Condor, 81:370375 @I The Cooper Ornithological Society 1979 OCCURRENCE AND FEEDING ECOLOGY OF THE COMMON FLICKER ON GRAND CAYMAN ISLAND ALEXANDER CRUZ AND DAVID W. JOHNSTON The Common Flicker (CoZaptes auratus) is with mangrove and buttonwood swamps. In wetter and widely distributed in the western hemi- more saline places, especially around North Sound (Fig. l), red mangrove (Rhizophora mangle) predomi- sphere from Alaska to Nicaragua and to the nates, but farther inland at seasonally drier sites white West Indies (Cuba and Grand Cayman). Al- mangrove (Lagunculariu rucemosa), black mangrove though mainland populations have been (Auicenniu nitida), and buttonwood (Conocarpus er- well studied (e.g., Noble 1936, Bent 1939, ecta) combine to form a thick forest. Near North Sound Short 1965a, 1967, Bock 1971), details on these mangrove-buttonwood swamps are best devel- oped and the trees often reach heights of 18-20 m. the abundance, life history, ecology, and Open pastures. In places, the limestone forest has behavior of Colaptes aurutus on Cuba (C. been cleared for pasture. Important introduced grasses a. chrysocudosus) and Grand Cayman (C. of these pastures are Guinea grass (Punicum maximum) a. gundluchi) have not been reported. Short and Seymour grass (Andropogon metusus), with scat- tered shrubs such as Comocladia dentata and trees (196513) discussed the variation, taxonomy, such as Bursera simaruba, Roystonea sp., and Man- and evolution of West Indian flickers, John- gifera indica. ston (1970, 1975) summarized some aspects Scrub woodland. Abandoned pastures and other of the ecology of the Grand Cayman Flicker, cleared areas revert to woods consisting of species such and Cruz (1974) examined the probable as maiden plum (Comocladia pinnatifolia), red birch (Burseru simaruba), and logwood (Huematoxylum evolution and fossil record of West Indian cumpechianum). Open and, later, dense stands of near- woodpeckers. ly pure logwood develop on drier upland sites. Older The present study of the Grand Cayman stages frequently include thatch palm (Thrinax argen- Flicker was initiated in 1965 and continued tea) and red birch (logwood-thatch palm-red birch as- sociation). The woodland averages about 6 m in height, intermittently until 1973, covering all sea- sometimes forms a nearly impenetrable forest, and is sons. Our objectives were to learn the dis- most common in the middle of the island. tribution, habitat preferences, foods, and Limestone forest. Originally this type of forest cov- foraging ecology of these birds and to com- ered most of the drier upland portions of Grand Cay- pare our data with those on mainland flick- man (Swabey and Lewis 1946), especially on the north- ern and eastern sections where limestone ridges are ers. Investigations of Florida flickers were common. It is a sparse vegetation cover of low forest undertaken during 1969-1973, covering all and tall scrub growing mainly on bare limestone. Little seasons. soil is present except for that deposited in small crev- ices or washed down to level areas. There is no distinct STUDY AREAS forest stratification, and heights vary from low scrub to a thin forest with trees rarely exceeding 12 m in height, GRAND CAYMAN with occasional emergence of red birch and fig (Ficus The island lies approximately 290 km south of Cuba populneu) up to and over 18 m. Characteristic trees and 480 km northeast of Honduras, the nearest point include mahogany (Swietenia mahagoni), manchineel in Central America. Much of Grand Cayman (185 km*) (Hipponmane munchella), cedar (Cedrela odor&a), is less than 5 m in elevation, although an east-west red birch, balsam (Clusiu f&a), fig and other hard- forested ridge on its north side reaches 20 m in places. woods. Temperatures are fairly constant (mean annual high Ruderal habitats. Where the native vegetation has 30°C) and annual mean precipitation is 1,549 mm been cleared for houses, an important and distinctive (Johnston 1975). A dry season extends from November ecological community has developed. House sites, for to April. example, include clearings for small gardens, intro- To obtain as complete a picture as possible of the duced shrubs, and shade and fruit-bearing trees. Some biology of the Grand Cayman Flicker, we visited many of the characteristic trees include sea grape, red birch, distinct habitats ranging from mangrove woodland to mango, papaya (Carica papaya), guava (Psidum guu- limestone forest (Fig. 1). A brief description of these juua), naseberry (Manilkaru zupoda), thatch palm, and communities follows (modified from Johnston 1975). coconut palm. Strand woodland. This association is characteristic of coastal areas. Common trees are sea grape (Cocco- FLORIDA Zoba uuifera), almond (Terminaliu cutuppa), seaside Mainland birds were observed in various natural and mahoe (Thespesia populnea), Australian pine (Casunr- modified communities in and near Gainesville, Ala- ina equisetifofolia), and coconut palms (Cocos m&era). chua County, throughout the year from 1969 to 1973. Commonly the trees are wind-pruned, desiccated in Gainesville, located in northcentral Florida, has a mild appearance, and no more than 5 m tall. Strand wood- climate. The mean annual high temperature is 31°C land occupies a distinct band, usually not more then and the mean annual precipitation is 1,486 mm 30 m wide. (N.O.A.A. 1973). Miller (1950) and Monk (1965) have Mangrove woodland. Extensive areas are covered described much of the vegetation of this area. 13701 GRAND CAYMAN FLICKER 371 METHODS at least to family; fragmented insects were identified to order in nearly all cases and often also to family. POPULATION DENSITY Similar methods were used to identify fruit and other Traditional techniques for measuring bird populations, vegetable material found in the stomachs. such as transect counts or territory-mapping, proved to be impossible in the rough and uneven terrain of BODY MEASUREMENTS Grand Cayman. The absence of trails for accurately We measured the birds to see if any body structure of measuring distances in most of the woods made it dif- possible ecological significance was sexually dimor- ficult to measure precisely flicker population densities. phic. Bill length was measured from the anterior mar- A semi-quantitative method was devised to provide gin of the nostril to the tip; the tarsometatarsus was relative indices of abundance. Ten censuses, each of measured from its posterior proximal end to the distal about two hours duration in the early morning were edge of the most distal unbroken scale crossing the taken in representatives of each of the major ecological bases of the two forward toes. We weighed all the spec- formations during December, June, and August. After imens. all individual birds recorded during each census were counted, relative scores were derived as follows: U RESULTS (Uncommon), 5-20 individuals/20 h; FC (fairly com- mon), 20-100 individuals/20 h. MEASUREMENTS C. a. gundlachi is the smallest race of the FORAGING ECOLOGY species, with little or no overlap in mea- Habitat use, foraging, and feeding methods of the birds surements with North American forms (Ta- in the study areas were studied by adapting methods ble 1). The data indicate that it is essentially used by MacArthur (1958), Cody (1974), and Cruz monomorphic, males averaging only slight- (1977). The technique involved walking a predeter- ly larger than females in all measurements mined route until a bird was encountered. If the bird was foraging, its sex, foraging zones, and behavior were (see also Short 1965b). noted. The following zones were identified: ground, stumps, shrubs, trees, and aerial. The trees were di- HABITAT, DISTRIBUTION, AND ABUNDANCE vided into three main feeding zones (areas): trunk, in- Grand Cayman Flickers occurred through- ner branches, and outer branches. Each of these main out the island wherever there was forest, zones was in turn divided into three subzones: lower, middle, and upper. Feeding behavior patterns were from mangrove woodlands to dense lime- categorized as follows: ground gleaning, limb glean- stone forest (Fig. 1). Table 2 shows relative ing, fruit and seed gleaning, tree probing, ground prob- abundances of flickers in various commu- ing, epiphyte probing, tree pecking, ground pecking, nities. The birds were most numerous in the scaling, and stooping (flying to prey on the ground). An individual observation was terminated if the bird limestone and mangrove forests, and scarc- changed behavior or moved more than 1.5 m. We at- est in logwood and ruderal sites. Flickers tempted to observe as many flickers as possible and to occurred in habitats where the diversity of follow each individual for as long as possible. tree species ranged from low (one species), FOODS such as mangrove and logwood forests, to high (lo-15 speies) such as limestone for- We collected 19 adults on Grand Cayman and 9 adults in Florida for stomach analyses. The stomach and in- est. The birds were absent from pasture and testinal tract were removed soon after death and pre- cultivated areas, despite scattered trees. served in 75% alcohol. Later the food samples present were separated into food classes and analyzed by vol- FORAGING ECOLOGY ume and by frequency of occurrence. Food volumes were ascertained with reasonable accuracy by noting Chi-square tests for homogeneity indicated the displacement of water in a graduated cylinder ac- no significant differences in frequencies of curate to 0.1 ml. Whole invertebrates were identified occurrence of any of the foraging categories