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Ecology and conservation of the marbled murrelet online

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redwood, mostly within state and federal parks, with the
highest detection numbers in stands >250 ha. In excess of
200 detections for single-survey mornings have been recorded
at some survey stations in remaining unharvested stands
within parks in California, including Redwood National Park
and Prairie Creek State Park in Humboldt County (Ralph
and others 1990); and Big Basin State Park in San Mateo
County (Suddjian, pers. comm.).

Federal listing of the Marbled Murrelet as threatened
(U.S. Fish and Wildlife Service 1992) has created a need for
information about the role of habitat and landscape features
for the murrelet.

We conducted two studies to examine the relationships
of the murrelet to habitat and landscape characteristics within
old-growth forests, as defined by Franklin and others (1986).
In isolated stands in fragmented landscapes (the Stand Study),
we compared murrelet detections with stand size, structure,



1 Wildlife Biologist and Research Wildlife Biologist, Pacific South-
west Research Station, USDA Forest Service, Redwood Sciences Labora-
tory, 1700 Bayview Drive. Arcata, CA 95521



and landscape characteristics. In large contiguous stands of
old-growth in state and federal parks (the Park Study), we
examined murrelet detections with landscape features, such
as elevation and topography. We confined our study to old-
growth forests, because previous studies indicate murrelets
nest only in forests with these characteristics.

Methods

The survey methods followed the intensive survey
protocol of Ralph and others (1993). To maximize the number
of visual detections, we selected station positions at the
edges of the isolated stands or at interior locations with
openings in the canopy whenever possible. Observers could
move within a 50-m radius of the station.

We estimate that, for an individual forest stand, four
surveys are needed to determine with a 95 percent probability
that murrelets are present (appendix A). If below canopy
behaviors were observed, we categorized the stand as
Occupied (see below) for analyses. During 1992 and 1993
for the Stand Study, we attempted to survey each isolated
stand at least four times between 15 April and 7 August.
Surveys at each stand were distributed throughout the survey
period whenever possible. However, due to difficult access
for some stands, surveys in some areas were temporally
aggregated. To eliminate potential effects from aggregated
surveys, detection levels were standardized for seasonal
variation (see Analyses below).

For the 1993 Park Study, within the boundaries of the
large stands of old-growth forests in national and state parks
(fig. 1\ stations were placed in a matrix over the landscape,
as illustrated in figure 2. We surveyed all sections of park
stands with adequate accessibility. We placed stations 400
meters apart on roads and trails, and 400 meters out
perpendicular to trails, creating a matrix. Ralph and others
(1993) found that observers detect few birds at distances
>200 m, therefore, we assumed each station covered a 200-
m radius circle, approximately 12.5 ha. Due to safety
considerations for observers hiking to stations in pre-dawn
hours, we limited stations to within 400 meters of a trail or
road. Stations were surveyed once during the survey season.
We attempted to avoid surveys at adjacent stations on the
same morning.

The species' range in northern California was determined
by examining the results of inland surveys conducted from
1988 through 1992 by government agencies and private
landowners. Murrelet use for each stand or station was
determined by the number and type of detections. All survey
stations were digitized into a Geographic Information System



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V



Oregon border



f*

cs



County
Locations




Stale and National Parks within

Redwood National Park boundaries
(Del Norte and Humboldt Counties)



Humboldt Redwoods State Park
(Humboldt County)




Big Basin Redwoods State Park
(San Maleo County)



Figure 1 Location of state and national parks surveyed during the summer of 1993. Shaded areas represent
distribution of old-growth forests within the parks.



(CIS) database (ARC/INFO 6.1.1) and grouped by distances
from the ocean by 10-km bands from to 60 km (fig. 3).

Definition and Selection of Isolated Study Stands

Isolated stands were located by examining habitat maps
of private lands, state and federal parks, and national forests.
The maps were drawn from interpretation of aerial photographs.
For the stand selection process, stand size was estimated from



measurements on the maps. Stands were randomly selected
from size categories of 2 to 20 ha, 21 to 40 ha, 41 to 100 ha,
and greater than 100 ha. If the stand was accessible, it was
visited and visually inspected. If the stand was old-growth or
residual forest, the stand was surveyed, if not, then another
stand was selected. Upon completion of field work, station
locations and stand perimeters were adjusted on maps according
to ground-truthing, then digitized into a CIS database.



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Chapter 20



Inland Habitat Relationships in California



Marbled Murrelet
Survey Stations - 1993



Prairie Creek
State Park




Tributary drainage
Major drainage

General slope

Minor ridge
~* Major ridge
Occupied site



Figure 2 Spatial and topographical distribution of a subset of Marbted Murretet stations surveyed
at Prairie Creek Redwoods State Park during the summer of 1993. Occupied sites are shaded in
groups to illustrate possible associations with topographical features.






Stand area, perimeter length, and distance from salt
water were derived from the CIS database. For stands with
inclusions of non-forested area within the stand, we added
the length of the lines around the stand and around the
inclusions for the total perimeter measurements. Perimeter,
therefore, is a measure of the amount of forest edge in and
around the stand.

Stand type was characterized as residual or old-growth.
This variable is a measure of harvest history for the stand,
but is not a direct measure of years since the last disturbance.
Old-growth stands contained trees greater than 90 cm diameter
at breast height (d.b.h.) with no history of timber harvest and
some evidence of decadence in the canopy. Residual stands



had some history of partial removal of large trees with the
remaining dominant trees greater than 90 cm d.b.h.. Some
stands with contiguous areas of old-growth and residual
were classified as mixed.

Stands also were classified by density as determined by
interpretation of aerial photographs. Density was defined as
the percent of the old-growth canopy cover (dominant and
codominant trees): sparse, <25 percent; low, 25-50 percent;
moderate, 51-75 percent; and dense, >75 percent Species of
dominant trees (>50 percent) was determined from aerial
photography and verified by vegetation information after
visiting the stand. For the purpose of this study, a stand was
a single, isolated group of old-growth trees surrounded by



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Chapter 20



Inland Habitat Relationships in California



Kilometers From Coast 10 20 30 40 50 60



Pacific Ocean




10 km




Figure 3 Distribution of Marbled Murrelet survey stations in northern California. Stations are
located on private and public lands and surveys were conducted one or more seasons from 1 988 to
1 994. Open circles represent one survey station or a group of stations in one isolated stand. In areas
with high concentrations of stations, open circles appear filled in or shaded.



non-forested or harvested habitat. If groups of trees were
less than 160 meters apart they were considered one stand.
Stands that met all of the following criteria were
included in the group of potential survey sites: old-growth
or residual stands with dominant and codominant trees that
comprised at least 20 percent canopy cover; size between 2
ha and 400 ha; distance from coast less than 40 km (25
miles); dominant vegetation type of coast redwood (Sequoia
sempervirens) or Douglas-fir (Pseudotsuga menziesii) at



elevations of less than 1,000 m; and safely accessible by
road or well-defined trail.

Analyses

Standardization for Seasonal Variation

Various factors may influence the numbers of detections
of murrelets at inland locations, including environmental
conditions, time of year (O'Donnell and Naslund, this



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volume), and observer (O'Donnell, this volume). To help
eliminate the effects of observer bias, all stands were surveyed
by two or more observers. The influence of weather on
numbers of detections appears to be highly variable (Naslund
and O'Donnell, this volume). The effect of weather is
probably stochastic with respect to survey days, and we
assumed it did not have an overall impact at a site because
surveys were distributed throughout the breeding season.
The seasonal variation in detection levels, however, has
been well documented and quantified at several sites in
California (O'Donnell and Naslund, this volume). To identify
differences in murrelet use (detection levels) of stands in
our study, we first accounted for the effect of season on
detection levels.

Morning surveys were conducted throughout the breeding
season in multiple years at three sites in Humboldt County.
The sites at Lost Man Creek (Redwood National Park) and
James Irvine Trail (Prairie Creek Redwoods State Park)
were surveyed from 1989-1993. The Experimental Forest
site was surveyed in 1989, 1990, 1992, and 1993. We
attempted to monitor each site weekly. Data from these three
sites was used to calculate standardization factors.



Standardization

The following method was used to calculate a factor to
standardize the number of detections for seasonal differences.

1 . We examined the distribution of detections (fig. 4)
over all years for the three sites and used a Kruskal-
Wallis test to determine that the distributions by
season were similar for the three sites (P < 0.0001).
Surveys from all sites and years then were pooled.

2. We calculated the mean number of detections per
survey for the period 15 April to 12 August, that we
refer to as the summer mean.

3. We then calculated the mean numbers of detections
per survey for each 10-day interval, the interval mean.
Detection levels for periods longer than 10 days
began to show the effects of seasonal variation.

4. The ratio of each of the 12 interval means and the
summer mean was calculated (interval mean/summer
mean = standardization factor).

The 10-day intervals and corresponding standardization
factors calculated for the data from the three sites are presented
in table 1.



250 -r



200 -



O 150



&

6



g 100



50



All sites combined
Experimental Forest
James Irvine Trail
Lost Man Creek




Q



10
CM



(0



>

CD



CO

10
CM



-
r



10 Day Period



3
CO



Figure 4 Mean Marbled Murrelet detections from forest surveys at three sites in northern California: James Irvine
Trail, Prairie Creek Redwoods State Park; Lost Man Creek, Redwood National Park; and the USDA Forest Service
Experimental Forest, Klamath. Means for the three sites combined by 10 day intervals also are presented. Surveys
were conducted 3-4 times per month most years from 1 989-1 993 and points represent the means for 1 0-day intervals.



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Table 1 Ten-day intervals and corresponding standard-
ization factors for seasonal variation of mean Marbled
Murrelet levels at three sites in northern California



Interval


Standardization factor


April 15 to April 24


0.86


April 25 to May 4


0.51


May 5 to May 14


0.82


May 15 to May 24


1.01


May 25 to June 3


0.95


June 4 to June 13


0.77


June 14 to June 23


0.68


June 24 to July 3


1.04


July 4 to July 13


1.22


July 14 to July 23


1.59


July 24 to August 2


1.04


August 3 to August 12


1.03



Thus for surveys conducted at the three sites from 14
July to 23 July, numbers of detections per survey were on
average 1 .59 times greater than the summer mean; surveys
conducted from 15 May through 24 May had numbers of
detections which were about equivalent to the summer mean;
and numbers of detections for surveys from 25 April to 4
May averaged about half of the summer mean.

In applying the standardization, we made the assumption
that the relationship between detections at any site on a
given day and the mean detection levels for the summer
period at that site would be the same as the relationship we
found at the three test sites. We have compared data with
one site with very low activity and found the seasonal curves
were similar. Standardized mean detection levels were
calculated for all stands and stations and this measure used
for all analyses.

Stand Study: Isolated Stands

Multiple Regression

We examined the relationship between standardized mean
detection levels for the stand, referred to as the dependent
variable, and the following independent variables: stand
size, Patton's index of perimeter to area (Patton 1975) which
was used as a measure of the edge or shape, distance from
salt water, density of old-growth trees, type of stand, and
dominant tree species. As a transformation of the standardized
mean detection level, we used the square root of the mean
for the multiple regression.

Logistic Regression

For each stand we summarized the detections and
behaviors for all surveys conducted during the study to
determine the status of the stand. If no murrelets were detected



during any of the surveys, then the status was "Undetected."
Stands with murrelet detections were assigned a status of
"Present" or, if occupied behaviors (Paton, this volume;
Ralph and others 1 993) were observed, a status of "Occupied."
Using logistic regression (SAS Institute, Inc. 1991)
with maximum likelihood analysis of variance, we examined
the relationship between a selection of independent variables,
and status. We compared response variables Present
(including Occupied stands) and Undetected, and response
variables Occupied and Unoccupied (all stands with a status
of Undetected or Present). For the stands with murrelets
present we compared Occupied stands, with stands with a
status of Present.

Park Study: Large Contiguous Stands

Elevation and position on the landscape were estimated
from topographic maps to give a measure of topography for
each station. Landscape position was described as one of
five categories: (1) in the bottom of a major drainage, a
drainage covering a large length of the landscape and isolated
by parallel ridges; (2) in the bottom of a tributary (or minor)
drainage, a drainage flowing into a major drainage, or a
short, steep drainage flowing directly into the ocean; (3) on
top of a major ridge, a ridge running parallel to a major
drainage; (4) on top of a minor ridge, a ridge line that
originated from the major ridge and was generally
perpendicular to a major drainage; and (5) on a general
slope, a station not on a ridge nor in a drainage.

When stations were located on slopes or ridges, it was
possible to detect murrelets calling in the drainages. The
topography within 100 m of the stations was similar to the
topography at the station itself. To help isolate the effects
of topography, we included only detections within 100 m
of the observer.

Results

Stand Study: Isolated Stands

We identified 286 potential study stands in Del Norte,
Humboldt, Trinity, San Mateo, and Santa Cruz counties
meeting the criteria in the four size categories 2 to 20 ha (n =
184); 21 to 40 ha (n = 39); 41 to 100 ha (n = 35); >100 ha (n
= 28). We located few stands >2 1 ha, therefore, we surveyed
all accessible stands in those categories. From these potential
study stands we selected and surveyed 152 stands as follows:
2 to 20 ha (n = 86); 21 to 40 ha (n = 22); 41 to 100 ha (n =
23); >100 ha ( = 21). Due to weather conditions, three
stands were surveyed only three times.

Density of the combined dominant and codominant tree
cover and presence of redwood trees were positively and
significantly (F 0>05 = 2.428, df model = 10, P = 0.0105, R 2 =
0.1625) related to mean murrelet detection levels in the
multiple regression model. Because only 16 percent of the
variation in the system was explained by the model, the
predictive ability was limited. Other variables examined
were not related to mean detection levels.



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Chapter 20



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The logistic regression model included density of old-
growth (dominant and co-dominant) tree cover, tree species,
and stand size as variables explaining the differences between
sites with no detections and those with murrelets present
(table 2). Stands with higher density classifications, and
with redwood as the dominant tree species, were more likely
to have murrelets present. Results also indicated a very
minor effect of smaller stands increasing the likelihood of
murrelet presence. We found, however, no significant effect
of stand size on the status of murrelets in the stands
(Undetected, Present, or Occupied), when tested by Chi-
square contingency table (df= 6, % 2 = 3.294, P = 0.7721)
(table 4). Using these variables accounts for virtually all of
the variability in the model.

For stands with a status of Occupied (n = 37), compared
with all Unoccupied stands (n =115), old-growth tree density
and tree species were significant variables (table 3) for
predicting observations of occupied behaviors. Stands in
higher density classes with redwood as the dominant species
were more likely to be classified as Occupied.

Among stands with murrelet detections (n = 62), we
found no differences in habitat variables between stands
with a status of Occupied (n = 37) and Present (n = 25).

Park Study: Large Contiguous Stands

Central California

Big Basin Redwoods State Park was surveyed in a matrix
of 37 survey stations. The elevation ranged from 240-500 m
and we divided stations into four equal categories (table 5).
We found the mean detection levels and the number of
Occupied stations higher for stations in lower elevation
categories. The proportion of Occupied stations was not
significantly different (P > 0.05) among topography categories
(table 5). Occupied behaviors were observed in all topography
categories, and the only station with a status of Undetected
was on a major ridge.



Table 2 Results of logistic regression analysis for stands in California (n =
152) with a status of murrelets Present (Present and Occupied) (a = 62) and
Undetected (a = 90). Only variables with significant contribution to the
model are presented





Regression




Chi-square


Variable


coefficient


Chi-square


probability


Tree species'


1.8101


9.43


0.0021


Cover density 2


0.8755


5.76


0.0164


Stand size


-0.0206


5.45


0.0195



'Coast redwood (Sequoia sempervirens) or Douglas-fir (Pseudotsuga
menziesii) >50 percent of stand.

2 Percent dominant and codominant tree cover.



Table 3 Results of logistic regression analysis for stands in California
(n = 752; with status of Occupied (n = 37) and stands with murrelets Present
or Undetected (UnoccupiedXn = 115). Only variables with significant
contribution to the model are presented



Variable


Regression
coefficient


Chi-square


Chi-square
probability


Tree species 1
Cover density 2


1.9243
1.0831


5.86
6.64


0.0155
0.0100



'Coast redwood (Sequoia sempervirens) or Douglas-fir (Psuedotsuga
menziesii) >50% of stand.

2 Percent dominant and codominant tree cover.



Northern California

We surveyed 352 stations in the 8 stands within northern
California parks. We found that topography had a major
influence on murrelet use (P < 0.0001). The mean detection
levels were three times higher in major drainages (table 6)
than on the major ridges.



Table 4 Percent of stands by murrelet use or status in each size category of stands surveyed in California for
the Stand Study. Stands with a designation of Present had murrelet detections, but no observations of below
canopy, or Occupied behaviors





Percent of stands by murrelet use (status)




Not detected Present


Occupied


Stand size (ha)


n


n


Percent n Percent


n


Percent


2-20


86


55


63.9 14 16.3


17


19.8


21-40


22


12


54.6 3 13.6


7


19.8


41-100


23


12


52^ 5 21.7


6


26.1


>100


21


11


5Z4 3 14.3


7


33.3



Totals



152



90



59.2



16.4



37



24.3



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Table 5 For central California: Summary of detections 1 and status for Marbled Murrelet stations surveyed in old-growth forests within state and national
parks during the summer, 1993



Landscape variable


Mean
number of
detections 2


Number of stations (n)


s.d.


Range


Occupied


Present


Absent


Total


Topography
















Tributary drainage


55


42


30-104


3








3


Major drainage


74


53


1-177


10


3





13


General slope


58


31


1-97


7


1





8


Minor ridge


34


31


1-83


5


2





7


Major ridge


11


14


0-37


3


2


1


6


Elevation
















240-305 m


70


53


1-177


10


2





12


306-360 m


64


36


13-122


10


1





11


361 -420m


35


31


1-946


4





10


10


421 -500m


4


6


0-122


1


1


4


4



'Includes only detections within 100 meters of observer
Standardized detections



Table 6 For northern California: Summary of detections 1 and status of Marbled Murrelet stations surveyed in old-growth forests within the state and national
parks during the summer, 1993



Landscape variable


Mean
number of
detections 2


Number of stations (n)


s.d.


Range


Occupied


Present


Absent


Total


Topography
















Tributary drainage


22


33


0-134


18


19


54


91


Major drainage


30


28


0-160


67


25


17


109


General slope


14


17


0-83


40


67


22


129


Minor ridge


16


19


0-107


19


29


18


66


Major ridge


10


13


0-51


14


27


6


47


Elevation
















21-100 m


28


30


0-160


83


53


27


163


101-200 m


16


18


0-83


46


66


36


148


201-300 m


12


13


0-56


19


37


19


75


301-500 m


4


6


0-22


10


11


18


39



'Includes only detections within 100 meters of observer
Standardized detections



The proportion of Occupied stations was significantly
higher at stations of less than 100-m elevation than at stations
>200 m (P < 0.0001) (table 6). The proportion of stations
with no detections was significantly higher in the >300 m
category and significantly lower in the <100 m category.

Inland Range

We found highest frequencies of presence (89.05 percent)
and occupancy (21.91 percent) at stands and stations within
10 km of the coast (table 7). The proportion of Occupied
sites decreased in the 10- to 20-km band. The number of
stations with detections declined by more than 99 percent
from the 30- to 40-km to the 40- to 50-km band, although



four times the number of stations were surveyed in the 40- to
50-km band. The proportion of Occupied stations declined
rapidly beyond 30 km from the coast.

Discussion

Stand Study

The most important factor in indicating Occupied stands
was density of the old-growth cover, that is, the percent of
the area covered by the crowns of old-growth trees. Occupied
stands had a higher percentage of old-growth cover than
stands with murrelets only present, or in stands with no
detections. These relationships are consistent with those



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Online LibraryCalif.) Pacific Southwest Forest and Range Experiment StatEcology and conservation of the marbled murrelet → online text (page 34 of 70)