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The Wilson Journal of Ornithology 129(4):792–803, 2017
BIRDS AND BURROWS: AVIFAUNA USE AND VISITATION OF
BURROWS OF GOPHER TORTOISES AT TWO MILITARY SITES IN
THE FLORIDA PANHANDLE
K. NICOLE WHITE1,2,3 AND TRACEY D. TUBERVILLE1
ABSTRACT.—The United States Department of Defense (DoD) has a dual mission of maintaining military readiness and
stewardship of its natural resources. The DoD invests more than $334 million on land and species management on their
properties, which support high levels of biodiversity and harbor a disproportionate number of threatened, endangered, and at-
risk species. The gopher tortoise (Gopherus polyphemus) occurs on 28 DoD installations in the southeastern United States.
Because more than 350 species have been documented to use their burrows, the gopher tortoise is considered a keystone
species. However, few species of birds have previously been documented as burrow associates. In this study, we compare
bird species richness, visitation frequency, and behaviors at gopher tortoise burrows at two Department of Navy properties
(Santa Rosa County, Florida) that differed in size, training intensity, habitat diversity, and proportion of habitat suitable for
gopher tortoises. We detected a total of 33 species of birds and documented previously unreported behaviors of foraging, dust
bathing, and wing-flashing display behaviors at tortoise burrows. Although species richness between sites was not
significantly different, frequency of visitation was greater at the site with less military training activity. Our findings
underscore the importance of even small military installations in supporting local biodiversity and the need to further explore
gopher tortoise burrows as a potential resource for avifauna. Received 23 August 2016. Accepted 4 February 2017.
Key words: avifauna, burrow associate, camera trap, Gopherus polyphemus, species richness.
Ecosystem management and biodiversity con-
servation are part of the mission of the United
States Department of Defense (DoD; Boice 1999).
The DoD manages .12 million ha. Although
these holdings represent only 3% of all federally
owned lands in the United States, densities of
endangered and threatened species are three times
higher on military lands compared to other federal
lands (Stein et al. 2008). An estimated 250
installations support at least one federally-listed
species and .375 installations are considered to
harbor ‘significant natural resources’ (Boice 2006).
The high biodiversity often associated with
military lands has been attributed to limited human
access and protection from development (Boice
2006), as well as the heterogeneous disturbance
regime resulting from spatial variation in training
intensities within installations (Warren et al. 2007).
In addition to supporting high levels of
biodiversity, DoD lands are frequently identified
as having a critical role in conservation and
recovery of individual rare or at-risk species, such
as the Red-cockaded Woodpecker (Picoides bor-
ealis; USFWS 2003) and the gopher tortoise
(Gopherus polyphemus; USFWS 2011, 2013).
The gopher tortoise—an iconic species of the
longleaf pine ecosystem—has been documented
on at least 28 military installations within its range
in the southeastern United States (Wilson et al.
1997). It occupies open canopy sites with deep
sandy soils in which it constructs its own burrows.
The burrow and its apron (the loose mound of sand
at the burrow entrance) provide tortoises a site for
foraging, reproduction, and refuge from fire,
predators, and thermal extremes (Jackson and
Milstrey 1989, Pike and Mitchell 2013). Because
their burrows are used by more than 65 vertebrate
and 300 invertebrate species, gopher tortoises are
considered both a keystone species (Eisenberg
1983, Catano and Stout 2015) and ecosystem
engineer (as defined by Jones et al. 1997, Kinlaw
and Grasmueck 2012, Pike and Mitchell 2013).
Previous studies have documented a variety of
vertebrates at tortoise burrows, although disruptive
sampling protocols, such as live trapping and
scoping with burrow cameras, have taxonomically
biased observations towards non-avian species
(Frank and Lips 1989, Lips 1991, Knizley 1997),
likely resulting in an underestimate of the overall
importance of the gopher tortoise to avifauna.
Density of gopher tortoise burrows is correlated
with increased mammal and reptile species
diversity (Catano and Stout 2015), but effects on
bird species diversity remain unknown. However,
1 University of Georgia’s Savannah River Ecology Lab,
P.O. Drawer E, Aiken, SC 29802, USA.2 Current address: University of Georgia’s Savannah
River Ecology Lab, P.O. Drawer E, Aiken, SC 29802,
USA.3 Corresponding author; e-mail: [email protected]
792
in other systems, greater bird species richness has
been attributed to the effects of ecosystem
engineers on the vegetation or insect communities
(e.g., Joseph et al. 2011). Bird density and species
richness are significantly greater in black-tailed
prairie dog colonies (Cynomys ludovicianus) than
in adjacent prairie in South Dakota (Agnew et al.
1986). The degu (Octodon degus), another small
mammalian ecosystem engineer, is associated with
increased invertebrate diversity, and granivorous
birds foraged more frequently and consumed more
in a shorter period than in areas with lower density
of surface runways created by O. degus (Root-
Bernstein et al. 2013).
As part of an unrelated study on gopher tortoise
reproduction and social behavior on two military
installations in the Florida panhandle, we moni-
tored burrows at each installation for 12 months
using remote wildlife cameras. We incidentally
recorded observations of birds visiting tortoise
burrows. We report overall bird species richness
detected at burrows at each site, calculate visitation
frequency of each bird species observed at
burrows, and report how birds were observed
using tortoise burrows and burrow aprons. Al-
though our monitoring efforts were not designed to
experimentally test hypotheses regarding differ-
ences in either gopher tortoise or bird activity
between sites, based on characteristics of the two
sites we can make some initial predictions. The
two installations, though separated by a short
distance, differed in several important ways that
might be expected to influence species diversity.
Naval Air Station (NAS) Whiting was larger in
size, but with less habitat diversity, lower propor-
tion of habitat suitable for gopher tortoises, and
greater intensity of military training compared to
Holley Outlying Field (OLF). Thus, we predicted
bird diversity and bird visitation at gopher tortoise
burrows to be greater at Holley OLF than at NAS
Whiting despite its smaller size.
METHODOLOGY
Study Sites.—We conducted our research at two
Department of Navy properties ~38.6 km apart in
Santa Rosa County in the Florida panhandle—
NAS Whiting and Holley OLF. NAS Whiting and
Holley OLF were both established in 1943.
Although they are in close proximity to each other
and fall under the same management complex,
they vary in military training intensity and
proportion of area suitable for gopher tortoises.
NAS Whiting is a 1,623-ha active airfield that
employs ~3,000 military and civilian personnel.
Combined, helicopters and small single-engine
airplanes engage in an average of 500 training
flights per day, 1.2 million training flights per year
(R. Cherry, pers. comm.). Substantial infrastruc-
ture exists on NAS Whiting, including buildings,
airstrips, and roads (405 ha, 25%). The remaining
1,218 ha is composed of open fields that occur
adjacent to runways (730 ha, 45% of total area)
and forested habitats (487 ha, 30% of total area),
which include a mixture of planted pine and
mature pine stands and patches of native scrub oak
habitat (Greene et al. 2008). Forested habitats are
managed through infrequent thinning, clear cut-
ting, and prescribed fire. However, stand quality
degrades rapidly without regular disturbance such
as fire or thinning, resulting in marginal habitat
conditions for gopher tortoises in most of the
forested habitats across the installation. Open
fields are mowed monthly during spring and
summer to maintain vegetation height require-
ments necessary for installation operations. These
open fields are the primary habitats on the
installation with the ground forage necessary to
support tortoises. Mowing is typically excluded
within small buffers around each marked tortoise
burrow (Smith et al. 2015), creating spatial
heterogeneity within the mowed fields. Although
234 tortoise burrows were detected at NAS
Whiting during a 2011 survey, only 58 tortoises
were documented (24.8% occupancy rate; Tuber-
ville and Grosse 2011). Because gopher tortoises
maintain more than one burrow, occupancy rates
are typically well below 100% and vary because of
a number of factors, including habitat quality
(McCoy and Mushinsky 1992). Gopher tortoises at
NAS Whiting occur in relatively isolated clusters
across the installation, with most active burrows
occupying airfields and rights-of-way or the
immediately adjacent forest (Fig. 1).
Holley OLF is a 283-ha decommissioned
auxiliary airfield with no active infrastructure
(Fig. 2). Although small planes may use the
airstrip for low approaches, it is not actively used
for ground training. Unused airstrips and roads
compose 28 ha (10%) of the total area. The
remaining 90% of the property consists of mature
pine stands (170 ha), open field (99 ha), and native
793White and Tuberville � AVIAN USE OF GOPHER TORTOISE BURROWS
scrub oak (14 ha; Greene et al. 2008). Addition-
ally, Holley OLF features two ephemeral wetlands
in the southeastern and southwestern edges of the
property. Mature pine stands are burned infre-
quently and open fields are mowed using a similar
regime as NAS Whiting. Tuberville and Grosse
(2011) recorded 109 burrows with an occupancy
rate of 19.2% (21 tortoises). Like NAS Whiting,
FIG. 1. Distribution of burrows of gopher tortoises on NAS Whiting in 2011 in Santa Rosa County, Florida. Top image
depicts occupied tortoise burrows detected during a survey in 2011 to illustrate the fragmented distribution of tortoises across
the installation. Inset (bottom) shows focal burrows monitored with wildlife cameras October 2013–September 2014 in the
South Field.
794 THE WILSON JOURNAL OF ORNITHOLOGY � Vol. 129, No. 4, December 2017
tortoise burrows are primarily in open field areas
surrounding the airstrip (Fig. 2), although the
native scrub oak habitat canopy remains open and
also supports some tortoises.
Burrow Monitoring.—We monitored active
gopher tortoise burrows at both NAS Whiting
and Holley OLF using remote wildlife cameras
(TrophyCam model 119736C, Bushnell Outdoor
Products, Overland Park, KS, USA) during
October 2013–September 2014. Cameras were
placed only at active burrows and relocated as
needed as tortoises shifted burrows. Active
FIG. 2. Distribution of occupied burrows of gopher tortoises (circles) detected in a survey in 2011 and focal burrows
monitored with wildlife cameras October 2013–September 2014 on Holley OLF military installation in Santa Rosa County,
Florida.
795White and Tuberville � AVIAN USE OF GOPHER TORTOISE BURROWS
burrows are not always occupied but exhibit recent
signs of tortoise activity on the apron (the mound
of sand outside burrow entrance), such as tracks or
fresh sand from digging. We positioned cameras to
maximize the view of both the entrance and apron.
We programmed each camera to capture a burst of
three photos with 5-sec intervals between each
triggering event. We visited the installations every
4–6 weeks to check cameras and download photos.
At NAS Whiting, we maintained 7–10 cameras
among two clusters of burrows (~35 m apart) at the
southern edge of the South Field (Fig. 1 inset) for a
total of 3,329 camera days (i.e., sum of days each
camera was operational). At Holley OLF, we
operated 7–9 cameras at active burrows (Fig. 2) for
a total of 2,668 camera days. Total camera
numbers operational at each site at any given time
varied because of active burrow availability,
camera malfunction, and inclement weather con-
ditions (i.e., flooding of monitored burrows and
associated cameras).
Data Summary and Analysis.—We visually
inspected all photos captured on all cameras. For
each photo with a bird, we identified the
individual(s) to species when possible. Individuals
that could not be identified by us or by
ornithologists we consulted were excluded from
the analyses. For each individual, we recorded the
date, study site, burrow ID, and behavior of the
individual. Upon reviewing photos, we identified
three behaviors of birds that were repeatedly
detected by wildlife cameras at tortoise burrows
or aprons: foraging, wing-flashing, and dust
bathing. Foraging behaviors included observations
of birds with beak to the ground, scratching in the
sand, or with an insect or other prey item in its
beak. Wing-flashing is a type of displaying
behavior typical in mockingbirds although its
function is not well-understood (Hailman 1960,
Hayslette 2003). Wing-flashing is characterized by
both wings being opened upwards towards the
back in a series of quick, jerky movements, then
closed. Dust bathing, which birds perform for
feather maintenance, parasite control, and thermo-
regulation (Elphick et al. 2001), involved birds
clearly agitating the sand and flapping their wings.
All other behaviors, such as resting or sitting on
the apron, were classified as unknown.
We quantified the number of newly detected
bird species each month at gopher tortoise burrows
at each installation to develop species accumula-
tion curves for each site. To create the curves, we
pooled data from cameras at each installation to
calculate the cumulative number of species
detected across all monitored burrows. To compare
the frequency of burrow use or burrow visitation
among bird species (irrespective of site), we
recorded the number of days each species was
detected at any monitored burrow at either site
(max 1 visit per day, with data pooled across all
burrows at both sites). Data were pooled because
of the close proximity of cameras, vagility of birds,
and inability to distinguish individuals of same
species in photos. Thus, reported visitation rates
are conservative and underestimate total visitation
by birds.
To test for differences in total bird visitation
frequency between Holley OLF and NAS Whiting,
we used chi-square analysis to compare the
observed number of visits by birds that were
detected at burrows at each site to expected
frequencies that accounted for differences in
survey effort (i.e., camera days) between sites.
Additionally, we compared observed species
richness and number of unique species at each
site to expected values (also corrected for
differences in survey effort) using chi-square
analysis to test for differences between sites. All
analyses were performed in program R (R Core
Team 2008).
RESULTS
Monitoring duration varied among burrows
because of changes in tortoise activity or occu-
pancy status at monitored burrows. During the 12-
month study, we monitored a total of 15 burrows at
NAS Whiting for an average of 230 6 96 days
(mean 6 1 SD) per burrow. At Holley OLF, we
monitored 18 burrows for an average of 147 6 78
days per burrow. In total, we documented 599
visits by 33 species of birds representing 16
taxonomic families. We were unable to identify
birds to species for 26 visits, which were excluded
from further analysis. Twenty species (60.6%) had
not previously been reported in the literature as
associates of tortoise burrows. Species document-
ed included year-round residents (n ¼ 18), winter
residents (n ¼ 11), summer residents (n ¼ 2), and
migrants (n ¼ 2, species whose migration route
796 THE WILSON JOURNAL OF ORNITHOLOGY � Vol. 129, No. 4, December 2017
passes through the Florida Panhandle; Sibley
2000).
Although Holley OLF tended to have greater
bird diversity than did NAS Whiting in all metrics
we calculated, most comparisons were not statis-
tically significant. We documented 25 bird species
representing 14 families at Holley OLF and 19
species representing 10 families at NAS Whiting
(Table 1), but species richness was not significant-
ly different between the two sites (X2¼ 2.292, P¼0.13; Table 1). Eleven bird species (33%) were
documented at both Holley OLF and NAS
Whiting. More species were unique to Holley
OLF (14 species or 42%) than to NAS Whiting (8
species, 24%), but these differences were not
statistically significant (X2 ¼ 4.500, P ¼ 0.086).
However, we did observe significantly more visits
to tortoise burrows by birds at Holley OLF than
NAS Whiting (n ¼ 330, n ¼ 243 visits,
respectively), even after survey effort was ac-
counted for (X2 ¼ 39.748, P , 0.001). At Holley
OLF, species richness continued to increase
throughout the monitoring period. In contrast,
species richness at NAS Whiting plateaued
halfway through the monitoring period (Fig. 3),
suggesting additional monitoring was unlikely to
result in additional species detected at burrows of
gopher tortoises.
We calculated species-specific frequency of
burrow use as the number of days a species was
documented visiting any monitored tortoise bur-
row at either site (Fig. 4). Most species (n ¼ 25;
76%) were documented at burrows ,10 days
during the 12-month monitoring period. However,
some species were frequent visitors to tortoise
burrows, including Savannah Sparrows (Passer-
culus sandwichensis; 60 days), Northern Mock-
ingbirds (Mimus polyglottos; 41 days), Vesper
Sparrows (Pooecetes gramineus; 33 days), Wild
Turkeys (Meleagris gallopavo; 31 days), and
Eastern Bluebirds (Sialia sialis; 28 days). Seasonal
residents and migrants were on average more
frequent users of tortoise burrows or aprons than
year-round residents (mean¼ 12.6 6 20.9 days vs.
10.3 6 11.1 days, respectively). However, across
species, year-round residents were more consistent
visitors of the tortoise burrow or apron than
seasonal residents and migrants (standard devia-
tion ¼ 11.1 days vs. 20.9, respectively).
Most birds were observed using the burrow
apron rather than the tortoise burrow itself; none
were observed entering the burrow. Activity of
birds during most visits to burrow aprons could not
be categorized (493 of 573 visits). However, for
visits in which activity could be categorized (80
events), foraging was the most commonly ob-
served behavior (n ¼ 65 events). We documented
13 bird species foraging at tortoise burrows, 2
species dust-bathing (4 events), and only 1 species
displaying (11 events; Table 1).
DISCUSSION
Ours is the first study to report such high usage
of gopher tortoise burrows by birds. Based on the
number of visits detected and the diversity of
species observed visiting burrows, we suspect the
results of our study are not anomalous. Although
many species were recorded only once or twice
based on our conservative calculation of visits
(max of one visit per species per day), Savannah
Sparrows and the Palm Warblers were detected at
least 60 and 64 days respectively. Eastern
Bluebirds, Wild Turkeys, Northern Mockingbirds,
and Vesper Sparrows were also recorded .25
monitoring days. We observed only one bird
species that had previously been categorized as a
‘frequent’ visitor to gopher tortoise burrows—the
Northern Bobwhite (Colinus virginianus; Jackson
and Milstrey 1989).
Camera monitoring also revealed a variety of
uses of tortoise burrow aprons by birds. We
documented birds foraging, dust bathing, and
displaying. Mammal and reptile use of burrows
for overwintering habitat, foraging, and refuge has
been relatively well documented (Landers and
Speake 1980, Eisenberg 1983, Milstrey 1986,
Jackson and Milstrey 1989, Jones and Franz 1990,
Lips 1991). In this study, the most commonly
observed activity by birds was foraging on the
burrow apron, which had not previously been
reported in the literature. Species observed at
tortoise burrows in this study ranged widely in
their dietary preferences. Most species (n¼ 21) are
omnivorous, subsisting either primarily on inver-
tebrates or seeds but adjusting their diets season-
ally with availability of other forage options. Of
the remaining species with more specialized diets,
seven were insectivorous, two were granivorous,
and three were carnivorous (Rodewald 2015).
Tortoise burrows host an abundance of inverte-
797White and Tuberville � AVIAN USE OF GOPHER TORTOISE BURROWS
TABLE 1. Bird species documented using remote-sensor wildlife cameras at burrows of gopher tortoises during October
2013–September 2014 at two Department of Navy installations (NAS Whiting and Holley OLF) in Santa Rosa County,
Florida. Residency classified based on species distribution or migrancy status in the Florida Panhandle in the given season
(Sibley 2000).
Common name Scientific name Holley OLF NAS Whiting Residencya Behaviorb
Gallinaceous birds
Northern Bobwhitec Colinus virginianus X YR F(4)
Wild Turkeyc Meleagris gallopavo X X YR F(6), DB(1)
Doves
Common Ground-Dovec Columbina passerina X YR
Mourning Dovec Zenaida macroura X YR F(1)
Plovers
Killdeer Charadrius vociferous X YR
Wading Birds
Cattle Egret Bubulcus ibis X YR
Raptors
Red-tailed Hawk Buteo jamaicensis X X YR
Great Horned Owl Bubo virginianus X YR
American Kestrel Falco sparverius X YR
Crows
American Crowc Corvus brachyrhynchos X X YR F(1)
Wrens
House Wren Troglodytes aedon X WR F(1)
Carolina Wrenc Thryothorus ludovicianus X YR F(1)
Thrushes
Eastern Bluebirdc Sialia sialis X X YR F(31)
Swainson’s Thrush Catharus ustulatus X M
American Robinc Turdus migratorius X X YR
Mockingbirds and Thrashers
Gray Catbirdc Dumetella carolinensis X WR
Brown Thrasherc Toxostoma rufum X X YR
Northern Mockingbird Mimus polyglottos X YR F(7), WF(11)
Warblers
Palm Warbler Setophaga palmarum X X WR F(6)
Pine Warblerc Setophaga pinus X YR F(2)
Yellow-rumped Warbler Setophaga coronata X WR
Prairie Warbler Setophaga discolor X M
Sparrows
Chipping Sparrow Spizella passerina X X SR
Field Sparrow Spizella pusilla X WR
Vesper Sparrow Pooecetes gramineus X X WR F(1), DB (3)
Savannah Sparrow Passerculus sandwichensis X X WR F(3)
Grasshopper Sparrow Ammodramus savannarum X WR
LeConte’s Sparrow Ammodramus leconteii X WR
Song Sparrow Melospiza melodia X WR
White-throated Sparrow Zonotrichia albicollis X WR
Cardinal and Buntings
Northern Cardinal Cardinalis cardinalis X X SR
Indigo Buntingc Passerina cyanea X YR
Blackbirds
Red-winged Blackbird Agelaius phoeniceus X YR
a Residency status classified as year-round resident (YR), a summer migrant (SR), a winter resident (WR), and migrant (M; Sibley 2000).b Behaviors classified were foraging (F), dustbathing (DB), and wing-flashing (WF). Number of detected events in photos given in parentheses.c Species previously documented at burrows of gopher tortoises (Jackson and Milstrey 1989 and references therein).
798 THE WILSON JOURNAL OF ORNITHOLOGY � Vol. 129, No. 4, December 2017
FIG. 3. Species accumulation curves for birds detected at burrows of gopher tortoises at NAS Whiting and Holley OLF
military installations, Santa Rosa County, Florida using remote wildlife cameras October 2013–September 2014.
0
10
20
30
40
50
60
70
detisiVsyaDforeb
muN
Bird Species
FIG. 4. Visitation frequency of bird species at burrows of gopher tortoises at NAS Whiting and Holley OLF military
installations in Santa Rosa County Florida. Frequencies represent the number of monitoring days during October 2013–
September 2014 that each species was documented at any burrow at either installation (max one visit per day).
799White and Tuberville � AVIAN USE OF GOPHER TORTOISE BURROWS
brate species (Young and Goff 1939), some of
which may be attracted to the unique microclimate
offered by the burrow and its apron (Kaczor and
Hartnett 1990, Pike and Mitchell 2013) or to the
presence of tortoise feces as a nutrient resource
(Lips 1991). These insects can in turn attract
insectivorous birds. Likewise, the greater concen-
trations of seeds of legumes and fruits found in
tortoise feces that are often deposited in the burrow
vicinity (Jackson and Milstrey 1989, Boglioli et al.
2000) provide food resources for granivorous
birds. We suggest that given the diversity and
abundance of forage options at gopher tortoise
burrows, the sandy aprons (which can be up to 1
m2; Kaczor and Hartnett 1990) may serve as visual
cues for birds.
Other uses of gopher tortoise burrows by birds
reported in the literature or anecdotally include use
of burrows by Bachman’s Sparrows (Peucaea
aestivalis) as refuge from avian predators (Dean
and Vickery 2003). Additionally, Florida Scrub-
Jays (Aphelocoma coerulescens) have been ob-
served entering gopher tortoise burrows, presum-
ably as a refuge, after being experimentally
translocated from their home territory (R. Bow-
man, pers. comm.). Similarly, burrows of desert
tortoises (Gopherus agassizii) in the U.S. south-
west provide shelter from extreme heat for several
local bird species, including Horned Larks (Ere-
mophila alpestris) and Black-throated Sparrows
(Amphispiza bilineata; Walde et al. 2009, 2016).
Burrows of other fossorial species, including the
European rabbit (Oryctolagus cuniculus) and the
aardvark (Orycteropus afer), are frequently used
for shelter by both avian and non-avian fauna
(Galvez Bravo et al. 2009, Whittington-Jones et al.
2011). Our study adds to the growing body of
evidence that burrows of fossorial animals can
serve as an important resource for sympatric
species.
Although the species richness we observed at
NAS Whiting and Holley OLF represents only a
fraction of annual bird richness documented in the
county during the same monitoring period as this
study (33/253; eBird 2016), the diversity of birds
documented at tortoise burrows and the number of
visits detected was surprising. As expected,
burrow visitation frequency by birds was signifi-
cantly greater at Holley OLF than Whiting OLF
and may reflect overall patterns of bird diversity
between the two sites. Presumably, the lower
visitation frequency at Whiting OLF is because of
increased human activity and greater aircraft
training intensity, although our study was not
designed to test this hypothesis. However, the
sheer number of flights (average 500/day) and the
low altitude of aircraft near monitored gopher
tortoise burrows would have created chronic noise
disturbance. Although experimental studies are
limited, accumulating evidence indicates that noise
is an important determinant of habitat quality for
wildlife (particularly birds) and that birds may
avoid areas with high noise disturbance or alter
their behavior or activity patterns in response to
noise disturbance, including those caused by
military aircraft (Smit and Visser 1993, Pepper et
al. 2003, Barber et al. 2010).
We also detected greater bird species richness,
more bird families, and more unique bird species
at Holley OLF than NAS Whiting. While these
trends were not statistically significant, they may
be of biological relevance. Given the lower
monitoring effort at Holley OLF, its smaller size,
and that it is almost completely surrounded by
residential development (Fig. 2), it is remarkable
that we observed bird species richness that is at
least on par with that detected at the much larger
NAS Whiting. We suspect that the diversity of
habitat types in close proximity to each other, in
combination with low training intensity, collec-
tively contributed to the diversity of birds detected
at gopher tortoise burrows at Holley OLF. In
addition, the more urbanized surroundings of
Holley OLF may have concentrated species within
its boundaries by providing an oasis. Additionally,
avifauna at Holley OLF may have benefited from
its proximity to Eglin Air Force Base, which has
some of the largest tracts of intact longleaf pine
flatwood forest in the region and is only 2 km from
Holley but .10 km from NAS Whiting (Jacobson
and Marynowski 1997). Avifaunal richness in-
creases with proximity to protected areas (Loss et
al. 2009), and the proximity of Holley OLF to
Eglin AFB could contribute to the high level of
species richness. Previous studies have also noted
the value of DoD lands to conservation of avifauna
(Nott et al. 2003, Eberly and Keating 2006, Rivers
et al. 2010). Our findings help underscore the
importance of even small protected areas in
supporting local biodiversity (Crooks et al.
2004), especially in proximity to other protected
lands.
800 THE WILSON JOURNAL OF ORNITHOLOGY � Vol. 129, No. 4, December 2017
The value of military lands in sustaining
biodiversity, including rare and at-risk species, is
widely recognized (NatureServe 2004, Stein et al.
2008). In fact, DoD lands harbor more rare and at-
risk species than any other federal agency in the
United States (Stein et al. 2008), placing a
disproportionate burden of management for these
species on Department of Defense, which commits
more than $112 million to conservation and
management of these species a year (Khoury and
Leone 2015). Balancing the sometimes-conflicting
missions of maintaining military readiness and
conserving biodiversity is becoming increasingly
difficult as training demands on installations
increase at the same time land use changes outside
installations continue to erode regional biodiversi-
ty and ecological integrity (Lee Jenni et al. 2012).
In addition, other demands are being placed on
installations, including increased contribution to
energy conservation initiatives through on-site
production of renewable energy (Booth et al.
2010, Van Broekhoven et al. 2012). For example,
since concluding our monitoring project, a large
portion of Holley OLF where gopher tortoises
occurred has been designated for solar production,
resulting in displacement of resident tortoises and
potentially negatively impacting other species that
use their burrows. As a growing number of
military installations are repurposed (Burton and
Williams 2001), particularly those that have been
decommissioned or no longer contribute to
changing military training needs, we hope that
the potential contribution of these lands to the
biodiversity mission of DoD will continue to be
recognized. As DoD lands host some of the most
biodiverse habitats in the country, preserving them
when they are past their military use may be key to
continued preservation of the species that depend
on them (Havlick 2007, 2011).
Conclusions
Although our results represent just 1 year of
monitoring, they reveal a heretofore underappre-
ciated interaction between birds and gopher
tortoise burrows, the significance of which remains
unknown. Protection of gopher tortoises on
military installations may have positive effects on
bird conservation, aligning with the ecosystem or
community approach to conservation by the
military laid out by Boice (1999). Our findings
indicate that further non-invasive monitoring is
warranted to better understand the role of ecosys-
tem engineers on the vertebrate community,
especially in remnant natural areas and military
lands. We recommend that future controlled
studies be designed explicitly to quantify the
influence of gopher tortoises and their burrows on
local bird species richness and identify mecha-
nisms contributing to such patterns. Further, use of
video clips instead of photos, would be more
effective for understanding bird usage of tortoise
burrows and may clarify much of the ‘unknown’
behavior we observed in this study.
ACKNOWLEDGMENTS
Funding and support for this project was provided by the
Department of Navy (Agreement Number W9126G-13-2-
0027) and by Department of Energy under award DE-FC09-
07SR22506 to the University of Georgia Research Founda-
tion. We thank R. Cherry for project assistance with logistics
and installation access, R. Smith for regional-level support,
K. Buhlmann for field help and guidance setting up cameras,
and M. McPherson for field assistance. We also thank S.
Pruett, R. Cooper, and B. DeGregorio for donating their time
to help two herpetologists identify birds and to R. Chandler
for encouraging us to publish these findings. Finally, we
would like to thank R. Bowman and two anonymous
reviewers for their invaluable feedback and reviews of an
earlier version of this manuscript.
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