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HARVARD UNIVERSITY of the Library Museum of Comparative Zoology FEB 9 J 1992 OCCASIONAL PAPERS HARVARD of the UNIVERSITY MUSEUM OF NATURAL HISTORY The University of Kansas Lawrence, Kansas NUMBER 146, PAGES 1-16 16 JANUARY 1992 IMPERIAL SHAGS AND OTHER BIRDS OF THE LAGO GENERAL VINTTER AREA, CHUBUT PROVINCE, ARGENTINA Pamela C. Rasmussen1 3 Philip S. Humphrey1 , , AND JULIETA MuNIZ-SaAVEDRA2 LagoGeneralVintter(orLagoGeneralPaz,and inChile,LagoPalena) is a large Andean lake traversing the international border between ChubuWt Province, Argentina, and Aysen Province, Chile, at 43°56' S and 71°40' (Fig. 1: Department of the Interior, 1954). This area supports a variety of habitats, including steppe, heavy Nothofagus forest, second growth, puna, and the lake and its shores. ThelakeisdrainedfromtheeastendbytheRioCorcovadoorCarrenleufii (Fig. 1),whichcurvesnorththroughChile,thenwest,finallyemptyinginthe m PacificOceanastheRioPalena.LagoVintterisat925 inelevation(Paynter, 1985) and is surroundedon all but the east side by hills, the tallestofwhich is Cerro Rinon (1,814 m) on the lake's south shore. The east endofthe lake is bordered by barren steppe with which stuntedNothofagus scrub is inter- mingled, especially in ravines. Slightly farther west, the area is mostly ecotonalbetweenforestandsteppeandishighlyvariableincharacter,buthas mostlylarge steppeshrubs,grass,andstuntedNothofagus.Westofthiszone, theforestbecomesprogressivelymorematureandlessdisturbed.Wedidnot 'Museum ofNatural History and Department ofSystematics and Ecology, The University ofKansas, Lawrence, Kansas 66045-2454, USA. 2Centro de Ecologfa Aplicada del Neuquen (CEAN). C.C. No. 7. Junin de los Andes CP8371. Provinciadel Neuquen.Argentina. 3PresentAddress: Calvert Marine Museum, P.O. Box 97, Solomons, Maryland 20688, USA. ©MuseumofNaturalHistory,TheUniversityofKansas,Lawrence. UNIV. KANSAS MUS. NAT. HIST. OCC. PAP., No. 146 CHILEP-'T.='TARGE'NTINAf 5km 10km Fig. 1. Map of the Lago Vintter area and major localities cited in text. The numerous tributaries ofthe RioCorcovadoare not shown. Inset: mapofPatagonia; areaenlarged shown byblackrectangle. findbamboo,animportantcomponentoftheforestfarthernorthinPatagonia. A gendarmeria (police station) is situated nearthe southeastendofthe lake; the areacurrently has very few human residents, although touristcabins are W situated 2 km ofthe gendarmeria. Anumberofrecentpublicationsdeal withbirdsofsimilarhabitatsfarther northinPatagonia,especiallyaroundLagoNahuelHuapi(Vuilleumier, 1972; Contreras, 1975; Grigera, 1976; Ralph, 1985; Iglesias, 198W9), but few data exist on birds of Chubut Province between 43-45°S and of 71°W. The nearest Chilean localities from which birds have been reported are Lago Verde (44°14'S, 71°50'W; Goodall et al.. 1964) and Balmaceda (45°55'S, 71°41"W; Philippi, 1939, 1943), and only afew species were noted at these localities. Some of the localities from which specimens were collected by Pemberton (Wetmore, 1926) are relatively near Lago Vintter. G. F. Gerling collectedbirdsatLagoVintterbetween2Februaryand29April 1902(Lynch Arribalzaga, 1902), and recorded 36 species in the area; no more recent information exists on the avifauna ofthis locality. PhilipS. Humphreyvisited LagoVintterinJanuary 1989andverifiedthe existenceofacolonyofImperialShagsthathadbeenrumoredtooccurthere. He and Pamela C. Rasmussen (PCR) then visited Lago Vintter in January 1990 to study the systematics, food habits, and conservation needs of this IMPERIALSHAGS OFLAGOVINTTER,ARGENTINA newlydocumentedpopulation ofshags. In addition, daily observationsthey made on othermembers ofthe avifauna are summarized here. HABITATS Localitiescitedinthispaperaregivenaskilometers—anddirectionfromthe LagoVinttergendarmeria(—Fig. 1 ). asfollows: 20SE open dry steppe with rocky outcrops; 10-15 SE moist steppe with areas of shr—ubs and small marshypatches (Fig. 2); 17 NE(BocaoftheRioCorcovado) mouthofthe RioCorcovado.mainlysurroundedbysparse,lowsteppe,but—withpatchesof stuntedNothofagusscrub,mainlyinravines; (gendarmeria) policestation situated in ecotonal vegetation c—omprising a mixture of scrub steppe and W Nothofagus(Fig.3);2 (caWbi—ns) situatedinmature,butartifWici—allyopened forestborderingthelake; 3 densenaturalmatureforest;4 ahillside extendingfromthelake level totimberline, saidtohaveburned30yearsago (R. Laurin, perWs.—com.) and still only lightly regenerated with low, scrubby vegetation; 5 heavy mature f—orest surrounding a grassy bog with scat- NW tered, stuntedNothofagus; 5 (Isla Los Conejos) a rocky island in the centerofthe lake, with one steep cliffface on the SEendofthe island (Fig. 4),andwoodedslopeslackingcliffsontheNandSsides.Wedidnotvisitthe west end ofthe island. ft**j*m+ Fig. 2. Moiststeppe 10kmsoutheastofLagoVinttergendarmeria. withshrubs andmarshy patches. UNIV. KANSAS MUS. NAT. HIST. OCC. PAP., No. 146 Fig.3. Areaneargendarmeria,withecotonalvegetationcomprisingscrubsteppe andNothofagus. MATERIALS AND METHODS WevisitedLagoVintter 16-26January 1990aspartofastudytodetermine the systematic andconservation statusofthe Imperial Shag (Phalacrocorax atriceps) ofnorthwestern Patagonia. Mostofeachday was spentobserving birds; noteworthyobservationsmadeonthe Imperial Shagandotherspecies are presented here in addition to an annotated list ofbird species seen (see Appendix). Species referred to as "abundant" were seen daily in large numbers. "Common,, species usually were found daily in smallernumbers. Numbersobservedaregivenforspeciesthatwereobservedinfrequently,and habitat is cited in each case. The stomach contents of four Lago Vintter cormorant specimens were preserved in 70% ethanol and later identified by Julieta Muniz-Saavedra. Bony fragments were stained with alizarin red and stored in glycerin. Total numbers of individual prey items were estimated by the most abundant element. ScientificnamesusedinthispaperarethoselistedbyNavasandBo(1977), with the exceptionofAsthenes (= Thripophaga), and English names follow Narosky andYzurieta (1987). IMPERIAL SHAGS OFLAGOVINTTER,ARGENTINA SPECIES ACCOUNTS Phalacrocoraxatriceps, Imperial Shag The Imperial Shag has been recorded as breeding in inland continental watersonlyinLagoNahuel Huapi(Krieg, 1940).PSHreceivedunconfirmed reportsofacolonyofthisspeciesatLagoVintter(B. Mayer,inlitt.) in 1988. HevisitedthelakeinJanuary 1989anddocumentedtheoccurrenceofasmall colonyofthisspecies;onespecimen(MuseoArgentinodeCienciasNaturales No. 53352) that had washed up on the lake shore was salvaged at that time. On ourvisit in 1990, wecollectedfouradditional specimens, forwhich data are presented inTable 1. The factthatGerling didnotrecord this species on hisvisitin 1902(LynchArribalzaga, 1902)suggeststheirrecentarrivaltothe lake. We frequently saw individuals foraging close to shore; thus, it seems unlikelyGerlingcouldhavemissedseeingthespeciesduringhislengthystay ifit were present at that time. However, he did notrecord several otherbird species that we found to be common. Theonly shagcolonythatwelocatedwasonacliffonthe SWendofIsla Los Conejos (Fig. 4). The rock face was steep and limited in extent, and on 24January 1990fiveyoungremainedonthecliffafteralladultshadleftowing to our approach. Three of these young were well-grown and lacked natal Table 1. Specimen data forImperial Shags fromLagoVintter. Measurements are giveninmm.MACN=MuseoArgentinodeCienciasNaturales;KU=TheUniversity of KansasWMuseum of Natural History. LF = largest follicle; Bursa = Bursa of Fabricius; = weight in grams. 6 UNIV. KANSAS MUS. NAT. HIST. OCC. PAP.. No. 146 down;onewasbeginningtolosenataldownonthehead,andonewasahalf- grown nestling old enough to stand erect. Several nests were seen, some of whichwereaslargeasanyseeninotherstudylocalitiesalongmarinecoasts, but three of the young were on much smaller nests. On 25 January 1989, several large downy young were seen on the upper ledges ofthe cliffface. The largestgroupofadults weobservedatLagoVintterwas aflockof55 birds flying around the island. Owing to extended heavy winds during our stay, we could not census the population accurately, nor could we visit the western part ofthe lake to search forothercolonies. Based on observations in 1989and 1990, we believe the total population on the lake is at least 100; R.Laurfn(pers.com.)hasinformallyestimatedthepopulationtobebetween 200 and 300. Whenweapproachedthecolony,bothin 1989and 1990,alladultsleftlong beforewearrived.Theyflewwellawayfromtheboat,incontrasttoImperial Shags at marine coastal localities and at Parque Nacional Nahuel Huapi, whicharecuriousandoftenflynearordirectlyoversmallboats.Thisbehavior oftheLagoVinttershagsprobablyreflectspersecutionbylocalswhobelieve they feed on large numbers ofyoung trout (3 species ofSalmonidae). Although trout were introduced successfully to Lago Vintter, none oc- curredinthestomachsofthefourshagspecimenswecollected(Table2).The exclusivefooditemfoundwasGalaxiasmaculatus,asmallbottom-dwelling fish. Several of the fish recovered from the shags had hyperinflated swim bladders, suggesting that the shags caught them atconsiderable depths. The Fig. 4. Cliff face on southeastern end of Isla Los Conejos, where cormorant colony is located.