Urbanization, birds and ecological change in northwestern Trinidad

Urbanization, Birds and Ecological Change in Northwestern Trinidad L. SCHUYLERFONAROFF

Department of Geography, University of Maryland, College Park, Maryland 20742 and Georgetown University School of Medicine, USA

ABSTRACT

TABLE I

Systematic List o f Port-of-Spain Garden Species Trinidad, located on the continental shelf of northern South America, is an environmentally and culturally diverse Frigate bird island that is an ideal natural laboratory for observing and Fregata magnificens Cattle egret monitoring ecological change. Aspects of the Port-of-Spain Bulbulcis ibis Black vulture and northwestern peninsular hinterland are discussed as Coragyps atratus American golden plover possible source areas for the recruitment of urban garden Pluvialis dominica American ringed plover birdlife. Comparative bird lists are presented from a local Charadrius hiaticula Hudsonian curlew garden area and a neighbouring secondary forest-open Numenius phaeopus Willet woodland. Preliminary studies suggest that neighbouring Catoptrophorus semipalmatus E. dowitcher open savanna habitats supply the majority of species able Limnodromus griseus Rufous-winged ground to adapt to urban garden conditions despite the great Columbigallina talpacoti dove taxonomic diversity in other nearby habitats. The continuous Green or blue-winged landscape change is briefly illustrated in map form. Current Forpus passerinus parakeet research concerning adaptation and colonization of new Common ani areas indicates that considerable caution must be exercised Crotophaga ani Barn owl in relating ecological areas to particular breeding populations Tyto alba Pygmy owl and recruitment potential. Carefully designed fieM studies Glaucidium brazilianum Lawrence's swift are called for which may have a bearing on the colonization Chaetura cinereiventris Short-tailed swift process and the administration of conservation activities. Chaetura brachyura Amazilia tobaci Common emerald Lack of hard data in these areas is emphasized. Anthrocothorax nigricollis Black-throated mango Chrysolampis mosquitis Ruby topaz Lophornis ornata Tufted coquette Synnalaxis albescens White-throated spinetail Thamnophilus doliatus White-barred bush shrike Tyrannus melanocholicus Kingbird INTRODUCTION Pitangus sulphuratus Kiskadee Elaenia flavogaster Common elaenia Barn swallow During the 1965-72 period, extensive ecological Hirundo rustica Troglodytes aedon House wren work was carried out in the Caribbean area, much of Mimus gilvus Mockingbird it on Trinidad where considerable bird-netting and Turdus fumigatus Cocoa thrush field observations were made. Prompted by a basic Turdus nudigensis Bare-eyed thrush Pepper-shrike interest in the population biology of urban and Cyclarhis guianensis Bananaquit suburban faunas and recognizing the growing pro- Coereba flaveola Dendroica petechia E. yellow warbler fessional interest in such studies, the following brief Seiurus noveboracensis N. water thrush comments and observations from the Port-of-Spain Spiza americana Dicksissel area are presented. Molothrus bonariensis Glossy cowbird Boat-tail Little is known concerning the way birds adapt to Quiscalus lugubris Yellow oriole the urban habitat and basic observations are un- lcterus nigrogularis Leistes militaris Soldier bird common. Unlike other parts of the island such as the Thraupis virens Blue tanager Arima Valley, where the New York Zoological Thraupis palmarum Palmiste Society located a tropical field station, the north- Saltator coerulescens Grey-breasted saltator Picoplat western peninsular arm of Trinidad escaped close Sporophila intermedia Black-headed seed eater scrutiny due to the rapidly expanding Port-of-Spain Sporophila nigricollis Volatina jacarina Glossy grassquit and the long-term tenure of the US Naval base just 258 BiologicalConservation,Vol.6, No. 4, October1974--OAppliedScience Publishers Ltd, England,1974~Printedin Great Britain

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Fonaroff : Urbanization, Birds and Ecological Change in Northwestern Trinidad

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SPECIES I

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TYPES

Fig. 1. Percentage occurrence of high forest in relation to savanna bird species in major Trinidad habitats.

beyond the suburban area of town. Initially I was amazed at the paucity of current field data for the avifauna of the city area and its northwestern hinterland (Junge & Mees, 1961) and with this in mind I offer the following environmental comments and systematic lists. Figure 1 illustrates the percentage composition of savanna and high forest bird species in five major habitats in the island. It is based on 264 nesting and migratory species observed and netted during the study period. Forty-four species were observed in or from a small garden area and cultivated playing field on the northern fringe of the urban area (Table I). The garden area itself is floristically and physiognomically similar to urban garden areas described from other parts of the humid tropics.

SOME PHYSIOGRAPHIC

AND ZOOGEOGRAPHIC

RELATIONSHIPS

Figure 2 suggests some reasons for the obvious geomorphic and vegetative similarities with the ranges of the Venezuelan mainland from which it is separated by the Boca Grande Channel (17.7 km wide). This channel is shallow, eustatic, and, as E. L. Joseph (a local historian) correctly noted in 1838, ' . . . an unscientific person who observes these ranges conjectures that they must have been joined at some remote period'. This periodic and close association is still apparent in inter-regional comparisons of plant and bird lists. Statistical tests (regression of similarity coefficients against distance) overwhelmingly support the notion of similarity in birdlife to the neighbouring

areas of Guyana and Venezuela. In addition it probably suggests recent contact. Only one endemic bird species is found on Trinidad. On the other hand, although the strand vegetation is essentially pantropical in character, the island is structurally and biogeographically separated in its significant elements from all of the Lesser Antilles to the north. However the filter that Boca Grande Channel now represents is an environmentally interesting one. If one may assume experimentally for the moment that pioneer ('propagule') arrival is theoretically a stochastic process, colonization by pioneer species seems to be governed largely by chance events (Simberloff & Wilson, 1969), including local conditions and historical antecedents (habitat diversity, area size and location). Figure 2 shows vegetation maps for 1797, 1924 and 1950, and illustrates the magnitude and rapidity of landscape change, most of which is a result of modification by man. The description of the Boca Grande Channel islands by the English novelist Charles Kingsley while botanizing in Trinidad a century ago is unrecognizable today. These historical reconstructions represent three of probably many intervening, transitory combinations of land use and vegetative patterning. Recent ecological insights from studies in population biology and island biogeography suggest that, just as some basic characteristics of the dispersal area must be known, an understanding of the biotic character of the receiving area is necessary in questions relating to its colonization. Some features of the colonization process can be easily identified, for example certain resident species which seem to be in transit to Trinidad. The rufous nightjar (Caprimulgus rufus) and Venezuelan wood rail (Aramides axillaris) are common on the islands but quite rare on Trinidad

260

Biological Conservation 62 °

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Fig. 2. Historical reconstructions of major land use patterns in Northwestern Trinidad. (ffrench, 1967). Also, the smooth and mouse-coloured flycatchers (Sublegatus arenarum and Phaeomyias murina) are common on the isles but rare and probably not yet nesting on Trinidad itself. The allied ant-wren (Formicivera grisea) and the short-tailed hawk (Buteo brachyurus) appear to nest intermittently on the isles but not on Trinidad. Only the bananaquit (Coereba flaveola) seems capable of exploiting the wide range of available habitats. It is interesting to note that the changing land-use

patterns have occurred in a most unusual cultural and environmental milieu (Fonaroff, 1968). For example, while the major rainfall divisions extend in a northsouth direction (with a declining east-west gradient), the major topographic configurations have an eastwest orientation. The resulting checkerboard of local and micro-environments, accentuated in the northwest by rugged and often steep-sided valleys, has required local cultural groups to adopt a variety, and frequently changing set, of land-use strategies. The

Fonaroff : Urbanization, Birds and Ecological Change in Northwestern Trinidad

mainland and channel island avifaunas seem to retain the 'option to wait' until suitable environmental corridors on the northwest peninsula are presented. However, current research trends suggest that little of the colonization process will be understood in the absence of critical field data relating to the population ecology of specific species. The mainland-peninsula corridor still requires detailed field studies of territorial

261

requirements, density compensation on environmentally different channel islands, clutch size, predator-prey relations, settling densities and other observations necessary for an understanding of the difficulties of dispersal in relation to capacity to colonize.

PORT-OF-SPAIN AND ITS BIOTIC HINTERLAND TABLE II Systematic List o f Secondary Forest-Open Woodland Species By Rank-Order of Dry Season Netting Frequency Manacus manacus Pipra erythrocephala * Coereba flaveola Glaucis hirsuta Ramphocelus carbo Pipromorpha oleanginea Dendrocincla fuliginosa Amazilia chionopectus Tachyphonus rufus Tiaris fuliginosa * Turdus nudigensis * Turdus fumigatus *Seiurus noveboracensis Tangara violacea Thamnophilus doliatus Platyrinchus mystaceus * Volatinia jacarina *Cyclarhis guianensis Tangara mexicana Cyanerpes caeruleus *Saltator coerulescens *Anthrocothorax nigricollis Myiophobus fasciatus Myrmotherula axillaris Tolomomyias flaviventris Formicarius analis Phaethornis longuemareus Galbula ruticauda Chlorestes notatus Playa rninuta Thraupis palmarum Chlorophanes spiza Elaenia flavogaster Tachyphonus luctuosus Sporophila minuta Chloroceryle americana Xiphorhynchus guttatus Myrmeciza longipes Dacnis cayena Cyanerpes cyaneus Habia rubica Crotophaga ani Leptotila rufaxilla Hylophilus aurantifrons Thraupis virens Leptotila verreaux

* Port-of-Spain garden species.

White-bearded manakin Golden-headed manakin Bananaquit Rufous-breasted hermit Silver-beaked tanager Ocre-bellied flycatcher Brown woodcreeper White breasted emerald Parson Sooty grassquit Bare-eyed thrush Cocoa thrush N. water thrush Setup White-barred bush shrike Broad bill Glossy grassquit Pepper shrike Sulphur-bellied tanager Yellow-legged grampo Grey-breasted saltator Black-throated mango Striped petchary White-flanked antbird Yellow-vented flatbill Antthrush Raquette Jacamar Saphir Lesser chestnut cuckoo Palmiste Green honeycreeper Common elaenia Little parson Red-bellied finch Green kingfisher Cocoa woodhewer Antbird Turquoise honeycreeper Red-legged grampo Ant-tanager Common ani Grey-fronted dove Ocre-fronted hylophilus Blue tanager White-front dove

On the basis of the implications of the preceding comments, the Port-of-Spain hinterland would seem to have more potential as a recruitment area for local birds than the appended list indicates. Table II lists a rank-order of netting frequency during the dry season in a secondary forest and open woodland environment on the northwest peninsula (species caught only once are excluded). As indicated earlier, until closer attention is given to ecological and historical forces at work, and bearing in mind the incredible habitat diversity nearby, the urban bird life cannot yet be considered to have reached a state of stability. It is possible for example, to experience habitat changes of enormous proportions along a 16 km traverse from Port-of-Spain. Table III presents examples of local landscapes and their associated vegetation cover and bird fauna. The major source area for the local garden species as suggested by these preliminary data seems to be the savanna area (69 per cent) despite the proximity of a varied range of habitats and the high taxonomic diversity of their avifaunas. Under present conditions, open-habitat species seem more capable of adapting to man-made conditions than do forest species (7 per cent). What the future holds in store for many species is difficult to assess. It is apparent that faunal change in habitat, range, and diversity is occurring, however imperceptible the process may be. Certainly it is not difficult to detect some change since the writing of Leotaud, Trinidad's nineteenth century physiciannaturalist. The nature and direction of future changes are largely unpredictable and theoretically more complex than had been anticipated even in the recent past. On an island-wide basis the options seem great. A listing of the 264 species netted and observed by habitat throughout the island during the study period is given in Table IV. In conclusion, caution is necessary in equating particular breeding populations with environmental stability and habitat differences. However, it is unmistakable that the open woodland and secondary forest landscape has the capacity to accommodate a greater number of both high forest and savannaoriented species than any other local habitat type. This

Biological Conservation

262

TABLE I H

Ecological Relationships of Major Bird Families Topographic forms

Vegetative associations

Representative bird fauna

Coastal mangrove swamps often with fresh water behind Littoral beach strand

Rhizophora--Avicennia--Langunicularia; often with Pterocarpus or Roystonea palm swamps behind

Flatlands--dissected alluvial plain

Dependent upon local conditions these wet/dry savannas can be of the Parkland Type (tall bunch-grass, open, orchards, pine or palm) or Herbaceous Type (short bunch-grass, sedge) Curatella, Cecropia, Maxmiliana

Columbidae (6 sp) Psittacidae (6 sp) Trochilidae (7 sp) Tyrannidae (15 sp) Fringillidae (9 sp)

Piedmont, rolling hills 'foothills'

Lower half of Lower Montane, evergreen, or in drier sheltered, rainshadow areas, including channel islands, semi-evergreen or semi-monsoon forest. May be two storied with lower crowns 12-18 m, upper ones 21-27 m Cordia, Cedrela, Tabebuia, Ficus, Vitex. May be up to 50 per cent deciduous on NW coast and island area, with Lonochocarpus, Machaerium, Bursera

Trochilidae (7 sp) Picidae (6 sp) Formicariidae (6 sp) Tyrannidae (14 sp) Thraupidae (11 sp) Coerebidae (5 sp)

Mountains--transverse valleys, largely precipitous

Upper parts of lower evergreen through Montane 'Rain' Forest, small elfin woodland. Much secondary growth. Licania, Sterculia, Chrysophyllum, Eschweilera, Clusia (elfin summit)

Acciptridae (4 sp) Apodidae (5 sp) Picidae (5 sp) Formicariidae (5 sp)

Coccoloba--Terminalia--Cocos, often with Roystonea or Manilkara woodland behind. Pithecolobium, Cereus, Capparis

presumed high niche diversity represents a habitat that is predominantly the result of human agency and has evolved in the active presence of man over a long period of time. The visible results are complicated plant formations and even more complicated vegetative boundaries. Carefully designed studies of faunal adaptations in such areas seem basic in an attempt to understand habitat selection in the transition areas from forest to local rural and urban garden conditions.

Ardeidae (14 sp) Rallidae (4 sp) Laridae (10 sp) Tyrannidae (7 sp) Psittacidae (5 sp) Icteridae (7 sp) Anatidae (7 sp)

ACKNOWLEDGEMENTS The Ministry of Health of the Government of Trinidad and Tobago, the US Office of Naval Research and the Faculty Research Grants Committee of the University of Maryland have provided laboratory and financial support and are gratefully acknowledged.

References

TABLE IV

High forest Habitat exclusive or largely so Total species

Open woodCoastal land and Scrub and secondary savanna forest swamp

18

19

8

70

59

110

122

129

FFRENCH, R. P. (1967). The avifauna of Chacachacare Island. J. Trin. Fld Nat. Club, pp. 45-6; also other intermittent runs of this journal. FONAROFF, L. Schuyler (1968). Man and malaria in Trinidad: Ecological perspectives of a changing health hazard. Ann. Ass. Am. Geogr., 58, pp. 525-555. JUNGE, G. C. A. & MEES, G. F. (1961). The avifauna of Trinidad and Tobago. Rijksmuseum van Natuurlijke Historic, Leiden. SIMBERLOrV,D. S. and WILSON,E. O. (1969). Experimental zoogeography of islands: The colonization of empty islands. Ecology, 50, pp. 278-296.