the residual stands (sensu Lehmkuhl and others, this volume;

Rosenberg and Raphael 1986) A long history of logging and

high incidence of fires were primarily responsible for the

much smaller stand sizes and more fragmented landscapes in

the Oregon Coast Ranges (Agee, this volume; Carey and

others, this volume; Spies and others 1988). As a result, edge

habitats were probably more abundant and closer to stands in

the Oregon Coast Ranges and exerted a stronger influence on

richness and abundance than in other provinces. Quantifying

the characteristics of fragmentation over the landscape and

determining their effects across the provinces was beyond

the scope of this study. Such analyses are available for the

southern Washington Cascades (Lehmkuhl and others, this

volume).

Our province comparisons are highly uncertain because not

all the provinces were surveyed in the same year. Yearly variation and covariation in bird abundance are expected to be

high at any one site and fluctuate more widely with the more

abundant species (see Holmes and others 1986). Temporal

sampling variation included fewer birds detected in the

southern Washington Cascades during the cool and wet

spring of 1984 compared to 198.5 (Manuwal and Huff 1987);

birds not surveyed in 1984 in the Oregon Coast Ranges, but

only in 1985 and 1986; and only 68 percent of the Oregon

Cascade stands were sampled in 1985.

In summary, distinct provincial patterns were suggested, and

bird abundance appeared to be higher in the Oregon Coast

Ranges, although natural variability in avian communities

seemed to be high within and among provinces. Significant

differences between the provinces must be considered in relation to sample design problems-namely, the widely varying

elevation and sampling frequency that limit extrapolation of

results beyond the study areas sampled.

Stand-Age Patterns

No broad differences were found in bird abundance patterns

related to forest age (fig. 14C). Bird communities of oldgrowth stands showed great overlap with those of young and

mature stands. The vegetation in the old-growth stands was

distinguished from younger forest by only a small set of

structural attributes, such as tree density, mean stand diameter, and basal area (Spies and Franklin, this volume).

General homogeneity of many stand attributes indistinguishable among stand age-classes may have discouraged the

development of unique bird associations along the sere. Bird

community patterns at this broad level of analyses, for example, were probably closely tied to plant species composition,

which did not differ significantly between age-classes, except

for a few minor species (Spies, this volume).

Significant age-class differences were detected for bark and

aerial foragers (figs. 10, 11) and likewise for 16 bird species

in at least two of three provinces (figs. 3-5). Seven of eight

hole or bark nesters, six of which were bark foragers, reached

their highest abundance in mature and old-growth stands. In

northwestern California Douglas-fir stands, 12 bird species

(excluding raptors) were positively correlated with stand age

during spring (Raphael 1984), but only 2 of the 12 were hole

or bark nesters. Only the chestnut-backed chickadee was

positively associated with stand age in both northwestern

California and in at least two of provinces in Oregon and

Washington.

Bark-forager abundance in northwestern California, modeled

now as being >30 percent below the historical (prelogging)

populations, has been projected to return to near historical

populations if forested landscapes, excluding reserves and

stream-management zones, are managed at l00-year harvest

rotations (Raphael and others 1988). If populations were

modeled similarly for Oregon and Washington, bark-forager

abundance seems unlikely ever to approach prelogging

populations because bark-forager abundance was so much

higher in older than younger Douglas-fir forests here compared to northwestern California. The strong association

between bark-forager abundance and stand age in Oregon

and Washington may be a function of the increase in large

snags (>50 cm d.b.h.) as stands age (Spies and Franklin, this

volume). Large snags have been identified as crucial for

bark-foraging and hole-nesting bird species (see Davis and

others 1983; Lundquist and Mariani, this volume; McClelland

1977; Zamowitz and Manuwal 1985). Generally more than a

century is required to replace large snags once they are

removed. Large snags would essentially disappear in forests

managed on l00-year rotations, except in buffer strips,

riparian corridors, and reserves. Therefore, we would expect

bark-forager and hole-nester abundance to remain well below

prelogging populations.

Most of the species detected in the study stands were habitat

generalists with widespread geographic distribution and occupying a diverse array of habitats. Much fewer in number

were those species with a distribution restricted primarily to

the Pacific forest belt (sensu Raphael and others 1988). The

birds in this group that reach their highest abundance in

mature and old-growth forests were assumed to be the most

sensitive to short-rotation management. This group included

two resident species, the chestnut-backed chickadee (fig. 3)

and the red-breasted sapsucker (fig. 5), and one migrant,

Vaux’s swift (fig. 5), which winters from Mexico south to

Venezuela (American Ornithologists’ Union 1983). The

abundance patterns derived for Vaux’s swifts and redbreasted sapsuckers, however, were based on limited data

and from detection distances of < 150 m. We advise interpreting and using these results judiciously.

201
Relations to Habitat

The study design was limited to an extensive approach (sensu

Van Home 1986), observing repeatable patterns in the relation of birds to their habitat over a broad geographic area.

The vegetation characteristics selected for multivariate regression models predicted only a small proportion of the variance

of species richness, total abundance, and species grouped by

residency and by foraging guild (table 7). Probable causes

for the high degree of unexplained variability in this pattemoriented approach are numerous (see Verner and others 1986:

207-258). The variability may be because of the effects of

weather on bird populations and the interaction of weather,

prey, predators, competitors, and parasites (O’Neil and Carey

1986); because species’ abundances were not a good measure

of habitat quality, were independent of stochastic variation,

and were not measured consistently between observers

(Rotenberry 1986, Van Home 1983, Verner 1985); because

means were used to characterize within-habitat heterogeneity;

or because of influences outside the stand that were not

measured, such as alteration of distant wintering grounds or

changes in the landscape nearby.

Understory foragers were most strongly related to the measured habitat variables (table 7). We suspect this may be a

result of lower sampling error for the understory foragers

than for other foraging guilds. The understory foragers used,

for the most part, only the vertical strata within a few meters

of the forest floor. The sampling error associated with estimating abundances in this stratum was probably lower than in

strata much farther from the observer. Likewise, measuring

habitat characteristics within strata used by understory foragers is considerably easier to measure than the vegetative

attributes used by species in the canopy, on tree limbs and

boles, or in canopy gaps.

Consistent prediction of habitat associations do not necessarily imply cause and effect (Rotenberry 1986). In some instances, the vegetation variables measured had little direct

biological meaning for the bird populations being predicted.

For example, the canopy foragers were positively and negatively associated with certain forest-floor variables, such as

percentage cover of moss and percentage cover of plants

<0.5 m tall (table 7). As indirect measures of habitat quality,

these variables most likely are identified with a complex set

of stand attributes that alone are highly variable and poor

predictors. Nevertheless, the management applicability of

indirect indicator variables needs to be tested.

The most positive association between bird abundance or

richness, and vegetation or stand structure was with live

deciduous-tree characteristics (for example, density, basal

area, importance value). The deciduous-tree component, most

strongly associated with young stands and long-distant migrants, was likely a result of natural reestablishment of the

forest after fire. In intensively managed, short-rotation

conifer plantations of Douglas-fir, deciduous trees are discouraged, or, if possible, eliminated during stand reestablishment. Based on results from naturally regenerated stands,

maintaining a small component of deciduous trees (for example, bigleaf maple) on harvestable timberlands most likely

would have a positive effect on bird populations.

Acknowledgments

We are indebted to D. Manuwal, F. Gilbert, and A. Carey,

principal investigators of breeding-bird community studies in

the southern Washington Cascades, Oregon Cascades, and

Oregon Coast Ranges, respectively. To more than 50 field

observers who persevered during months of surveying birds

under damp conditions in the crisp dawn air, we thank you

for your dedication. Portions of this manuscript were reviewed and improved by comments of J. Lehmkuhl. We

thank M. Raphael, S. Hejl, and an anonymous reviewer for

their valuable comments.

This paper is contribution 126 of the Wildlife Habitat Relationships in Western Washington and Oregon Research

Project, Pacific Northwest Research Station, USDA Forest

Service. q

202
Appendix

Table g-Designations for residency and detectability of birds by foraging guild

Birda

Residencyb Detectabilityc

Birda

Residencyb DetectabilityC

Common raven 3

Northern pygmy-owl 3

Olive-sided flycatcher 3

Aerial foragers

Dusky/Hammond’s flycatcher’

Vaux’s swift’

Western flycatcher

M

M

M

1

3

1

Bark foragers

Brown creeper’

Hairy woodpeckerd

Pileated woodpeckerd

Red-breasted nuthatchd

Red-breasted sapsuckerd

Canopy foragers

Band-tailed pigeon

Black-capped chickadeed

Black-headed grosbeak

Black-throated gray warbler

Chestnut-backed chickadeed

Evening grosbeak

Golden-crowned kinglet

Gray jay

Hermit/Townsend’s warbler’

Nashville warbler

Pine siskin

Purple finch

Red crossbill

Steller’s jay

Western tanager

Yellow-rumped warbler

M

R

M

M

R

R

R

R

M

M

R

R

R

R

M

M

4

4

3

1

1

2

1

1

1

1

1

1

3

2

2

1

Understory foragers

American robin R 2

Blue grouse R 3

Dark-eyed junco R 1

Hermit thrush M 2

Hutton’s vireo 1

MacGillivray’s warbler M 1

Northern flickerd

R 3

Orange-crowned warbler M 1

Rufous hummingbird M 1

Rufous-sided towhee R 4

Song sparrow R

S wainson’s thrush M 4

Townsend’s solitaire M 3

Varied thrush R 2

Wilson’s warbler M 1

Winter wren R 1

Wrentit R 1

a

 Species mentioned in text but not part of the community data analysis

were mourning dove, belted kingfisher, red-winged blackbird, northern

oriole, and spotted owl.

R = year-long resident; M = long-distance migrant; blank = not included in

residency analysis.

c

 Species were assigned to one of three detectability groups, as

follows: 1 = majority of detections were within 50 m of the count

station; 2 = the majority of detections were beyond 50 m, and species

were detected at least twice in any particular stand, 3 = the majority

of detections were beyond 50 m, species generally have large territories, and single occurrences (that is. a species was detected only

once in a stand) accounted for >30 percent of all the stands in which

a species was detected; 4 = species detected in <3 percent of the stand

counts, no abundance was calculated.

d

 These birds are hole- or bark-nesting species.

e

 We did not distinguish between dusky and Hammond’s flycatchers or

between hermit and Townsend’s warblers because they were difficult to

identify in the field.

203
Table 9-Vegetation variables and type of data transfomatlons performed (ARC = arcsine (square root(x)); 

LOG = log (x + 1); SQRT = square root (x + 0.375); SQRT’ = square root (x); blanks indicate untransformed values) 

Variable Transformation Variable Transformation 

Live-tree variables: 

Mean number of tree species 

Density 

Bigleaf maple 

Douglas-fir 

Golden chinkapin 

Grand fr 

Incense-cedar 

Pacific madrone 

Pacific silver fr 

Red alder 

Western hemlock 

Western redcedar 

western yew 

Total tree density 

Trees 5-9 cm d.b.h. 

Trees 10.24 cm d.b.h. 

Trees 25.49 cm d.b.h. 

Trees 50.99 cm d.b.h. 

Trees 100-149 cm d.b.h. 

Trees 2150 cm d.b.h. 

Needle-leaved evergreen tees 

Broad-leaved evergreen trees 

Deciduous trees 

Pine trees 

Basal area 

Bigleaf maple 

Douglas-fir 

Golden chinkapin 

Grand fir 

Incense-cedar 

Pacific madmne 

Pacific silver fir 

Red alder 

Western hemlock 

Western redcedar 

Western yew 

Total basal area 

Needle-leaved evergreen trees 

Broad-leaved evergreen trees 

Deciduous trees 

Pine trees 

Importance valw” 

Needle-leaved evergreen trees 

Bmad-leaved evergreen trees 

Deciduous trees 

Pine trees 

LOG 

SQRT 

LOG 

SQRT 

LOG 

LOG 

SQRT 

SQRT 

LOG 

SQRT 

LOG 

La? 

Bigleaf maple 

Douglas-fu 

Golden chinkapin 

Grand fir 

lncemecedar 

Pacific madmne 

Pacific silver fir 

Red alder 

Western hemlock 

Western redcedar 

Western yew 

Mean d.b.h. of live tree? 

Mean height of dominant trees 

Equitability index 

Tree density by diameter classesc 

Tree basal area by height classes 

Stand condition variables: 

Density 

Trees with fire scm 

Trees with excavated cavities 

Trees with natural cavities 

Trees with root cavities 

Trees with small amount of mossnichen 

Trees with moderate amount of moss/lichen 

Trees with heavy amount of moss/lichen 

Percentage 

Trees with fire mu-s 

Trees with excavated cavities 

Trees with natural cavities 

Trees with small amount of mass/lichen 

Trees with moderate amount of moss/lichen 

Trees with heavy amount of moss/lichen 

Snag variables: 

Density 

Decay-class-1 snagsd 

Decay-class-2 snags 

Decay-class-3 snags 

Decay-class-4 snags 

Decayc1ass-5 snags 

Snags 1.5-5.0 m tall 

Snags lOJOan d.b.h. and 5.15 m tall 

Snags lo-50 cm d.b.h. and >15 m tall 

Snags >50 cm d.b.h. and 5-15 m tall 

Snags >50 cm d.b.h. and >15 m tall 

Douglas-fir snags >1.5 m tall 

Western hemlock snags >1.5 m tall 

ARC 

LOG 

LOG 

LOG 

SQRT 

SQRT 

LOG 

LOG 

ARC 

LOG 

LOG 

MG 

LOG 

E$?T 

LOG 

LOG 

SQRT 

SQRT 

LOG 

204 
Table 9-continued 

Variable Transfommion 

Decay-class-l snags 

Decay-class-2 snags 

Decay-class-3 snags 

Decay-class-4 snags 

Decay-class-5 snags 

All snags 

Volume 

Decay-class-l snags 

Decay-class-2 snags 

Decay-class-3 snags 

Decay-class-4 snags 

Decay-class-5 snags 

All snags 

Douglas-fir snags 

Western hemlock snags 

Relative frequency 

Douglas-fir snags’ 

Western hemlock snags 

Relative dominance 

Douglas-fir snagd 

Western hemlock snags 

Mean height of all snags 

Mean d.b.h. of all snags 

Biomass of all snags 

Log variables: 

Density 

Decay&s-l logs 

Decayclass- logs 

Decay-class-3 logs 

Decay-class-4 logs 

Decay-class-5 logs 

Lags ~30 cm in diameter at large end 

Logs 30-W cm in diameter at large end 

Logs >60 cm in diameter at large end 

All logs 

Biomass 

Decay-class-l logs 

Decay-class-2 logs 

Decay-class9 logs 

Decay-class-4 logs 

Decay-class-5 logs 

All logs 

VOlUIllC 

Decayclass-1 logs 

Decay-class-2 logs 

Decay-class-3 logs 

Decay-class-4 logs 

Decayclass- logs 

Logs ~30 cm in diameter at large end 

Logs 30.60 m in diameter at large end 

Logs >60 cm in diameter at large end 

AU logs 

Percentage cover of logs 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

ARC 

ARC 

LOG 

LOG 

SQRT 

SQRT 

SQRT 

SQRT 

LOG 

LOG 

SQRT 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

LOG 

SQRT 

E 

SQRT 

SQRT 

LOG 

Variable Transfomation 

Understory variables: 

Percentage cover by 

MOSS 

Lichens 

FeIIlS 

GEWeS 

Herbs 

Evergreen sbmbs 

Deciduous shrubs 

Deciduous mes $8 m tall 

Evergreen nees 58 m tall 

Berry (Vaccinim spp.) shrubs 

Rubus species 

Grasses, herbs. and ferns 

Plants <0.5 m tall 

Plants 0.5-2.0 m tall 

Plants 2-4 m tall 

ARC 

LOG 

LOG 

ARC 

LOG 

SQRT 

LOG 

ARC 

SQRT 

SQRT 

205 

Winter Bird Communities in the Southern

Washington Cascade Range

Mark H. Huff., David A. Manuwal, and Judy A. Putera

Authors

MARK H. HUFF is a research wildlife biologist, and JUDY

A. PUTERA is a wildlife biologist, USDA Forest Service,

Pacific Northwest Research Station, Olympia, Washington

98502; DAVID A. MANUWAL is a professor, Wildlife

Science Group, College of Forest Resources, University of

Washington, Seattle, Washington 98195.

Abstract

Winter is a critical season for many resident bird species.

Bird communities in eight Douglas-fir forest stands, four midseral(65-140 years old) and four late-seral(325-600 years

old), were surveyed for three winters (9 December-19 March)

from 1983-84 to 1985-86 in southern Gifford Pinchot National Forest. Birds in each stand were surveyed eight times

each winter by using 8-minute counts at 12 counting stations

150 m apart along a line. For all three winters, median species richness and mean total abundance were substantially

higher in late- than in mid-seral forests. Of the four major

guilds exam&d-bark insectivores, canopy insectivores,

understory seed-eaters and insectivores, and canopy seedeaters-mean abundance was consistently higher in late- than

mid-seral stands. Red crossbills, chestnut-backed chickadees,

red-breasted nuthatches, and gray jays were strongly associated with late-seral stands in winter.

Introduction

Forests dominated by Douglas-fir are prevalent over the montane landscape west of the Cascade Range in Washington

and Oregon (Franklin and Dyrness 1973). Although many

aspects of Douglas-fir forests have been studied intensivelyperhaps more than any other forest in the world-the distribution, abundance, and basic life-history characteristics of

many animal species that inhabit these forests during the

winter still need to be determined. The breeding success and

persistence of resident species are undoubtedly linked to the

winter season (see Fretwell 1972). The availability of food

resources and habitat structural features that provide roost

sites and thermal cover are crucial to the survival of animals

active during the winter.

Manuwal and Huff (1987) reported on the abundance of

spring and winter birds in 16 Douglas-fir forest stands in the

southern Washington Cascade Range. They found that seasonal changes in abundance were greater in young (42- to

75-year-old) and mature (105- to 165-year-old) than in oldgrowth (250- to >5OO-year-old) stands, and bird species

richness and total abundance were greater in old-growth than

in younger stands during winter. Their data also suggest that

old-growth forest stands provide better winter habitat for

many species (such as gray jay, red-breasted nuthatch, brown

creeper, and red crossbill) than did young or mature stands.

207
Our objectives were to compare winter bird species composition and abundance in old-growth forests to younger forests

sampled for three consecutive winters within a small geographic area, to identify vegetative characteristics that explain

the abundance patterns of birds in winter, and to provide a

foundation for asking specific questions and making hypotheses about the distribution, abundance, and resource needs of

birds in winter throughout the Douglas-fir region.

Met hods

Study Area

To sample winter birds, four mid-seral(65 to 140-year-old)

and four late-seral(325 to >500-year-old) stands were

selected subjectively from the Wind River Ranger District of

the Gifford Pinchot National Forest (see frontispiece). Main

selection criteria were easy access during winter and a wide

range of interstand variability. The study stands were a subset of those reported in Manuwal and Huff (1987), and all

were naturally regenerated after fire. Age of mid-seral stands

was determined by increment coring at least five dominant

Douglas-fir trees at breast height, adding 5 to 7 years for

growth to breast height, and averaging the estimates (Spies

and others 1988). Age of old-growth stands was determined

by aging stumps in nearby clearcuts, along trails, or sometimes from increment cores on dominant trees (Spies and

others 1988). Ages estimated for the old-growth stands are

reliable to + 50 years (T. Spies, pers. comm.).

A study stand was defined as an area with relatively homogeneous structure, disturbance history, vegetation composition, physiography, and soil (Manuwal and Huff 1987). The

study stands ranged from 91 to 760 ha. ‘Differences in stand

size between late-seral (x= 565 ha; SD = 292 ha) and

mid-seral stands (x’= 408 ha; SD = 225) were assumed to be

minor because all stands were generally large. Stand fragmentation resulting from clearcutting was minimal (J. Lehmkuhl,

pers. comm.). Only one late-seral stand had evidence of past

logging near the sample area, about 200 m away.

Sampling

Vegetation-Sampling and stand summaries of vegetation

were provided by T. Spies (pers. comm.). Our primary objective for vegetation analysis was to determine and contrast the

structure and composition of our mid- and late-seral stands.

Spies measured about 300 vegetation and site variables at

each stand. We subjectively identified about 100 variables to

be used for further analyses based on their potential importance to birds in winter. These included variables related to

plant species composition, abundance of live and dead woody

vegetation, and stand structural characteristics.

Annual cone-crop ratings of Douglas-fir and western hemlock, obtained from a regional summary of forests of the

southern Washington Cascades (Anon. 1983-85), were used

to measure food resources available for seed-eating birds.

Each year, the cone crop was subjectively rated by species

by a scale of 1 to 5: absent/failure = 1, very light = 2,

light = 3, medium = 4, and heavy = 5. Because cone-crop

ratings were nearly identical for western hemlock and

Douglas-fir from 1983-85, we averaged their ratings together. The cone crop of Douglas-fir and western hemlock

was rated at each study stand during winter 1985-86. Using

the same rating scale, cone crop was rated over a 20-m

radius at each of 12 bird-counting stations and averaged for

each stand.

Birds-We followed the protocol of field methods established for birds by the Old-Growth Forest Wildlife Habitat

Program (Carey and Spies, this volume), with minor adjustments for winter sampling. Birds were surveyed by the pointcount method (see Verner 1985) over three winters (9

December to 19 March) from 1983-84 to 1985-86. Surveys

were done only during acceptable weather, avoiding rain,

high winds, and snowstorms or other conditions that would

seriously inhibit detecting birds. Each stand was surveyed

eight times each winter using 8-minute counts at 12 stations

spaced 150 m apart along a line. Survey lines, fitted into

each stand to maximize efficiency and stand homogeneity

(for example, similar slope), were generally rectangular

(600 x 300 m) or linear (1650 m).

Each observer identified all bird species based on sight or

sound and estimated the ground distance to the detection

location. Birds flying through or over the canopy received

different codes according to their vertical stratification rather

than distance estimates. Birds in flocks-three or more birds

using similar resources together-received one distance estimate based on the central location of the flock. Observers

were trained not to record an individual bird more than once,

although the interstand and intrastand movements of large

flocks of birds increased the likelihood of double counting,

and not to record birds that were outside the sampled stand.

During the first two winters (Manuwal and Huff 1987), two

observers visited a stand on the same day, surveying birds

simultaneously but taking opposite routes. Simultaneous surveys were deemed necessary because of limited funds and

the additional safety it provided for observers traversing

mountainous terrain during winter. Time elapsed between the

two observers counting at the same station ranged from 4

hours to 15 minutes. We summed the counts from the 12 stations by each observer separately. In total, the two observers

visited each stand four times, and abundance was reported as

a mean of the eight visits to each stand each winter.

Surveys conducted during the third winter, 1985-86, did not

use a simultaneous approach (two observers per day per

stand); rather, one observer visited each stand each day. The

eight total visits/stand were rotated between two observers.

208
Biases were introduced by our sample design; as a consequence, our results were interpreted cautiously. Verner (198 1)

categorizes bird-survey biases into four general sources:

observer, bird species, site selection, and sample schedule; a

thorough discussion of these biases can be found in Ralph

and Scott (198 1). Our comparisons between winters were

assumed to be suspect because different observers were used

between winters, and the sampling technique was modified

for the 1985-86 surveys. Hence, we made few comparisons

between winters and highlighted only the most extreme differences: those we subjectively assumed to be real and not a

result of sampling error. On the contrary, we assumed withinwinter comparisons between mid- and late-seral stands to be

unaffected by the design problems.

The skill and experience of field observers to detect and identify birds, estimate flock sizes, monitor bird movements, and

estimate detection distances accurately was crucial to minimizing the error associated with sampling birds. Although some

differences between observers were to be expected, determining the exact magnitude to correct this error was too costly

to measure and analyze. We took indirect measures to minimize interstand observer variability, however, by apportioning the eight samples per stand equally between the two observers for every stand. An unknown amount of disturbance

by observers, either repelling or attracting birds, occurred

during the surveys, however.

Some potential sampling errors related to species and sample

schedule that could not be controlled in the experimental design included the rate of detectability during winter (bird present but not detected); the differential detectability between

species and between stands; the rate of bird mortality between

species and stands, and the effects of weather-especially

temperature-over the season, on bird presence and cue emission. Unknown sample error related to site selection and survey design included potential differences in the total area

sampled per stand resulting from differences in shape of survey routes, intersample area homogeneity, including the elevational change within and between stands; differences in

stand history and stand age; and degree of landscape fragmentation surrounding the sample area, which was assumed

to be minor.

Data Analysis

Limitations of the data-This study was designed as a

simple survey of winter bird abundance. The data were exploratory in that stands were chosen subjectively, sample size

was small, and some biases were uncontrolled. No hypotheses were tested and, consequently, no overall alpha level was

designated. We reported P-values using nonparametric tests

as a way of showing the trends in variation among the stands

sampled. Because an a priori goal of this study was to identify which species and guilds are more abundant in old-growth

forests than in younger forests, we reported P-values from

one-tailed tests.

Vegetation-All comparisons between the four mid- and

four late-seral stands of vegetation characteristics were made

with the Mann-Whitney U test where nl = 4 and n2 = 4

(Siegel 1956). Because no a priori goals were established for

vegetation analysis, two-tailed tests were used to examine

differences between mid- and late-seral stands. The association between different vegetation variables was measured by

using Spearman rank correlation in which rs

 was the coefficient of association. Vegetation variables were assumed to be

correlated if rs was 20.643 (n = 8; significance level for twotailed test = 0.100).

Birds-Only birds detected 175 m from the counting station

(half the distance between stations) and species detected

during more than one survey (vagrants removed) at a given

stand were included in the main analysis. A separate supplemental analysis using all bird detections was used for wideranging and nocturnal species, such as hawks and owls,

which were poorly sampled by the point-count method, and

for species not easily detected <75 m from a counting station.

Median bird species richness was determined as the median

number of bird species per stand per winter. Distribution and

abundance patterns combined from all three winters and all

stands were plotted together to identify species patterns. The

distribution categories, based on the proportion of stands in

which a species occurred, were widespread, >67 percent;

irregular, 33 to 66 percent; and local, <33 percent of the

stands per winter Abundance categories were common, >8;

uncommon, 2 to 8; and scarce, <2 birds detected of a given

species per eight visits.

All comparisons of total abundance, species abundances, and

abundance within avian guilds between the four mid- and

four late-seral stands were made using the Mann-Whitney U

test, where n1 = 4 and n2 = 4. The avian guilds, each identified by forest structure and spatial components and by preferred food, were canopy seed eaters; canopy insectivore;

bark insectivores; and understory seed eaters and insectivores.

Species were placed in a guild based on field observations

and compiled literature (fig. 1). Nearly all the observed species could be categorized into one of the four guilds. Gray

and Steller’s jays, because of their low numbers and omnivorous diets, were not included in the guild comparisons. Some

species regularly change or supplement their diets within and

between seasons with several different resources that are not

easily cross-categorized. Examples are chestnut-backed chickadees, identified as canopy insectivores, and red-breasted

209
nuthatches, identified as bark insectivores; both species also r,‘b----- 

rely on seeds in their diets during winter. Hence, we view 230 -.

E ,./’ /’ 

,d” ,’ A’ 

the guild framework only as a general guide for ordering 

abundance patterns. 

We compared our findings to a winter bird study of four midand four late-seral stands surveyed in 1984.85 and 1985-86 

near Mount Rainier National Park: the study used the same 

field methods as we did (Manuwal and Huff 1987; K. Aubry 

and J. Putera, unpubl. data). We used a two-tailed, MannWhitney (I test, where nl = 4 and n2 = 4 unless stated other- NoYemDer wcemQer January February March 

wise, to compare late- and mid-seral stands. Figure 34mulatiue snowfall over three wintm al the Wind River 

~Uational Fish Hatchery near Carsan, Washington 

Mean abundances of each species were paired by late- and 

mid-sexal stands within each survey year and study area. 30 -

Each pair was ranked by highest and lowest mean abundance 25 -~ 

and summed for mid- and late-seral stands. The continuity of 

the ranked distributions within and between winters were 2oL 

examined using the sign test (Siegel 1956). 0 15Ll’ 

Relation to habitat-Spearman rank correlation between 3 10.. 

vegetation variables and bird abundance (mean of the three izl 

winter surveys) was assumed to be associated if r1 Xl.643 

0” 5 

(n = 8: significance level for two-tailed test = 0.1). All vege- o 

tation variables associated with bird abundance were examined for colinearity. -5 -. 

Results July hug sept 00 NO” Dss 2s” Feb Marc” Alp’il my Ame 

Weather Figure bMon,ldy mean tempcrmms from July 1983 to June ,986 at the 

Weather records from the Carson Fish Hatchery, near Carson, Wind River National Fish Hatchery near Canon. Washington. 

Washington, showed that the wettest of the three winters was 

1983.84, but it also was the winter with the least snow month in the winters 1983-84 and 198586, while January 

(figs. 2, 3). More than twice as much snow fell in 1984.85 was the coldest month of 1984-85 (fig. 4). The survey 

and 1985-86 than in 1983.84. In 1985.86, the winter of season, December through March, was coldest in 1985.86, 

greatest snowfall, >65 cm of snow fell each month from averaging 0.4 ‘C, and warmest in 1983-84, averaging 1.8 ‘C 

November through February. December was the coldest (fig. 4). 

210 
Table l-Means and standard deviations of vegetation variables within mid- and late-seral stands 

in the southern Washington Cascade Range 

Vegetation variable 

Mid-snal Late-s& 

Mean SD Mean SD 

Density (stems KT ha): 

All live trees 

Live trees 5-9 cm d.b.h. 

Live trees lo-24 cm db.h. 

Live trees 25.49 cm d.b.h.< 

Live trees SO-99 cm d.b.h. 

Live trees >lOO cm d.b.h.c 

Live broadleaved deciduous trees 

Live Douglas-ti 

Live western hemlock 

Live Pacific silver rif 

Snags lo-49 cm d.b.h. and 5-15 m tall 

Snags lo-49 cm d.b.h. and >I5 m tall’ 

Snags >50 cm d.b.h. and>15 m tall” 

Basal area (n? per ha) 

All live frees 

Live deciduous veesc 

Live Douglas-fti 

Live western hemlock’ 

Live Pacific silver fr 

Volume (II? per ha): 

All snags 

All logs 

Diameter (cm): 

AU snags 

cover (percent): 

High shrub (0.5-2 m tall) 

Low shrub (<0.5 m tall) 

Deciduous shrub (O-2 m tau) 

112 588 

245 290 

337 379 

181 122 

65 71 

3 2 

17 9 

544 430 

98 128 

4 8 

59 36 

8 11 

2 2 

375 

497 

125 

5”: 

27 

7 

36 

172 

96 

8 

1 

11 

96 7 >0.500 

92 4 0.342 

43 8 >0.500 

16 3 0.200 

22 8 z-o.500 

7 0 0.028 

9 1 0.058 

14 0 0.028 

47 4 0.342 

78 0 0.028 

5 0 0.028 

1 2 0.114 

5 0 0.028 

53 

0.4 

49 

2 

13 

0.5 

11 

2 

72 11 

0.1 0.1 

38 17 

27 8 

3 2 

123 92 284 99 

150 69 299 45 

30 6 62 21 

52 

50 

54 

16 

11 

16 

- 

19 2 

35 8 

22 4 

- 

2 

3 

4 

0 

0 

2 

0 

0 

0 

3 

0 

pb 

0.114 

0.114 

0.342 

0.028 

0.028 

0.114 

0.028 

0.028 

0.028 

0.200 

0.028 

Vegetation and Stand Structure 

Mean total live-tree density was higher in mid- than lateseral 

stands but varied considerably between stands (table 1). In 

mid-seral stands, Douglas-fir and western hemlock averaged 

76 percent and 14 percent of the total density, respectively. 

In late-seral stands, the shade-tolerant species, western hemlock and Pacific silver fii, averaged 72 percent of the total 

density, whereas Douglas-fir averaged only 10 percent of the 

total density. Broadleaved deciduous trees were a minor component of the stand composition, with only 3 and 2 percent 

of the total density in mid- and late-seral stands, respectively. 

Nevertheless, the higher density of broadleaved deciduous 

trees in mid-seral stands (table 1) was visually evident within 

the stands. 

In contrast to total-tree density, mean total basal area was 

higher in late- than mid-send stands (table 1). Douglas-fir, 

despite its low density in late-seral stands, contributed 53 percent of the total basal area, primarily large trees. In late-seral 

stands, western hemlock and Pacific silver fii comprised 

only 38 and 5 percent of the total basal area, respectively. 

Douglas-fir dominated the basal area in the mid-seral stands, 

with 93 percent of the total basal area. 

211 
0.01 -I

0 1 2 3 4 5 6 7 8

Mean number of stands per year

Figure 5-General distribution and abundance of the major bird species

wintering in the study area, AMRO = American robin, BRCR = brown

creeper, CBCH = chestnut-backed chickadee, CORA = common raven,

DEJU = dark-eyed junco, EVGR = evening grosbeak, GCKI = goldencrowned kinglet, GRJA = gray jay, HAWO = hairy woodpecker. PISI =

eine siskin, PIWO = pileated woodpecker. RBNU = red-breasted nuthatch,

RBSA = red-breasted sapsucker, RECR = red crossbill, SOSP - song sparrow,

STJA = Steller’s jay, VATH = varied thrush, WTWR = winter wren, and

WWCR = white-winged crossbill.

Late-seral stands generally had more trees in the 5- to 9-cm

and >lOO-cm d.b.h.-classes; in mid-seral stands, density was

substantially higher in the 25- to 49-cm size-class (table 1).

Larger mean snag volumes and snag diameters were observed in late- than mid-seral stands (table 1). Very large

snags, >50 cm d.b.h. and >15 m tall, were nearly six times

more abundant in late- than mid-seral stands (table 1). Mean

density of snags 10 to 49 cm d.b.h. and 5 to 15 m tall was

eight times higher in mid- than late-seral stands. The volume

of logs on the forest floor was substantially higher in latethan mid-seral stands (table 1).

Mean cover estimates of high (0.5 to 2 m) and low (<0.5 m)

shrubs were higher in mid- than late-seral stands (table 1).

Deciduous shrubs had about twice the cover in mid- than

late-seral stands.

General Distribution and Abundance Patterns of Winter

Birds

Over the three winters sampled, 27 bird species were recorded in the eight study sites. Nineteen of the 27 species

were detected < 75 m from a counting station and at least

twice in a stand (fig. 5). The 11 species described below are

“characteristic” of the study region in winter, based on

their abundance and distribution. Canopy insectivores-the

chestnut-backed chickadee and golden-crowned kingletwere the most common and widespread species (fig. 5). Uncommon but widespread species were the bark-insectivoresred-breasted nuthatch and brown creeper, Also widespread

but scarce were the winter wren, gray jay, and hairy woodpecker. Seed eaters-pine siskins and red crossbills-were

detected irregularly but were common relative to most other

species (fig. 5). Uncommon and irregular species were the

white-winged crossbill and varied thrush. Eight species were

classified as local and scarce because of their low detection

rate and limited distribution (fig. 5), they were assumed to be

a numerically minor component of the winter bird

community.

Bird Species Richness

During all three winters, median bird species richness was

higher in late- than mid-seral stands. The largest differences

were detected in winters 1983-84 and 1984-85, when the

median by year was 10 (range = 9 to 11) and 11 (range = 8

to 11) species in late-seral stands and 7 (range = 5 to 8) and

6 (range = 5 to 7) species in mid-seral stands. In 1985-86,

the difference was less; median bird species richness was 11.5

(range = 10 to 14) species in late-seral and 10.5 (range = 9 to

14) species in mid-seral stands.

Total Abundance

In our study region (Wind River), mean total abundance was

substantially higher in late- than mid-seral stands for all three

winters (table 2). In 1983-84, nearly three times more birds

were detected in late- than mid-seral stands (Mann-Whitney

U [hereafter U] = 0; P = 0.014). In winters 1984-85 and

1985-86, late-seral stands had more than twice the number

of birds than mid-seral stands (1984-85: U = 0; P = 0.014)

(1985-86: U = 1; P = 0.029). Total abundance over the three

winters averaged 48 and 113 birds per stand per visit in midand late-seral stands, respectively.

The largest differences in total abundance between winters

were from 1984-85 to 1985-86 within both mid- and lateseral stands (table 2), when about 5- and 6-fold increases

were detected, respectively. Although differences in total

abundance between 1983-84 and 1984-85 were small relative

to the high number of birds detected in 1985-86, nearly twice

as many birds were detected in late-seral stands in 1983-84

than in 1984-85.

Guilds

Over the three winters, more birds were detected in the canopy seed-eater guild than the other three guilds examined,

although marked differences occurred between winters

(table 3). In 1983-84 and 1984-85, most of the detections

were canopy insectivores, whereas in 1985-86, canopy seed

eaters comprised nearly 70 percent of the birds detected

(table 3). In all three winters, detections of bark insectivores

were substantially fewer than of canopy insectivores; understory seed eaters and insectivores were detected in very low

numbers (table 3).

212
Table 2-Means and standard deviations of total abundance of birds (mean number oi 

dctectionsksit) in mid- and late-seral stands in the southern Washington Cascade 

Range 

Table J-Percentages of birds in four guilds detected over 3 

winters in the southern Washington Cascades 

Guild 1983.84 1984-85 1985.86 Combined= 

canopy seed 23 16 69 

campy insect 52 56 21 

Bark insect 21 25 5 

Understory insect/ 

seed 4 3 5 

Total loo 100 100 100 

’ Data paoled across all three winters. 

Table 4-Significance levels of one-tailed Mann-Whitney 

U tests of differences between late and mid-seral stand 

counts (mean number of birds detected/visit) by guilds and 

by years, with the apriori assumption that abundance was 

higher In late-seral stands 

Winter 

Winter 

Late-~& stands had consistently higher mean bird abandances than mid-se& stands for all four guilds examined 

(fig. 6). In winters 1983-M and 1984-85. the canopy seed 

eaters were uncommon to common in late-seral stands, yet 

they were detected in low numbers or not detected (1984-85) 

in mid-seral stands (fig. 6, table 4). In winter 1985-86, seed 

eaters were relatively common in both mid- and late-semi 

standa, but were nearly three times more abundant in 

late-seral stands (fig. 6, table 4). 

213 
Table S-Sign tests of the number of bird species with 

abundance (mean number of detections/visit) highest in late- lateseral stands (fig. 7). In 1984-85, all species had mean 

compared to mid-seral stands wer 3 winters at Wind River and abundances either highest in late-seral stands or the same as 

2 winters at Mount Rainier mid-seral stands (fig. 7). In 1985-86, only the winter wren 

was more abundant in mid-seral stands (fig. 7). 

Mean abundance of bark insectivores over the three winters 

fluctuated from 2.3 to 4.0 to 1.3 times more abundant in latethan mid-seral stands (fig. 6, table 4). Generally, differences 

in abundance of understory insectivores and seed eaters and 

overstory insectivores between late- and mid-seral stands 

were less than the differences for other foraging guilds. In 

1983-84, however, detections of overstory insectivores in 

late-seral stands substantially outnumbered those in mid-seral 

stands (fig. 6, table 4). 

Species Patterns 

Mean abundances of species detected in late- and mid-seral 

stands were compared over the three winters, and more species reached their highest mean abundance in late- than midseal stands (fig. 7, table 5). In 1983-84, the golden-crowned 

kinglet was the only species more abundant in mid- than 

Red crossbills were not detected in mid-seral stands in 1983- 

84 and 1984-85, yet substantial numbers of them were detected in late-sad stands (fig. 8) (1983-84 and 1984-85: 

U = 0; P = 0.014). In 1985-86, when detections of red crossbills were high in both late- and mid-seral stands, variability 

between stands was also high (fig. 8) (U = 7; P = 0.443). 

Mean abundance of red-breasted nuthatches in late-seral 

stands varied little between 1983-84 and 1985-86 (fig. 8) but 

was substantially higher than mid-seral stands in 1983-84 

(U = 1; P = 0.029) and 1984-85 (V = 0; P = 0.014). In 1985- 

86, differences in abundance between mid- and late-seral 

stands were noticeably less (fig. 8) (U = 4; P = 0.100). 

Counts of red-breasted nuthatches, using a 3-year average, 

were 13.5 times higher in late- than in mid-seral stands. 

Mean abundance of chestnut-backed chickadees was consistently higher in late-seral stands in all three winters, but differences varied between winters (fig. 8). The most substantial 

difference between mid- and late-seral stands was in 1983- 

84 (U = 0; P = 0.014). Even though mean abundance of 

chestnut-backed chickadees was low in both mid- and lateseral stands in 1984-85, abundance was consistently higher 

in late-seral stands (U = 0; P = 0.014). Chestnut-backed 

chickadees, like red crossbills, were detected more often in 

1985-86 than in previous winters, but variability between 

214 
Table 6-Means and standard deviations of the abundance (mean number of dete4onshisit) of 

seed eaters in mid- and lateaeral stands over 3 winters, using 811 distances sod distances < 15 m 

Mid-seral stage 

Species winter 

Pine siskin: 

1983-84 

1984.85 

1985.86 

Sl75"l All d&tames : _ 

Mean SD Mean SD Mean SD Mean SD 

b 

-2 1 1 22 

49 

39 3: 6: 3: 

11 32 1 1 

144 4: 190 64 

Red crossbill: 

1983.84 

1984.85 

1985.86 

White-winged crossbill: 

1985-86 

” ” 2 2 7 5 47 

1; ” 6 - 27 4 16 76 ii 

8 3 19 1 15 15 30 

49 

7 

9 

13 

- 

Table 7-Percentage of detectionshIslt of seed-eaten in midand late-seral stands wer 3 winters, using all distances and 

distances 575 m 

Mid-semi stage Late-seral stage 

Species and winter 

Pine siskin: 

1983.84 

1984-85 

1985.86 

Red crossbilk 

1983.84 

1984.85 

1985.86 

White-winged 

1985.86 

crossbill: 

mid- and late-sexal stands was also higher (U = 6; P = 0.343). 

Using a 3-y&w mean, chestnut-backed chickadee abundance 

was 2.7 times higher in late- than mid-seral stands. 

The gray jay, relatively rare. in both mid- and late-seral stands 

(fig. 8). was 4.2 times commoner in late than in mid-seral 

stands. We detected substantially more gray jays in late- than 

mid-seral stands in 1983-84 (Cr = 2; P = 0.057) and 1984-85 

(LI = 1; P = 0.029) relative to 1985-86 (U = 4; P = 0.171). 

Supplemental Analysis of Troublesome Species 

By examining the data using no limit on the detection distance (see Methods, Data AnalysisBirds), we found four 

additional species, northern pygmy-owl, pileated woodpecker, 

common raven, and northern goshawk, with sufficient detections to at least identify some patterns. The northern pygmyowl, a forest bird that has not been well studied in the Pacific 

Northwest, showed the most striking pattern: all 12 detections 

over the three winters occurred in late-seral stands. The three 

other species were detected in both mid- and late-seral stands 

but slightly more often in late-seral stands: pileated wwdpecker had 58 percent of 43 detections in late-seral stands; 

common raven had 59 percent of 162 detections; and northern goshawk had 57 percent of 14 detections in late-send 

stands. 

The seed eaters, red and white-winged crossbills and pine 

s&in, were often detected in large numbers z-75 m from a 

count station (table 6). Nevertheless, the proportion of detections within late and mid-seral stands generally remained 

the same for either detections 575 m or all detections (tables 

6 and 7). 

Relations to Habitat 

The abundance of eight bird species showed suong correlations with certain of the vegetation variables measured. 

Chestnut-backed chickadees, pine siskins, and red-breasted 

nuthatches increased in abundance as the density of Douglasfirs decreased (table 8). The abundance of red crossbills and 

brown creepers increased with western hemlock basal area. 

Low density of live Douglas-firs and high basal area of live 

215 
Table 8Spearman rank correlations of vegetation variables highly correlated with mean 

abundance of birds in the southern Washbxton Cascade Range during the winter 

Species Vegetation variable 

Hair, wocdwcker 

G&jay - Deciduous trees (m2 per ha’) - 

Chesmut-backed chickadee Douglas-fir (no. pa ha) 

Red-breasted nuthatch Douglas-fir (no. per ha) 

Brown creeper Western hemlock (m2 per ha’) 

Golden-crowned kinglet Douglas-fir (m2 per hat) 

Red crossbill Western hemlock (m* per ha.‘) 

Pine siskil Douglas-fir (no. per ha) 

’ Spearman rank correlation coefficient. 

k Two-railed test. 

r Basal area. 

Live trees 25.49 cm d.b.h. (no. cer ha) a.74 0.050 

4.68 0.079 

4.88 0.010 

-0.95 0.001 

0.64 0.100 

-0.79 0.035 

0.74 0.050 

-0.83 0.020 

4 

Western hemlock 

western hemlocks were strongly associated with the late-seral 

stands (table 1). In addition, gray jay abundance was negatively associated with the basal area of live deciduous trees, 

and hairy woodpecker abundance decreased as density of 

medium-sized live trees (25 to 49 cm in d.b.h.) increased 

(table 8). 

A poor cone crop was produced by western hemlock and 

Douglas-fir in the southern Washington Cascades before the 

1983-G! and 1984-85 surveys, but a good cone crop was 

produced before the 1985-86 surveys (fig. 6). Seed-eater 

abundance, substantially higher in 1985-86 than in 1983-84 

and 19&1-85 (fig. 6), generally paralleled the annual variation 

associated with the cone crop. 

The 1985 cone crop surveyed in the study stands during winter 1985-86 rated substantially larger in late- than mid-seral 

stands for both tree species (fig. 9) (U = 0; P = 0.014). Generally, seed eater abundance was high in srands with large 

cone crops of Douglas-fK and western hemlock (fig. 9). 

Discussion 

Results generally confirmed earlier studies showing that 

old-growth (late-seral) stands in general provide better 

winter habitat for most bird species than do younger forests 

(Manuwal and Huff 1987). For example, total bird abundance in late-seral stands was at least double that of mid-seral 

stands (table 2); nearly every major species detected in the 

study stands had higher mean abundances in late-seral stands 

(fig. 7): and seed-eating and bark-foraging species were conspicuously more abundant in late-seral stands (fig. 6). Gray 

jays, red-breasted nuthatches, and red crossbills appeared to 

prefer old-growth over younger stands. Only the brown 

creeper, previously identified by Manuwal and Huff (1987) 

as being significantly more abundant in old-growth forests, 

showed an unexplainable trend counter to earlier results 

(fig. 7). 

216 
During winters 1984-85 and 1985-86, our results were similar to those from near Mount Rainier: more birds were detected in late- than mid-seral stands (Mount Rainier, 1984-85:

U = 4; P = 0.342) (Mount Rainier, 1985-86: nl = 3; n2 = 4;

U = 0; P = 0.028); mean total abundance was higher in 1985-

86 than 1984-85; and mean total abundance in 1985-86 was

similar between the study regions (late-seral stands: n1 = 3;

n2 = 4; U = 6; P = >0.500) (mid-seral stands: U = 7;

P > 0.500) (table 2). Only in 1984-85 was mean total abundance different between regions (mid-seral stands: U = 2;

P = 0.228) (late-se& U= 0;P = 0.028) (table 2).

At both Mount Rainier and Wind River, more species

reached their highest mean abundance-in late- than in midseral stands. Overall, 71 percent of the comparisons between

bird abundances in mid- and late-seral stages were highest in

late-seral stands, 6 percent highest in mid-seral stands, and

23 percent the same. At Wind River, 77 percent of the mean

abundance comparisons were highest in late-seral stands, but

at Mount Rainier, 59 percent were highest in late-seral stands.

Species that were consistently more abundant in late-seral

stands in four or more comparisons between winters and

study areas were the chestnut-backed chickadee (sign test;

n = 5, x = 5; P = 0.031), red crossbill (n = 5, x = 5;

P = 0.031), gray jay (n= 4, x = 4; P = 0.063), and redbreasted nuthatch (n = 4, x = 4; P = 0.063) (fig. 7). Conversely, no species was consistently more abundant in midseral stands. In addition, pine siskins were notably higher in

late-seral stands (n = 4, x = 4; P = 0.063). although few, they

were not detected in 38 percent of the late- and 88 percent

of the mid-seral stands in winters 1983-84 and 1984-85

(tables 6,7).

Pronounced fluctuations in abundance between years and

seasons are typical of bird populations (for example, Hejl

and others 1988, Holmes and others 1986, Smith 1982b). Not

only were substantially more birds detected in 1985-86 than

in the previous two winters (table 2), but abundance within

all four guilds was higher in 1985-86 in both mid- and lateseral stands, except for bark insectivores in late-seral stands

(fig. 5). Explaining the reasons for observed fluctuations between years is difficult, primarily because interactions within

the environment are complex and difficult to measure thoroughly. Different observers between winters, a modification

of the survey design in 1985-86, and differential detectability

between winters potentially related to weather (figs. 2,4)

could account for some or all of the differences. Because

total abundance increased more than 5-fold from 1984-85 to

1985-86, more birds were likely present in 1985-86 than in

previous winters, despite the potential biases and the fact that

birds may have responded to availability of critical resources

before and during the winter of 1985-86.

Variations in the number of birds detected between winters

were exemplified by the seed eaters, namely red and whitewinged crossbills and pine siskins. Detections of seed eaters

increased 26-fold from 1984-85 to 1985-86 and accounted

for 69 percent of the birds detected in 1985-86 (table 3). We

believe that the abundance and movements of seed eaters, as

reported elsewhere (for example, Benkman 1987, Bock and

Lepthien 1976, Haapenen 1966), was closely associated with

the type and size of conifer cone crop produced. During our

3-year study, the abundance of seed eaters closely tracked

the cone crop of Douglas-fir and western hemlock within the

southern Washington Cascades region (fig. 6).

Higher basal area of western hemlocks in late- than in midseral stands (table 1) is one of several factors that may

explain the higher number of detections of seed eaters in

late-seral stands (table 4, fig. 6). Western hemlock, a prolific

seed producer, has heavy cone crops more regularly than

does Douglas-fir and, unlike Douglas-fir, produces large

quantities of seed even in dense-canopied stands (Fowells

1965). Furthermore, western hemlock releases its seed slowly

throughout the winter, but 70 to 90 percent of Douglas-fir

seeds can be dispersed before the end of October (Isaac

1943), possibly before many of the seed eaters arrive on

their southward migration.

A possible explanation for the higher number of detections

of bark foragers in late- than mid-seral stands (table 4, fig. 6)

could be a shift in foraging activities and substrate use by

resident bark foragers during the winter (Morrison and others

1985, Travis 1977), most likely in response to seasonal

differences in insect prey location and availability (Connor

1979b). In a companion study in the southern Washington

Cascades, bark foragers-such as red-breasted nuthatchesexhibited shifts in foraging behavior during the winter, most

notably in old-growth stands, by significantly increasing their

use of large-diameter Douglas-firs relative to their availability and by using a lower position on the tree bole away from

tree branches (Lundquist and Manuwal 1990). They also

found that bark-foraging species, except for the brown

creeper, foraged primarily on trees >50 cm in d.b.h. in both

spring and winter but used trees >50 cm in d.b.h. more

frequently in winter than in spring.

The abundance of brown creepers and red-breasted nuthatches, which feed by probing bark crevices while searching

for arthropods, may in part be related to the concentration of

prey sites. Bark arthropod abundance and availability are

positively correlated with tree size, bark characteristics, and

possibly tree species (Morrison and others 1985, Nicolai

1986). In the southern Washington Cascades, bark furrows of

Douglas-fir-used extensively by arthropods-increase in

depth and surface area with increasing bole diameter

217
(Mariani and Manuwal 1990). We suspect that the higher

number of large-diameter trees (>100 cm in d.b.h.) in latethan mid-seral stands (table l), and the well-protected furrows they provide for overwintering arthropods may have

resulted in higher counts of bark foragers in late-seral stands.

Chestnut-backed chickadees foraged on tree species in proportion to availability in late-seral stands during spring, but

shifted during winter to western hemlock significantly more

than it was available (Lundquist and Manuwal 1990).

Western hemlock comprised 46 and 38 percent of the total

tree density and basal area, respectively, in our late-seral

stands and was nearly twice as dense and 13 times higher in

basal area in late- than in mid-seral stands. This difference

may explain why more chestnut-backed chickadees were

detected in late- than in mid-seral stands (fig. 8), but the

reasons they prefer western hemlock in winter are still not

clear.

Based on the substantial differences in bird abundance between mid- and late-seral stands, we recommend that additional studies be done to substantiate the observed patterns

over a wider geographic area.

Acknowledgments

We thank B. Biswell, J. Buchanan, C. Chappell, M. Emers,

and D. Leversee for their field assistance; R. Lundquist for

field assistance and dam management; J. Mariani and K.

O’Halloran for data management; F. Samson for directing

fieldwork in 1985-86; and K. Aubry for technical and financial assistance and for providing the inspiration to finish this

study. We are indebted to J. Verner, S. Hejl, J. Rotenberry,

and C. Raley for their valuable comments on earlier drafts of

this manuscript.

This paper is contribution 108 of the Wildlife Habitat Relationships in Western Washington and Oregon Research

Project, Pacific Northwest Research Station, USDA Forest

Service. 

218
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