BIOLOGICAL REPORT 82(10.130)

JANUARY 1987

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Library

National Wetlands Research Center

U. S. Fish and Wildlife Service

700 Cajundome Beulevard

Lafayette. La. 70506

HABITAT SUITABILITY INDEX

BLACK-SHOULDERED KITE

MODELS:

and Wildlife Service

SK

361

.U54

no. 82- 10 .130

Department of the Interior
MODEL EVALUATION FORM

Habitat models are designed for a wide variety of planning applications

where habitat information is an important consideration in the decision

process. It is impossible, however, to develop a model that performs equally

well in all situations. Each model is published individually to facilitate

updating and reprinting as new information becomes available. Assistance from

users and researchers is an important part of the model improvement process.

Please comp 1ete thi s form fo 11 owi ng app1i cati on or revi ew of the mode 1. Feel

free to include additional information that may be of use to either a model

developer or model user. We also would appreciate information on model

testing, modification, and application, as well as copies of modified models or

test results. Please return this form to:

National Wetlands Research Center

U.S. Fish and Wildlife Service

1010 Gause Boulevard

Slidell, LA 70458

Thank you for your assistance.

Species __ Geographic

Location------------------------------------

Management Action Analysis __

Habitat or Cover Type(s)------------------------------------------------- Type of Application: Impact Analysis _ Baseline Other------------------------ Variables Measured or Evaluated---------------------

Was the species information useful and accurate? Yes No

If not, what corrections or improvements are needed?------------------------
Were the variables and curves clearly defined and useful? Yes No

If not t how were or could they be improved? __

Were the techniques suggested for collection of field data:

Appropriate? Yes No

Clearly defined? Yes No

Easily applied? Yes No

If not. what other data collection techniques are needed?

Were the model equations logical? Yes No

Appropriate? Yes No

How were or could they be improved?

Other suggestions for modification or improvement (attach curves.

equations. graphs. or other appropriate information)

Additional references or information that should be included in the model:

Model Evaluator or ~eviewer Date --------------- ------- Agency _

Address ---------------------------------------

Telephone Number Comm: _ FTS _
Biological Report 82(10.130)

January 1987

HABITAT SUITABILITY INDEX MODELS: BLACK-SHOULDERED KITE

by

Craig A. Faanes

Northern Prairie Wildlife Research Center

U.S. Fish and Wildlife Service

Jamestown, ND 58401

and

Rebecca J. Howard

National Wetlands Research Center

U.S. Fish and Wildlife Service

1010 Gause Boulevard

Slidell, LA 70458

Performed for

National Wetlands Research Center

Research and Development

Fish and Wildlife Service

U.S. Department of the Interior

Washington, DC 20240
This report should be cited as:

Faanes, C.A., and R.J. Howard.

black-shouldered kite. u.s.

13 pp.

1987. Habitat suitability index models:

Fish Wildl. Servo 8iol. Rep. 82(10.130).
PREFACE

The black-shouldered kite habitat suitability index (HSI) model is

intended for use with the habitat evaluation procedures (HEP) developed by the

U.S. Fish and Wildlife Service (1980) for impact assessment and habitat

management. The model was developed from a revi ew and synthesis of existi ng

information, and includes unpublished information that reflects the opinions of

persons familiar with black-shouldered kite ecology. It is scaled to produce

an index of habitat suitability between 0 (unsuitable habitat) and 1.0

(optimally suitable habitat). Assumptions used to develop the HSI model and

guidelines for model application, including techniques for measuring model

variables, are described.

Model documentation is provided for several reasons. First, the

documentation provides a means of explaining the model's structure and its

inherent assumptions. Second, the model-building process involves considerable

judgment on the part of the model builder, and documentation provides the

insights necessary to modify the model when these judgments are inconsistent

with local or new knowledge. Finally, the documentation should facilitate

reformulation of the model to meet individual study constraints of time and

human resources.

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

of proven cause and effect. The model has not been field tested. 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

habitat-based approach to fish and wildlife management. Please send any

comments or suggestions you may have on the black-shouldered kite HSI model to

the following address.

Information Transfer Specialist

National Wetlands Research Center

U.S. Fish and Wildlife Service

1010 Gause Boulevard

Slidell, LA 70458

iii

CONTENTS

PREFACE iii

ACKNOWLEDGMENTS vi

INTRODUCTION 1

SPECIFIC HABITAT REQUIREMENTS 2

Food and Foraging Habitat.......................................... 2

Nesti ng Cover 6

Water. 6

Special Considerations.............................................. 7

HABITAT SUITABILITY INDEX (HSI) MODEL 7

Mode 1 App1i cab i 1i ty 7

Model Description.................................................. 8

Suitability Index (SI) Values for Model Variables 8

HSI Determi nation 9

Field Use of Model................................................. 9

Interpreti ng Model Output 10

REFERENCES 11

v
ACKNOWLEDGMENTS

We woul d 1ike to express our appreci ati on to Rey Stende11, Director of

the U.S. Fish and Wildlife Service's (FWS) Northern Prairie Wildlife Research

Center (NPWRC), Jamestown, North Dakota, for his many suggestions on model

development, for sharing his thorough knowledge of black-shouldered kite

biology, and for his willingness to provide editorial comments. Brian R.

Chapman, Corpus Christi State University, Texas, provided unpublished

information on kite feeding ecology in south Texas. Harold Kantrud and

Douglas Johnson, NPWRC, provided helpful comments on earlier drafts of the

manuscript. Evaluations of the structure and functional relationship of the

model were provided by personnel of the FWS National Wetlands Research Center.

Additional reviews were obtained from FWS Ecological Services personnel at

Corpus Christi, Texas; Houston, Texas; and Sacramento, California. Funding

for model development and publication was provided by the FWS. Patrick Lynch

prepared the cover illustration.

vi
BLACK-SHOULDERED KITE (Elanus caeruleus)

INTRODUCTION

The black-shouldered kite inhabits a disjunct range extending from

California, Texas, and (formerly) Florida, south intermittently to Chile and

Argentina (American Or-rri tho l oqi sts ' Union 1983). Prior to the 19601s, this

species occurred in low numbers across much of its range. Population

decreases appeared to be common during this time, especially in Mexico and

Central America (Eisenmann 1971).

Populations of black-shouldered kite have changed considerably within the

limited area of its U.S. range. Although considered common and widespread in

California in the late 18001s, the species was largely extirpated from much of

the State by the early 1900ls (Grinnell and Miller 1944). In Texas,

Oberholser (1971) considered this species to be restricted as a breeding bird

to the southeastern region of the State.

Since 1960, the population status and range of this raptor in North

Ameri ca have improved markedly. The bl ack-shoul dered kite has also rapi dly

colonized habitats throughout much of Central America south to Panama

(Eisenmann 1971), regions uninhabited just a few years ago. Today the

black-shouldered kite in California is a common species of open and cultivated

bottomland. During 1964-78, the mean number of kites recorded per hour in

California increased from 0 to 10 (Pruett-Jones et al. 1980). Warner and Rudd

(1975) concluded that, in California1s Sacramento Valley, the black-shouldered

kite increased predominantly in irrigated agricultural areas where the

California meadow mouse (Microtus californicus) occurred.

In south Texas, Oberholser (1971) considered this species common to

scarce in Cameron and Hidalgo Counties, although records of extralimital

occurrence exist for Galveston and Brazoria (San Bernard National Wildlife

Refuge) Counties. The known historic range in Texas included upstream

portions of the Rio Grande to near Rio Grande City, and inland areas to Lee

County (Oberholser 1971). Analysis of Christmas Bird Count data provides some

indication of the gradual increase in numbers of black-shouldered kites in

south Texas during the period 1962-65 (Pruett-Jones et al. 1980). At present,

black-shouldered kites appear to be well-established in south coastal Texas

and along the upper Texas coast. Although the California population has

historically been considered the largest in North America, recent data (Larson

1980) suggest that the Texas population may now be larger.

1
SPECIFIC HABITAT REQUIREMENTS

Because there is a paucity of inforaation on the blacK-shouldered kite in

Texas, much of the following analysis is based on information from California

and other portions of the range where thi s speci es has been more thoroughly

studied.

Suitability of habitat for the black-shouldered kite is dependent on the

availability of prey and nesting sites. Characteristics of the prey species

that affect their suitability are size, behavior (activity period), and

population density. Habitat characteristics affecting prey availability

include vegetation type, density, and height.

Food and Foraging Habitat

The black-shouldered kite is an obligate predator on diurnal small

mammals (Stendell 1967, 1972). Brown and Amadon (1968) suggested that

movements and nesting by this species are largely governed by concentrations

of mice, usually voles. Stendell (1972) found the black-shouldered kite to be

nomadic, hunting where small mammals were abundant, and leaving when the prey

population decreased. Hawbecker (1940) noted a correlation between the

nesting of black-shouldered kite and vole density, and suggested that a high

vole population was necessary for successful nesting by kites.

During a 3-year study in California, voles (primarily Microtus

californicus) made up 83%, 85%, and 88%, respectively, of the items in

regurgitated pellets although densities per acre during the same 3 years were

25, more than 45, and less than 1, respectively (Stendell and Myers 1973).

Waian (1973) concluded from pellet analysis and direct observation that

black-shouldered kites in his Santa Barbara Coastal Plain study area were .

nearly obligate predators on M. californicus; M. californicus was the IIIost . common species captured during small-mammal trapping efforts. Oberholser

(1971) postul ated that the meadow mouse (Mi crotu5 sp.), whi te-footed mouse

(Peromyscus sp.), and house mouse (Mus musculus) were the principal food items

of the black-shouldered kite in south Texas. Brian R. Chapman (Corpus Christi

State University, Corpus Christi, Texas; pers. comm.), however, has suggested

that the hispid cotton rat (Sigmodon hispidus) supplies most of the prey base

for the black-shouldered kite in south Texas. In the southern portion of its

range, ~. hispidus exhibited biomodal annual population fluctuations (Cameron

and Spencer 1981). Maximum population densities occurred during autumn, but

there were spring peaks (Texas x = 14/ha). Minimum densities in Texas (x =

0.5/ha) occurred in winter and summer. Mus musculus may fill the void created

by reduced numbers of ~. hispidUs. -

The hispid cotton rat occurs most frequently in grass-dominated habitats

(Odum 1955; Goertz 1964; Fleharty and Mares 1973; Kaufman and Fleharty 1974).

Goertz and Long (1973) reported this species in perennial grasses and forbs

near pond edges. Grass beight and dens tty are important components of cotton

rat habitat (Goertz 1964; Kaufman and Fleharty 1974). Cameron (1977) captured ~. hispidus in areas of mixed grass and brush in south coastal Texas.

McClenaghan and Gaines (1978) trapped this species in old fields of cultivated

brome (Bromus sp.) in early stages of sec~ndary succession.

2
, The uu of ~. htl,idu~ ~y the black-slwuldcired kite 15 f....rther suppor-ted

by Raun~s (1960) report that cotton rats were the priMary food of cOMon

barn-QWls (Tyto alba) in Texas. R.C. Stendell (U~S. Fish and Wildlife

Service, Jamestown, North Dakota; pers. comm.) stated that common barn-owls

are illportant predators on Microtus californicus in California areas that

support black-shouldered kites. Given the general characteristics of ~.

tt~~. pl es its hAbitat .ffiflities, 'this spec ies probably replaces~.

~icus in the Texas portion of the black-shouldered kites' range.

Across much of its extensive range, the black-shouldered kite uses

habitats that are surprisingly similar in structural terms. Thurber and

Serrana (1972) reported that preferred habitat in El Salvador was "open

country, usually pastures, dominated by occasional small trees such as ceibas

(Ceiba pentandra).11 These areas were originally lowland forest. In Humboldt

County, Cal iforni a, thi s speci es occupied a mosai c of topography i ncl udi ng

tall and short growths of rank grass, salt marsh, and pasture (Bammann 1975).

Oberholser (1971) described the preferred south Texas habitat of

b1ack-shcul dered kite as "open , usually rather dry, s 1i ghtly brushy savannah

or agricultural country with scattered clumps of trees and a permanent water

source. II He stated, "t.hus the coastal plain in the extreme southern tip of

the state with its patches of grass, tilled fields, sand dunes, palm groves,

and marshes, resacas and willow-lined streams of the Rio Grande system is

primary white-tailed kite [black-shouldered kite] country in the Lone Star

State. II Rappole and Blacklock (1985) listed the black-shouldered kite as a

species associated in the Texas coastal region with mesquite savanna and

prairie habitat. Some use of mesquite chaparral habitat was also noted.

The black-shouldered kite appears to be one of few raptors that have

benefited by human alteration of the landscape. Thurber and Serrana (1972)

concluded that among the factors contributing to the black-shouldered kite

population increase in El Salvador was lithe introduction of cattle adapted to

the hot lowlands, mechanization of agriculture, and the temporary control of

malaria. All of these made profitable the clearing and drainage of the

coastal plains. 1I The authors also stated that small rodents multiplied in the

human-created habitats.

Peter L. Ames (pers. comm., cited by Eisenmann 1971) believed that

black-shouldered kites in the Sacramento-San Joaquin Delta of California

benefi ted greatly from the IIfragmented agri cultura1 pat.tern" and from

year-round irrigation, which not only provided new habitat, but also supported

a high mouse population in lush pasturage throughout the winter. Pruett-Jones

et al. (1980) postulated that "t.hi s long-term increase [in kite numbers] was

possible because of favorable densities of meadow mice in agricultural areas,

and perhaps less severe cycling of rodent populations. II R.C. Stendell (pers.

comm.) also bel i eved that human di sturbances may reduce the amp1i tude of

microtine cycles. Waian (1973) stated, however, that "modern agricultural

methods render land used in these ways [lemon and avocado orchards, vegetable

farming and cattle grazing] unsuitable for mouse populations of sufficient

size to support kites. 1I Presumably, this statement refers to the large scale,

highly intensive, and mechanized farming characteristic of southern

3
California. Waian (1973) believed that kites typically inhabit marsh margins,

grasslands, and oak woodlands.

Kites foraged almost exclusively over grasslands in a San Diego County,

California, study; areas of willow (Salix spp.) mulefat (Baccharis viminea)

and Salicornia were virtually ignorea--(Henry 1983). The grassland was

composed primarily of low vegetation less than 0.3 m tall. The willow/mulefat

thickets were 2-3 m in height and were almost impassable by foot. The

Salicornia marsh was also very dense with vegetation approximately 0.3-0.6 m

tall.

Bammann (1975) provided data on cover types used by black-shouldered

kites for hunting in Humboldt County, California. Black-shouldered kites were

observed hunting over the fo 11 owi ng vegetation types: (1) tall rank grass,

(2) short rank grass, (3) rush, (4) saltmarsh, (5) short grazed pasture, and

(6) tall grazed pasture. The percentage of time black-shouldered kites spent

hunting in each of these habitat types is listed in Table 1.

Table 1. Amount of time black-shouldered kites hunted in six habitat types in

Humboldt County, California (from Bammann 1975).

Major vegetation type

Tall rank grass

Short rank grass

Saltmarsh

Rush

Tall grazed pasture

Short grazed pasture

% Total

vegetated area

a

1. 62

1. 58

3.35

1. 61

3.32

67.27

% Total time

hunted by kites

72.99

12.29

7.43

4.70

0.40

1. 79

aThese values do not total 100.0% because five other vegetation types occurred

on the study area (sand dunes, pine forest, row crops, willow thickets, and

brush) but were not used by hunting kites. Thus, their area was not used in

the analysis.

Tall rank grass occurred primarily along berms and in several protected

or occasionally flooded fields not subjected to grazing or cultivation.

Herbaceous vegetation i ncl uded ryegrass (Lol i um perenne), Kentucky bl uegrass

(Poa pratensis), orchardgrass (Dactylis glomerata), velvetgrass (Holcus

lanatus), and coastal saltgrass (Distichlis spicata). Associations of these

plant species grew 15 to 45 cm tall. Grass clumps and seed stalks up to 2 m

in height were present.

4
Short rank grass included perennial ryegrass, Kentucky bluegrass,

orchardgrass, velvetgrass, and several forbs. Most short rank grass on

Bammann's study area had been cut for hay during the previous summer. Grasses

in these fields were used infrequently for cattle pasture. The vegetation of

the pastures ranged in height from 10 to 30 cm, while that along fence lines

was 30 to 60 cm tall.

Rush vegetation was found in poorly drained fields and along some

drainage ditches. Vegetation made up primarily of Juncus patens and ~.

effusus and covering over 30% of the area was considered rush habitat. Those

areas <30% were classified by their physiognomic characteristics. Generally,

the principal plant species in this habitat grew 30 to 60 cm in height.

Salt marshes were dominated by pickleweed (Salicornia virginica) which

covered mud flats above the high tide line. This vegetation was 5 to 20 cm

tall. Associated with the pickleweed was a cordgrass-saltgrass type dominated

by Spartina foliosa and Distichlis spicata. Vegetation in the cordgrasssaltgrass type ranged from 15 to 50 cm in height and was dense.

Short grazed pasture was the most extensi ve habitat on Bammann I s study

area. Common plant species included Italian ryegrass (Lolium multiflorum),

Kentuc ky b1uegrass , ve 1vetgrass , bentgrass (Agros tis te nuis), orchardgrass ,

rush, and plantain (Plantago lanceolata). Because of constant heavy grazing,

this vegetation type was generally <15 cm in height, litter accumulation was

largely absent, and the area had the appearance of a mowed lawn.

The vegetative composition of tall grazed pasture was very similar to

short grazed pasture except that Juncus spp., velvetgrass, and orchardgrass

were the prevalent species. In general, the vegetation grew to 40 cm in

height and was considered luxuriant.

No hunting was observed over residential sites, water, farm buildings,

roads, pine forest, row crops (primarily pototoes), gravel, mud, willow

thi ckets, or brush; these habitat types made up about 8% of the study area.

However, kites hunt over small grain fields in the central valley of

California (R.C. Stendell, pers. comm.).

Kites spent 97.4% of their time hunting over four vegetation types--tall

rank grass, short rank grass, saltmarsh, and rushes (Table. 1). These habitats

were used by hunting kites to a greater extent than expected on the basis of

relative amount of area. The percentage of attack success within three of the

habitats was similar--55.5% in rush habitat, 52.8% in short rank grass, and

50.5% in tall rank grass. Kites expended the majority of their hunting effort

and captured the bulk of their prey in tall rank grass, even though prey was

probably more vulnerable in other habitats. Visual estimates of prey

abundance suggested that small mammal populations were greatest in tall rank

grass. Bammann (1975) believed that areas of tall rank grass about 10 ha in

size were sufficient to support prey populations large enough to maintain

several kites during winter.

5
The black-shouldered kite nesting season in south Texas ranges from March

to September. Nesting birds have been found in areas extending from 0 to

198 m above mean sea level (Oberholser 1971). Nesting typically occurs in

wetlands and op~n brushlands, usually near water or along streams. The nest,

a rather frail platfor"·of sticks, leave,. weed stalks, .and similar ma-bri.als,

is usually located in a tree or bush (Oberholser 1971). Nesting by

black-shouldered kites in California has been reported for the months of

February through August with a peak in activity for March, April, and May

(Waian 1973). Nesting habitat was described as oak woodlands or trees along

marsh edges.

In San Diego County, California, Dixon et a1. (1957) reported that

black-shouldered kites nest in "any suitable tree of moderate height. II Dixon

et a1. (1957) listed pepper (Schinus molle), avocado (Persea gratissima),

orange (Citrus sinensis), eucalyptus (Eucalyptus masculata), and olive (Olea

europaea) trees among the introduced species used for nest placement.

Native tree species included cottonwood (Populus fremontii), black willow

(Salix nigra), live oak (Quercus agrifolia), sycamore (Platanus racemosa),

and toyon (Photinia arbutifolia). In the Santa Barbara Coastal Plain,

black-shouldered kites built nests in eucalyptus, willow (Salix sp.), live

oak, coyote bush (Baccharis pilularis), Monterey pine (Pinus radiata), and

Monterey cypress (Cupressus macrocarpa) (Wai an 1973). R. C. Stende11 (pers.

comm.) stated that nest sites are not a limiting factor for the kite because

they select a wide array of tree species. Stendell also reported that

black-shouldered kites place their nests at the top of dense shrubs or trees,

1-18 m above ground. Hawbecker (1942) stated that any suitable tree may be

used for nesting if it is near the required food source. Henry (1983) noted

that nest site distribution for black-shouldered kites tends to be loosely

clumped in areas where prey is locally abundant in San Diego County,

Cal i forni a.

Water

Little information exists on the dietary water requirements of the

black-shouldered kite. R.C. Stendell ( pers. comm.) stated that blackshouldered kites kept in captivity were never observed to drink. The

assumption can be made, however, that much of their physiological water is

obtained from their prey, as is the case for most raptors. Microtine

rodents requi re free- standi ng water for reproduction, and thei r numbers are

reduced during a drought (Church 1966). In addition, rodents probably

respond to fl uctuations in vegetation growth as i nfl uenced by the ava ilability of water. In California, the number of kites recorded on Christmas

Bird Counts during a year with heavy rainfall was significantly greater

than the number of kites recorded the previous year (Pruett-Jones et al.

1980). Pruett-Jones et al. interpreted this relationship lias indicative

of a very sensitive response of the (white-tailed) kite to environmental

conditions and changing rainfall patterns as they affect the kite ' s prey

species."

6
Special Considerations

There is SOllie controversy over whether the bIack-sbcul dered kite is

territorial. Hawb@cker (1942) reported two pairs nesting within Il2 M of eath

other for 3 y@ars, ~nd only once was the male of one pair seen driving away

the male of the adjacent pair. Dixon et al. (1957) reported no territorial

fighting among the kites they studied, and stated this species seems to be

more tolerant of conspecifi cs than other raptors. Wai an (1973), however,

found that nesting pairs exhibited territorial behavior and hunted primarily

within their territories. Territory size varied from 18 to 51 ha for 5 pairs

studied. Henry (1983) believed that black-shouldered kites are highly

territorial throughout the nesting cycle based on extensive observations of 11

nesting pairs. Territory size was determined for 5 pairs and ranged from 53

to 120 ha. He argued that previous reports of nonexistent or weakly developed

territoriality were based on insufficient qualitative observations.

Foraging habitat is not necessarily adjacent to the nest site. Henry

(1983) observed one nesting pair of black-shouldered kites that defended a

small (0.06 km2 ) foraging area in a basin located 1.9 km from their nest at

the top of a mesa.

Black-shouldered kites are reported to hunt in group associations

(Stendell 1972) and to use repeatedly the same area for roosting, especially

in the non-nesting season. Group hunting is believed to be associated with

unusually high or peak prey populations (Waian 1973). Bammann (1975) reported

that, although the night roost on his study area was not located, the flight

time from roost to hunting territory was about 30 min each way. Waian (1973)

believed that black-shouldered kites traveled up to 32 kID from their daytime

hunting territories to a night communal roost during the winter on his study

site near Santa Barbara. Birds rarely remained at nesting territories

year round.

HABITAT SUITABILITY INDEX (HSI) MODEL

Model Applicability

The black-shouldered kite HSI model was developed from information on

habitat use in California. Because little information exists on habitat use

in Texas, the model must be used with caution in the Texas coastal prairies

and pasturelands and the Rio Grande Delta region. The model was developed to

evaluate the potential quality of black-shouldered kite habitat throughout the

year. It is applicable in grassland, savanna, and emergent wetland habitats.

Minimum habitat area. Minimum habitat area is defined as the minimum

amount of contiguous habitat requi red for an area to be occupied by a

particular species. No specific data on minimum area requirements for the

black-shouldered kite could be found in the literature. Henry (1983) and

Waian (1973), however, did provide some data on home range (see Special

Considerations). Based on their studies, it is recommended that this model

only be applied to study areas larger than 20 ha.

7
Verification level. The model was reviewed by Rey C. Stendell, U.S. Fish

and Wildlife Service (FWS), Northern Prairie Wildlife Research Center,

Jamestown, North Dakota, and by Brian R. Chapman, Corpus Christi State

University, Texas. Although reviewers ' comments have been incorporated where

possible, the authors are responsible for the final version of the model. The

model has not been field-tested.

Model Description

Although black-shouldered kites appear to benefit from agricultural

practices and associated increases in rodent populations, this model was

.developed for evaluating nonagricultural habitat (i.e., grasslands and

wetlands) quality. It is not designed for application in agricultural

habitats.

Litt1equanti tati ve research has been done on habi tat requi rements of

black-shouldered kites. The HSI model is based on information on habitat use

by hunting black-shouldered kites provided by Bammann (1975). It considers

the percentage of the study area that is composed of the four cover types

hunted most frequently by kites in Bammann's (1975) California study: tall

rank grass, short rank grass, rush, and salt marsh. Nesting cover is not

included in the model. Because black-shouldered kites will nest in a variety

of tree speci es at vari ous hei ghts from the ground, the model assumes that

suitable nesting sites will be available.

Suitability Index (SI) Values for Model Variables

Suitability indices were assigned to each of the four cover types in the

model based on preferential use of the cover types by hunting black-shouldered

kites (Table 2). Preference was determined by comparing Bammann's (1975)

information on the availability (percentage of total vegetated area) of the

cover type and the percentage of time the cover type was hunted over.

Descriptions of the cover types are provided in the Specific Habitat

Requirements section.

Table 2. Suitability indices for cover types in the blackshouldered kite habitat suitability index model.

Cover type

Tall grasslands

Short grasslands(cut for hay

the previous year)

Rush

Saltmarsh

8

Suitability index

1.0

0.5

0.3

0.25
HS1 Determination

The presence of water must be considered before determining the HS1 value

for a site. As noted previously in this report, prey species of the

black-shouldered kite are dependent on permanent sources of water. If such a

source (e.g., wetlands, streams, or drainage ditches) is present, the model may

be app1i ed to the site. The fo 11 owi ng equation is used to determi ne the

habitat suitability index value for black-shouldered kite habitat. (Note that

percentage values should be expressed as decimals for use in the equation

[e.g., 50% = 0.50]).

(1)

where Ai = percentage of study area that is tall grasslands,

A2 = percentage of study area that is short grasslands,

A3 = percentage of study area that is rush, and

A4 = percentage of study area that is salt marsh.

Hypothetical data sets presented in Table 3 illustrate the determination

of HS1 values for black-shouldered kite habitat using Equation 1. The data

sets were se 1ected to represent hi gh, moderate, and low qual i ty habi tats.

Table 3. Suitability indices (51) and habitat suitability indices (HS1) for 3

hypothetical data sets.

Data set 1 Data set 2 Data set 3

Percentage Percentage Percentage

Cover type composition 51 composition 51 composition 51

Tall grasslands 90% 1. 00 25% 1. 00 0% 1.00

Short grasslands 0% 0.50 25% 0.50 25% 0.50

Rush 10% 0.30 40% 0.30 0% 0.30

Saltmarsh 0% 0.25 10% 0.25 75% 0.25

HS1 0.93 0.52 0.31

Field Use of Model

The black-shouldered kite HS1 model is developed for evaluating

nonagricultural habitat value only and should not be applied in agricultural

areas. The study area for black-shouldered kites should consist of only

grass 1and, savanna, and emergent wetland cover types. Compositi on of cover

types within the study area can be determined by line transect sampling (Hays

et al. 1981), from available cover maps, or from aerial photographs.

9
The model includes the major assumption that nesting and roosting sites

for black-shouldered kites will be available and, therefore, do not need to be

measured as a model variable. This assumption was made based on the following

facts:

1. Several literature references indicate that this kite will nest in

any species of tree or shrub that is of moderate height.

2. Nesting black-shouldered kites have been noted to fly 1.9 km from a

nest tree to a foraging area (Henry 1983).

3. During the winter, communal night roosts may be as far as 32 km from

daytime foraging territories (Waian 1973).

The user should evaluate the validity of the assumption for each field

application. The model should not be applied if it appears that trees or

shrubs for nesting and roosting are absent in the study area or within a 2 km

distance. Similarly, if a development project has a significant impact on

woody vegetation in an area where such vegetation is scarce and widely

scattered, the project may eliminate black-shouldered kite use of the area.

Interpreting Model Outputs

The HSI value obtained by applying the black-shouldered kite model may

have no relationship to the actual population level on a study area. Kite

numbers may be regulated by nonhabitat factors (e.g., competition, disease)

excluded from the HSI model. The model is useful in comparing the relative

potential of two sites, or of a single site at two points in time, to support

black-shouldered kites.

10
REFERENCES

American Ornithologists' Union. 1983. Check-list of North American birds.

Allen Press, Lawrence, Kans. 877 pp.

Bammann, A.R. 1975. Ecology

wintering white-tailed kites.

Arcata, Calif. 81 pp.

of predation and social interactions of

M.S. Thesis. Humboldt State University,

Brown, L., and D. Amadon. 1968. Eagles, hawks and falcons of the world.

Vol. 1. Hamlyn House, Feltham, N.Y. 414 pp.

Cameron, G.N. 1977. Experimental species removal: demographic responses by

Sigmodon hispidus and Reithrodontomys fulvescens. J. Mammal. 58:488-506.

Cameron, G.N., and S.R. Spencer. 1981. Sigmodon hispidus. Mammal. Species

158: 1-9.

Church, R.L. 1966. Water exchanges in California vole (Microtus californicus). Physiol. Zool. 39:326-340.

Dixon, J.B., R.E. Dixon, and J.E. Dixon.

white-tailed kite in San Diego County,

1957. Natural hi story of the

California. Condor 59:156-165.

Eisenmann, E. 1971. Range expansion and population increase in North and

Middle America of the white-tailed kite (Elanus leucurus). Am. Birds

25:529-536.

Fleharty, E.D., and M.A. Mares. 1973. Habitat preference and spatial

relations of Sigmodon hispidus on a remnant prairie in west-central Kansas.

Southwest. Nat. 18:21-29.

Goertz, J.W. 1964.

rat populations.

The influence of habitat quality upon density of cotton

Ecol. Monogr. 34:359-381.

Goertz, J.W., and R.C. Long. 1973. Habitats of five species of rat in

Louisiana. Am. Midl. Nat. 90:460-465.

Grinnell, J., and A.H. Miller. 1944. The distribution of the birds of

California. Pacific Coast Avifauna No.7. Cooper Ornithological Club,

University of California, Los Angeles. 608 pp.

Ha11, E. R. 1981.

Sons, New York.

The mammals of North America.

1,181 pp.

11

2 vol s. John Wi 1ey and
Hawbecker, A.C. 1940. The nesting of the white-tailed kite in southern Santa

Cruz County, California. Condor 42:106-111.

Hays, R.L., C.S. Summers, and W. Seitz. 1981. Estimating wildlife habitat

variables. U.S. Fish Wildl. Servo FWS/OBS-81/47. III pp.

Henry, M.E. 1983. Home range and territoriality in breeding white-tailed

kites. M.S. Thesis. San Diego State University, Calif. 128 pp.

.Higgins, K. F., and W.1. Barker. 1982. Changes in vegetation structure in

seeded nesting cover in the prairie pothole region. U.S. Fish Wildl. Servo

Spec. Sci. Rep. Wildl. No. 242. 26 pp.

Kaufman, D.W., and E.D. Fleharty.

rodents in north-central Kansas.

1974. Habitat selection by nine species of

Southwest. Nat. 18:443-452.

Larson, D. 1980. Increase in the white-tailed kite populations of California

and Texas - 1944-1978. Am. Birds 34:689-690.

McClenaghan, L.R. Jr., and M.S. Gaines. 1978. Reproduction in marginal

populations of the hispid cotton rat (Sigmodon hispidus) in northeastern

Kansas. Occas. Pap. Mus. Nat. Hist. Univ. Kans. 74:1-16.

Oberholser, H.C.

Press, Austin.

1971. The bi rdl i fe of Texas, Vo 1. 1.

530 pp.

University of Texas

Odum, E. P. 1955. An eleven year history of a Sigmodon population. J.

Mammal. 36:368-378.

Pruett-Jones, S. G., M. A. Pruett-Jones, and R. L.

tailed kite in North and Middle America:

population changes. Am. Birds 34:682-688.

Knight.

current

1980.

status

The whiteand recent

Rappole, J.H., and G.W. Blacklock. 1985. Birds of the Texas coastal bend.

Abundance and distribution. Texas A&M University Press, College Station.

126 pp.

Raun, G.G. 1960. Barn owl pellets and small mammal populations near Mathis,

Texas, in 1956 and 1959. Southwest. Nat. 5:194-200.

Rebel, R.J., J.N. Briggs, A.D. Dayton, and L.C. Hulbert. 1970. Relationships

between visual obstruction measurements and weight of grassland vegetation.

J. Range Manage. 23:295-297.

Stendell, R.C. 1967. Food and feeding behavior of the white-tailed kite near

Santa Barbara, California. M.A. Thesis. University of California, Santa

Barbara. 56 pp.

Stendell, R.C. 1972. The occurrence, food habits, and nesting strategy of

white-tailed kites in relation to a fluctuating vole population. Ph.D.

Dissertation. University of California, Berkeley. 224 pp.

12
Stendell, R.C., and P. Myers. 1973. White-tailed kite predation on a

fluctuating vole population. Condor 75:359-360.

Thurber, W.A., and J.F. Serrana. 1972. Status of the white-tailed kite in El

Salvador. Condor 74:489-491.

U.S. Fish and Wildlife Service. 1980. Habitat evaluation procedures (HEP).

ESM102. U.S. Fish Wildl. Serv., Washington, DC. n.p.

Waian, L.B. 1973. The behavioral ecology of the North American white-tailed

kite (Elanus leucurus majusculus) of the Santa Barbara Coastal Plain. Ph.D.

Dissertation. University of California, Santa Barbara. III pp.

Warner, J.S., and R. L. Rudd. 1975. Hunting by the white-tailed kite (Elanus

leucurus). Condor 77:226-230.

13
:'0272 -UU

REPORT DOCUMENTATION II. REJOORT NO. 12.

PAGE Biological Report 82(10.130)

... TItle end I4Ibtltle

Habitat Suitability Index Models: Black-shouldered Kite

7. AuttIof'(.)

Craig A, Faanes a and Rebecca J. Howard b

1. Reclpl.nt'. AcC...lon No.

I. R.port O.te

January 1987

L Performln. O...nlzetlon Rept. No.

,. Performl~ O...nlzetlon N.me .nd Add,...

aNorthern Prairie Wildlife

Research Center

U.S. Fish and Wildlife Service

Jamestown, ND 58401

12. Sponsorin. O...nlutlon N.m••nd Addre••

bNational Wetlands Research Center

U.S. Fish and Wildlife Service

1010 Gause Blvd.

Slidell, LA 70458

10. ProlectlT..k/Worll Unit No.

11. Cont,.ct(C) 0' Grllnt(G) No.

National Wetlands Research Center

Research and Development

Fish and Wildlife Service

U.S. Department of the Interior

Washington, DC 20240

II. Supplem.nt.ry Not••

-IL Abstrllct (Limit: 200 wo,ds)

13. Type of R.port &. Pe,iod Covered

I".

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

evaluating black-shouldered kite habitat quality. The model is scaled to produce an

index between 0 (unsuitable habitat) and 1.0 (optimal habitat). Habitat suitability

index models are designed for use with the Habitat Evaluation Procedures previously

developed by the U.S. Fish and Wildlife Service. Guidelines for model application are

provided.

17. Document An.lysis •. O.scriptors

Mathematical models

Birds

Wildlife

b. Id.nt'fi.,./C>\)en·Ended T.rms

Habitat Suitability Index

Habitat

Habitat management

c. COSATI Field/Group

IL Av.lI.bllity St.tement

Unlimited release

(5•• ANSI-l39.18)

Impact assessment

Black-shouldered kite

Elanus caeruleus

Ill. Security CI... (This Report)

Unclassified

20. Security Class (This P••e)

Uncl assifi ed

21. No. of P••••

13

22. Price

OPTIONAL FOR" 272 (4-77)

(Fo,me,ly,NTlS-35)

Dep.rtm.nt of Comm.rc.
Take Pride in America

Preserve OurNatural Resources

DEPARTMENT OF THE INTERIOR

u.s. FISH AND WILDLIFE SERVICE

As the Nation's principal conservation agency, the Department of the Interior has responsibility for most of our .nat ionally owned public lands and natural resources. This includes

fostering the wisest use of our land and water resources, protecting our fish and wildlife,

preserving the-environmental and cuttural'values of our national parks and historical places,

and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in

the best interests of all our people. The Department also has a major responsibility for

American Indian reservation communities and for people who live in island territories under

U.S. administration.