The Condor92970-981 Q The Cooperomithological society 1990 PATTERNS OF ELEVATIONAL AND LATITUDINAL DISTRIBUTION, INCLUDING A “NICHE SWITCH,” IN SOME GUANS (CRACIDAE) OF THE ANDES J. V. REMSEN, JR. AND STEVEN W. CARDIFF Museumof Natural Science,Louisiana State University,Baton Rouge, LA 70803 Abstract. A recentlydiscovered population of Chamaepetesgoudotii (Sickle-winged Guan) in the easternAndes of southernPeru and northern Bolivia is anomalousin its high-elevation (above 3,000 m) distribution; populationsfrom central Peru to not-themColombia are found generallybelow 2,100 m. Several hypothesesare evaluated to accountfor the origin of such an unusualdistribution. No evidence for long-distancedispersal or human introduction was found (and previous claims of introduction by ancient civilizations to account for disjunct distributions of two other speciesof New World birds are disputed). We propose that the current pattern is the result of fragmentation of a once continuousdistribution. Hypotheses concerning the cause of the fragmentation and maintenance of the current pattern are evaluated. The relative consistencyof elevational distributions of Andean bird speciesover broad latitudinal ranges (and dramatic differences in speciescomposition with changesin elevation) provides circumstantial evidence against an autecologicalhypothesis that would proposethat ecologicalrequirements are met for C. goudotiionly in the two disjunct regions. If potential competitors are restrictedto congeners,no supportcan be found for a hypothesis basedon interspecificcompetition. However, if the field of potential competitorsis expanded to include morphologically similar confamilials, a striking pattern of generally nonoverlap- ping distributions in terms of elevation and latitude is revealed. Most striking is the reversal in elevationsoccupied by C. goudotiiand Penelopemontagnii. The reliance on interpretation for evaluating competing hypothesesmakes such analysesinherently unsatisfying. Key words: Guans;Andes; Penelope; Chamaepetes;patterns of distribution;interspecijc competition. INTRODUCTION inhabitants and are among the first birds ac- quired for collectors by local hunters or men- Three specimens of the Sickle-winged Guan tioned when inquiring about the local avifauna. (Chamaepetesgoudotii) collected by Cardiff in Thus, the discovery of this population resembles humid Temperate Zone forest of Dpto. La Paz, the rediscovery of the White-winged Guan (Pe- Bolivia, in June 1980 represented an 800&m nelopealbipennis) within sight of the Pan-Amer- southerlyrange extension and establishedthe first ican Highway in Peru (Williams 1980). Both cases records for Bolivia (Cardiff and Remsen 1981). illustrate that the distributional limits of many Such a range extension was not entirely surpris- South American birds are still not well estab- ing becauserecent fieldwork in the forested An- lished. desof northwestern Bolivia has produced 12 new Although this major extension in latitudinal speciesfor Bolivia previously unrecorded south distribution for C. goudotiiwas of zoogeographic of central or southern Peru (Parker et al. 1980, interest, the elevationat which the Bolivian pop- Cardiff and Remsen 198 1, Schulenberg and ulation was discovered was more significant. Remsen 1982, Remsen and Traylor 1983) de- Throughout its range in the Eastern Andes from spite visits by several earlier workers (including Colombia to central Peru, C. goudotiioccurs at M. A. Carriker, who spent 12 days at Hichuloma, low elevations, usually below 2,100 m. Yet the at the same elevation as, and only 2 km from, newly discovered southern populations, includ- the guan locality). It was a surprise, however, ing additional specimens collected subsequently that a cracid would pass undetected for so long, in Dpto. La Paz (Remsen 198 5) and Dpto. Puno, only 2 hr on the main road from the city of La southern Peru (specimensat Museum of Natural Paz. Cracids are almost always familiar to native Science, Louisiana State University, LSUMNS) were found 1,000 m higher, at 3,000-3,300 m. ’ ’ Received23 February 1990. Final acceptance15 Such a dramatic latitudinal switch in eleva- July 1990. tional range is unusual in Andean forest birds, I9701 DISTRIBUTION PATTERNS IN GUANS 971 most of which occur within relatively consistent workers, and some expeditions may not record elevational limits throughout most of their lati- the speciesat all but then find it on return visits. tudinal range (Chapman 1926, Graves 1985, Nevertheless, we are reasonably certain that LSUMNS specimens, pers. observ.). In this pa- C. goudotii does not occur at elevations below per, we first describe the pattern of elevational approximately 2,800 m south of 11%. Since 1979, distribution of C. goudotii and other guans (Crac- approximately 190 person-days have been spent idae) of the Andes, and then attempt to deter- by personnel of the Museum of Natural Science, mine why this speciesshows such an odd pattern Louisiana StateUniversity, in humid forestabove of distribution. 3,000 m in the area occupied by the newly dis- covered, high-elevation population of C. gou- METHODS dotii (see Cardiff and Remsen 198 1 and Remsen Specimen localities for montane guans were ob- 1985 for localities in La Paz; the locality in Dpto. tained from museums with major collections of Puno, Peru, is “Valcon, 5 km NNW of Quiaca, Andean birds (see Acknowledgments). We feel 3000 m,” 6-l 8 October 1980). This effort pro- that we located most guan specimens with lo- duced seven specimensand several sight records. cality data sufficiently precise to allow plotting By comparison, approximately 220 person-days of latitude and elevation. Latitudes were taken have been invested at the same latitudes but be- primarily from the ornithological gazetteers of low 2,600 m in La Paz and Puno without re- the Andean countries (Paynter et al. 1975; Payn- cording C. goudotii (2,575 m, Sacramento Alto, ter and Traylor 1977, 1981; Paynter 1982; Ste- 8 km by road north Chuspipata, Dpto. La Paz, phens and Traylor 1983). If the specimen label Bolivia, 20 July-8 August 1979; 2,000 m, Abra did not include elevation, the gazetteers were de Maruncunca, 10 km southwestof San Josede1 used to determine if the elevation could be as- Oro, Dpto. Puno, Peru, 9 November-6 Decem- certained with reasonable precision. A substan- ber 1980; 1,650 and 1,350 m, Serrania Bellavis- tial number of specimens could not be used be- ta, 35-36 and 47 km, respectively, by road north cause their elevations could not be determined. of Caranavi, Dpto. La Paz, Bolivia, 10 June-2 For specimensfor which the elevation was given July 1979 and 10 July-2 August 1980, respec- as a range, e.g., “2000-2400 m,” the midpoint tively). Therefore, we believe that the unusually of the range was used as the elevation, unless the high and compressed elevational range of the specimen was from near an upper or lower limit newly discovered southern population is not a of the species’ overall elevational distribution, in sampling artifact. which case the specimen was not used. We are even more certain that C. goudotii does not occur above 2,300 m elevation north of 11%. RESULTS AND DISCUSSION LSUMNS expeditions in central and northern A plot of specimen localities of C. goudotii on Peru have loggedover 500 person-daysin humid the eastern slope of the Eastern Andes (Fig. 1) forest above 2,300 m without finding any C. gou- reveals that the species’ elevational distribution dotii. switches dramatically from below 2,100 m to What processeswould produce this elevational above 3,000 m at about 11% We are certain that switch? What factors maintain the present pat- the high-elevation population does not represent tern of limits of distribution? These zoogeo- wandering or migratory individuals: guans are graphical questions are difficult to answer be- sedentary birds, with no known cases of long- cause (a) the historical processescan never be distance movement or vagrancy (Delacour and ascertained with complete certainty, leaving in- Amadon 1973). ference as the primary methodology, and (b) ex- Whether the observed pattern is a sampling periments to test hypotheses concerning large- artifact, however, deserves consideration. Al- scaledistribution patterns are usually logistically though C. goudotiican be locally common (John- intractable, especially for flying birds (Diamond son and Hilty 1976), it usually occurs in low 1986a). The remainder of this paper represents densities, and this probably plays a more im- our attempt to answer thesequestions for C. gou- portant role than shynessin determining whether dotii. or not it is recorded at a site. Some members of We consideredthree hypothesesconcerning the a field party may never seethe bird over a period processthat might account for this unusual ele- of weeks, even though seen several times by co- vational “niche switch” pattern of distribution: 972 J. V. REMSEN, JR. AND STEVEN W. CARDIFF (1) long-distance dispersal, (2) human introduc- of C. goudotii was deliberately or accidentally tion, and (3) vicariance. We then consideredtwo introduced by primitive peoples. Becauseguans hypothesesthat might explain how such an un- are potential sources of food for humans, this usual pattern might be maintained: (1) autecol- hypothesis deservesspecial consideration. ogy and (2) interspecific competition. A thorough evaluation of the human intro- duction hypothesis would require extensive, original research on the anthropology and ar- HISTORICAL HYPOTHESES chaeology of the region. Such an analysis