Ornithological Monographs 24

LAND

BIRD

GRAND

THE

COMMUNITIES
BAHAMA

STRUCTURE
OF

AN

OF

ISLAND:

AND

DYNAMICS

AVIFAUNA

BY

JOHN

T.

EMLEN

Department of Zoology
University of Wisconsin

ORNITHOLOGICAL

MONOGRAPHS
PUBLISHED

THE

AMERICAN

BY

ORNITHOLOGISTS'
1977

NO.

UNION

24


LAND

BIRD

GRAND

THE

COMMUNITIES
BAHAMA

STRUCTURE
OF

AN

OF

ISLAND:

AND
AVIFAUNA

DYNAMICS


ORNITHOLOGICAL

MONOGRAPHS

This series,publishedby the AmericanOrnithologists'
Union, hasbeenestablished
for major paperstoo long for inclusionin the Union'sjournal, The Auk. Publicationhasbeenmadepossiblethroughthe generosityof Mrs. Cafil Tucker and the

Marcia Brady Tucker Foundation, Inc.

Correspondence
concerning
manuscripts
for publicationin the seriesshouldbe
addressedto the Editor-elect,Dr. MercedesS. Foster, Department of Biology,
Universityof SouthFlorida, Tampa, Florida 33620.
Copiesof OrnithologicalMonographsmay be orderedfrom the Assistantto the
Treasurerof the AOU, Glen E. Woolfenden,Departmentof Biology,Universityof
SouthFlorida, Tampa, Florida 33620. (See price list on back and inside back
cover.)

OrnithologicalMonographsNo. 25, xi + 129 pp.
Editor of A.O.U. Monographs,John William Hardy

SpecialAssociateEditorsof this issue,FrancesC. James,Department
of Biology, Florida State University, Tallahassee,and Ned K.
Johnson,Museumof VertebrateZoology,Universityof California,
Berkeley
Assistant Editor, June B. Gabaldon

Author, John T. Emlen, Departmentof Zoology,Universityof Wisconsin, Madison, 53706

First receivedDecember 1975; accepted,October 1976; final revision,
December

1976

Issued November 22, 1977

Price $9.00 prepaid ($8.00 to AOU Members)
Library of CongressCatalogueCard Number 77-90792
Printedby the Allen Press,Inc., Lawrence,Kansas66044
Copyright ¸

American Ornithologists' Union, 1977
ii


LAND

BIRD

GRAND

THE

COMMUNITIES
BAHAMA

STRUCTURE
OF

AN

OF

ISLAND:

AND

DYNAMICS

AVIFAUNA

BY

JOHN

T.

EMLEN

Department of Zoology
University of Wisconsin

ORNITHOLOGICAL

MONOGRAPHS
PUBLISHED

THE

AMERICAN

BY

ORNITHOLOGISTS'
1977

NO.

UNION

24


iv


TABLE

PREFACE

OF

CONTENTS

........................................................................................................

1--INTRODUCTION
2--METHODS

......................................................................................

...............................................................................................

xi
1

2

HABITAT MEASUREMENTS ..........................................................................

2

ANALYSIS OF HABITAT DISTRIBUTION .........................................................

3

BIRD POPULATION MEASUREMENTS ...........................................................

4

WITHIN-HABITAT

4

3--GRAND

DISTRIBUTION AND ACTIVITY MEASUREMENTS ..............

BAHAMA

ISLAND

THE ENVIRONMENT

..................................................................

...................................................................................

Geology ...............................................................................................

5
5

5

Physiographic
history............................................................................ 5
Climate ................................................................................................

6

Recent history ......................................................................................

6

THE BIRDS ................................................................................................

7

Geographicdistributionof the breedingspecies.................................

7

Originsand routesof invasion..............................................................

8

Colonizationpatterns............................................................................ 10
Turnover

4

rates ......................................................................................

THE HABITATS

AND

THEIR

BIRD

COMMUNITIES

........................

VEGETATION PATTERNS ..............................................................................

11

12
12

Generaldescription
................................................................................ 12
The structure of Grand Bahama habitats ............................................

13

Groupingof standsinto habitattypes.................................................. 15
Alignment of standsalonggradients....................................................
THE BIRD COMMUNITIES

............................................................................

19
21

Communitystructure............................................................................ 21
Bird speciesdiversity............................................................................ 25
Total bird density............................................................................
DISCUSSION-•DIVERSITY

AND DENSITY CORRELATES ................................
V

28
30


5-•BIRD

DISTRIBUTION

THROUGH

THE

HABITATS

..........................

DYNAMICS OF DENSITY DISTRIBUTION ......................................................

Conceptsand models ............................................................................

32

32

32

Habitat distributionpatterns................................................................. 33
HABITAT

SELECTION

.................................................................................

36

Distributionby types............................................................................ 36
Distribution along gradients............................................................... 36
DISPERSION

AMPLITUDES--SPECIALIZATION

............................................

39

Dispersionof speciesthroughthe 25 stands........................................ 39
Dispersionby types .............................................................................. 39
Dispersionalong gradients....................................................................
DENSITY

DISPERSION RELATIONS ...........................................................

OVERLAP AND SIMILARITY

41
48

..........................................................................

51

Measuring overlaps ..............................................................................

51

Overlap and phylogeneticrelationships................................................ 52
Overlap and geographicderivation...................................................... 52
Ecologicalspacing................................................................................
6--THE

PINE

FOREST

COMMUNITY-•SEASONAL

PROCEDURES AND DEFINITIONS

CHANGES

..........

54
55

.................................................................

55

SEASONAL CHANGES ....................................................................................

58

The breedingseasoncommunity.......................................................... 59
The wintering community...................................................................

60

The transientcommunity...................................................................

62

IMPACT

OF THE WINTER

7--SPATIAL

DISTRIBUTION

VERTICAL

MIGRANT

INVASION ........................

WITHIN

DISTRIBUTION-•LAYERS

THE

PINE

FOREST

_...................

63

..................

66

............................................................

67

Vegetativestructureand avian utilizationat five levels...................... 67
Populationstructurein the five layers.................................................
COMPARTMENT

DISTRIBUTION ....................................................................

70
70

Physicalcharacteristics
of the compartments
........................................ 72
Bird speciesdistributionthroughthe compartments............................ 73


Populationstructurein the compartments
............................................ 75
Seasonalchangesin spatialdistribution.............................................
8--GUILD

DISTRIBUTION

WITHIN

CONCEPTS AND DEFINITIONS

THE

PINE

FOREST

........................

......................................................................

76
80
80

PROCEDURES ...............................................................................................

81

THE FORAGING GUILDS OF THE GRAND BAHAMA PINE FOREST ................

83

Ground-gleaning herbivores ................................................................

83

Stemseedpluckers................................................................................

94

Fruit and bud harvesters .....................................................................

94

Nectar sippers......................................................................................

95

Sap and cambium eaters ......................................................................

96

Foliage browsers..................................................................................

96

Ground-gleaningcarnivores..................................................................

96

Ground pouncers.................................................................................

97

Flower probers...................................................................................... 97
Shrubfoliage gleaners.......................................................................... 97

Shrub stem drillers ..............................................................................

98

Pine bark and wood drillers ................................................................

98

Bark gleaners........................................................................................

98

Pine twig gleaners................................................................................

99

Pine coneprobers................................................................................ 100
Pine needle gleaners..............................................................................

101

Air sallyers........................................................................................... 102
Air screeners ...........................................................................................

103

GUILD BIOMASS AND FOOD ABUNDANCE .....................................................

103

GUILD STRUCTURE AND COMMUNITY DYNAMICS .......................................

106

Guild structureand diversity................................................................ 106

Dispersionof speciesthroughthe guilds.............................................. 106
SPECIES OVERLAP AND COMPETITION .......................................................

ACKNOWLEDGMENTS
SUMMARY

................................................................................

.....................................................................................................
vii

109

111
112


CONCLUSIONS
LITERATURE

..............................................................................................
CITED

APPENDIX---SPECIES

115

.................................................................................

115

ACCOUNTS

118

............................................................

ooo

V1H


LIST

Figure

OF

FIGURES

1. Plant types and foliage compartments...............................................................
2. Map of the westernBahama Islands ....................................................
3. Continental and Antillean ranges of the breeding land birds of Grand
Bahama

..................................................................................................

4. Faunal derivation of the breeding land birds of Grand Bahama ..................

4
6
9

10

5. Map of Grand Bahama Island showingextent of forests and location of
survey stands ...............................................................................................

12

6. Cross-island profile showing vegetation zones and positions of survey
stands

7.
8.
9.
10.

...............................................................................................

13

Submaturepine forests on Grand Bahama Island ............................................ 14
Young pine forest types and open stands............................................................ 15

Other Grand Bahama habitat types .................................................................... 16
Distribution of the 25 survey stands on canopy height-canopycover
coordinates

.....................................................................................

17

11. Distribution of the 25 standson habitat gradient diagrams ..................
20
12. Bird speciesdiversity plotted on habitat gradient diagrams ........................... 26
13. Species number and diversity plotted against foliage height diversity at
25 sites .........................................................................................................

27

14. Bird species
numberand diversityplottedagainstvegetationdensity(volume)
at 25 sites ..............................................................................................................

15.
16.
17.
18.
19.

Total bird density plotted on habitat gradient diagrams ...........................
Total bird densityplotted againsttotal vegetationvolume ..................
Hypothetical density distribution through habitats of declining quality .......
Decreasingdensitythrough 10 favored standsfor 34 common species.......

Habitat distribution of Grand Bahama specieswith respect to tree, shrub,
and exposedground cover ..........................
20. Habitat distributionof Grand Bahama specieswith respectto vegetation
height and arboreal foliage volume ....................................................................

28

29
31
33
34
40
42

21. Habitat distribution of Grand Bahama specieswith respect to shrub type
and shrub plus ground cover foliage volume .................................................
22. Permanent resident densitiesplotted on habitat gradient diagrams ................
23. Winter residentdensitiesplotted on habitat gradient diagrams ........................
24. Density in preferred stand plotted against dispersionamplitude ...............

44
46
47
51

25. Ordination of the Grand Bahama bird speciesfor similarity of habitat
selection

.................................................................................................

58

26. Physioguomicstructureand compositionof the submaturepine forests........ 59
27. Temporal limits of the seasonalbird communitiesof Grand Bahama ..........
62
28. Monthly changesin size and composition of the pine forest bird com.......................................................................................................

63

29. Geographic sourcesof the migrant invaders•species .......................................
30. Geographic sourcesof the migrant invaders--numerical representation....
31. Relation of arian insect gleaner biomass to food resource levels in 7

munities

64
65

32.
33.
34.
35.
36.
37.

compartments .....................................................................................

66

Vertical distributionof commonspeciesin the pine forests...................

Speciesdiversityand densityin 5 equal layers of the pine forests.........
Relative abundanceof speciesin the 5 equal layers ..........................
Winter invader and permanentresidentrepresentationin the 5 equal layers ....
Compartmentdistributiondiagramsfor 30 pine forest species ....................
Relativeabundanceof speciesin the 4 major compartments...........................

67
69
71
71
74
75

38. Relative abundanceof speciesin 16 foraging guilds ........................................ 85

ix


TABLES
Table

1. Vegetation measurements in the 25 Grand Bahama habitats ..............................
2. Bird densities at the 25 habitat sites--winter 1969 ..............................................

14
22

3. Relation of dispersiontypesand behaviortypesin Grand Bahama land birds .... 35
4. Percent distribution of the 34 common bird speciesthrough the 25 survey
stands

........................................................................................................................

37

5. Distribution of speciesthrough 7 habitat types on Grand Bahama Island ........ 48
6. Positionand dispersionof 5 pine foliage gleanersalong 9 gradientsof the pine
forest habitat

............................................................................................................

7. Habitat specialization along 7 gradients for various elements of the Grand
Bahama land bird community ...............................................................................
8. Overlap in habitat selectionin winter ..................................................................
9. Habitat overlap and geographic derivation ............................................................
10. Habitat overlap and residency status ....................................................................
11. Physiognomic characteristicsof the submature pine forests ...............................
12. Dominant tree and shrub speciesin submature pine forests ................................
13. Size, density and biomass of the 4 residency elements in the 3 seasonal pine
forest

commtmities

................................................................................................

50

50
53
54

54
56
57
60

14. Residencystatus, density, and biomassof member and visitor speciesin the 3
seasonalpine forest communities ......................................................................... 61
15. Vertical distribution of bird populations in the wintering commtmity of the
pine forest ................................................................................................................
68
16. Volume and structural characteristicsof the major habitat compartments of
the pine forests ....................................................................................................... 72
17. Demographic characteristicsof the bird populations in the 4 major compartments of the pine forest ........................................................................................77
18. Compartmentpreferencesof membersof the wintering and breedingcommunities

19.
20.
21.
22.
23.
24.
25.
26.

.........................................................................................................................

78

Guilds and guild provincesrecognized in the submature pine forests ............. 82
Foraging guild distributionsof members of the pine forest bird commtmity .... 84

Speciesdensitiesin the foraging guilds ................................................................ 86
Biomass of each speciesin the foraging guilds .................................................... 88
Percent speciesdensity compositionof foraging guilds .................................... 90
Percent biomasscompositionof foraging guilds ................................................. 92
Foraging methods of members of the needle-gleaningguild ............................. 102
Composition and structure of the 18 foraging guilds of the Grand Bahama
forest

communities

.................................................................................................

107

27. Overlap in guild membershipin the wintering commtmity ............................... 110
28. Overlap in guild membershipin the breedingseasoncommtmity........................ 111


PREFACE

This monographhad its beginning24 yearsago when I undertooka study of
the habitat distribution

and structure of several communities of land birds in

Central Africa. As I launchedinto this project it becameclear that available
techniques
were totally inadequatefor the quantitativeanalysesI neededand
that it was up to me to developnew ones. Some progresswas made that year
with a systemfor describing

andmeasuring
habitats(Emlen 1956), but I returned
to the Stateswith no soliddata on eitherpopulationdensitiesor habitatrelations.
Returningto other researchactivities,I postponedfurther fieldwork on these
problemsuntil 1967 when I was able to devotea springsemesterto a studyof
the structureand dynamicsof the winteringbird communities
of a grass-bushland
area in southernTexas (Emlen 1972). The vegetativestructurewas relatively
simplehere,and besidesimprovingmy techniques
of habitatdescriptionI worked
intensivelyon developing
censusmethodsfor smallland birds,methodsthat would
provideabsolutedensityvaluesby equatingvariablesin transectcountswith the
detectabilitycharacteristics
of eachspecies(Emlen 1971).
After testingthesehabitat measurementand censustechniquesin a variety of
situations,I selectedthe extensivepinelandforestsof the southeastern
statesand
neighboringBahamaislandsfor the type of studyI had tried to conductin Africa
15 yearsbefore. The work of William B. Robertsonin this area provideda valuable backgroundon ecologicalconditionsand faunal composition(Robertson
1955), and I beganthe studiesdescribedin this monographin Januaryof 1968.
During the 20 yearssincethe conceptionof this project,approaches
to the study
of communityecologyhave changedconsiderably.Important new conceptson
the niche, competition,and communitydynamicshave appeared,and emphasis
has shiftedstronglyfrom descriptivestudiesto model buildingand testing. Work
in the old patternseemsdimmedby the brillianceof thesenew studies.But I am
repeatedlyimpressedthat the imaginativecreationsof theoreticalecologistsrarely
survivelong in this modernera of scientificfermentunlessthey are built on solid
empiricaldata. Most of the speculationsand interpretationsin this monograph

will doubtlessbe ephemeralas our scienceprogresses;
I only hope that the materials on which they are basedwill prove to be solid and clearly presented.

xi


1--INTRODUCTION

This monograph
represents
an attemptto analyzethe populationstructureand
dynamicsof a definitiveavifauna.Unlike a typicalfaunalstudyit focuseson the
densities
and ecological
distributions
of species
throughthe habitatsand foraging
substrates
of the vegetation
and undertakes
to evaluateand interpretsomeof the
factorsunderlyingcommunitystructureand regulation.My approachis descriptive
with an attemptto presenta broadand balancedpictureof the entiresystem.
I selected
an islandasthe sitenot because
of a particularinterestin the problemsof insularity,but becausean islandcommunityis shieldedby surrounding
water barriersfrom the confusionof irregularingressand egressby speciesthat
belongonlyperipherally
or reallydo notbelongat all.
As an islandsite for the study,Grand Bahamawas large enoughto provide

an assortment
of habitattypes,yet smallenoughto minimizethe confusing
effects
of regionalnomadismand local geographicvariation. One type, lowland pine
forest,was represented
extensivelywhile otherswere restrictedto small blocks
or beltsadequate
to holdonlylimitedpopulations.GrandBahamais particularly
well situatedfor observingthe extent and impact of seasonalmigrant invasions
on the structureand integrityof residentcommunities.Little ornithological
work
has been done on Grand Bahama, but the avifauna of the region has been well
coveredduringthe past 50 years.
The fieldwork was done during the months of January through May in 1968
and 1969. In 1968 I spentalternate2-week periodson Grand Bahamaand in
southernFlorida censusingthe bird populationsand plotting their distribution
throughthe vegetationof the pine forestsfor comparativematerial. In 1969 I
spent the entire period on Grand Bahama, measuringcommunity structuresand
populationdensitiesat 25 survey sites during January, February, and March,
and conductingfurther censusand behaviorobservations
in the pine forestsin
April and May. I returnedfor brief visitsin Januaryand May of 1971 to check
severaldetailsand to collectmaterialon avian food resourcesin the pine foliage.
The studycoveredthe small land birds only, thosethat interacteddirectlyin
exploitingthe resourcesof the terrestrialvegetationand its invertebrates.Other

membersof this trophicassemblage,
especiallythe lizards,shouldlogicallyhave
beenincluded. They are a minor elementexceptin the shrubsand groundvegetation, but their omissionis due primarilyto my limitedversatilityand lack of time.
The rationale for ecologicalanalysisin this study is to recognizethree hierarchicalsystems

of decreasing
inclusiveness
throughwhichdispersioncan be charted:
a habitat level, a within-habitat compartmentlevel, and a substratelevel. Individual birds are regardedas ranging through the various subdivisions
of these
systemsbut concentratingtheir activitiesin those subdivisionswhere conditions
are most favorablefor their morphologicaland physiologicalcharacteristics.The
organization
of thismonograph
is basedon thisapproach.After presenting
backgroundmaterial in the first three chapters,! examineacross-habitatdistribution
in chapters4 and 5, and then compartmentand substratedistributionin the pine
foresthabitat in chapters6, 7, and 8.
Descriptivematerialon the bird specieswith scientificnamesand quantitative


2

ORNITHOLOGICAL

MONOGRAPHS

NO.

24

data on ecologicaland distributionalcharacteristics
is presentedin an appendix.
Nomenclaturefor North American speciesfollows the A.O.U. Checklist (1957)
and supplements

(1973); for the Antilleanspecies
I havefollowedBond (1971).
2--METHODS

SELECTION OF SURVEY SITES

I first surveyedthe physiognomic
and floristiccharacteristics
of the vegetation
of the islandto determinethe natureand rangeof habitatvariationand to provide
a basisfor selectingappropriatetractsfor intensivestudy. I thenselected25 tracts
representingthe full range of variationbut each showingmaximuminternal uniformity of structureover at least20 ha. Sketchmapsof eachtract were prepared,
and transectroutes0.9-1.8 km in lengthwere laid out bisectingthe most typical
portion of the tract, avoidingedges,and taking advantageof existingtrails and

roadways.Threetractsin the submature
pineforeststhat dominated
the island
were used for intensivestudiesof within-forestdistributionin 1968 (chapters 6,
7, and 8). The other 22 representedvarioushabitat types and, togetherwith the
3 submature forest areas, were used for studies of across-habitatdistribution in
1969 (chapters4 and 5).
HABITAT

MEASUREMENTS

The vegetationat each of the 25 sites was sampledalong a seriesof habitat
dimensionsof presumedimportanceto the birds. Data were recorded according
to a systematicplan in the 3 submaturepine forest tracts and less formally for
the other 22 tracts.

In

the 3 submature

forests the measurements

were

made

at stationslocatedby random number serieswithin each of 60 blocks (20 in each
stand) 66 m long and 90 m wide, evenly straddlingthe transectroute. Each
station point served as the center for measurements(trunk diameter, height,
crown diameter,crown depth, and distance)of the nearesttree in each of three
size classes(emergent, canopy, subcanopy)in each of four radial quadrants.
Twenty points surroundingeach station point (at 3-m intervals) along 4 equispacedradii) were used for data on tree canopy, shrubvegetation,and ground
vegetation. Tree canopy (presenceand type) was recordedwith a zenith sighting device (Emlen 1967); shrub type, height, crown diameter,and species,and
ground cover type, depth, and density were recordedby plumb line contacts.
A total of 240 data pointswas thus obtainedfor most arborealdimensions,and
1200 for the others.

Becauseof time limitations,vegetationevaluationson the other 22 tracts were
madeby lesssystematic
sampling,pacing,and subjectivecomparisonwith diagrammatic representations
of canopycover. A shorthandsystem(Emlen 1956) was
usedin whichvegetationtype,foliagetype,foliagedensity,canopyheight,canopy
cover, and patchinesswere recordedin formulae representingthe tree, shrub,
and groundcoverstrata.
For within-habitat'distributionstudiesthe vegetationin all standswas apportionedinto compartments

basedon plant type, vertical zone, and horizontalzone
in the tree, shrub, and-groundcover strata (Fig. 1). I recognized7 plant types


1977

EMLEN:

GRAND

BAHAMA

BIRD

COMMUNITIES

3

in the forestfrom deadstumpsand emergentpines(toweringabovethe dominant
canopy) to ground cover, 5 vertical divisionsor levels in each plant from the
lower stem to upper crown, and 5 horizontaldivisionsarrangedas concentric
zonesaroundeachplant from the tree trunk or shrubcore to the peripheryand
the emptyspacearoundand betweenplants. Any point in the entirespacebetweenthe canopytop and the groundis thus assignable
to 1 of 175 compartments
in this system.In practice,many compartments
were nonexistent,
undetectable,
or unmeasurable,
and for data analysisthe numberwas reducedby combinations
and eliminations

to 11.

The volumeof standingvegetation(numberof m3 of spacecontainingplant
stemsof foliage) was calculatedfor the 3 vegetationstrata and the 1! recognized
compartments
of eachstand. Viewing the averagetree crown as a verticalcylinder
with roundedtop and bottom, I multipliedthe mean crown depth in metersby
0.75 by the canopycoverin m3 per ha for each tree classto give a volumetric
densityvalue in m• per ha. A similar procedurewas used for the shrub and
groundvegetationstrata. Volumesfor all compartmentsper ha were derivedby
calculatingthe percentrepresentation
of each in its stratumand multiplyingby
the stratumvolume. Volume of the air spacebetweenplants was obtainedby
subtracting
all compartment
volumesfrom the total spacebetweengroundsurface
and tree tops. Values for bark and wood surfaceson tree trunks and stumps
were calculatedin surfaceunits (m 2) by multiplying mean trunk circumference
in theupperandlowerhalf of treesby the trunklengths.
The complexityof the habitat is important as a comprehensive
environmental
parameterin communitystudiesbut is difficultto reduceto a simple,meaningful
index. In this study I followed the procedureintroducedby MacArthur and
MacArthur (1961), using the densityof vegetationin three horizontallayers
corresponding
to the trees,shrubs,and groundcover as the basisfor calculating
an overall habitat diversityindex. Becauseof marked differencesin texture and
screeningcharacteristicsof the foliage in the three layers on Grand Bahama,

however,andbecause
of the presumed
importance
of twigsand stemsas perching
substrates,
I used the presenceor absenceof standingvegetationin blocksof
volumetric space as the basis of measurementsrather than the leaf surface or
foliage screeningmeasuresadoptedby the MacArthurs. The information theory
equation(H' = p• loge pi) was usedto calculatethe index values. Natural logarithmswere usedin all diversitycalculations.
ANALYSIS OF HABITAT DISTRIBUTION

The relativepositionsof the 25 standswith respectto three basichabitat fea-

tures-canopyheight,canopycoverage,and foliagetype--are graphicallydisplayedin Figure10. The groupings
of symbolsin this figureprovidea relatively
objectivebasisfor recognizing7 habitat typesuseful in generaldiscussions
of
speciesdistributions.This approachof plotting standpositionson bicoordinate
gridswasalsousedasthebasisfor tracingthe quantitative
distribution
of species
and of variouscommunityattributesalongselectedhabitatgradients(Fig. 11).
Densityor indexvaluesfor a species
are simplyenteredat the coordinate
position


4

ORNITHOLOGICAL

MONOGRAPHS

/.

Emergent

•.•/
•
I

/
/
/

/

• ! • /'• //f'•

/

/• •

........
........
--- ....

/

YJYYoYYYY¾

.,,o

NO.

24

Pines

Subcanopy
Pines
DeadPineStumps
Broadleaf
Trees

// •"•-----Canopy
Pines
/-----Shrubs

(3size
crosses)

/

/--Ground Cover

o.1,,,
o,,,
L,Io,looJQ
3o,H1,,,,9,.,1,
0o-T/o

Qcl,..........
SEVEN

PLANT

TYPES

Crown

Trunk
Top
• Lower
-- --M,I.

Upper OpenSpoce

Air

Shrubs

Space

Upper

Lower

Ground
Cover
FIVE
LEVELS

FIVE
CONCENTRIC
ZONES

ELEVEN

COMPARTMENTS

Fromm 1. Plant types and foliage compartmentsused in structural analysesof the forest
habitat. M.O. = middle outside, M.I. = middle inside, L.O. = low outside, L.I. -----low
inside.

of eachstandin thesediagrams.The resultingpatternsprovidegraphicportrayals
of densityandattributedistributions
alongtheselected
gradients.
BIRD

POPULATION

MEASUREMENTS

Populationdensitiesfor all bird specieswere obtainedfrom transectcounts
convertedto absolutevaluesby applyinglocally determineddetectabilitycoefficientsbasedon the lateral distributionpattern of detectionpoints (Emlen 1971).
All counts were started within

a half hour after local sunrise and extended for

from 1.2 to 2.1 hours. I alwayswalked the transectsalone, coveringthe route

without deviationsat between1.0 and 1.6 km/hr. All detections,visual or auditory, were recorded.
WITHIN-HABITAT

DISTRIBUTION

AND ACTIVITY

MEASUREMENTS

In addition to identifyingeach bird and estimatingits lateral distancefrom
the trail, I was able to recordbasicinformationon activity and positionwithin
the habitat for most of the detections tallied on the census transects. These ob-

servations
includedactivitywhenfirst detected(whetherforaging,singing,resting,
being agressive),plant type in which located, vertical position (level) in the
plant, radial position(zone) in the plant, and heightabovethe ground. Weather
conditions(temperature,
cloudcover,wind directionand speed,wetnessof vegetation) were alsorecordedfor all trips afield.
Close attention to the task of detectingand recordingall birds encountered
on the morningtransectcountsprecludedsustainedobservationsof behavior and


1977

EMLEN:

GRAND

BAHAMA

BIRD

COMMUNITIES

5

foragingmethods. Unscheduledobservationtime later in the day was used for.
suchwork as well as for measuringvegetation,findingnests,and mappingterritories.

In these unscheduled observations I recorded the basic information

de-

scribedaboveplusdata on ageof the subjects,
presenceand activityof conspecific
and allospecific
associates,
the foragingperch,the food substrate,
and the foraging method. After an observationor seriesof observations
in one place I evaluated the local habitat selectionby recordingthe type, size, and densityof foliage
within approximately1 m of the bird, and the proportionof tree cover,shrub
cover,and exposedgroundcoverwithin an estimated36-m radius (1 acre).
I usedspacedobservationunits rather than secondsof continuousobserving
on the assumptionthat they would give a more balancedand representative
pictureof foragingactivityby a population.In orderto furthersuppress
biasesrelated
to atypicallocal conditionsor individualidiosyncrasies,
I attemptedto distribute
observations

as widelyas possiblein theseactivityobservations.Where one individual or an uncommonspeciesremainedfor continuousobservation,I spaced
the entries at a minimum of • min, and limited the record to 5 entries in a series.

For compartmentdistributionanalyses,the bias inherentin selectedobservation
situations
wasavoidedby usingonlythe transectcounttallies.
3--GRAND
TI-IE

BAHAMA

ISLAND

ENVIRONMENT

Geology.-•Geologically,
Grand BahamaIsland is a long low ridge of oolitic
limestoneof Pleistoceneage, risingat its highestpoint to only about 10 m above
sea level. The groundsurfaceis heavilyerodedwith innumerablepits and deep
solutionholes. Soil is essentiallyabsent,the organicmaterialsdepositedfrom the
vegetation
leachingor settlingto thebottomof theholes.
Physiographic
history.--Beinga tectonicallystableborder ridge of the Little
BahamaBank (Fig. 2), the surfacearea of Grand Bahamaexpandedmany fold
when sea levelswere low duringthe Pleistocene
glacialepochsand alternately
shrankto zero or nearlyzero duringthe interglacialperiod of high sealevel. Thus
the terrestrialflora and fauna were probably annihilatedrepeatedlyby marine
inundation,the last suchepisode,accordingto data from southernFlorida, end-

ing about80,000 yearsago (Alt and Brooks1965). No directland connections
exceptwith neighboring
Abaco Islandhave existedsincethe tertiary. During
the Pleistoceneice advances,however, the broad low surfaceof the Little Bahama
land mass,of which Grand Bahama is a part, extendedto within 50 km of the

Great Bahamaland massto the southwhich, in turn, approachedto within 35
km of Cuba. All of this complexhasbeenseparatedfrom the peninsulaof Florida

sinceat leasttertiarytimesby the deepand relativelywide (105 km) rapidly
flowingcurrentof the Florida straits.

Since
emerging
fromthedeep
seas
oftheSangamon
interglacial
period
(80,000
years ago) Grand BahamaIsland has fluctuatedin size from its present1200
km2 or smaller to 16,500 km2, the area of the Little Bahama Bank of which it is

a part. Estimatesof a sea-levelsubsidence
to the -120 m mark duringthe last
Wisconsinice advance(about 15,000 years ago) (Milliman and Emery 1968)


6

ORNITHOLOGICAL

FIGURE 2.

MONOGRAPHS

NO.

24

Map of the western Bahama Islands showingtheir position with relation to neigh-

boring land masses and to shallow "banks" that mark the extent of the island areas
during Pleistoceneglacial periods.

would indicate an expansionto about 15,000 km2 at that time. Since then the

seahasbeenrisingslowly,reachinga stageof -7 m about4,000 yearsago (Scholl
et al. 1969). At this level the island of Grand Bahama must still have been six

or eighttimesits presentsizeand formeda continuous
land masswith neighboring Abaco Island. The major shrinkingin size has occurredover the past few
thousand
yearsduringwhichsealevelshavebeenrisingat about0.5 m per 1,000
years(Schollet al., op. cit.).
Clirnate.--The climateof Grand BahamaIsland is subtropicalwith temperaturesrangingfrom a mean of 20.3øC in Januaryto 28.2 in July (data from the
Freeportairport). Annual rainfall averages1,216 mm and occursthroughout
the year with about twice as much in summeras in winter. The trade winds
producea dominantsoutheasterly

air flow varyingin directionand intensityunder
the influenceof cyclonicdisturbances
to the north. Hurricanesoccuroccasionally
in late summer,the most recentseverestormshitting the islandin 1941 and 1949.

Recenthistory.--GrandBahamawas almostundisturbed
and essentially
unpopulateduntil 1929 when extensivetimber cuttingwas initiated. Most of the
timberwasstrippedfrom the islandfor minepropsor pulp duringthe late 1940's


1977

EMLEN:

GRAND

BAHAMA

BIRD

COMMUNITIES

7

and 1950's,but reproduction
has beenrapid sincethat time, and no extensive
cuttingother than local clearancefor real estatedevelopment
has been done
since1959. Standscut between 1946 and 1949 were 10 and 12 m high in 1968

and possessed
a lush shrubunderstoryon the southhalf of the Island, lesslush
on the north half. Standscut duringthe 1950's showedvariousstagesof recovery

re_flecting
meangrowthratesof roughly0.5-0.6 m per year. Height,density,
and understory
vegetation
are secondarily
influenced
by irregulargroundfires
and occasional
crownfires. A few smalltractsof pine wereapparentlydenuded
by saltwaterencroachments
duringstorms.
The principalmethodusedin timbercuttingin the 1940'sand 1950'swas to
removeall treesotherthan saplingsand a few tall scatteredstems(aboutfive
treesper acre) usedfor anchoring
the haulinggearand supposedly
as seedtrees
for forestreproduction.The remainingsmalltreesand brushwere then usually
levelledand burned. This procedurehasresultedin rathereven-aged
standswith
a scatteringof slenderrelic "emergents"
abovethe dominantyoungcanopy. One
patchof about4.4 km• on the northsidewascompletely
clearedand kept open
for habitationand farmingduringthe early lumberingperiod. Abandonedfor
10-12 years,it is now vegetatedwith bracken,coarseforbs, and tall grasses,
and exceptfor the narrowcoastalstripsand a few urbanareasand golf courses,

constitutes
the only openland on the island.
Furtherdisturbances
causedlargelyby real estateoperationssince1959 include
the construction
of the city of Freeport-Lucayawest of the Island'scenter,now
coveringabout30 km-ø,and a networkof unpaveddevelopment
roadspenetratingin an irregularnetworkintonearlyone-halfof theIsland'sinterior.
THE

BIRDS

At the time of this study (1968-69) there were apparently33 speciesof land

birdsexcluding
birdsof preybreedingon GrandBahamaIsland. Thirty of these
were permanentresidents,and three were summerresidentsmigratingin from
winter rangesto the south. An additional34 speciesmovedin from the north
duringthe winterseason,and 8 morewerepresentbrieflyas transients
duringthe
springmigrationperiod.
Geographicderivation of the breedingspecies.--Grand Bahama, an oceanic
island,containsno relict continentalspeciesin its breedingfauna and has been
populatedentirely by over-watercolonizationfrom the neighboringcontinents
and islands. Becauseof the relative recencyof its final emergenceas an island

capableof supporting
a terrestrialfauna,it presents
a goodopportunity
to study

the geographic
originsof its colonists.The two primary sourcesare obviously
the North American continent to the north and west and the Antillean Islands to

the south.The nearestland on the continentis 105 km awayacrossthe deepand
geologically
ancientFloridastraits(Fig. 2). Cuba,the nearestand alsothe largestof theAntilles,liesabout500 km away,but onelarge"steppingstone"(Andros
Island) and a seriesof smalleroneshavebeencontinuously
availablefor dispersing birdssinceGrandBahama's
emergence.
The waterbarriersto the southand
north of Androswere about 35 and 50 km wide respectively
at lowestsea level
15,000yearsago,andare 190 and180 km wideat thepresenttime.


8

ORNITHOLOGICAL

MONOGRAPHS

NO. 24

AbacoIsland,lying about30 km to the eastof Grand Bahama,is merelyanother ridgeon the Little BahamaBank, and, not surprisingly,
has a very similar
avian fauna.

Originsand routesof invasion.--In the absenceof a direct record of invasions
and colonizations,

the presentgeographicrangesof the membersof the fauna
providethe bestavailableindicationof originsand routesof invasion.The direction andextentof the rangesof eachof the 33 membersof the breedingland bird
fauna are graphicallyportrayedin Figure 3. Circlesto the left of the central
circlein this diagramindicatecontinentalaffinities;circlesto the right indicate
Antilleanaffinities.The degreeof shadingin eachlateralcirclereflectsthe closenessof phylogenetic
relationship
of the relatedformsin eachof four increasingly
remoteregions.Informationincorporated
in thesediagrams,togetherwith analyses
of avian dispersalin the area by Chapman(1891) and Bond (1963), provides
a basisfor tentativedeductionson the geographicderivationof each memberof
the Grand Bahamacommunity. The deductionsare presentedin code form at
the right of each speciesdiagramin Figure 3. A graphicrepresentation
of the
deducedoriginsand routesof invasionis presentedin Figure 4.
Of the 32 species(exludingthe introducedHouse Sparrow), 7 are best representedby conspecifics
or othercloselyrelatedformson the continentto the northwestand are accordingly
considered
to have arriveddirectlyfrom North America.
Two of these,the wide-rangingMourningDove and the Blue-grayGnatcatcher,
have apparentlydevelopedno taxonomically
recognizedmorphological
changes
sincecolonizingGrand Bahama(Co). Four, the Hairy Woodpecker,the BrownheadedNuthatch, the Yellow-throatedWarbler, and the Pine Warbler have been

recognized
by taxonomists
assubspecifically
distincton thoisland(C•), andone,
the BahamaYellowthroat,is consideredto have evolvedto full speciesstatus(C2).

The ancestorsof 11 of the communitymembersappearto have come from
North or CentralAmericarelativelyrecentlybut reachedGrand Bahamaby way
of the Greater Antilles. All of thesehave changedmorphologicallyin the course
of their Caribbeanperegrinations.The sequenceof eventsin the courseof their

historyof dispersal
requires
considerable
speculation,
but threespecies,
the Cuban
Nighthawk,NorthernMockingbird,
andYellowWarbler,apparently
subspeciated
in the Greater Antillesbefore spreadingnorth into the Bahamas(C• A0); one,
the Ground Dove, has severaldistinctracesin the West Indies, all differentfrom
the continentalforms, and probablyhas subspeciated
at least twice in reaching
Grand Bahama (C• A•). Five speciesare found in the Greater Antilles as well
as in the Bahamasand belongto superspecies
or siblingspeciesgroupsalsooccur-

ring on the North Americancontinent.Their ancestraldispersalroutesthus
probablyincludedearlyinvasions
of the GreaterAntilleswheretheyspeciated
beforespreading
northwardto the Bahamas.Two of these,the Black-whiskered
Vireo andOlive-capped
Warbler,showno furthermorphological
changes

en route
to the northern Bahamas (C2 A•). Two species,the Bahama Swallow and the
Thick-billedVireo, I regardas belongingto superspecies
groupswith specifically

distinctrepresentatives
on severalAntilleanislandsaswell as the Bahamas.Ancestorsof the Grand Bahama forms probably speciatedseveral times en route

to theirpresentrange(C2 A2). The interpretation
of the BahamaSwallow(Cal-


1977

EMLEN:

GRAND BAHAMA BIRD COMMUNITIES

White-cr,
Pigeon
Zenoido
Dove

A0
A0

Mourning
Dove

9

CiAo

CO

Brown-hd.
Nuthotch
Northern
Mockingbird
Bahoreo
Mockingbird

GroundDove

CtAi

Red-legged
Thrush

AI

K.-W.
QuoilDove
Smooth-billed
Ani
Cubon
Nighthowk

A0
Blue-groy

Gnotcotcher
AO
Thick-billed
Vireo
CtAO BIk-whlskered
Vireo

CO
CgA
2
C2A
0

Cubon
Era.Hummer
Bohomo
Woodstot
HoiryWoodpecker

A1
A2
C•

Bohomo
Bononoquit
Yellow
Worbler
Boh.
Yellowthr.
Worbler

C•Ao
C

Red-bellß
Woodp.

C2AI Olive-copped
Worbler

C2A
0

Groy
Kingbird
Loggerheod
Flyc.

AO
AI

Stolid
Flycotcher
Gr.Ar•tilleon
Pewee
Bohomo
Swollow

C2Ai House
Spotrow

C2At Striped-hd.
Tonoger
C2A2 BIk-foced
Grossquit

Bohomo
Pine
Worbler
Bohomo
Yellowthroot

A•

C2
X0
A

Gr.AntilL Bullfinch

FIGURE3. Continental and Antillean ranges of the breeding land birds of Grand Bahama
Island. The presenceof the sameor relatedforms (samesubspecies,
species,superspecies)
is indicated at four increasinglyremote stationsin each of the two directions. (Except
for the Bahama Swallow, taxonomy follows Bond (1971) and the AOU Checklist

(1957) and supplementsthereof (1973). My deductionsconcerningthe geographic
derivationof each form on Grand Bahama are indicated by symbolsat the right of the
diagrams. Symbolsfor degree of relationshipare: Solid circle = same subspecies;
circle with cross= samespecies,different subspecies;
circle with horizontalline = same

superspecies,
different species;
diagonalline cuttingcircle = limited occurrence;vertical
line cuttingcircle = recent colonizer. Symbolsfor deducedderivationare: C = North
American continental origin, A ---- Antillean origin, CA = Continent via Antilles.
X • introducedby modernman, /1 ----subspeciated
with invasion,/2 • speciatedwith
invasion, 70 = no change recorded.

lichelidon)as congenericwith Lamprochelidon
is basedon a compositeof taxonomists'opinions(L. Short in litt.).

The 14 speciesclassedas of Antillean origin belongto generathat probably
derivedat an earlyperiodfrom ancestralformsin eitherCentralor SouthAmerica
(Bond 1963). Five of these,the White-crownedPigeon, the Zenaida Dove, the
Key WestQuail Dove, the Smooth-billed
Ani, and the Gray Kingbird,now have
dispersed
rangesin the WestIndiesandshowno taxonomically
recognized
changes
in their northward extensioninto the Bahamas (A0). Nine specieshave undergonetaxonomically
recognized
changes
in the Bahamas;
eightof these,the Cuban
EmeraldHummingbird,
Loggerhead
Flycatcher,BahamaMockingbird,Red-legged

Thrush,BahamaBananaquit,Striped-headed
Tanager,Black-facedGrassquit,and


i0

ORNITHOLOGICAL

c-

MONOGRAPHS

NO.

24

FROM

AMERICAN
CONTINENT
CA- FROM
CONTINENT
VIA ANTILLES

Cc
C2

C,

ClA1

C

C2A1
C2A2

A2
A•

Ao
A-FROM

ANTILLES

FIGURE4. Faunal derivation of the speciescomprising the breeding land bird fauna of the
Grand Bahama Island. Each arrow represents a group of species. The width of the
arrow indicates the number of species in the group. A cross line on the arrow shaft
showsthat subspeciationhas occurred; a double line, that full speciation has occurred.
The symbolsat the baseof each arrow match thoseusedin Figure 3.

Greater Antillean Bullfinch, to the subspecieslevel (A•)
Woodstar, to the specieslevel (A2).

and one, the Bahama

Colonization
patterns.--Generalizations
basedon patternsof dispersion
through
island chains can provide suggestions
on colonizationhistoriesand sequences.

Of the seven speciescolonizing Grand Bahama directly from North America
only two have pushedfarther into the Antillesthan the first few northernBahama
Islands (cf. Fig. 3) and thesetwo, the Mourning Dove and the Pine Warbler,
occurringas distinctsubspecies
in the Greater Antilles, may have reachedthose
sitesby an earlier invasionor a separateinvasionfrom Central America. Such
patternsof limited and essentiallyunbrokenpenetrationof the island chain suggestrecentinvasion,i.e. an earlystagein taxondispersion
asvisualizedby Ricklefs
and Cox (1972) in their taxon cycle model for archipelagos.From the other
direction,the Southeast,Grand Bahamais at the end of a long islandchain of
dispersion. The 25 speciesconsideredto have come by this route tend to show
the extendedand broken distributionpatternsthat characterizeadvancedstages
in the taxoncycleof Ricklefsand Cox.
Theseobservations
suggestthat membersof the Antillean faunal elementhave,
in general,a longerhistoryin the northernBahamaIslandsthan thoseof the

NorthAmericanelement.Otherfactorsmustbe considered,
however,especially
the vegetationpatternsthroughthe Bahamasand the habitat characteristics
of


1977

EMLEN:

GRAND

BAHAMA

BIRD

COMMUNITIES

11

the bird species.Pine forestsdominateGrand Bahama and the other northern
islands,while brushyvegetationcoverthe islandsto the southand east. With the
exceptionof the MourningDove, a highly eurytopicspecies,all sevenof the
colonizersfrom North America are pine forest inhabitantson Grand Bahama,
eventhe Gnatchatcherand the Yellowthroat,whichelsewhereare characteristically
broad leaf forest and marshlandbirds respectively.This does not conform with
Ricklef and Cox's generalizationthat recent (stage I) colonizerstend to occupy
open, coastal, or disturbed habitats. On Grand Bahama these habitats are, in

fact, occupiedby speciesbelongingto the Antilleanelement,speciesthat according to the island penetrationand broken distributioncriteria, should be in advancedstagesof the taxoncycle.
More direct evidencethat the bird speciesof the North American elementof
pinelandbirds did not invade the northern Bahamasuntil quite recently comes
from fossil pollen data indicating that pines were uncommon in the southern
Florida vegetationuntil about 5,000 years ago (Watts 1971). T/he conditions
of rising sea levels and permeablelimestonerock associatedwith this spreadof
pine forestsin Florida must have also existedand could have producedsimilar
effectson the Little BahamaBank. BahamianPines (Pinuscaribaea)probably
reachedGrand Bahamafrom the south (Howell 1972), but whetherthe present
forestswere established
before the postglacialperiod of sealevel elevationis unknown. Avian fossil materialsfrom New ProvidenceIsland (Brodkorb 1959)
indicatethat arborealbird speciesand hence trees were presenton the Great
Bahama Bank to the southeastduring the last glacial stage of the Wisconsin
glaciation.

Turnoverrates.--The faunal historyof an islandsuch as Grand Bahama is of
coursemore than a progressive
succession
of colonizations.Many extinctionsand
replacements
have undoubtedlyoccurredover the millenia, and some species
may have had a historyof repeatedextinctionsand recolonizations.MacArthur
and Wilson (1967) proposedthat the number of speciespresenton an island at
a giventime reflectsan equilibriumbetweenthe colonization
rate relatedparticularly to distancefrom colonization
sources,and the extinctionrate relatedparticularlyto islandsize. Recentstudieson previouslysurveyedislandsoff southern
California(Diamond1969), in the SouthPacific(Diamond1970), in the Virgin
Islands (Robertson 1962), the Cayman Islands (Johnston1975), and on Mona
Island near Puerto Rico (Terborgh and Faaborg 1973) suggestthat a considerable number of both extinctions and new colonizations have occurred on all of

theseislandsduringthe past 50-75 years. Suchdata, if accurate,suggestthat
turnoverratesof roughly1.0-1.5% per year may be representative
for islandsof
the size and positionof Grand Bahama,but other observers(Lynch and Johnson
1976, Lack 1976) have challengedthese values as artifacts of modern human
intervention.

Historical data do not exist to permit direct estimatesof colonizationor extinctionrateson Grand Bahama. One species,the WestIndian Red-belliedWoodpecker,listed as an uncommonspeciesin coastalscrubforestby Bond in 1936,
was apparentlymissingin 1968-69, and two speciesnot noted by Bond, the
MourningDove and HouseSparrow,were presentlocally and in small numbers


12

ORNITHOLOGICAL

MONOGRAPHS

NO.

24

Mangrove
flats
:[•

Hawksbill

Creek

LacayaBeach

KM

FIGURE5. Map of Grand Bahama Island showingin A the distributionof pine forestsand
mangroveflats and in B the locationof the 25 standssurveyedin this study.

in the latter years. The BahamaMockingbird,not reportedon Grand Bahama
by Bond, was collectedin 1960 (Schwartzand Klinikowski1963) and was seen
by severalamateurobserv.
ersduringthe early60's and by me in 1969.
4--THE

HABITATS

AND

THEIR

BIRD

COMMMUNITIES

The term bird communityis usedin this chapterto designateall the birds that
co-occupyan area of habitat at a particularseasonand henceinteractdirectly
with each other. The fauna of Grand Bahama Island is thus composedof an
array of communitiesdifferingboth spatiallyand temporally. Variation is continuousalongboth axes,but I have assigneda seriesof spatialcategories
on the
basis of localities or vegetation types, and of temporal categorieson the

basisof the arrival and departureperiodsof seasonalmigrants.In this chapter
I examinethe spatialdistributionof the birds presenton the Island between10
Januaryand 31 March 1969 while the winter migrantswere still present,i.e.
the winteringcommunities.
VEGETATION

PATTERNS

General description.--Mostof the interior of Grand Bahama Island (roughly
80% of the land surface) is coveredwith moderatelydenseforestsof Caribbean


1977

EMLEN:

1õ16

SOUT. V

CO•ST

$0

I00

75

GRAND

14

9

6

4

V

V

V

V

75

200

200

I

2

VV

BAHAMA

:5 13

VV

BIRD

COMMUNITIES

1719212410222õ23

VVV

VV

13

õ

7

8 1820

12

II

V V

V

VVV

V

VNORTH
COAST

500

I00

500

0 C

o

FmURE 6. Cross-islandprofile (schematic) transectingthe major vegetationzones and types;
approximate average widths of zones are given in meters. The positions of the 25
survey standswith respect to the vegetation zones are indicated above the diagram; the
numberscorrespondto thosein Table 17 and the map in Figure 5.

Pine (Pinus caribaea). Much of this forest was clear cut during the late 1940's
and early 1950's, but the very rapid growthhas restoredthe appearanceof submature forest over most of the area. Broad tidal flats with open, low mangrove
scrubseparatethe pine forestsfrom the sea on the north or leeward side of the
island. The higherwindwardfront on the southernshoresupportsa seriesof
parallel vegetationbelts generallyprogressingfrom a narrow beach backed by
low sanddunesand occasional
palms,througha narrowcoastalstripof halophytic
grasses,herbs, and low denseshrubsand a strip of dense 3-m-high broad-leaf
scrubwith pocketsof cattail marsh to a wider band of 4-5 m scrub that blends
back into the pines. The distributionof thesemajor vegetationtypesis mapped
in.Figure5 and shownin a cross-island
profilein Figure6.
Photographs
in Figure7 depictconditionsin the submaturepine forestsas they
appearedin 1968; thosein Figure 8 show the vegetationin recentlycut forests
and in one older stand. Vegetationfeaturesof other habitat types are shownin
Figure 9.
The structure of Grand Bahama habitats.--Measurements and evaluations of

habitatfeaturesconsidered
to be significantto birdsare presented
in Table 1 for
eachof the 25 standssurveyedin this study. Includedare featuresof each of the

threestratain the vegetation
plus an indexof overallhabitatcomplexityor diversity. The figuresin eachcaseare averagesfor conditionswithin the stand.
Mean tree height varied from 2 m in a recentlycut stand (stand #24-•est. 4
yrs.) to 16 m (max. 22 m) in the oldestof the submatureforests(#1-•est. 30+
yrs.). Trunk diametersin thesetwo standsaveraged5.5 cm and 28 cm (max.
35 cm) respectively.
Old cut stumpsrarelyexceeded
35 cm in diameterat any
site, suggesting
that this approximates
the maximumsize attainedlocallyby the
Carib Pine in undisturbed

forests.

Exceptfor two badlydisturbed
sitesand onemarginalpine-broadleaf
thicket,
tree canopycovervariedfrom 19-45% with densitiesas greatas 60% in patches
of up to 3fiha. In severalstandstherewere2 distinctheightclasses
reflecting2
major disturbancesspaced8-10 years apart. In such casesthe lower stratum