Status of the Virgin Islands Screech-Owl

J. Field Ornithol., 69(4):557-562

STATUS OF THE VIRGIN ISLANDS SCREECH-OWL

JORGEA. MORENO Departmentof Environmental,Population and OrganismicBiology Universityof Colorado CampusBox B-334 Bould• Colorado 80309 USA and Instituto de Educacitn Ambiental MetropolitanUniversity R[o Piedras, Puerto Rico 00928 USA

Abstract.--TheVirgin IslandsScreech-Owl Otus nudipes newtoni is a little-studiedtaxon whose current statusis uncertain. It historicallyoccurred on severalsmall islandsimmediately east of Puerto Rico in the Caribbean. In an effort to assessits current status,I carried out surveys on St.John, St. Croix, and St. Thomas, the three largestof the United StatesVirgin Islands. Acousticand visualsurveys were carried out nightly for a 3-wk period during August1995. Playbackrecordings of owl callsfrom the PuertoRico subspecies did not elicit anyresponses during surveys,nor did I seeany owls.I concludethat this taxon is extinct,because the three sampledislands contained the largestremaining patchesof appropriatehabitat for this species.

ESTATUS DE OTUS NUDIPES NEWTONI

Sinopsis.--E1Mficaro Pequefio de las IslasVirgenes Otus nudipesnewtoni es una especiepoco estudiadacuyo estatusactual es incierto. Hist6ricamente ocurri6 en varias islas pequefias imnediatamenteal este de Puerto Rico en el Caribe. En un esfuerzopara evaluarsu estatus actual, realiz• estudiosen St.John, St. Croix y St. Thomas, las cualesson las m/rsgrandes de las IslasVirgenes Estadounidenses.Llev• a cabo censosvisuales y acfisticosnocturnos por tres semanasdurante agostode 1995. No pude lograr respuestasusando una grabaci6ndel cantode la subespeciede PuertoRico, ni observeindividuos. Concluyo que estasubespecie estgtextinta, porque las tres islasmuestreadas contienen las parcelasm•s grandesde hgtbitat apropiado. The Puerto Rican Screech-OwlOtus nudipesis endemic to the Puerto Rico region (defined to include Mona, Monito, Puerto Rico, Culebra, Vieques,and the U.S. and BritishVirgin Islands), although related genera and speciesoccur on other Greater Antillean islandsand Central America (Bond 1980, Burton 1992). Two subspeciesare recognized, O. n. nudipes from Puerto Rico proper and O. n. newtonifrom Vieques, Culebra, St. John, Tortola, Virgin Gorda, St. Croix and Guana Island (American Or- nithologists'Union 1983, Raffaele 1989, Sibleyand Monroe 1990). O. n. newtoni was named in 1860 from skins collected on St. Croix (Lawrence 1878). These birds were purportedlyduller, grayer,and lessrufescent abovethan Puerto Rican specimens (Wetmore 1927). Howard and Moore (1991) list a third subspecies,A. n. krugii, from the LesserAntilles, but the taxon is not generallyrecognized. Indeed, Lawrence(1878) synony- mized Gymnoglaux(=Otus) krugii with O. nudipesover 100 yearsago. Although O. n. nudipesis still common on Puerto Rico, particularlyin the forested interior mountains and northwestern.karst region (Biaggi 1983, Wiley 1986, Raffaele 1989, Rivera-Milan1995, Pardiek et al. 1996), O. n. newtoniis rare in its historical range or may be extinct (Raffaele

557 558] J.A. Moreno J.Field Ornithol. Autumn 1998

1989). Based on the amount of habitat available on different islandswith- in the historicalrange and recent reports (see below), the probabilityof encounteringthis speciesis greatestin the United StatesVirgin Islands. I reviewthe historicalstatus of the Virgin IslandsScreech-Owl and report the resultsof a study to assessthe current statusof this taxon on the islandsof St. Thomas, St. Croix, and St. John.

HISTORICAL STATUS Vieques.--TheVirgin IslandsScreech-Owl has been reported from Vie- ques,where it is now thought to be extinct (Raffaele 1989). As far as I have been able to ascertain,the Vieques record originated with a com- ment by Wetmore (1927), who wasinformed that a residenthad seena small owl severalyears earlier on the island. Basedon this datum, it is unlikely the owl hasresided on Viequesin the immediatepast; fossil data are required to verifyif it ever did. I searchedVieques for this speciesfor one week in June 1979 withoutsuccess. Culebra.--I was unable to find written remarks regarding the presence of this specieson Culebra. In over twenty research-relatedvisits to this island spanning 10 yr, I never sawnor heard this species.On two occasions (1980 and 1986), I used playbackrecordings but never obtained a re- sponse. St. Croix.--When described, A. n. newtoni was considered rare on St. Croix, although a breeding population existed. E. Newton (in Newton and Newton1859) obtainedyoung birds on 30 May 1857and 1 Sep.1858. Adultswere taken in earlyJune 1857 and 11 May 1858. No additional recordsare availableuntil over a centurylater, when Leck (1975) wrote of unverifiedsightings in westernSt. Croix and Nellis (1979) saw two birds. Norton (1986) positsthat the latter record pertains to Asiofiarn- meus. St.John.--Riise (in Newton 1860) collectedseveral birds from this island. Norton (1981) reports a singleowl sightingon St.John but suggests that it may have been a vagrant O. n. nudipesor Asiofiammeus. St. Thomas.--Eggsand skinswere obtained from St. Thomas (Cassin 1860), although the taxon was consideredrare (Knox 1852). No further reports of owlsfrom this island have appearedin the literature. Nellis (1994, pers. comm.) informs me of recent unverified sightingsby resi- dents, however. Guana Island.--S. Lazzell (1993, pers. comm.) reported owl pellets from this island. No confirmed sightingshave been recorded, however. Tortolaand Virgin Gorda.•Although reported as part of the historical distribution,I have been unable to verify recordsfor theseislands.

MATERIALS AND METHODS I visited St. Thomas, St. Croix, and St. John during August 1995. Al- though Augustdoes not coincidewith the maximal calling period of O. nudipesin PuertoRico (Rivera-MilSn1995; W. Arendt, pers.comm.), the speciescalls throughout the year (pers. obs.; R. Perez, pers. comm.). I Vol.69, No. 4 VirginIslands Screech-Owl [559

T^BLE 1. Island visited,dates visited,total km sampled,and number of points surveyed during surveysfor the Virgin IslandsScreech-Owl.

Point counts Total km Total Island Datesvisited surveyed Playback Aural points St. Croix 9-14 Aug. 1995 31.5 44 50 94 St. Thomas 15-20 Aug. 1995 26.4 39 40 79 St.John 21-25 Aug. 1995 45.0 12 20 32 assumedthat owls in the Virgin Islandswould also call year-round.Al- though I confirmed that Screech-Owlswere callingin both Puerto Rican dry and moist forestsby telephoningcolleagues on Puerto Rico on most surveynights, the possibilityexists that my searchcoincided with a period of low calling activityin the Virgin Islands.However, my pastexperience with owls on Puerto Rico suggeststhat individualsof this specieswill al- most alwaysrespond to taped callsif they are present. On each island, I conductedsurveys nightly between 1930 h and mid- night (Table 1). This is the time of maximal calling activityfor the pop- ulations on Puerto Rico (pers. obs.;C. Ruiz, pers. comm.). Surveyscon- sistedof point countswhere assistantsand I stoppedat pre-determined intervals (usuallyevery 0.3 km, although if it was unsafe to stop at a particular site we drove ahead until a suitable area was found) and lis- tened for owls.We drove between17 and 33 km per hour to minimize engine noise and increase our ability to detect calls between points counts.At least one assistantaided every night, except on the night of 14 August when I conducted the surveyalone. Assistantshad prior ex- perience in owl samplingmethods. Two approacheswere used to detect this species.Aural surveysinvolved listeningfor calling owlsat, and between,point stations.During playback surveys,I attempted to elicit responsesby playing a taped territorial call from O. n. nudipesrecorded on Puerto Rico. Playbackrecordings have been used effectivelyto surveynocturnal bird speciessuch as owls (John- son et al. 1981, Halterman et al. 1987, Bibby et al. 1993, Pardiecket al. 1996). The call was played continuouslyfrom a Sony stereo tape player for 8-10 min at each point station. (De Geus and Bowles [1991] recom- mended a samplingperiod of 10 min when surveyingEastern Screech- Owls, Otus asio).Calls could be heard up to 0.4 km from the tape player. My assistantsand I were able to detect animal calls (e.g., dogsbarking) from as far awayas 0.75 km at somesites. Although I did not record cloud coverand wind speedat the different sites,surveys were carried out during clear and calm conditions.However, Pardiek et al. (1996) found no correlations between these variables and callingactivity of Otusnudipes on Puerto Rico. I identified surveysites using three sourcesof information: areasiden- tified by Virgin IslandsDivision of Wildlife personnel,by the staff of the U.S. Park Serviceon St.John and U.S. Fishand Wildlife Servicepersonnel 560] J.A. Moreno J.Field Ornithol. Autumn 1998 on St. Croix; records of past sightingsfrom the literature and personal communicationwith observers;and on-siteevaluation of habitat. I quali- tativelyassessed habitats as being suitablefor the owl if they possessedthe followingcharacteristics: large trees (native or introduced) with potential to form cavities(e.g., mango, ceiba,large palms,etc.) and a relativelywell developed and moist understory. On Puerto Rico, siteswith these char- acteristicsappear to harbor the most oMs (Biaggi 1983, Pardieck et al. 1996). O. nudipesis known to nest in cactuscavities in the GuanicaForest of Puerto Rico (R. P•rez, pers. comm.), but this behaviorwas never reported in the Virgin Islands.Although owlsinhabit urban areasin Puerto Rico, and may do so in the Virgin Islands,I would expect their numbers to be low at these sites.However, to ensure thoroughness,I completed aural surveyswithin the main townsevery other night. I stoppedadjacent to randomly chosenwood lots and housessurrounded by dense vegeta- tion for ten minutes, but did not play owl calls.These data points are not indicated in Table 1. I interviewedlocal wildlife officialsto assesswhether they had seen or heard owlsin the immediate past.

RESULTS Surveys.--Noowls were detected in any locality on the three sampled islands.I feel confident that all appropriate habitat was adequatelysur- veyedand that the probabilityof havingmissed a calling owl wassmall. Interviews.--I interviewedand playedthe call of the owl to experienced wildlife workers on each island. Not one individual had ever heard the call while doing field work. All agreed they would have remembered this unusual call if it had been heard. After discussingD. Nellis's sightingsof owlson St. Croix with him, we concludedthat the observationpertains to Asiofiammeus. The relatively large size of the owlshe saw,their behavior (flying up from a grassyfield to a stump and back to the ground) and the locality (a grassyfield I visited) are not consistentwith O. nudipes.

DISCUSSION Although it is alwaysdifficult to state with certainty that a taxon is extinct, the availabledata stronglysuggest the Virgin IslandsScreech-Owl is extinct on St. Thomas, St.John, and St. Croix. Becausethe latter three islandscontain the largestremaining patchesof appropriatehabitat with- in the historicalrange, the taxon is most likely globallyextinct as well. O. nudipesprobably has not re-colonizedthese islands from PuertoRico for one of two reasons.First, O. nudipesdoes not appear to be as good a disperseras the more widespreadA. fiammeus (Burton 1992). For ex- ample, while carrying out wildlife surveysin the small islandsbetween Puerto Rico and the U.S. Virgin Islands,I havecome acrossboth breeding pairs and singleindividuals of A. fiammeus,but never of O. nudipes.Al- ternatively, O. nudipesmay reach the Virgin Islands but, for unknown reasons,cannot persist. Vol.69, No. 4 Vii'ginIslands Screech-Owl [561

The Virgin IslandsScreech-Owl most likely succumbedto the destruc- tion of native forestsin the latter part of the 19th century.Beginning in earnest after 1750, over 90% of the forest cover on each island was cleared for plantation crops,mostly sugar and cotton. This speciesrequires old- growth treeswith cavitiesin which to nest. Today,between 6-7% of the U.S. Virgin Islandsare forested (Lugo et al. 1981). The taxonomic statusof O. n. newtoniis problematical,as the name was assignedbased on only slight plumage color differences(Lawrence 1878). W. Arendt (1997, pers. comm.) hasbanded severaldifferent col- ored morphs of this specieswithin a singleforest in Puerto Rico, and I have observed owls with newtoni coloration in southwestern Puerto Rico. These observationssuggest the subspecificdesignation is not valid. If a reavaluationof this speciesresults in synonimizingthe two taxa, efforts may be initiated to studythe feasibilityof re-introducingthe owl to the Virgin Islandsfrom Puerto Rico.

ACKNOWLEDGMENTS

I would like to thank the following individuals without whose help this study could not have been completed:Jorge Salivaof the United StatesFish and Wildlife Serviceon Puerto Rico, David Nellis and Judy Pierce of the Virgin IslandsDivision of Wildlife, Tom Kelley of the National Park Service on St. John, and Mike Evans (USFWS) and his brilliant wife, Maggie, on St. Croix. Luis (Kentucky)Rodriguez, Carlos Ruiz and Mari PlazaMunet toiled long nights in all or some of the islands.Mary Pachecoof the Institute of Environmental Education (Metropolitan University) provided invaluablelogistic assistance. Raul P6rez-Ri- vera, Wayne Arendt, C. Ray Chandler, and Jim Chase offered helpful suggestionsthat im- proved the manuscript.This studywas funded by the U.S. Department of the Interior, Fish and Wildlife Servicethrough grant number 1448-000-4-94-9152.

LITERATURE CITED

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