abundance and distribution of raptors in the sierra …

ORNITOLOGIA NEOTROPICAL 15: 501–512, 2004© The Neotropical Ornithological Society

ABUNDANCE AND DISTRIBUTION OF RAPTORS IN THE SIERRA DE SAN JAVIER BIOLOGICAL PARK, NORTHWESTERN

ARGENTINA

Pedro G. Blendinger1, Patricia Capllonch2, & M. Eva Alvarez1

1Universidad Nacional de Tucumán, Laboratorio de Investigaciones Ecológicas de las Yungas, CC 34, 4107 Yerba Buena, Tucumán, Argentina.

E-mail: [email protected] 2Universidad Nacional de Tucumán, Centro Nacional de Anillado de Aves, San Martín 1545,

4000, Tucumán, Argentina.

Resumen. – Abundancia y distribución de aves rapaces en el Parque Biológico Sierra de San Javier,noroeste de Argentina. – Presentamos los patrones de utilización de hábitat para 27 especies de aves rapa-ces del Parque Biológico Sierra de San Javier. Registramos en total 20 especies diurnas y 7 de hábitos noc-turnos; 70% de ellas habitan con regularidad el área relevada. En los hábitat principales, realizamos unanálisis cualitativo de la abundancia y de la distribución temporal estacional de las especies. Las especiesmás abundantes son residentes permanentes, ampliamente distribuidos en Sudamérica. La riqueza de espe-cies fue mayor para los carnívoros y menor para los insectívoros en los tres hábitat principales del parque,mientras que los carroñeros fueron el grupo funcional más abundante en los tres casos. Discutimos la con-tribución del parque para la conservación de especies de aves rapaces susceptibles de extinguirse a escalalocal. El Milano pico garfio (Chondrohierax uncinatus) y el Taguató negro (Buteo leucorrhousi) poseen altoriesgo de extinción local, debido a su disminución numérica, susceptibilidad a la alteración del hábitat y alprogresivo aislamiento del parque. Ocho especies utilizan con regularidad el tipo de hábitat donde suabundancia es mayor [Jote real (Sarcoramphus papa), Aguilucho cola corta (Buteo brachyurus), Halcón montéschico (Micrastur ruficollis) y Lechucita canela (Aegolius harrisii) en el bosque montano subtropical; Milanoblanco (Elanus leucurus), Chimango (Milvago chimango), Halconcito colorado (Falco sparverius) y Lechucita viz-cachera (Speotyto cunicularia) en los bosques alterados]. Estas especies son potencialmente útiles como indi-cadoras de la calidad del hábitat y para evaluar el impacto de la modificación y fragmentación de los hábitatnaturales sobre la vida silvestre del parque. Aceptado el 10 de Mayo de 2004.

Abstract. – We describe patterns of habitat use for 27 species of raptors in the Sierra de San Javier Biolog-ical Park in northwest Argentina. Twenty diurnal and seven nocturnal species were recorded; 70% of themregularly inhabit the area. For the main habitats, we present a qualitative analysis of species seasonal distri-bution and abundance during the dry and wet seasons. The most abundant species were permanent resi-dents that are widely distributed in South America. Species richness was highest among carnivores andlowest among insectivores in the three main habitats of the park, while scavengers were the most abundantfunctional group in all habitats. We discuss the importance of the park for the conservation of species sus-ceptible to local extinction. The White-rumped Hawk (Buteo leucorrhous) and the Hook-billed Kite (Chon-drohierax uncinatus) seem to be at high risk of local extinction because of their decrease in number,susceptibility to forest degradation, and the progressive isolation of the park. Eight species regularly usedthe habitat where their abundance was highest [King Vulture (Sarcoramphus papa), Short-tailed Hawk (Buteobrachyurus), Barred Forest-Falcon (Micrastur ruficollis), and Buff-fronted Owl (Aegolius harrisii) in the maturesubtropical montane forest; and White-tailed Kite (Elanus leucurus), Chimango Caracara (Milvago chimango),American Kestrel (Falco sparverius), and Burrowing Owl (Speotyto cunicularia) in disturbed forests]. These spe-

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cies are potentially useful as indicators of habitat quality and in assessing the impact of habitat fragmenta-tion and modification on the park’s wildlife.

Key words: Argentina, conservation, ecological indicator, raptor, subtropical montane forest, Tucumán.

INTRODUCTION quantitative data were given. Vides Almo-

Subtropical montane forests of northwesternArgentina are subject to ongoing degradationresulting from deforestation followed by agri-cultural use (Kapelle & Brown 2001).National and provincial parks and reserves(Brown et al. 2001) currently protect less than10% of these forests. Lack of information onthe biology of species that inhabit these for-ests, and on factors affecting them, limits anyserious attempt to manage subtropical mon-tane forests. Due to increasing pressure ofhuman activities on these areas, it is impera-tive to document species’ occurrence andpopulation status in natural environments,data that will be useful in park management.

Raptors that depend on undisturbed for-ests to complete their life cycles are believedto be especially sensitive to habitat modifica-tion and fragmentation (Thiollay 1985, Jullien& Thiollay 1996, Bildstein et al. 1998). Otherraptors, however, appear to be favored by dis-turbed habitats (Reichholf 1974, Whitacre etal. 1990, Jullien & Thiollay 1996) and maybenefit from increased forest clearing and cat-tle ranching (Olrog 1985). These observationssuggest that raptor species may be used asindicator species to accurately assess bothquality and quantity of habitats available forothers species of interest (Landres et al. 1988,Vides Almonacid 1991).

Present knowledge about population sta-tus and habitat requirements of raptor speciesin northwestern Argentina is rudimentary, asit is for most forest-dwelling raptors of SouthAmerica (Bierregaard 1998). Olrog (1985)qualitatively described the effects of defores-tation on raptor populations inhabiting thehumid forests of northern Argentina, but no

nacid (1989) made a preliminary analysis ofbird conservation in the Sierra de San JavierBiological Park, including raptors.

At present time, the biodiversity of thispark is at high risk of reduction because ofprogressive isolation due to modification ofthe surrounding forest, combined with thenarrow shape of the park and its small size,making more difficult the persistence of spe-cies with low population size and large terri-torial requirements (Vides Almonacid 1991,1992). In this context, raptors are predicted tobe one of the most threatened groups. Wepresent information on abundance and habi-tat use of raptor species of the Sierra de SanJavier Biological Park in northwestern Argen-tina, obtained during 11 years of fieldwork inthe area.

STUDY AREA

The study was conducted in a 14,000-ha pro-tected area, the Sierra de San Javier BiologicalPark (26º45’S, 65º23’W), Tucumán Province,Argentina. The park occupies about 70% ofthe Sierra de San Javier, between 600 and1875 m in elevation. The climate is warm andwet in summer, and temperate and dry in win-ter; intermediate seasons are short. The meanannual temperature in the humid forest variesfrom 18.8°C in the mountain foothill (420 m)close to the park to 13.9°C at 1400 m. Meanannual rainfall is about 1200 mm in the humidforest (Vides Almonacid 1992), although hor-izontal precipitation resulting from passinglow clouds increase as much as 40% theannual precipitation (Hunzinger 1995). Rain-fall is considerably lower in the northern sec-tor of the sierra, with a mean annual of 485

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mm in the foothill (Vides Almonacid 1992).Three main plant communities can be dis-

tinguished based on vegetation structure and

composition. The first one is the montanechaco (Fig. 1), a xerophytic woodland in thenorthwestern sector of the sierra, covering

FIG. 1. Xerophytic woodland or montane chaco in the Sierra de San Javier Biological Park.

FIG. 2. Subtropical mountain forest in the Sierra de San Javier Biological Park.

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close to 20% of the study area. The tree layeris characterized by Schinopsis haenkeana, associ-ated with Caesalpinia paraguarensis, Tipuana tipu,Aspidosperma quebracho-blanco and Ruprechtiaspp. The second community is represented bythe yungas or “selva tucumano-boliviana”, asubtropical montane forest (Fig. 2) coveringmost of the sierra between 600 and 1300–1500 ma.s.l. Cinnamomum porphyria, Blepharo-calix salicifolius, Anadenanthera macrocarpa,Parapiptadenia excelsa, and Terminalia trifloraare the main tree species. The temperatecloud forest, dominated by alder (Alnus acumi-nata) and pine (Podocarpus parlatorei), replacesthe subtropical montane forest at higher alti-tudes (1300 to 1800 m). The subtropicalmontane forest and temperate cloud forestare jointly dealt with. The third communitycorresponds to mesophytic grasslands (Fig.3), composed primarily of Festuca bunch grass,occurring at higher altitudes above the tim-berline, and covering less than 10% of thesierra.

METHODS

Accounts are based on a combination of sam-pling methods. Between May 1994 and June1995, we recorded birds via transects alongstreams and foot trails. Thirty four transectswere walked during daytime at a slow andsteady pace. Transect length varied dependingon site accessibility. The largest samplingeffort (46 observation hours) was made in themontane subtropical forest (67%); the sam-pling effort was lower in the mesophyticgrassland (12%) and montane chaco (21%),and was proportional to the area covered byeach plant community. The sampling effortwas similar during wet and dry seasons. Wealso covered five transects at dawn and dusk,though most observations of nocturnal rap-tors were made during non-systematic sam-plings. For each transect, we registered thenumber of all individuals seen or heard, theiractivity and habitat. Additionally, we includedseveral non-systematic observations made

FIG. 3. Mesophytic grassland growing above the timberline in the Sierra de San Javier Biological Park.

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between 1985 and 1995, when species pres-ence and number of sightings per habitat wererecorded when we visited the park. Althoughthe usefulness of partial counts of birds anddetection by indirect methods is limited(Fuller & Mosher 1981), this approach tomake inventories of raptor species of forestenvironments is pertinent when little infor-mation is available (Whitacre & Turley 1990).

More than 660 raptor sightings wererecorded during the study. Species accountsgiven here are supplemented with observa-tions by Vides Almonacid (1989, 1992), andwith specimens of the bird collection at theInstituto Miguel Lillo (IML). According totheir frequency of occurrence in the transectsand to the overall number of sightings, specieswere classified into four semi-quantitative cat-egories of relative abundance: (1) abundant,observed during at least 50% of the transectcounts; (2) common, regularly seen, but onless than 50% of the transect counts; (3)uncommon, fewer than 10 sightings duringthe study; and (4) occasional, observed onlyonce. Occurrence and seasonal variation inabundance were evaluated for wet (October–March) and dry seasons (April–September),for each habitat considered. Raptors wereclassified as residents, summer migrants, orwinter migrants. We considered as summermigrants those species observed only duringthe rainy season, as winter migrants, thoseobserved in the dry season, and as residentsthose observed in both seasons. Raptors wereclassified as insectivores, carnivores or scaven-gers, according to their main food type in thediet (Jullien & Thiollay 1996, P. G. Blendingerpers. observ.). Correspondence analysis (CA)was used for exploring the relationshipsbetween raptor assemblages in habitat use.

RESULTS

Twenty diurnal and seven nocturnal raptorspecies were recorded. Considering the park

area as a whole, 6 species were abundant [e.g.,Black Vulture (Coragyps atratus), TropicalScreech-Owl (Otus choliba)], 11 common [e.g.,King Vulture (Sarcoramphus papa), BicoloredHawk (Accipiter bicolor), Short-tailed Hawk(Buteo brachyurus)], 7 uncommon [Great BlackHawk (Buteogallus urubitinga) and Stygian Owl(Asio stygius) among others], and 3 occasional[Andean Condor (Vultur gryphus), Sharp-shinned Hawk (Accipiter striatus), and Bat Fal-con (Falco rufigularis)]. Seventeen species wereresidents, six were winter migrants [CinereusHarrier (Circus cinereus), Red-backed Hawk

Humid forest

135

5

Grassland

5

1

5carnivoresinsectivoresscavengers

Xeric woodland

6

3

4

FIG. 4. Species richness in raptor functionalgroups in the three main habitats of the Sierra deSan Javier Biological Park, based on 660 raptorsightings. The figures represent the number ofindividual species.

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(Buteo polyosoma), Great Black Hawk, Black-chested Buzzard-Eagle (Geranoaetus melanoleu-cus), Tucuman Pygmy-Owl (Glaucidium tucu-manum), and Burrowing Owl (Speotytocunicularia)], and one, Peregrine Falcon (Falcoperegrinus anatum), a migrant from the North-ern Hemisphere, seen only in summer.

Transects were walked for 68 h duringdaytime, period during which 240 birds of 17species were observed; during the 5 h of noc-turnal observation, six species were recordedfor a total of 15 sightings. Four speciesaccounted for 79% of the diurnal records:Black Vulture (39%), Roadside Hawk (Buteomagnirostris) (21%), Turkey Vulture (Cathartesaura) (12%), and Crested Caracara (Caracaraplancus) (7%). Each of the remaining speciesaccounted for less than 5% of the observa-tions.

Based on the total raptors recorded, carni-vores were the most speciose functionalgroup in all three main habitats (Fig. 4). How-ever, in the grasslands, the number of scaven-ger species was similar to that of carnivores.Insectivores had the lowest species richness inall three habitats.

Scavengers were the most abundant func-tional group in the humid forest and in thexeric woodland while, in the grassland, mostof the individuals were carnivores (Fig. 5).Insectivores represented less than 5% of allraptors in humid forest and xeric woodland;no insectivorous species were recorded in thegrassland.

The first two axes in the correspondenceanalysis explained 60% of the variation inspecies composition from different habitatsand seasons (Fig. 6). Three groups of specieswere defined. The Andean Condor character-ized the first group corresponding to wetseason occurrence in grassland; only fewother species were recorded at the same timein this habitat. Species composition of wetand dry season samples from humid forestwas similar based on their proximity in the

ordination diagram. They were defined by thepresence of Barred Forest-Falcon, BicoloredHawk, Great Black Hawk, Buff-fronted Owl,Stygian Owl, Short-eared Owl (Asio flammeus),Barn Owl (Tyto alba) and Peregrine Falcon.Finally, samples from both seasons in xero-phytic woodlands and the dry season in grass-land were close together in the ordinationspace, mostly because of the presence ofCinereus Harrier, Red-backed Hawk, Aplo-mado Falcon (Falco femoralis), and BurrowingOwl, among other species in the three sam-ples.

Grassland

1311

carnivoresinsectivoresscavengers

Humid forest

76

2

91

Xeric woodland

10

342

FIG. 5. Raptor abundance in three functionalgroups of species recorded during 73 h of transectswalked in xerophytic woodlands, humid forests andmesophytic grasslands. The figures represent thenumber of raptors.

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SPECIES ACCOUNTS

We include only those species observed in thepark between 1985 and 1995.

Turkey Vulture (Cathartes aura). An abundantresident in forest and an abundant winter visi-tor in the high montane bunch grass. It wasrarely observed in groups of more than twoindividuals.

Black Vulture (Coragyps atratus). An abundantresident in all habitats of the park. Usuallyseen in small groups of two or three individu-als, although groups of up to 20 individualswere seen flying over the lowest slopes (600 to800 m).

King Vulture (Sarcoramphus papa). A commonresident species. It is regularly seen in the tem-perate cloud forest of Podocarpus and Alnus. Itis less abundant in the foothills with second-ary forest and in areas outside the park. Bothyoung and adults were seen flying over meso-phytic grasslands.

Andean Condor (Vultur gryphus). Occasional inthe park. A single adult was seen in Decemberflying over the Sierra de San Javier at 1650 m.

White-tailed Kite (Elanus leucurus). A commonspecies in open habitats. It is a permanent res-ident in clearings and cultivated fields lowerthan 700 m in elevation. The species also usesthe outer areas of the park where a fledgling

FIG. 6. Ordination diagram of raptor assemblages of the three main habitats in the Sierra de San JavierBiological Park observed during the wet and dry seasons.

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was seen in a cropland. It was also observedin the montane grassland and flying over thesubtropical montane and the temperate cloudforest.

Cinereus Harrier (Circus cinereus). A commonwinter migrant in the montane grassland; thisis a non-breeding migrant in the lower mon-tane areas of northwestern Argentina.

Bicolored Hawk (Accipiter bicolor). A commonresident in the subtropical montane forest. Inwinter, it was observed hunting in open areasclose to forest or flying over secondary for-ests and agricultural fields.

Sharp-shinned Hawk (Accipiter striatus). A sin-gle individual was observed in a clearing inthe foothills bordering the montane forest.

Great Black Hawk (Buteogallus urubitinga). Inwinter, an uncommon migrant along streamsand rivers of the park’s wet forest. Recordedbetween 700 and 1000 m in elevation.

Black-chested Buzzard-Eagle (Geranoaetus mel-anoleucus). A common winter migrant in thetemperate cloud forest and montane grass-lands above 1500 m. Non-breeding individu-als visit the lowlands and low montane areas,migrating both latitudinally and altitudinallyfrom their breeding grounds in southern andwestern Argentina.

Red-backed Hawk (Buteo polyosoma). Thiscommon species is a winter migrant in highmontane grassland and foothill clearings. It isan uncommon migrant in the montane chaco.In the subtropical montane forest, it was onlyobserved flying high over the canopy. Non-breeding individuals visit the lower montaneareas of northwestern Argentina.

Short-tailed Hawk (Buteo brachyurus). Resi-dent in the subtropical montane forest, this

species is common in winter and uncommonin summer. During winter, it can also befound in foothill secondary forests. Onlyone individual was observed in the montanechaco. Out of 16 sightings, 11 were inlight color morph and 4 were in dark colormorph.

Roadside Hawk (Buteo magnirostris). An abun-dant resident species occupying all main habi-tats at all elevations; it is more abundant inlowland forests near clearings. Usually aloneor in pairs, Roadside Hawks use to occupy thesame area the year-round, even in the ecotonebetween thetemperate cloud forest and highgrasslands at 1700 m.

Crested Caracara (Caracara plancus). An abun-dant resident in the subtropical montane for-est, where it is seen most frequently inclearings and ravines. It is a winter visitor inthe montane chaco and high elevation grass-lands. Regularly observed in clearings border-ing the park.

Chimango Caracara (Milvago chimango). Notobserved inside the park, but is an uncom-mon resident in foothill clearings and agricul-tural fields outside the park.

Barred Forest-Falcon (Micrastur ruficollis). Anabundant resident in the subtropical montaneforest, and less abundant in lowland second-ary forests. It is an uncommon winter visitorin the Alnus and Podocarpus temperate cloudforest. In the montane chaco, it was recordedonly in the most humid forest.

American Kestrel (Falco sparverius). Anuncommon resident; observed only in clear-ings near the edge of the park, mostly below900 m.

Bat Falcon (Falco rufigularis). Occasional inthe montane chaco. Uncommon species in

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the entire region where it reaches its southerndistribution limit.

Aplomado Falcon (Falco femoralis). An uncom-mon species, occurring in the edges of thesubtropical montane forest and in the mon-tane chaco.

Peregrine Falcon (Falco peregrinus). Common inthe park; mainly seen in disturbed areas. Falcop. cassini, a winter migrant from southernArgentina, is seen only between May andJune. F. p. anatum, a regular summer migrantfrom the northern hemisphere, is seen inclearings and fields from November toMarch.

Barn Owl (Tyto alba). Common in the park,regularly observed in old buildings. Seen inclearings in the subtropical montane forest(600 to 1200 m) and secondary forests.

Tropical Screech-Owl (Otus choliba). An abun-dant resident in many habitats. One pair wasobserved breeding in May and June in thesubtropical montane forest.

Tucuman Pygmy Owl (Glaucidium tucu-manum). An uncommon winter migrant inthe temperate cloud forest and lowland sec-ondary forests.

Burrowing Owl (Speotyto cunicularia). Anuncommon winter migrant in the park. Bur-rowing Owls were observed in open areassuch as agricultural fields and high montanegrasslands at 1800 m.

Stygian Owl (Asio stygius). An uncommonresident in the subtropical montane for-est. Observed in mature forests, at forestedges, and in exotic Eucalyptus woodlands,at 700 m elevation. A single individualwas observed in the montane chaco near thepark.

Short-eared Owl (Asio flammeus). Observedonce in secondary forests in the park at 700m. Short-eared Owls are uncommon in thefoothills and clearings near the park.

Buff-fronted Owl (Aegolius harrisii). A commonresident species in the subtropical montaneand Alnus and Podocarpus cloud forests;recorded between 900 and 1600 m.

DISCUSSION

The four most abundant raptor species in theSierra de San Javier Biological Park (in orderof abundance, Black Vulture, Roadside Hawk,Turkey Vulture, and Crested Caracara) are res-idents that use all main habitats in the parkand are widely distributed in South America.Most of them are scavengers, the prevailingfunctional group in all habitats. Several otherspecies (e.g., White-tailed Kite, Red-backedHawk, American Kestrel, and BurrowingOwl), occasionally seen in the park, preferredclearings, secondary forests, and pastures, justoutside the Park boundaries. These speciesalso were present in the park’s Festuca grass-lands.

Several species from wet forests, such asBicolored Hawk, Great Black Hawk, BarredForest-Falcon, Stygian Owl and Buff-frontedOwl, were rarely, if ever, recorded in the otherhabitats sampled. Most of these species arecarnivores, the most speciose functionalgroup in the park. Species compositionchanged less seasonally in forested than ingrassland areas. Without taking in account theoccasional record of the Andean Condor, thegrassland wet season assemblage was charac-terized by few widely distributed species,whereas the dry season assemblage wasdefined by the presence of winter migrants(i.e., Cinereus Harrier, Red-backed Hawk andBlack-chested Buzzard-Eagle)

The main habitat found in the park, thesubtropical montane forest, was the most

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thoroughly sampled; as a consequence, thespecies list of the humid forest is better docu-mented (Vides Almonacid 1991, 1992; N.P.Giannini pers. com.; P.G. Blendinger & P.Capllonch pers. observ.). The other habitatswere less intensively covered and other rap-tors could be recorded there in the future,mainly in the xerophytic woodland. Somespecies are probably more widely distributedin the park than our data suggest. For exam-ple, Vides Almonacid (1992) observed Tucu-man Pigmy Owls in all forested areas andBarred Forest-Falcon, in both Podocarpus andAlnus forests. In addition, Burrowing andTucuman Pigmy owls are common yearround in areas outside the park. Our sight-ings, however, include 27 of the 31 speciesrecorded for the park. The following specieswere not seen: Swallow-tailed Kite (Elanoidesforficatus) (Vides Almonacid 1989), Hook-billed Kite (Chondrohierax uncinatus) (IML Col-lection; Vides Almonacid 1989, 1992),Crowned Eagle (Harpyhaliaetus coronatus)(Budin 1976), and White-rumped Hawk(Buteo leucorrhous) (IML Collection).

Nineteen species regularly use the parkforests, provided that occasional (AndeanCondor, Crowned Eagle, Sharp-shinnedHawk, Swallow-tailed Kite, Bat Falcon andShort-eared Owl) and open-area species(White-tailed Kite, Cinereus Harrier, Red-backed Hawk, American Kestrel, ChimangoCaracara and Burrowing Owl) are notincluded. We did not record two (White-rumped Hawk and Hook-billed Kite) of these19 forest species. The White-rumped Hawkwas recently recorded in the Podocarpus forestsof the park (N.P. Giannini pers. com.); addi-tionally, three (one male, two female) speci-mens collected in the park between 1901 and1930 are preserved in the IML Collection.The presence of Hook-billed Kites in thepark was documented by Vides Almonacid(pers. com.) and by two (one male, onefemale) specimens in the IML Collection, col-

lected between 1960 and 1970. According toOlrog (1985), populations of both speciesseem to have decreased in wet forests ofnorthwestern Argentina between 1960 and1980, presumably because of extensive defor-estation. Hook-billed Kites tend to use pri-mary forests in French Guiana (Jullien &Thiollay 1996), although they also occurred inforest edges and slight fragmented forest. Asthe Sierra de San Javier forests are becomingincreasingly isolated from the remaining mon-tane forests, it is expected that some moresensitive species might disappear from thearea (Vides Almonacid 1991). Of the forestssurrounding the Sierra de San Javier, one thirdwas foothill forest, which has been com-pletely replaced by croplands and human set-tlements with a population larger than500,000 habitants. On the remaining bordersof the park, continuous deforestation andreplacement of forested areas by agricultureand the advance of urbanization contribute toisolate the forests of the park from others for-ested areas. It has been suggested that sometropical forest raptors, including the Hook-billed Kite, are susceptible to habitat frag-mentation (Whitacre et al. 1991, Alvarez-López & Kattan 1995, Jullien & Thiollay1996). The paucity of records for the White-rumped Hawk and the Hook-billed Kite forthe last 30 years in the Sierra de San Javier,coupled with the possible effect of forest deg-radation and progressive isolation of thepark’s habitats, suggests that both speciesmight be highly susceptible to local extinc-tion.

Three additional species, Bicolored Hawk,Short-tailed Hawk and Stygian Owl, wereconsidered by Vides Almonacid (1989) to bein danger of local or regional extirpation.However, there is not enough historical infor-mation to establish trends in their populationlevels. These species are residents of the sub-tropical montane forest, are present in themontane chaco, and have been recorded in

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clearings and plantations of Eucalyptus andPinus outside the protected area, mostly dur-ing the winter. Thus, we predict that thesespecies might be more abundant than sug-gested by Vides Almonacid (1989). Jullien &Thiollay (1996) found that the BicoloredHawk was restricted to continuous and littledisturbed primary forest in tropical rain for-ests. However, in subtropical montane forestsof NW Argentina, we often saw BicoloredHawks perching or chasing small birds in for-est-edges and logged forests, soaring or flyinghigh over the canopy, or crossing wide gaps infragmented forests. Year round presence ofBicolored Hawks, Short-tailed Hawks andStygian Owls in the park and their use of dis-turbed habitats are possible indications oftheir plasticity and ability to tolerate partialhabitat modifications.

Because of their large area requirementsand trophic specialization, raptors have beenproposed as indicator species of habitat qual-ity. It is thought that an area of habitat suffi-cient to maintain a viable population of allmembers of a raptor assemblage should belarge enough to maintain many other speciesas well. Most species with narrow habitatpreferences can be considered as potentialindicators for monitoring ecological changesin biotic communities (Jullien & Thiollay1996). In the Sierra de Jan Javier, a more com-plete study is needed to determine which spe-cies would be most useful as indicators. Weproposed that King Vultures, Short-tailedHawks, Barred Forest-Falcons, and Buff-fronted Owls could be used as indicators ofundisturbed subtropical montane forest con-ditions. The Short-tailed Hawk was proposedto serve as an indicator species of undisturbedforests in southeastern Brazil (Albuquerque1995) although, for northwestern Argentina,the presence or absence of this species doesnot seem to provide enough evidence of for-est suitability for wildlife. On the other hand,White-tailed Kites, Chimango Caracaras,

American Kestrels, and Burrowing Owls arepossible indicator species of a high degree ofmodification of forested habitats in the Sierrade San Javier. All eight species are regularlypresent in their preferred habitats, contribut-ing to their potential use as indicator species.

ACKNOWLEDGMENTS

We are grateful to Janet Braun, Rubén Bar-quez and David Whitacre whose commentsand criticisms improved an early draft of themanuscript. We thank Raymond McNeil andtwo anonymous reviewers for their valuablecomments on the manuscript, and to RobertoVides Almonacid, who provided us with valu-able information. Thanks to Alfredo Grauand Ana Levy for the pictures of the montanechaco and mountain forest.

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Budin, O. A. 1976. Contribución al conocimientode las aves del Parque Biológico. PublicaciónEspecial, Univ. Nacional de Tucumán,Tucumán, Argentina.

Fuller, M. R., & J. A. Mosher. 1981. Methods ofdetecting and counting raptors: a review. Stud.Avian Biol. 6: 235–246.

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