that the distribution of the Elf Owl was limited not only by the distribution of the giant cactus in which it nests exclusively, but also was limited by the distribution of two woodpecker species whose old nesting-holes are used by the owl.
The geographical region that a species occupies represents a range of environmental conditions that the species is able to tolerate. Over this range of environments, the species may respond differently in terms of the adjustments it makes which enhance its survival, growth, or reproduction. In northern Germany and the eastern United States, the Starling is migratory, but in the Faeros where the climate is oceanic it is a permanent resident (Hesse etal.,
1937).
The ecological factors which affect a species often become more evident when there are changes in the distribution or behavior of animals. The change in status of the Hooded Crow and the
Blackbird in southern Sweden from spring migrant to year-round resident was found to be a result of the general warming of the climate in Scandanavia since the 1880's (Welty, 1975). The extension of the breeding ranges of the Robin, House Wren, and Song
Sparrow southward into Georgia appears to be associated with the clearing of forests. It is thought that the availability of food and nesting sites determined their earlier distributional limits rather than climatic factors (Pettingill, 1970).
The decline in numbers of so many species in recent years points to the degree of urgency in understanding the relationship between animals and their environment. Timber practices in eastern
Texas have greatly reduced the availability of nesting and roosting trees for the Red-Cockaded Woodpecker which is now on the list of rare and endangered species (Lay and Swepston, 1975). The decline in numbers of the endangered Attwater's Prairie Chicken has been attributed to the loss of prairie habitat to farming and over- grazing (Cottam, 1962). Boyd (1962) cited several man-induced factors that have influenced changes in the bird life of
Massachusetts. Some of these factors include: clearance of wood- lands, insecticide use, and even the reduction of vegetation cover as a result of the change from wooden to wire fences.
The geographical range of the Acorn Woodpecker (Melanerpes formicivorus) extends from western North America to northern South
America. The species is highly specialized for utilizing the oak
(Quercus) community for food, storage, and nesting. Bock and Bock 4
(1974) observed that the limits of distribution coincided not with the distribution of the genus Quercus but with "points where oak variety dropped to only one common species, specifically to Quercus garryana Dougl. in the Pacific Northwest and to Quercus gambelii
Nutt. in the Rocky Mountain region (Peck, 1941; Weber, 1972)."
Their study supported the central hypothesis that "populations of
Acorn Woodpeckers are limited not only by the overall abundance of oaks but also by the number of oak species present, since the probability or magnitude of acorn crop failure in an oak community should vary in some inverse way with oak species diversity."
The Acorn Woodpecker has been the subject of extensive research in California (Ritter, 1921, 1922, 1938; MacRoberts, 1970;
MacRoberts and MacRoberts, 1976; Troetschler,1976; Swearingen,
1977). MacRoberts and MacRoberts (1976) have characterized the behavior and social organization of this species in central coastal
California based on observations of over 60 groups. They found that
Acorn Woodpeckers live in year-round groups which store food and breed cooperatively. Group size varied from 2 to 15 individuals with an average between 5 and 6. Acorns provide a major food source from late summer through the winter. Acorns are stored individually in "sockets" drilled by the woodpeckers in dead limbs and trees.
These storage granaries are filled and defended jointly by the members of the group. They also defend their territory including sap trees, hawking perches, nests, and roosts. Groups usually have only one nest in which the members incubate, brood and feed the young jointly. The reproductive rate was between .2 and .3 young 5 per adult.
Bock and Stacey (1977) have found that in southern Arizona where acorn crops are poor, the behavior and social organization are quite different from those observed in California. The approximate average group size was only two individuals. Birds were migratory, leaving the area in winter and returning in the spring. There was a large turnover in the birds that returned, most being unbanded birds. The reproductive rate was between .3 and
.4 young per adult, slightly higher than the rate in California.
Their study indicated that southern Arizona was marginal habitat for Acorn Woodpeckers.More importantly their results
"reveal a behavioral and ecological plasticity not previously suspected for this species." It was suggested that the degree of sociality in this species is environmentally determined.
Their study suggests that within the range of a species, population and behavioral characteristics may change in response to different environmental conditions. In examining such a situation, it must be assumed that the species has maintained its integrity throughout its range. This assumption is very significant especially in this situation which seems to involve a highly evolved behavioral system and the maintenance of environmental plasticity.
The northern distributional limits of the Acorn Woodpecker has recently been extended. In 1940, Gabrielson and Jewett gave
Lane County, Oregon as the northern limit of its distribution. In
1952 this species was recorded in Corvallis by Walker and in Salem by Jewett in 1954. Verner in 1965 reported Acorn Woodpeckers in 6
The Dalles, Oregon and suggested that similar habitat across the
Columbia River in Washington would likely contain this species.
This new range includes regions which are thought to represent marginal habitat since there is no diversity of oak species. II. STATEMENT OF PURPOSE AND APPROACH
The extension of the northern limits of the Acorn Woodpecker
range allows the investigation of several important questions which
are basic to our understanding of the geographical ecology of this
species:
1. What factors might be involved in the recent extension of the
Acorn Woodpecker range? Does the habitat within this extension
of the range appear to be marginal?
2. What habitat characteristics are related to woodpecker presence
and abundance in this part of the range of the species?
3. Do populations in the northern extension of the range show
plasticity toward different environmental conditions as
suggested by Bock and Stacey (1977)?
This study was designed to describe the population and habitat characteristics of Acorn Woodpeckers in the northern extension of their range. Since it would not be possible to examine all important characteristics, I have limited the scope of this study to some of those characteristics that have been shown to be good indicators of the ecology of this species. These characteris- tics are outlined below.
Woodpecker Population Characteristics
1. Distribution - present limits of the Acorn Woodpecker range
2. Status - abundance and stability
3. Group size
4. Home range Habitat Characteristics
1. Oak characteristics
a. age of stand
b. number of dead limbs
c. density of stand
d. acorn productivity
2. Habitat utilization
a. number and size of storage granaries
b. types of storage granaries
c. number of nesting cavities
3. Plant community characteristics
a. understory species and percent coverage
b. land characteristics
4. Animal community characteristics
a. species present
These characteristics were examined in relation to one another, in relation to the recent extension of the Acorn Woodpecker range, and in relation to woodpecker characteristics observed in other portions of its range.
This study is descriptive in nature and does not involve any manipulations of the woodpecker community. III. METHODS
Acorn Woodpeckers were located by driving through rural areas
and using binoculars to search out any oak stand for woodpecker
signs. The "swiss cheese" appearance of the storage granaries makes
them easily observed from a distance with binoculars.
Eight woodpecker groups in. Benton County, Oregon were used to
characterize woodpecker population and habitat relations. Stands
of oaks in this area that did not contain woodpeckers were noted and
eight were used to characterize oak communities not containing woodpeckers.
Surveys
Areas in northern Oregon and southern Washington were surveyed
for the presence of Acorn Woodpeckers using the method described.
This survey included areas where Acorn Woodpeckers had been reported
(refer to Introduction) and areas which have been suggested as potential habitat. These areas included the Willamette Valley
between Corvallis and Portland, areas along the Columbia River in
Oregon and Washington between Portland and The Dalles, and areas in
Washington between Longview and Lacey.
The survey was done March 22-25, 1978 when the oaks were without foliage and easily inspected for woodpeckers. A more
extensive search of the mid-Willamette Valley was done on April 8,
1978, to find as many populations as possible and to make notes on
the location and the characteristics of the habitat. The areas that 10 were surveyed are shown in Figure
Acorn Woodpecker Characteristics
Eight woodpecker groups were selected in Benton County
(Figure 2). An attempt was made to select populations throughout
the county. However, only one population was found north of
Corvallis and it did not prove to be a suitable group for study as
it was in a residential area. Two other criteria were used in the
final selection: accessibility and permission of owner.
The following data were collected for each group:
1. Group Size. The number of birds was estimated by direct observa-
tion and counting. The number of birds in the two largest groups
was estimated from simultaneous sightings by two observers in
separate portions of the area. In the larger groups all birds may not have been seen simultaneously, so that the estimated number of birds actually represents a minimum number of birds occupying an
area.
2. Home Range. Home range was operationally defined as the area
the woodpeckers used for storage and nesting. Also included were
the areas in which woodpeckers were observed repeatedly. The
dimensions of the major part of the home range were measured
directly and the area was calculated. In some cases, the area of
certain portions could not be measured directly because they were
inaccessible. An estimation of the area of these portions was
computed indirectly from estimates of the density and the number of
trees in the area. The number of trees in the home range was 11
Lacey
Chehalis
WASHINGTON
Longvlew
Portland PACIFIC The Dalles
OCEAN 4,,
4Salem OREGON foo C or v a II I s,-k
Eugene
1
Figure 1. Areas surveyed for Acorn Woodpeckers (shaded). The locations of Acorn Woodpecker groups are marked by x s. 12
Figure 2. Acorn Woodpecker groups located in Benton County, Oregon. The eight groups examined in this study are marked with xis and have reference letters. All other groups are marked with ois.
BP = Bike Path W = Watenpaugh FG = Fair Grounds R = Rondeau V = Volmering FB = Finley - Barn B = Brooks FP = Finley Pond 0 I 2 13
Scale inMiles
99W
Harrison Street
FG CORVALLIS Highways 20 B 34
99 W
Bel !fountain Road
FB A. William L. Finley National xFPWildlife Refuge 0 14 determined by direct count.
3. Amount of Storage and Nesting Space. Each tree in the home range of the eight woodpecker groups was examined for the presence of storage limbs. The number of storage holes in each storage limb was determined by direct count using binoculars. At the same time these observations were made, the number of nesting cavities and their orientation was determined.
4. Habitat Characteristics. The density of each oak stand was determined from the total number of trees in the home range of a group and the area that the home range included. An area varying from 40 m x 30 m to 40 m x 70 m, depending on the size of the home range, was outlined and divided into 10 m x 10 m quadrants. The corner points of these quadrants were used as a reference in sampling the trees in the stand. The diameter of the trees closest to the corner point in each of the four quadrants surrounding the corner point was measured at breast height. The number of dead limbs greater than 10 centimeters (cm) in diameter and the number of storage limbs and nest cavity limbs were recorded for each tree sampled. If there was not a tree within five meters of the corner point, no tree was recorded for that quadrant.
Because most oak stands contained very little understory cover, a random sampling method was not used to estimate coverage.
Instead, coverage was determined by a subjective estimation of the total amount of the home range area that was covered by shrub species. These species were identified and recorded. 15
Observations were also made on the use of the land and the other animals associated with the oak stand.
Charactersitics of Oak Stands not Containing Acorn Woodpeckers
Eight oak stands not containing Acorn Woodpeckers were selected in Benton County (Figure 3). All stands were within four miles of a stand containing Acorn Woodpeckers but did not directly adjoin occupied stands. As with occupied stands, accessibility and permission of owner were the primary criteria of selection.
The same habitat characteristics measured, for oak stands containing woodpeckers were also measured for the stands not containing woodpeckers.
In each stand, an area 40 m x 40 m was outlined and divided into 10 m x 10 m quadrants. Density was determined directly by counting the number of trees in the 1600 m2 area outlined. The method of using the corner points as sampling points as previously outlined was used to sample the trees. The diameter at breast height (DBH) and the number of dead limbs (> 10 cm) were recorded for each tree.
To estimate understory coverage, the 1600 m2 area was divided into 400 m2 quarters, each containing four 100 m2 quadrants. One of these four quadrants was randomly selected for each 400 m2 quarter.
The amount of the quadrant covered by shrub understory was estimated and the species were identified and recorded.
Observations were also made on land use and animal associates of these areas. 16
Figure 3. Eight oak stands in Benton County, Oregon not containing Acorn Woodpeckers.
T = Timberhill FS = Fire Station TW = Tennis West S = Southwood Park R = Radke MF = Midwest Fabrication F1 = Finley I F11'Finley II 0 I 2 3 17 I I i Scale inMiles
*T 99W
Harrison Street
TW FP. CORVALLIS x Highways 20 34
Plymouth Road
99 W
MF
Bellfountain Road
William L. Finley National F, Wildlife Refuge 18
Statistical Analysis
Twelve variables were measured for each Acorn Woodpecker group. These include: number of birds per group; number of storage limbs; mean number of storage limbs per tree; number of storage holes; mean number of holes per storage limb; number of nest cavities; number of trees in home range; area of home range; density of stand; mean DBH of trees; mean number of dead limbs per tree; percent of area covered by shrub species. The first six are considered population characteristics, the others considered habitat characteristics. Correlation coefficients and their level of significance were computed for each couplet of characters.
Nonsensical combinations were ignored.
Regression analyses were used to determine the relationship between the habitat variables and the number of woodpeckers occupying the area. F-tests were performed to determine the significance of the regressions and t-tests were used to determine the significance of regression coefficients.
Four variables were measured on each stand not containing woodpeckers. These include a density of stand; mean DBH of trees; mean number of dead limbs per tree; percent of area covered by shrub species.
These data were analyzed in relation to the data collected in oak stands containing woodpeckers. The student' t-test was used to determine if there were significant differences in the means of these variables. Hotelling's T2 statistic (Morrison, 1976) was 19
used to test multivariate means of occupied and non-occupied stands.
Probability values for T2 values were computed from F-tables using
the relationship:
N1 + N2 p 1
F - T , with p and NI + N2 p 1 (N1 + N2 - 2) p degrees of freedom where: N1 = number of observations in group 1
N2 = number of observations in group 2
p = number of variables considered
Regression techniques were used to determine how Acorn
Woodpecker presence might be related to the habitat characteristics.
An indicator variable (1 = woodpecker habitat, 0 = non-woodpecker
habitat) was used as a dependent variable and the habitat variables were used as independent variables. F-values and t-values were
computed to determine the significance of the regression and the
regression coefficients. 20
IV. RESULTS
Surveys
Nineteen Acorn Woodpecker groups were located in Benton
County, Oregon (Figure 2). Thirteen groups were located in the mid-
Willamette north of Benton County (Figure 1). No woodpeckers or woodpecker signs were found along the Columbia River or in
Washington. In these areas, oak communities that appeared to be potential habitat for Acorn Woodpeckers usually were occupied by
Lewis Woodpeckers.
The habitat characteristics associated with the 32 groups located by these surveys are given in Table 1. Eighteen of the groups were found in residential or work areas (barns, equipment yards, private residences). Thirteen provided shade or pasture for livestock. Ten were characterized by moderate to abundant under- story.
Thirty-one of the thirty-two groups had storage limbs indicating that Acorn Woodpeckers are year-round residents in this portion of their range.
Acorn Woodpecker Characteristics
Raw data are given in Appendix I. The average group size was
4.25 with a range of two to eight individuals. The group with the largest number of woodpeckers included the largest number of storage limbs, 128, and the greatest number of storage holes, 7,447. 21
Table 1. Habitat characteristics of 32 oak stands containing Acorn Woodpeckers.
Understory Residential moderate or work to abundant) Pasture area
% of groups having characteristic 31 41 56
% of groups where characteristic was extensive 15.5 25 37.5
% of groups where characteristic was present but not extensive 15.5 16 18.5
% of groups not having characteristic 69 59 44 22
There were two groups containing only two birds and they were
associated with the fewest number of storage limbs and storage
holes.
The number of nest cavities in the home ranges of these eight
groups was surprisingly large, varying from 3 to 52. It is not
known as to how many of these cavities are used by the birds or even
how many were made by Acorn Woodpeckers. They were found throughout
the home range.
The correlation coefficients between the variables measured
on oak stands containing woodpeckers with values greater than .74
are given in Appendix II. Only two of the coefficients between
population and habitat characteristics were significant (P < .05):
mean tree diameter-at-breast-height (DBH) with mean number of
storage limbs per tree and mean number of dead limbs per tree with
the mean number of storage limbs per tree (Table 2).
Of particular interest was the relationship between habitat
characteristics and the number of woodpeckers occupying an area.
However, none of the habitat variables showed significant
correlations to the number of woodpeckers. The relationships between woodpecker number and number of trees in the home range and woodpecker number and mean number of dead limbs per tree are given
in Figures 4 and 5. Neither of these relationships was significant.
It was expected that the dependency of woodpeckers upon the oak trees for food and space for nesting and storage would be evidenced by these relationships since number of trees and mean number of dead limbs per tree are related to the availability of 23
Table 2. Correlation coefficients with probabilities less than .05 between population and habitat characteristics of Acorn Woodpeckers.
Habitat Population Level of characteristic characteristic r-value significance
i number of DBH storage limbs .93 < .001 per tree
-Rnumber "R number of of dead limbs storage limbs .95 P < .001 per tree per tree 24
r .37
BP
ac w
w a. FP 0n0
0) 4 cc FG 2co R FB
100 200 300 400 NUMBER OF TREES inhomerange
Figure 4. The number of woodpeckers in the group as a function of the number of trees in the home range. 25
.41
BP (359)
* V (110) Cc
0 0 5. FP (72) 0 0 L- 4- B (158) O c" w 3- FG (235") W (84) R FB (148)
1 1 1 2 3 MEAN NUMBER OF DEAD LIMBS PER TREE
Figure 5. The number of woodpeckers in the group as a function of the mean number of dead limbs per tree. Numbers in parentheses are the number of trees in the home range. 26 resource requirements. Closer examination of the data showed that home ranges having lower mean numbers of dead limbs per tree include a greater number of trees, when supporting the sameornearly the same number of woodpeckers. The product of the mean number of dead limbs/tree and the number of trees in the home range represents the number of dead limbs in the home range. This variable did show a significant correlation (r = 80, .005 < P < .01) to the number of woodpeckers occupying an area. This relationship is shown in
Figure 6.
The number of dead limbs in the home range was correlated to the number of storage limbs in the home range (r = 80, p < .01) and the number of storage holes (r = .91, p < .001). These relationships are shown in Figures 7 and 8.
The number of birds that an area can support depends upon the winter food supply (MacRoberts and MacRoberts, 1976). This factor is related to the amount of storage space available. The signifi- cant correlation between the number of storage holes in each area and the number of woodpeckers occupying the areaillustrates this relationship (Fig. 9). If all available space (dead limbs) is used for storage, then the number of storage holes would determine the upper limit to group size. The number of dead limbs used for storage represents only 12 to 33 percent utilization for the 8 groups studied.
Land use characteriStics associated with the eight groups are given in Table 3. All but one group were in areas used by man
(residential yard or work area) or by livestock (pasture or shade). 27
r = .80
BP
(1) V wCC w 0 O 5- FP O a
U_c"4- O c
w 3- FG W 2
Z 2, R FB
I -
100 200300 400 500 600 700 NUMBER OF DEAD LIMBS In home range
Figure 6. The number of woodpeckers in the group as a function of the number of dead limbs in the home range. 28
r .91
130- BP
120-
100 - J V 90-
4D 8 0 O FG E 70-
b.. oe 60. .c cr c50 B w m 40- FP z 30- FB 20-
10-
0 0 100 200 300400 500 600 700 NUMBER OF DEAD LIMBS In home range
Figure 7. The number of storage, limbs as a function of the number of dead limbs in the home range. 29
r= .84
8' BP U) 7 w 01 z 6- w (.9 u) 5" 00z FG v) 0D 3 w m 2 FP Bw z FB
R 100 200 300 400 500600 700 NUMBER OF DEAD LIMBS inhome range
Figure 8. The number of storage holes as a function of the number of dead limbs in the home range. 30
r.88
BP
7 V
Y B- U
5. FP 0
0 4. /". 0Di
3 .FG 2 z 2 R .F8
0 0 1000200030004000 5000600070100 NUMBER OF STORAGE HOLES
Figure 9. The number of woodpeckers in the group as a function of the number of storage holes. 31
Table 3. Land use characteristics of eight oak stands containing Acorn Woodpeckers.
Pasture or Residential shade for yard or Wildlife livestock work area habitat
Rondeau x
Bike-Path
Volmering
Brooks x
Watenpaugh
Finley (B)
Finley (P) x
Fair Grounds x
% of groups having characteristic 62.5 75 12.5
(B) Barn (P) Pond 32
Only three areas had understory. Two of these were the only areas not associated with livestock. The shrub species recorded for each area are given in Appendix III.
Characteristics of Oak Stands not Containing Woodpeckers
Raw data for eight oak stands are given in Appendix IV. The mean DBH ranged from 26.6 cm to 53.4 cm and mean numbers of dead limbs per tree ranged from .43 to 2.11. Two of these unoccupied stands, Radke and Midwest Fabrication, showed Acorn Woodpecker signs indicating that they had supported groups at some time in the past.
These two stands had the highest mean DBH's (53.4 cm, 50.8 cm) and mean number of dead limbs per tree (2.11, 2.00) of the eight non-woodpecker stands.
Land use characteristics of the eight stands are given in
Table 4. Four of these stands were associated with residential or livestock areas. Two of these were the two stands showing wood- pecker signs. The scrub species recorded for each area are given in
Appendix III.
Comparison of Characteristics of Oak Stands Which Do and Do Not Contain Acorn Woodpeckers
The trees in oak stands containing Acorn Woodpeckers were significantly larger in diameter (t 6.11, d.f. = 574, P < .001) and had significantly more.dead limbs (t = - 5.23, d.f. = 574,
P < .001) than trees in oak stands not containing woodpeckers.
Figure 10 shows the relationship between these two variables. 33
Table 4. Land use characteristics of eight oak stands not containing Acorn Woodpeckers.
Pasture or Residential shade for yard or Wildlife livestock work area habitat
Fire Station
Timberhill
Finley I
Finley II
Southwood Park
Radke
Tennis West
Midwest Fabrication
% of groups having usage 12.5 37.5 62.5 .61
m 5.50 8, 2 a 0 I..
0 floe 0_ _le *el' op_ u-2.75 . ip lois 0 CC ***** , , 4, a ,:: W I. 4% .14 1:13 .. 2 .. ,,,. , 60 ,.11'00 b. O.** . 40, 4% es .4 9. . :, - AP 0.00 .:: 9.0 34.4 62 84.4 TREE DBH (cm) Figure 10. The number of dead limbs as a function of tree DBH. 35
There is a correlation (r = .61, t = 18.5, d.f. = 574, P < .001) between the size of the tree (which is related to its age) and the number of dead limbs it has. This relationship is graphically more evident when comparing the mean DBH and mean number of dead limbs for each of the 16 stands (Figure 11).
The mean density of the eight oak stands containing wood- peckers was found to be significantly less (t = - 1.90, d.f. = 14,
P < .05) than that of the eight stands not occupied (Figure 12). difference was found in the mean percent coverage between these groups (Figure 13).
Regression Models Predicting Acorn Woodpecker Number and Presence
The number of dead limbs per stand was the best single indicator of woodpecker group size (r = .80, R2 = .64). The next best variable was found to be the mean DBH which in addition to the number of dead limbs per stand accounted for 71 percent of the variation in woodpecker number. These regressions are shown in
Table 5.
However, the variable "number of dead limbs per stand" is not a completely independent variable since it depends on the number of trees the woodpeckers select to use. If this variable and the other non-independent variable, number of trees in home range, are not considered, the best single predictor of woodpecker number is the mean number of dead limbs per tree (r = .41, t = 1.11, d.f. = 6,
.1 < P < .2). If the variable "density of stand" is added to the model, the r-value increases to .70. Figure 14 is a plot of the 36
.96
4-
2- ire
z
0 25 30 35 40 45 50 55 60 65 70 MEAN DBH PER STAND( cm)
Figure 11. The mean number of dead limbs per tree as a function of the mean DBH of the stand. DENSITY OF( trees/I00 STANDN meters2) cm oO CO 111111111111111111111111111111111111111IIMMIIIIIMMIMM 111111111111111111111111111111111111111111=11 (i) 1111111111111111111111111111011111111111111 11111111111111111 1111111111111111111111 -n ®1111 MI II II MI III III IV 1 II I MN 1111 M 1111 NI II 111 O P;) 121111111011111aMill111111111111111111111111111 O IMMINIMMENIMEMEMINIERIMMI LC o n.) PERCENT COVERAGE oUl oCD o- 4 a) up 3o_ (I) 053o CO- 111111111111111111111 < N.P M a jj- 11111111111111111111111H111111111111111111111111 -. 1 to-4coxn -n-TI--13 IIIIIIIIIIIIIIIIIIM to "rt 11111111111111111 111111111111111111111111111111111111 PK rn (1) ininsainissmicamm0111111111111111111111 CD -4Z issimmonmaimismoommi111111111111111 8£ Ta: 39
Table 5. Regression models predicting Acorn Woodpecker group size considering the number of dead limbs per home range.
Model F Probability
No. of woodpeckers = 10.89 .01 < P < .725 + .012 (no. of dead 1, 6 d.f. limbs/stand) R2 = .64
No. of woodpeckers = 6.20 .01 < P < .05 - 1.56 + .012 (no. of dead 2, 5 d.f. limbs/stand + .049 (iT DBH) R2 = .71 40
r = .70
ti. 0 W BP wcr5 FG 2 w FP Z °4 oa_ w o 1- 03 c.)
.FB a. °R
2 3 4 5 6 7 NUMBER OF WOODPECKERS
Figure 14. Relationship between the number of woodpeckers in a group and the number predicted by the model: Number of (mean number of dead = - 4.20 + 1.38 (density) + 2.30 woodpeckers limbs per tree) 41 values predicted by this model against the actual values. Sample regressions of the number of woodpeckers against combinations of the four habitat variables are given in Table 6. None of these regressions had probabilities of less than .05.
Sample regressions of the indicator variable for woodpecker presence (0 = non-woodpecker stand; 1 = woodpecker stand) against the four original habitat variables are shown in Table 7. All of the models had probabilities greater than .05 and had non-significant regression coefficients (P > .05). Hotelling's T2 statistics for combinations of the habitat variables are given in Table 8. 42
Table 6. Regression models predicting Acorn Woodpecker group size not considering the number of dead limbs per home range.
Model F Probability
No. of woodpeckers = 1.20 P > .25 2.42 + .838 (mean number of dead 1, 6 d.f. limbs/tree) R2 = .17
No. of woodpeckers = 2.42 .1 < P < .25 - 4.20 + 2.30 (mean number of 2, 5 d.f. dead limbs/tree) + 1.38 (density of stand) R2 = .49
No. of woodpeckers = 1.28 P > .25 - 2.91 + 2.68 (mean number of dead limbs/tree) 3, 4 d.f. + 1.32 (density) - .039 (mean DBH) R2 = .49 43
Table 7. Regression models predicting Acorn Woodpecker presence.
Model F Probability
I = .983 - .143(density) 3.60 .05 < P< .1 R2 = .20 1,14d.f.
I = 1.18 - .148(density) 3.34 .05 < P < .1 - .648(coverage) 2,13 d.f. R2 = .34
I = 1.73 - .197(density) 2.13 .1 < P <.25 - .704(coverage) 3,12d.f. - .008(R DBH) R2 = .35
I = 3.12 - .249(density) 1.97 .1 < P <.25 - .662(coverage) - .058(W DBH) .571(R no. dead limbs/tree) R2 = .42 44
Table 8. T2values for combinations of variables measured in stands occupied by Acorn Woodpeckers and those not occupied.
Variables included T2 F d.f. Probability
Density 5.50 3.34 2,13 .05< P <.1 Coverage
Density Coverage 7.46 2.13 3,12 1< P<.25 Mean DBH
Density Mean DBH 5.67 1.64 3,12 1< P<.25 Mean number of dead limbs/tree
Density Mean DBH Mean number of dead 10.03 1.97 4,11 .1< P<.25 limbs/tree Coverage 45
V. DISCUSSION
A possible hypothesis about the recent extension of the Acorn
Woodpecker range is that it is related to the development of Quercus garryana forests in the Willamette Valley. Prior to settlement by immigrants in the 1840's, oak savannas were maintained by periodic ground fires thought to be set by the native indians. The control of these fires after settlement allowed the development of closed- canopy oak forests (Thilenius, 1964).
Thilenius (1968) found that the mean age of forest form 11.1. garryana in the mid-Willamette Valley was 90 years. The establish- ment of these forests occurred shortly after the period of settle- ment. The age of the oak stands occupied by Acorn Woodpeckers is approximately 80 to 120 years (estimated from DBH measurements and data presented by Thilenius, 1964).
Thelinius (1964) notes that:
. . . at no time during the developmental period were these (Quercus garryana] communities free from man-caused influences. Heavy livestock grazing, wood cutting, etc. were important factors of their environment.
These influences help to explain why the majority of the oak stands occupied by woodpeckers were associated with livestock or residential areas. The thinning of oak stands used for livestock may account for the low densities of areas occupied by woodpeckers.
The livestock may increasethe number of flying insects in these oak stands which provide an important food source for this species.
The question concerning the suitability of habitat for Acorn 46
Woodpeckers in the Northwest centers primarily around the question of acorn productivity. Since Q.. garryana is not an important commercial species, a relatively small amount of research has been done on this species as compared to the highly-valued eastern oaks.
For this reason, the discussion of acorn productivity is based primarily on the general characteristics of growth and production established by studies done in the eastern and central United States.
Several factors are known to affect acorn production. Gysel
(1956) summarized them as: species; characteristics of individual trees; age; climate; and crown exposure. The conditions required to produce good acorn crops may vary among species. Climate and other environmental factors may have different effects on various species (Gysel, 1956).
Studies of southeastern oaks have shown that younger, smaller trees have comparatively low productivity (Downs and McQuilkin, 1944;
Cypert, 1951). The effect of climatic factors has often been seen--
"the killing of oak flowers as the result of low temperatures in the spring" (Gysel, 1956). However, temperature extremes are generally rare for the Willamette Valley (Thilenius, 1964). Precipitation occurs primarily in the winter months with very little occurring during the summer. In years when precipitation is abnormally low
(as occurred in 1977), acorn corps may be affected. In talking to people concerning the use of their land for the present study, it was mentioned that acorn crops in 1977 were relatively poor.
However, in other areas used in this study acorns appeared to be plentiful, indicating that the magnitude of drought effects may 47 depend on local characteristics as well.
Another factor Gysel (1956) discussed was crown exposure.
Acorn production of the exposed area of the crown has been shown to be much greater than that of the lower unexposed portions. The importance of light for acorn production is also evidenced by studies showing lower production by suppressed trees in forest stands. The association of Acorn Woodpeckers with oak stands having significantly lower densities may be an indication of the importance of this light factor in acorn production.
It appears that acorn production levels in this area are sufficient to support Acorn Woodpeckers. Stored acorns have remained in granaries through the summer in some cases. However, I have also observed that in a few areas (in particular, the two groups containing only two individuals) acorn stores were exhausted by spring. It appears that birds make use of alternate food sources when they become available even when acorn stores remain. During the winter months, birds were also observed flycatching and possibly ground-feeding and gleaning for food.
Another factor that should be considered in determining habitat suitability is the availability of dead limbs for acorn storage and nesting cavities. The factors that cause limbs to die are probably as numerous and diverse as those affecting acorn production. They, however, have not been investigated quite so thoroughly.
Warming (1925) writes that "the shade cast by younger branches retards the assimilatory activity of the leaves on older 48 branches, and thus renders impossible the normal development of buds and ripening of wood" resulting in the death of the branch.
Kramer and Kozlowski (1960) attribute the death of shaded lower branches in forest stands to competition for water with the exposed upper branches. They speculate that the increased photosynthetic activity of the exposed branches results in a higher diffusion gradient for water. The lower photosynthetic activity of the shaded branches have a lower diffusion gradient which decreases their ability to compete for water.
Baker (1934) states that in dense stands, "side branches die out early in life while they are yet small." These small limbs quickly decay and fall off. In less dense stands, "the crowns are long and persistent with large limbs which, when dead, are long in decaying and dropping off." This factor may also be a reason for the association of Acorn Woodpeckers with less dense oak stands, as they use the slowly decaying limbs for granaries.
In considering the factors influencing acorn production and dead limb availability together, it becomes more clear as to why
Acorn Woodpeckers are only recent immigrants to this area. Most basically, habitat had to be available that could supply both requirements of the woodpecker. The wide-spreading savanna oaks most probably produced suitable acorn crops as a result of large canopy exposure, but probably did not provide the dead limbs that seem to be a product of forest stands. The widely-spaced oaks would also be difficult habitat in which to maintain social cohesion and the fire factor may also have deterred their movement 49 into these areas.
The development of mature oak forests provided both resources.
Oak stands with lower tree densities would have more dead limbs and greater acorn production than higher density stands. It was with these lower density stands that Acorn Woodpeckers were associated.
Each of the variables useful in predicting the number of woodpeckers in a group can be related to their possible effects on acorn productivity or dead limb availability (refer to Tables 5 and
6). These variables include the number of dead limbs in the home range, the number of dead limbs per tree, the mean DBH, and the density of the stand which have already been discussed in relation to the availability of these resources.
The only significant (P < .05) regressions were those in which the number of dead limbs per stand was included. Although there was a strong correlation between this variable and the group size, the percent utilization of these dead limbs was quite low.
It does not seem probable that dead limbs are limiting unless wood- peckers select limbs on the basis of criteria other than size (dead limbs greater than 10 cm in diameter were counted--grossly decayed or broken limbs were omitted). The strong correlation between the number of storage limbs and the number of dead limbs available may be an indication of selective usage of dead limbs. Factors such as limb height, orientation, or size class may narrow the availability of suitable limbs.
If all suitable dead limbs are being used fully, then the amount of storage space could be a limiting factor in group size as 50
MacRoberts and MacRoberts (1977) suggest. However, trends in analysis (refer to Figure 5) seem to indicate that as group size increases the home range is extended to include sufficient numbers of dead limbs. If this is the case, group size would only become limited when all available space for home range extension is used.
Regression analysis of the habitat variables, excluding the number of dead limbs per home range and the number of trees per home range, showed that density and mean number of dead limbs per tree to be the most informative variables. Both of these variables were positively related to Acorn Woodpecker number. However, these variables are not independent of each other. As previously reviewed, very dense stands have smaller dead limbs which quickly drop off and decay. The less dense stands have larger dead limbs which persist. Therefore, maximizing the number of woodpeckers would most probably involve intermediate values of both variables because of their interaction.
The inability to differentiate woodpecker habitat from non- woodpecker habitat may indicate that some of the unoccupied stands are suitable habitat that the woodpeckers have not yetoccupied.
However, it must also be considered that some other factor or factors determine woodpecker presence that have not been evaluated.
The characteristics of Acorn Woodpeckers examined in this study are similar to the general description of this species in
California. In the northern extension of their range, this species is characterized by year-round groups of individuals sharing a common area and storing food cooperatively. However, a few 51 differences were observed that can be related to habitat differences in this area.
MacRoberts and MacRoberts (1976) reported that woodpecker groups usually used one or more large, isolated trees as storage granaries. They found that the average number of granaries was 2.1 with a range of one to seven (n = 53). Acorn Woodpeckers observed in this study maintained large numbers of small granaries. The average number was 75.2 with a range of 16 to 128 (n = 8). There were virtually no large dead trees and only a few small ones in the home ranges of these groups.
The spacing of granaries throughout the area would increase the difficulty of resource defense. In California, where suitable habitat is in short supply, resource defense is very important to the survival of the group (MacRoberts and MacRoberts, 1977). In
Oregon where outside population pressures are not so great and available habitat does not seem to be limited, this does not appear to be a problem. During the course of this study, I saw only one interaction that I would classify as territorial behavior.
In his discussion of the formation of bonds between animals,
Konrad Lorenz (1966) wrote:
The principle of the bond formed by having something in common which has to be defended against outsiders remains the same, from cichlids defending a common territory or brood, right up to scientists defending a common opinion and--most dangerous of all--fanatics defending a common ideology. In all these cases, aggression is necessary to enhance the bond.
If it is supposed that the defense of a common storage granary helps to maintain social cohesion in Acorn Woodpecker groups the loss of 52 this central identity may be a factor that could allow the break- down of group integrity.
However, there is little evidence that this has yet occurred.
My observations of vocal and visual displays by Acorn Woodpeckers indicate that these groups do maintain a high degree of social cohesion. I could not observe differences between these displays and those described by MacRoberts and MacRoberts (1976) for
California populations.
Christmas bird counts from 1960 to 1977 show the increase in abundance of Acorn Woodpeckers in the Willamette Valley (Figure 16).
Acorn Woodpeckers have apparently not become established in
Washington. It is possible that the gradual northward extension of the range has not yet reached Washington. However, the abundance of
Lewis' Woodpeckers observed in potential habitat may be a factor hindering the initial establishment of Acorn Woodpeckers, as acorns are also the major winter food of Lewis' Woodpeckers. Bock (1970) stated that Lewis' Woodpeckers may be prevented from occupying oak stands by competition with Acorn Woodpeckers. It also is conceiv- able, however, that Acorn Woodpeckers could be prevented from becoming established in an area if Lewis' Woodpeckers are already present.
It appears that once Acorn Woodpeckers become established and develop storage facilities they will persist as long as acorns are available. The abundance of oak habitat would allow woodpeckers to forage well outside their home range should acorn crops be unusually low. 53
1963-65 1966-68 1969-71 1972-74 1975-77 YEARS Figure 15. Christmas Bird Counts from 1963 to 1977 of the number of Acorn Woodpeckers seen in Corvallis and Salem, Oregon 54
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Cottam, C. 1962. Is the Attwater Prairie Chicken doomed? Audubon 64:328-330.
Cypert, E. 1951. Suggestions for the management of oak forests for mast production. Mimeo paper presented at the S. E. Assoc. Game and Fish Commissioners Conf. Edgewood Park, Miss. 8 pp. (cited by Gysel, 1956).
Downs, A. A. 1944. Estimating acorn crops for wildlife in the southern Appalachians. Jour. Wildl. Mgmt. 8:339-340.
Downs, A. A., and W. E. McQuilkin. 1944. Seed production of southern Appalachian oaks. Jour. Forestry 42:913-920.
Elton, Charles. 1927. Animal Ecology. Sidgwick and Jackson, Ltd., London.
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Gysel, Leslie W. 1956. Measurement of acorn crops. Forest Science 2:305-313.
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Thilenius, John F. 1964. Synecology of the white-oak (Quercus garryana Douglas) woodlands of the Willamette Valley, Oregon. Ph.D. Thesis. Oregon State University.
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Troetschler, Ruth G. 1976. Acorn Woodpecker breeding strategy as affected by Starling nest-hole competition. Condor 78: 151-165.
Verner, J. 1956. Northern limit of the Acorn Woodpecker. Condor 67:265.
Walker, K. G. 1952. Northward extension of the range of the Acorn Woodpecker in Oregon. Condor 54:315.
Warming, Eug. 1925. Oecology of Plants. Oxford Univ. Press., London. 422 pp.
Weber, W. A. 1972. Rocky Mountain Flora. Colorado Associated University Press, Boulder. 438 pp. (cited by Bock and Bock, 1974).
Welty, Joel C. 1975. The Life of Birds. W. B. Saunders Company, Philadelphia. APPENDICES Appendix I. Population and habitat characteristics of Acorn Woodpeckers in eight oak stands in Benton County, Oregon.
WOODPECKER CHARACTERISTICS HABITAT CHARACTERISTICS
o Mean DU Number of Mean number Mean number Number of Density of treesMean number Coverage Number of storage of storage Number of of holes Number of trees in Area of of stand in stand of dead by woodpeckers limbs in limbs per storage per storage nest home home range (trees per (centi- limbs per shrub JrISTAuP,---hgrne,-MWM____txte__, __11.01e_s______limb___cosItle,_ _J-wige___ 1me1ecs__,L,__100.m11_ _metq_K§1 ____ee___specie...,
Rondeau 2 16 .11 326 20.38 3 148 5362 2.76 38.1 .90
Bike-Path 8 128 .36 7447 58.18 32 359 8874 4.05 41.4 1.76 0
Volmering 7 94 .85 7104 75.57 52 110 8661 1.27 66,1 3.60 0
Brooks 4 52 .33 2460 47.31 18 158 4969 3.18 41.5 1.80 .33
Watenpaugh 3 64 .76 2270 35.47 12 84 9655 .87 64.4 3.55 0
Finley (B) 2 31 .18 1828 58.97 3 171 8814 1.94 43.5 1.57 .75
Finley (F) 5 39 .54 2561 65.67 18 72 3364 2.14 57.5 2.43 .33
Fair Crounds 3 78 .33 4496 57.64 20 235 4608 5.10 36.9 1.02 0
Mean 4.25 62.8 .43 3561.5 52.40 19.8 167.1 6788.4 2.66 48.7 2.07 AR
Standard. Deviation 2.25 36.5 .26 2560.0 17.54 16.1 93.4 2449.6 1.42 17.1 1.04 .28 58
Appendix II. Correlation coefficients greater than .74 of variables measured in Acorn Woodpecker areas.
r Correlation Variable Variable coefficient
Number of trees in home range density .75
density DBH - .81 density '31- dead limbs/tree - .75
x DBH Tc dead limbs/tree .97 x DBH Tc storage limbs/tree .93
i dead limbs/tree x storage limbs/tree .95
# of storage limbsin home range # of storage holes .94 II of storage limbsin home range # dead limbs in home range .91 # of storage limbsin home range # cavities .77
II storage limbs # of woodpeckers .82
# storage holes // dead limbs in home range .84 # storage holes # cavities .90 # storage holes # of woodpeckers .88
11 of dead limbs in home range # of woodpeckers .80
# cavities # of woodpeckers .86 59
Appendix III. Shrub species recorded in 16 oak stands in Benton County, Oregon
)4 U) 0 M P 00 P-1 4-I..0 ,..0..---....0-r1r-i Cl) 03 ,..00.0 ODPIP-I 4-)vI F-I'0 CUF-T- .61 0 0s--s-0MN-I}-1H0 3 0 M .1.-4 (Ti }-I -)...0 o 4J CdP.I $4 tO oL.,,o cr) s1 ,3 (i) (f) N I a.) ..x o 0.) 01 (1) CU 01,.0 (1)-1 (1) '0 W E0 cll,--i,--1 P W,0,--1ri +-).. 03 GrL,.10 4-1 00r4 W E000'0G0
Species .E7-II .i7-,1 i=1 E'lf) gTo' ctsi g '..1 irl g4 i=44 c2g
Corylus cornuta (California Hazel) Berberis aquifolium (Oregon Grape) Amelanchier florida (Pacific Serviceberry) xx xxx x Crataegus douglasii (blk. hawthorn) x x x xxx Malus diversifolia (OR crab apple)
Osmaronia cerasiformis (Indian plum) xx xxx Prunus virginiana (com. chokecherry) xx Rosa gymnocarpa (little wild rose) x xx xx xx Rosa rubiginosa (sweet briar rose) xx xxxxx xx Rubus laciniatus (evergr. blk. berry) Rubus thyrsanthus xx (Himalaya berry) Rubus vitifolius (wld. blk. berry) xx Cytisus scoparius (Scotch broom) Rhus diversiloba (poison oak) xx xxxxx Symphoricarpos albus (snowberry) x xx xxxxx xx Symphoricarpus mollis (creeping snowberry) 60
Appendix IV. Characteristics of eight oak stands not containing Acorn Woodpeckers.
Density ofMean Mean number stand DBH of dead limbs Percent trees/100 m2(cm) per tree Coverage
Fire Station 5.00 37.3 1.38 .27
Timberhill 2.25 41.7 1.42 .58
Finley I 5.56 30.7 .71 .01
Finley II 5.94 34.1 1.13 .65
Southwood Park 2.56 44.9 1.29 .38
Radke 3.06 53.4 2.11 .002
Tennis West 5.69 26.6 .43 .29
Midwest Fabrication 2.69 50.8 2.00 .81
Mean 4.09 39.93 1.30 .37
Standard Deviation 1.48 8.88 .53 .27