The Condor 87:471483 0 The Cooper Ornithological Society 1985 HABITAT ASSOCIATION PATTERNS OF FOREST AND STEPPE BIRDS OF NORTHERN PATAGONIA, ARGENTINA C. JOHN RALPH ABSTRACT. -1 censusedbirds acrossa moisture gradient in northern Patagonia, Argentina, in the vicinity of Bariloche. Over a 60-km distance, the 12 sitesranged from grasslandat lower elevations to upland climax Nothofagusforests of the eastern Andes. Here, I correlated bird abundance and diversities with various vegetation measures.Using all sites, bird diversities and abundanceswere posi- tively correlated with various foliage measures.When grasslandswere excluded, however, an inverse relationship was found: birds were more diverse and abundant in the lower stature shrub communities than in complex forests. Multiple regres- sion analysesof this apparently paradoxical situation indicated that certain species of plants probably had important effects on community structure. As a habitat in a region becomes more com- nearby, dense beech forests. Vuilleumier also plex, the bird community in that habitat usu- thought that bird speciesdiversity was higher ally becomes more complex as well (e.g., in the scrub-steppe habitat. A re-calculation MacArthur and MacArthur 196 1, Willson (Church 1974) of his data, however, showed 1974). In southern Argentina, however, Vuil- that Vuilleumier’s diversity values (H’) in the leumier (1972) concluded that the southern two habitats were essentially identical (dense beech (Nothofagus)forests had a less complex forest- 1.993; scrub-steppe forest- 1.837). avifauna than nearby, simpler, scrub areas. In One other study has suggestedthat bird species order to describe the avifauna, its habitat as- diversity was unrelated to vegetation com- sociations,and to test this seemingly paradox- plexity (Howell 197 1). This study, although ical situation, I sampledthe avifauna and vege- intensive, had samples drawn from very few tation associationsof the region in the spring study sites. of 1980. In this paper, I describethe vegetation The avifauna of Patagonia is relatively little types, the bird species associated with each described,at least in terms of population num- type, and their interrelationships. bers. My study is the first detailed quantifi- After the pioneering work of MacArthur and cation of these birds and their habitat associ- MacArthur (196 l), many studies have con- ations. Such data are important becausemost firmed their initial finding that, for terrestrial ecological generalizations are based on north- communities, the number of bird species,as ern hemisphere temperate communities. well as their diversity, are strongly positively Comparative data from other areas can pro- correlated with aspectsof the structural com- vide information on the applicability of these plexity of vegetation (e.g., MacArthur 1964, generalizations. Recher 1969, Karr and Roth 197 1, Pearson and Ralph 1978). That is, the more complex METHODS the structure or composition of the vegetation, the more likely it is that the habitat will contain STUDY SITES more bird species (higher richness) or more In the region of my study (eastward from the even abundancesof the species(evenness). This crest of the Andes in southern Argentina), an- relationship is usually interpreted as evidence nual rainfall diminished from more than 2,000 for the underlying dependence of birds upon mm to 200 mm over about a 50-km area (De their habitat, and thus, lends some degree of Fina 1972). The vegetative growth pattern re- predictability. flected this moisture gradient. Although there Exceptions to this pattern should be of in- was some effect of elevation and temperature terest becauseof what they may reveal about on the vegetation, De Fina considered it com- the pattern itself or the systemsit attempts to paratively small. Owing to a varied topogra- summarize. Thus, it is of interest that Vuil- phy, the habitat types were somewhat patchy leumier (1972) regarded the northern Pata- in this region, with each “patch” occupying gonian forest bird communities of southern severalhundred or more hectares.Habitats be- Argentina as such an exception. Although his came uniform only where the more or lesscon- data were few, they indicated that more species tinuous grasslandsteppe was reached at about of birds inhabited the structurally simpler 200 mm annual rainfall. scrub-steppehabitats than the more complex, In the region of this moisture gradient, I 14711 472 C. JOHN RALPH I -_ \ BARILOCHE \ E ; ,i CREST OF (-ANDES \ \ ) I o,,,y,,,;o‘ \ \ Km \ FIGURE 1. Map of study locations in northern Patagonia,Argentina. The letters refer to the locations described in Methods. selected 12 sites (Fig. 1) at which to census and lower in the altitudinal gradients. The lo- birds and measure vegetation. I made no at- cation of the sites on Figures 1 to 4 are indi- tempt to selectany certain habitat type; rather, cated by the letter following their namesbelow. at any given site, I used the largest area of Grasslandsites. Bunchgrass Grassland (A) - reasonably contiguous, similar vegetation 42 km north-northeast of Bariloche, on open, (summarized in Table 2), with a minimum size windswept hills, 2 km south of Arroyo Corral. of approximately 25 ha. Censusstations at each The vegetation was less than 0.5 m tall, and site were at least 100 m from what I judged to consistedof primarily bunchgrass(Festuca sp.) be the edge of another habitat type. The only and a small prickly shrub, Mulinum spinosum. exception to theselast two rules was the Sedge- I estimate that annual rainfall was probably scrub Site (see below), which was only about 300-500 mm. 5 ha, and several of its stationswere within 25 Cactus Grassland (B)-a mixed grass-scrub m of the edge. The vegetation data that I gath- area within 1 km south of Laguna Blanca, an ered, basedon an index to foliage density, were alkaline lake 20 km southeastof Zapala, Neu- subjectedto a cluster analysis procedure (SAS q&n. The vegetation was mostly lessthan 1.5 1979), which confirmed the vegetation (struc- m tall, and consistedof primarily bunchgrass, tural) similarity of the stations at each site. a small cactus,and two small shrubs(less than That is, the great majority of the censussta- 0.5 m tall), one being Acaena ovulifoliu.Rain- tions at a site were more similar to each other fall was probably 200-400 mm annually. than to stations at other sites. The rainfall at Herbaceous Grassland (C)-73 km north of the twelve siteswas extrapolated from the data Bariloche and 4 km east-northeastof Caleufti, in De Fina (1972) from measurementshigher NeuquCn, 0.5 km to the south of Rio Caleufu. PATAGONIAN BIRD HABITATS 413 It resembled the Cactus Grassland Site, with massof bamboo. Rainfall was probably 1,500- similar rainfall, but had less bunchgrassand 2,000 mm annually. more Mulinum and herbs. Beech (antarctica-dombeyi-bamboo)For- Scrub-cedarsites. Scrub-sedge (D)-an oa- est (IS)-at Ruca MalCn, near the northwest sis of shrubs in a swale surrounded by grass- end of Lago Correntos, and 19 km north- land, on low hills near the BunchgrassGrass- northwest of Villa la Angostura. It was a mixed land Site at Arroyo Corral and with similar forest, lo-30 m high, and consisted of pri- rainfall. The area of this patch was about 5 ha. marily Nothofagusdombeyi and some N. ant- The vegetationwas a mixture of grassland,with arctica,with a Berberisand Chusqueaunder- barberry (Berberissp.) l-2 m high and a small story. Except for the addition of N. antarctica, (2-3 m high) tree, probably Maytenusboaria. the forest resembled that of the previous site, Scrub-beech (E)-4 km east-southeast of with rainfall probably 1,500-2,000 mm. Bariloche, and 0.5 to 1.5 km south of the Beech (pumilio-dombeyi-bamboo) Forest southern base of Cerro Otto. The vegetation (L)-a beech forest 8 km east-southeastof the consistedof several shrub species,mostly 2-3 summit of Mt. Tronador, within 1 km of Rio m in height. Nothofagusantarcticus was the Castafio Overo. It was similar to the Llao Llao most common shrub, occasionally reaching 5 Peninsula site, but had an almost equal mix- m in height. Diosteajuncea, Berberis spp., and ture of Nothofagusdombeyi and N. pumilio. Lomatia hirsutawere less common. This was Rainfall was probably about 2,000-2,500 mm. the “Nothofagussteppe ” of Vuilleumier (1972). Rainfall was probably 500-700 mm. CENSUS PROCEDURES Sparse Cedar Forest (F)-3.5 km southeast I censusedbirds in the three grasslandsites by of the junction of the Rio Cuyin Manzano and using variable distance strip censuses(Emlen the Rio Traful, and 6 km east-southeast of 197 l), which I believe are the most appropri- Confluencia, Neuquen. The cedar (Austroced- ate for habitat of such low stature. Each seg- ruschilensis), often 5-8 m high, was the most ment that was 0.1 km long was tallied sepa- abundant plant, followed by shrubsof the gen- rately. I measured the vegetation at the end of era Diostea,Lomatia, and Berberis.Rainfall every fifth (0.5-km) segment. At sites of taller was probably 400-600 mm. stature, I censusedthe birds by usinga variable Dense Cedar Forest (G)-2.5 km northeast distance station count (Reynolds et al. 1980) of Confluencia, at the junction of Rio Limay with stations 100 m apart on a line through and Rio Traful, Neuqutn. Similar to the pre- the habitat. Vegetation was measured at each ceding site in rainfall, its vegetation differed station. I believe that any differences that re- largely in having a higher density of cedar. sulted from comparing data by using the two Southernbeech forest sites. Beech (dom- different censusmethods are minimal and do beyi-no bamboo) Forest (H)- 1.5 km north- not affect speciesrichness or diversity calcu- east of the preceding site in a rather steep- lations. sided canyon, it had an overstory lo-30 m I censusedbirds on about 75% of the morn- high, of primarily Nothofagusdombeyi and ings between 7 November and 10 December Austrocedrus.The understory was Berberisand 1980.