Habitat Use and Survival of Preflight Wild Turkey Broods
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Research Article
Habitat Use and Survival of Preflight Wild Turkey Broods
BRIAN L. SPEARS,1,2 Department of Range, Wildlife, and Fisheries Management, Box 42125, Texas Tech University, Lubbock, TX 79409-2125, USA
MARK C. WALLACE, Department of Range, Wildlife, and Fisheries Management, Box 42125, Texas Tech University, Lubbock, TX 79409-2125, USA
WARREN B. BALLARD, Department of Range, Wildlife, and Fisheries Management, Box 42125, Texas Tech University,
Lubbock, TX 79409-2125, USA
RICHARD S. PHILLIPS, Department of Range, Wildlife, and Fisheries Management, Box 42125, Texas Tech University,
Lubbock, TX 79409-2125, USA
DERRICK P. HOLDSTOCK, Department of Range, Wildlife, and Fisheries Management, Box 42125, Texas Tech University,
Lubbock, TX 79409-2125, USA
JOHN H. BRUNJES, Department of Range, Wildlife, and Fisheries Management, Box 42125, Texas Tech University, Lubbock, TX 79409-2125, USA
ROGER APPLEGATE, Kansas Department of Wildlife and Parks, P.O. Box 1525, Emporia, KS 66801-1525, USA
MICHAEL S. MILLER, Texas Parks and Wildlife Department, Pampa, TX 79065, USA
PHILLIP S. GIPSON, Kansas Cooperative Fish and Wildlife Research Unit, 205 Leasure Hall, Kansas State University, Manhattan, KS 66506, USA
ABSTRACT Wild turkey (Meleagris gallopavo) broods spend the first several days of life on the ground until poult flight capabilities are
attained. This is a critical period of wild turkey life history, with poult survival ranging from 12% to 52%. We measured vegetation in plots
used by Rio Grande wild turkey (M. g. intermedia) preflight broods at 4 sites in southwest Kansas and the Texas Panhandle, USA, to determine
microhabitat selection for ground roosting and to determine if microhabitat was related to poult survival. Hens selected ground-roost locations
with more visual obstruction from multiple observation heights than random sites. Plots surrounding ground roosts had 1) greater visual
obstruction; 2) increased tree decay; 3) higher percent grass, shrub, litter, and forb cover; and 4) lower percent bare ground cover than random
sites. Grass, shrubs, and downed trees appeared to provide desired cover for ground-roosting broods. Poult survival increased with age of poult,
size of brood, and density of shrubs 1–2 m tall. Plots used by broods ,10 days old with above average survival contained more visual obstruction
and shrubs than plots used by broods 10–16 days old with above average survival, signifying a shift in habitat use by successful broods as poults
attain flight abilities. Density of shrubs 1–2 m tall in brood-use areas appears to be important for poult survival to 16 days of age on southern
Great Plains rangeland habitats. Ground-level vegetative cover appears to be a significant factor in preflight poult survival. Provisions of
ground-level vegetative cover should be considered during wild turkey brooding periods where increased poult survival is desired. (JOURNAL
OF WILDLIFE MANAGEMENT 71(1):69–81; 2007)
DOI: 10.2193.2005-676
KEY WORDS brood, ground roost, habitat, Meleagris gallopavo intermedia, poult, Rio Grande wild turkey, survival.
The first 2 weeks posthatch are the most critical period for Phalen et al. 1986, Campo et al. 1989, Sisson et al. 1991,
wild turkey (Meleagris gallopavo) survival, with observed Edelmann et al. 2001). Habitat parameters that facilitate
survival rates ranging from 12% to 52% during this period predator avoidance may increase preflight poult survival
(Vander Haegen et al. 1988, Sisson et al. 1991, Peoples et al. (Porter 1980, Hurst et al. 1996). Everett et al. (1980),
1995, Miller et al. 1998b, Paisley et al. 1998). Several factors Speake et al. (1985), and Peoples et al. (1995) suggested that
may affect preflight poult survival, including predation, habitat management for wild turkeys should focus on
weather, starvation, and disease (Hurst et al. 1996, Roberts facilitating preflight poult survival by maintaining high-
and Porter 1998, Rolley et al. 1998). Mammalian predation quality brood habitat.
appears to be the single greatest factor in preflight poult Habitat use by wild turkey broods has been studied across
mortality (Speake et al. 1985, Palmer et al. 1993, Roberts a wide geographic area (Williams et al. 1973, Metzler and
and Porter 1998). Speake 1980, Pack et al. 1980, Porter 1980, Hennen and
Survival rates reportedly increase after poults reach Lutz 1996). Brooding hens appear to select for specific
approximately 2 weeks of age (Speake et al. 1985, Vangilder habitat composition (Porter 1980, Healy 1985, Hennen
et al. 1987, Peoples et al. 1995, Hubbard et al. 1999). By 1999, Edelmann et al. 2001) and habitat types. Lack of
this point, poults are able to escape ground predators by available vegetation structure that allows preflight poults to
flushing to trees and roosting in trees at night. These escape predation may lead to low preflight poult survival
observations suggest that ground escape and roost cover are rates. Correlating vegetation structure with preflight poult
essential for poult survival during the first 2 weeks of life. survival rates is essential in identifying desirable habitat
Previous studies indicated that turkey broods select for cover management plans. However, previous studies of wild
types with specific tree density, tree size, shrub density, turkey preflight broods simply used locations of broods as
minimum vegetation height, canopy, percent ground cover, an index of habitat preference and quality, and relatively few
and visual obstruction 1 m in height (Pack et al. 1980, studies of preflight poult brood habitat use examined
1
E-mail: brian_spears@fws.gov
relationships between survival rates and vegetative param-
2
Present address: Upper Columbia Fish and Wildlife Office, 11103 eters (e.g., Porter 1980, McCabe and Flake 1985, Schemnitz
E. Montgomery Drive, Spokane, WA 99206, USA et al. 1985, Phalen et al. 1986, Campo et al. 1989, but see
Spears et al. Wild Turkey Brood Habitat Use and Survival 69Metzler and Speake 1980). Assessment of habitat use by
broods may change depending on landscape organization
(Pack et al. 1980, Phalen et al. 1986, Sisson et al. 1991,
Hennen 1999) or determination of habitat availability
(McClean et al. 1998). Thus, use may not always be an
accurate index of habitat quality (Van Horne 1983) or brood
resource preference.
Lack of information on daily poult survival in broods 14
days old may further obscure habitat–poult survival relation-
ships. Unfortunately, few studies have examined preflight
poult survival 2 weeks posthatch. Rio Grande wild turkey
(M. g. intermedia) poult survival appears to increase at 9–10
days (Hennen 1999, Spears et al. 2005), not at 14 days as
reported for other wild turkey subspecies. Timing of flight
attainment by Rio Grande wild turkey poults corresponds
with timing observed in other subspecies (Williams 1974,
Healy 1992). This suggests that daily survival rates 2
weeks posthatch, undocumented in other subspecies, should
correspond with what Hennen (1999) and Spears et al.
(2005) observed in the Rio Grande subspecies.
We examined relationships between microhabitats used
and survival of preflight Rio Grande wild turkey poults at 4
sites in southwest Kansas and the Texas Panhandle, USA.
We hypothesized that specific habitat characteristics in-
creased preflight poult survival. Our objectives were to 1)
describe ground roosts and distances moved by ground-
roosting poults, 2) determine timing of first brood tree-
roost, 3) determine vegetation characteristics selected by
ground-roosting broods, and 4) determine correlations Figure 1. Rio Grande wild turkey preflight poult study sites, Kansas and
Texas, USA, 2000 and 2001. (CNG, Cimarron National Grassland;
between poult mortality rates and the physiognomy of GHWMA, Gene Howe Wildlife Management Area; MWMA, Matador
habitat utilized within the first 2 weeks posthatch. Wildlife Management Area)
STUDY AREA area was dry at the surface, except for occasional flooding.
We conducted our study at 4 sites (Fig. 1). The first site was in Precipitation was usually ,41 cm per year and was
southwest Kansas, where Rio Grande wild turkey population concentrated from April to September (United States Forest
numbers have declined since the mid-1980s (Kansas Depart- Service, unpublished data). The other 3 study sites were
ment of Wildlife and Parks, unpublished data). The south- located in the Rolling Plains of Texas. This region was
west Kansas study site was centered in the Cimarron National characterized by 55–76 cm of annual rainfall. Elevation
Grassland (CNG) in Morton County, but it included parts of ranged from 242 m to 909 m. Topography was gently rolling
Stevens County, Kansas, and Baca County, Colorado, USA. hills dissected by narrow intermittent stream valleys flowing
The CNG was located within the High Plains province of the northwest to southeast.
Great Plains (Cable et al. 1996). Elevation ranged from 955 The first Texas site was centered on the Matador Wildlife
m to 1,121 m. Topography included rock cliffs, sand dunes, Management Area (MWMA), where turkey populations
grassy fields, and the Cimarron River basin. Sand sagebrush were thought to be declining (Texas Parks and Wildlife,
(Artemisia filifolia) prairie was adjacent to the river corridor. unpublished data). The MWMA was 11,410 ha and located
Grasses in the area included sand bluestem (Andropogon north of Paducah in Cottle County. The MWMA was
hallii), blue grama (Bouteloua gracilis), sideoats grama located in the Mesquite Plains subregion of the Rolling
(Bouteloua curtipendula), sand dropseed (Sporobolus cryptand- Plains. The area was traversed by the confluence of the
rus), sand lovegrass (Eragrostis trichodes), prairie sandreed Middle and South Pease rivers. Mesquite (Prosopis glan-
(Calamovilfa longifolia), and buffalo grass (Buchloe dacty- dulosa)–grass savanna dominated, but sand sagebrush,
loides). These grasses, as well as sagebrush, four-wing saltbush shinnery oak (Quercus havardii), sand plum (Prunus
(Atriplex canescens), rabbitbrush (Chrysothamnus sp.), snake- angustifolia), acacia (Acacia spp.), netleaf hackberry (Celtis
weed (Gutierrezia sarothrae), and plains yucca (Yucca glauca) reticulata), honey mesquite (Prosopis juloflora var. glandulosa),
dominated the fields and hills adjacent to the Cimarron River and redberry juniper (Juniperus pinchotii) were also common.
corridor. Grasses, cottonwood (Populus deltoides), and tam- Native grasses included bluestems and gramas. Cottonwood,
arisk (Tamarix chinensis) groves dominated the river basin western soapberry (Sapindus drummondi), and hackberry
(Cable et al. 1996). A major part of the Cimarron River in this (Celtis occidentalis) lined riparian corridors (Hodge 2000).
70 The Journal of Wildlife Management 71(1)The second Texas site was on the Gene Howe Wildlife under approved Texas Tech University Animal Care and
Management Area (GHWMA), where Rio Grande wild Use Protocols (no. 99917 and no. 01173B). We captured 45
turkey numbers were apparently at high density and adult hens, 15 juveniles, and 15 adult gobblers at each site in
increasing. The GHWMA consisted of 2,138 ha and was 2000 and 2001 and equipped them with backpack-mounted
located in Hemphill County, Texas, along the Canadian transmitters (AVM Instruments, Livermore, CA; Advanced
River, also in the Mesquite Plains subregion of the Rolling Telemetry Systems [ATS], Isanti, MN). We continued
Plains. Vegetation was similar to the MWMA, with trapping efforts from January through mid-March or until
meadows of native grasses and cottonwood, soapberry, target numbers were reached. Transmitters had a mortality
common hackberry, black walnut (Juglans nigra), western signal delay of 4.5 hours (AVM) or 8 hours (ATS). We
soapberry, sumac (Rhus aromatica), and tamarisk groves in sexed, aged (Pelham and Dickson 1992), and weighed
the riparian corridor. A narrow transition zone separated captured birds. We recorded temperatures with a rectal
riparian corridors and sandhills (Hodge 2000) dominated by thermometer, banded birds with aluminum leg bands, and
sand sagebrush. released processed birds on-site.
The third Texas site was on the Salt Fork of the Red River We located transmitter-equipped birds 2 times per week
in eastern Donley and western Collinsworth counties in the following trapping to determine general movement patterns,
Texas Panhandle. This site appeared to have a high-density mortality, and onset of nesting. We determined incubation
turkey population that was thought to be increasing (Texas by the continuous location of a hen at a specific point
Parks and Wildlife, unpublished data). Seventy-nine percent (Miller et al. 1998a, Keegan and Crawford 1999). We
of Donley County and 55% of Collinsworth County were triangulated incubating hens on nests to within 50 m
rangeland. Elevation ranged from 632 m to 995 m. Annual (Everett et al. 1980) and monitored individual hen
rainfall averaged between 52 cm and 55 cm, with the incubation periods to determine hatch date.
majority of precipitation occurring from April to October. We located up to 7 transmitter-equipped hens with
Vegetation consisted of cottonwood, honey locust (Gleditsia successful nests at each site each year through walk-in
triacanthos), black locust (Robinia pseudo-acacia), Texas triangulations as soon as possible after hatching and flushed
sugarberry (Celtis laevigata), and netleaf hackberry trees in them from their brood. We hand-captured up to 5 poults
riparian areas, and rolling hills of yucca, grama grasses, per brood (Peoples et al. 1995, Hubbard et al. 1999), leaving
bluestem, post oak (Quercus stellata), and snakeweed range- 1 poult of each brood for the hen to return to while we
land (McEwen et al. 1973, Williams and Crump 1980). processed captured poults (Peoples et al. 1995). We did not
Cattle grazed all 4 areas during this study. At CNG, the flush broods during extreme heat (.358 C) or within 2
national grasslands were rotationally grazed whereas private hours of sunset. We placed poults in an insulated cooler
lands were used seasonally or yearlong. Stocking rates were with either a hot water bottle to serve as a heat source during
not available, but use was generally moderate (40–50% of cool weather or with moist towels for comfort during
standing crop). Riparian areas were not excluded from warmer parts of the day. We removed captured poults .35
grazing. Cattle grazing occurred on selected parts of the m from the capture location to prevent the hen from hearing
GHWMA throughout the study period. Cattle use varied peeping from poults that were being processed. We weighed
markedly with the diverse patterns of ownership at this site and equipped poults with model 384 transmitters (ATS).
but, where grazed, use was moderate to heavier (up to 60% Transmitters weighed 1.8 g, were 10.5 mm long, 20 mm
estimated) in some riparian areas. Cattle grazing also wide, 4 mm thick, and had a 10-cm antenna. We shaved a
occurred on the MWMA throughout the study period. patch matching the footprint of the transmitter with an
No riparian areas were excluded from grazing unless that electric razor on each poult’s back and attached a transmitter
pasture was deferred for that year. Cattle were rotated with Supergluet (Bowman et al. 2002) in 2000 and
among pastures to achieve moderate use, although use was Superglue or Superglue gel in 2001, both cyanoacrylate
heavier around windmills and in riparian areas. The Salt adhesives. As soon as transmitter attachment was dry
Fork consisted of several large ranches that primarily used (approx. 45–60 min), we relocated and flushed brooding
deferred rotation systems with their cow–calf operations. hens and returned equipped poults to the brood (Hubbard et
Grazing access to riparian areas was allowed. Stocking rates al. 1999).
were unknown and highly variable, although use was usually We conducted walk-in locations on instrumented broods
light to moderate. With grazing rotations, deferments, or 1–4 times per day. We discretely approached the trans-
landownership patterns, most turkeys had ungrazed pastures mitter-equipped hen to within 30 m until we could visually
available to them throughout the nesting period. Grazed locate her. Once we located the hen, we used radiotelemetry
pastures provided areas with herbaceous and woody cover to check for the presence of each transmitter-equipped poult
for turkey nesting at all 4 sites. known to be with that brood. When we could not easily
visually locate broods (e.g., broods were hiding in dense
METHODS brush), we estimated their location to within 10 m by
We prebaited locations on study sites during winter months circling them at a distance .30 m and estimating their
with whole kernel corn and milo. We used drop and rocket location through triangulations of radio signals.
nets (Baldwin 1947) to capture juvenile and adult turkeys We made every effort to ensure that locations represented
Spears et al. Wild Turkey Brood Habitat Use and Survival 71those of undisturbed broods. Observations of telemetered recording the lowest visible 0.1-m band on the visual turkeys during walk-in locations suggested that common obstruction pole. We indexed total hiding cover, or total responses of hens and broods were to either freeze obstruction, by recording total number of visible 0.1-m immediately when an observer was detected or to continue bands. We considered bands visible if any portion could be to move slowly away. When a brood appeared to change seen. locations due to observer presence, we terminated observa- We quantified ground cover along each of the plot’s 10 4- tions and chose another brood for relocation during that m transects that had been used to estimate visual portion of the day. For broods that appeared to be moving obstruction. We determined ground cover (categorized as prior to detection, we placed locations at the point of first grass, forb, crop, shrub, litter, bare ground, or other) by visual contact. sighting through an ocular tube with crosshairs at one end We located brood ground roosts at the beginning of each held vertically. We recorded the ground cover category 10 day by locating and observing ground-roosting hens. We times at 40-cm intervals along each 4-m transect between made telemetry triangulations to within 10 m when we the sighting and visual obstruction pole. could not visually observe hens. We flagged locations of We defined shrub cover as woody-stemmed vegetation ground roosts for vegetation measurements to be made after .0.5 m in height and ,10 cm in diameter. We indexed brood departure. We documented each turkey hen or poult shrub cover by recording number of shrubs within a 2 3 20- location with Universal Transverse Mercator coordinates. m belt transect that was walked with a 2-m long pole held We tracked broods in the above manner until all poults in a horizontally at 0.5 m from the ground along the 20-m brood began to roost in trees. centerline transect. We identified shrub stems that inter- We located and visually inspected instrumented poults sected the pole to species and placed individual plants into that were separated from their brood to determine their fate height classes of 0.5–1 m, 1–2 m, 2–4 m, 4–6 m, or .6 m. (Peoples et al. 1995). Poult transmitters had a limited range We classified woody stems 10 cm diameter at breast (10–100 m), and we found transmitters with preyed-upon height that intersected the pole as trees, and classified woody poult remains several hundred meters from known brood stems ,0.5 m in height as ground cover. locations during our study. Transmitters from these poults We classified trees .10 cm diameter as overstory. To could easily be lost without extensive searches. We did not quantify overstory, we recorded the species and diameter at document any transmitter failures during this study. Bow- breast height (or diam below trunk splitting) for all trees man et al. (2002) reported no failures and .29-day originating within plots. Following Thomas et al. (1979), retention times for this transmitter model attached with we recorded tree decay class for each tree within the plot. these methods on pen-raised poults, and Spears et al. (2002) We also recorded number of coarse woody debris (single reported a mean retention time of 20.4 days for these large branches, logs, or fallen trees originating outside of the transmitters and this technique on wild turkey poults. We plot) for each plot. therefore considered poults equipped with transmitters that In addition to the above measurements, we measured were lost as unlikely to survive on their own and most likely visual obstruction of each actual ground-roost location with to have been carried off by predators. Our survival rate the visual obstruction pole. We recorded visual obstruction 4 estimates may be biased low if these poult losses were in fact m from the ground roost at 0.25-m, 0.5-m, and 1-m height transmitter failures. intervals from all 4 cardinal directions. We considered To determine vegetation characteristics of brood-use areas, readings from the 1-m height standard plot readings. we measured vegetation characteristics within 10 3 20-m Readings from the 0.25-m and 0.5-m heights more closely plots at ground-roost, habitat-use, and random locations. simulated head height and thus natural vision height of Ground-roost plots were centered on the overnight brood- possible mammalian predators such as raccoons (Procyon roosting locations. Habitat-use plots consisted of any plot in lotor), foxes (Vulpes spp.), bobcats (Lynx rufus), or coyotes which a radioequipped poult was observed, including (Canis latrans). Poles from which observations were taken daytime ground-roost plots. We centered plots on poult or were marked at 0.25-m intervals to standardize height brooding hen locations and oriented them north–south observations. We averaged measurements from each height along the 20-m axis. to determine overall ground-roost visual obstruction. We We indexed vegetative visual obstruction with a 1-m tall defined vegetative species utilized for roosting cover as the vertical visual obstruction pole 2.5 cm in circumference species of individual plant under which a brood or poult was marked with 0.1-m vertical bands (Robel et al. 1970). We located. In the case of nonliving material, we recorded cover attached a 1-m pole to the visual obstruction pole by a 4-m in categories such as natural debris pile, man-made debris string to standardize readings (Robel et al. 1970). We pile, or dead standing material. observed the visual obstruction pole from a perpendicular We made identical plot and ground-roost vegetation distance of 4 m and a height of 1 m. We recorded 10 visual measurements in 10 3 20-m paired random plots located 50 obstruction readings along a 20-m centerline transect in m from each ground-roost or habitat plot in a random each plot, each 2 m apart, alternating sides of the centerline. cardinal direction. We treated the center of each ground- We measured ground-level hiding cover, which we roost random plot as a random ground-roost location. We determined as the lowest height of 100% obstruction, by made vegetation measurements at all ground-roost and 72 The Journal of Wildlife Management 71(1)
random sites within 1 week following observation at a differences where data violated the assumption of equal
ground roost and within 2 weeks following observation at variances.
other brood locations. We used paired t-tests to evaluate Except where noted, we used a significance level of 0.05
differences between ground roosts and paired random plots for all calculations. We give means 6 standard error. We
to identify selection of specific characteristics in which used Microsoft Excel and StatisticaÓ (Statsoft, Inc., Tulsa,
broods ground roosted. OK) or SAS (Cantor 1997) for all computer analyses.
We used proportional hazards regression (SAS procedure
PHREG; Cantor 1997) to detect attributes of hens, poults,
RESULTS
and habitat that influenced risks to poult or brood survival. Ground Roosts
Explanatory variables we tested included hen age, hen Ground roosts typically consisted of a nest-like bowl of
weight (at time of hen capture), brood size, poult weight (at flattened grass or soil scratched out by the hen. Observations
time of poult capture), poult age, and visual obstruction. We of the shape of roost bowls and poult dropping patterns
examined both individual poult and overall brood survival, suggested poults roosted underneath the hen’s tail, but
defined as 1 poult within a brood surviving to tree poults also appeared to roost underneath the wing or breast
roosting. For these analyses, we considered all poults within feathers. Distances between consecutive ground roosts
a brood to be the same age. We also defined 2 survival averaged 614 6 145 m (range ¼ 0–2,733 m). We observed
periods of 0–9 days and 10–16 days posthatch within which 2 instances where a brood used a ground-roost spot twice,
to conduct separate analyses based on Spears et al. (2005). including the reuse of a nest bowl the first day after hatch at
We interpreted risk ratios following Allison (1995:117) and MWMA. Broods continued to ground roost on all study
present differences at the a ¼ 0.10 level. areas for several days after some poults in the brood were
We tested poult survival–habitat correlations separately observed flying to trees, suggesting that hens will ground
within the 0–9-day and 10–16-day posthatch periods. We roost until all members of the brood are able to do so.
used poult survival days (PSD) in each period as an index of Broods first tree-roosted 11–16 days posthatch (x̄ ¼ 13.714
survival for each brood in each period. We calculated PSD 6 0.438 days, n ¼ 14). We observed broods tree-roosting for
the first time on large, horizontal trunks or limbs 3–5 m
as the mean number of days transmitter-equipped poults in
high, by themselves or with other roosting broods.
a particular brood survived. A poult in the 0–9-day survival
We measured variables at 420 ground-roost and associated
period survived 0 days if killed the day of hatch and 10 days
paired random plots across the 4 study sites: 58 roost and 56
if alive at the end of the ninth day. A poult in the 10–16-day
random plots from 8 broods on GHWMA, 95 roost and 95
period survived 0 days if killed on the tenth day posthatch
random from 10 broods on the CNG, 24 roost and 24
and 7 days if alive at the end of the 16th day. We
random from 7 broods on MWMA, and 34 roost and 34
normalized PSD using a modified arcsine square-root
random from 8 broods on the Salt Fork. Actual ground-
transformation (Zar 1999). We assessed normality and
roost locations at all 4 sites had more ground-level visual
heterogeneity of variances with Shapiro–Wilk (Shapiro and
obstruction (determined by the lowest visual obstruction
Wilk 1965) and Hartley’s tests (Hartley 1940).
pole dm observed) and more total visual obstruction
We performed multivariate forward stepwise regression (P (determined by the total number of obstruction pole dm
¼ 0.15 to remove or enter; Pope and Webster 1972) to observed) than random points at all 3 observation heights (P
determine important habitat variables for predicting PSD in , 0.001; Table 1). Plots surrounding ground roosts also had
each survival period. We used a general linear model more ground-level visual obstruction than random plots
multivariate analysis of variance to test whether relation- (lowest obstruction band visible x̄ ¼ 2.7 vs. x̄ ¼ 2.0; P ,
ships between PSD and habitat variables in resulting models 0.001), more total visual obstruction (x̄ ¼ 7.9 obstruction
were the same among sites. Where selected variables did not bands visible vs. x̄ ¼ 8.7; P , 0.001), less bare ground (x̄ ¼
differ, we pooled data among sites. Where variables differed 6.7% vs. x̄ ¼ 12.9%; P , 0.001), and more trees (x̄ ¼ 3.2 vs.
among sites, we tested differences within each site x̄ ¼ 1.8; P ¼ 0.028) and overstory canopy (x̄ ¼ 4.2 canopy hits
separately. vs. x̄ ¼ 2.6; P ¼ 0.013) than random plots (Table 1). There
To further examine survival–habitat relationships, we used were also study site–specific differences in overnight
t-tests to assess habitat characteristic differences in plots ground-roost site selection (Table 2). Brooding hens on
used by broods 0–9 days old with below average and above CNG used ground-roost locations with more ground-level
average PSD. We also assessed survival–habitat relation- visual obstruction at 0.5-m observation heights (lowest
ships for broods 10–16 days old with t-tests comparing obstruction band visible x̄ ¼ 3.6 vs. x̄ ¼ 2.5; P , 0.001) and
habitat variables in plots used by broods 10–16 days old with plots with more coarse woody debris (x̄ ¼ 12.4 vs. x̄ ¼ 7.4; P
below average and above average PSD. Finally, we used t- ¼ 0.011) and trees in a more decayed state (tree decay index
tests to determine differences in habitat use between age x̄ ¼ 3.2 vs. 2.7; P ¼ 0.044) than at paired random plots.
classes of broods by comparing broods with above average Brooding hens on MWMA also used ground-roost
PSD 0–9 days to those with above average PSD 10–16 days locations with more ground-level visual obstruction at the
posthatch. We used Welch’s approximate t-tests and 0.5-m observation height (lowest obstruction band visible x̄
associated degrees of freedom (Zar 1999) to determine ¼ 3.5 vs. x̄ ¼ 2.5; P ¼ 0.001). Brooding hens on Salt Fork
Spears et al. Wild Turkey Brood Habitat Use and Survival 73Table 1. Habitat values measured in plots used as ground night-roosts by preflight Rio Grande wild turkey broods versus random plots at 4 sites in southwest
Kansas and the Texas Panhandle, USA, May–August, 2000 and 2001.
Used plots Random plots
Variable x̄ SE x̄ SE t25 P
a
Roost 1-m lowest dm visible 2.837 0.130 1.890 0.088 6.293 ,0.001
Roost 1-m total dm visibleb 7.621 0.171 8.882 0.121 7.245 ,0.001
Roost 0.5-m total dm visiblec 5.966 0.216 7.900 0.161 9.598 ,0.001
Roost 0.25-m lowest dm visibled 3.812 0.137 3.218 0.155 4.530 ,0.001
Roost 0.25-m total visiblee 4.172 0.253 6.557 0.202 9.291 ,0.001
Plot lowest dm visiblef 2.683 0.105 2.026 0.096 6.056 ,0.001
Plot total dm visibleg 7.907 0.150 8.655 0.163 5.681 ,0.001
Canopy hits (x/20)h 4.166 0.611 2.631 0.426 2.681 0.013
No. of shrubs 4–6 mi 0.128 0.071 0.094 0.048 0.375 0.711
No. of shrubs .6 mi 0.126 0.118 0 0 1.066 0.297
% grass coverj 0.469 0.036 0.473 0.032 0.154 0.879
% bare groundj 0.067 0.011 0.129 0.016 4.618 ,0.001
% forb coverj 0.205 0.022 0.204 0.017 0.042 0.970
% litter coverj 0.119 0.015 0.104 0.013 1.400 0.174
No. of treesk 3.222 0.593 1.789 0.460 2.338 0.028
Mean tree dbh (cm) 24.708 3.336 24.101 2.685 0.142 0.855
Mean tree height (m) 5.000 0.602 5.482 0.694 1.216 0.238
Mean height lowest branch (cm) 94.815 14.298 88.590 13.781 0.015 0.511
a
Mean lowest decimeter visible (all or part) on obstruction pole at ground-roost location from 1-m observation height, 4 m from pole.
b
Mean total decimeters visible (all or part) on obstruction pole at ground-roost location from 1-m observation height, 4 m from pole.
c
Mean total decimeter visible (all or part) on obstruction pole at ground-roost location from 0.5-m observation height, 4 m from pole.
d
Mean lowest decimeter visible (all or part) on obstruction pole at ground-roost location from 0.25-m observation height, 4 m from pole.
e
Mean total decimeters visible (all or part) on obstruction pole at ground-roost location from 0.25-m observation height, 4 m from pole.
f
Mean lowest decimeter visible (all or part) on 10 obstruction pole readings in plots surrounding ground-roost locations from 1-m observation height, 4 m
from pole.
g
Mean total decimeters visible (all or part) on 10 obstruction pole readings in plots surrounding ground-roost locations from 1-m observation height, 4 m
from pole.
h
Number of overstory canopy hits at 20 evenly spaced intervals on perimeter of plots surrounding ground-roost locations.
i
Plot sample within 2 3 20-m belt transect along centerline.
j
100-point sample within plot.
k
Total in plot.
used ground-roost locations with more ground-level visual during this period, with Salt Fork having higher mean PSD
obstruction at the 0.5-m observation height (lowest (8.917 6 0.48, n ¼ 9 broods) than GHWMA (6.085 6
obstruction band visible x̄ ¼ 4.1 vs. x̄ ¼ 2.4; P ¼ 0.015), 1.082; n ¼ 8 broods, t15 ¼ 2.489, P ¼ 0.025) and CNG
and plots with more shrubs 0.5–1 m tall (x̄ ¼ 112.4 vs. x̄ ¼ (7.225 6 0.522; n ¼ 10 broods, t17 ¼ 2.371, P ¼ 0.030).
54.6; P ¼ 0.030) and more total number of shrubs (x̄ ¼ 140.0 Mean PSD for MWMA (8.385 6 0.491; n ¼ 8 broods) was
vs. x̄ ¼ 62.7; P ¼ 0.022) than at paired random sites (Table in-between and did not differ from Salt Fork (t15 ¼ 0.773, P
2). ¼ 0.451) or from CNG and GHWMA (F2,23 ¼ 2.350, P ¼
0.118). Overall PSD 10–16 days posthatch averaged 5.63 6
Survival and Survival–Habitat Relationships
2.1 days (n ¼ 24 broods). Means did not differ among study
Four percent of transmitter-equipped poults (5 of 115, from
sites during this period (F3,18 ¼ 0.302, P ¼ 0.823).
3 broods) were lost. For inclusion in survival analyses, we
categorized these poults as mortalities following their last Percentages of transmitter-equipped poults surviving the
known location. Risk of brood mortality (all telemetered entire 16-day period were 27% (9/33) on GHWMA, 29%
poults dying) decreased with hen weight at time of initial (10/34) on CNG, 40% (10/25) on MWMA, and 36% (10/
capture ([0.635 1] 3 100 ¼ 39.5%/kg of hen wt; P ¼ 28) on Salt Fork.
0.0002), brood size (5.6%/added poult; P ¼ 0.0295), and We measured vegetation characteristics in 442 habitat-use
brood age (6.0%/d; P , 0.0001; Table 3). Individual plots used by 35 broods 0–9 days old: 89 plots on
poults had decreased risks of mortality with increased hen GHWMA, 205 on CNG, 74 on MWMA, and 74 on Salt
weight at time of initial capture (50.4%/each additional kg Fork. We measured vegetation characteristics in 142 plots
of hen wt; P , 0.0001), brood size (6.3% for each used by 22 broods 10–16 days old: 40 plots on GHWMA,
additional poult in brood; P ¼ 0.0271), and poult age 66 on CNG, 15 on MWMA, and 21 on Salt Fork.
(8.4% for each additional d of age; P , 0.0001). Broods Using the Cox proportional hazards model, increased
10–16 days old had 66.7% less (P ¼ 0.0001) risk of density of shrubs 1–2 m decreased risk of brood mortality
mortality than those 0–9 days old. 1.4% per shrub stem (P ¼ 0.0210; Table 3). Increased
Overall PSD 0–9 days posthatch averaged 7.66 6 0.372 density of shrubs 1–2 m also decreased risk of poult
days (n ¼ 35 broods). Mean PSD differed among study sites mortality 1.4% per shrub stem (P ¼ 0.0070; Table 4).
74 The Journal of Wildlife Management 71(1)Table 2. Habitat values measured in plots used as ground roosts by preflight broods of Rio Grande wild turkey versus random plots at 4 sites in southwest
Kansas and the Texas Panhandle, USA, May–August, 2000 and 2001.
Used plots Random plots
Sitea Variable x̄ SE x̄ SE df t P
b
GHWMA Roost 0.5-m low dm visible 3.706 0.359 3.004 0.259 4 1.667 0.171
Coarse woody debrisc 0.934 0.615 0.452 0.372 4 1.903 0.130
No. of shrubs 0.5–1 md 25.102 10.982 14.153 4.708 4 1.812 0.144
No. of shrubs 1–2 md 5.534 3.702 4.680 1.948 4 0.394 0.714
No. of shrubs 2–4 md 0.745 0.512 0.763 0.324 4 0.030 0.977
Total no. of shrubsd 32.371 14.988 19.633 6.416 4 1.659 0.173
Mean % shrub covere 0.185 0.064 0.113 0.035 4 1.637 0.177
Mean tree decayf 1.337 0.184 1.0 0 4 2.141 0.253
CNG Roost 0.5-m low dm visible 3.638 0.327 2.494 0.176 9 3.215 ,0.001
Coarse woody debris 12.382 2.209 7.392 1.327 9 3.180 0.011
No. of shrubs 0.5–1 m 2.469 0.712 1.629 0.402 9 0.627 0.087
No. of shrubs 1–2 m 0.254 0.126 0.188 0.074 9 0.394 0.714
No. of shrubs 2–4 m 0.316 0.140 0.141 0.064 9 1.298 0.226
Total no. of shrubs 2.987 0.825 1.672 0.444 9 2.188 0.056
Mean % shrub cover 0.039 0.010 0.024 0.005 9 1.843 0.098
Mean tree decay 3.164 0.247 2.664 0.334 9 2.381 0.044
MWMA Roost 0.5-m low dm visible 3.462 0.216 2.50 0.127 4 8.603 0.001
Coarse woody debris 0.937 0.324 1.35 0.768 4 0.791 0.473
No. of shrubs 0.5–1 m 9.133 2.142 9.02 2.193 4 0.605 0.961
No. of shrubs 1–2 m 8.533 1.011 4.633 1.300 4 2.410 0.074
No. of shrubs 2–4 m 2.240 0.326 1.233 0.347 4 1.881 0.133
Total no. of shrubs 19.907 2.758 15.233 2.435 4 1.281 0.270
Mean % shrub cover 0.147 0.029 0.114 0.026 4 0.976 0.384
Mean tree decay 2.372 0.114 2.411 0.216 4 0.259 0.808
Salt Fork Roost 0.5-m low dm visible 4.113 0.329 2.357 0.368 5 3.655 0.015
Coarse woody debris 2.442 1.143 2.031 1.030 5 0.606 0.571
No. of shrubs 0.5–1 m 112.422 32.709 54.556 21.554 5 2.989 0.030
No. of shrubs 1–2 m 21.694 7.936 7.506 3.982 5 1.838 0.125
No. of shrubs 2–4 m 1.611 0.970 0.533 0.299 5 1.684 0.153
Total no. of shrubs 135.950 38.621 62.650 22.195 5 0.024 0.022
Mean % shrub cover 0.261 0.071 0.165 0.053 5 1.946 0.109
Mean tree decay 0.935 0.462 2.034 0.176 5 1.946 0.146
a
Gene Howe Wildlife Management Area (GHWMA), Cimarron National Grasslands (CNG), Matador Wildlife Management Area (MWMA), Salt
Fork of the Red River (Salt Fork).
b
Mean lowest decimeter visible (all or part) on obstruction pole at ground-roost location from 0.5-m observation height, 4 m from pole.
c
Number of coarse woody debris in plot.
d
Plot sample within 2 3 20-m belt transect along centerline.
e
100-point sample within plot.
f
For all trees in plot.
Number of shrubs 1–2 m tall and mean diameter at breast the model (F2,30 ¼ 6.69, P ¼ 0.004; Table 5). The
height of trees explained 32% of variation in 0–9-day PSD. relationship between 0–9-day PSD and individual variables
Both variables were positively correlated with PSD, and a of number of shrubs 1–2 m (F3,19 ¼ 1.036, P ¼ 0.399) and
significant positive relationship existed between PSD and diameter at breast height (F3,19 ¼ 0.926, P ¼ 0.447) did not
differ among sites. The relationship between 0–9-day PSD
and the combined variables was not different among sites
Table 3. Cox proportional hazards model of Rio Grande wild turkey brood
survival (1 poult surviving) for (n ¼ 33) broods observed at 4 sites in
southwest Kansas and the Texas Panhandle, USA, May–August, 2000 and Table 4. Cox proportional hazards model of Rio Grande wild turkey poult
2001. survival for broods (n ¼ 33) observed at 4 sites in southwest Kansas and the
Texas Panhandle, USA, May–August, 2000 and 2001.
Hazard
Variable na df Levels v2 P ratio Hazard
Variable na df Levels v2 P ratio
Likelihood ratio 557 7 94.2661 ,0.0001
Hen age 557 1 0.8394 0.3596 0.901 Likelihood ratio 557 5 151.5157 ,0.0001
Hen wt 557 1 13.9360 0.0002 0.635 Hen wt 557 1 32.8181 ,0.0001 0.497
Brood size 557 1 4.7378 0.0295 0.944 Brood size 557 1 4.8850 0.0271 0.937
Brood age 557 1 27.6282 ,0.0001 0.940 Brood age 557 1 44.3041 ,0.0001 0.916
Shrub density 557 1 0.5–1.0 m 2.8674 0.0904 1.002 Shrub density 557 1 0.5–1.0 m 3.3704 0.0664 1.002
557 1 1.0–2.0 m 5.3252 0.0210 0.991 557 1 1.0–2.0 m 7.2664 0.0070 0.986
557 1 2.0–4.0 m 0.3351 0.5627 1.009 557 1 2.0–4.0 m 0.3755 0.5400 0.986
a a
We based sample size upon telemetry locations of broods. We based sample size upon telemetry locations of broods.
Spears et al. Wild Turkey Brood Habitat Use and Survival 75Table 5. Multiple regression coefficients and standard errors of habitat plots were sand sagebrush on CNG; sand sagebrush, sand
variables in order of importance for 0–9-day-old Rio Grande wild turkey
poult survival at 4 sites in southwest Kansas and the Texas Rolling Plains,
plum, shinnery oak, sumac, and honey mesquite were most
USA, during May–August, 2000 and 2001.a common at the Texas sites. Mottes of shinnery oak often
completely concealed broods but allowed poults to move
Standard
Variable Coeff. SE coeff. SE t28 P about freely.
Although mean diameter at breast height was included in
Intercept 6.038 0.150 7.469 ,0.001 the model explaining PSD, trees did not appear to be
No. of shrubs
1–2 m 6.038 0.150 0.602 0.031 3.656 0.001 important to poult survival on their own. Number of trees
Tree dbh (cm) 0.032 0.005 0.207 0.031 1.257 0.219 and mean diameter at breast height of trees in brood plots
a did not differ between broods with below and above average
Model: R2 ¼ 0.323, F2,28 ¼ 6.685, P , 0.004.
PSD 0–9 days posthatch (Table 6). Neither mean diameter
at breast height (F3,27 ¼ 2.07, P ¼ 0.13) nor mean number of
(F9,19 ¼ 1.471, P . 0.25). Plots used by broods ,10 days trees (F3,31 ¼ 1.68, P ¼ 0.19) in brood-use plots differed
old with above average PSD had more shrubs 1–2 m than among sites. With the exception of honey mesquite, trees in
those used by broods ,10 days old with below average PSD these areas were generally limited to riparian areas and
(x̄ ¼ 8.3 vs. x̄ ¼ 2.2; P ¼ 0.005; Table 6). windbreaks. Trees most commonly found in brood-use plots
Among all plots measured, shrubs 1–2 m tall were more were plains cottonwood at CNG; common hackberry, black
common at Salt Fork (x̄ ¼ 4.974 6 0.941) than at walnut, and western soapberry at GHWMA; netleaf
GHWMA (x̄ ¼ 2.700 6 0.408; F1,1604 ¼ 4.916, P ¼ hackberry and honey mesquite at MWMA; and Texas
0.027), CNG (x̄ ¼ 0.305 6 0.058; F1,694 ¼ 31.741, P , sugarberry, netleaf hackberry, honey mesquite, and post oak
0.001), and MWMA (x̄ ¼ 2.794 6 0.307; F1,544 ¼ 4.025, P at Salt Fork.
¼ 0.045). The mean number of total shrubs was also higher Forward stepwise regression on habitat variables resulted
in plots measured at Salt Fork (x̄ ¼ 32.508 6 4.542) than at in a number of shrubs 2–4 m tall being the only variable
GHWMA (x̄ ¼ 13.436 6 1.737; F1,604 ¼ 15.385, P , included in the model predicting 10–16-day PSD (y ¼ 6.505
0.001), CNG (x̄ ¼ 3.224 6 0.304; F1,694 ¼ 53.541, P , 0.386 [shrubs 2–4 m]; R2 ¼ 0.164). However, simple
0.001), and MWMA (x̄ ¼ 9.576 6 1.746; F1,544 ¼ 18.666, P regression analysis showed no significant relationship
, 0.001). Mean number of shrubs 1–2 m tall within plots between number of shrubs 2–4 m and PSD during this
used by broods was greater at Salt Fork (x̄ ¼ 5.274 6 1.171) period (F2,20 ¼ 3.93, P ¼ 0.061). Furthermore, the
than at GHWMA (x̄ ¼ 2.759 6 0.452; F1,444 ¼ 3.933, P ¼ relationship between 10–16-day PSD and number of shrubs
0.048) and at CNG (x̄ ¼ 0.349 6 0.074; F1,513 ¼ 22.468, P 2–4 m did not differ among sites (F6,14 ¼ 1.651, 0.10 . P .
, 0.001). Most common shrubs 1–2 m tall in brood-use 0.25). The most common shrub 2–4 m in plots used by
Table 6. Differences between habitat variables in plots used by Rio Grande wild turkey broods ,10 days old with below average and above average poult
survival days (PSD) on 4 sites in southwest Kansas and the Texas Rolling Plains, USA, May–August, 2000 and 2001.
Below average PSD Above average PSD
Variable x̄ SE x̄ SE t32 P Welch’s t df P
Lowest dm visiblea 2.302 0.111 2.497 0.105 1.227 0.102
Total dm visibleb 8.414 0.130 8.092 0.134 1.624 0.096
% grass coverc 0.469 0.033 0.432 0.034 0.732 0.873
% shrub coverc 0.107 0.022 0.144 0.024 1.048 0.211
% bare groundc 0.101 0.020 0.072 0.010 1.426 0.163
% forb coverc 0.192 0.022 0.227 0.018 0.211 0.235
% litter coverc 0.130 0.024 0.124 0.014 0.257 0.799
No. of shrubs 0.5–1 md 10.783 4.938 36.467 14.846 1.642 24 0.114
No. of shrubs 1–2 md 2.194 0.607 8.338 1.896 3.086 23 0.005
No. of shrubs 2–4 md 0.910 0.268 1.509 0.303 1.361 0.183
No. of shrubs 4–6 md 0.139 0.059 0.215 0.739 31 0.465
Total no. of shrubsd 13.914 5.214 46.663 16.264 1.917 23 0.067
No. of treese 2.540 0.508 3.206 0.497 0.890 0.380
Mean tree decayf 2.114 0.317 2.211 0.209 0.267g 0.792
Mean tree dbh (cm) 24.070 4.323 23.944 2.611 0.025g 0.980
a
Mean lowest decimeter visible (all or part) on 10 obstruction pole readings in plots surrounding ground-roost locations from 1-m observation height, 4 m
from pole.
b
Mean total decimeters visible (all or part) on 10 obstruction pole readings in plots surrounding ground-roost locations from 1-m observation height, 4 m
from pole.
c
100-point sample within plot.
d
Plot sample within 2 3 20-m belt transect along centerline.
e
Total in plot.
f
For all trees in plot.
g
df ¼ 29.
76 The Journal of Wildlife Management 71(1)Table 7. Differences between habitat variables in plots used by Rio Grande wild turkey broods 10–16 days old with below average and above average poult
survival days (PSD) on 4 sites in southwest Kansas and the Texas Rolling Plains, USA, May–August, 2000 and 2001.
Below average PSD Above average PSD
Variable x̄ SE x̄ SE t20 P Welch’s t df P
a
Lowest dm visible 2.508 0.182 2.224 0.112 1.313 0.205
Total dm visibleb 8.231 0.169 8.518 0.148 1.082 0.292
% grass coverc 0.480 0.064 0.449 0.055 0.307 0.762
% shrub coverc 0.132 0.045 0.095 0.024 0.766 0.101
% bare groundc 0.035 0.013 0.091 0.019 0.718 0.094
% forb coverc 0.253 0.042 0.195 0.028 1.109 0.281
% litter coverc 0.101 0.132 0.169 0.026 2.316 19 0.031
No. of shrubs 0.5–1 md 42.405 22.700 10.977 5.535 1.345 5 0.231
No. of shrubs 1–2 md 5.064 2.125 2.348 0.874 1.421 0.171
No. of shrubs 2–4 md 2.036 0.922 0.549 0.147 1.593 5 0.169
No. of shrubs 4–6 md 0.550 0.238 0.174 0.095 1.786 0.089
Total no. of shrubsd 50.055 24.986 14.024 6.334 1.398 5 0.215
No. of treese 2.628 0.548 4.533 0.953 1.733 19 0.098
Mean tree decayf 2.271 0.301 2.198 0.186 0.209g 0.837
Mean tree dbh (cm) 28.801 5.360 29.068 4.311 0.035g 0.973
a
Mean lowest decimeter visible (all or part) on 10 obstruction pole readings in plots surrounding ground-roost locations from 1-m observation height, 4 m
from pole.
b
Mean total decimeters visible (all or part) on 10 obstruction pole readings in plots surrounding ground-roost locations from 1-m observation height, 4 m
from pole.
c
100-point sample within plot.
d
Plot sample within 2 3 20-m belt transect along centerline.
e
Total in plot.
f
For all trees in plot.
g
df ¼ 19.
broods 10–16 days old was tamarisk, composing 38% of all did not tree-roost until all poults in a brood were capable of
shrubs 2–4 m present, followed by mesquite (22.5%), reaching a suitable roosting spot. Delayed tree-roosting
western soapberry (15%), hackberry (7%), shinnery oak would subject poults capable of roosting in trees to greater
(6%), and woolybucket bumelia (Bumelia lanuginosa; 6%). risks of predation on the ground, enhancing the need for
The only habitat variable that differed between plots used by high-quality ground-roost habitat until all poults can tree-
broods with below and above average PSD 10–16 days roost.
posthatch was percent litter cover, with more litter being Brooding hens at 3 of our sites selected ground-roosting
present in plots used by more successful broods (x̄ ¼ 17% vs. areas with increased hiding cover 0.5–2 m tall. This cover on
x̄ ¼ 10%; P ¼ 0.031; Table 7). our study sites was provided mostly by shrubs. Brooding
Successful broods appeared to shift habitat use as poults hens at CNG also selected areas with more coarse woody
began to attain flight abilities. Plots used by ground- debris and decayed trees. Fallen trees were in a more decayed
roosting broods 0–9 days old with above average PSD had state than standing trees, and thus the presence of fallen
more visual obstruction (x̄ ¼ 8.1 obstruction bands visible vs. trees increased the average index of tree decay for a plot.
x̄ ¼ 8.5; P ¼ 0.050), more shrubs 1–2 m (x̄ ¼ 8.6 vs. x̄ ¼ 2.3; Selection for roost areas with increased woody debris and
P ¼ 0.007), and more shrubs 2–4 m (x̄ ¼ 1.5 vs. x̄ ¼ 0.5; P ¼ tree decay suggests that brooding hens also sought out fallen
0.007) than did ground-roosting broods 10–16 days old branches and trees as ground-roosting cover.
with above average PSD (Table 8). Number of shrubs 1–2 m tall was the most important
habitat variable explaining poult survival 0–9 days posthatch
DISCUSSION at all of our study sites. Shrubs of this height category were
Rio Grande wild turkey broods in our study appeared to sufficiently large to provide hiding cover for both poults and
seek out specific habitat components providing ground-level the brooding hen, and provided vegetation into which
horizontal visual obstruction, both for ground roosting and poults could escape. Radioequipped broods located in and
use throughout the day. These components appeared among shrubs of this height were often completely
particularly important in facilitating poult survival ,10 concealed. Mean PSD 0–9 days posthatch at Salt Fork
days after hatch, the period prior to general poult flight was greater than at GHMWA and CNG. Correspondingly,
attainment during which poult mortality is the highest. number of shrubs 1–2 m in areas used by broods was higher
Average time to first brood tree-roost in our study was at Salt Fork than any other site. This correlation further
between 13 days and 14 days posthatch, similar to that suggests the importance of the presence of shrubs in this
observed in other subspecies (Barwick et al. 1970). Broods height category to poult survival during this time period.
continued to ground roost after individual poults within the Rio Grande and eastern (M. g. silvestris) wild turkey
brood were observed flying to trees. This suggests that hens preflight broods in other studies used areas with greater
Spears et al. Wild Turkey Brood Habitat Use and Survival 77Table 8. Differences between habitat variables in plots used by Rio Grande wild turkey broods 0–9 days old with above average poult survival days and broods
10–16 days old with above average poult survival days on 4 sites in southwest Kansas and the Texas Rolling Plains, USA, May–August, 2000 and 2001.
0–9 d old 10–16 d old
Variable x̄ SE x̄ SE t34 P Welch’s t df P
a
Lowest dm visible 2.467 0.105 2.221 0.108 1.617 0.115
Total dm visibleb 8.101 0.140 8.518 0.148 2.033 0.050
% grass coverc 0.429 0.036 0.449 0.055 0.330 0.743
% shrub coverc 0.148 0.025 0.095 0.376 1.777 0.142
% bare groundc 0.072 0.011 0.091 0.019 0.0931 0.358
% forb coverc 0.226 0.019 0.195 0.028 0.953 0.347
% litter coverc 0.124 0.015 0.167 0.026 1.570 0.126
No. of shrubs 0.5–1 md 37.812 15.544 10.978 5.535 1.626 23 0.117
No. of shrubs 1–2 md 8.648 1.967 2.348 0.874 2.927 25 0.007
No. of shrubs 2–4 md 1.549 0.316 0.549 0.147 2.874 26 0.007
No. of shrubs 4–6 md 0.218 0.088 0.174 0.095 0.346 0.732
Total no. of shrubsd 48.368 17.005 14.024 6.334 1.893 24 0.071
No. of treese 3.331 0.506 4.533 0.953 1.114 23 0.277
Mean tree decayf 2.293 0.203 2.198 0.186 0.336g 0.739
Mean tree dbh (cm) 23.481 3.831 29.068 4.311 1.143g 0.262
a
Mean lowest decimeter visible (all or part) on 10 obstruction pole readings in plots surrounding ground-roost locations from 1-m observation height, 4 m
from pole.
b
Mean total decimeters visible (all or part) on 10 obstruction pole readings in plots surrounding ground-roost locations from 1-m observation height, 4 m
from pole.
c
100-point sample within plot.
d
Plot sample within 2 3 20-m belt transect along centerline.
e
Total in plot.
f
For all trees in plot.
g
df ¼ 32.
herbaceous vegetative height and visual obstruction 1 m were located hiding up to 15 m from hiding brooding hens,
(Metzler and Speake 1980, Healy 1985, Hennen 1999). suggesting that hens and poults hid in the immediately
Trees and shrubs have been observed to create the majority available vegetation upon being alerted. Moreover, preflight
of ground cover at this height in other wild turkey habitats poults did not have the ability to move large relative
(Schmutz et al. 1990). distances to find cover within the time between being
Average diameter at breast height of trees in brood use alerted by the hen and being located by the observer.
areas was positively correlated with poult survival 0–9 days Components other than available habitat, such as weather
posthatch, but was not different between sites with different (Roberts and Porter 1998) and hen ability to raise a brood,
survival rates or between broods with below average and may also affect poult survival. We were not able to
above average PSD. Increased diameter at breast height does determine important weather variables, such as rainfall,
increase visual obstruction and thus ground-level hiding accurately in specific brooding areas and were therefore
cover. We observed broods ground roosting against large tree unable to determine effects on survival. No difference
bases and under or against downed logs. Hen coloration existed in our study in poult survival to 16 days of age
blended well with logs and tree bases, and trees that hens between juvenile and adult hens (Spears 2002), suggesting
ground roosted against often provided 100% visual obstruc- inexperience in raising a brood was not a factor in poult
tion 1 m from 2 cardinal directions. survival. Hen weight can be used as an index of health. An
Shrubs in the 2–4-m height category appeared unsuitable increase in hen weight at initial capture (1–2 winters prior to
for poult hiding cover. Most shrubs 2–4 m in plots used by that breeding season) appeared to affect poult survival (P ,
ground-roosting broods 10–16 days of age were tamarisk, 0.0001). However, this effect in our model is related to
followed by mesquite and soapberry. Tamarisk shrubs change per kilogram in hen weight. Hens averaged 4.8 kg at
consisted of dense stems that did not provide space at time of capture. One kilogram would represent a change of
ground level in which poults could hide, whereas mesquite approximately 20% of hen body weight.
and soapberry trunks did not provide cover at ground level Studies of eastern wild turkeys suggested that brooding
into which poults could enter. hens selected clearings (Sisson et al. 1991) for their
Hens in habitats with dense brush were often able to increased level of invertebrate availability for poults (Hill-
observe the researcher and warn poults to hide before the estad and Speake 1970, Hurst and Stringer 1975, Martin
researcher located the brood. This problem is unavoidable in and McGinnes 1975). Our study and others support an
a study such as ours and may bias brood locations toward alternate hypothesis: preflight broods use clearings for
areas with more visual obstruction. However, we observed predator avoidance, facilitated by their ground-level vege-
poults of this age most commonly hiding immediately in tation components. First, adequate insect abundance for
situ when warned by the hen. Transmitter-equipped poults poults is available in wooded areas. Harper et al. (2001)
78 The Journal of Wildlife Management 71(1)found that biomass of Hexapoda, insects preferred by turkey predator avoidance. However, certain lower-quality vegeta-
poults, was not different among forest stands of different tive species (i.e., tamarisk) may replace that which could
ages and openings, and found twice as many invertebrates in provide desired cover.
forest strata than in openings. Hurst and Stringer (1975) Low-growing shrubs appeared to provide the optimal
observed that average animal percent intake by poults ,1 escape services for preflight poults in the southern Great
week old was higher in pine forest and hardwood cover types Plains habitats we studied. Managers desiring to increase
than in forest openings. Martin and McGinnes (1975) Rio Grande wild turkey preflight poult survival in these
found that, although insect abundance was higher in forest areas should manage for increased shrubs as hiding cover in
clearings than forest, poults consumed the same amount of brooding areas from May through the end of July, the peak
insects in both cover types. Healy (1985) found that poults periods of hatching for Rio Grande wild turkey populations.
obtained adequate insect intake in forested areas if ground- Shrubs we observed providing high-quality hiding or escape
cover dry weight was 40–300 g/m2. Second, we found that cover included shinnery oak and sand sagebrush. Shrubs we
ground-level vegetation characteristics were directly related observed providing little or no services to preflight poults
to poult survival. Relationships between poult survival and included tamarisk, mesquite, and western soapberry. Tam-
ground-cover characteristics in forest stands and openings arisk and mesquite were especially notorious for invading
was not examined in some studies that concluded broods and dominating shrub habitats in these areas. Activities to
selected forest openings or pastures for insect abundance control or remove these shrubs should be considered. Upper
(e.g., Hillestad and Speake 1970, Martin and McGinnes limits of ground-level vegetation appear to exist for wild
1975). Clearings often provided ground-level vegetative turkey poult productivity (Healy 1985). This needs to be
structure that allowed brooding hens to detect predators and examined for Rio Grande wild turkey broods.
cover that facilitated poult predator avoidance (Pack et al. Previous habitat management suggestions for wild turkey
1980, Sisson et al. 1991, Harper et al. 2001). Preflight broods included maintaining a diverse mosaic of high-
broods also selected for wooded cover types when they quality habitats (Metzler and Speake 1980, Campo et al.
provided understory vegetative structure similar to that of 1989). Relationships between survival and habitat parame-
clearings. Rio Grande wild turkey broods in Colorado and ters in our study support these recommendations. We
Kansas selected areas containing wooded riparian areas observed a shift in habitat type use by successful broods not
when this cover type was not readily available (Schmutz et yet tree-roosting occurring between 0–9 days and 10–16
al. 1990, Hennen 1999). Broods 1–14 days old in days after hatch. Successful broods ,10 days old used plots
Mississippi, USA, selected for bottomland hardwood cover with more ground-level visual obstruction and shrubs 1–2 m
types, which had ‘‘moderately dense herbaceous ground than successful broods 10–16 days old. At 10–16 days of age,
cover that resembled that of an open field habitat’’ (Phalen most poults can fly to trees. This ability may reduce the need
et al. 1986:402). Hubbard et al. (2001) indicated that for ground-level cover, but increases the importance of
increasing woody cover in an area occupied by transmitter- roosting trees. Interspersion of shrubs 1–2 m with trees in
equipped poults increased survival. Most woody cover on brood-use areas appears optimal for poult survival to 16 days
their study site included a ‘‘diverse vegetative understory,’’ posthatch in these habitats.
which ‘‘may have contributed to decreased poult mortality’’ Forested areas may contain ground-level vegetation
(Hubbard et al. 2001:169). characteristics that adequately facilitate preflight wild turkey
In areas where forest stands do not include high-quality poult survival. These areas may already constitute high-
ground-level habitat, preflight turkey broods may ultimately quality foraging areas and hiding cover for preflight broods,
use clearings as a refuge from predation, not for their relative as well as a variety of vertical habitat structure (i.e., mix of
insect abundance, especially in areas where high predator shrubs and trees) for use by broods of varying ages and flight
densities occur in wooded habitats (Priest et al. 1995). Use abilities. Thus, forest clearings may not necessarily be a
of clearings for predator avoidance or insect abundance can required land-cover type in high-quality turkey brood
only be assessed through examination of relationships habitat. Managers of forested areas should consider under-
between forest and clearing vegetative parameters, poult story characteristics present and the services they provide to
survival, and insect abundance in different cover types. turkey broods prior to clearing areas for the sake of
Knowledge of actual reasons for selection of specific habitat providing clearings.
types may allow managers to make better decisions
regarding habitat management for turkeys based on ACKNOWLEDGMENTS
individual area characteristics. We thank T. Barnett and numerous field technicians that
aided in data collection. Texas Parks and Wildlife Depart-
MANAGEMENT IMPLICATIONS ment, Kansas Department of Wildlife and Parks (Federal
Ground-level vegetation structure appears to be a key factor Aid Grant W-54-R), the National Wild Turkey Federation,
in facilitating wild turkey poult survival. In terms of wild and the Texas Chapter (Superfund) of the National Wild
turkey ecology, physiognomy may be more important than Turkey Federation provided equipment, logistical help, and
floristics; a variety of species and vegetation types may funds. Employees from Texas Parks and Wildlife Depart-
provide the hiding and escape cover necessary for poult ment, Kansas Department of Wildlife and Parks, and
Spears et al. Wild Turkey Brood Habitat Use and Survival 79You can also read
