Abstract.- Epicrates monensis is a endangered Critical Habitat, Predator boa endemic to the Puerto Rico Bank. Principal Pressures, and the components analysis, based on data collected during five years of study and 200 captures of this Management of Epicrafes species, was used to identify predator, prey, and habitat variables critical to survival of the snake. monensis (Serpentes: Management recommendations are discussed. Boidae) on the Puerto Rico Bank: A Multivariate Analysis1

Peter 9. Tolson2

Epicrates monensis is a small (ca. < 1 interactions. The rarity of the snake m snout-vent length) semi-arboreal has made habitat analysis difficult; boid snake (fig. 1) that exhibits an ex- one cannot define critical habitat if tremely disjunct distribution on the the snake cannot be observed. Prior Puerto Rico Bank. The Mona boa (E. to my work, fewer than 13 specimens m. monensis) is endemic to Isla Mona, of the boa had been encountered, and a large island in the Mona Passage habitat descriptions were largely an- between Hispaniola and Puerto Rico ecdotal with no attempts to quantify (Schmidt 1924). The other subspecies, those factors important in determin- the Virgin Islands boa (E.m. granti), ing population levels (Div. of Fish is found on scattered islands and and Wildlife, USVI 1983; USFWS cays from La Cordillera eastward 1984,1986). through the Virgin Islands, including The parameters dictating the dis- St. Thomas, Tortola, and Virgin tribution and abundance of animal Gorda (Stull1933; Nellis et al. 1984; species within a habitat are often di- Mayer and Laze11 1988). The boa is verse. They include not only the apparently absent from Puerto Rico physical structure of habitat, such as and the other large islands on the vegetational composition and spatial bank. Judging from the present dis- he terogeniety (Rotenberry and Wiens tributions, the historical range of Ep- 19801, but also species composition icra tes monensis encompassed virtu- (Matthews 1985; Moulton, 1985) and ally the whole length of the Puerto other aspects of community structure Rico Bank. Today, unfortunately, the which are less easily defined, such as Figure 1 .- Epicrates monensis granti. snake is endangered (USFWS 1980) competition (Cody 1974) or preda- Above-adult female, Cayo Diablo, Puerto Rico. Below-juveniles born at the Toledo and absent from far more islands on tion pressure. In the West Indies, Zoological Gardens 14 July 87. the bank than it is resident-doubt- particularly on the Puerto Rico Bank, less the result of a long history of ex- utilization of a particular habitat by the Puerto Rico Bank (Barbour 1917, tirpation. It is improbable that the the endemic herpetofauna is not only 1930; USFWS 1986; Div. of Fish and decline of the boa can be traced to a dependent on the structural attrib- Wildlife, USVI 1983). single causative factor; more likely utes of vegetative cover and the com- Principal components analysis the survival of the snake at certain position of the endemic animal com- (PCA) is a multivariate statistical localities is due to a complex series of munities, but also on the number and technique that has been used by com- biotic, environmental, and stochastic severity of feral and exotic animal munity ecologists to model distribu- introductions that have occurred. tions of animal populations in a 'Paper presented at symposium, Man- Colonizations (accidental or other- multidimensional habitat space de- agement of Amphibians, Reptiles, and Small Mammals in North America. (Flag- wise) of the roof rat, Rattus rattus, the fined by a correlation matrix of habi- staff, AZ July 19-2 1, 1988.) house cat, Felis catus, and the tat variables (See Wiens and Roten- lPeter J. Tolson is Curator of Amphibians mongoose, Herpestes auropunctatus, berry 1981 and Matthews 1985). My and Reptiles, Toledo Zoological Society, have profoundly influenced the sur- current work with Epicrafes monensis 2700 Broadway, Toledo, OH 43609. vival and distribution of endemics on utilizes PCA to correlate the abun- dance of the boa with certain critical elements of habitat structure and in- dices of population densities of pre- ferred prey species and predators. Compilation of such data is ex- tremely important in establishing the critical dimensions of the boa niche, the identification of suitable release sites for snakes born in captivity, and the selection of likely search localities for surveys of previously unde- scribed populations of the snake. By using PCA, we also hoped to extract independent patterns of covariation, such as the degree of niche overlap with Alsophis, which might explain certain distributional anomalies of the boa populations.

t------1 Methods 5 km lsla Mona Study Areas

This study is based on habitat analy- 1 67'55' sis of 24 different localities on the fol- lowing islands and cays of the Puerto Rico Bank: Buck Is., Cas Cay, Cayo Diablo, Cayo Icacos, Cayo Lobos, Congo Cay, Great St. James Cay, Isla Mona, Outer Brass Cay, Salt Cay, Cayo Icacos Saba Cay, and Steven Cay from Feb- ruary 1986 through April 1988. Some La Cordillera islands had several plots. Sites were chosen at random without regards to presence or absence of boas, but an Cayo Lobos attempt was made to select sites so that sampling included the full spec- trum of habitat available to the boa. Figures 2 and 3 illustrate the location ~8~1~of sampling plots included in the - shrdy. Cayo Diablo

Vegetational Profiles of Study Sites

Subtropical dry forest is the habitat where E. monensis is most commonly observed, particularly on Isla Mona and St. Thomas. It is characterized by small (< 5 m) deciduous trees with small, coriaceous or succulent leaves and thorns, spines, and secondary Figure 2.-Location of sampling plots in Puerto Rico. Above-plots on lsla Mona. Below-plots defensive compounds (Ewe1 and on La Cordillera. Whitrnore 1973). Examination of the present range of the boa indicates consisted of CassythialOpuntia that it matches the occurrence of dry tangles. Ficus-dominated forest was subtropical forest on the Puerto Rico present on Mona 1 and Congo 2. Bank (Ewe1 and Whitmore 1973). Guinea grass, Panicum maximum, This is most apparent on St. Thomas, dominated the transect on Buck 2 where E. monensis is restricted to the and Acacia macracantha on Buck 3. A dry eastern end of the island despite basic summary of the vegetation of presumably suitable habitat else- the smaller cays is given in Heatwole where (Nellis et al. 1984). Common et al. (1981). Figures 4 through 7 il- tree species include Burseria lustrate four typical vegetational simaruba, Cephalocerekts royenii, types at transect sites: Coccoloba Pictetia aculeata, Bucida buceras, grove (Buck 11, mixed palm/shru- Figure 4.-Coccsiobcl uvffera habitat on Guaiacum officinale,Leucaena glnuca, bland (Diablo 2) OpuntialCassythin Buck 1. Tamarindis indica, Melicoccus bijuga- tangles (Diablo 3) and grassland tus, Acacia ssp., and Capparis cynoph- (Buck 2). allophora (Little and Wadsworth 1964). In addition, on our dry forest plots (as,Icacos 1, Congo 1, Outer Geornorphology and Topography Brass 1, and Gt. St. James I), we en- of Study Sites countered many Byrsonima lucida, Euphorbia petiolaris, and Metopium Geomophology of the various islands toxiferum. On Buck 1, Diablo 1, Gt. St and cays studied varied considera- James 3, and Mona 2 the vegetation bly, from the steep-sided metamor- consisted of tree species with com- phic topography of St. Thomas and pound trunks, primarily Coccoloba associated cays (Heatwole et al. 1981) uvifera, Hippomane mancinella, and to the cemented dune structure of La Figure 5.-Mixed Cocos and scrubland habitat on Cayo Diablo. The vegetation at Thespesia populnea. Sabal palm groves Cordillera (Kaye 1959a). Isla Mona is the center of the island is primarily Cas- were present on Outer Brass 2 and composed primarily of a Pleistocene syfhia vine growing over Opuntia cactus. Salt 2. Salt-tolerant shrublands pri- limestone plateau surrounded by marily composed of Suriana and sheer cliff (Kaye 1959b). In fact, most Tournefortia just above the high tide islands of the bank have significant line was the dominant vegetation on limestone deposits, with varying Diablo 2, while Diablo 3 primarily amounts of metamorphic rock, in-

I Outer Brass Is 2 '7) Congo cay

Figure 6,- Aromatic beachfront shrubland, primarily Suriaaa and Tourneforfia, near Diablo 2.

Buck Is Cay 90

U. S. Virgin Islands

Figure 7.-Guinea grass, Panicum maxi- Figure 3.-Location of sampling plots, U.S. Virgin Islands. mum, habitat on Buck 2. cluding gneiss and basalt, present as spent searching larger islands and parameters (table 1).Predator den- well. The cays of La Cordillera are three to five days for smaller cays. sity estimates include indices of exceedingly low, with maximum ele- Only 1 night was spent on Cayo Lo- abundance for likely predators of E. vations under 15 m. In the Virgin Is- bos, as the native vegetation was all monensis: the roof rat, Rattus rattus, lands the cays are of moderate eleva- but completely destroyed by human the pearlyeyed thrasher, Margarops tion with eroded limestone hills ap- activity and all densely vegetated ar- fuscatus, and the Puerto Rican racer, proaching 50-300 m in height. An eas could be searched repeatedly in a Alsophis portoricensis. Rattus densities overview of the geology of the Virgin single night. Our experience with were estimated using removal trap- Islands is given in Schuchert (1935). multiple recaptures of the same indi- ping over a 3-day span on 100-m vidual indicates that the snakes for- transects with Victor snap traps age every night under most circum- spaced every 5 m. Presence of Felis stances. Within each 24-hour period catus was determined by direct ob- 4 hours per night were spent search- servation. Because of the extreme The climate of the Bank is essentially ing likely foraging sites such as vine wariness and trap-shy nature of the subtropical to tropical. Temperatures tangles, terminal branches of trees, Felis on study plots, only their pres- of the coastal areas range from over- palm crowns, and beachfront vegeta- ence or absence was recorded. night lows of ca. 15' C to daytime tion. During the daylight hours, refu- Prey density data includes of highs approaching 35 " C. Rainfall, gia sites such as debris piles, termite population densities for Anolis cris- especially on Puerto Rico, is geo- nests, and palm axils were examined. tatellus and Ameiva exsul. Anolis, Also- graphically variable (Briscue 1366). After capture, the time, capture phis, Ameiva, and Margarops were Areas within the range of E. monensis height, habitat description, ambient counted by having two observers typically receive < 750 mm of rainfall temperature, refugium temperature, slowly walk the transects and count- per year. and cloaca1 temperature of each ing the individuals of each species snake were recorded. Later, sex, observed within a 5 m distance on body mass, snout-vent length (SVL), each side of the transect line. On Sampling Techniques and caudal length (CL) were re- Cayo Diablo, independent estimates corded. The snakes were examined of Ameiva and Anolis cristatellus The presence or probable absence of for reproductive condition, presence populations were gathered by sur- the boa on a particular cay was de- of injuries, and parasite infestation. veys of 5 m2 quatrats. Anolis cristatel- termined by active searching of all Snakes were marked using the tech- lus perch heights were measured habitat types during surveys (carried nique of Brown and Parker (1976) with a metric tape except on Cayo out independently of habitat analy- and released at the point of capture. Lobs and Salt Cay. Canopy height sis) from April 1983 to September Habitat variables recorded in- was estimated for each habitat with 1987. Typically 2 weeks or more were cluded both physical and biological the help of a metric tape. Vegetative composition was determined by sub- jective stratified sampling using 10 m2 quadrat plots (Clarke 1986);plant samples were taken for species iden- tification from each island. Vegeta- tion coverage data indicates the per- centage composition of five different classes of vegetation: trees (trunk cir- cumference at shoulder height > 25 cm), palms, Qpuntia cactus, shrubs and small trees (trunk circumfer- ences < 25 cm), and grasses. Vegeta- tion structural data includes the number of dominant plant species, the height of the canopy, and the continuity of the vegetation (a meas- ure of the difficulty for the boa to crawl from one plant to another without going to the ground). Plants were identified by David W. Nellis and the author. I attempted to use continuously tributes of vegetation are all impor- only two to five dominant plant spe- distributed standarized environ- tant contributors to variance in the cies (table 2). Captures and sightings mental variables whenever possible. PCA patterns. Factor patterns for the of the Mona boa have been limited to Absence of a particular predator or first six principal components are three distinct localities: dry plateau prey species on a given a sample plot given in table 1. Principal component forest adjacent to Uvero and Pajaros did not always indicate its absence I accounts for 23.4% of the variance. (Campbell and Thompson 1978; Riv- from the island on which the plot This component clusters habitats ers et al. 1982) Coccoloba uvifera was situated. Only male Anolis perch with high shrub and palm densities, groves of Pajaros (M. Frontera, Pers. heights were used for the statistical low numbers of single trees, vegeta- Cornm.), and Cwos groves and analysis, as female and juvenile A. tional continuity, and low canopy nearby vegetation adjacent to Playa cristatellus tend to frequent the heights. Important biotic charasteris- Sardinera (C. Rodriguez pers. ground under all circumstances (Ki- tics of this space include Felis pres- comm.). The Virgin Islands boa has ester et al. 1975). Mean male Anolis ence and low Ratfus, Margarops, and been encountered repeatedly on only perch height data were pooled for Alsophis densities with high Anolis two islands: St. 'Thomas and &yo each island for character 16 of the perch heights. Principal component II Diablo. All specimens from St. Tho- PCA data matrix, as some plots were accounts for an additional 17.0%of mas were captured on the east end sf completely devoid of Anolis. the variance observed. This axis de- the island near Red Hook. Two speci- scribes sites having low grass den- mens were found beneath a lime- sity, high compound tree densities, stone slab during construction of the Statistical Analysis canopy height > 3 m ,and high Vessup Bay Estates housing subdivi- Ameiva densities. Principal compo- sion, another was taken from a stone Principal components analysis was nent I11 accounted for '3.1.2%of the wall, and a third was found as a performed using the Statistical variance and suggested an associa- roadkill near Smith Bay. R. Thomas Analysis System "SAS" release 5.16 tion between low Ameiva density, captured a specimen crawling in a (SAS Institute 1985).Significant habi- low compound tree density, low viney tangle ca. 2.4 rn high (Sheplan tat components, which included both grass density, high shrub density, and Sshwartz 197'4). biotic and structural variables of the and canopy height > 3 m. Factor IV 'The Red Hook area is dominated collecting localities (e.g. those which accounted for another 10.7% of the by xeric forest composed primarily accounted for > 10%of the total vari- variance and clustered high Alsophis of Burseria, Crofon, and Acacia. No ance in the data), were clustered on and Anolis densities with Felis ab- habitat data is available for E. m. the basis of their association within sence and low palm density. Compo- granfi on Tortola. I have received re- the PCA data matrix. The second nents V-VI were less significant in ports that the boa was present in the step of the analysis compared the the PCA (e.g. each accounted for < 10 palm forest of Outer Brass Island (J. relative abundance of E. monensis at % of the variance) but added some LaFlace pers. comm.) but I was un- each collecting locality with habitats interesting ecological information to able to find ~t there even after five described by the significant axes of the habitat analysis. Principal compo- trips to the island. Virgin Islands the principal components. Regression nent V clustered high Rattus density residents also report the boa as in- analysis, ANOVA, and descriptive with low Mmgarops density; princi- habiting Great St. James Is. (D. Neilis statistics (mean, standard deviation, pal component VI grouped high Mar- pers. comm.), Great Carnanoe: etc.) were performed using Statview garops density with low Anolis den- Necker Is., and Virgin Gorda, (Mayer 512) on an Apple Macintosh Plus. sity. and Lazell 19881, but these sightings have not been confirmed by biolo- gists. Grant (1932) mentioned anec- Results Habitat Utilization by Epicrates dotally (he did not capture the monensis holotype himself) that "the boa is Multivariate Analysis of Habitats found on rocky cliffs on Tortola and The vegetational profiles of climax Guana Islands." The PCA indicates that biotic factors, plant communities (and E. monensis On Cayo Diablo, Coccoloba uvifera plant composition, and structural at- collection localities) in the dry forest is the habitat most commonly associ- may differ considerably depending ated with foraging E. monensis. Of the 3Theuse of trade and company names on island size, geology, geomorphol- 79 active snakes we captured, 51 is for the benefit of the reader; such use does not constitute an official endorsement ogy, rainfall, and history of human or were found in Coccoloba, ten in Cae- or approval of any service or product by feral mammal disturbance. However, salpinea, nine on Cassythia, seven in the U. S. Department of Agricutture to the most dry forest habitats on the Bank Suriunn, and two in Opuntia. Twenty- exclusion of others that may be suitable. are structurally simple, with usually three percent of the snakes were ac- tive at heights > 2 m. Of these, 67% This Anolis/Epicrates association is Feral Mammal Abundance and had SVLs > 400 mm. Seventy-five reinforced by PCA (see below). My Epicrates msnensis Distribu8isns percent of juvenile snakes (under 300 field logs indicate that the greatest rnm SVL) foraged at heights < 1.5 m, success in finding foraging Epicrates Of the 10 islands surveyed for this but regression analysis indicated that occurs when observations of sleeping study, only three were completely these differences were not statisti- Anolis are > 12 lizards/h. Numerical devoid of rats: Cayo Diablo, Cayo cally significant. Of the 149 inactive counts of sleeping Anolis and the Icacos, and Steven Cay. These islands snakes taken from refugia, 43% were times between sightings are regularly have high Ameiva and Anolis densi- in Cocos or Sabal ads, 36% were in noted in my field book as a rough ties, but only Diablo Cay harbors a termite nests, and 21% were under guide to potential hunting success in population of the boa. It also has the rocks or debris. Fifty-one percent of a study locality. highest densities of Epicra tes monensis snakes taken from termite nests were Anolis cristatellus is the primary found anywhere on the bank, > 100 females; over half of these were prey species of E. monensis, and the snakes/hc at some localities. Those gravid. Gravid females use termite mean foraging height of the snake (x islands with heavy rat densities (ca. nests or sun-baked debris to ther- = 1.356, SD = 1.079 N = 54) is close to 20 rats/hectare~-Buck Is., Cas Cay, moregulate and may elevate their the mean perch height of sleeping and Salt Cay-have lower Ameiva and body temperatures to over 33" C. Anolis (x males = 1.816 m, SD = 0.993, Analis densities and apparently no N = 17; x females = 1.323 m, SD = boa populations, despite suitable ,681, N = 14; x juveniles = 1.417 m, habitat. Rat densities are not always Prey Density and Epicrates SD = 0.169, N = 5). correlated with low Anolis densities, monensis Distributions High Ameiva densities are also a however. Some islands, such as common component of localities Outer Brass and Congo, have Anolis The greatest concentrations of Ep- with high boa densities, although I densities apparently high enough to icrates monensis are in areas observed only one instance of a boa support populations of the boa, but (particularly Coccoloba groves) with feeding on Ameiva, which are their perch heights (table 2) are sig- Anolis densities > 60 Anolis/100 m2. strongly diurnal. nificantly different from those Anolis inhabiting rat free islands. ANOVA to define critical boa habitat. Several reintroduction apparently exist in a performed on the regression line (y = vegetative parameters which cluster number of localities, the extant boa -5.548~+ 1.127) which plots Anolis together in the PCA are descriptive populations are so fragmented and perch height vs. rat density on my of habitat where I or others have reduced in numbers that it is crucial study islands (Tolson and Campbell encountered E. monensis repeatedly. to protect those areas now support- in prep) shows a negative correlation These include areas with high shrub ing the boa. This may be difficult. (p = .0137) between rat density and and palm densities coupled with a Historically, vegetation on Puerto Anolis perch height. This is not low canopy and vegetational conti- Rico and the Virgin Islands has been surprising. Anolis cristatellus resident nuity. These values describe plot severely disrupted, and 17th-18th on rat-infested islands exhibit a typi- habitat on Diablo 2, Icacos 2, and cer- century land use patterns on the U.S. cal escape behavior. Male Puerto tain sites within the Red Hook area Virgin Islands may partially explain Rican A. cristatellus escape to the can- of St. Thomas. Either high shrub or the limited distribution of the boa on opy when threatened (Heatwole high palm densities coupled with the east end of St. Thomas and its 1968), but those on Congo Cay, Outer vegetational continuity and lower absence from St. John. Even now Brass, and Salt Cay all run to the canopy are found on Diablo 3, Icacos enormous pressures exist for contin- ground when disturbed, even when 3, and Mona 1. Of these two subsets ued development on the east end of suitable cover on the ground is lack- of PC I, boas occur on Diablo 2 and 3, St. Thomas. Construction around ing. At night, the Anolis are not usu- Mona 1, St. Thomas, and almost cer- Red Hook seems to have accelerated ally found sleeping exposed on vege- tainly inhabited Icacos 1 and 3 at one in recent months, perhaps in re- tation, but rather under rocks. This is time. sponse to the decline of interest rates extremely unusual behavior for A. In PC 11, habitat correlates include in the United States, and three rela- cristatellus (E. Williams pers. comm.). high compound tree density, high tively undeveloped areas on the east Although one does not often canopy height, vegetational continu- end-Red Hook Mountain, Cabrita discover E. monensis on islands ity, and low grass density. This is a Point, and Water Point-all have proj- which are infested with rats, some perfect structural and compositional ects in progress that do not involve sympatry does occur. Isla Mona and description of Diablo 1, which has federal funding. The management St. Thomas are islands with moder- the highest population of E. monensis authority on St. Thomas, U.S. Virgin ate rat densities and extant (although I have ever encountered, and Mona Islands-the Division of Fish and apparently dwindling) populations 2-another locality where E. monensis Wildlifehas no control over such of E. monensis. Interestingly, at locali- has been observed (Campbell and development. ties where Epicrates coexists with Rat- Thompson 1978). It seems clear from In contrast, Puerto Rican islands tus, there are also significant num- these data that the unifying variable with populations of Epicrates monen- bers of introduced mammalian which causes an intersection of these sis are in no imminent danger of de- predators such as Felis and Herpestes two differinghabitat types is vegeta- velopment. Cayo Diablo is part of the (table 2). tional continuity-an interlocking of Reserva Forestal de La Cordillera, the branches of shrubs or the tree and Isla Mona is likewise a Forest canopy. I believe this vegetational Preserve (although it was once pro- Discussion characteristic is essential to E. monen- posed to develop the island as a sis foraging success and survival. It deep-water oil port). A problem does PCA and E. monensis Habitat probably not only decreases the exist, however, with habitat destruc- Utilization search time between encounters with tion on isolated cays caused by sleeping Anolis while foraging, but it campers and fishermen (Heatwole The Puerto Rico Bank encompasses a also potentially limits the encounters and Mackenzie 1967). Coccoloba trees total land area in excess of 9,300 km2, between the boa and Felis and Her- in the larger groves-areas where the of which 1700+ km2 (or 17.6%)is cov- pestes. Fortunately, at least some greatest densities of E. monensis are ered with subtropical dry forest tracts of subtropical dry forest and found-are often used as firewood by (Ewe1 and Whitmore, 1973). This Coccoloba have remained relatively visitors. A survey done in 1987 of xeric forest is widely distributed undisturbed on the Virgin Islands, damage to Coccoloba stands on Cayo throughout the range of Epicrates Isla Mona, and Puerto Rico and its Diablo showed that many trees sus- monensis, yet the boa, as far as we offshore satellites. Much suitable tained some sort of damage caused know, occupies only seven islands of habitat does exist-even near popu- by human activity, primarily ma- the 243 that make up the banks-ef- la ted areas. chete cuts and burns from fires fectively exploiting only 0.04% of the While habitats throughout the started at the bases of the trees. land area available to it. PCA helped Bank are presumably underutilized to identify those factors which seem by E. monensis, and suitable areas for Effects of Feral Mammals run with rats at night. Rats may also threat to Epicrates monensis. The yel- affect boa populations by preying on low-crowned night heron, Nyctanassa My analysis shows that Rattus and Anolis directly or by influencing their violacea, and the Puerto Rican screech Felis are a primary influence on com- perching behavior, (indicated by the owl, Otus nudipes, are two potential munity composition on the Puerto negative correlation between rat den- predators of the boa. While popula- Rico Bank. Felis presence is associ- sity and Anolis perch height (table 1: tions of Otus are declining on the ated with low Alsophis, Margarops, PC I) or selection of sleeping sites. If bank (IUCN 1981) those of the heron and Rattus density (table 1: PC I); Fe- lizards rarely rest in the canopy at seem quite stable. I have repeatedly lis absence is associated high Anolis night but rather seek refuge sites on observed herons foraging at night in and Alsophis densities in PC IV (table the ground, there would be poten- boa habitat on both Isla Mona and 1). Clearly the presence of Fdis in E. tially disastrous consequences for Cayo Diablo. Examination of the de- monensis habitat is a mixed blessing. boa foraging success. Rattus also ap- bris beneath heron rookeries on Cayo Cats present a great danger to Ep- parently affect Margarops density Diablo has revealed numerous frag- icrates because they hunt at night. (table 1: PC V). ments of Anolis and Ameiva skin and Several instances of cat predation of There can be little doubt that the skeletal materials, usually ribs, verte- Epicrates have been reported on St. Indian mongoose, Herpestes auropunc- brae, and jaw elements. No snake Thomas (D. Nellis pers. comm.) In tatus, threatens Epicrates mmonensis di- remains have been found, but my co- fact, in April and May of 1988 two E. rectly as well, but I believe the risk to workers and I are continuing to in- monensis were rescued from cats on Epicrates is sometimes exaggerated. vestigate this potential problem. I St. Thomas and were incorporated Herpestes predation on endemic West also found that Anolis densities and into the captive breeding program at Indian snakes is well documented perch heights are reduced (table 2) the Toledo Zoological Gardens. In (Maclean 1982), but the mongoose is on plots with high pearly-eyed contrast, however, on islands where a stictly diurnal, terrestrial predator; thrasher densities. In PC I (table 1) boas and rats coexist-Isla Mona and Epicrates monensis is nocturnal and high Anolis perch heights are associ- St. Thomas-there are also significant arboreal. Herpestes poses the greatest ated with low thrasher density. populations of Felis. Cats feed on danger to the diurnal West Indian These birds also prey on Anolis, and Rattus and may keep rat populations racers, genus Alsophis, and are di- are so common in some areas they at levels low enough to permit sur- rectly responsible for the extinction could easily depress Anolis popula- vival of the boa. Their apparent ad- of Alsophis sancticrucis on St Croix tion numbers. Principal component verse affect on Alsophis and Marga- and the extirpation of A. portoricensis VI (table 1) couples high thrasher rops density-two potential predators from St. Thomas and St. John. In con- density with low Anolis density. of E. monensis-may also be of some trast, I have found Epicrates monensis Two arthropods are potential small benefit in certain circum- abroad during the daylight hours on predators of E. monensis: the land stances. Weiwandt's (1977) observa- only two occasions over a period of crab Gecarcinus and the hermit crab tion of cat predation of Alsophis on several years. It seems that Herpestes Caenobita clypeatus. Searches of ter- Isla Mona corroborate the PC I link- would have the greatest chance of restrial refugia for Epicrates have re- age of cat presence with low Alsophis capturing Epicrates when the latter is vealed that these snakes are nearly density. resting in some moderately acces- always absent from areas occupied I cannot be certain whether Rattus sible location during the day-in by Gecarcinus and Caen~bita.This is affectboa populations by acting pri- loose sections of termite nests, for especially true in termite nests. marily as a constraint on their re- example. Feral pigs Gus scrofa) may Snakes only occupy areas of the nest source levels or by direct predation. also threaten the Mona boa to some that are inaccessible to crabs. If Although I have been unable to dem- degree, either by eating them or by weathering or disturbance causes a onstrate that rats forage on boas, I destroying vegetation, such as terres- section of termite nest to become have every reason to suspect that trial bromeliads, that may act as habitable for crabs it is abandoned by they do. Rattus is known to prey on snake refugia. I have no data on the Epicrates, despite their prior use of lizards (Whitaker 1978). While sur- magnitude of this threat. the refugium for several past field veying for boa populations on the seasons. In hundreds of examinations Bank I found habitat (Congo Cay, of refugia over the past five field sea- Outer Brass Cay) which provides op- Natural Predators sons, I found Epicrates in association timal foraging opportunities for the with Caenobita on only one occasion: I boa (e.g. vegetation associated with The Puerto Rico Bank has no extant found a gravid female thermoregu- population densities of > 60 Anolis/ species of native mammalian preda- la ting under a discarded tarpaulin in 100 m2 on rat-free islands) but had no tors, but two nocturnal avian preda- the midst of several Caenobita on 7 or few boas and were virtually over- tory species may pose a limited September 1987. Evidence for preda- tion by the aforementioned species is The fragmentation of E. monensis Predator Eradication on Suitable strictly circumstantial, but the fact into several small demes may have Offshore Islets remains that over 17% of the Ep- left several populations without the icrates captured have obvious genetic resources to survive changing Rat control programs should be initi- wounds, scars, or partially ampu- environments, and doubtless allowed ated immediately on those islands tated tails. This is strong evidence stochastic processes such as disease, with habitat suitable for E. monensis. that some form of natural predation prey fluctuations, or storms to extir- Preliminary studies of rat eradication is occurring. pate many isolated populations. I as- using anticoagulant poisons on some sume that the influences of random small cays near St. Thomas have pro- events on the present distribution of duced promising results (Division of Climatic/Stochastic Events the native herpetofauna complicates Fish and Wildlife, USVI 1983). It is the multivariate analysis by introduc- critical, however, that time and fund- The apparent extirpation of the snake ing more variance into the correla- ing be committed for follow up stud- from the majority of the islands on tion matrix. These factors may ex- ies on any islands made the subject the Bank relate not only to the arrival plain the absence of snakes from is- for a rat control program. This must of European man on the Bank and lets with suitable habitat, as some of be done to ensure that immunity to the habitat destruction which fol- these islands may have inadequate poisons has not evolved or that lowed, but also to climatic, eustatic, food resources or lower probabilities populations are being replenished by and stochastic events, many of which of recolonization. recolonization from St. Thomas. had profound influences on habitat. It is unlikely that Felis or Herpeste During the late Pleistocene several will ever be eradicated from larger climatic and eustatic events occurred Management Recommendations islands such as Isla Mona or St. Th that apparently set the stage for the mas, but Felis control programs nr decline of E. monensis on the Bank. The forces threatening Epicrates in force on Mona should be conti~ Foremost among these was a dra- monensis are complex. Solutions for ued to further reduce populations matic change in the climate of Puerto the recovery of the boa will not be and should be expanded to inch ' - I Rico. From a relatively xeric climate, simple, but I am optimistic about the Cayo Icacos. It is important to co~ Puerto Rico became progressively chances of success. My management vince management authorities tha more mesic during the late Pleisto- recommendations are summarized feral mammal control measures on cene. Today, over 81% of Puerto below. the Bank must be increased, and Rico's vegetation is classified as quickly. moist or wet forest (Ewe1 and Whit- It is a credit to the evolutionary re more 1973). Pregill(1981) and Pregill Saving Boa Habitat silience of this little snake that it has and Olson (1982) describe the effect survived at all. Few endangered spe- this climatic change had on the xeric- This may be impossible on St. Tho- cies have been exposed to such a adapted Puerto Rican herpetofauna. mas, but with luck the boa may coex- wide range of adverse effects and This extreme climatic shift may have ist with man (as it now does) at some have still survived. It is my fervent resulted in the extirpation of E. relatively developed localities. Con- hope that this, and other endemic monensis on Puerto Ri~o.~In addi- tinued protection of Isla Mona and species of the Caribbean, will not be tion, sea levels rose nearly 100 m La Cordillera are absolutely neces- exterminated in the wake of the liv- about 8,00040,000 years ago and sary. ing human debris, such as Rattus rat- separated the Virgin Islands from Continued protection and man- tus, that we have allowed to pollute one another and from Puerto Rico, agement should be extended to those the islands of the West Indies. transforming what was a contiguous cays now protected by the Division land mass into a scattered series of of Fish and Wildlife, U.S. Virgin Is- islets and cays spread over nearly lands-particularly Congo Cay, Outer Captive Breeding for 400 km. Many of these cays now Brass Cay, Salt Cay, Savana Island Reintroduction Purposes have extremely low elevations (Heat- and Steven Cay-as these sites might wole and Mackenzie 1967). eventually be utilized for reintroduc- Captive propagation can figure sig- tion programs. The smaller islands nificantly in the recovery of this should be off limits to casual visitors snake (USFWS 1986) The current co- 41t is unclear why E. monensis is absent to prevent habitat damage and hu- operative breeding plan for E. monen- from the dry forest in southwestern Puerto Rico. Habitat in the Guanica forest seems man persecution of the snakes. sis should be expanded to more quite suitable for the boa: perhaps brtf-~er American Associa tion of Zoological survey work will result in its discovery there. Parks and Aquarium member institu- tions, and Species Survival Plan des- Literature Cited graphy of the Puerto Rican Bank. ignation should be sought for the Atoll Research Bulletin No. 251:l- snake immediately to facilitate ge- Barbour, Thomas 1917. Notes on the 5%. netic management of the captive herpetology of the Virgin Islands. Heatwole, Harold. and Frank Mack- population. Proceedings of the Biological Soci- enzie 1967. Heqxtsgeography of For the present, until genetic ety of Washington 30:97-104. Puerto Rita 3'-Pale~ge~graphy, analysis has been completed, the Barbour, Thomas 1930. Some faunis- faunal sirniliaritgr, and endemism, strategy of deme integrity mainte- tic changes in the Lesser Antilles. Evolution 21 A29-438. nance should be continued, with St. Proceedings of the New England Kaye, Clifford A. 1959a. Shoreline Thomas founders and La Cordillera Zoological Club 11:73-$5. features and quaternary shoreline founders managed as separate popu- Briscoe, C.B. 1966. Weather in the changes in Puerto Rics. US.Geo- lations. Continuous outcrossing Luquillo Mountains of Puerto logical Survey Professional Paper within demes facilitated by a random Rico. U.S.D.A. Forest Service Re- 327-B:49-240. pair mating scheme should be en- search Paper ITF-3,250 p. Institute Kaye, Clifford A. 1955%. Geology of couraged. Fortunately, the first cap- of Tropical Forestry, Rio Piedras, Isla Mona, Fuerto Rico, and notes tive breeding has already taken Puerto Rics. on the age of the Mona Passage. place, the proximate factors critical Brown, William S. and William S. U.S. Geological Survey Prafes- to reproduction have been identified Parker 1976. A ventral scale clip- sianal Paper 3I?-E:'H4'f -198. (Tolson and Tuebner 1987), and there ping system for permanently Kiester, A. Ross, George C. Gorman, is no reason why the captive popula- marking snakes (Repiilia, Seven- and David Colon Arroyo 1975. tion cannot be expanded quickly for tes). Journal of Herpetology Habitat sePec tion behavior of three reintroduction attempts within five lO(3)247-249. species of Anolis lizards. Ecology years. Campbell, Howard W. and Frederick 56:220-225. I firmly believe that we are finally G. Thompson 1978. Observations Little, Elbert E. Jr. and Frank H. at the point where we can look for- on a captive Mona Island boa, Ep- Wadswoath 11964. Common trees ward to augmenting boa popula- icrates monensis monensis Zenneck. of Fuerto Rico and the Virgin is- tions, rather than helplessly watch Bulletin of the Maryland Herpeto- lands. U.S. 1[4epar6mentof Agricul- them decline. logical Society 14(2)98-99. ture, Agriculture Handbook 249. Clarke, Robert 1986. The handbook 548 p. Washington, D.C. of ecological monitoring. 298 p. MacLean, William I?. 1982. Reptiles Acknowledgments Clarendon Press, Oxford. and amphibians of the virgin Is- Cody, Martin L. 1974. Competition lands. 54 g. roPnacmillan Caribbean, This research was conducted as part and the structure of bird commu- London. of USFWS recovery activities under nities. Monographs in Population Mayer, Gregory C. and James D, the support of the Institute of Mu- Biology 7. Princeton University Lazell 1988. Distributional records seum %rvices conservation program Press, Princeton, New Jersey. for reptiles and amphibians from (Grant IC-70095-87) and the Toledo Division of Fish and Wildlife, U.S. the Puerto Rico Rank. Herpeto- Zoological Society. I am extremely Virgin Islands 1983. Rat control on logical Review 1961):23-24. grateful to Dr. David W. Nellis, Divi- small tropical cays. 26 p. Unpub- Matthews, William J. 1985. Distribu- sion of Fish and Wildlife, U.S Virgin lished report. tion of midwestem fishes on Islands, Drs. Eduardo R. Cardona Ewel, Jacob J. and John .L. Whitmore mu1 tivariake environmental gradi- and Jose A. Vivaldi, Departments de 1973. The ecological life zones of ents, with emphasis on Notropis Recursos Naturals, Commonwealth Puerto Rico and the U.S. Virgin lu trensis. American Midland of Puerto Rico, and to Hilda Diaz- Islands. U.S.D.A. Forest Service Naturalist 113(2):225-237. Sol tero and Robert Pace of the Res. Paper ITF18.71 p. Institute Moulton, Michael P. 1985. Morpho- USFWS Caribbean Field Office for of Tropical Forestry, Rio Piedras, logical similarity and coexistence their counsel and logistical support Puerto Rico. of congeners: an experimental test during the execution of this project. Grant, Chapman 1932. Herpetology with introduced Hawaiian birds. I thank Earl W. Campbell 111, Jorge of Tortola; notes on Anegada and Oikos 44:301-305. L. Pinero, and Carlos Diez for their Virgin Gorda, British Virgin Is- Nellis, David W., Norton, Robert L., assistance in the field, which was of- lands. Journal of the Department and William P. MacLean 1984. On ten given under difficult conditions. Agriculture of Puerto Rico 16:327- the biogeography of the Virgin Is- C. Ray Chandler and Earl W. 329. lands boa, Epicrafes monensis Campbell I11 aided in the statistical Heatwole, Harold, Levins, Robert, granti. Journal of Herpetology, analysis. and Michael D. Byer 1981. Biogeo- 17(4):413-417. Pregill, Gregory K. 1981. Pleistocene and Aquariums Regional Confer- Weiwandt, Thomas A. 1977. Behav- herpetofaunas from Puerto Rico. ence Proceedings 1987:606-613. ior, ecology, and management of 72 p. Miscellaneous Publications U.S. Fish and Wildlife Service 1980. the Mona ground iguana, Cyclura Museum of Zoology, University of Status of Virgin Islands boa clari- stegnegen. Ph. D. dissertation, Cor- Michigan, No. 71. fied. Endangered Species Techni- nell University, Ithaca, New York. Pregill, Gregory K. and Storrs L. cal Bulletin, Department of Inte- Whitaker, A. H. 1973. Lizard popula- Olson 1981. Zoogeography of rior, U.S. Fish and Wildlife Serv- tions on islands with and without West Indian land vertebrates in ice, Endangered Species Program, Polynesian rats, Rattus exulans relation to Pleistocene cli- Washington, D.C. 5:12. (Peale). Proceedings of the New maticcycles. Annual Review of U.S. Fish and Wildlife Service 1984. Zealand Ecological Society 20: 121- Ecology and Systematics 1275-98. Mona boa recovery plan. 14 p. 130. Rivero, Juan A., Rafael Joglar, and U.S. Fish and Wildlife Service, At- Wiens, John A. and John T. Roten- Idabella Vazquez. 1982. Cinco lanta, Ga. berry 1981. Habitat associations nuevos ejemplares del culebron de U.S. Fish and Wildlife Service 1986. and community structure of birds La Mona Epicrates m. monensis Virgin Island tree boa recovery in shrubsteppe environments. Eco- (0phidia:Boidae). Caribbean Jour- plan. 23 p. U.S. Fish and Wildlife logical Monographs 5(l)21-41. nal of Science 17(1-07-13. Service, Atlanta, Ga. Rotenberry, John T. and John A. Wiens 1980. Habitat structure, patchiness, and avian communi- ties in North American shrub- Appendix A. steppe vegetation: a multivariate analysis. Ecology 61 :1228-1250. PCA Variables Measured on Island Study Plots. §AS Institute 1985. SAS users guide: statistics Version 5.957 p. SAS In- Variable Description stitute Inc. Cary, North Carolina. Schmidt, Karl P. 1926. The amphibi- Predator ans and reptiles of Mona Island, Ratfus density Rats captured/trap hour West Indies. Field Museum of Felis presence Present = 1, absent = 0 Natural History Publications Alsophis density Mean no. Alsophis observed/day on transect 12(12):149-163. Margarops density Mean no. Margarops observed/day on transect Sheplan, Bruce R. and Albert Prey Schwartz. 1974. Hispaniolan boas Anolis density Mean no. Anolis/5 m of transect of the genus Epicrates and their Ameiva density Mean no. Ameiva/5 m of transect Antillean relationships. Annals of Anolis perch height Mean perch height in m of male Anolis the Carnegie Museum 45(5):57- Coverage 143. Percent cover C trees No.compound trees/no. woody plants Stull, Olive G. 1933. Two new sub- Percent cover S trees No. single trees/no. woody plants species of the family boidae. 4 p. Percent cover palms No. palms/no. woody plants Occasional Papers of the Museum Percent cover Opuntia No. Opuntia/no. woody plants of Zoology, University of Michi- Percent cover grasses Grassland area/total area gan, Number 267. Structural Tolson, Peter J. 1987. Phylogenetics Vegetational continuity Contiguous = 1, high = .75, Moderate = .5 of the boid snake genus Epicrates low = .25, absent = 0 and Caribbean vicariance theory. Canopy height >3 m = 1,l-2 m = .5, <1 m = 0 68 p. Occasional Papers of the Mu- Plant diversity No. of dominant plant species on plot seum of Zoology, University of Michigan, Number 115. Tolson, Peter J. and Victoria A. Tuebner 1987. The role of social manipulation and environmental cycling in propagation of the boid genus Epicrates: Lessons from the field and laboratory. American Association of Zoological Parks