Florida Grasshopper Sparrow Distribution, Abundance, and Habitat Availability
Michael F. Delany, Matthew B. Shumar, Molly E. McDermott, Paul S. Kubilis, James L. Hatchitt, and Rosanna G. Rivero
Southeastern Naturalist, Volume 6, Number 1 (2007): 15–26
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2007 SOUTHEASTERN NATURALIST 6(1):15–26
Florida Grasshopper Sparrow Distribution, Abundance,
and Habitat Availability
Michael F. Delany1,*, Matthew B. Shumar2, Molly E. McDermott3,
Paul S. Kubilis1, James L. Hatchitt4, and Rosanna G. Rivero1
Abstract - Remote sensing, geographical information system applications, and
ground and aerial assessments revealed a fragmented distribution of 44,933 ha of
potential habitat for the endangered Ammodramus savannarum floridanus (Florida
Grasshopper Sparrow) with most of this habitat (30,262 ha, 67%) located on conservation
lands. A continued decrease in available habitat since 1996 was indicated.
Searches of potential habitat and information from surveys at known locations found
278 male Florida Grasshopper Sparrows at seven sub-populations during 2004. No
previously unknown breeding aggregations were found. The current distribution
evinces a considerable contraction in range compared to historic distribution; however,
other breeding aggregations may exist on private property (10,718 ha) where
access was denied. Three formerly large sub-populations on Avon Park Air Force
Range have declined and are now near extirpation. The low number of individuals
and the paucity and fragmented distribution of suitable dry prairie will be limiting
factors for recovery of this sedentary subspecies. Habitat expansion and management,
and demographic improvements at existing locations may restore some Florida
Grasshopper Sparrow sub-populations. Large areas (> 377 ha) of protected potential
habitat in Manatee, DeSoto, and Glades counties offer the best opportunities for the
establishment of additional sub-populations (> 50 pairs) to achieve recovery goals.
The cooperative effort of public land managers from various agencies and of private
landowners will be needed to prevent the extinction of this bird.
Ammodramus savannarum floridanus Mearns (Florida Grasshopper
Sparrow) is an endangered subspecies endemic to the south-central prairie
region of Florida (USFWS 1999). Breeding aggregations (sub-populations)
are known from only 6 locations, and fewer than 1000 individuals may exist
(Delany et al. 1999). The recovery objective is to down-list the sparrow to
threatened when > 10 protected locations contain stable, self-sustaining subpopulations
of > 50 breeding pairs (USFWS 1999). However, only two
extant sub-populations—Three Lakes Wildlife Management Area (WMA)
and Kissimmee Prairie Preserve State Park—meet recovery criteria. One
other protected sub-population occurs on the Prairie Lakes Unit of Three
Lakes WMA, and 3 sub-populations occur on Avon Park Air Force Range.
Florida Grasshopper Sparrows on protected lands are monitored with annual
1Florida Fish and Wildlife Conservation Commission, 4005 South Main Street,
Gainesville, FL 32601. 2PO Box 32, Donegal, PA 15628. 343 Francis Street,
Uniontown, PA 15401. 4Armasi Inc., 3966 Southwest 98th Drive, Gainesville, FL
32608. *Corresponding author - mike.delany@myFWC.com.
16 Southeastern Naturalist Vol. 6, No. 1
point-count surveys, and grassland habitat is maintained for sparrows with
prescribed fire every 2 to 3 years (Delany et al. 1999). Basic information on
population trends and habitat use is needed to develop and implement
conservation strategies for the sparrow (USFWS 1999).
Florida’s dry prairie is a variable and poorly known suite of plant communities
(Bridges and Reese 1999). The habitat type is characterized as flat,
open expanses dominated by fire-dependent grasses, Serenoa repens (Bart.)
Small (saw palmetto), and low shrubs (Abrahamson and Hartnett 1990). Dry
prairie occupied by Florida Grasshopper Sparrows (Fig. 1) is treeless and
ranges from thick (34% shrub cover), low (57 cm) saw palmetto scrub to
grass pastures with a sparse (< 10% shrub cover) or patchy cover of shrubs
and saw palmetto (Delany et al. 1985). The area of native prairie in Florida
has been greatly reduced by agriculture (Davis 1967), and this probably
caused the extirpation of the sparrow from some former breeding locations
(Delany and Linda 1994). The conversion of natural habitats on private
lands in south-central Florida to agriculture and urban development is accelerating
(Kautz 1998, Kautz et al. 1993), and continued habitat fragmentation
will have detrimental effects on the Florida Grasshopper Sparrow (Perkins et
Potential habitat needs to be identified and searched for additional Florida
Grasshopper Sparrows (Delany et al. 1999, USFWS 1999). Our objectives
were to ascertain the current location of potential habitat for Florida Grasshopper
Sparrows in south-central Florida and determine the distribution and
abundance of the subspecies. We used remote sensing and GIS applications to
Figure 1. Dry prairie on Avon Park Air Force Range, Highlands County, FL. The
location was dominated by saw palmetto and native grasses, and occupied by Florida
Grasshopper Sparrows. Photograph © by Barry Mansell.
2007 M.F. Delany et al. 17
identify and map potential habitat. Areas of potential habitat were verified and
searched for Florida Grasshopper Sparrows, and information was obtained on
the status of sub-populations on protected lands.
Potential habitat for Florida Grasshopper Sparrows was estimated from a
consensus of several data sources and confirmed by ground and aerial
assessments. We obtained digital land-cover information for south-central
Florida (30-m resolution, 1994 and 1995 Landsat Thematic Mapper data)
processed into standard land-cover types, and a data file of Universal Transverse
Mercator (UTM) coordinates for 1672 individual Florida Grasshopper
Sparrow locations derived from point-count surveys and banding data from
across all habitat occupied during 1996–1999 (Delany et al. 1999). Using
ArcView (ESRI 1990) software, the Landsat land-cover file was overlain on
the file of sparrow locations to determine the dominant land cover of occupied
areas. Water Management District land-use land-cover (LULC) files
from 1995 identifying pasture, shrub and brush land, and mixed rangeland
categories also were projected to create a complementary profile to verify
land-cover results from the Landsat analysis. Areas similar in composition
to occupied locations (potential habitat) were identified in Florida south of
28o 30' latitude, and polygons surrounding each area were digitized using
ArcView (ESRI 1990). Because A. savannarum Gmelin (Grasshopper Sparrows)
avoid small grassland patches and forested edges (Vickery 1996),
polygons < 100 ha or with a narrow configuration (< 1128 m wide, the
diameter of a 100-ha circle) were excluded from the dataset.
Because the Landsat dry prairie land-cover category included opencanopy
pineland (10–15% cover) unsuitable for Grasshopper Sparrows,
scanned aerial photographs (3-m resolution, USGS 1995 digital orthographic
quarter quads) were geo-referenced to the polygon vector data to
detect trees. Polygon outlines were viewed with aerial photograph backdrops
and visually inspected. Polygons containing trees were eliminated
from the dataset or redrawn to exclude tree cover. Distances between the
edges of polygons were measured using ArcView (ESRI 1990). Landowners
of potential habitat were determined using Land Use Mapping System
(LUMS) property appraiser data files and county plat maps.
The dry prairie land-cover category and Ilex glabra [L.] Gray
(gallberry)/saw palmetto compositional group (a shrub and graminoid
community associated with wet flatwoods) were portrayed when Florida
Grasshopper Sparrow locations were viewed in context with the Landsat
land-cover data. However, some occupied areas showed very little of either
land cover. The LULC data generally coincided with the satellite data, but
also indicated some potential habitat where there was no indication of the
dry prairie or gallberry/saw palmetto land coverage based on the Landsat
data. In this case, the LULC data were presumed to be something other
than potential habitat and were not included. In cases where the amount of
18 Southeastern Naturalist Vol. 6, No. 1
relevant Landsat coverage was sparse (< 25%) but overlain by relevant
LULC data, it was included in the delineation of potential habitat.
Landowners and managers were mailed information about the Florida
Grasshopper Sparrow and contacted by telephone for permission to verify
habitat suitability and conduct sparrow surveys. We visited areas of potential
habitat to assess their suitability and determine if a search for Florida
Grasshopper Sparrows was appropriate. Habitat evaluations were based on:
1) vegetative cover—the presence of species characteristic of the dry prairie
plant community and the absence of trees; 2) vegetation structure indicative
of recent fire—grasslands that were low in height (< 100 cm) with about
20% bare-ground; and 3) landscape context—large (> 100 ha) areas with a
configuration that minimizes edge, and proximity to other patches of suitable
habitat. Our criteria for designating potential habitat were similar to
those used by Shriver and Vickery (1999) to describe “high quality habitat”
for Florida Grasshopper Sparrows.
From 7 April to 22 May 2004, surveys were conducted between 0650 and
0955 by two to four searchers who walked transects at 200-m intervals across
potential habitat, stopping frequently to make visual and auditory observations.
Transect start and end points were recorded with a GPS unit (Magellan
GPS 300 and 315). Surveys were conducted during low-wind (< 10 km/hr)
conditions and during mornings with no fog or precipitation. A tape recording
of the territorial song of the male Grasshopper Sparrow was used to elicit
responses from any males in the area. Information was obtained on the
presence or absence of Florida Grasshopper Sparrows, survey location, and
general habitat description. Information on the status of populations on public
lands during 2004 was obtained from land managers who conducted pointcount
surveys according to Walsh et al. (1995). Point-count survey methods
were the same for all years and locations (three 5-minute unlimited-distance
observations during the breeding season); however, the number of points
sampled differed by year at some locations.
Because of concerns of land-use restrictions if an endangered species
was found, most private landowners denied access to verify habitat (40
polygons), and owners of four polygons could not be contacted. For these
areas, visual assessments were conducted aerially from a Bell Jet Ranger
helicopter during 16.1 hours of flight time at an altitude of < 122 m from 7
February to 28 March 2006. Flights were first made over areas of Three
Lakes WMA and Kissimmee Prairie Preserve State Park currently occupied
by Florida Grasshopper Sparrows, to develop an aerial search image
for suitable habitat. A GPS receiver and topographical maps were used to
navigate to the center point of each polygon of potential habitat where
access was denied. Large polygons were circled until a complete view of
the area was obtained. “High quality” habitat identified during 1996 aerial
assessments by Shriver and Vickery (1999) also were visited to determine
their current suitability, and we searched for additional potential habitat
2007 M.F. Delany et al. 19
Remote-sensing and GIS applications, and ground and aerial verification
revealed a fragmented distribution of potential habitat (44,933 ha)
for Florida Grasshopper Sparrows (Fig. 2), with most of this habitat
(30,262 ha, 67%) on protected lands. Mean polygon size was 1248 ha (SD
= 1248, N = 36) and ranged from 233 to 5355 ha. Mean distance from the
edge of extant sub-populations to the edge of the nearest unoccupied
polygon was 10.4 km (SD = 9.01, N = 7) and ranged from 2.3 to 29.3 km.
Large-scale maps and landowner or manager contact information are
available from the senior author.
We searched for Florida Grasshopper Sparrows in 12 polygons, obtained
data for seven polygons on conservation areas that were sampled
during existing point-count surveys, and acquired information on a subpopulation
on private property (USFWS 2002) (Figs. 2 and 3). A total of
278 male Florida Grasshopper Sparrows were detected at seven disjunct
Figure 2. Areas
(36 polygons) of
for Florida Grasshopper
1994 and 1995
2004 ground and
2006 aerial assessments.
occupied by Florida
were searched but
no Florida Grasshopper
and light gray
20 Southeastern Naturalist Vol. 6, No. 1
sub-populations: Three Lakes WMA (2), Avon Park Air Force Range (3),
Kissimmee Prairie Preserve State Park (1), and the privately owned Beaty
Ranch (1; USFWS 2002). Sparrow occurrence on Kissimmee Prairie Preserve
State Park was considered to be one sub-population, and distribution
reflects the location of point-count survey sampling grids. Survey results
from 2004 are in Table 1, and specific locations of extant sub-populations
are shown in Figure 3. No previously unknown breeding aggregations were
Figure 3. Conservation areas (light gray), polygons of potential habitat (dark gray),
and locations of Florida Grasshopper Sparrows (black), 2004. For Avon Park Air
Force Range, locations are from top to bottom: Bravo Range, OQ Range, and Echo
Range. Florida Grasshopper Sparrows on Kissimmee Prairie Preserve State Park
were considered one sub-population.
2007 M.F. Delany et al. 21
found. For all potential habitat detected, Florida Grasshopper Sparrow subpopulations
occupied 10 polygons (20,852 ha), 11 polygons (13,364 ha)
were surveyed without detecting additional birds, and 15 polygons (10,718
ha) were unsearched.
Most potential habitat for Florida Grasshopper Sparrows occurred in
disjunct patches within the former dry prairie land cover mapped by Davis
(1967). Our delineation of potential habitat using remote sensing and GIS
applications detected four of the seven locations known to be occupied.
Bravo Range was not selected because the amount of relevant Landsat
coverage was sparse (< 25%) and not supported by LULC data. Though the
site was occupied, a high percentage of bare-ground cover at this military
target classified it as disturbed land marginally suitable for Grasshopper
Sparrows. The Prairie Lakes Unit of Three Lakes WMA was not selected
because of changes in vegetation since Landsat data were obtained. Rollerchopping
and prescribed fire since 1999 improved habitat for the sparrow,
and translocation of 18 juveniles to this location during 2001 and 2002
(Florida Fish and Wildlife Conservation Commission [FWC], Tallahassee,
FL, unpubl. data) may have established a new sub-population. The location
of an estimated 12–20 male Florida Grasshopper Sparrows in a 371-ha
Paspalum sp. L. (bahia grass) pasture and 3 males in an adjacent 17-ha
pasture on the Beaty Ranch in Okeechobee County (USFWS 2002) were not
detected in our search for potential habitat or during aerial surveys by
Table 1. Number of male Florida Grasshopper Sparrows detected during distribution and point
count surveys at all known locations, 1996–1998 and 2004. The number of point count stations
is in parentheses.
Males Males Prairie
Location County 1996–1998A 2004 (ha) Source
Three Lakes WMA S. Glass, FWCB
Main population Osceola 94 (161) 124 (169) 4000
Prairie Lakes Unit Osceola – 6 841
Avon Park Air Force Range J. Tucker, ABSC
Bravo Range Polk 21 (39) 1 (39) 581
OQ Range Highlands 49 (67) 4 (82) 700
Echo Range Highlands 67 (119) 10 (118) 1195
Kissimmee Prairie PreserveD Okeechobee 111 (137) 107 (188) 8470 P. Miller, DEPE
Adams RanchF Osceola – 18 171 This study
Beaty Ranch Okeechobee – 8 388 USFWS, unpubl.
AFrom Delany et al. (1999). Point count survey methods were the same as in 2004. Each point
sampled about 12 ha.
BFlorida Fish and Wildlife Conservation Commission.
CArchbold Biological Station.
DNot all available habitat was sampled. This population is probably much larger.
EDepartment of Environmental Protection.
FContiguous with main population at Three Lakes WMA.
22 Southeastern Naturalist Vol. 6, No. 1
Shriver and Vickery (1999). Improved pastures (plowed and planted with
non-native grasses) were not considered potential habitat for Florida Grasshopper
Sparrows (see Delany and Linda 1994). A breeding location in an
improved pasture on Kissimmee Prairie Preserve State Park was similarly
overlooked. Advantages and caveats associated with remote sensing and
GIS applications in ornithological research were reviewed by Shaw and
Atkinson (1990) and Glen and Ripple (2004). Despite some errors, Landsat
coverage supported by other relevant data sources were useful not only to
perform initial assessment of occupied and potential habitats, but also to
optimize the process of selection and delineation of these areas. However,
after this initial stage, ground and aerial assessments were the best methods
to verify habiat suitability and improved our results.
Searches of large areas of potential habitat on Myakka River State Park
(718 ha, Manatee County) and conservation easements in DeSoto County
(782 ha) (this study) and Glades County (2490 ha) (Delany et al. 2000) failed
to locate Florida Grasshopper Sparrows. Areas of seemingly potential habitat
are often unoccupied by the sparrow (Howell 1932, Walsh et al. 1995).
Some patches of dry prairie may be unused because of their isolation from
Historically, most dry prairie was found within the Kissimmee River
Basin and west of Lake Okeechobee (Davis 1967). Because of variation in
methods and the inclusion of different plant communities, estimates of the
extent of historical dry prairie and changes in coverage are difficult to
interpret. Kautz et al. (1993) calculated 830,000 ha of pre-settlement dry
prairie from Davis (1967), and used 1985–1989 Landsat imagery to estimate
561,114 ha of remaining dry prairie statewide in the 1980s. Shriver and
Vickery (1999) estimated that only 19% (156,000 ha) of the original dry
prairie remained in central peninsular Florida, and their aerial assessment of
eight counties identified 63,968 ha of “high-quality” habitat for Florida
Grasshopper Sparrows in 1996. Our estimate of 44,933 ha of suitable dry
prairie indicates a continued loss of potential habitat for Florida Grasshopper
Sparrows. Compared to results from Shriver and Vickery (1999), we
identified smaller patches of dry prairie and found potential habitat outside
their search area.
Previous information indicated a more widespread distribution of Florida
Grasshopper Sparrows (reviewed in Stevenson and Anderson 1994) and may
reflect a formerly greater coverage of dry prairie. The current distribution of
Florida Grasshopper Sparrows at only seven locations within about 900 km2
evinces a considerable contraction in range compared to their historic occurrence.
The six males found on the Prairie Lakes Unit of Three Lakes WMA
(3.2 km from the main population) may be a recently formed breeding
aggregation due to habitat improvements and translocation of sparrows. Not
all potential habitat was sampled at Kissimmee Prairie Preserve State Park,
so this sub-population is probably larger than our data indicate. All three
sub-populations on Avon Park Air Force Range have declined in size and are
2007 M.F. Delany et al. 23
near extirpation. Intermittent extirpations of small populations (< 10 individuals)
of grassland birds are to be expected (Curnutt et al. 1996); however,
the synchronous decrease of formerly large sub-populations (see Delany et
al. 1999, and Shriver and Vickery 1999) at Avon Park Air Force Range is
cause for concern.
The low number of Florida Grasshopper Sparrows and the paucity and
fragmented distribution of suitable dry prairie will be limiting factors for
recovery. Current protected areas of dry prairie may not provide adequate
habitat to meet recovery goals. In addition to Three Lakes WMA and
Kissimmee Prairie Preserve State Park, eight additional sub-populations of
> 50 breeding pairs are needed to down-list the sparrow to threatened
(USFWS 1999). A sub-population of > 50 breeding pairs of Florida Grasshopper
Sparrows may require 1348 ha of contiguous prairie habitat
(Delany et al. 1995). We found 12 polygons that met this size criterion,
with 11 located entirely or partly on protected lands, including 6 polygons
with extant sub-populations. One 1392-ha polygon of potential habitat was
located entirely on private property in southwest Highlands County.
Perkins et al. (2003) recommended 4000 ha of prairie to support a subpopulation,
but only three polygons of potential habitat met their size
criterion. Habitat expansion and management and demographic improvements
may restore Florida Grasshopper Sparrows on Avon Park Air Force
Range. With further land-management and translocation efforts, the Prairie
Lakes Unit of Three Lakes WMA also may support a sub-population of >
50 pairs. Because of its large size and protection, potential habitat on
Myakka River State Park (Manatee County) and conservation easements in
DeSoto and Glades counties offer the best opportunities for the establishment
of additional sub-populations to achieve recovery goals. However,
these locations were > 47.4 km from extant Florida Grasshopper Sparrows.
Banding studies indicated that dispersal limitations imposed by habitat
fragmentation may be problematic for the formation of new sub-populations
(Delany et al. 1995, Perkins and Vickery 2001, but see Miller 2006). The
distance between extant sub-populations and the nearest potential habitat
(> 2.3 km) may inhibit colonization. Although even low dispersal rates can
promote the persistence of meta-populations (Brown and Kodric-Brown
1977), recovery of this sparrow may require active translocation to facilitate
the formation of new sub-populations. The efficacy of experimental translocations
at Three Lakes WMA need to be evaluated. Methods and results of
translocations need to be thoroughly documented (Fischer and Lindenmayer
2000, Scott and Carpenter 1987), and pending evaluation, other locations
assessed for possible translocations. Without adequate habitat acquisition
and management to improve connectivity, translocation may be an important
alternative for saving endangered species (Lublow 1996).
Increasing the area of dry prairie and improving the connectivity of subpopulations
were the most effective management options for improving the
viability of the Florida Grasshopper Sparrow (Vickery and Perkins 2003).
24 Southeastern Naturalist Vol. 6, No. 1
Larger prairies (> 4000 ha) would support a greater number of sparrows, and
a concomitant increase in core area (> 400 m from edge) may improve
reproduction (Perkins et al. 2003). Because Grasshopper Sparrow density
and reproduction is usually negatively correlated with edge (Vickery 1996),
the shape of grasslands (perimeter to area ratio) should also be a factor in
land acquisition, restoration, and management.
Immediate and intensive efforts are needed to restore Florida Grasshopper
Sparrows on Avon Park Air Force Range. The sparrow appears to be responsive
to habitat improvements (Delany 1996, Perkins and Vickery 2005), and
management actions (e.g., adequate prescribed fire to reduce woody vegetation
and promote grass coverage, and removal of intervening and encroaching
woody vegetation) may promote optimal breeding conditions (see Delany and
Linda 1998a,b) and expand potential habitat. The feasibility of restoring
improved pastures to more prairie-like conditions should be investigated to
increase potential habitat in former dry prairie once occupied by Florida
Grasshopper Sparrows. Although plant species composition may differ from
native prairie, structural features of restored grasslands may provide suitable
breeding habitat for Grasshopper Sparrows (Fletcher and Koford 2002). The
removal of pine plantations to improve the connectivity of sub-populations
should be considered.
Other breeding aggregations may exist on unsearched private lands
where access was denied, and landowners should be contacted periodically
for permission to conduct surveys. Search efforts should be expanded to
include improved pastures with some remaining native vegetation that may
provide suitable breeding habitat, and Florida Grasshopper Sparrow reproductive
success in these improved pastures needs to be determined. The
cooperative effort of public land managers from various agencies as well as
private landowners will be needed to prevent the loss of this sparrow.
This study was funded by the Florida Nongame Wildlife Trust Fund and US Air
Force through US Army medical research acquisition activity award DAMD 17-00-2-
0023, and USFWS grant agreement 401815G180. We thank P. Ebersbach, P.B. Walsh,
S.M. Cumberbatch, T.F. Dean, K.B. Donnelly, and L.M. Torres, who effectively
promoted this effort. This publication does not necessarily reflect the position or policy
of the US Government, and no official endorsement should be inferred. We thank L.
Adams (Adams Ranch, Inc.), R. Bateman (Bright Hour Ranch), M. Chanen (Cargill
Fertilizer), G. Paul (Bob Paul, Inc.), R. Overstreet (Overstreet Ranch), C. Wilson (Latt
Maxcy Corp.), and M. Folk and S. Woiak (The Nature Conservancy’s Disney Wilderness
Preserve) for access to private property. M.H. Friedman and J.W. Tucker, Jr.
participated in surveys. T. Macklin piloted the helicopter and helped search for dry
prairie. J. Bridges, D. Donaghy, P. Miller, D. Myers, D. Smith, and W. VanGelder
provided logistical support. S. Glass, J. W. Tucker, Jr., and P. Miller provided
information about Florida Grasshopper Sparrow populations on public lands. K.E.
Miller, T.E. O’Meara, D.W. Perkins, J.F. Quinn, Jr., J.A. Rodgers, Jr., and two
anonymous reviewers commented on previous drafts of this paper.
2007 M.F. Delany et al. 25
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