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Characteristics of Managed Forest Habitat
Selected for Nesting by Merriam's Turkeys
Brian F. Wakeling 1 and Harley G. Shaw2
I
Abstract - Nest site selection by Merriam's turkey (Meleagris gallop avo
memam/) was studied on the Mogollon Rim, Arizona, from 1987 through
1991. Compared with measured habitat availability, nests had higher shrub
and deciduous tree seedling densities (e < 0.001). Nests also had more
cover comprised of shrubs, deciduous trees, and rock (E < 0.001, E. < 0.001,
and E 0.036, respectively). This cover averaged a greater height than at
random sit~s (e 0.032). Green foliage volumes at nests werfJ greater (E<
0.05) and horizontal visibilities were lower (E < 0.001). Nest sites were
selected in stands that had clumped understory (E 0.032) and overstory
0.003). Basal
distributions (E < 0.001), and patchy forest canopies (e
areas were greater on nest sites (E < 0.001). Steep slopes were selected
(E. < 0.001) for nesting purposes and canyons were the selected landform
(E. < 0.001). Although turkeys nested in logging slash, slash piles were
avoided.
=
=
=
=
To date, little timber harvest has occurred on slopes >40%, inadvertently
protecting much nesting habitat. Timber treatments that promote small scale
patchiness, such as uneven-aged management or group selection harvests,
can emulate vegetational characteristics of nesting habitat. Leaving loosely
scattered slash, especially near the base of trees, can provide suitable nest
sites in stands with ~ 50% canopy coverage.
Not all timber treatments, however, negatively influence
turkey populations. In some cases timber harvest improved the
suitability of tuIkey brood range (Mollohan and Patton 1991).
Additionally, turkeys have used second growth timber
extensively for feeding in some locations (Rumble 1990).
Limited infonnation was available on nest site selection in
southwestern Merriam's turkey range. Because timber halvest
did not affect habitat selection by turkeys in a consistent manner
(Scott and Boeker 1977, Mollohan and Patton 1991), loss of
nesting habitat was considered to be a potential cause of reduced
turkey numbers. Nesting habitat may be especially critical in
affecting southwestern tUIkey populations. Generally, only adult
(2 year old) hens nest in the southwest (Goemdt 1983, Crites
1988, Wakeling 1991, Stone 1993). In addition, relatively few
hens live beyond the age of 3 (Wakeling 1991). We studied
nesting habitat selection by Merriam's tUIkey to detennine how
management activities affected habitat use.
Funding for this project was provided through Federal Aid
in Wildlife Restoration Act Project W-78-R. R. Day, lR. Wegge,
M. Senn, D. Skinner, K. Berger, C.M. Mollohan, E. Ozog, L.M.
INTRODUCTION
Merriam's tUIkey populations in the southwest may have
declined from historic levels (Shaw 1986, Green 1990).
Alterations to forest habitat by land management practices
probably contributed to the decline (Shaw 1986). Tutkeys select
habitat characteristics based upon specific behavioral activity
such as feeding or loafmg (Rumble 1990, Mollohan and Patton
1991). Manipulations to forest structure can reduce habitat
suitability (Scott and Boeker 1977).
1 Brian F. Wakeling is a Research Biologst with the Arizona
Game and Fish Department, 2221 West Greenway Road, Phoenix,
AZ 85023.
2 Harley G. Shaw is a Wildlife Biologist with General Wildlife
Services, P.O. Box 370, Chino Valley, AZ 86323.
359
Schiavo, C.A. Staab, C. Hart, B.S. Holt, W.A. Rosenberg, C.H.
Lewis, and V. Fitzpatrick provided field assistance. We are
grateful to R.A. Ockenfels for critical review of an earlier draft
of this manuscript. CD. Chevalier made helpful suggestions that
improved the poster presentation
STUDY AREA
2
The 335 mi Chevelon Study Area (CSA) was located
approximately 40 mi south of Wmslow, Arizona, along the
Mogollon Rim. Elevations ranged from 5500 ft in the northern
portion to 7900 ft in the southern portion Annual precipitation
averaged 18.6 in, with 2 conc~ntrations, the first occurring
during winter stonns in Janwuy through March, and the second
during summer storms in July through early September (Natl.
Oceanic and Atmos. Admin 1991). Five habitat associations
were identified on the CSA based upon terrestrial ecosystem
swveys (Laing et al. 1989). These associations were mixed
conifer, ponderosa pine (Pinus ponderosa)-Gambel oak
(Quercus gambelii), pinyon (P. edulis)-juniper (Juniperus spp.),
aspen (Populus tremuloides), and forest meadow associations
(fig. 1). Mixed conifer associations were dominant above 7600
ft, and extended along east facing slopes and drainages. This
habitat included Douglas-fir (Pseudotsuga menziesii), white fir
(Abies conc%r), limber pine (Pinus jlexilis), and Rocky
Mountain maple (Acer glabrum). Ponderosa pine dominated
west facing slopes below 7600 ft and above 6000 ft. Below
6000 ft, pinyon-juniper was dominant with ponderosa pine
stringers in drainages. Gambel oak occurred in all associations,
in pockets in the mixed conifer and pinyon-juniper associations,
and as a widespread conspecific with ponderosa pine. At
elevations below 7000 ft, pinyon and alligator juniper (Juniperus
deppeana) became increasingly abundant.
Logging and grazing have been and remain major commercial
land uses on the CSA. Logging began in the late 1930's and
most ponderosa pine stands on level terrain have been logged
at least once. Little logging has occurred on steeper slopes of
major canyons.
Legend
§
Mixed Conifer
fSZl
Ponderosa Pinel
Gambel Oak
•
•
Ponderosa Pinel
Pinyon-juniper
~
Pinyan/ Juniper
R
D
Forest Meadows
Aspen
Water
Figure 1. - Vegetation associations present on Chevelon
Study Area, Arizona (based on Laing et at 1984).
were not approached for 1-2 weeks to prevent premature nest
abandonment. Nests were then located and monitored daily to
detennine dates that hens left nests.
Habitat Mensuration
METHODS
Habitat characteristics of each nest site were measured after
the hen and brood abandoned the nest area following predation
or hatching. Percent slope was measured with a clinometer.
Landfonn was classified as minor canyon «200 ft wide), major
canyon (~200 ft wide), or ridgetop-flat. Canopy structure was
classified as single storied, multiple storied-uniform, or multiple
storied-clumped (i.e. gave an uneven-aged appearance).
U nderstOlY and overstory were classified as clumped or evenly
distributed. Stem densities of shrubs and deciduous seedling «1
in diameter breast height [DBHD, sapling «1 to 5 in DBR),
and mature (>5 in DBH) trees were determined on a 0.01 ac
circular plot centered on the nest. Stem density of conifers was
Merriam's tuIkey hens were captured during winters of 1987
through 1990, using box traps, drop nets, and rocket nets
(described by Wakeling 1991). Hens were equipped with
motion-sensing backpack radio telemetty units (felonics, Mesa,
AZ and AVM Electronics, San Francisco, CA) and released at
the capture site.
Nest sites were located by monitoring radio instrumented hens
~2X weekly. Hens were suspected of nesting when >2
consecutive locations were within 114 mile of each other and
motion-sensing transmitters indicated inactivity. Inactive hens
360
.u
measured on a 0.1 ac circular plot, also centered on the nest.
Basal area was detennined from DBH measurements taken on
all conifers encountered on this plot.
Four 25-ft line intercept transects were established, each
radiating from site center at right angles to one another. The
first transect was randomly oriented. These transects were used
to determine canopy cover, within 18 in of ground, from rock,
down wood, grass, foms, shrubs, deciduous trees, and coniferous
trees. The distance from which a tuIkey silhouette, placed at site
center, could no longer be seen was detennined in 4 directions,
parallel to line intercept transects. Average height of cover was
ocularly estimated. Green foliage 'volume was detennined at
each site according to MacArthur and MacArthur (1%1).
Identical measurements were -taken at random plots to
represent habitat availability (Marcum and Loftsgaarden 1980).
We generated random Universal Transverse Mercator
coordinates by computer and plotted them on 7.5' USGS
topographic maps. Once a point w~ located on the ground, we
stepped off a random distance in a random direction This
endpoint was considered random plot center.
Table 1. - Mann-Whitney
values, probabilities, and mean
values for habitat parameters at nest and random sites
on the Chevelon Stud~ Area.
Mean
Mean
Nest
Random
P
Habitat Parametefi
11
<0.001 5960
1017
485.5
Shrub Density
Deciduous
<0.001 2228
169
524
Seedling Density
Deciduous
0.006 300
10
726
Sapling Density
Mature
Deciduous Tree
0.006 120
7
728
Density
Conifer Tree
0.193
50
60
808.5
Density
10.8
503
0.010
6.0
Grass Cover
7.3
545.5
0.031
4.4
Forb Cover
0.036
14.4
8.1
Rock Cover
552.5
Down Wood
755
0.896
12.7
12.4
Cover
Deciduous Tree
<0.001
0.1
408
1.7
Cover
Conifer Tree
718.5
0.621
2.0
2.0
Cover
<0.001
3.0
0.7
394.5
Shrub Cover
<0.001
49
143
111
Silhouette Visibility
187
<0.001
54
18
Slope
Data Analysis
The Mann-Whitney 11 test was used to test differences in
non-oonnal continuous data (Zar 1984:138). We used Student
t-tests to test for differences between nonnal continuous data
(Zar 1984:126). Chi-square contingency table analysis was used
to test categorical data (Zar 1984:62). Multiple categories were
evaluated using Bonferroni simultaneous confidence intelValS
(Neu et al. 1974). All tests were considered significant at ~ ~
0.05 with the exception of Bonferroni confidence intelValS.
Because these confidence intervals take into account
simultaneous tests which affect individual alpha levels, the .
overall alpha level was set at ~ ~ 0.1 (Byers et al. 1984).
aDensities are presented per acre, cover as percent canopy
cover between 0-18 in of ground, visibility In ft, and slope as percent
Feet Above Nest Bowl
100
90
80
70
60
50
40
30
20
RESULTS
10
o
Habitat parameters were measured at 67 nest sites and 29
random plots. Shrub and deciduous seedling, sapling, and mature
tree densities were higher at nest sites than at random plots
(Table 1). Nest sites also had more 0-18 in cover comprised of
shrubs, deciduous trees, and rock (Table 1). This cover averaged
a greater height at nest sites (mean = 10.6 in) than at random
plots (mean = 8.2 in) a-test, ~ = 0.032). At nest sites, green
foliage volumes below 15 ft were greater (Fig. 2) and horizontal
visibility distances shorter (Table 1) than at random plots. Nest
sites were selected in stands that had clumped understory and
overstory distributions (Table 2). Multiple storied-clumped forest
canopies were favored (Table 2). Basal areas were greater in
stands at nest sites (mean = %.1 triac) than at random sites
(mean = 57.0 ft2/ac) a-test, ~ < 0.001). Steep slopes were
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Foliage Volume (sq ft/cu ttl
- - Nest Sites
-t- Random Plots
Figure 2. - Foliage volume (MacArthur and MacArthur 1981) on
nest and random sites on the Chevelon Study Area, Arizona.
abcdPoints With the same letter are significantly different from each
other (I-test, f. 0.05).
selected (Table 1) for nesting pwposes and canyons were the
selected landfonn (Table 2). Although tuIkeys frequently nested
in scattered logging slash, slash piles were only used twice.
Less grass and fom cover was found at nest sites than at
random plots (Table 1). No differences could be detected
between nest sites and random plots in conifer tree densities or
canopy cover from conifer trees or down wood.
361
Table 2. -
Nest and random site proportions, Bonferroni confidence intervals around nest site proportions, Chi-square
values, and probabilities for habitat parameters on the Chevelon Study Area.
Habitat Parameter
Observed
Available
CI
X2
f.
Landform
Minor Canyon
Major Canyon
Ridgetop-Flat
n
Understory Distribution
Even
Clumped
0.473
0.400
0.127
55
0.069
0.138
0.793
29
0.330-0.616
0.259-0.541
0.031-0.223
0.222
0.778
0.448
0.552
28
0.111-0.333
0.667-0.889
0.127 -0.355
0.645-0.873
54
0.448
0.552
29
0.000
0.264
0.736
53
0.071
0.572
0.357
27
0.000-0.000
0.135-0.393
0.607 -0.865
n
54
Overstory Distribution
Even
Clumped
0.241
0.759
n
Canopy Structure
Single Story
Multi-Uniform Stories
Multi-Clumped Stories
n
37.07
<0.001
4.58
0.032
6.72
<0.001
12.02
0.003
DISCUSSION
MANAGEMENT IMPLICATIONS
In our study, steep slopes were selected for nesting. Merriam's
turkey appear consistent in selection for steep slopes throughout
their range (Goemdt 1983, Mackey 1984, Crites 1988, Hengel
1990). This selection may assist nesting turkeys in eluding
detection by ground predators. Additionally, hens may take
advantage of the incline to gain flight if disturbed.
Other characteristics selected at nest sites in our study seem
to provide hens with hiding cover. Greater amounts of shrub
and deciduous vegetation, rock, and green foliage volumes
function to obscure nesting hens. Obscurity and camouflage
would help hens avoid predator detection while nesting.
Merriam's turkey consistently select nest sites that provide
greater cover (Goemdt 1983, Hengel 1990, Rumble 1990).
Although turkeys selected nest sites in stands that had
clumped multiple canopies, it is difficult to determine whether
this was a true selection for canopy characteristics or selection
for steep slopes, where these characteristics predominated. The
importance of clumped overstories is not readily apparent.
Clumped overstories may simply be indicative of suitable
understories. Nest sites in our study not located in canyons were
frequently in stands that had been treated with a group selection
halvest, yielding a clumped overstory. While steep slopes were
selected for, clumped overstories may also be important,
although to a lesser degree.
Given adequate availability of other important features, such
as water and suitable brood habitat, we believe Merriam's turkey
select nesting habitat based upon 1) slope steepness and 2)
suitable hiding cover. 1\ukeys select nest sites in habitats that
are steep (>30% slope) and have short (<70 ft using a turkey
silhouette) horizontal visibility distances.
Characteristics of habitat where nests are' generally found
include modemte to high basal area of conifer trees and high
densities of shrubs and deciduous trees, arranged in a small scale
mosaic. For management purposes, horizontal visibility
distances is simpler to evaluate than cover composition and
quantity. The distance at which a turkey silhouette is obscured
is an appropriate mpid measure of habitat suitability for nesting
purposes. Mollohan and Patton (1991) found a correlation (r =
0.853) between horizontal visibility distance of a turkey (HVDt)
and that of a person (HVDp). The relationship between the 2
measures was HVOt = 0.39 X HVDp. Thus, horizontal visibility
distance at which a person is obscured can be used to evaluate
habitat suitability for nesting. Obscuring cover may be
comprised of herbaceous vegetation, shrubs, trees, steep slopes,
or rocks.
Whenever possible, timber treatments should be avoided on
slopes>30%. Tunber treatments that leave modemte basal areas
(70-90 ft?lac) in small (1-4 ac) patches favor retention of nest
site characteristics. Scattering logging slash following harvest,
mther than leaving slash piles, will result in habitat more suitable
for nesting. Any treatment that increases horizontal visibility
distance will reduce site suitability for nesting. Our results are
consistent with nesting habitat recommendations suggested by
Hoffman et al. (1993).
Timber treatments that result in characteristics described
for nest sites can be used to retain or create suitable nesting
habitat. Treatments such as group selection harvests or
uneven-aged management appear to facilitate this
management goal. Even aged management approaches appear
less suitable.
362
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363
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