Nesting Habitat and Abundance of

Snag-Dependent Birds in the Southern

Washington Cascade

Richard W. Lundquist and Jina M. Mariani

I

I

Authors

RICHARD W. LUNDQUIST is a wildlife biologist, Raedeke

Associates, Seattle, Washington 98115. JINA M. MARIANI

is a wildlife biologist, USDA Forest Service, Deer Lodge

National Forest, Butte, Montana 59703.

Abstract

We examined abundance patterns and nesting-habitat use of

eight cavity-nesting bird species and the brown creeper, by

using point-count data collected during the breeding seasons

of 1984 and 1985 and nesting data collected from 1983 to

1986 in the southern Washington Cascade Range. Naturally

regenerated Douglas-fir/western hemlock forest stands were

sampled, representing one of three general age-classes: young

(55-80 years), mature (95-190 years), and old-growth (210-

730 years). Stands within the old-growth age-class also

represented a variety of moisture conditions.

Woodpeckers showed no clear and consistent abundance

patterns among forest age- and moisture-classes. Vaux’s

swifts were consistently more abundant in old-growth stands

(all moisture-classes) in both 1984 and 1985. During both

1984 and 1985, chestnut-backed chickadees were most abundant in wet old-growth stands, red-breasted nuthatches were

most abundant in dry old-growth stands, and brown creepers

were most abundant in mesic old-growth stands. In general,

counts of most of the bird species we studied were lowest

and most variable in young and mature stands.

We found few consistent bird-habitat correlations, Numbers

of both chestnut-backed chickadees and Vaux’s swifts correlated most strongly with density of live trees >lOO cm in

diameter at breast height (d.b.h.), and swift counts correlated

with density of snags >50 cm d.b.h. Except for swifts, relative abundances of snag-dependent bird species were not

well-predicted by densities of snags, perhaps because all forest stands sampled were naturally regenerated and contained

numerous snags.

Except for chestnut-backed chickadees, few nests of any

cavity-nesting species were found in young stands. Most of

the chickadee nests found in young stands, however, were in

old remnant snags, not in trees produced in the current

stands. Cavity nesters disproportionally selected large, hard

snags for nesting. In particular, selection of hard snags by

hairy woodpeckers in this study area contrasted with findings

of other studies in the Pacific Northwest, on which current

management guidelines have been based. Woodpeckers and

creepers used western white pine snags disproportionately,

but chickadees and nuthatches nested primarily in Douglas-fir

and western hemlock. Disproportionate use of certain tree

221
species for nesting was probably closely related to their

decay characteristics. Sample plots centered on nest trees of

all species contained higher densities of large, hard snags

than randomly sampled vegetation plots. Management recommendations for Douglas-fir forests of the Washington Cascades include retention of tall, hard snags > 76 cm d.b.h. for

all species. White pine snags are particularly important for

woodpeckers and creepers, and Douglas-fir and western hemlook snags should be retained for chickadees and nuthatches.

In designing snag-retention areas, managers should provide

adequate snag distribution over large areas, live-tree replacement, and patches of older stands.

Introduction

Two of the goals of the Old-Growth Forest Wildlife Habitat

Program were to identify species that may depend on or find

optimum habitat in old-growth forests and to determine features of these stands that distinguish them as better habitatparticularly species that depend on elements lacking in managed forests. Snags are often removed, either because of

safety or fire hazard, or because they are commercially useful

(Lowery and others 1977, Snellgrove 1977, Snellgrove and

Fahey 1977, USDA Forest Service 1976).

Several studies have shown the importance of snags to many

wildlife species, especially birds, for nesting, feeding, shelter,

communication, and resting (Balda 1975, Conner and others

1975, Haapanen 1965, Marcot 1983, McClelland 1977,

Raphael and White 1984). Although cavity-nesting birds and

snags have been studied in various locations in the Pacific

Northwest (Bull 1980, Cline and others 1980, Madsen 1985,

Mannan and others 1980, Zamowitz and Manuwal 1985), to

date no study has examined habitat preferences in the productive Douglas-fir/western hemlock forests of the Washington

Cascade Range. Because use of nesting and foraging habitat

by cavity-nesting birds in these forests may differ from that

in other regions of North America or other forest types in the

Pacific Northwest, forest managers need specific local information to provide adequate habitat for these species in light

of conflicting values placed on snags. In response to this

need, we began our study in 1983. Our objectives were to

compare relative abundance estimates of snag-dependent bird

species across an array of Douglas-fir forest stands of different age- and moisture-classes; to examine the relation between bird abundance estimates and densities of live trees

and snags in these stands; to characterize nesting sites of bird

species in various stand age-classes and to evaluate use of

forest habitat elements for nesting in relation to their availability; and to discuss management considerations for cavityand bark-nesting birds in the Southern Washington Cascades

Province.

Methods

Study Area

This study was done in the Southern Washington Cascades

Province (Franklin and Dyrness 1973) west of the Cascade

Crest in the Gifford Pinchot National Forest and in Mount

Rainier National Park. Forty-eight forest stands represented

young (55-80 years old, n = l0), mature (95-190 years old,

n = l0), and old-growth (210-730 years old, n = 28) ageclasses (see frontispiece). All stands originated from natural

disturbance; that is, they have undergone no silvicultural

manipulation. All stands were in the Western Hemlock Zone

(Franklin and Dyrness 1973); because of limited availability

of sufficiently large stands, particularly low-elevation old

growth, eight stands (six old-growth, one mature, one young)

were above 1000-m elevation at the upper end of the Westem Hemlock Zone, where the transition to the Pacific Silver

Fir Zone begins. Stands ranged from 404- to 1218-m

elevation.

During spring and summer of 1986, cavity-nesting birds were

studied on a subset of 17 stands in the Packwood and Randle

Ranger Districts of the Gifford Pinchot National Forest and

in the southern part of Mount Rainier National Park. Six

stands were young, five were mature, and seven were

old-growth.

The general study area is dominated by a maritime climate

(Brubaker, this volume) characterized by cool, wet winters

and warm, dry summers. Most precipitation occurs between

October and April, but annual and monthly precipitation can

vary greatly among years.

Vegetation Sampling

Vegetation and habitat characteristics were measured in

nested circular plots (0.05 and 0.2 ha) centered on each of

12 bird count stations systematically located in each stand.

We tallied live trees by species and diameter at breast height

(d.b.h.) (l- to 10-, 11- to 50-, and >50-cm classes in the 0.05-

ha plot plus a >lOO-cm class in the 0.2-ha plot). We counted

snags by species, diameter-class (l0-19 cm in the small plot

and 20-49 and 250 cm in the large plot), and decay-classes

(1 to 4, from hardest to most decayed, modified from Cline

and others 1980). Sampling criteria conformed with standard

protocols established for other studies.

To obtain more detailed information on snag attributes and

densities, snags (standing dead trees 210 cm in d.b.h. and

22 m tall) were also characterized, measured, and tallied in a

30-m-wide belt transect consisting of 11 l00-m-long segments along lines between bird counting stations in each

stand. All snags 250 cm in d.b.h. and the first five snags in

each of two smaller d.b.h.-classes (l0-19 cm and 20-49 cm)

counted within each segment were characterized by species,

diameter (cm), height (m), decay-class, number of limbs,

222
bark remaining (percent), top condition (intact or broken),

needle presence, presence and number of excavated cavities,

and presence of woodpecker feeding sign. All subsequent

snags in the two smaller diameter-classes in each segment

were then tallied by decay- and height-class (2-5 m, >5 m).

Bird Abundance Counts

Bird populations were sampled on all stands during the spring

breeding seasons of 1984 and 1985 by the point-count method. Verner (1985) and selected references in Ralph and Scott

(1981) describe the technique in more detail. For a more detailed description of the sampling design and constraints, see

Carey and Spies (this volume). In the southern Washington

Cascades, each stand contained 12 count points systematically located 150 m apart and at least 75 m from roads or

edges of adjacent habitat.

Each stand was visited six times between 25 April and 12

July 1984, and between 30 April and 28 June 1985. During

each visit, detections of all bird species were recorded during

8-minute periods at each counting station after a l-minute

pause on arrival at the station. To the extent possible, observers avoided double-counting of individual birds from

multiple stations during each visit to a stand, particularly

with wide-ranging species such as woodpeckers.

Observers were trained and tested in bird identification (both

aural and visual cues) and distance estimation for 1 week

beginning each sampling season to improve consistency

among observers (Kepler and Scott 1981). Stands were

assigned so that at least two observers visited each stand

alternately during a given season (and across seasons) where

possible. Limited time and resources and long distances

between groups of stands prevented us from attaining a more

optimal stand assignment as a way of limiting observer bias

and variability. Fifteen observers assisted in the bird counts,

of which three participated both years.

Nest- and Cavity-Tree Searches

In 1983-85, nests were most often discovered during routine

bird counts. Stands were also searched after morning counts

or on days when weather prohibited counting. In 1985, we

devoted additional days exclusively to nest searches on a

subset of stands.

In 1986, one observer systematically searched a subset of

stands for nests between 22 May and 3 July. Each stand was

visited twice: searches began in the early morning and continued until the entire stand was covered, usually by midafternoon. Only one stand was visited per day. Two field

assistants briefly helped search two stands in each forest

age-class. Search time was standardized as much as possible

on all sites during all years. Because some areas were

sampled more years than others (for example, Wind River

pilot studies), however, total search time differed among

stands that were not included in the 1985 and 1986 searches.

We confirmed activity at potential nest or roost trees following the criteria of McClelland (1977) except that for purposes

of analysis, we treated active roost and active nest sites together as active trees. Where no adult was observed entering

a cavity, the tree was termed simply a “cavity tree.” We

classified inactive cavities into the following categories

based on general cavity size and shape (dimensions compiled

from Bent 1964): pileated woodpecker (7.6-11 cm, oval);

northern flicker (6.9-7.5 cm, round); unidentified small woodpecker, representing both hairy woodpeckers and red-breasted

sapsuckers (3.8-5.1 cm, round); and unidentified nonwoodpeckers, representing chestnut-backed chickadees and redbreasted nuthatches (12.5 cm, irregularly shaped).

Characteristics recorded for each nest and cavity tree included the following: tree species, status (live or dead and

top condition, after McClelland 1977), decay-class (after

Cline and others 1980), diameter-class, and height (m);

percentage of bark remaining; number of limbs >l m long

remaining; origin of tree (current or previous forest stand)

and presence of fire scar; and surface evidence of heartwood

decay. Decay evidence was classified as in McClelland

(1977). Additional nest characteristics included height of

active nest above ground (m) and evidence of use by birds

(either direct or indirect).

We sampled vegetation characteristics surrounding each nest

and cavity tree in concentric 0.05-ha and 0.2-ha circular

plots, centered on the nest tree, in a manner identical to that

used for vegetation plots surrounding the bird-count stations.

Data Analysis

We used simple counts to analyze point-count bird abundance data. Raphael (1987a) showed that simple counts can

provide as good an estimate of relative abundance as more

complex techniques (Burnham and others 1980, 1981; Emlen

1971,1984; Reynolds and others 1980), when analyses are

limited to within-species trends across similar (forested) habitats. Thus, for our analyses, we assumed equal detectability

of each bird species among forest age- and moisture-classes.

Because all stands received equal sampling effort in both

years, we report number of detections recorded during count

periods per visit (total count at each stand divided by six

visits) for each species and year. For wide-ranging and less

frequently encountered species such as woodpeckers, we

departed from the standard protocol by including detections

beyond the 75-m limit. For the smaller woodpeckers, detection distances did not exceed 150 m, and for the larger species, none exceeded 250 m. In addition, Vaux’s swifts were

typically detected while foraging on the wing in or near the

223
forest canopy. As a result, we included all detections of

swifts that were apparently using the stand, even though no

distance estimate could be made because of their movements.

Differences in bird species’ abundances among forest ageand moisture-classes were tested by a series of one-way

analyses of variance (ANOVA) and multiple range tests (Zar

1984). ANOVA is generally robust to small departures from

normality and to moderate heterogeneity of variances when

sample sizes are nearly equal (Sokal and Rohlf 1981). We

log-transformed bird counts [log10(x+l)] before analysis to

meet the underlying assumptions of normality and equality

of variances more closely. The log transformation, as opposed

to others, best approximated normality and made the means

independent of variances. Based on Bartlett’s test (Sokal and

Rohlf 1981) on the log-transformed data, sample variances

were sufficiently homogeneous (P > 0.05).

We should caution, however, that the inferential statistical

procedures performed on our data should be viewed as exploratory, rather than as conclusive demonstrations of statistical significance. Although the study stands represent a wide

range of geographic and environmental conditions in the

region, they do not represent a random sample. Moreover,

bird count stations were not sampled randomly. Therefore,

conclusions on abundance patterns or relation to habitat

should be viewed with caution.

We examined associations between counts of each bird species and habitat variables in two different but related ways.

First, we computed Spearman rank correlation coefficients

(SPSS, Inc. 1986) to look for significant correlations between

tree and snag densities and counts of each bird species. For

this analysis, we first summarized vegetation data into the

seven most commonly occurring tree species (or groupings),

with the four d.b.h. classes of live trees and two decay-classes

(hard = classes 1 and 2, and soft = classes 3 and 4) of snags.

This large set of variables was reduced to 22 (appendix

table 7) by examining highly significant correlations among

vegetation variables. Any pairs of variables with correlations

>O.5O (explaining >25 percent of each other’s variances)

were either combined into one, or the more ecologically interpretable variable was retained, whichever was appropriate.

Thus, variables such as all live trees >l00 cm d.b.h. or live

western hemlock < 50 cm d.b.h. were created.

In computing a large number of correlations, some may

appear statistically significant (that is, P < 0.05) because of

random sampling error. We therefore focused on correlations

with the same sign (positive or negative) in both years, and

emphasized those that were significant at P < 0.01. We

considered conflicting results, such as correlations that were

positive one year and negative the next, as possible evidence

of Type I error (Marcot 1984, Meslow and Keith 1971).

Even correlations that are consistently significant demonstrate

numerical association only, not necessarily some biologically

meaningful cause.

Second, we further investigated associations between birdabundance counts and tree and snag densities by means of

stepwise multiple linear regression (Kleinbaum and Kupper

1978, using SPSS, Inc. 1986). This approach generated equations explaining each bird species’ abundance from vegetation variables and was used for descriptive, rather than predictive, purposes. The stepwise procedure evaluates each

variable to be entered while controlling for variables already

in the equation. Because of low sample size (n = 48 stands)

and some remaining intercorrelations, we generated a new,

smaller set of uncorrelated vegetation variables using factor

analysis (Afifi and Clark 1984). The initial factors, each of

which is a linear combination of all (22) original variables

and explains a known amount of the total variance in vegetation data, were extracted by principal components analysis

with the Varimax rotation to ease interpretation. We interpreted the factors with a minimum eigenvalue of 1.0

(Battacharyya 1981) by examining the relative sizes of

correlations (“loadings”) between the factors and original

variables.

Bird counts and vegetation variables were first logtransformed for regression analyses to meet underlying

distributional assumptions more closely. We regressed

transformed counts of each bird species on vegetation factor

scores separately for 1984 and 1985 data. Because of the

number of equations generated and time limitations, we were

unable to search for better fits with polynomial and interaction terms, which may explain some species distributions

more fully (Meents and others 1983). We evaluated the accuracy of each regression 2equation by the adjusted coefficient

of determination (adjusted R ), an unbiased measure of the

percentage of total variation in bird abundance explained by

the equation (Sokal and Rolff 1981: 661; Zar 1984: 336) and

by the standard error of estimate for the equation [(MSE),

Kim and Kohout 1975: 331; Draper and Smith 1981: 20,34].

We also explored among-species variation in nest-tree

characteristics by means of principal components analysis

without rotation. Seven of the 11 nest-tree variables used in

the analysis were entered as dichotomous variables, coded as

0 if the attribute was absent and 1 if it was present. These

included top condition (broken, intact), tree condition (alive,

dead), fire evidence (absent, present), and four tree species

variables: Douglas-fir, western hemlock, western white pine,

and other. A variable describing number of limbs (>1 m long)

present was coded into intervals of 10 branches: 1 to 10

224
(coded 1), 11 to 20 (coded 2), and so on, or 0 if absent. We

entered the other variables-tree diameter, tree height, and

percentage of bark remaining (arcsine-transformed)-as

continuous variables.

As with the regression analyses above and in other studies

(Conner and Adkisson 1977, James 1971, Rotenberry and

Wiens 1981, Whitmore 1977), principal components analysis

is often used as a data reduction and ordination technique to

describe habitat relationships among breeding bird species.

For this analysis, however, it was used only as a first-order

exploratory tool to identify attributes that accounted for

much of the variation in nest trees.

For all nests except those of brown creepers, we used twogroup linear discriminant function analysis (Lachenbruch

1975), using SPSSX (SPSS, Inc. 1986) to compare nest-site

vegetation structure with samples representing general stand

vegetation structure. We selected stand vegetation plots

(those centered at bird-counting stations not containing nest

trees) randomly from those stands where nests were found in

two ways, and a separate analysis was done for each of

them. The first sample was stratified so that the number of

“random” plots equaled the number of nest-site vegetation

plots in each forest age-class. This gave each age-class the

same weight in both groups (nest site and random) and

equalized the sample size of each group in the data set. The

second sample was stratified to equalize the groups by stand

to correct for disproportionately large numbers of nest plots

on any given stand.

We included 15 variables in the analysis: percentage cover

by logs (decay-class 1); percentage cover by deciduous

shrubs or trees 0-2 m and 2-15 m tall; total canopy cover

(>15 m tall) (all percentage-cover variables recorded on an

octal scale); average height of dominant canopy trees (in 8-m

intervals); total density of live trees 1 to 10 cm, 11 to 50 cm,

51 to 100 cm, and >l00 cm in d.b.h.; total density of hard

snags 10 to 19 cm, 20 to 49 cm, and > 50 cm in d.b.h.; total

density of soft snags 20 to 49 cm and > 50 cm in d.b.h.; and

density of stumps and stubs (snags <5 m tall and 210 cm in

d.b.h.). All variables for the analysis were log-transformed.

We recorded nest-site vegetation data for 58 of the active

nests and for 23 of the trees with inactive cavities (“random”

search data) for a total sample size of 81.

We performed the stepwise discriminant analyses using

Wilks’ method, and the single function derived was evaluated

by the significance of the chi-square statistic based on Wilks’

lambda (SPSS, Inc. 1986). We interpreted the discriminant

function by examining the magnitude of the pooled withingroup correlations between the discriminant score and the

original variables (structure matrix) (Hull and Nie 1981,

Raphael and White 1984, Williams 1981). We used classification techniques (SPSS, Inc. 1986) based on the same data set

used to derive the discriminant function to assess the ability

of the function to separate the groups effectively. The

proportion of cases correctly classified according to actual

group membership indicated the success of the betweengroups separation. Further discussions of the theory and

application of discriminant analysis can be found in Williams

(1981, 1983) and Afifi and Clark (1984).

Where sample sizes permitted, we compared use of snag

diameter-class, species, and condition for nesting with availability in the forest by means of log-likelihood G-tests,

which are analogous to, and often preferred over, chi-square

analysis (Sokal and Rohlf 1981: 704; Zar 1984: 52-53). We

used Williams’ (1976) correction to the G-statistic to obtain

a better approximation to the chi-square distribution, even

with only one degree of freedom. This correction appears to

be superior to the Yates correction for continuity in such

cases (Sokal and Rohlf 1981).

Because of small sample sizes for any one bird species, some

pooling was necessary. Also, our samples were not large

enough to analyze data comprehensively in multiway contingency tables and to search for interaction among the dimensions. Thus, we analyzed each tree attribute (diameter,

species, decay-class) separately. Expected frequencies were

calculated from the appropriate snag-density distributions on

the stands from which the data came. Because the distribution of snags differed between forest age-classes, we evaluated the use of trees by nesting birds separately in each forest

age-class, where possible. For most of the tests, however,

small samples forced us to pool young with mature stands

(hereafter termed “second growth”). Because live trees with

nests or cavities constituted only a small fraction of the total,

they were excluded from the tests.

Results

Bird Abundance Among Stand Types

Total counts of the four woodpecker species were generally

too low and variable to detect significant differences among

the five stand types in either 1984 or 1985 (table 1). All four

were detected in all age- and moisture-classes, but not in all

stands. Hairy woodpeckers were the most frequently detected, and red-breasted sapsuckers were relatively rare. Except

for sapsuckers, total counts of woodpeckers were lowest in

mature stands. Counts in old-growth stands varied substantially with moisture-class. Hairy woodpeckers were slightly

more common in wet old-growth stands in both years; no

consistent pattern was found among old-growth moisture

classes between years for northern flickers or pileated

woodpeckers.

The four nonwoodpecker species treated here were encountered more frequently than woodpeckers. Mean counts of

these species were slightly lower in 1984, but the general

225
Table I-Mean number’ of snag-dependent bird species detected per census, based on point counts in the 

southern Washington Cascades, spring 1984 and I!% 

Species Ye= 

Pilcatcd woodpecker 

Northern flicker 

Hairy woodpecker 

Red-breasted sapsucker 

Chestnut-backed chickadee 

Red-breasted nuthatch 

Brown creeper 

Vaux’s swift 

1984 

1985 

1984 

1985 

1984 

1985 

1984 

1985 

1984 

1985 

1984 

1985 

1984 

1985 

1984 

1985 

Forest type 

3.85 A 

2.15 A 

4.00 

I .“” x 2.50 B 

t.40 AB 3.40 BC 

.17A .I3 A 

.28 A .58 A 

0.42 0.28 0.12 

.I5 .3O .20 

.I3 .20 .52 

.55 .42 .37 

1.07 .55 .57 

1.32 .92 .65 

.07 .07 .07 

0.17 

.69 

1.43 

2.20 

2.01 

1.78 

.43 

.58 

1.54 

6.35*** 

2.72* 

1.10 

3.26* 

4.78” 

6.41*** 

11.68*** 

patterns were similar in both years. Vaux’s swift was the 

only cavity-nesting species with counts significantly higher 

in old growth (all moisture-classes) than in the other forest 

age-classes (P < 0.001) (table 1). Chestnut-backed chickadccs were more common in wet old-growth stands, significantly so in 1985 (i’ < 0.001). Red-breasted nuthatchcs were 

generally more abundant in dry old-growth stands, significantly so in 1984 (P i 0.05). For nuthatches, however, multiple range tests failed to separate mean counts in dry oldgrowth stands from the other stand types, which may indicate 

that at least one ‘Type II” error was committed in the analysis; it can result from small sample sizes (causing a lack of 

statistical power) OT highly variable counts within a given 

stand type (Zar 1984). On the other hand, the overall 

ANOVA result could have been a Type I error, but at least 

the trends were consistent between years. 

Brown creeper counts differed significantly among the stand 

t-es in both years (P < 0.05). In 1984, creepers were significantly less abundant in young stands than all the other stand 

types. In 1985, multiple range tests failed to detect any significant differences among stand types. Although abundance 

patterns differed between 1984 and 1985, creeper counts 

were highest in mesic old-growth stands both years. 

Bird Abundance in Relation to Tree and Snag Densities 

Correlation analysis-Few bid-habitat correlations were 

consistently significant in both years. Chestnut-backed chickadee and Vaux’s swift counts were most strongly (positively) 

correlated with density of total live trees >loO cm d.b.h. in 

both years (table 2). Chickadee numbers also correlated positively with live redcedars 51 to 100 cm in d.b.h. and redcedar snags >50 cm in d.b.h. Swift counts correlated positively with several other kinds of trees and snags that 

reached maximum densities in old-growth stands (all live 

Abies and other conifers up to 100 cm in d.b.h., live western 

hemlock 51 to 100 cm in d.b.h., and snags 250 cm in d.b.h.). 

Brown creeper counts correlated positively with densities of 

hard Douglas-fir snags >50 cm in d.b.h. 

Red-breasted nutbatches correlated positively with densities 

of live vine maple and negatively with redcedar snags 20 to 

49 and >50 cm in d.b.h. Haby woodpecker count correlated 

positively only with the density of live hemlocks 51 to 100 

cm in d.b.h.; pileatcd woodpecker, northern flicker, and 

sapsucker counts did not correlate consistently with any of 

the vegetation variables tested. 

Factor analysis of vegetation variablesSix factors were 

derived that had eigenvalues greater than 1.0, three of which 

explained at least 10 percent of the total variance (table 3). 

226 
Table 2--Spearman rank correlation coefficients between

mean counts of snag-dependent birds and densities of live

Table 3-Factors derived by factor analysis on 22 vegetation

trees and snags

variables, including percentage of total variation explained,

highly associated variables, and factor loadings

Yeara

Bird species

Variable” (tree 1984 1985

sizes in cm d.b.h.) (n = 47) (n = 46)

Percentage Cumulative Highly associated

of total percentage variablesb

Factor a variation variation (tree sizes in cm d.b.h.)

Factor

loadings

Live PSMEc l-100 -0.87

All PSME snags 20-49 -.82

All live trees >lOO .70

Live Abies 1-100 .64

All snags l0-19 -.57

Live hardwoods 1-100 -.77

All TSHE snags 20-49 .74

Live TSHE 51-100 .69

AlI Abies snags 20-49 .66

All TSHE snags 550 .60

All 20-49 A THPL .82

Live THPL l-50 .80

All THPL snags 250 .67

Live THPL 51-100 .64

All PIMOsnags 250 .87

All PIMO snags 20-49 .71

Live otherconif. l-100 .66

Hard PSME snags 550 .64

Soft PSMEsnags 250 .87

Stumps and stubs .80

Live TSHE l-50 .67

Pileated woodpecker (none)

Northern flicker (none)

Hairy woodpecker Live TSHEb51-100 0.32* 0.34”

Red-breasted sapsucker (nc4

Chestnut-backed

chickadee All live trees > 100 .30* ,404’

Live THPL51-100 .30* .40**

Stumps and stubs -.33’ -.35*

THPL snags 250 .32* .37’

Red-breasted nuthatch Live ACCI l-50 .4344 .46**

THPL snags 20-49 -.41”9 -.45**

THPL snags 250 -.32” -.40**

Vaux’s swift AU live trees l-100 .64*** .68***

Live PSME l-10 -.55”‘” -.56’**

Live Abies I-100 .39** .41’4

Live “conifers” l-l 00 .53’“’ .46’*

Live TSHE 51-100 .434’ .63”**

Live THPL 51-100 .43”” .47””

All snags IO-19 -.31* -.37*

Hard PSME snags 250 .30* .38’*

All TSHE snags 250 .46*’ .44**

Brown creeper Hard PSME snags 250 .39”” .32’

’ Only coefficients significant for both seasons and those significant at

P < 0.05 are shown.

b Tree species codes are as follows: ACCI, vine maple; PSME, Douglasfin TSHE, western hemlock, THPL, western redcedar; Abies. Pacific

silver fir, grand fir. and noble fir; “conifers,” all other conifers except

those above.

Together they accounted for 78 percent of the total variance.

Variables with high positive loadings on the first factor included densities of live trees > 100 cm in d.b.h. and live

Abies 5100 cm in d.b.h., both of which tend to be higher in

cooler, moister old-growth stands. Variables with high negative loadings on factor 1 were those typically more abundant in younger stands: densities of live Douglas-fir SlOO cm

in d.b.h., Douglas-fir 20 to 49 cm in d.b.h., and all snags 10

to 19 cm in d.b.h. Thus, stands with high scores on the first

factor tended to be older, wetter stands, and those with low

scores tended to be younger stands.

The second factor (14.6 percent of the total variance) was

highly positively associated with trees and snags that were

most abundant’in mesic old-growth conditions: densities of

western hemlock snags, both 20 to 49 cm and 150 cm in

d.b.h., live western hemlock 51 to 100 cm in d.b.h., and

Abies snags 20 to 49 cm in d.b.h. The factor was also highly

negatively associated with densities of live hardwoods 1100

cm in d.b.h. The third factor (12.8 percent of the variance)

1 31.7 31.7

2 14.6 46.3

3 12.8 59.0

4 7.4 66.5

5 6.2 72.7

6 5.5 78.2

a Factors listed are those extracted by principal components analysis that

pd eigenvalues greater than 1.0.

Variables listed for each factor are those most highly associated with it

(that is, with high factor loadings), as determined by the varimax rotation.

’ Tree species codes are as follows: PIMO, western white pine; PSME.

Douglas-fir, TSHE, western hemlock, THPL, western redcedar; Abies,

Pacific silver fir, grand fir, and noble fir; “conifers,” all other conifers

except those above.

was highly positively associated with western redcedar:

snags 20 to 49 cm and 250 cm in d.b.h. and live trees GO

cm and 51 to 100 cm in d.b.h.

Factors 4 (7.4 percent), 5 (6.2 percent), and 6 (5.5 percent)

each accounted for much less of the total variance. Variables

with high (positive) loadings on factor 4 were generally

those most abundant in drier old-growth sites: western white

pine snags 20 to 49 cm and 250 cm in d.b.h., live other conifers, including pines, 5100 cm in d.b.h., and hard Douglas-fir

snags >50 cm in d.b.h. Factor 5 was most strongly associated

(positively) with soft Douglas-fir snags ~50 cm in d.b.h., and

factor 6 was most strongly associated with forest elements

more abundant in younger stands: total stumps (natural) and

stubs, as well as live western hemlock trees <50 cm in d.b.h.

Multiple regressions-The multiple regression equations of

all bird species accounted for less than half of the observed

variation in total counts (table 4). Except for Vaux’s swifts

and red-breasted nuthatches, the factors entering regression

equations for all bird species were not consistent between

years. Two factors (1 and 5) entered the equations for swifts

227
Table AResults of stepwise multiple linear regression of mean total count!? of snag-dependent

bird species with vegetation factors derived from factor analysis of 22 live tree and snag

variables (see table 3 for lists of variables highly associated with each factor)

Year, bird species Step Variable

Multiple Adjusted

R R2 SEEb P

Spring 1984:

Pileated woodpecker

Northern flicker

Hairy woodpecker

Red-breasted sapsucker

Chestnut-backed chickadee

Red-breasted nuthatch

Vaux’s swift

Brown creeper

Spring 1985:

Pileated woodpecker

Northern flicker

Hairy woodpecker

Red-breasted sapsucker

Chestnut-backed chickadee

Red-breasted nuthatch

Vaux’s swift

Brown creeper

1

1

2

1

1

2

1

1

2

1

1

1

1

2

3

4

Factor 1

Constant

(Factor 6)

(Factor 1)

constant

(none entered)

(Factor 3)

constant

Factor 5

(Factor 2)

constant

(Factor 3)

Constant

Factor 1

Factor 5

constant

(none entered)

(none entered)

(none entered)

Factor 5

constant

(none entered)

Factor 1

constant

(Factor 3)

Constant

Factor 1

Factor 2

Factor 5

Factor 4

constant

(none entered)

0.29 0.06 0.28 0.048

.45 .17 .26

.32 .08 .21

.51 .23 .21

.36 .11 .34

.64 .38 .39

.38 .12 .29

.54 .27 .21

.41 .15 .32

.67 .39 .43

007

.03 1

.OOl

.012

.ooo

.OlO

.ooo

.004

.ooo

a Bird coun~ and stem densities were log-transformed for the analysis. See the methods section for a description of

badjusted R .

Values given are standard error of predicted (estimated) bird counts, based on the transformed counts. SEE values

were computed as: SEE = @Sms/(N-k-l)], where SSres = the sums of squares of residuals, N is the number of stands

for a given year, and k is the number of independent variables in the equation (Kim and Kohout 1975: 331; see also

Draper and Smith 1981: 20 and 34, and Marcot 1984: table 12). Small prediction errors mean the abundance of a given

bird species was tightly associated with the given habitat variables, but large prediction errors suggested a loose association.

each year, with factors 2 and 4 also entering the 1985 equa- 3, with a negative coefficient, so nuthatch counts were typition. Thus, high swift counts were associated with high densi- tally higher in stands with a smaller component of redcedar.

ties of trees and snags abundant in old-growth stands, particu- This analysis therefore echoed the correlation analysis for

larly live trees ~100 cm in d.b.h., soft Douglas-fn snags, and, both species.

in 1985, also with western hemlock and white pine snags and

live trees. Both equations for nuthatches included only factor Different factors entered each equation for chestnut-backed

chickadees. Factor 5, reflecting a positive association with

hard Douglas-fir snags, and factor 2 (with a negative coefficient) entered the 1984 equation, but only factor 1, reflecting

228
Table S-Active nests and roosts of 9 snag-dependent bird

species 1983-86, by forest age-class

Forest age-class

Young Mature Old-growth

Bird species (n = 10) (n= 10) (n = 28) Total

Pileated woodpecker 0 2

Northern flicker 1 0 2 t

Hairy woodpecker 3 1 14 18

Red-breasted sapsucker 0 2 2 4

Yellow-bellied sapsucker’ 0 0 1 1

Chestnut-backed

chickadee 12 3 6 21

Red-breasted nuthatch 1 3 15 19

Brown creeper 6 7 15 28

Vaux’s swift 0 0 1 1

Total 23 16 58 97

’ This nest was pooled with those. of the red-breasted sapsucker for

statistical analyses.

an association with wet old-growth conditions (particularly

live trees >lOO cm in d.b.h.), entered the 1985 equation. For

hairy woodpeckers, northern flickers, pileated woodpeckers,

and red-breasted sapsuckers, the factors entered equations for

only one of the years. No factors entered creeper equations

either year, although in preliminary regression runs using

individual variables rather than factors, density of hard

Douglas-fir snags 250 cm in d.b.h. (with a positive coefficient) was the only variable that entered both years’ equations (Mariani 1987).

Nest-Tree Characteristics

We found 109 active nests and roosts of 10 snag-dependent

bird species in the southern Washington Cascades from 1983

to 1986. Most of these (n = 98) were on the study stands; the

rest were in similar habitat types outside the study stand

boundaries. The analyses presented here focus on 96 nests

and roosts of the following eight species found on the study

stands: pileated and hairy woodpeckers, northern flicker, redbreasted and yellow-bellied sapsuckers, chestnut-backed

chickadee, red-breasted nuthatch, and brown creeper (table 5);

the single Vaux’s swift nest was excluded from the analyses.

Restricting analysis to nests found on the study stands

allowed for direct comparison between nest site and study

site habitat characteristics.

Most (62 percent) of the active nests and roosts of woodpeckers, nuthatches, and creepers were found in old-growth

stands (table 5). In contrast, most chestnut-backed chickadee

nests were found in young stands. Of the additional 127

trees with cavities of uncertain use found in 1985 and 1986,

55 percent were also in old-growth stands but because 58 percent of our study stands were old-growth, average numbers

of nests found per stand were similar for all forest ageclasses.

Condition-Few active or inactive nests found on the study

sites were in live trees. Although we did not specifically test

for use of dead versus live trees for nests or roosts, these

data suggest a disproportionate selection of dead trees. Most

trees (85-87 percent) on our study sites were alive, but the

vast majority of nest and cavity trees were dead. Furthermore, all live trees harboring nests had dead or broken tops.

Size-The mean diameter of all active nest trees found on

the study sites was 76 cm, and the mean tree height was 25 m

(table 6). Nest trees ranged from 18 to 167 cm in d.b.h. and

from 3 to 60 m in height. Mean nest-tree diameters for all

bird species were greater than 50 cm; trees with nests of

northern flickers had the largest mean nest-tree diameter, and

those of brown creepers had the smallest. Flicker nest trees

averaged the tallest, and chickadee nest trees the shortest.

Nuthatches tended to excavate cavities closest to the top of

the nest tree (averaging less than 2 m from the top), and

pileated woodpeckers nested farthest from the top (averaging

21 m).

Mean diameter for trees with inactive cavities closely paralleled those of the active nest trees for the respective species

(or groupings), even though sample sizes were sometimes

small (pileated woodpeckers and northern flickers). In particular, the mean diameter of cavity trees used by small woodpeckers was nearly identical to that of active hairy woodpecker and red-breasted sapsucker nests. The mean diameter

of nonwoodpecker cavity trees was between those of active

chickadee and nuthatch nests.

On average, trees with inactive cavities were generally

shorter, and except for pileated woodpeckers, inactive cavities were also located closer to the ground than active nests

(that is, nest-hole height was lower), but this difference may

reflect observability bias because active nests higher in trees

are easier to spot than inactive ones. Trees with inactive

cavities of nonwoodpeckers resembled nest trees of chickadees more closely than those of nuthatches in terms of tree

height and height of the cavity above ground. Thus most

inactive nonwoodpecker cavities may have been inactive

chickadee nests.

The majority of nest trees of both woodpeckers and nonwoodpeckers were >50 cm in d.b.h. (fig. 1). Only two nests

(brown creepers) were found in trees ~20 cm in d.b.h. Loglikelihood G-tests showed that all cavity-nesting species

(grouped as woodpeckers and nonwoodpeckers) used large

(>50 cm in d.b.h.) snags disproportionately in all forest ageclasses, no matter whether tests included all nest and cavity

229
Table &Mean and standard deviation of diameter at breast height (d.b.h.1, height, nest-hole height, and 

diameter at the nest of all active nest trees of snag-dependent birds on study sites 

Tree d.b.h. Tree height 

(4 (4 

Nest height 

(4 

Diameter at 

nest (cm) 

Red-breasted nuthatch 

Brown creeper 

AU species 

Old growth trees (active and inactive) (G-tests, P < 0.001) or active trees 

alone (P < 0.05). or whether the smallest category (lo-19 cm 

in d.b.h.) was included or not (P < 0.05). 

Tests that examined use of snags by diameter-class by small 

woodpeckers (all but pileated woodpecker and northern 

flickers) revealed significant selection of snags (>50 cm in 

d.b.h. (P < O.COS), with one exception: active nest trees of 

small woodpeckers in old growth (0.10 < P < 0.25). Although not statistically significant, 14 of those 17 trees were 

>50 cm in d.b.h. 

Brown creepers appeared more flexible than cavity nesters 

in their use of snag diameter-classes. Although creepers 

appeared to select large-diameter snags in old-growth stands 

(P < 0.05), no such pattern was apparent in second growth, 

where 20. to 49-cm-d.b.h. snags were used most often 

(fig. 1). The mean diameter of creeper nest txes, however, 

was slighdy greater than 50 cm (table 6), and these analyses 

excluded three nests found in live trees, all >90 cm in d.b.h., 

two in Douglas-fir and one in a western redcedar. 

Decay-The distribution of active nests among snag decayclasses differed somewhat from that of trees with inactive 

cavities. Of all active woodpecker nest trees, 92 percent (22 

of 24) were in decay-classes 1 and 2, only 61 percent of all 

trees with inactive woodpecker cavities were in these classes. 

A similar trend held for nonwoodpecker trees: 59 percent 

(22 of 37) of the active trees and 36 percent (20 of 55) of 

the inactive nees were in decay-classes 1 and 2 (appendix 

table 8). This discrepancy may reflect the fact that some inactive trees had old holes with no conclusive evidence of 

230 
recent use. Because old or inactive brown creeper nests are 

difficult to detect, the sample includes only active creeper 

nest trees. The vast majority of creeper nest snags (80 percent, 20 of 25) were in decay class 2. 

When use of snag decay-classes was compared to availability, small sample sizes again forced us to pool some decayclasses. Brown creepers nested in decay class 1 and 2 snags 

(pooled together for testing) more frequently than expected 

in all stand age-classes (G-tests, P < 0.05). Similarly, in 

old-growth stands, woodpeckers, chickadees, and nuthatches 

used snags in decay-classes 1 and 2 disproponionately, no 

matter whether we considered only active trees or included 

inactive trees as well (P < 0.001) (fig. 2). 

In second-growth stands, woodpeckers used snag decayclasses 2 and 3 more frequently than expected (P < 0.001) 

(fig. 2), but the sample included both active and inactive nest 

trees. Active chickadee and nuthatch nests were found in 

snags in decay-classes 2 and 3 (pooled) more frequently than 

expected (P < 0.025), but trees with inactive cavities were 

found in decay-class 3 snags more than expected (P < 0.001) 

(fig. 2). 

Tree speciesActive nestz of cavity-nesting birds were 

found most commonly in three tree species in the southern 

Washington Cascades: Douglas-fir, western hemlock, and 

western white pine. A wide variety of bee species held nests 

in old growth; most nests found in young and mature stands 

were in Douglas-fir. 

In old growth, woodpeckers used western white pine more 

than expected (active nests, P < 0.01); active plus inactive 

trees, P < 0.001) (fig. 3A). Active nests of all woodpeckers 

in old growth were most commonly found in western white 

pine; inactive cavities were most commonly in Douglas-fir. 

Chickadees and nuthatches nested in western hemlock snags 

more frequently than expected in old growth, especially 

when considering only active nests, but not significantly so 

(0.10 <P < 0.25 in both tests). 

In second-growth stands, woodpeckers used Douglas-fir 

snags slightly more than expected, but not significantly so 

(0.10 <P < 0.25) (fig. 3B). Too few active woodpecker nests 

were found in these stands to evaluate tree species use without including inactive trees. Nonwoodpeckers also used 

231 
Douglas-fir more than expected, but use differed from availability only when we included both active and inactive trees 

together (P < 0.005). In young stands alone, nonwoodpeckers 

(mostly chickadees) also nested in Douglas-fii more than 

expected (r < 0.025). 

Like woodpeckers, brown creepers nested most tiequcntly in 

westun white pine snags in old-growth stands, and the proportional use of this species was greater than expected (based 

on availability) in second growth as well (fig. 3). Sample 

sizes were too small to test this selection in either forest ageclass separately, but creepers used white pine snags significantly more than expected (P < 0.05) when tested over all 

stands combined. 

Principal Components Analysis of Nest Tree 

Characteristics 

Five principal component axes had eigenvalues greater than 

1.0, four of which accounted for at least 10 percent of the 

total variance each. All five together accounted for 81 percent 

of the total variance.. The first principal component (27 percent of the total variance) was most highly positively correlated with the number of limbs and most highly negatively 

correlated with Douglas-fir and with fire evidence. Thus, 

high values on this axis represented trees with more limbs 

(and generally less decay): low values corresponded to trees 

that had fire scars and were more likely to be Douglas-fir. 

The second principal component, which accounted for nearly 

20 percent of the total variance, was most highly positively 

correlated with tree height, diameter, and western white pine 

and most highly negatively correlated with western hemlock. 

Thus, nest trees with high values on this axis were taller, 

larger trees with intact tops likely to be western white pine, 

whereas trees with low values were more likely to be western hemlocks. Little additional insight was gained by intcrpreting the third and fourth components, each of which 

accounted for much less variation (13 percent and 11 percent, 

respectively). 

A plot of mean (and standard error) principal component 

scores along the first two axes illustrates spatial relationships 

among bird species’ nest-tree characteristics (fig. 4). Among 

the active nests, along axis 1, pileated and hairy woodpeckers, 

sapsuckers, red-breasted nutbatches, and brown creepers 

tended to nest in trees with more branches remaining than 

did northern flickers and chestnut-backed chickadees. The 

latter species tended to nest in Douglas-firs with fire evidence. The second axis furtixr separated woodpeckers and 

creepers from chickadees and nuthatches. Woodpeckers and 

creepers tended to nest in taller, larger trees and more often 

in white pine. The exceptionally large standard error for 

sapsuckers was probably the result of a very small sample 

size (n = 3). together with a high degree of variability in 

nest-tree characters. 

232 

4 

-1 

Comparison of Nest-Site Vegetation With General Stand 

Characteristics 

Both discriminant function analyses comparing nest-site vegetation plots with randomly sampled stand vegetation plots 

produced generally similar results. In both runs, higher proportions of nest sites (77-87 percent) were correctly classified 

by the discriminant functions than were random plou (72.74 

percent). 

Five variables entered discriminant equations in both runs: 

hard and soft snags >50 cm in d.b.h., stumps and stubs, and 

total canopy cover. The first variable entered, that which best 

distinguished nest sites from random pIlo& was either soft 

snags 20 to 49 cm in d.b.h. or hard snags >50 cm in d.b.h. 

Based on consistent early entry into the equations and on 

relatively high conelations with the canonical discriminant 

functions, the two latter variables, together with total density 

of stumps and stubs, wwe the most important variables discriminating nest sites from random plots. As a plot of mean 

and standard deviation discriminant scores for the two runs 

including active nest sites shows, nest sites generally had 

higher densities of hard snags >50 cm in d.b.h. and stumps 

and stubs, and lower densities of soft snags 20 to 49 cm in 

d.b.h., than did the random study-site samples (fig. 5). 
- 

I Stand Level Match 

-4 -2 0 2 4 

Discriminant Function 1 

+ Soft snags 10.19, 20-49 cm 

Hard s”a9s >50 cm - 

Stumps & stubs + 

I f I I I 

-4 -2 0 2 4 

Discriminant Function 1 

Hard snags ~-50 cm __) 

Stumps & stubs, canopy cover--) 

+ Soft snags 10.19, 20-49 cm 

Bird Abundance Among Stand Types 

Only the Vaux’s swift was significantly more abundant in 

old-growth stands (all moisture-classes) during both years. 

Although no other species showed such a strong association 

with old growth, mean counts of other species reached maximum abundance in one of the old-growth moisture-classes, 

and patterns were not always consistent between years. Few 

of these patterns were statistically significant, but the fact that 

counts of most species were often lowest or more variable in 

young or mature stands may suggest that these species fmd 

more consistently suitable conditions in a specific moistoreclass of old growth (that is, chickadees in wet old growth, 

nut-hatches in dry old growth, and creepers in mesic old 

gro”+fJO. 

Merely to demonstrate significantly higher abundance in a 

particular habitat type does not necessarily mean that fitness, 

as defined by survival and reproductive success, is higher in 

that habitat (Van Home 1983). The true evaluation of habitat 

quality can be made only by including such demographic data 

for comparison among sites (Wiens and Rotenbeny 1981a). 

In this study, gathering extensive demographic data on several bird species at once on study stands distributed over such 

a wide geographic range was impractical. Measures of variation in abundance, such as coefficients of variation (CV), 

however, may pmvide a way of evaluating habitat quality 

(Marcot 1984). This use is based on observations that in less 

preferred habitats, which were saturated only in high-density 

years, populations may fluctuate more than in preferred 

habitats, which were saturated except in lowest-density years 

(Krebs 1971; O’Connor 1981, 1986). Coefficients of variation 

varied greatly from year to year and from species to species, 

but the highest for each species were most often in mature 

stands. Although we did not test for statistical differences 

among coefficient of variation for any bid species, this 

comparison may suggest that mature stands were less suitable habitat than old growth for snag-dependent birds. 

Several factors may have contributed to the observed lack of 

year-to-year consistency in bid abundance among stand 

types. For instance, harsh winter wealher can affect populations of permanent-resident species (Gaud and others 1986, 

Graber and Graber 1979, Hejl and Beedy 1986, Hejl and 

others 1988, McClelland 1977) and may explain the generally lower mean coonts we observed in 1984 than in 1985. 

The winter of 1983-84, although similar to long-term means, 

included periods of substantially higher precipitation and 

lower temperatures than either the next winter or those 

means. Several authors (Be&y 1982, Hejl and Beedy 1986, 

Hejl and others 1988, Raphael and White 1984) have found 

similar decreases in both permanent and summer resident 

species after harsh winters in coniferous forests in California. 

In addition, observer bias or variability may have contributed 

to the lack of consistency in abundance patterns (or habitat 

associations) between years. Problems such as variation in 

different observers’ training, experience, hearing ability, 

knowledge of local birds, and attentiveness can conceal patterns present in the system studied or cause spurious patterns 

to occur (see references in Ralph and Scott 1981). Although 

the effects of observer bias on OUT data are not known, we 

attempted to minimize it by conducting training sessions 

each season, having each stand visited by more than one 

observer during each year, and maintaining as much continuity of observers between yeas as possible. 

233 
The lack of clear, consistent abundance patterns of woodpeckers among forest age-classes may also be a problem of

scale (Wiens 1981a). Woodpecker home ranges may be as

large as the area encompassed by the array of count stations

on each stand, and much larger for pileated woodpeckers

(Bull and Meslow 1977, Mannan 1984b). Although we can

assign some association or importance of one or more forest

age-classes to wide-ranging species such as woodpeckers, the

ability to evaluate habitat quality based solely on relative

abundance patterns of these species is necessarily limited

when the sampling unit (the stand) is small relative to homerange size. Evaluations of woodpecker occurrence or abundance over larger scale areas that encompass home ranges of

many breeding pairs might provide better indices of habitat

quality.

A related problem is that higher counts of the more wideranging species do not necessarily indicate the presence of

nesting pairs. For example, pileated woodpecker counts were

relatively high in young stands in both years. No nests or

roosts of pileated woodpeckers were found in those stands

during our study, but the stands had many snags with recent

evidence of pileated feeding. Thus, young unmanaged stands

may provide good feeding but not nesting habitat for pileated

woodpeckers. This difference may be true for other woodpecker species, too, because few nest or roost trees of any

woodpecker species were found in young (or mature) stands.

Other factors complicating the analysis of bird abundance

patterns among the stand types are elevation and latitude.

The study stands were, by design, distributed over a relatively

wide geographic range and, by necessity, over a wide elevational range within this forest type in the southern Washington Cascades. Manuwal and others (1986) found that total

bird abundance varied inversely with both elevation and latitude: counts were generally higher in stands lower in elevation and situated farther south in the study area, regardless of

stand age. The same was true of the species we studied.

The bird count data were admittedly short term (only 2 years

of data). Gaud and others (1986) argue that recommendations

based on only 1 or 2 years’ data may be inaccurate, and

suggests a minimum of 5 years of study to adequately

account for yearly fluctuations in bird abundance. The continuation of long-term monitoring on similar stands in the

southern Washington Cascades will help clarify the relation

of bird abundance patterns to forest stands of different ageclasses.

Bird-Habitat Relationships

Relatively few correlations between cavity-nesting bird

counts and snag and live-tree densities were consistent or

interpretable. The significant correlations found between

counts of woodpeckers or nuthatches and trees they were

seldom observed using (or the negative associations) may be

spurious, or the habitat variables may represent other features

not sampled explicitly. The biological significance of the

association between hairy woodpeckers and large, live hemlocks is not apparent, except that these trees may serve as

future sources of potential nest trees (Zarnowitz and Manuwal

1985).

On the other hand, chestnut-backed chickadees, principally

foliage-gleaners, correlated positively with densities of large

overstory trees, which probably provide an optimum foraging

environment. This correlation may be due to greater abundance of either insects or cones. Large, dominant conifers,

particularly Douglas-fir, that are more exposed to the sun’s

rays are known to produce more cones than codominant trees

(Fowells 1965). Similarly, Raphael and Barrett (1984) found

that abundance of chickadees, which reached its maximum in

old-growth stands in northwestern California, correlated with

a principal component axis associated with higher densities

of largest Douglas-fir (>90 cm in d.b.h.). In another study in

California (Morrison and others 1987), chickadees were positively associated with mean canopy height, which clearly

relates to the size of the largest trees.

The association of chickadees with very large western redcedars probably accounted for their greater abundance in wet

old-growth stands, as densities of redcedars equaled or

exceeded Douglas-firs of comparable size there. Because

chickadee numbers were more consistently correlated with

live trees than with snags, characteristics of foraging habitat

may have been more important than nesting habitat in determining chickadee abundance, given that large, decayed snags

and stubs suitable for nesting were relatively abundant in all

stands.

Vaux’s swifts correlated most strongly with the kinds of

trees that provide suitable nesting habitat: very large live

trees (mainly Douglas-fir, western hemlock, and western

redcedar) and large snags (Douglas-fir and hemlock). Large,

broken-topped trees (live or dead) with the trunks hollow at

the top are known to harbor nests of Vaux’s swifts (Baldwin

and Zaczkowski 1963, Jewett and others 1953). During the

1983 pilot study, one swift nest was found in a brokentopped redcedar snag (77 cm in d.b.h., 10 m tall) in an oldgrowth stand. The need for large broken-topped trees probably accounts for the strong association of swifts with old

growth, because these trees are most abundant there. The

greater number of large, overstory trees and resulting broken,

multilayered canopy in old growth, may however, also provide an optimum foraging environment for swifts, which are

aerial foragers. Broken, multilayered canopies of old-growth

stands may allow greater access to flying insects surrounding

overstory trees than would closed, continuous canopies of

younger stands.

234
Based on our regression analyses, abundance of cavitynesting birds was not well predicted by live-tree and snag

densities. Others (Marcot 1984, Morrison and others 1987,

Raphael and Barrett 1984) have also found that habitat

variables explain little of the variance in bird abundance.

Morrison and others (1987) found their final regression

models to predict presence or absence of bird species adequately, but the equations did not clearly track the variation

in abundance between years (but see comments by Hejl and

others 1988). Problems in elucidating bird-habitat relationships via correlation or regression analysis can result from a

variety of factors, including, but not limited to, the following: nonlinear or nonmonotonic relationships; incomplete

sampling of habitat gradients; variability in species’ responses to habitat features; sampling scale; or not sampling

the correct variables (Best and Stauffer 1986). Each is

discussed briefly below.

The relation of bird abundance to habitat features can be

linear, curvilinear, or otherwise nonmonotonic (Best and

Stauffer 1986, Colwell and Futuyama 1971, Meents and

others 1983). Some authors (Madsen 1985, Raphael 1980)

have found the relation of cavity-nesting bird abundance to

snag densities, particularly large snags, to be curvilinear.

Meents and others (1983) found that although linear birdhabitat relationships were most common, polynomial variables increased the amount of variance explained by

regression equations.

The lack of consistent associations between these bird species and snag densities (the kinds most often used for nesting)

may also have been because all the stands were naturally

regenerated and contained numerous snags or because they

were all canopied stands. The lack may thus be viewed as a

form of incomplete sampling of habitat gradients. Most

recent studies that demonstrated stronger cavity nester and

snag associations in western coniferous forests have included

managed stands, where some or all snags have been removed

(Balda 1975, Madsen 1985, Mannan and others 1980,

Raphael and White 1984, Zamowitz and Manuwal 1985).

On our study stands, snag densities may have been above a

threshold (sensu Raphael 1980), so that other factors were

more predictive of (and limiting to) snag-dependent bird

populations. We suspect correlations would be stronger if

managed stands or clearcuts lacking high densities of remnant snags were included in the analysis (Verner and Larson

1989).

Even if strong relationships are found, they may change,

depending on whether or not the entire habitat gradient is

examined (Colwell and Futuyama 1971, Wiens and

Rotenberry 1981b). For example, Best and Stauffer (1986)

found that snag density could be deemed to have little

influence on habitat suitability for downy woodpeckers and

house wrens if samples from areas of low snag-density were

not analyzed. Examination of the entire gradient revealed not

only increased suitability at higher snag densities (relative to

low densities), but differences between the two species’

suitability indices at lower densities.

A third factor concerns the relative abundance and detectability of the bird species under study. Some species are typically encountered less frequently than others, and the less

frequently a species is encountered, the more variable its observed response to habitat features (Best and Stauffer 1986).

Thus, in this study, the more wide-ranging woodpeckers may

have been no less responsive to variation in snag densities

than, say, swifts and chickadees, but the relative infrequency

with which the woodpeckers were encountered may have

made count data insufficient to detect possible relationships.

For species with large home ranges relative to the sampling

array on each stand, low probability of encounter relates

back to a problem of scale. As discussed above, sample

stands may be too small to evaluate habitat relationships of

woodpeckers. In addition, habitat variables and bird counts

summarized as stand means may be too coarse to account for

the possibility that some species may be using only small

portions of each stand. Such patterns of use may contribute

to the lack of significant correlations or cause spurious ones

to appear.

Abundance of cavity-using birds is not necessarily correlated with or a function of densities of snags; other, unmeasured variables may be more important. Nevertheless, our

findings, as well as those of others (Balda 1975, Madsen

1985, Mannan and others 1980, Raphael and White 1984,

Zamowitz and Manuwal 1985), certainly attest to the importance of snags to cavity-using birds, particularly in terms of

management for these species.

Nest Tree Characteristics

Size-Although a variety of kinds of trees harbored nests,

our analyses clearly revealed disproportionate use of trees

with certain attributes by cavity- and bark-nesting birds. Our

findings agree with other studies that have demonstrated

disproportionate use of large-diameter snags as nest trees

(Madsen 1985, Mannan and others 1980, Raphael and White

1984, Zamowitz and Manuwal 1985). Mean nest-tree diameters in this study were generally larger than those reported

from the Olympics of Washington (Zarnowitz and Manuwal

1985), but smaller than in the Oregon Coast Range (Mannan

and others 1980, Nelson 1989). Hairy woodpeckers typically

nested in snags of substantially larger diameter in this study

area (and the Oregon Coast Range) than reported from studies

in the northern Rockies (Harris 1982, McClelland 1977) the

Blue Mountains of Oregon (Bull 1980), the east slope of the

Cascades in northern Washington (Madsen 1985), or the Sierras of California (Raphael and White 1984). Unfortunately,

because our data and those from the Oregon Coast Range

235
were from natural stands, many of which were old growth,

we could not assess the extent to which cavity-nesting birds

can successfully use smaller snags where larger ones are not

available, as was shown for white-headed woodpeckers in

the Sierra Nevada (Milne and Hejl 1989). Future studies

must specifically address that question.

Presumably, large-diameter trees offer better thermal insulation and more room to house larger clutches, thereby enhancing reproductive success (Karlsson and Nilsson 1977). Not

surprisingly, nest trees of the largest bird species-pileated

woodpeckers and flickers-were typically larger (at breast

height and at cavity height) than the mean for all species. The

smallest bird species, however-chickadees and nuthatcheslikewise nested in large-diameter trees. Creepers, which

typically nest under slabs of bark, showed more plasticity in

nest-tree size-selection than the cavity nesters. Other factors,

such as decay state, tree species, and bark characteristics,

were more important in determining the suitability of potential nest trees for this species.

Decay-The disproportionate use of hard snags by woodpeckers, most commonly hairy woodpeckers, contrasts with

the findings of Mannan and others (1980) in Oregon (but see

Nelson 1989), who found nests of hairies most often in

decay-class 3, although their data included only seven nests.

The only exception among the woodpeckers in our study was

the flicker, which nested most frequently in decay-class 3

snags, most of which in young stands were in fire-scarred,

remnant snags.

Because they are less well-equipped for cavity excavation,

chickadees and nuthatches might be expected to nest in trees

in more advanced decay stages. In second growth, this was

generally true, and, as with flickers, most nests were in remnant snags. In old growth, however, their disproportionate

use of all hard snags may be explained partially by the observation that nest holes were near the tops of snags (or even

live trees) where the wood was most severely decayed and

resembled conditions in more rotten snags. The selection of

decay-class 2 snags by creepers probably relates to the

greater percentage of remaining bark, as well as relative

firmness of the sapwood.

Tree species-Only three tree species contained active nests:

Douglas-fir, western hemlock, and western white pine. The

disproportionate use of white pine by. woodpeckers and

creepers is important in that it is a relatively minor, but

widely distributed, forest component throughout western

Washington. White pine has a patchy distribution and has

declined in this century since the introduction of the fungus

(Cronartium ribicola) that causes white pine blister rust

(Allen 1959, Fowells 1965, Boyd 1980).

Our findings differ, however, from other studies of cavitynesting birds in Douglas-fir forests in the Northwest. In

Oregon, all cavity nesters apparently used Douglas-fir more

than expected, based on availability (Nelson 1989). In the

Olympics of Washington, woodpeckers-mostly hairy

woodpeckers-appear to nest primarily in western hemlock

(Zarnowitz and Manuwal 1985). Thus, even within the

Western Hemlock Zone in the Northwest, woodpeckers use

tree species to different degrees in different areas.

Chickadees and nuthatches, nesting primarily in Douglas-fir

and hemlock, were apparently less selective than woodpeckers as to nest-tree species. This analysis was complicated,

however, by the fact that most of the nuthatch nests were

found in old growth (in hemlocks), whereas most chickadee

nests were found in young stands (in Douglas-firs). It is not

clear why most chickadee nests were found in younger

stands, given that chickadees were more abundant in old

growth, except that nests may have been easier to see in

young stands.

Selection of tree species by primary excavators probably

relates to relative decay characteristics of trees, as well as the

sizes of each tree species available (Conner and others 1976,

Jackson 1977, McClelland 1977). The progression and rate

of decay of snags results from the interaction of biotic and

abiotic factors over time and varies with size and age of the

tree at death, species, and geographic location (Kimney and

Fumiss 1943). Because Douglas-fir snags decay more slowly

than most other species (Buchanan and Englerth 1940, Cline

and others 1980), and because decay usually proceeds from

outside inward (Kimney and Fumiss 1943, Wright and

Harvey 1967), this species is especially suitable for nests of

the weaker excavators, chickadees, nuthatches, and flickers.

These traits also underscore the importance of large, remnant

Douglas-fir snags as the most suitable nest sites for chickadees in young stands, both in this area and in the Oregon

Coast Range (Mannan and others 1980). Without these large,

remnant snags, abundance of breeding chickadees probably

would have been lower in young stands.

Western hemlock, a common snag species on the study

stands, is much less durable than Douglas-fir and often harbors fungal heart rot while it is still living (Buchanan and

Englerth 1940, Engelhardt 1957). The importance of fungal

heart rot to woodpecker nesting is well known (Conner and

others 1976, Jackson 1977, Kilham 1971, McClelland 1977,

Shigo and Kilham 1968). The susceptibility of hemlocks to

heart rot fungi probably makes them attractive to hairy

woodpeckers and sapsuckers. Because hemlock snags remain

standing a relatively short time, cavity nesters would have to

use this species while the trees were still alive or within the

first several years after death. These attributes undoubtedly

contributed to the frequent use of hard hemlock snags, as

well as occasional live trees, by cavity nesters.

236
Western white pine, compared to its relative rarity (< 5 percent of available snags), was the species most frequently

used by woodpeckers for nesting. Although reasons for its

decline are relatively well known, information relating to

decay rates of dead trees is nearly lacking. The common

infections of this species by fungal heart rots (Fowells 1965),

its apparent resistance to uprooting (Cline and others 1980),

and the durability of sapwood and major limbs (pers. obs.)

probably account for the suitability of western white pine as

woodpecker nest sites. McClelland (1977) and Madsen

(1985) similarly attributed woodpecker selection of western

larch in Montana and northcentral Washington, respectively,

to decay of the heartwood in combination with relatively

sound sapwood. The rarity of large white pine snags only

underscores their importance to woodpeckers in this portion

of the Washington Cascades.

Nest tree surroundings--Our finding that nest sites of

cavity-nesting birds contained higher densities of large, hard

snags-the kinds in which they typically nested-agrees with

other studies that have reported nests of excavators in dense

patches of snags (Bull 1980, Harris 1982, Madsen 1985,

Raphael and White 1984). We do not know whether this

observation implies selection of dense patches of snags by

the birds, or whether it is simply an artifact of the patchy

way in which trees are killed by insects or disease. Also, we

do not interpret this observation to mean that isolated snags

do not have value as nesting habitat. In fact, some nest trees

that were used in successive years were not located within a

group of snags.

I Conclusions anld Magnagement Considerations

In recent years, much attention has focused on the specific

problem of providing adequate numbers of suitable snags

through time and space in intensively managed forests (Davis

and others 1983; Neitro and others 1985; Thomas and others

1976, 1979). Our purpose here is not to rework these guidelines, but only to refine or augment them with information

specific to Douglas-fir/western hemlock forests of the

Washington Cascades.

Nest Sites

We concur with Evans and Conner (1979a), Raphael and

White (1984), and Madsen (1985), among others, who argue

for the use of mean nest-tree diameters as a guideline for

snag management. Managing for minimum diameters of

trees known to be used could cause a gradual decline in

cavity-nesting bird populations (Conner 1979a). We therefore

recommend managing for snags of at least 76 cm in d.b.h.,

the mean d.b.h. of all active nests, where possible in this

area. This diameter is notably larger than those recommended

by Thomas and others (1979) for the Blue Mountains or

Neitro and others (1985) for westside forests, particularly for

hairy woodpeckers and sapsuckers. Woodpeckers appear to

nest in larger trees in Douglas-fir forests (Mannan and others

1980, Nelson 1989, this study, Zarnowitz and Manuwal

1985) than in eastside forests, though sample sizes are relatively small from most study areas. Snags no less than 50 cm

in d.b.h. should be given top priority in managing for cavityand bark-nesting birds because this broad size-class was used

disproportionately for nesting by all bird species we studied.

Emphasis should be placed on the largest snags available in a

given area, because larger snags remain standing longer,

retain bark longer, and support a larger variety of wildlife

(Cline and others 1980, Conner 1979a, Evans and Conner

1979).

Managers must also consider the decay state of snags. Our

study suggests that most woodpeckers (particularly hairy

woodpeckers) prefer hard snags for nesting; softer snags

were generally avoided. Neitro and others (1985: 144), however, assumed that hairy woodpeckers used primarily decay

stages 4 and 5, in contrast to red-breasted sapsuckers, which

used stages 2 and 3. Our results and those of Mannan and

others (1980) and Nelson (1989) do not agree. The number

of hard snags required for the most common woodpecker

species in the western Cascades would be vastly underestimated if the guidelines of Neitro and others (1985: 145,

table 9) are followed. On the other hand, weaker excavators,

such as flickers, chickadees, and nuthatches, were more

likely to nest in soft snags, as might be expected, but

depending on the forest age-class and the characteristics of

available snags, even these species nested frequently in

harder snags and defective live trees.

The species of snag is also important. Given the species’ relative rarity in the forest, large, hard western white pine snags

should be retained wherever they occur in areas managed for

woodpeckers. Retaining white pine snags for woodpeckers

will benefit brown creepers as well. Chickadees and nuthatches, on the other hand, nested primarily in Douglas-fir

and hemlock snags and were seldom found nesting in white

pine. Obviously, comprehensive management schemes designed to provide for all cavity-nesting bird species must

consider the needs of each species in the community. Meeting the snag requirements of one species will not necessarily

meet the needs of other species (Mannan and others 1984).

Besides nesting in different types of snags than woodpeckers

do, chickadees and nuthatches were not found to nest in old

woodpecker holes, except in two instances. Although some

birds may have fashioned their cavities from old woodpecker

feeding holes or “false-start” cavities, most chickadee and

nuthatch nests appeared to be solely the work of the nesting

pair. These species chose trees of suitable species, size, and

decay states and nested in locations appropriate to their abilities to excavate their own cavities. Suitable snags were sufficiently abundant in most of these natural stands to provide

237
sites for nest cavities. Perhaps the presumed energetic efficiency of using old woodpecker holes was partially offset by

possible fouling of holes caused by previous use or risk of

predation in larger holes, thus making them less attractive or

more harmful than newly excavated holes (Short 1979).

Conceivably, as snags--especially large ones-become

scarcer in managed forests, noticeable changes in patterns of

nest-site use from increased competition, because of lower

snag availability, could occur. Possible changes include:

smaller average diameter of nest trees (Milne and Hejl

1989); use of the smallest diameter portion of trunks (or

limbs) capable of supporting nest-cavity dimensions (Short

1979); greater use of old woodpecker cavities by chickadees

and nuthatches as more easily excavated sites became

scarcer; greater use of defective live trees; or greater

interference competition (Miller 1967) among bird species,

which would effectively reduce the number of available (that

is, unoccupied) snags. Pressures caused by the reduction of

the snag resource, if sufficiently severe, could lower

reproductive success of cavity-nesting birds or cause

population declines outside of unmanaged areas or

old-growth reserves. The list of possible changes could serve

as hypotheses to test in examining responses of cavity

nesters to changes in the snag resource under different

management schemes.

Another important consideration is that, in the younger

stands, very few nests were found in trees that arose from the

current stands. The only species found nesting commonly in

young stands, chestnut-backed chickadees, used remnant

snags primarily. Thus, even under natural conditions, stands

less than 80 years old have limited numbers of suitable nest

trees for most cavity nesters. Stands initiated after clearcutting, with few, if any, remnant snags, would likewise contain

few suitable nest trees. Given the target rotation ages of managed forests, roughly comparable to the young stands we

studied, recommendations for retention of old growth where

possible, strips of trees and snags along riparian corridors,

patches of snags (and live trees) in clearcuts, as well as areas

of longer rotations (Neitro and others 1985) become critical

for maintaining populations of cavity-nesting birds. Modem

silvicultural techniques have enabled foresters to produce

larger trees that can serve as potential nest trees in shorter

periods. Younger, faster-growing trees, however, tend to

decay more rapidly after death than do older, slower-growing

trees (Kimney and Furniss 1943), so the number of snags

provided may have to be adjusted.

Foraging Sites

In managing for cavity- and bark-nesting birds, characteristics

of foraging habitats should not be overlooked (Conner 1980).

Birds may focus foraging activities on different species and

sizes of trees from those used for nesting, and foraging

activities may change seasonally (Conner 1981, Lundquist

and Manuwal 1990). For example, in our study area,

creepers, chickadees, hairy woodpeckers, and nuthatches

foraged on large-diameter (>50 cm), live Douglas-fir more

than expected based on availability, and chickadees appeared

to shift to western hemlock in the winter (Lundquist and

Manuwal 1990). Retention of large live trees, either in old

growth or longer rotation patches, could also benefit species

such as Vaux’s swifts indirectly by serving as future sources

of large snags (Mannan and Meslow 1984).

Implementing Snag Management

Harvest of old-growth forests, and shorter rotations, resulting

in the prevalence of relatively young second-growth forests,

will make the success of snag-management policies even

more crucial for snag-dependent wildlife in the future. The

Pacific Northwest Region (USDA Forest Service 1985)

recommends managing dead and defective live trees to maintain viable populations of cavity-dependent wildlife at 40 percent of their population capacities on commercial forest

lands. This policy was intended to set minimum standards

and a baseline for managing Northwest forests. Although

significant progress has been made in establishing and carrying out management programs in the last decade, Bull and

‘others (1986b) report considerable inconsistency in the numbers of snags being maintained on National Forest Districts.

Nearly one-third-of the Districts surveyed reported fewer

snags than necessary to maintain cavity-nesting bird populations (as defined by Thomas and others 1979). Similarly,

Morrison and others (1986) concluded that although current

guidelines for maintaining large snags in the Tahoe National

Forest in California were appropriate, they were not being

implemented effectively.

Recommendations that may help-attain snag-management

goals in balance with human needs include retaining more

snags than the minimum required to support targeted cavitynesting bird populations. This recommendation allows for

unforeseen losses, such as to windthrow or firewood cutters

or uncertainties regarding natural fall rates of snags. It will

also allow for removing trees that may pose safety threats

while still maintaining enough trees for wildlife. Neitro and

others (1985) discussed in detail innovative ways of selecting

suitable types of snags compatible with logging safety regulations. In view of possible increases in demand for fuelwood

(Force 1986), management plans should include ways to

minimize impacts on snags provided for wildlife, such as

restricting access to critical areas or limiting the size of snags

cut. Producing large snags at high cost-either as direct or

“opportunity” costs-and then leaving them unprotected from

fuelwood cutters makes no sense, particularly where the

number of snags is below stated goals (Bull and others 1986b,

Morrison and others 1986).

238
Spatial distribution of snags is also important in designing

management plans. Although our study and others (Bull

1980, Raphael and White 1984) have found cavity nesters in

relatively dense patches of snags, lone snags may also provide suitable nest sites. Priority should be given to suitable

snags (appropriate size, decay stage, and species) whether

they occur in clumps or singly, to allow for adequate distribution over a large area. Adequate cover can be provided

around lone snags in the form of live trees, which are also a

source of future snags. Such flexibility in management will

help prevent suitable snags of several cutting units from

being crowded too close together to be usable.

Monitoring is essential to assess snag numbers and losses,

their use by wildlife, and the implementation and effectiveness of snag-management programs. Given that the complete

ecological and economic role of snags and cavity-dependent

wildlife is not fully understood at present, management

schemes must be carefully designed and flexible enough so

that future management options are not lost. As new information and understanding are gained, programs can be modified

as required to ensure the continued health of avian communities in managed forests.

Acknowledgments

This research was done in partial fulfillment of the requirements for the degree of Master of Science at the University

of Washington for each of the authors. We gratefully acknowledge the advice and support of the members of our

graduate committees: D.A. Manuwal, A.B. Carey, and C.D.

Oliver (Lundquist); and D.A. Manuwal, S.D. West, and K.J.

Raedeke (Mariani). We express our appreciation to M.Q.

Affolter, B. Booth, J.B. Buchanan, C.B. Chappell, M. Emers,

K.W. Hegstad, A. Hetherington, M.H. Huff, A.B. Humphrey,

D.A. Leversee, D.A. Manuwal, K. Newgard, B.R. North,

M.J. Reed, B.A. Schrader, L.W. Willimont, and K. Ziegler

for assistance with the field work. B.G. Marcot, R.L. Hutto,

K.G. Smith, and J. Verner provided valuable comments on

earlier drafts of the manuscript. We thank USDA Forest

Service personnel at the Gifford Pinchot National Forest and

at Mount Rainier National Park for their assistance. Computer

funds were made available through the Academic Computer

Center at the University of Washington. We gratefully

acknowledge the support of L.F. Ruggiero, A.B. Carey, F.B.

Samson, and K.B. Aubry, USDA Forest Service, Olympia.

This study was funded by USDA Forest Service contracts

PNW-83-219 and PNW-86-244.

This paper is contribution 114 of the Wildlife Habitat

Relationships in Western Washington and Oregon Research

Project, Pacific Northwest Research Station, USDA Forest

Service. 0

239
Appendix

Table 7-Stern counta variables and codes used in bird and

vegetation correlation and regression analyses

Code Description

Coarse variables:

LT4 Live trees >100 cm d.b.h.

TSTP Stumps and stubs (snags <5 m tall, >l0 cm d.b.h.)

SS All small snags l0-19 cm d.b.h.

Species-specific variables:

DFD13 Live Douglas-fir l-100 cm d.b.h.

WHD12 Live western hemlock l-50 cm d.b.h.

WHD3 Live western hemlock 51-100 cm d.b.h.

RCD12 Live western redcedar l-50 cm d.b.h.

RCD3 Live western redcedar 51 - 100 cm d.b.h.

ABD13 Live Abies spp. l-100 cm d.b.h.

CPD13 Live other conifers l-100 cm d.b.h.

VMD12 Live vine maple l-50 cm d.b.h.

HDD13 Live other hardwood spp. l-100 cm d.b.h.

DFS34 All Douglas-fir snags 20-49 cm d.b.h.

DFS5 Hard Douglas-fir snags (DC I-II) > 50 cm d.b.h.

DFS6 Soft Douglas-fir snags (DC III-V) > 50 cm d.b.h.

WHS34 All western hemlock snags 20-49 cm d.b.h.

WHS56 All western hemlock snags > 50 cm d.b.h.

RCS34 All western redcedar snags 20-49 cm d.b.h.

RCS56 All western redcedar snags > 50 cm d.b.h.

ABS34 All Abies spp. snags 20-49 cm d.b.h.

WPS34 All western white pine snags 20-49 cm d.b.h.

WPS56 All western white pine snags > 50 cm d.b.h.

a All stem counts were converted to densities (number per hectare). a

 Includes two sapsucker nest snags with missing data.

Table 8-Comparison of active nest trees and trees with

inactive cavities of woodpeckers and nonwoodpeckers

among decay classes by forest age-class

Hole-nester group/

tree-use status

Decay-class

I II III Iv Total

Woodpeckers/active

Old-growth

Mature

Young

7 12 1 0 20

0 0 1 0 3

a

1 2 0 0 3

Total 8 14 2 0 26

Woodpeckers/inactive

Old-growth

Mature

Young

Total

2 25 12 1 40

1 7 4 0 12

0 5 8 1 14

3 37 24 2 66

Nonwoodpeckers/active

Old-growth

Mature

Young

4 10 4 0 18

0 5 1 0 6

0 3 7 3 13

Total 4 18 12 3 37

Nonwoodpeckers/inactive

Old-growth

Mature

Young

1 10 11 3 25

0 6 4 1 11

0 3 13 3 19

Total 1 19 28 7 55

240