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Influence of fire on Bachman's Sparrow, an endemic North American songbird

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Abstract

Bachman's sparrow (Aimophila aestivalis), a near endemic songbird of the longleaf pine (Pinus palustris) ecosystem, is known to respond positively to prescribed fires. The influence of season (growing vs. dormant) and frequency (1 to ≥4 yr since burning) of fire on density of Bachman's sparrows, however, is poorly understood. We examined effects of fire on density of Bachman's sparrows in longleaf pine forests at the Conecuh National Forest, Alabama, and Blackwater River State Forest, Florida, USA. Density of Bachman's sparrows was greater the first 3 years after burning than ≥4 years after burning, and season of burning had little effect on the density of Bachman's sparrows. Percent coverage by grass had a greater influence on density of Bachman's sparrows than either season or frequency of burning. Percent canopy cover had a strong negative effect on coverage of grass but had a weaker effect on grass at stands burned frequently during the growing season. Growing-season fires (Apr–Sep) did not adversely affect density of Bachman's sparrows. Results from our study suggest that management and restoration of longleaf pine communities probably can be accomplished best by burning on a 2–3-year rotation during the growing season, when most fires historically occurred. Suppression of fire, or burning at intervals >4–5 years, will greatly reduce or eliminate habitat required by Bachman's sparrows.
INFLUENCE OF FIRE ON BACHMAN’S SPARROW, AN ENDEMIC
NORTH AMERICAN SONGBIRD
JAMES W.TUCKER, JR.,1, 2 Department of Biological Sciences, Auburn University, AL 36849, USA
W. DOUGLAS ROBINSON,3Department of Biological Sciences, Auburn University, AL 36849, USA
JAMES B. GRAND, USGS, Alabama Cooperative Fish and Wildlife Research Unit, School of Forestry and Wildlife Sciences,
Auburn University, AL 36849, USA
Abstract: Bachman’s sparrow (Aimophila aestivalis), a near endemic songbird of the longleaf pine (Pinus palustris)
ecosystem, is known to respond positively to prescribed fires. The influence of season (growing vs. dormant) and
frequency (1to ≥4 yr since burning) of fire on density of Bachman’s sparrows, however, is poorly understood. We
examined effects of fire on density of Bachman’s sparrows in longleaf pine forests at the Conecuh National Forest,
Alabama, and Blackwater River State Forest, Florida, USA. Density of Bachman’s sparrows was greater the first 3
years after burning than ≥4 years after burning, and season of burning had little effect on the density of Bachman’s
sparrows. Percent coverage by grass had a greater influence on density of Bachman’s sparrows than either season
or frequency of burning. Percent canopy cover had a strong negative effect on coverage of grass but had a weaker
effect on grass at stands burned frequently during the growing season. Growing-season fires (Apr–Sep) did not
adversely affect density of Bachman’s sparrows. Results from our study suggest that management and restoration
of longleaf pine communities probably can be accomplished best by burning on a 23-year rotation during the
growing season, when most fires historically occurred. Suppression of fire, or burning at intervals >45years, will
greatly reduce or eliminate habitat required by Bachman’s sparrows.
JOURNAL OF WILDLIFE MANAGEMENT 68(4):1114–1123
Key words: Aimophila aestivalis, Alabama, Bachman’s sparrow, fire ecology, Florida, habitat management, habitat
restoration, longleaf pine ecosystem, Pinus palustris, prescribed fire.
1114
The longleaf pine ecosystem once dominated the
coastal plain of the southeastern United States and
extended from Virginia to Texas (Wahlenberg
1946). Forests within this ecosystem were charac-
terized by large, widely spaced longleaf pines with
a dense ground cover of grasses and forbs
(Chapman 1932). Longleaf pine forests are among
the most species-rich plant communities in North
America (Peet and Allard 1993) and are unusual
because most of the plant diversity is in the ground
cover (Simberloff 1993). Frequent fire resulting
from a high incidence of lightning strikes is the pri-
mary agent responsible for development and struc-
ture of longleaf pine forests (Chapman 1932), but
anthropogenic effects of burning by Native Ameri-
cans also might have had an effect (Krech 1999).
The longleaf pine ecosystem is among the most
heavily impacted of all forested ecosystems (Noss
1989, Simberloff 1993). Disruptions of natural
fire regimes and conversion to other land uses
have resulted in the loss of 95% of this once-
extensive ecosystem (Outcalt and Sheffield 1996).
Concurrent with the loss of longleaf pine forests,
populations of many species characteristic of
these forests (e.g., red-cockaded woodpecker
[Picoides borealis]) have declined and become
threatened with extinction. Previous studies
(e.g., Tucker et al. 1998, 2003) suggest that pre-
scribed burning benefits bird species associated
with longleaf pine forest, but information that
assesses the importance of frequency and season
of burning on bird populations in the longleaf
pine ecosystem is lacking. In particular, studies of
species utilizing the understory of longleaf pine
forests are needed because most sensitive species
occupy that stratum of the forest. Although the
understory structure of these forests also strongly
affects red-cockaded woodpeckers (James et al.
1997), the relatively strict habitat requirements of
Bachman’s sparrow are more directly related to
understory vegetation (Dunning and Watts 1990).
Bachman’s sparrow is 1of the few bird species
endemic to the continental United States and is
largely endemic to longleaf pine forests (Jackson
1988). Bachman’s sparrow is among the species
of highest management concern within the
southeastern United States (Hunter et al. 1994)
and is classified as threatened or endangered by
several states (Dunning 1993). Like most threat-
ened species associated with longleaf pine
1Present address: Archbold Biological Station,
APAFR Field Office, 475 Easy Street, Avon Park, FL
33825, USA.
2E-mail: jtucker@archbold-station.org
3Present address: Department of Fisheries and Wild-
life, 104 Nash Hall, and Oak Creek Laboratory of Biol-
ogy, Oregon State University, Corvallis, OR 97331, USA.
J. Wildl. Manage. 68(4):2004 1115
FIRE AND BACHMAN’S SPARROWS Tucker et al.
forests, Bachman’s sparrows are adversely affect-
ed by the loss of herbaceous ground cover result-
ing from disruption of natural fire regimes (Dun-
ning and Watts 1990, Plentovich et al. 1998,
Tucker et al. 1998). Bachman’s sparrows nest and
forage on the ground, and they require a dense
ground cover of herbaceous vegetation (Dun-
ning 1993). Several studies (e.g., Dunning and
Watts 1990, Plentovich et al. 1998, Tucker et al.
1998) have documented the importance of under-
story vegetation and used evidence from botani-
cal studies (e.g., Platt et al. 1988, Waldrop et al.
1992, Streng et al. 1993) to suggest that frequent
fire, and particularly growing season (Apr–Sep)
fires, are needed to maintain the dense herba-
ceous ground cover required by Bachman’s spar-
rows. However, no studies have directly examined
the influence of frequency and season of fire.
Our objective was to examine the influence of
season and time since burning on density of
breeding Bachman’s sparrows. We took advan-
tage of a landscape-level fire management plan
executed by the adjacent Conecuh National For-
est in Alabama and Blackwater River State Forest
in Florida that included both dormant- and grow-
ing-season fires. Historically, active management
by fire had been used during winter to avoid
impacts on breeding birds, yet natural fires
occurred most often during late spring and sum-
mer, coinciding with the season of electrical
storms (Robbins and Myers 1992). Recent shifts
to burning during the “natural fire season” have
again raised concerns that nesting birds may be
threatened by such activities. Our aim was to eval-
uate whether such concerns for numbers of
breeding Bachman’s sparrows are warranted.
METHODS
Study Sites
During April 1999, we established counting
points at 180 stands, 110 stands in the Conecuh
National Forest (hereafter, Conecuh) and 70 in
the Blackwater River State Forest (hereafter,
Blackwater; Table 1). Stands were forest manage-
ment units ranging in size from 6.2to 247.5ha
(median = 68.2ha, 95% of stands ≥13.4ha). All
stands were dominated by mature (>50 yr old)
longleaf pines. Prevalent grasses included wire-
grass (Aristida stricta) and bluestems (Andropogon
spp. and Schizachyrium spp.), and prevalent
shrubs included gallberry (Ilex glabra) and yaupon
(I. vomitoria). All stands were selected based on
season (growing season, Apr–Sep; and dormant
season, Oct–Mar) and frequency (15yr since
last burned; i.e., post-burn age) of burning. We
had few opportunities to examine stands imme-
diately after growing-season fires; therefore, post-
burn age of stands burned in the growing season
correspond to number of full growing seasons
after burning (i.e., not including season when
burn occurred).
Stand Selection
We used stand maps to identify potentially suit-
able stands, and a single counting point was
established in each stand meeting the following
criteria: (1) point-count center located ≥100 m
from a stand edge, and (2) point-count center
≥150 m from the edge of any other treatment
group (i.e., another season–frequency combina-
tion included in our study). Thus, all points were
≥300 m from any other counting point. In addi-
tion, all points within a treatment were ≥800 m
apart during 1999, but burning between years con-
verted some stands initially in different treatment
groups into equivalent treatments for the field
season of 2000. However, all points within a treat-
ment group during 2000 were still ≥400 m apart.
Initially, we attempted to locate 1520 stands
within 10 treatment groups (i.e., 2seasons within
each of 5post-burn age groups). However, few
Table 1. Number of stands examined by season of burning and
number of growing seasons since burning (burn group) for the
study of breeding Bachman’s sparrows during 1999 and 2000
at Conecuh National Forest (CNF), Alabama, USA, and Black-
water River State Forest (BSF), Florida, USA.
1999 Field season 2000 Field season
Season Burn Burn
Location burneda group Stands group Stands
CNF Growing 1 15 1 30
CNF Growing 2 14 2 15
CNF Growing 3 25 3 2
CNF Growing 4 7
CNF Dormant 1 15 1 13
CNF Dormant 2 22 2 15
CNF Dormant 3 11 3 20
CNF Dormant 4 8 4 8
BSF Growing 1 5 1 1
BSF Growing 2 5 2 3
BSF Growing 3 4 3 4
BSF Growing 4 28 4 26
BSF Dormant 1 5 1 15b
BSF Dormant 2 5 2 5
BSF Dormant 3 6 3 4
BSF Dormant 4 12 4 12
aGrowing season = Apr–Sep; Dormant season = Oct–Mar.
bOne stand burned 17 Apr 2000 treated as dormant season
2000 burn, because vegetative growth most similar to that of
stands burned in dormant season 2000.
J. Wildl. Manage. 68(4):20041116 FIRE AND BACHMAN’S SPARROWS Tucker et al.
stands >3 years post-burn were available at
Conecuh, and no stands burned during the dor-
mant season of 1996 were available at either
Conecuh or Blackwater. Thus, sample sizes with-
in treatment groups were unequal and the sam-
pling design was unbalanced (Table 1). To exam-
ine the influence of fire history in more detail, we
reviewed the management histories of each stand
and recorded the year and season for each fire
dating to 1990. We used these data to derive 3
variables summarizing the number of fires within
the last 10 years for the growing season, the dor-
mant season, and the 2seasons combined.
Point Counts
We conducted point counts at each of the 180
stands between 16 April and 26 June 1999 and
between 20 April and 31 May 2000. Point counts
were 7min in duration, beginning with 3min of
recording all birds seen or heard, followed by 1
min of broadcasting a tape recorded song of Bach-
man’s sparrow, and ending with another 3-min lis-
tening period. We recorded the distance and
direction to each bird detected during the point
counts but restricted the analysis to Bachman’s
sparrows detected within 100 m of the counting
points. Plastic flagging tied at 50- and 100-m inter-
vals from counting points aided in estimating dis-
tances to birds. We made a complete rotation of all
180 stands before returning to a stand for an addi-
tional count. Within a rotation of counts, we
grouped stands into routes containing stands
located in the same general area and randomized
the order routes were surveyed to reduce potential
bias resulting from seasonal effects. The order
stands within each route were surveyed was alter-
nated such that counts at each stand were distrib-
uted equally among the first 4hr of daylight. Two
observers visited the points: J. Tucker visited each
point 3times in 1999 and 2times in 2000, and D.
Robinson visited each point once in both years.
Statistical comparisons revealed that the number
of Bachman’s sparrows per count did not differ
between observers in either year (paired sample t
≤0.659, P≥ 0.511, df = 179).
Thirty-one of the stands (30 at Conecuh and 1
at Blackwater) were burned during the growing
season of 1999. Before these stands were burned,
we had completed 2point counts at 11 stands, 3
point counts at 2stands, and 4point counts at 18
stands. Twenty-eight other stands were burned
during winter 19992000, and no stands were
burned during breeding season 2000 because of
a severe regional drought.
Vegetation Surveys
We sampled vegetation at 86 stands during July
and August 1999, using a random stratification to
select stands for vegetation sampling. When pos-
sible, 5stands were selected at random from each
treatment group at both Conecuh and Blackwa-
ter. For the older burn groups (≥4 yr), we
attempted to select 10 stands at random from
Blackwater because all the older sites at Conecuh
had been burned.
At each sampled stand, we generated 10 sets of
random coordinates to dictate the location of
sampling points within a 100-m radius of the
counting point. At each sampling point, we used
a 10-factor cruising prism to measure basal area
and a spherical densiometer to measure canopy
cover. In addition, a random compass bearing was
used to orient a 10-m transect at each sampling
point. At each 1.0-m interval along the transect,
we held a 4.0-m pole in a vertical position and
recorded the presence of each plant species that
contacted each 0.1-m height interval of the pole.
Percent ground cover by vegetation types (e.g.,
grasses, forbs, shrubs) was estimated by the per-
centage of 1.0-m intervals along the transect
where the vegetation type contacted the pole.
Statistical Analyses
We used distance sampling (Buckland et al.
2001) to estimate probability of detection and
density (birds/ha) of Bachman’s sparrows. Data
were truncated to include only birds detected
within 100 m of the counting points. In addition,
we included only the counts conducted before
stands were burned during 1999, and sampling
effort was accounted for in our estimates of den-
sity. We used program Distance (Thomas et al.
2003) to model the influence of time since burn-
ing (TSB; average number of growing-season
days since burning), percent shrub cover (arcsine
square root transformed), and basal area of trees
(log transformed) on probability of detection at
the 86 stands where vegetation data were collect-
ed during 1999. To maximize our power of
detecting significant effects among post-burn
groups and season of burning, we also estimated
probability of detection and density using data
from all 180 stands post-stratified by year of study
and included TSB as a covariate. Based on pre-
liminary examinations of the data (Buckland et
al. 2001), we used a hazard-rate function with no
adjustments to model probability of detection.
In all analyses involving vegetation data, we
used arcsine square root transformations (Zar
J. Wildl. Manage. 68(4):2004 1117
FIRE AND BACHMAN’S SPARROWS Tucker et al.
1984) to normalize the distributions of variables
measured as percentages (e.g., canopy cover)
and used the natural logarithm for basal area of
trees. We used 2-way analysis of variance
(ANOVA) to examine the influence of season of
fire and post-burn age on dependent variables.
Although densities of Bachman’s sparrows were
not normally distributed, subjecting ranks of the
data to ANOVA (Zar 1984) yielded equivalent
results to parametric ANOVA. Thus, violations of
assumptions for parametric analysis did not influ-
ence results, and only results from parametric
ANOVA are presented. Repeated measures
ANOVA could not be used because burning
between years of study caused inconsistent
changes in season of fire and post-burn age, so we
analyzed years separately. Including location (i.e.,
Conecuh and Blackwater) in 3-way ANOVA
resulted in missing and/or small group sizes (see
Table 1); therefore, Tucker (2002) analyzed these
data separately by location. Results from those
analyses were consistent between locations (Tuck-
er 2002) and nearly identical to results with loca-
tions pooled. We therefore present only results
with locations pooled to simplify the presenta-
tion. We used Tukey’s HSD test for multiple com-
parison testing.
We used standard least-squares linear models
(PROC REG; SAS Institute 1999) to examine the
influence of vegetation structure, season of burn-
ing, and TSB on density of Bachman’s sparrows.
Only data collected in 1999 at stands where vege-
tation was measured (n =86) were included in
this analysis. We used an information–theoretic
approach to direct model selection and parame-
ter estimation (Burnham and Anderson 2002,
Anderson et al. 2000). Model selection was based
on using Akaike’s Information Criterion correct-
ed for small sample size (AICc), which allows
selection of the most parsimonious model from a
candidate set of models (Burnham and Anderson
2002). We used AICcweights to calculate parame-
ter estimates and their precision across all models
(i.e., model averaging and unconditional vari-
ances), which incorporated uncertainty of model
selection and reduced bias compared to parame-
ter estimates from a single best model (Burnham
and Anderson 2002). We calculated AICcusing
residual sum of squares from the least-squares
models (Burnham and Anderson 2002).
We used knowledge and experience in devel-
oping an a priori set of candidate models (Burn-
ham and Anderson 2002). Because previous stud-
ies (see Plentovich et al. 1998, Tucker et al. 1998,
and especially Haggerty 2000) have found per-
cent coverage of grass to be a pervasive factor
influencing the presence and abundance of
Bachman’s sparrows, percent coverage of grass
(arcsine square root transformed) was the only
vegetation variable considered in the models. We
tested for colinearity between percent coverage
of grass and TSB using Spearman’s rank correla-
tion and found that these 2variables were not
correlated (rs= 0.045, P= 0.680, n =86).
We perceived percent coverage by grass to be
the most important vegetation variable influenc-
ing Bachman’s sparrows, and we therefore also
modeled percent coverage by grass as a function
of canopy cover and burn history to examine the
influence of management on grass. We also used
AICcto evaluate these models. We expected many
of our vegetation variables to be correlated, and
we expected that canopy cover, an index of sun-
light reaching the forest floor, would be the veg-
etation variable having the most direct effect on
percent coverage by grass. The 3variables for
burn history (number of fires in the previous 10
yr during the growing season, dormant season,
and both seasons combined) were not indepen-
dent, so we included only 1of each in individual
models. We did not include TSB in modeling per-
cent coverage of grass because TSB is largely
dependent on burn history; that is, stands with
small values of TSB are more likely to have been
burned more times than stands with larger values
of TSB, and vice versa.
RESULTS
Density of Bachman’s Sparrows
Bachman’s sparrows were common at Conecuh
and Blackwater. We detected Bachman’s sparrows
(at unlimited distances) in 156 of the 180 stands
in both years (91 [1999] and 94 [2000] of the 110
stands at Conecuh and 65 and 62 of the 70 stands
at Blackwater). Restricting detections of Bach-
man’s sparrows to ≤100 m of counting points
resulted in 147 and 149 of the stands (87 and 88 at
Conecuh and 60 and 61 at Blackwater) having ≥1
detection for analysis in 1999 (568 total detections)
and 2000 (505 total detections), respectively.
Hazard-rate models with no adjustments and
no covariates were the most parsimonious mod-
els for estimating probability of detection. At the
86 stands where vegetation data were collected
during 1999, a model without any covariates
(AICcweight = 0.562) was ≥5.5times more likely
to be the best model for estimating probability of
J. Wildl. Manage. 68(4):20041118 FIRE AND BACHMAN’S SPARROWS Tucker et al.
detection than models that included TSB, shrub
cover, or basal area of trees (individually or in
combination) as covariates (AICcweights ≤0.103).
Probability of detection at the 86 stands during
1999 was estimated to be 0.76 (95% CI: 0.70 to
0.83). Probability of detection by year of study
using data from all 180 stands was estimated better
by a model that did not include TSB (AICcweight
= 0.756) than a model that included TSB (AICc
weight = 0.244). Probability of detection at the
180 stands was similar in 1999 (0.60, 95% CI: 0.50
to 0.70) and 2000 (0.65, 95% CI: 0.50 to 0.84).
The effect of season of fire and post-burn age
on density of Bachman’s sparrows during 1999 was
significant (F7, 172 = 3.084, P= 0.004). Season of
last burning did not affect density of Bachman’s
sparrows (F1, 172 = 0.092, P= 0.762) but post-burn
age did (F3, 172 = 6.156, P= 0.001; Table 2A). Den-
sities of Bachman’s sparrows were greater in
stands during the first 3growing seasons after
burning than they were in stands ≥4 growing sea-
sons after burning (P≤0.044; Table 2A).
Similarly, the ANOVA model for breeding sea-
son 2000 was significant (F7, 172 = 3.948, P<0.001).
Density of Bachman’s sparrows did not differ be-
tween seasons of burning (F1, 172 = 0.168, P= 0.683)
but did differ among post-burn ages (F3, 172 =
7.037, P<0.001). Density of Bachman’s sparrows
was greater at stands 2years after burning than at
stands 1, 3, and ≥4 years after burning (Table 2B).
A contrast of stands 1, 2, and 3years since burn-
ing with stands ≥4 years since burning revealed
that the results from breeding season 2000 were
consistent with results
from breeding season
1999, and stands ≤3
years since burning had
greater densities of
Bachman’s sparrows than
stands ≥4 years since
burning (F1, 172 = 4.634,
P= 0.033).
Vegetation
Characteristics
The 2-way ANOVA
examining the influence
of season of burning and
post-burn age found dif-
ferences (P<0.05) in
percent coverage of bare
ground, standing dead
shrubs, forbs, live shrubs,
and vines (Table 3).
None of the models suggested interactions
between season of last burning and post-burn age
(F3, 78 ≤2.419, P≥ 0.073).
Standing dead shrub was the only vegetation
variable to differ (P<0.05) between seasons of
burning (Table 3A), but percent coverage of bare
ground, standing dead shrubs, forbs, live shrubs,
and vines all differed (P<0.05) among post-burn
ages (Table 3B). Bare ground, standing dead
shrubs, and forbs tended to decrease with post-
burn age, and live shrubs and vines tended to
increase with post-burn age (Table 3B).
Model Selection
The linear model containing variables describ-
ing percent coverage of grass (GRASS) and TSB
was identified as the best model for explaining the
variation in density of Bachman’s sparrows (Table
4). The 95% confidence intervals (±2 SE based on
unconditional variances) around the model-aver-
aged parameters suggested that GRASS (β= 1.26,
95% CI: 0.53 to 1.98) had a large influence on den-
sity of Bachman’s sparrows, but TSB (β = –0.0005,
95% CI: –0.0018 to 0.0008) had a relatively weak
influence compared to grass (Fig. 1).
The best model for explaining variation in per-
cent coverage of grass included percent canopy
coverage (CANOPY COVER) and number of
growing-season fires in the previous 10 years
(Table 5). The model that included canopy
COVER, number of growing-season fires, and the
interaction between the 2variables also was a
plausible model (Table 5). The 95% confidence
Table 2. Resultsafrom 2-way analysis of variance comparing mean density (number/ha) of
breeding Bachman’s sparrows by season of burn and years since burning (burn groups) at
stands in the Conecuh National Forest, Alabama, USA, and Blackwater River State Forest,
Florida, USA, during (A) 1999 and (B) 2000.
No. of Burn No. of
Seasons stands Means (±SE) groups stands Meansb(±SE)
(A) Breeding season 1999
Growing (Apr–Sep) 96 0.425 (0.033) 1 40 0.481 (0.050) A
Dormant (Oct–Mar) 84 0.439 (0.035) 2 46 0.529 (0.047) A
3 46 0.453 (0.048) A
4 48 0.264 (0.046) B
(B) Breeding season 2000
Growing (Apr–Sep) 88 0.447 (0.045) 1 59 0.449 (0.044) A
Dormant (Oct–Mar) 92 0.471 (0.035) 2 38 0.670 (0.054) B
3 30 0.352 (0.076) A
4 53 0.364 (0.047) A
aInteractions between season and burn groups were not significant (
P
> 0.1), and those
statistics are not presented.
bMeans followed by different letters differed (
P
< 0.05) in Tukey’s (HSD) multiple compar-
isons. An independent contrast of burn groups 1, 2, and 3 against 4 for breeding season
2000 revealed that abundance was greater 3 years after burning than 4 years after burning
(
t
= 2.15,
P
= 0.033).
J. Wildl. Manage. 68(4):2004 1119
FIRE AND BACHMAN’S SPARROWS Tucker et al.
intervals around the
model-averaged parame-
ters indicated that
canopy cover had a large
influence on grass (ß =
0.960, 95% CI: –1.749
to –0.172), but number
of growing-season fires
(β= –0.016, 95% CI:
0.164 to 0.132) and the
interaction of canopy
cover and number of
growing-season fires (β=
0.071, 95% CI: –0.094 to
0.236) was relatively weak
compared to canopy
cover. Akaike weights
indicated 3.3and 5.3
times greater support for
the model including the
number of growing-sea-
son fires in the last 10
years versus the top-
ranked models contain-
ing number of dormant-
season fires and total
number of fires, respec-
tively (Table 5). A plot of
regression lines for per-
cent coverage of grass by
percent canopy cover at
the minimum and maxi-
mum number of grow-
Table 3. Means (±SE)aand test statistics from 2-way analysis of variance comparing vegeta-
tion variables by (A) season of burning and (B) years since burning (burn group) at Conecuh
National Forest, Alabama, USA, and Blackwater River State Forest, Florida, USA, during 1999.
(A)
Seasonc
Growing Dormant Statisticsd
Variableb(
n
= 44) (
n
= 42)
F P
Grass 72.8 (3.4) 66.3 (3.3) 2.32 0.132
Bare 0.4 (0.2) 0.5 (0.2) 0.14 0.711
Dead 3.2 (0.7) 5.3 (0.7) 4.12 0.046
Fern 11.8 (1.7) 13.2 (1.7) 0.35 0.555
Forb 27.5 (1.9) 23.3 (1.9) 2.33 0.131
Litter 24.9 (2.5) 30.3 (2.4) 3.00 0.087
Shrub 58.7 (2.1) 61.1 (2.0) 0.74 0.393
Vine 10.4 (1.9) 16.5 (1.9) 3.51 0.065
Canopy 37.7 (1.8) 39.1 (1.7) 0.30 0.586
Basal area 54.9 (2.5) 54.1 (2.5) 0.06 0.808
(B)
Burn groupe
Group 1 Group 2 Group 3 Group 4 Statisticsd
Variableb(
n
= 20) (
n
= 16) (
n
= 29) (
n
= 21)
F P
Grass 72.8 (4.7) 67.7(5.5) 69.9 (3.9) 67.7 (4.8) 0.19 0.899
Bare 1.2 (0.2) A 0.2 (0.3) B 0.2 (0.2) B 0.3 (0.2) B 4.93 0.003
Dead 9.4 (1.096) A 4.8 (1.1) B 2.2 (0.8) B 0.6 (1.0) C 19.53 < 0.001
Fern 13.9 (2.4) 11.7 (2.7) 9.6 (2.0) 14.9 (2.4) 0.91 0.440
Forb 32.1 (2.7) A 20.8 (3.1) BC 23.1 (2.3) BC 25.6 (2.7) AB 3.34 0.023
Litter 22.6 (3.5) 26.2 (4.0) 29.0 (2.9) 32.6 (3.5) 1.63 0.190
Shrub 46.0 (2.9) A 56.5 (3.3) B 67.2 (2.4) C 69.8 (2.9) C 14.27 < 0.001
Vine 6.3 (2.7) A 12.3 (3.1) AB 14.6 (2.2) B 20.7 (2.7) B 5.08 0.003
Canopy 39.1 (2.5) 41.6 (2.9) 38.1 (2.1) 34.9 (2.5) 1.12 0.347
Basal area 54.8 (3.5) 59.4 (4.0) 54.9 (2.9) 48.8 (3.5) 1.36 0.261
aMeans are for untransformed data. Arcsine square root of proportions used in analyses of
percentages, and natural logarithm used for basal area.
b Variables are percent cover, except for basal area (feet2/acre).
cGrowing season = Apr–Sep; Dormant season = Oct–Mar.
dInteraction terms were not significant (
P
> 0.05) for any analysis and are not presented.
e Within rows, means not sharing a common letter differ (
P
< 0.05) in Tukey’s (HSD) multi-
ple comparisons.
Table 4. Variables, number of parameters (
K
), coefficient of determination (
R
2), Akaike’s Information Criterion adjusted for small
sample size (AIC
c
), AIC
c
, and AIC
c
weights (
w
i
) for the a priori set of candidate models considered in the analysis examining
the influence of percent coverage of grass, season of burning, and number of growing season days since burning (TSB) on den-
sity of Bachman’s sparrows in longleaf pine stands (
n
= 86) in the Conecuh National Forest, Alabama, USA, and Blackwater River
State Forest, Florida, USA, during 1999. All models include intercept and parameter for residual variance.
Model
KR
2 AIC
c
AIC
c
w
i
TSB Grass 4 0.306 –260.999 0.000 0.466
TSB Grass TSB*Grass 5 0.308 –258.926 2.073 0.165
TSB Grass Season 5 0.307 –258.761 2.238 0.152
TSB Grass Season Season*Grass 6 0.308 –256.668 4.331 0.053
TSB Grass Season TSB*Grass 6 0.308 –256.638 4.361 0.053
TSB Grass Season Season*TSB 6 0.307 –256.448 4.551 0.048
TSB Grass Season TSB*Grass Season*Grass 7 0.311 –254.658 6.341 0.020
TSB Grass Season Season*TSB Season*Grass 7 0.308 –254.295 6.703 0.016
TSB Grass Season TSB*Season TSB*Grass 7 0.308 –254.265 6.734 0.016
TSB Grass Season TSB*Grass Season*Grass Season*TSB 8 0.311 –252.224 8.775 0.006
Grass 3 0.202 –251.125 9.873 0.003
Grass Season 4 0.207 –249.455 11.543 0.001
Grass Season Grass*Season 5 0.208 –247.359 13.639 0.001
TSB 3 0.102 –241.008 19.991 <0.001
TSB Season 4 0.108 –239.326 21.673 <0.001
TSB Season TSB*Season 5 0.108 –237.071 23.927 <0.001
Season 3 0 –231.742 29.257 <0.001
J. Wildl. Manage. 68(4):20041120 FIRE AND BACHMAN’S SPARROWS Tucker et al.
ing-season fires revealed that the interaction of
canopy cover and growing-season fires resulted
from a greater influence of canopy cover at
stands that were burned fewer times in the grow-
ing season (Fig. 2A).
DISCUSSION
We acknowledge that our methodology for sam-
pling Bachman’s sparrows may have resulted in
overestimation of densities. We did not separate
detections of Bachman’s sparrows before and after
broadcasting the tape-recorded song, but we
believe that any bias resulting from luring birds
closer from beyond 100 m was equal across stands.
We did not find significant effects of covariates
on probability of detection, suggesting that
detection of the playback by Bachman’s sparrows
also was equal across stands. Thus, we believe that
our results are valid, but our estimates of density
should be viewed as relative rather than absolute.
The need for frequent fires to maintain the lon-
gleaf pine ecosystem has been well documented
(Engstrom et al. 1984). Although evidence sug-
gests that most naturally occurring fires would have
occurred during the growing season, the season of
greatest lightning activity (Robbins and Myers
1992), our results suggest that season of burning
had little effect on vegetation structure (Table 3) or
density of Bachman’s sparrows (Table 2). However,
the analyses focused on the season of last burning,
and most stands had burn histories that included
both dormant-season and growing-season fires.
Thus, results might have differed if stands had long
histories of burning exclusively in 1season or the
other. Results from modeling percent coverage
of grass by number of growing-season fires in the
previous 10 years (Fig. 2B) also suggest that
results for season of burning may have been con-
founded by variation in burning histories.
We did not examine density of Bachman’s spar-
rows immediately after growing-season fires. Thus,
future research should focus on examining the
influence of timing of fire within the growing sea-
son. For example, fires in late April and early May
could destroy a high percentage of reproductive
effort late in the nestling or early fledgling stages
of the first nesting cycle (Tucker 2002) and result
in low annual recruitment if a high percentage of
annual recruitment
results from early-season
nesting attempts (see Sto-
ber 1996). Shriver et al.
(1996, 1999) found that
burning Florida dry
prairies in mid-June
resulted in an extended
breeding season for
Florida grasshopper spar-
rows (Ammodramus savan-
narum floridanus) whereas
burning in July did not.
Our analysis of TSB
suggested that density of
Bachman’s sparrows be-
gan to rapidly decline 3
years after burning
(Table 2). Although this
trend was clear during
Fig. 1. Regression lines for minimum (20%) and maximum
(98%) measures of percent coverage of grass recorded in lon-
gleaf pine stands in the Conecuh National Forest, Alabama,
USA, and Blackwater River State Forest, Florida, USA, as a
function of number of growing-season days since burning
(TSB) show the positive influence of grass and negative influ-
ence of TSB on density (birds/ha) of Bachman’s sparrows.
Table 5.Variables, number of parameters (
K
), coefficient of determination (
R
2), Akaike’s Infor-
mation Criterion adjusted for small sample size (AIC
c
), AIC
c
, and AIC
c
weights (
w
i
) for the a
priori set of candidate models considered in the analysis examining the influence of percent
canopy cover and burn historyaon percent coverage of grass in longleaf pine stands (
n
= 86)
in the Conecuh National Forest, Alabama, USA, and Blackwater River State Forest, Florida,
USA, during 1999.
Variables in modelb
KR
2AIC
c
AIC
c
w
i
Growing10 Canopy 4 0.3501 –273.540 0 0.399
Growing10 Canopy Grow10*Canopy 5 0.3601 –272.623 0.916 0.252
Dormant10 Canopy Dorm10*Canopy 5 0.3492 –271.169 2.371 0.122
Total10 Canopy Total10*Canopy 5 0.3417 –270.184 3.356 0.075
Total10 Canopy 4 0.3216 –269.855 3.685 0.063
Dormant10 Canopy 4 0.3187 –269.483 4.056 0.052
Canopy 3 0.2952 –268.763 4.776 0.037
Growing10 3 0.0928 –247.054 26.486 7 × 10–7
Dormant10 3 0.0832 –246.152 27.387 5 × 10–7
Total10 3 0.0206 –240.474 33.065 3 × 10–8
aBurn history variables were the number of times a stand was burned in the previous 10
years during the growing season (Growing10), dormant season (Dormant10), and both sea-
sons combined (Total10).
bAll models include an intercept and parameter for residual variance.
J. Wildl. Manage. 68(4):2004 1121
FIRE AND BACHMAN’S SPARROWS Tucker et al.
the breeding season of
1999, the trend was not
as evident during breed-
ing season 2000. Tucker
(2002) found that repro-
ductive success appeared
to mirror abundance of
Bachman’s sparrows in
Conecuh. Studies of
Bachman’s sparrows on
Florida dry prairies found
both breeding densities
and reproductive success
were similar during the
first 3breeding seasons
following dormant-sea-
son fires (Shriver and
Vickery 2001), but densi-
ties increased immediate-
ly following mid-June and
July fires relative to sites
≥2 years since burning
(Shriver et al. 1999). Gob-
ris (1992) also found that
densities of Bachman’s
sparrows in loblolly pine
(Pinus taeda) forests in
Georgia were greatest the
first 3years after burning.
As suggested by previ-
ous studies of Bachman’s
sparrows (e.g., Haggerty
2000), percent coverage
of grass appeared to have a large influence on the
presence of Bachman’s sparrows (Fig. 1). Hagger-
ty (2000) found that percent coverage of grass and
litter were the only vegetation measurements that
consistently appeared important across the geo-
graphic distribution of Bachman’s sparrows.
Although density of Bachman’s sparrows may be
correlated with several measures of vegetation
structure other than grass (e.g., shrub cover), only
percent coverage of grass was included in the a pri-
ori list of candidate models. This is because most
variables that are correlated with density of Bach-
man’s sparrows either influence coverage of grass
(e.g., canopy and shrub cover) or are influenced
similarly to grass by these variables (e.g., forb
cover). Litter cover was not considered in the mod-
els because it was predicted to increase with TSB;
that is, litter will be consumed by fire and then
begin accumulating after fire. Our analyses of the
influence of season and post-burn age on vegeta-
tion structure (Table 3) largely concur with this
logic. For example, coverage by grasses and forbs
tended to be greatest in the first few years after
burning and then began to decline, whereas cov-
erage by shrubs, vines, and litter tended to increase
with time since burning (Table 3B). Surprisingly,
we found few differences in vegetation measure-
ments between seasons of burning, but most
trends with TSB followed patterns that would be
predicted following fire (see Engstrom et al. 1984).
MANAGEMENT IMPLICATIONS
Our study suggests that optimal habitat for
Bachman’s sparrows in longleaf pine forests is
maintained by burning on a 2- or 3-year rotation;
density of Bachman’s sparrows rapidly declined
with burning rotations >3 years. Season of burn-
ing appeared to have little influence on density
of Bachman’s sparrows, but additional research
focusing on timing of fire within the growing sea-
son is needed. In particular, future research
should address the influence of timing of fire
Fig. 2. Regression lines for minimum and maximum values of (A) number of growing-season
fires in the previous 10 years, and (B) percent canopy cover suggest that percent coverage
by grass (arcsine square root transformed) was affected more strongly by canopy cover when
stands were burned fewer times during the growing season and/or by number of fires in the
growing season at stands with greater canopy cover.
J. Wildl. Manage. 68(4):20041122 FIRE AND BACHMAN’S SPARROWS Tucker et al.
within the growing season on the reproductive
success of Bachman’s sparrows.
Our conclusions have strong implications for
the management and restoration of longleaf pine
communities. Similar to most species associated
with the longleaf pine ecosystem, including many
rare and endemic species, Bachman’s sparrows
depend on the condition of herbaceous ground
cover. Thus, Bachman’s sparrows probably serve
as a good indicator for evaluating the influence
of management activities on much of the diversi-
ty within longleaf pine forests.
Because evidence suggests that most naturally
occurring fires would have occurred during the
growing season, and we did not find evidence for
adverse effects of growing-season fires on density
of Bachman’s sparrows, the optimal strategy for
burning longleaf pine forests appears to be grow-
ing-season fires on a 2- or 3-year rotation. If con-
straints (e.g., drought) prevent burning during the
growing season, burning during the dormant sea-
son probably will be more beneficial than post-
poning until suitable conditions occur during a
future growing season. Considerations of the pos-
sible effects on species-of-concern wintering in
longleaf ecosystems should be dealt with on a
case-by-case basis (Tucker and Robinson 2003).
Regardless of season of burning, longleaf pine
forests should be burned every 2or 3years to
maintain high-quality habitat for Bachman’s
sparrows. As a conservative measure, annual burn-
ing—especially during the growing season—should
be discouraged until information is available
addressing long-term effects. An exception to
annual burning might be during the initial stages
of restoration. Finally, our research was in the
region containing the greatest concentration of
longleaf pine that remains (Outcalt and Sheffield
1996), and the large-scale fires (≥400 ha) that typ-
ically occur in this region did not appear to have
negative effects. However, spatial scale of burning
might be a greater concern for fragmented land-
scapes where suitable unburned stands do not
occur in close proximity (Seaman 1998).
ACKNOWLEDGMENTS
This research was supported by grants from the
U.S. Geological Survey, Biological Resource Divi-
sion, Species at Risk Program; a Frances M. Pea-
cock Scholarship from the Garden Club of Amer-
ica administered through the Cornell Laboratory
of Ornithology; and the Walter F. Coxe Research
Fund of the Birmingham Audubon Society. The
research has contributed greatly from partner-
ships among the following organizations and
agencies: Department of Biological Sciences,
Auburn University; Solon Dixon Forestry Educa-
tion Center, School of Forestry and Wildlife Sci-
ences, Auburn University; Alabama Cooperative
Fish and Wildlife Research Unit, Auburn Univer-
sity; U.S. Geological Survey, Biological Resource
Division; U.S. Department of Agriculture, Forest
Service, Conecuh National Forest; Florida Depart-
ment of Agriculture and Consumer Services,
Blackwater River State Forest; Alabama Depart-
ment of Conservation and Natural Resources,
Division of Wildlife and Freshwater Fisheries; and
the Longleaf Alliance. R. Johnson, R. Lint, T.
Arrington, P. Brinn, C. Cook, J. Klempa, and R.
Mullins provided logistic support during field
work. Assistance of J. Doherty in sampling vege-
tation is gratefully acknowledged.
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... Through discussions with USFWS program staff, we identified three longleaf pine associated bird species as most important for evaluating current success of PFW stands in meeting management objectives. The primary species of interest was Bachman's Sparrow (Peucaea aestivalis), a ground-nesting species dependent on herbaceous understories characteristic of frequently burned longleaf pine stands (Tucker et al., 2004(Tucker et al., , 2006, including young stands . Bachman's Sparrow is of high conservation concern throughout its range (Rosenberg et al., 2016), is an indicator of suitable structure for open-canopy pine wildlife species (Hannah et al., 2017;McIntyre et al., 2019), and, as described above, also indicates whether the stands are within desired ecological conditions. ...
... To further assess stand suitability for the three focal bird species, we sampled vegetation at all point count locations using the center of the point as the mid-point on a 20-m transect (Tucker et al., 2004). We randomly established the azimuth of each transect using a random number generator. ...
... We did not attempt to locate source populations near our study areas, so we did not confirm occurrence in the vicinity of each site. However, preferred vegetation characteristics for Bachman's Sparrows are well established (Wilson et al., 1995;Haggerty, 1998;Plentovich et al., 1998;Tucker et al., 1998Tucker et al., , 2004Tucker et al., , 2006Provencher et al., 2002;Allen et al., 2006;Jones, 2007, 2009;Jones et al., 2013;Winiarski et al., 2017;Fish et al., 2018). Based on the average vegetation characteristics of our sampled stands, it is apparent that the majority of stands in our study were unlikely to support Bachman's Sparrows even if colonization were possible. ...
Article
Longleaf pine (Pinus palustris) forests have become a major focus of large-scale restoration efforts across the southeastern United States over the past two decades, but the success of these efforts are not often measured. One example is Partners for Fish and Wildlife (PFW), which is administered by the U.S. Fish and Wildlife Service (USFWS) and designed to assist private landowners with longleaf pine (Pinus palustris) planting. An objective of this program is to provide habitat for species like the Bachman’s Sparrow (Peucaea aestivalis), which is reliant on fire-maintained longleaf pine savannas. To assess this program’s success, we conducted avian point counts and vegetation surveys in longleaf pine stands enrolled in the Mississippi PFW program during 2018–2019. We surveyed 51 stands (≥16 ha; ≤16 years old) and conducted 194 point count surveys. Across all stands, coverage of woody vegetation averaged 38% (SD = 20%), herbaceous cover 39% (23%), and canopy closure 68% (25%). We detected 6 Bachman’s Sparrows in 3 stands at 4 points (5.8% of stands, 2.1% of points), indicating the stands are providing inappropriate conditions for this species due to inadequate prescribed burning. We detected Prairie Warblers (Setophaga discolor) in 37 stands (72%) and at 94 points (48%), and Northern Bobwhites (Colinus virginianus) in 43 stands (83%) and at 101 points (52%), indicating PFW stands are providing habitat for declining shrubland species. If providing habitat for grassland birds like Bachman’s Sparrow continues to be an objective for PFW stands in the Southeast, we recommend stricter requirements for landowner enrollment in the program (e.g., agreements to maintain a burn interval of ∼2 years), and more assistance in meeting those requirements. More broadly, maintenance of appropriate disturbance regimes will be critical to restoration of disturbance-dependent forests and may require longer-term investment than is customary.
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... Different vegetation characteristics may be selected at different stages of the Bachman's sparrow life cycle. For example, low woody shrubs are important microhabitat for nesting (Jones et al., 2013;Winiarski et al., 2017a) and escape cover (Winiarski et al., 2017b), but too much woody shrub from lack of fire leads to low bird densities and territory abandonment (Tucker et al., 2004;Brooks & Stouffer, 2010;Taillie et al., 2015). Nestsites are often located in areas with bare ground and little grass (Jones et al., 2013;Winiarski et al., 2017a), but grass seed is a necessary component of Bachman's sparrow's adult diet (Wolf, 1977) and grass is used to build nests (Haggerty, 1995). ...
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Full-text available
Many wild populations of animals conform to the ideal despotic distribution (IDD) in which more competitive individuals exclude less competitive individuals from high quality resources. Body size and aggressiveness are two important traits for resource defense, and they positively covary so that larger individuals are usually more aggressive. Using Bachman’s sparrows, we tested the hypothesis that larger birds are more aggressive and are thus able to compete for the best quality territories. We found that larger males were more aggressive, and more aggressive birds fledged at least one young. However, we did not find consistent relationships between aggressiveness and habitat characteristics. Our results suggest that Bachman’s sparrows meet most of the predictions of the IDD. Frequent ecological disturbances, such as fires, might disrupt the IDD or make it difficult to detect. Additional studies are needed to test for relationships between ecological disturbances and territorial behaviour.
... (Wiregrass). Bachman's Sparrows have specialized habitat requirements and will abandon sites without frequent fire (i.e., every 2-3 years) as dense woody vegetation encroaches and outcompetes herbaceous groundcover (Engstrom et al. 1984;Taillie et al. 2015;Tucker et al. 2004Tucker et al. , 2006. ...
... Female selection of intermediate densities of grass cover are consistent with several recent studies of habitat selection by male sparrows, all suggesting an upper threshold of grass density at which Bachman's Sparrow use declines (Brooks and Stouffer 2010, Tallie et al. 2015, Winiarski et al. 2017b. Although it is known that Bachman's Sparrow presence increases with grass density or cover (Allen and Burt 2014; Dunning and Watts 1990;Dunning et al. 2020;Fish et al. 2018;Plentovich et al. 1998;Tucker et al. 1998Tucker et al. , 2004, there is an upper limit where too much grass cover impedes efficient movement (Brooks and Stouffer 2010, Haggerty 1998, Taillie et al. 2015. ...
... On Fort Bragg, females selected for patches of woody understory vegetation, similar to males in another region of North Carolina (Winiarski et al. 2017b). Although presence of woody vegetation generally is considered detrimental to Bachman's Sparrow occupancy and reproductive success (Brooks and Stouffer 2010, Fish et al. 2019, Haggerty 1998, Taillie et al. 2015, Tucker et al. 2004, previous studies examined habitat selection at the home-range scale or larger. On a smaller scale, woody understory provides song perches for male Bachman's Sparrows (Dunning and Watts 1990, Jones et al. 2013, Winiarski et al. 2017b) and escape cover for males, females, and fledglings (Dean and Vickery 2003;Fish et al. 2018Fish et al. , 2020Meanley 1959;Pulliam and Mills 1977). ...
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Peucaea aestivalis (Bachman’s Sparrow) is a declining songbird endemic to the southeastern US, but lack of basic life-history information for females, including a description of habitat selection, limits effective management. We investigated survival, home-range size, and habitat selection of female Bachman’s Sparrows during the breeding season at Fort Bragg Military Installation, NC. We attached radio-transmitters to female sparrows between April and June in 2014–2016 and recorded locations of females every2–4 days. We estimated seasonal survival and home-range size and, in 2016, we modeled habitat selection of female sparrows within their home range. Estimated breeding-season(90 days) survival (0.941) was greater than a published estimate from South Carolina(0.794), and home-range size (1.48 ha, SE = 0.16) was similar to a published estimate for females and multiple published estimates for male sparrows (min–max = 1–5 ha). Females selected habitat patches with greater woody vegetation and intermediate grass densities than at random locations, suggesting that woody vegetation provides escape and nesting cover for female sparrows. Survival, home-range size, and habitat selection of female Bachman’s Sparrows did not differ substantially from males in other studies. Therefore, management focused on male sparrows may concurrently conserve habitat requirements for females.
... In contrast, there has been a reduction in prescribed fire application over the last decade in the region encompassing the northern limits of shortleaf pine and the southern extent of the historical distribution of oakpine savanna in Missouri, Kentucky, and Tennessee (Melvin 2018). Still, P. aestivalis density remains high (~0.5 territorial males hectare -1 ; Tucker et al. 2004), or increases (Wilson et al. 1995), in areas with frequent fire-return intervals (≤ 3 years). That longleaf pine savannas have benefitted most from this prescribed fire activity is perhaps why research on P. aestivalis has become so focused on its association with this particular habitat. ...
... Peucaea aestivalis did occur locally in portions of the extralimital region into the 1980s (Fig. 2D), but it is unclear whether the extralimital regions that were colonized contained productive habitats. Furthermore, we know that suitable conditions at the scale of individual territories are best maintained by frequent, ≤ 3-year, fires (Tucker et al. 2004) and this presents additional challenges today (Stephens et al. 2019). Today, P. aestivalis is most abundant in portions of the southeastern U.S. that fall within the former range of longleaf pine (Figs. 1, 2E), a region that leads the nation in its application of prescribed fire (Melvin 2018). ...
... The Bachman's Sparrow (Aimophila aestivalis) is a species of concern due to its population decline ( Sauer et al. 2004) and large reductions in range (Dunning 1993). The impact of prescribed fire and timber management on Bachman's Sparrow abundance (Dunning and Watts 1990;Gobris 1992;Plentovich et al. 1998;Tucker et al. 1998Tucker et al. , 2004) and habitat occupancy (Wan A. Kadir 1987;Haggerty 1998Haggerty , 2000) have been well documented. The sparrow's secretive nature, however, makes it difficult to obtain basic information on its reproduction, survival, movement, and homerange dynamics (Dunning 1993). ...
... were more abundant in regeneration stands (0.8-1.3%) than in mature pine stands (0.1-0.4%); thus, differences in home-range size between habitats may be a reflection of greater seed resources and arthropod productivity in early regeneration habitats than in mature pine habitats managed for Red-cockaded Woodpeckers. In examining previous studies on Bachman's sparrows across their range (Wan A. Kadir 1987;Dunning and Watts 1990;Gobris 1992;Haggerty 1998Haggerty , 2000Plentovich et al. 1998;Tucker et al. 1998Tucker et al. , 2004), we observed that, in general, sparrow densities and arthropod communities were reduced with succession of understory vegetation. ...
... This study suggests that mechanical hardwood reduction on sites with old-field ground cover that are managed intensively for bobwhite will not dramatically influence Bachman's Sparrow populations via changes in vital rates. Combined with previous work on Bachman's Sparrow fire-dependency (Tucker et al. 2004, Jones et al. 2013, our study suggests a moderate midstory canopy may not limit vital rates when management includes frequent prescribed fire. Although we were unable to explore it with this study, population density may be an important factor in cases where population restoration rather than maintenance is underway and small populations are a target of management. ...
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Where historical fire regimes have been disrupted, reduction in woody vegetation is often used to maintain or restore habitat for grassland and early successional birds. In pine savanna ecosystems of the southeastern USA, mechanical hardwood canopy reduction can restore pine savanna communities and is often employed on privately owned lands to improve habitat for the Northern Bobwhite (Colinus virginianus), although scant empirical evidence exists of its effects on target or non‐target species. We measured the response of a pine savanna specialist, the Bachman's Sparrow (Peucaea aestivalis), to large‐scale hardwood reduction in a before–after–control–impact design on two properties where two‐year fire‐return intervals were established and the Bachman's Sparrow population was stable. We investigated the effects of mechanical hardwood reduction on Bachman's Sparrow daily nest survival, cause‐specific nest mortality and adult male annual survival. During the four‐year study, we monitored 107 Bachman's Sparrow nests, recorded 49 nest predation events, and banded 113 adult male Bachman's Sparrows. We found Bachman's Sparrow nest and adult survival were resilient to changes in the hardwood canopy and did not differ significantly between treatment and control sites. Average annual adult male survival was 0.41 (0.32–0.52) and daily survival rate of nests with surveillance declined annually from 0.94 (0.92–0.96) to 0.88 (0.83–0.92). The identity of predators at nests was dominated by two snake species, black racer (Coluber constrictor) and corn snake (Pantherophis guttata). We found evidence for opposing treatment effects on the frequency of nest depredations by the dominant species; racers responded positively and corn snakes responded negatively. Our results suggest a moderate midstory canopy does not limit Bachman's Sparrow vital rates when management includes frequent prescribed fire. Our results also suggest hardwood reduction to mitigate nest predation may be complicated with a diverse predator suite.
... Bachman's Sparrows (Peucaea aestivalis) are primarily associated with fire-maintained longleaf pine (Pinus palustris) communities with an understory dominated by wiregrass (Aristida stricta), but also occur in treeless, dry prairies in some parts of their range (Shriver et al. 1999). Bachman's Sparrows are sensitive to the amount of woody understory cover in breeding territories, typically abandoning areas with infrequent prescribed fire application and increasing cover and height of the woody understory (Engstrom et al. 1984, Tucker et al. 2004, Taillie et al. 2015. However, in frequently burned longleaf pine forests in southeastern North Carolina, territories of male Bachman's Sparrows typically included patches of woody cover within a matrix of grass-forb cover (Winiarski et al. 2017b). ...
Article
en Fledgling ecology remains understudied for many passerine species, yet information about the fledgling life stage is critical for understanding full‐annual life cycles and population recruitment. We examined the survival, habitat selection, and movements of fledgling Bachman’s Sparrows (Peucaea aestivalis) in a longleaf pine‐wiregrass (Pinus palustris‐Aristida stricta) community managed with frequent prescribed fire. We captured and marked 36 fledglings on the day of fledging and used radio‐telemetry to relocate them daily until independence during three breeding seasons (2014–2016). We visually confirmed the status of fledglings as live or dead during daily relocations and determined causes of mortality. We measured vegetation characteristics at fledgling locations and compared them to the characteristics of vegetation at the locations of adult males. We used a Known Fates analysis in Program MARK to estimate fledgling survival, and generalized linear mixed effect models to determine habitat selection. Estimated fledgling survival until independence was 0.31 (SE = 0.08), with most mortality during the first 4 d post‐fledging. Fledglings with longer wing chords had higher rates of survival than those with shorter wing chords, possibly due to an increased ability to evade predators. Fledgling movements were restricted primarily to natal territories. Fledgling Bachman’s Sparrows were located in areas with greater woody plant, forb, and grass cover and less bare ground than available in natal territories. Similar to fledglings of other songbirds, understory woody and herbaceous plants appear to provide critical cover for fledgling Bachman’s Sparrows, and maintenance of such cover should receive consideration in management plans for longleaf pine communities. RESUMEN es Volantones de Chingolo de Bachman en un ecosistema de pinos de hoja larga: supervivencia, movimientos y selección de hábitat La ecología de los volantones permanece poco estudiada para muchas especies de paseriformes, sin embargo, la información sobre la etapa volantona de la vida es fundamental para comprender los ciclos de vida anuales completos y el reclutamiento de la población. Examinamos la supervivencia, la selección del hábitat y los movimientos del Chingolo de Bachman (Peucaea aestivalis) en una comunidad de pino hoja larga‐pasto alambre (Pinus palustris ‐ Aristida stricta) manejada con frecuentes incendios controlados. Capturamos y marcamos 36 volantones el día del abandono del nido y utilizamos radiotelemetría para reubicarlos diariamente hasta la independencia durante tres temporadas de cría (2014–2016). Confirmamos visualmente el estado de los volantones como vivos o muertos durante las reubicaciones diarias y determinamos las causas de mortalidad. Medimos las características de la vegetación en las ubicaciones de los volantones y las comparamos con las características de la vegetación en las ubicaciones de los machos adultos. Usamos un análisis de Destinos Conocidos en el Programa MARK para estimar la supervivencia de los volantones, y modelos lineales generalizados de efectos mixtos para determinar la selección del hábitat. La supervivencia estimada de los volantones hasta la independencia fue de 0.31 (EE = 0.08), con la mayor mortalidad durante los primeros cuatro días después del abandono del nido. Los polluelos con cuerdas alares más larga tenían tasas más altas de supervivencia que aquellos con cuerdas alarer alas más cortas, posiblemente debido a una mayor capacidad para evadir a los depredadores. Los movimientos de volantones se restringieron principalmente a los territorios natales. Los volantones de Chingolo de Bachman se ubicaron en áreas con mayor cobertura de plantas leñosas, hierbas y pastos y menos terreno desnudo que el disponible en los territorios natales. Al igual que los polluelos de otras aves cantoras, las plantas leñosas y herbáceas del sotobosque parecen proporcionar una cobertura crítica para los volantones de Chingolo de Bachman, y el mantenimiento de dicha cobertura debería ser considerado en los planes de gestión para las comunidades de pinos de hoja larga.
... Additionally, we reviewed studies that provided context to habitat associations but lacked data concerning specific thresholds or ranges of suitable structure (i.e., basal area, DBH, canopy closure, midstory shrubs, understory composition; e.g., Fill et al., 2015a, Bried et al., 2011, Dunning and Watts, 1990. Several studies documented responses of focal species to forest management (e.g., Morris et al., 2013, Tucker et al., 2004, Burger et al., 1998, woodland and savanna restoration (e.g., Roach et al., 2019), agricultural programs (e.g., Evans et al., 2013, Potter et al., 2011, and urbanization (e.g., Schlossberg et al., 2011, Gifford et al., 2010. ...
Article
The decline of early successional and open forests and their wildlife inhabitants has resulted in increased efforts to understand and conserve these communities. Natural and anthropogenic disturbances that historically created and maintained open forest conditions have been disrupted, necessitating wildlife use of alternative habitat sources (e.g., pine plantations, utility rights-of way, abandoned agricultural fields) to carry out their life history. We reviewed available literature to estimate the range of structural conditions suitable for four open forest species in regional decline and compared these ranges to available structure in loblolly pine (Pinus taeda) forests managed for economic return. Species included Bachman’s sparrow (Aimophila aestivalis), northern bobwhite (Colinus virginianus), prairie warbler (Dendroica discolor), and eastern diamondback rattlesnake (Crotalus adamanteus). We estimated habitat availability and connectivity for each of these four species during a 60-year simulation on an economically- and operationally-feasible pine landscape (>22,000 ha) managed for sawtimber production in the West Gulf Coastal Plain. Habitat requirements, including minimum patch size and dispersal constraints, of Bachman’s sparrow, northern bobwhite, prairie warbler, and eastern diamondback rattlesnake are generally met by pine stands in stand establishment and thinned, mid-rotation stages. However, habitat availability in pine plantations may be highly ephemeral, tends to occupy the upper end of basal area and canopy closure tolerance, and may be more suitable for open woodland species (e.g., Bachman’s sparrow) than grassland species (e.g., northern bobwhite). The range of habitat associations in this literature review highlights the need to refine targets of structural metrics identified by open pine restoration initiatives to encompass the full range of conditions occupied by open forest species. Current literature is strongly biased to avian habitat associations. Few papers explore habitat associations of herpetofauna of conservation concern in the southeastern U.S., and these species tend to be less mobile and therefore, more vulnerable to landscape changes and the ephemeral nature of open vegetative structure in pine plantations.
Article
Prescribed fire is an essential management practice in pyrogenic ecosystems, but fire can also be a significant disturbance and source of mortality for both target and non-target species. Seasonal periods of animal inactivity may provide opportunities to design burn plans that minimize negative impacts to species of conservation concern, but few studies have rigorously examined this possibility. Using radiotelemetry, we studied overwintering behavior and interactions with fire in a forest-dwelling terrestrial turtle, the Eastern Box Turtle (Terrapene carolina carolina), over an eight-year period at two sites that use prescribed fire in forest management. Turtles at both sites selected predominantly hardwood forests and mesic habitats and avoided upland pine forests. Turtles buried deepest (2.9 – 3.2 cm) below the soil-litter interface in late February and then moved gradually shallower until emergence in early April. Emergence timing varied over a 58-day period, but was consistent within individuals from year to year. Turtles also maintained fidelity to refuge locations, but those overwintering in burned areas selected sites over twice as far from refuges used in previous years compared to those in unburned areas. The areas and habitats selected by turtles during winter served as refugia from fire, and those whose refuges did burn remained buffered from lethal temperatures even at shallow burial depths. The only fire-related injury or mortality occurred during seasons of surface activity. Timing burning and other forest management practices during periods of winter dormancy may thus minimize threats to turtle populations, but modifications to prescribed fire regimes must also be balanced with other management objectives.
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Many bird species have experienced short- or long-term population declines. However, the mechanisms and reasons underlying such negative changes are often not fully understood, making it difficult to identify effective conservation measures to recover populations. In this study, we focused on local changes in the abundance and distribution of calling male Corncrakes Crex crex in relation to: (1) within- and between-season site fidelity of adult males, (2) spatial distribution of territories in consecutive years and (3) the effect of habitat conditions on population size. We counted the number of calling males at ten randomly selected study plots (1 km2) in 2014–2018. Additionally, males were caught and individually marked in years 2015–2017. We found significant between-year changes in Corncrake abundance, from a 34% decrease to a 21% increase. On average, 32% of males established territories in the same locations as males recorded in the previous year. Breeding site fidelity was very low, with only 2–5% of males recaptured in the following year. Males selected areas characterized by higher values of NDVI (Normalized Difference Vegetation Index–higher values indicate more biomass) than on average within the study area. Population size in a particular year was significantly affected by the NDVI of the previous year but not by the NDVI in the current breeding season. We suppose that Corncrakes may exhibit a nomadic breeding behavior, and settle at territories when they encounter optimal habitat conditions. Moreover, as population size was negatively correlated with habitat conditions at the beginning of the previous breeding season, we suppose that local population changes may reflect more general trends in a whole population rather than local breeding success. Therefore, we highlight the need for better knowledge of Corncrake dispersal within the main European population and for the coordination of monitoring and conservation efforts, especially in those regions where most Corncrakes breed.
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The federally endangered Florida Grasshopper Sparrow (Ammodramus savannarum floridanus) prefers recently burned sites in an early successional stage (Delany et al. 1985). Management of the dry prairie ecosystem for this endemic bird has usually involved late fall and winter prescribed burns. However, naturally ignited fires on dry prairies usually occur in summer (Robbins and Myers 1992). Because this endangered sparrow probably evolved with summer wildfires, we sought to understand how prescribed summer burns affected this rare species. We studied the effects of three prescribed summer fires on Florida Grasshopper Sparrows at the Kissimmee Prairie Sanctuary (1993, 1994) and Three Lakes Wildlife Management Area (1994). Sparrows occupied the burned area one week after the fire, and remained reproductively active into September at Three Lakes. On the unburned control units, territorial behavior diminished by late July. In response to summer burns, Florida Grasshopper Sparrows initiated a second bout of breeding activity. This bimodel breeding phenology is strong support to the theory that this bird has evolved with frequent summer fires. These results suggest that summer burns are beneficial for Florida Grasshopper Sparrows and that fire management plans should consider the evolutionary and ecosystem dynamics of fire seasonality on Floridas’ unique dry prairie.
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Bachman's Sparrow (Aimophila aestivalis) has declined over much of its range in the last fifty years. To understand the role of habitat loss in this decline, we examined patterns of habitat occupancy by this species in two areas of South Carolina. At both sites we recorded relatively high densities of breeding sparrows in mature (>80 yr old) pine stands, and relatively low densities in young pine stands. Habitat occupancy varied between sites in clearcuts and middle-aged pine stands. Sparrows used areas with open understories and dense ground covers of grasses and forbs. Habitat occupancy differed between the two main study areas because these preferred vegetation characteristics were found in different habitats in the two areas. Timber management practices (especially burning rotations, site-preparation techniques, and thinning) have a strong effect on understory vegetation and, therefore, habitat suitability for the sparrow. Management practices that produce suitable habitat for Red-cockaded Woodpeckers (Picoides borealis) also provide habitat for Bachman's Sparrow. We believe that, even though the sparrow may use open habitats that appear to be relatively common, its habitat requirements are relatively strict, and that habitat loss may be an important factor in this species' population decline.
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Populations of Florida grasshopper (Ammodramus savannarum floridanus) and Bachman's sparrows (Aimophila aestivalis) are small and declining. Prescribed burning is the primary management tool used to maintain their grassland habitats, but the effects of this management practice on the breeding density and reproductive success of these populations are poorly understood. We conducted a 3-year spot-mapping study of 3 winter burn classes (0.5-yr, 1.5-yr, and 2.5-yr postfire) in native dry prairie on 2 sites in central Florida to determine the effects of fire management on breeding density and reproductive success of these 2 sparrows. Florida grasshopper sparrow densities were greater on recently burned plots (0.5 yr postburn: x̄ = 4.0 ± 1 territories/10 ha (x̄ ± SE); 1.5 yr postburn x̄ = 3.4 ± 0.8 territories/10 ha) than on plots that had not been burned in 2.5 years (x̄ = 1.8 ± 0.8 territories/10 ha). Grasshopper sparrow reproductive success was also higher in recently burned plots (0.5 yr postburn; x̄ = 1.6 successful territories/plot) than in 2.5-year burn plots (x̄ = 0.6 successful territories/plot). In contrast, Bachman sparrow breeding densities and reproductive success were not affected by fire management rotation. Our results indicate that a fire rotation of ≤3 years is necessary to maintain suitable breeding habitat for Florida grasshopper sparrows but does not appear to negatively affect breeding Bachman's sparrows.
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"Species-centered Environmental Analysis" (SCEA) is a procedure for diagnosing species-specific environmental factors that limit the size of a population. It attempts to identify presently recognized biotic and abiotic limiting factors. Then, through comparisons and applications of the principles of experimental design, it evaluates the relative importance of the factors and searches for new ones. The advantage of SCEA is that it frames ecological hypotheses in a context that spans population-, community-, and ecosystem-level processes while keeping the research focused on ecological factors that directly or indirectly affect the size of a focal population. In the case of the endangered Red-cockaded Woodpecker (Picoides borealis), which lives in a mature pine forests of the southeastern United States, four types of environmental factors have been shown to limit its numbers, even on public land: (1) insufficient habitat due to hardwood midstory encroachment, (2) a shortage of suitable cavity trees, (3) loss and fragmentation of habitat, and (4) demographic isolation. As part of the research to identify other potentially limiting environmental factors in the Apalachicola National Forest of northern Florida, we studied a sample of 87 social units (each unit usually a mated pair of birds with or without helpers, but sometimes a single bird). Each unit was defending a cluster of cavity trees and a foraging territory of open longleaf pine (Pinus palustris) forest. We then developed regression models for predicting within-population variation in the size, density, and productivity of social units from data on habitat variation. We found that variation in the bird variables was not significantly related to the sizes or densities of pine trees in these territories. It was, however, highly significantly related to the ground cover composition and the extent of natural pine regeneration, both of which are indirect indicators of local fire history. This suggests that, in addition to the four main causes, environmental processes driven by the history of fire are also limiting the Red-cockaded Woodpecker population. Additional support for this idea comes from the fact that female Red-cockaded Woodpeckers on the Apalachicola Ranger District tend to lay larger clutches of eggs in the first breeding season after their territories have been buried. Because fire history affects soil nutrient dynamics, which in turn affect ground cover composition, our present hypothesis is that nutrient dynamics are affecting the health of animal populations in the system, including that of the Red-cockaded Woodpecker. The path by which this process operates, the particular nutrients involved, and its importance relative to other factors that limit the populations need to be addressed experimentally. If nutrient dynamics are a previously unrecognized limiting factor for animal populations in this ecosystem, then the role of fire is not restricted to its ability to reduce vegetation in the midstory, and managers should acknowledge that different regimes of prescribed fire are likely to have different effects on animal, as well as plant, populations.
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Because managing pine habitats for red-cockaded woodpeckers (Picoides borealis) may result in reductions in habitat for certain neotropical migrant species, an apparent conflict exists between these species when managing stands of pine. However, other high priority species are likely to increase in areas managed for red-cockaded woodpeckers. The Partners in Flight prioritization scheme and research on bird-habitat relationships indicate that most high priority neotropical migrants in the East Gulf Coastal Plain are managed for best in bottomland hardwoods. In contrast, most high priority temperate migrant and resident bird species prosper in mature open pine habitat. Management conflict disappears when managing for red-cockaded woodpeckers and other pine associated species on a landscape scale. This process has ramifications for developing strategies to effectively conserve biodiversity in managed areas.
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After fire exclusion in 1966, annual breeding bird censuses were conducted on an 8.6-ha plot of oldfield pine forest in N Florida. Only 11 of 43 bird species were encountered every year of the study. Most finches and brush nesting species no longer occur on the study area while several species associated with mesic conditions have increased in abundance. -from Authors
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s Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academic journals and scholarly literature from around the world. The Archive is supported by libraries, scholarly societies, publishers, and foundations. It is an initiative of JSTOR, a not-for-profit organization with a mission to help the scholarly community take advantage of advances in technology. For more information regarding JSTOR, please contact support@jstor.org.