The ATLSS Cape Sable Seaside Sparrow Breeding Potential Index Model
Basic Model Description
M. Philip Nott and Jane Comiskey
The Institute for Environmental Modeling
University of Tennessee, Knoxville
Knoxville, TN 37996-1610
(Copyright University of Tennessee - 1997)
Introduction:
As part of the Central and Southern Florida Comprehensive Study Review
(Restudy) several future water management regimes have been proposed.
Each of these scenarios will affect potential breeding activity of the
Cape Sable seaside sparrow (Ammodramus maritimus mirabilis)
disproportionately across its range. We consider each of three distinct
drainage basin zones currently containing known sub-populations of the
sparrow.
We briefly describe these in order of importance relative to current
total population level of the sparrow. The first of these areas
includes the core of the sparrow's range and lies within the Long Pine
Key / South Taylor Slough drainage basin (Ingraham Highway area).
Effects on this sub-population will be most significant to the population
as a whole. Secondly, the westernmost sub-population occupies the East
Slough drainage basin adjacent to the western edge of Shark's slough below
Tamiami trail. This sub-population has been most affected by changes in
water delivery since 1992 which restricted breeding activity and also
resulted in drastic changes in vegetation patterns (Nott et al. in
press). Finally, we consider the peripheral and highly fragmented
sub-population within North Taylor Slough (and the southern portion of
Northeast Shark Slough), which comprises only a small percentage of the
total population.
We express the effects of proposed scenarios as changes in the spatial
pattern of breeding potential with reference to these three drainage
basins with separate sub-populations. For brevity's sake we refer to
them as the core, western and eastern areas, respectively.
Methods:
We estimate a sparrow breeding potential index (BPI) for those
landscape cells which have the appropriate habitat type (Muhlenbergia
dominated prairie) or on which sparrows have been observed to nest. The
sparrow BPI model is driven by input data from the South Florida Water
Management Model (SFWMM). These data, which are provided as daily
water depths for each 2 x 2 mile area in the region covered by the
model, are processed by the ATLSS landscape model into finer resolution
hydrology. Water depths at the 500-m scale of resolution for ATLSS
index models are based on a pseudo-topographic map which incorporates
information from a 28.5-meter resolution vegetation map (see HYDRO___.DOC
for a more detailed description of high resolution hydrology and
pseudotopography).
The sparrow BPI reflects the duration and spatial extent of the annual
dry season during which the water level in any cell remains below the
nesting threshold level of 16cm. Computation of the BPI is based on
knowledge of how hydrologic factors affect sparrow breeding success,
including critical water level thresholds for each stage of the
breeding cycle. We use water depth estimates to make spatially explicit
predictions of the number of potential breeding cycles for each
landscape cell. Each cell will have 0, 1, or 2 complete (45-day) cycles
per breeding season.
A sparrow breeding cycle consists of a period of exploration/mating (10
days for first cycle, 5 days for subsequent cycles), nest building, egg
laying, incubation of eggs, hatching, nestling stage, walking stage,
and fledgling stage. For sparrows to raise young successfully, a
window of 45 successive dry days between January 1 and June 30 is required
for the fledglings to reach the walking stage. If a cycle is
interrupted by rising water levels before the walking stage, we assume
breeding was unsuccessful and the nestlings die. A new cycle begins
with the next dry day.
We overlay the computed brood cycle grid with a habitat-type map,
utilizing known habitat preferences for sparrow colonization to compute
breeding potential indexes from cell by cell brood cycle counts.
Sparrows nest on landscape cells of short hydroperiod marl prairie
characterized by dense stands of graminoid species (typically
Muhlenbergia), usually below 1-m in height, uninterrupted by higher
vegetation (trees or shrubs that would give potential predators a perch
from which to survey the nesting area.) The vegetation map used is the
April 1996 version of The University of Florida Land Cover Classification
developed to support the Florida Gap Analysis Program (FGAP) vegetation
map. When selecting Muhlenbergia-dominated cells, we
exclude those 500-m resolution cells with lower than 15% overall
Muhlenbergia content, as determined by the proportion of constituent
28.5-m resolution cells categorized as Muhlenbergia (type 33) in the
FGAP map. In addition we include only those cells which are elements
of appropriately sized larger clusters of Muhlenbergia cells. Breeding
potential values for each cell are weighted by the higher of two values:
the proportion of Muhlenbergia in that cell or a weighting factor
reflecting the number of sparrows observed nesting and how recently
birds were observed there.
Using BPI estimates for cells with preferred habitat in each drainage
basin, we plot time series graphs showing the percentage of available
habitat in which successful breeding occurred over the 31-year period
for which SFWMM simulated hydrology is available. Three-panel maps are
used to show spatial comparisons between breeding potential for two
scenarios and display the differences between them. We present maps
which represent 31-year averages, and also construct comparisons for
selected years (i.e. high, low and average rainfall years as well as
other years showing significant trends).
It is important to note that the sparrow BPI reflects the effect of
hydrologic conditions for individual years. Obviously, sequences of bad
years will have more serious effects than bad years interspersed among
a number of good years. In the latter case the population may recover
during the drier years. Some compensation for effects of successive
dry years is provided in the BPI by computing a multiplicative
weighting factor which represents the mean over previous simulation
years of a term reflecting short and long hydroperiod effects for each
cell.
Estimates of scenario effects on the temporal patterns of population size
require use of the individual based demographic model currently
being developed. As the duration of wet year sequences within any
scenario approaches the maximum life span of the sparrow, the
probability of local extinction increases.
References:
Nott, M.P., O.L. Bass, Jr., D.M. Fleming, S.E. Killeffer, N. Fraley,
L. Manne, J.L. Curnutt, T.M. Brooks, R. Powell and S.L. Pimm. 1997.
Water levels, rapid vegetational changes, and the endangered Cape
Sable seaside sparrow. Animal Conservation (in press).
Lockwood, J.L., K.H. Fenn, J.L. Curnutt, A. Mayer and D. Rosenthal.
1997. Natural history of the Cape Sable seaside sparrow. Wilson
Bulletin (in press).
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Output associated with the ATLSS Cape Sable Seaside Sparrow Breeding
Potential Index Model.
In accordance with ATLSS file naming conventions, each file name will
consist of the characters: UVXXYYZZ.EXT
"U" or "_" => the Base, typically F for the F2050 base
or E for the C1995 base
"V" or "_" => the alternative scenario or base
"XX" => "BC" for the ATLSS Cape Sable Seaside Sparrow
Breeding Potential Index Model
"YYZZ" => 4 character mnemonic, described below
"."
"EXT" = "PDF" or "TXT" or "DOC" => PDF, tabular text or documentation
===============================================================
ATLSS Cape Sable Seaside Sparrow Breeding Potential Index
1. Maps
Map outputs used to characterize results of the Cape Sable Seaside Sparrow
Breeding Potential Index Model will consist of eight image files in PDF
file format. Each map shows a "Set" of model results, comparing one SFWMM
hydrologic scenario to another, following the conventions for ATLSS comparisons
of two model runs. Each map has three panels. The left panel displays index
values for either an alternative or base scenario; the right panel displays index
values for a base scenario (e.g., the Future without Project Conditions Case, or
F2050). The middle panel displays the cell-by-cell difference between index values
for the two compared scenarios (e.g., ALT-5 minus F2050).
Grid cells in the left and right panels are color-coded to represent the
(positive) values of the displayed index, which range between 0 and 1. Cell
colors in the center panel represent either positive (shades of gold) or
negative (shades of blue) differences between index values displayed in the left
panel and those in the right panel. Color keys are provided at the bottom of
each map. Each map depicts the model area at either a Fine (500-meter x 500-meter)
or Coarse (2-mile) scale of resolution.
For each of six selected years, images will provide a spatial display of
index values for that year. In addition, an image file is provided for
the mean of all simulated years. The selected years include years with
high, low, and typical rainfall, and several additional years that serve
to highlight differences between the compared scenarios.
The mnemonic characters are composed according to the convention:
"YY" = Last two digits of the year
"ZZ" = CR - Coarse (2 mile) resolution,
FR - Fine (500 meter) resolution
Listing of ATLSS Cape Sable Seaside Sparrow map files:
File Name Time Period
------------ --------------------------------------------
UVBC69ZZ.PDF A High Rainfall Year (1969)
UVBC70ZZ.PDF Highlight Scenarios (1970)
UVBC77ZZ.PDF A Typical Rainfall Year (1977)
UVBC83ZZ.PDF Highlight Scenarios (1983)
UVBC90ZZ.PDF A Low Rainfall Year (1990)
UVBC95ZZ.PDF Highlight Scenarios (1995)
UVBCMYZZ.PDF Mean of All Years (1965->1995)
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2. Time Series
Time series sets associated with the ATLSS Cape Sable Seaside Sparrow
Breeding Potential Index will display breeding potential values for three
applicable subregions only. These show percentage of available habitat in
which successful breeding occurred for each year.
File Name Description
--------- --------------------------------------------------------
UVBCTSZZ.PDF Percentage of available habitat in which successful
breeding occurred for each year in each of three subregions.
3. Histograms
None.
4. Tables
None.