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FWS/OBS-82/ 10.51

SEPTEMBER 1983

HABITAT SUITABILITY INDEX MODELS:

CLAPPER RAIL

~~a.a and Wildlife Service

. Department of the Interior
This model is designed to be used by the Division of Ecological Services in

conjunction with the Habitat Evaluation Procedures.
HABITAT SUITABILITY INDEX MODELS: CLAPPER RAIL

by

James C. Lewis

and

Russell L. Garrison

Georgia Cooperative Wildlife Research Unit

School of Forest Resources

University of Georgia

Athens, GA 30602

Project Officer

Ca rro11 Cordes

National Coastal Ecosystems Team

U. S. Fish and Wildlife Service

1010 Gause Boulevard

Sl ide 11, LA 70458

Performed for

National Coastal Ecosystems Team

Division of Biological Services

Research and Development

Fish and Wildlife Service

U. S. Department of the Interior

Washington, DC 20240

FWS/OBS-82/10.51

September 1983
This report should be cited as:

Lewi s , J. C., and

clapper rail.

R. L. Garrison. 1983. Habitat suitability index models:

u. S. Dept. Int. Fish Wildl. Servo FWSjOBS-82jl0.51. 15 pp.
PREFACE

The habitat use information and habitat suitability index (HSI) model for the

clapper rail in this report are intended for use in impact assessment and habitat

management. The model was developed from a review and synthesis of existing

information and is scaled to produce an index of habitat suitability between a

(unsuitable habitat) and 1 (optimally suitable habitat) (U.S. Fish and Wildlife

Service 1981). Assumptions used to transform habitat use information into the HSI

model and guidelines for model application are described.

This model is a hypothesis of species-habitat relationships, not a statement

of proven cause and effect relationships. The model has not been field-tested, but

it has been applied to three sample data sets which are included. For this reason,

the U.S. Fish and Wildlife Service encourages model users to convey comments and

suggestions that may help increase the utility and effectiveness of this habitatbased approach to fi sh and wi 1dl i fe management. Pl ease send any comments or

suggestions you may have on the clapper rail HSI model to:

National Coastal Ecosystems Team

U.S. Fish and Wildlife Service

1010 Gause Boulevard

Slidell, LA 70458

iii

CONTENTS

PREFACE . . . . . . . . ACKNOWLEDGMENTS . . . .

HABITAT USE INFORMATIOI

Food Requi rements . . .

Cover Requirements . Fall-Winter Habitat Requirements

Interspersion . . . • . . • • • • . . . • . • . • • .

Spatial Requirements . HABITAT SUITABILITY INDEX (HSI) MODEL

Model Applicability ..... Model Description. . . . .• . ....•..

Suitability Index (SI) Graphs for Model Variables

HSI Determination ..... Field Use of the Model

Interpreting Model Outputs

REFERENCES . • . . . • . . . . . .

v

iii

vi

1

2

3

4

4

5

5

5

5

8

10

12

12

13
ACKNOWLEDGMENTS

Development of the habitat suitability index model and narrative for clapper

rail was monitored, expertly reviewed, and constructively criticized by Dr. Robert

B. Hamilton, Associate Professor of Wildlife Management, Louisiana State University, Baton Rouge; Tip Han, Wildlife Biologist, Georgia Department of Natural

Resources, Social Circle; and Fred Ferrigno, Wildlife Biologist, New Jersey Department of Environmental Protection, Tuckahoe. Thorough evaluations of model structure and functional relationships were provided by Dr. Carroll Cordes and Rebecca

Howard of the U.S. Fish and Wildlife Service, National Coastal Ecosystems Team.

Model and supportive narrative reviews were also provided by Regional personnel of

the U.S. Fish and Wildlife Service. Model development and publication were funded

by the U.S. Fish and Wildlife Service. Recent U.S. Department of Agriculture publications (Soil Conservation Service 1982a, 1982b) have been used to standardize

the use of Latin names in this report.

vi
CLAPPER RAIL (Rallus longirostris)

HABITAT USE INFORMATION

The clapper rail is a member of the order Gruiformes, family Rallidae. It

inhabits estuarine tidal salt and brackish coastal marshes along the Atlantic, Gulf

of Mexico, and Pacific coasts. ~'angold (1977) listed seven subspecies in the

coastal United States (Table 1). The light-footed and California subspecies are

classified as endangered under the Endangered Species Act of 1973 with populations

estimated at less than 250 (Wilbur et al. 1979; National Fish and Wildlife Laboratory 1980a) and 5,500 (National Fish and Wildlife Laboratory 198Gb), respectively.

The cl apper rail is grayi sh, gray-brown, or tan. It has a

slightly downcurved bill, flanks barred with white, and a short tail

revealing a white patch. Overall length ranges from 33 to 48 cm

inches), and bill length is greater than 5 cm (2.0 inches).

short neck, a

cocked upward,

(13.0 to 18.9

Table 1. Range of coastal subspecies of clapper rail (Rallus longirostris) within

the United States.

Common name (subspecies)

Northern clapper rail (~. 1. crepitans)

Wayne cl apper ra il (~. 1. waynei)

Mangrove clapper rail (~. 1. insularum)

Florida clapper rail (~. 1. scottii)

Louisiana clapper rail (~. 1. saturatus)

Light-footed clapper rail (~. 1. levi pes)

California clapper rail (~. 1. obsoletus)

1

Range

Maine to South Carolina

South Carolina to southern tip of

Florida

Southern tip of Florida and

Flori da Keys

Florida west coast

Florida Panhandle to Mexico

Southern California coast

San Francisco Bay area, California
The northern and Wayne clapper rails are the only coastal migratory subspecies

in the United States although some other subspecies undergo population shifts (Oney

1954; Stewart 1954; Adams and Quay 1958). The migratory subspecies primarily

winter from South Carolina to Florida, a few hundred kilometers south of their

nesting range. Northward migration begins about April, and southward migration

begins in September.

Typical rail habitat in Georgia consists of 79% smooth cordgrass (Spartina

alterniflora), 20% black rush (Juncus roemerianus), and 1% salt flats or salt

meadows (Hon et al. 1977). Typical rail habitat of the west coast is salt marsh,

broken up by tidal sloughs, where cordgrass (Spartina foliosa) and glasswort

(Salicornia) are the conspicuous plants (National Fish and Wildlife Laboratory

1980a, 1980b). Salt marsh ecology has been reviewed by several authors (Teal 1958;

Teal and Teal 1969; Johnson et al. 1974; Reimold and Queen 1974).

The clapper rail is monogamous, and some subspecies may produce more than one

brood a year (Blandin 1963). Nesting occurs from February to late August; timing

varies with geographic location. Average clutch size is 9 or 10 eggs (Bent 1963;

Ferrigno 1966; Mangold 1974; Ripley 1977); clutch size is largest in the north.

The incubation period is 18 to 22 days. ~lale and female incubate eggs and brood

the young. After the young are able to feed themselves, usually at 35 to 42 days

of age, their parents cnase them from the parental territory (Johnsgard 1975). The

young are precocial and fledge 9 - 10 weeks after hatching (Adams and Quay 1958).

They are sexually mature in the first reproductive season after they fledge.

Food Requirements

Clapper rails feed on mud flats and along gently sloping banks of creeks,

ditches, bayous, or shorelines at low tide and in the marsh proper among grasses.

Rails feed by probing in mud or by picking up foods found on the ground surface or

on vegetation. The diet consists of parasitic worms (Ascaridae), clam worms

(Nereis spp.), snails (Littorina irrorata, Melampus sp., Nassarius obsoleta,

Polygyra sp.), clams (Molulidae), crabs (Sesarma spp , , Uca spp.), insects

(Phalaenidae), spiders (Lycosa spp., Clubiona spp.), fish (Poeciliidae, Fundulus

spp.), and rarely, plant material (Oney 1951,1954). Martin et al . (1951) reported

that the diet of 260 clapper rails was 96% animal matter.

The predominant food item for northern, Wayne, and Louisiana clapper rails

seems to be fiddler crabs (Uca ~), a common species whose ecology has been

discussed by Teal (1958) and ~1iller (1965). In New Jersey, fiddler crabs were most

abundant in tall smooth cordgrass (Ferrigno 1966). Crayfish are also an important

food of the western and southern subspecies of clapper rail. Important foods in

the Savannah River Delta, South Carolina-Georgia, were fiddler crabs, small cancroid crabs (Eurytium and Pano eus ) , and periwinkle (Littorina irrorata). The

Florida clapper rail eats crabs Sesarma reticulatum and Callinectes sapidus),

freshwater shrimp (Palaemonetes exilipes), fiddler crabs, mollusks, beetles, and

earwigs (Anisolabis maritima). Little is known about the food habits of the

mangrove clapper rail. The fall diet of 103 Louisiana clapper rails was mainly

fiddler crabs and snails (Littorina spp.) (Batemen 1965).

The winter diet of 18 California clapper rails contained 85% animal matter,

which included 56.5% plaited horse mussel (Modiolus {Volsella} demissus), 15%

spiders (Lycosidae), 7.6% clams (Macoma balthica), and 3.2% yellow shore crabs

2
(Hemigrapsus oregonensis) (Moffitt 1941). Since Moffitt's work it has become clear

that crabs are the staple diet of clapper rails in southern California (Jorgenson

1975; Sanford Wilbur, U.S. Fish and Wildlife Service, Portland, Oregon; pers.

comm.).

Cover Requirements

Clapper rails tend to concentrate along tidal creeks of marshes during the

breeding season. These concentration areas appear to be ancestral nesting grounds

having a long tradition cf use (Stone 1965). Nests are usually in dense cover near

water and built well above the high tide mark. Ground nesting occurs in some

areas, but most nests are about 20 to 35 cm (7.9 to 13.8 inches) above the ground

and 10 to 50 m (32.8 to 164.0 f t ) from other nests (Kozicky and Schmidt 1949;

Stewart 1951).

Nest material consists of surrounding vegetation such as dried cordgrass.

Many nests have vegetative ramps leading to them and the nests are covered with a

roof. The nest is funnel shaped with an average inside diameter of about 14.2 cm

(5.6 inches), inside depth of 5.3 cm (2.1 inches), and outside diameter of 23.6 cm

(9.3 inches) (Kozicky and Schmidt 1949).

On Long Island (MacNamara and Udell 1970), clapper rails nested in smooth

cordgrass, saltmeadow cordgrass (Spartina patens), and common reed (Phragmites

australis). The favored nesting sites in New Jersey were along tidewater creeks

where grasses were higher than in the rest of the ~arsh (38 - 51 cm, 15.0 - 20.1

inches). Presumably the tall grasses offered better protection to birds and nests

(Stone 1965). A few nests were found in dry areas and one was located on a dune

among bayberry (r~irica heterophylla) bushes 91 m (298.6 t t ) from water. Kozicky

and Schmi dt (l949 • also stuoy i ng in New Jersey, noted that 71% of the nests were

in smooth cordgrass more than 61 cm (24.0 inches) in height. In many instances

these taller grasses were the only vegetation not submerged by high tides. Eighty

percent of the nests in a Virginia study area were in tall (46 cm , 18.1 inches)

smooth cordgrass within 5 m (16.4 ft) of the tidal creeks (Stewart 1951).

Three hei qht zones of smooth cordgrass were recognized by Oney (l954) in

Georgia. The most suitable rail nesting habitat (68% of nesting attempts) was

medium height (61-122 em, 24-48 inches) smooth cordgrass bordering tall (1.2-2.4 m,

3.9-7.9 f t ) smooth cordgrass (Oney 1954). Tall zone smooth cordgrass, the second

most important nesting habitat, was present along creeks or ditches. The medium

height zone occurred on the gentle slope of levees a'vlay from drainage ditches. The

short smooth cordgrass zone was present in the lowest part of the marsh and was not

important for nesting.

In Florida, Howell (l932) found two nests of Wayne clapper ra t l s in small

mangrove bushes and a third in dense glasswort surrounded by mangroves. The

primary habitat of the mangrove clapper ra i : is reported as mangrove (Rhizophora

mangle and Avicennia germinans) forest, but the nesting habitat is not adequately

described (Owre 1981). Kale (l981) reported that Florida clapper rails nest in

cordgrass, rush, and possibly in shrubby mangroves. Thus, the three subspecies of

clapper rail found in Florida may occasionally nest in mangroves (Howell 1932; Kale

1981; Owre 1981).

3
Bateman (1965) noted the simi l art ty of the Louisiana clapper rail IS ecology in

Louisiana to that of clapper rails studied on the Atlantic coast. In Louisiana, I

smooth cordgrass at nest sites was taller and provided more cover than vegetation

at random sites within the marsh (Sharpe 1976). Holliman (1978), studying the

Louisiana clapper rail in Alabama, stressed the importance of smooth cordgrass and

suggested that rough estimates of rail populations could be made by inspecting

recent aerial photos and determining the area of smooth cordgrass marsh available

as rail habitat. From the above observations it seems evident that smooth cordgrass provides critical nesting habitat along the gulf coast.

The California clapper rail nests in cordgrass, glasswort, or at the base of

gumweed plants (Grindelia spp.) (DeGroot 1927; Wilbur and Tomlinson 1976; Gill

1979). The date of r.esting and tides determine in part the species of vegetation

used (Zucca 1954). Early nests are constructed in dense gumweed because cordgrass

growth has not yet occurred. Where nesting is disrupted by tidal flooding the

rails often renest in glasswort because it grows at higher elevations than gumweed

or cordgrass. The light-footed clapper rail nests most often on the ground at the

base of glasswort clumps on the elevated banks of tidal channels close to water

(Wilbur and Tomlinson 1976). Population densities of liqhr-foot.ed clapper rails

appear to be highest in those marshes with the most cordgrass (Jorgensen 1975).

For all subspecies, with the possible exception of the mangrove clapper rail,

Spartina spp. are an important component of nest cover, and proximity to water is a

characteristic of all nesting habitat.

Fall-Winter Habitat Requirements

Clapper rails are more dispersed within the marsh after nesting is completed

although the preferred habitat continues to be Spartina marsh. Fall-winter habitat

requirements have not been described in the literature. Tip Hon (Georgia Department of Naturai Resources, Social Circle; pers. comm.) stated that during fallwinter in Georgia, rails concentrate in habitat that differs visually from habitat

used for nesting. His banding studies indicated that rails disperse in September

from the nesting areas and reside in other portions of the marsh that traditionally

have provided good fall hunting opportunities. Rails spend more time in high areas

of the marsh ; n wi nter, presumab ly to escape hi gh storm ti des. Wi nter habi tat

appears to be stands of medium-height Spartina near sounds and larger tidal creeks,

and it contains fewer tidal streams and ditches than the nesting habitat. Large

racks of floating, dead cordgrass, usually deposited along the marsh side of creek

levees, are occupied by rails during high fall and winter tides. The lack of

detailed descriptions of winter habitat limits our ability to describe year-round

habitat needs.

Interspersion

Oney (1954) found that the average nest was about 7 In (23 ft) from the nearest

change in cover. This cover change was represented by variation in cordgrass

height and density rather than a plant species change. A general characteristic of

Spartina marshes is a pattern of diminishing plant height and stem density at

greater distances from tidally influenced bodies of water. Stewart (1951) found a

correlation between the density of nests lind the amount of edge between tali and

medium-height smooth cordgrass (20-46 CIIl or 8-18 inches). This relationship was so

4
important that reliable u.c i ces of rest density could be obtained by annually

counting the number of occupied nests in 5-rn (16.4-ft) vri de strips ot the

tall growth smooth cordgrass along tidal creeks. Ferrigno (196G) stated that the

tall Spartina alterniflora along ditches and ditched ponds proviaed more nesting

cover, edge, and food for a given acreage of marsh than any other plant species.

Fiddler crabs, the most important rail food in tJew Jersey, were mo st abundant in

the tall smooth cordgrass edge of the short marsh (Ferrigno 1966). An of the

above references indicate the importance of edge and interspersion for ideal rail

habitat. The most attractive edge parallels ti~al ditches, streams, and other open

bodies of water.

Spatial Requirements

Clapper rails exhibit intraspecific territorial behavior during the nesting

season (Johnsgard 1975). Holliman (1978) found that the minimum distance between

acti ve nestsin A1abarna was 10m (32. 8 ft). C1apper rail sin Lou i sian d had an

average minimum home range of 153.7 m (504 f t ) along canals and tidal ditches in

surnmer, and 487.3 m (1599 ft) in winter (Roth et al , 1972). In South Carolina

clapper' rails had a February through October home range not greater than 183-274 m

(600-900 ft) in radius (Blandin 1963).

HABITAT SUITABILITY INDEX (HSI) MODEL

Model Applicability

Geographic area and season. This model was developed for Atlantic, Cu l t of

Mexico, and Pacific coastal areas within the range of clapper rails. The mcde l is

useful during any season.

Minimum habitat area. Minimum habitat area is defined as the mlnlmum amount

of contiguous suitable habitat required for a species to successfully live and

reproduce. Little information about minimum habitat area was available in the

published literature. Holliman (1978) reported the existence of clapper rail

populations in two smooth cordgrass marshes less than 2 ha (5 acres) each and

surrounded by vegetation characteristic of freshwater marsh. He found that the

up-river distribution of clapper rails on three rivers was limited to small strips

of cordgrass less than 50 m (164 ft) long and 10 III (32.8 tt ) wide. Thus, these

Alabama data suggest that a conservative minimum habHat area would be 2 ha (5

acres). The HSI will be zero if less than 2 ha are available.

Verification level. Review and evaluation of the clapper rail HSI model were

provided by the following biologists: R. e. Hamilton, Louisiana State University,

Baton Rouge; T. Hon, Georgia Department of Natural Resources, Social Circle; and F.

Ferrigno, New Jersey Department of Environmental Protection, Tuckahoe. Their

comments were considered during preparation of the final model.

Model Description

This HSI model evaluates two clapper rail life requisites: food and cover.

Clapper rails are poor fliers and have small home ranges. It is assumed that food

5
and cover needs must be met in the same general habitat area. Thus, d si nq l c

equation simultaneously evaluates food and cover life requisites. Figure 1 shows

how the HSI is related to the food/cover life requisite and specific habitat

variables. The model is purposely designed to use variables that require a nri nimum

of field work. Variable data usually can be ccilectea frorn maps and aerial

photographs.

Food/cover component. The primary feeding habitat requirements described in

-the literature are (1) mud flats and gently sloping banks of creeks, ditches,

bayous, or shorelines at low tide and (2) the estuarine persistent emergent and

scrub/shrub mangrove wetlands.

During low tides, mud flats and exposed channels provide feeding habitat. The

literature does not specify the optimum amount of these tidal mud flats, but

clapper rails are not expected to regularly use those flats that are more than 15 m

(49.2 ft) from vegetative cover. Habitat is considered optimum when at least 50%

of the shoreline of persistent emergent and scrub/shrub mangrove wetlands is

bordered by tidal flats and exposed channels (VI).

Scrub/shrub mangrove and persistent emergent wetland habitats meet the second

feeding habitat requirement. Emergent wetland is a tract of periodically inundated

vegetation described by Cowardin et al. (1979) as an estuarine intertidal wetland

characterized by erect, rooted, herbaceous hydrophytes, mainly perennials. These

marshes usually include species of Spartina, Juncus, Salicornia, and Grindelia.

Shrubby mangrove wetland, the scrub/shrub wetland of Cowardin et al . (1979), fs

characterized by mangrove species not exceeding 6 m (19.7 f t ) in height and is

occasionally used by clapper re i l s, For any coastal unit being evaluated, the

highest Suitability Index (Sl) is attained when 100% of the land area is estuarine

persistent emergent or scrub/shrub mangrove wetland (V2).

The cover habitat requirements of clapper rails can be categorized into the

nesting and the non-nesting needs. For example, cover needs from late summer

through winter, when rails are more widely dispersed than during the nesting

season, are met by the emergent wetland and scrub/shrub mangrove wetland. Cover

requirements during the nesting season are more restricted.

The literature stresses that important nesting habitat is emergent or scrub/

shrub mangrove wetlands bordering ditches and tidal creeks. Important nesting

plants are Spartina, Salicornia, Grindeli~, and possibly mangroves. These genera

usually make up the vegetation bordering tidally influenced bodies of water. On

the east coast, most nests are located within 5 m (16.4 ft) of water (Kozicky and

Schmidt 1949; Stewart 1951), but the Louisiana rail nests at greater distances from

water (Sharpe 1976; Holliman 1978). The vegetated wetland bordering tidally influenced water (streams, rivers, ditches, sloughs, bayous, embayments) is preferred

nesting habitat; the optimum width of this fringe apparently varies with the subspecies or geographic location. This model uses a 15-m (49.2-ft) fringe, bordering

a tidally influenced body of water, as the area most suitable for nesting (V).

Coastal areas with a large water to vegetation interface (i .e., containing uneven

shorelines and with many embayments, streams, rivers, and ditches) are assumed to

provide the best nesting habitat. Areas with a high percentage of the total emergent and scrub/shrub mangrove wetlands within 15 m of water will have the highest

S1.

6
Habitat variable Life requisite Habitat

-....J

Percentage of shoreline of

persistent emergent and

scrub/shrub mangrove

wetlands bordered by tidal

flats or exposed tidal

channels

Percentage of area covered

by persistent emergent and

scrub/shrub mangrove

wetlands

Percentage of persistent

emergent and scrub/shrub

mangrove wetlands withiQ

15 m (49.2 ft) of tidally

influenced bodies of water

__----:77. Food/Cover Estuarine HSI

Figure 1. Relationship of habitat variables and life requisites to the HSI for clapper rail.
Plant height seems to be a factor in choice of nesting sites. But, the appropriate height varies with plant species, ground elevation, and local peak spring

tides. It seems unlikely that optimum plant height guidelines can be set that will

fit most locations and subspecies. Consequently, we do not include plant height as

a variable.

Interrelationship of life requisite components. Edge is a common feature of

the habitats that clapper rails select for feeding and reproduction. The wetland

border within 15 m (49.2 ft) of open, tidally influenced, salt or brackish water

seems optimum for food and nest sites. No other consideration is necessary except

it is assumed that at least 2 ha (5 acres) of contiguous habitat, of the appropriate plant species, must be present to support a rail population.

Suitability Index (SI) Graphs for Model Variables

This section contains suitability index graphs and equations to quantitatively

describe the relationships between estuarine habitat (E) variables and habitat

suitability for clapper rails. These graphs and equations are used to produce an

HSI. The data sources and assumptions associated with documentation of the SI

graphs are shown in Table 2. Map or field data should be collected for each

variable by using the techniques of Table 3.

Habitat

E

Variable

Percentage of shoreline of persistent

emergent and scrub/

shrub mangrove

wetlands that is

bordered by tidal

flats or exposed

tidal channels.

8

Suitability Graph

1.0

)( 0.8

Q)

"

c:

>- 0.6

::

:E 0.4 tU

.'!:

::J

CIJ 0.2

0.0

0 20 40 60 80 100

%
Habitat

E

E

Variable

Percentage of area

covered by persistent emergent and/or

scrub/shrub mangrove

wetlands.

Percentage of emergent

and scrub/shrub mangrove

wetland within 15 m

(49.2 ft) of tidally

influenced bodies of

water.

9

Suitability Graph

1.0

)( 0.8

CD

"C

c:::

>0. 0.6

:!::

.t:l 0.4 as

:!::

CIJ 0.2

0.0

0 20 40 60 80 100

%

1.

)( o.

CD

"C

c:::

- 0.6

>.

::

:c 0.4 as

:!::

CIJ 0.2

0.0

0 10 20 30 40 50

%
Table 2. Data sources and assumptions for clapper rail suitability indices.

Variables and source

Mango1d (1977)

National Fish and Wildlife

Laboratory (1980a)

V2 Kozicky and Schmidt (1949 )

Stewart (1951)

Oney (1954)

Bent (1963)

Wilbur and Tomlinson (1976 )

Holliman (1978)

V3 Kozicky and Schmidt (1949)

Stewa rt (1951)

Oney (1954)

Stone (1965)

Wilbur and Tomlinson (1976 )

HSI Determination

Assumptions

Barren tidal mud flats or mud banks are

feeding areas. The best habitat is

assumed to be that with at least 50% of

the persistent emergent and scrub/shrub

mangrove wetlands bordered by tidal

flats or exposed tidal channels.

Clapper rails nest and feed in the

persistent emergent and scrub/shrub mangrove wetlands. Survival depends upon

the availability of such wetlands.

Preferred nesting sites are within the

15-m (49.2-ft) fringe of wetland bordering tidally influenced bodies of water.

Coastal units with the highest percentages of persistent emergent and scrub/

shrub mangrove wetland in the 15-m strip

bordering water are assumed most

suitable.

To calculate an HSI, one must determine if the life requisites are provided at

some level greater than zero. If the area lacks suitable contiguous habitat of at

least 2 ha (5 acres) the HSI is zero.

In areas larger than 2 ha, the following steps must be taken to determine an

HSI for any application.

1. Review the section on model applicability for validity of the model for the

intended application.

2. Identify the boundaries of the evaluation area or areas and obtain data for

each model variable used in the model. Calculate the SI for each habitat

variable.

3. Calculate the HSI:

HSI

10
Table 3. Suggested measurement techniques and definition of habitat variables.

Variable (definition)

Percentage of wetland shoreline that

borders flat to gently sloping banks

or tidal flats exposed at low tide.

(Wetland shoreline is the persistent

emergent or scrub/shrub mangrove

wetlands that border sounds, rivers,

streams, embayments, sloughs, and

open coastline; tidal flats and banks

are predominantly unvegetated soil

substrate exposed at low tide; gently

sloping is a slope of 15° or less.)

Percentage of the total area that is

salt or brackish emergent or scrub/

shrub mangrove wetlands. (Emergent

wetland is a class within Cowardin

et al. [1979J estuarine-intertidal

wetland system and is characterized

by erect, rooted, herbaceous hydrophytes, predominantly perennials;

the scrub/shrub wetland is characterized by species of mangroves less

than 6 m [19.7 ftJ tall.)

Percentage of area of emergent or

scrub/shrub mangrove wetlands that

is within 15 m (49.2 ft) of tidally

influenced bodies of water. (Tidally

influenced bodies include streams,

rivers, ponds, embayments, sloughs,

and ditches that rise and fall in

response to tide.)

11

Suggested techniques

On maps or aerial photos use a map

measurer (Hays et al. 1981) to

determine the shoreline bordered by

gently sloping banks or tidal flats

exposed at low tide. Tidal flats

are usually depicted on coastal

maps, and the I-m (3.3-ft) contour

line indicates the presence of

gently sloping banks. With this

information and the mean tide

fluctation data, predict which

shorelines border banks or flats

suitable for clapper rail feeding

activities. Then measure the total

shoreline edge and calculate the

percentage of shoreline bordered by

suitable feeding habitat.

Refer to recent U.S. Geological Survey (USGS) photo quad maps,

other coastal maps, or aerial

photographs to identify emergent

and mangrove wetlands. Use a

stereoscope and photographs to

determine mangrove height and

identity. Use a dot grid or

planimeter to calculate area of

marsh. Divide acreage of marsh by

area of entire study unit to determine percentage of the area that is

marsh.

Measure total wetland-to-water edge

with a map measurer. Multiply by

15 (the 15-m band) to determine

square meters and then convert to

hectares. Divide area within the

wetland fringe by total area of

emergent and mangrove wetland

calculated for VI.
The primary value of an H5I is for comparing areas. Table 4 provides three

sample data sets that have been applied to the clapper rail model to calculate

H5I 's. The data sets are hypothetical, but represent realistic situations.

Table 4. Calculation of the suitability indices (5I) and the habitat suitability

index (H5I) for three sample data sets using the clapper rail habitat variables

(V) and model equation.

Model Data set 1 Data set 2 Data set 3

component Data 51 Data 51 Data 51

V1 50% 1.00 10% 0.20 80% 1.00

V2 90% 0.90 20% 0.20 60% 0.60

V3 7% 0.28 12% 0.48 60% 1.00

H5I 0.63 0.27 0.84

Field Use of the Model

Detailed laboratory or field sampling of habitat variables through time will

provide the most rel iable and repl icable H5I values. The data used to calculate

the 51 values should be accompanied by appropriate documentation to insure that

decisionmakers understand the quality of the data used in developing the H5I.

Interpreting Model Outputs

A clapper rail H51 determined by laboratory or field application of this model

may not reflect the population density of clapper rail in the study area because

other factors may have significant influence in determining species abundance. In

coastal areas where clapper rail populations are primarily regulated by habitatbased factors, the model should yield H51 values that have positive correlations

with long-term abundance. This correlation has not been tested, other than from

inference drawn from the literature to support the model. The proper interpretation of the H51 is one of comparison. If two areas have different H5I's, then the

area with the higher H5I should have the potential to support more clapper rails

than the area with the lower HSI.

12
REFERENCES

Adams, D. A., and T. L. Quay. 1958. Ecology of the clapper rail in southeastern

North Carolina. J. Wildl. Manage. 22(2):149-156.

Bateman, H. A., Jr. 1965. Clapper rail (Ra l lus longirostris) on Grand Terre

Island, Jefferson Parish, Louisiana. M. S. Thesis. Louisiana State

University, Baton Rouge. 144 pp.

Bent, A. C. 1963. Life histories of North American marsh birds. Smithsonian

Institute, U.S. Nat l , Mus. Bull. 135. Dover Publishers, Inc. reprint, New

York. (First published in 1928.) 490 pp.

Blandin, W. W. 1963. Renesting and multiple brooding habits of marked clapper

rails. Proc. Annu. Cont. Southeast. Assoc. Game Fish Comm. 17:60-68.

Cowardin, K. M., V. Carter, F. C. Golet, and E. T. LaRoe. 1979. Classification of

wetlands and deepwater habitats of the United States. U.S. Fish Wildl. Servo

Biol. Servo Program FWS/OBS-79/31. 103 pp.

DeGroot, D. S. 1927. The California clapper rail:

and habitat. Condor 29(6):259-270.

its nesting habits, enemies

Ferrigno, F. 1966. Some aspects of the nesting biology, population dynamics, and

habitat associations of the clapper rail. M. S. Thesis. Rutgers University,

New Brunswick, N.J. 68 pp.

Gill, R., Jr. 1979. Status and distribution of the California clapper rail

(Rallus longirostris obsoletus). Calif. Fish Game 65(1):36-49.

Hays, R. L., C. Summers, and W. Seitz. 1981. Estimating wildlife habitat variables. U.S. Fish v/ildl.Serv. Biol. Servo Program FWS/OBS-81/47. 111 pp.

Holliman, D. C. 1978. Clapper rail (Rallus longirostris) studies in Alabama.

Northeast. Gulf Sci. 2(1):24-34.

Hon, T., R. R. Odum, and D. P. Belcher. 1977. Results of Georgia's clapper rail

banding program.' Proc. Annu. Conf , Southeast. Assoc. Fish Wildl. Agencies

31:72-76.

Howell, A. H. 1932. Florida bird life. Fla. Dep. Game and Fresh Water Fish Comm.

and Bur. Biol. Surv., USDA. Coward-McCann, Inc., New York. 579 pp.

Johnsgard, P. A. 1975. North American game birds of upland and shoreline.

University Nebraska Press, Lincoln. 183 pp.

Johnson, A. S., H. O. Hillestad, S. F. Shanholtzer, and G. F. Shanholtzer. 1974.

An ecological survey of the coastal region of Georgia. Natl. Park Servo Sci.

Monogr. Ser. 3, U.S. Gov. Printing Office, Washington, D.C. 233 pp.

13
Jorgensen, P. D. 1975. Habitat preference of the light-footed clapper rail in

Tijuana fltarsh, California. M. S. Thesis. San Diego State University, Calif.

115 pp ,

Kale, H. W., II. 1981. Florida clapper rail. Pages 112-113 in H. W. Kale II, ed.

Rare and endangered biota of Florida. Vol. 2, Birds. University Presses of

Florida, Gainesville. 121 pp.

Koz i cky , E. L., and F. V. Schmidt. 1949.

New Jersey. Auk 66:355-364.

Nesting habits of the clapper rail in

MacNamara, E. E., and H. F. Udell. 1970. Clapper rail investigations on the south

shore of Long Island. Linn. Soc. (N. Y.) 71:120-131.

Mangold, R. E. 1974. Research on shore and upland migratory birds in New Jersey:

clapper rail studies, 1974 final report. U. S. Fish Wildl. Servo Accelerated

Res. Program, New Jersey Dep. Environ. Protect., Trenton. 17 pp.

Mangold, R. E. 1977. Clapper rail (Rallus longirostris). Pages 84-93 in G. C.

Sanderson ed. Management of mi gratory shore and upland game bi rds 111 North

America. Int. Assoc. Fish Wildl. Agencies. 358 pp.

Martin, A. C., H. S. Zim, and A. L. Nelson. 1951. American wildlife and plants:

a guide to wildlife food habits. Dover Publ., Inc., New York. 500 pp.

Miller, D. C. 1965. Studies of the systematics, ecology, and geographic distribution of certain fiddler crabs. Ph.D. Dissertation. Duke University, Durham,

N.C. 223 pp.

Moffitt, J. 1941.

43(6):270-273.

Notes on the food of the California clapper rail. Condor

National Fish and Wildlife Laboratory. 1980a. Selected vertebrate endangered

species of the seacoast of the United States: light-footed clapper rail.

U.S. Fish Wildl. Servo Biol. Servo Program FWSjOBS-80jOl.27. 7 pp.

National Fish and Wildlife Laboratory. 1980b. Selected vertebrate endangered

species of the seacoast of the United States: California clapper rail. U. S.

Fish Wildl. Servo Biol. Servo Program FWSjOBS-80jOl.27. 6 pp.

Oney, John.

Manage.

1951. Fall food habits of the clapper rail in Georgia.

15(1): 106-107.

J. Wildl.

Oney, John. 1954. Final report, clapper rail survey and investigations study.

Georgia Game Fish Commission, Atlanta, 50 pp.

Owre, O. T. 1981. Mangrove clapper rail. Pages 113-114 in H. W. Kale, II, ed.

Rare and endangered biota of Florida. Vol. 2, Birds. University Presses of

Florida, Gainesville. 121 pp.

Reimold, R. J., and W. H. Queen, eds. 1974.

Press, Inc., New York. 605 pp.

14

Ecology of the halophytes. Academic
Ripley, S. D. 1977.

406 pp.

Rails of the world. David R. Godine Publ., Boston, Mass.

Roth, R. R., J. D. Newsom, T.

seasona1 behavi or patterns

Louisiana coastal marshes.

Corrrn. 26:136-147.

Joanen, and L. L. McNease. 1972. The daily and

of the clapper rail (Rallus longirostris) in the

Proc. Annu. Conf. Southeast. Assoc. Game Fish

Sharpe, T. L. 1976.

Louisiana saltmarsh.

91 pp.

Productivity and distribution of the clapper rail in a

M. S. Thesis. Louisiana State University, Baton Rouge.

Soil Conservation Service. 1982a. National list of scientific names. Vol. 1,

List of plant names. U.S. Dep. Agric., SCS-TP-159. 416 pp.

Soil Conservation Service. 1982b. National list of scientific names. Vol. 2,

Synonymy. U.S. Dep. Agric., SCS-TP-159. 438 pp.

Stewart, R. E. 1951. Clapper rail populations of the Middle Atlantic States.

Trans. N. Am. Wildl. Conf. 16:421-430.

Stewart, R. E. 1954. Migratory movements of the northern clapper rail.

Banding 25(1):1-5.

Bi rdStone, W. 1965. Bird studies at Old Cap May. York. 484 pp.

Vol. 1. Dover Publ., Inc., New

Teal, J. M. 1958. Distribution of fiddler crabs in Georgia salt marshes. Ecology

39(2):185-193.

Teal, J. M., and M. Teal. 1969. Life and death of a salt marsh. Audubon/

Ballantine Publ., New York. 274 pp.

U.S. Fish and Wildlife Service. 1981. Standards for the development of habitat

suitability index models. 103 ESM, U.S. Fish Wildl. Servo Div. Ecol. Servo

n.p.

Wilbur, S. R., and R. E. Tomlinson. 1976. The literature of the western clapper rails. U.S. Fish Wildl. Servo Spec. Sci. Rep. Wildl. 194. Washington, D.C.

31 pp.

Wilbur, S. R., R. M. Jurek, R. Hein, and C. T. Collins. 1979. Light-footed rail

recovery plan. Region 1, Endangered Species Program, U.S. Fish Wildl. Serv.,

Portland, Oreg. 33 pp.

Zucca, J. J. 1954. A study of the California clapper rail. Wasmann J. Biol.

12(2): 135-153.

15
50272-101

REPORT DOCUMENTATION 11. REPORT NO.

PAGE-- FWSjOBS-82jl0.51

4. Title and Subtitle

13_ Recipient's Accession No.

-I

Habitat Suitability Index Models: Clapper Rail

1----------------------

7. Authorfs)

J. C. Lewis and R. L. Garrison I 9. Pe rf orrnj ng Organization Name and Address

Research Unit 11. Co ntr ac tt C) Or GrantCG) No.

12. Sponsoring Organization Name and Address

I

«»

I (G)

Na tl ona1 Coa sta I Ecosystems I eam -----u,:;;e of Report & Period Covered

Division of Biological Services

Fish and Wildlife Service

U.S. Department of Interior 14.

Washington, DC 20240

15. Supplementary Notes

-------------------------------------------------------J

ills. Abstract (Limit: 200 words)

I

A review and synthesis of existing information were used to develop a model

suitable for evaluating the quality of coastal habitat of clapper rails (Rallus

longirostris). The model is scaled to produce an index of habitat suitability

between 0 (unsuitable habitat) and 1 (optimally suitable habitat) for coastal

areas of the continental United States. Habitat suitability indices are

designed for use with Habitat Evaluation Procedures previously developed by

the U.S. Fish and Wildlife Service. Guidelines for clapper rail model applications and techniques for estimating model variables are discussed.

117. Document Analysis a. Descriptors

Mathematical models

Birds

Estuaries

b. Identifiers/Open-Ended Terms

Habi ta t

Habitat Suitability Index

Clapper rail

Rallus longirostris c. COSATI Field/Group

21. No. of Pages

vi + 15_

22.. Price

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Unc 1ass ifi ed

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Unlimited

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Lloyd Five Hundred Building, Suite 1692-

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bitat suitability index nmels : 19503

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