RAPTOR ABUNDANCE and HABITAT USE in a HIGHLY&Hyphen
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j. RaptorRes. 36(1):51-57 ¸ 2002 The Raptor ResearchFoundation, Inc. RAPTOR ABUNDANCE AND HABITAT USE IN A HIGHLY-DISTURBED-FOREST LANDSCAPE IN WESTERN UGANDA NATHANIEL E. SEAVY• AND CHRISTINE K. APODAC^ Departmentof Zoology,223 BartramHall, P.O. Box 118525, Universityof Florida, Gainesville,FL 32611-8525 U.S.A. ABSTRACT.--Weconducted roadsideraptor surveysin an area of western Uganda that included undis- turbed forest, agriculturalmosaics, and tea plantations.Between September 1997-April 1998, we sur- veyed three transects(51 km of roadway)twice each month, once during the morning and again in the afternoon. During these surveys,we detected 14 falconiform speciesand 77 individuals.We detected significantlymore raptorsduring morning than afternoon surveys.Wahlberg's Eagles (Aquila wahlbergi) and Long-crestedEagles (Lophaetus occipitalis) were observedmost frequently and were sightedconsis- tently throughout the study.Most raptors observedwere resident species,whereas Palearctic migrants comprisedless than 25% of all raptors,noteworthy considering their abundancein other African re- gions.We did not detect an equal number of raptors in all habitat types.Agriculture mosaicsaccounted for 61% of the habitatwe surveyedand 75% of all raptor detectionswere in thesehabitats. In contrast, tea plantationswere 14% of the area surveyed,but only 3% of all raptorswere detected there. Based on these results,we suggestthat tea plantations may be suboptimal habitat for larger, open-habitat raptors. We did not detect large, forest-dwellingeagles outside of large areas of undisturbed forest, which are probablycritical to their persistencein these landscapes. KEYWORDS: Uganda;roadside survey; conservation; habitat use,, deforestation; tea plantation; Aquila wahlbergi; Wahlberg'sEagle,, Lophaetus occipitalis; Long-crested Eagle. Abundancia de repacesy uso de habitat en un paisajede bosque altamente disturbadoen el oeste de Uganda RESUMEN.--Hicimosestudios de rapacesalrededor de las carreterasen un •trea del oeste de Uganda que inclunabosque sin intervenci6n,mosaicos agrfcolas, plantaciones de te. Entre septiembrede 1997- abril de 1998, estudiamostres transeptos(51 km de carreteras) dos veces cada mes, una vez en la mafianay otra en la tarde. Durante estosestudios detectamos 14 especiesfalconiformes y 77 individuos. Detectamossignificativamente m•ts especies durante los estudiosde la mafiana queen los de la tarde. Las ftguilasde Wahlberg (Aquila wahlbergi)y las ftguilasde crestaalargada (Lophaetusoccipitalis) fueron observadasrafts frecuentemente y fueron avistadasconsistentemente a lo largo del estudio.La mayoria de rapacesobservadas fueron especiesresidentes, mientras que las migratoriaspalearticas comprendie- ron menos del 25% de todas las rapaces,esto es digno de mencionarlo considerandosu abundancia en otrasregiones africanas. No detectamosun nfimero igual de rapacesen todoslos tipos de h•tbitats. Losmosaicos agricolas dieron cuentade 61% del h•tbitatque estudiamosy 75% de todaslas detecciones de rapacesestuvieron en esosh•tbitats. En contraste,las plantacionesde te fueron 14% del •trea estu- diada, pero 6nicamente 3% de todas las rapacesfueron detectadasalli. Basadosen estosresultados, sugerimosque las plantacionesde te pueden ser habitatssub 6ptimos para las rapacesm•ts grandes y de habitats abiertos. No detectamosgrandes •tguilasresidentes de bosque fuera de grandes •treasde bosqueno perturbado, los cualesprobablemente son criticospara su supervivenciaen estospaisajes. [Traducci6n de CdsarMarquez] When coinpared to Nearctic and Palearctic spe- edge of 79 raptors breeding in East Africa, they cies, Afrotropical raptors are relativelyunstudied. considered only 6.3% of these species "well- This deficiency was recently illustrated by Virani known,"while rating 60.8% "unknown."For many and Watson (1998); describing the state of knowl- of theseunknown species, little or no information exists on distribution, abundance, breeding biolo- 1 E-mail address:[email protected] gy,or feeding ecology--basicinformation for iden- 51 52 SE^vY ^ND APOD^CA VOL. 36, No. 1 tifying populations that are threatened by habitat the Makerere University Biological Field Station in KNP, alteration. Determination of populations that are averaged1778 mm between 1990-98 (L. Chapmanand C. Chapman unpubl. data) and peak periods of rainfall threatened is an important aspectof conservation, occurin April and October (Struhsaker1997). especiallyin areaswhere forestsare being cleared We conducted roadside raptor surveysalong three to support growing human populations. transects(19, 15, and 17 km in length; Fig. 1) between With ca. 104 people per kme, Uganda has one September1997-April 1998. We surveyedtransects twice of the densest populations in sub-SaharanAfrica each month, once in the morning (between 0800-1000 H) and again in the afternoon (between1500-1700 H), and it continuesto grow at a yearly rate of 2.6% usuallyon the sameday. Driving at speedsof 20-40 km/ (FAO 1999). This population has driven wide- hr with five observersin the vehicle, we stoppedbriefly spread deforestation. A hundred years ago, ca. to identify raptors on both sidesof the transectand re- 13% of Uganda was covered by moist, broadleaf corded the time, distancefrom the transect,habitat type, forest, but only 3% of this forest remains (Sayeret and activity (perched or flying) for each bird. During heavy rain we did not conduct surveys. al. 1992). The remaining forested areas, many in To quantify habitat availability, we visually estimated reservesand national parks, are under increasing habitat composition(10% increments)within 100 m of pressurefrom growingrural populations.Thus, in- either side of the road of each km traveled. For this anal- formation on raptor abundance and habitat use ysis,we recognized eight habitat types:mature forest, ag- both inside and outside of these protected areas is riculture/forest mosaic, agriculture/grassland mosaic, tea plantation, secondary vegetation, villages, papyrus important for management and conservationde- swamp,and lakeshore.MatureJbrest was primarily encoun- cisions. tered when transectspassed through portions of Kibale Roadside raptor surveyshave been widely used National Park. This forest is consideredmoist, evergreen to study relative abundance, community composi- forest, transitional between lowland rainforest and mon- tion, and habitat use of raptors (e.g., Woffinden tane forest (Struhsaker 1997). Canopy height ranges from 25-30 m, with a few trees as tall as 55 m, and com- and Murphy 1977, Ellis et al. 1990). Although lim- mon tree speciesinclude Diospyrosabyssinica, Markhamia itations of roadside surveys are well-recognized platycalyx,Celtis durandii, Uvariopsiscongensis, and Bosqueia (Millsap and LeFranc 1988, Bunn et al. 1995), the phoberos(Chapman et al. 1997). Agriculture/Jbrestmosaic method offers an efficient meansof describingrap- was characterizedby a patchwork of remnant forest frag- tor communities. Roadside raptor surveys have ments surrounded by subsistenceagriculture (primarily bananas, millet, cassava, and corn), fallow fields domi- been conducted in East Africa (Brown 1971, Thio- nated by elephant grass (Pennisetumpurpureum, 3-5 m 11ay1978, Sorley and Andersen 1994), but these tall), cattle pasture, pine and eucalyptusplantations, and efforts have occurred mostly in savannahabitats scatteredhouses. Similar to this habitat, agriculture/grass- that are characterized by high densities of large land mosaicwas also a patchwork of farmland, cattle pas- mammals, vultures, and eagles. Here we present ture, and forest plantations, but uncultivated land was covered by large areas of elephant grass,and there were results from eight months of roadside raptor sur- no remaining natural forest fragments.Agriculture/grass- veys in the Kabarole District of western Uganda. land mosaicoccurred in the southern portion of the study We describe the abundance and diversityof raptors area. Teaplantations are large fields of tea shrubs grown in mature forest, agriculture/forest mosaic, agri- in rows and trimmed regularly to maintain a uniform culture/grasslandmosaic, tea plantation, second- height of about 1 m. This crop is one of the few intensive, large-scale agricultural industries in western Uganda. ary vegetation,villages, papyrus swamp, and lake- Four other habitat types--secondaryvegetation, villages, pa- shore habitats. pyrusswamp, and shoresof cT'aterlakes•together comprised <10% of the area surveyed. STUDY AREIX AND METHODS Becausethe number of raptors detected per transect The studyarea (0ø13'-0ø41'N,30ø19'-30ø32'E) lies just waslow, we pooled surveyresults from the three transects north of the equator at the foot of the Ruwenzori Moun~ and considered them a single transect, though surveyed transin western Uganda (Fig. 1). This area is volcanic in on different days.We considered monthly surveysinde- origin and characterizedby rolling hills. Elevationranges pendent samplesand used a Wilcoxon signed-rankstest from 1100 m in the south to 1590 masl in the north. to compare distributions of raptor count data from Although historicallyforested, much of the land hasbeen morning and afternoon surveys.We investigated the re- cleared for subsistencefarming and banana (Musa spp.) lationship between monthly rainfall and raptor detec- and tea ( Theasivensis) plantations to support the growing tions (morning and afternoon surveyspooled) using human population. Within this agricultural landscape, Spearman rank correlation. We used Chi-squaregood- forest fragments