Ardeola 50(2), 2003, 223-235

GEOGRAPHIC VARIATION IN THE GREAT PAMPA-FINCH EMBERNAGRA PLATENSIS COMPLEX: EVIDENCE FOR TWO SPECIES

Floyd E. HAYES*1

SUMMARY.—Geographic variation in the Great Pampa-Finch Embernagra platensis complex: evidence for two species. Aims: The Great Pampa-Finch Embernagra platensis is represented by four subspecies belonging to two dis- tinct groups occurring in allopatry: (1) nominate E. p. platensis in the east; and (2) E. p. olivascens, E. p. gos- sei and E. p. catamarcanus in the west. Morphological variation within the complex was assessed to infer the taxonomic relationship between the two forms. Location: Southern South America. Methods: Several size, plumage and soft part traits were measured for 339 specimens and analysed with uni- variate and multivariate statistical methods. Results: I found no evidence for long-distance migration, conflicting support for Bergmann’s rule (body size negatively correlated with latitude and positively correlated with elevation), and more support for Gloger’s rule. The structure and colouration of the bill were the most diagnostic traits. The absence of intermediate spe- cimens and lack of clinal variation of bill colouration within each form demonstrates that intergradation eit- her does not occur or is potentially restricted to a narrow, still undiscovered contact zone. Conclusions: Given the likelihood that bill structure and colour, combined with other traits, may represent re- productive isolating mechanisms between the two groups, I tentatively propose the recognition of two species within the E. platensis complex: the monotypic Great Pampa-Finch, E. platensis, and the polytypic Olive Pampa-Finch, E. olivascens. Key words: Embernagra platensis, geographic variation, Great Pampa-Finch, South America, taxo- nomy.

RESUMEN.—Variación geográfica en el complejo de especies del Verdón Embernagra platensis: evi- dencias de dos especies. Objetivos: El Verdón Embernagra platensis de Sudamérica esta representado por cuatro subespecies que per- tenecen a dos grupos distintos en alopatria: (1) la raza nominada E. p. platensis en el este; y (2) E. p. olivas- cens, E. p. gossei y E. p. catamarcanus en el oeste. Se estudió la variación geográfica para inferir la relación taxonómica entre los dos grupos. Localidad: El sur de Sudamérica. Métodos: Algunas caracteristicas del tamaño, plumaje, y partes blandas fueron medidas para 339 especime- nes y analizadas con métodos estadísticos univariables y multivariables. Resultados: No se encontró evidencias de la existencia de migración a largas distancias, ni evidencias para comprobar la ley de Bergmann (el tamaño del cuerpo está correlacionado negativamente con la latitud y po- sitivamente con la elevación), pero si se encontraron evidencias para comprobar la ley de Gloger. La estruc- tura y coloración del pico fueron las variables com mayor poder diagnóstico. La ausencia de especimenes in- termedios y la ausencia de variación clinal de la coloración del pico en cada forma, demuestran que la gradación no existe o potencialmente está restringida a un área de contacto bien estrecho y no conocido. Conclusiones: Dada la probabilidad que la estructura y color del pico, combinado con otras caracteristicas, puedan representar mecanismos del aislamiento reproductivo entre los dos grupos, se propone tentativamen- te el reconocimiento de dos especies dentro del complejo de Embernagra platensis: el monotípico Verdón Grande, E. platensis, y el politípico Verdón Olivo, E. olivascens. Palabras clave: Embernagra platensis, variación geográfica, Verdón, Sudamérica, taxonomía.

* Department of Life Sciences, University of the West Indies, St. Augustine, Trinidad and Tobago. 1 Present address and correspondence: Department of Biology, Pacific Union College, Angwin, 1 Angwin Ave., CA 94508, USA. e-mail: [email protected] 224 HAYES, F. E.

INTRODUCTION possibly being intermediate. Ridgely & Tudor (1989) suggested that platensis and olivascens An accurate assessment of phylogenetic re- might represent distinct species. lationships and speciation processes among sis- The purpose of this study is to evaluate the ter taxa is premised upon a thorough unders- relationships between sibling taxa of the Great tanding of geographic variation, invariably Pampa-Finch by examining sexual dimorphism based upon (but not limited to) an analysis of and geographic variation of morphometric cha- museum specimens (Zink & Remsen, 1986; racters. The results of these analyses are further Remsen, 1995). A primary goal of such an used to (1) evaluate quantitatively Bergmann’s analysis is to evaluate the extent of gene flow rule, which predicts that body size is inversely between adjacent taxa in order to determine or correlated with temperature and humidity (Ja- infer whether primary intergradation (clinal va- mes, 1970); (2) evaluate qualitatively Gloger’s riation), secondary intergradation (hybridisa- rule, which predicts that populations in more tion), or the absence of intergradation (potential humid areas are more heavily pigmented than or complete reproductive isolation) occurs (e.g. those in drier areas (Zink & Remsen, 1986); Mayr, 1963, 1970; Gould & Johnston, 1972; and (3) infer the extent of reproductive isolation Zink & Remsen, 1986). among the taxa and implications for taxonomy. The Great Pampa-Finch Embernagra pla- tensis, a large, olive ‘tanager-finch’ whose ta- xonomic affinities remain unresolved (e.g. Isler Taxonomic background & Isler, 1987; Sibley & Ahlquist, 1990; Sibley & Monroe, 1990; Burns, 1997; Lougheed et In an early revision of Embernagra, Hell- al., 2000), is widely distributed east of the An- mayr (1938) recognised three subspecies of E. des in southern South America. It is a fairly platensis, which had been described initially common and relatively conspicuous inhabitant as separate species: nominate platensis in the of damp grasslands, where pairs or small east, olivascens in the west, and gossei in the groups are territorial and often sing while per- southwest (Fig. 1). Nominate platensis is the ched on the tops of bushes and fence posts (e.g. most widely distributed, the smallest, and the Wetmore, 1926; Belton, 1985; Ridgely & Tu- only race with prominent dusky streaking on dor, 1989; Fjeldsa & Krabbe, 1990; Sick, the back. Olivascens differs from platensis by 1993). It appears to be a sedentary species in averaging larger in size, having a more strongly which long-distance migration has not been re- curved, deeper orange beak with less extensive ported (Ridgely & Tudor, 1989; Chesser, dusky colouration on the upper bill, lacking 1994). streaks or only faintly streaked on the back, A polytypic species, the Great Pampa-Finch and having a paler loral region, chin and abdo- is represented by four described subspecies be- men (Chubb, 1918; Wetmore, 1926; Hellmayr, longing to two distinct groups: (1) nominate E. 1938; Short, 1975; Contreras, 1980). The extent p. platensis, widely distributed in the east; and of streaking on the back is highly variable; (2) E. p. olivascens, E. p. gossei and E. p. cata- some individuals of olivascens, especially from marcanus in the west (Paynter, 1970; Short, Bolivia (pers. obs.), have faintly streaked backs 1975; Contreras, 1980; Nores, 1986; Ridgely & approaching that of platensis, and worn indivi- Tudor, 1989). But as with many species of Ne- duals of platensis have essentially unstreaked otropical birds, their geographic variation and backs resembling olivascens (Wetmore, 1926; phylogenetic relationships remain poorly do- Hellmayr, 1938). cumented. In a survey of the Chaco avifauna, Gossei resembles olivascens, with which it is Short (1975) stated that platensis and olivas- most closely related, but averages larger in size, cens intergrade in the east-central Chaco. Ho- has a paler grey throat, chest and abdomen, du- wever, such intergradation has never been de- ller rectrices, and more greyish-green upper- monstrated. An analysis of 37 specimens of E. parts (Chubb, 1918; Wetmore, 1926; Contreras, platensis in Argentinian museums by Contreras 1980). Olrog (1963) synonymised gossei with (1980) remains the most detailed analysis of olivascens and subsequent authorities (e.g. geographic variation within the species, in Paynter, 1970; Short, 1975) adopted Olrog’s which only two specimens were described as treatment. However, Contreras (1980) exami-

Ardeola 50(2), 2003, 223-235 GEOGRAPHIC VARIATION IN THE GREAT PAMPA-FINCH EMBERNAGRA PLATENSIS COMPLEX 225

FIG. 1.—Distribution of Embernagra p. platensis, E. p. olivascens and E. p. gossei specimens examined in this study, and specimen localities for E. p. catamarcanus from Nores (1986). Localities indicated by numerals re- fer to the most southeasterly specimen of E. p. olivascens (1) and the nearest, possibly hybrid specimen of E. p. platensis (2) reported by Contreras (1980). [Distribución de los individuos de Embernagra p. platensis y E. p. olivascens examinados en este estudio y lo- calidades de los individuos de E. p. catamarcanus obtenidos de Nores (1986). Las localidades marcadas con un número representan al individuo más sureste de E. p. olivacens (1) y al más cercano y posible híbrido de E. p. plantensis (2) indicado en Contreras (1980).]

ned 13 specimens of gossei in Argentinian mu- The Great Pampa-Finch’s closest relative ap- seums and found them readily separable from pears to be the Pale-throated Serra-Finch (E. olivascens. longicauda), which is locally distributed in eas- A fourth subspecies, catamarcanus, was sub- tern Brazil (O’Brien, 1968; Mattos & Sick, sequently described by Nores (1986) from the 1985) and is the only other representative of region of El Campo del Arenal, Catamarca Pro- the genus (Paynter, 1970; Ridgely & Tudor, vince (hereafter Prov.), Argentina. It differs 1989). Embernagra appears to be closely rela- from olivascens and gossei by having a clearer ted to Emberizoides, which includes three re- grey chest, a greyer head and nape, yellower cognised species that are widely distributed in green tones on the wings, and whiter under- grasslands of eastern South America (Eisen- parts. The absence of dorsal streaks (Nores, mann & Short, 1982). 1986) suggests that it is most closely related to olivascens.

Ardeola 50(2), 2003, 223-235 226 HAYES, F. E.

MATERIAL AND METHODS length (WL), from bend of folded wing to tip of longest primary feather; and tarsus length (TS), I examined and measured 339 study skins from junction of tibiotarsus and tarsometatarsus of adult or subadult (moulting into adult plu- to distal junction of hind toe and tarsometatar- mage) E. platensis in American museums, in- sus. Tail length (TL), from base of tail to tip of cluding the Academy of Natural Sciences of longest rectrix, was measured (nearest mm) Philadelphia (ANSP), American Museum of with a wooden ruler to minimise damage to the Natural History (AMNH), Carnegie Museum specimens. The bill of E. platensis specimens is (CM), Field Museum of Natural History generally bicoloured, with a dark dorsal ridge (FMNH), Los Angeles County Museum sharply demarcated from the yellowish-orange (LACM), Museum of Comparative Zoology sides (Fig. 2). Using calipers, I measured (nea- (MCZ), United States National Museum of Na- rest 0.1 mm) the maximum height of pale co- tural History (USNM), and University of Mi- lour on the side of the bill (PB), from the lower chigan Museum of Zoology (UMMZ). These edge of the upper bill (Fig. 1). For each speci- included 240 specimens of platensis, 92 speci- men I also recorded the sex and mass (MS; ne- mens of olivascens and seven specimens of arest 0.1 g), when available, from the attached gossei. No specimens of catamarcanus were specimen labels. The sex was not identified in available for this study. seven specimens of platensis and three of oli- vascens; none of these specimens was used in the morphometric analyses described below. Geographic distribution I computed four dimensionless (scale-free) body shape ratios. These included bill width / The locality for each specimen was taken from bill length (BL/BW), bill length / wing length the specimen label and its longitude, latitude and (BL/WL), tarsus length / wing length (TS/WL) elevation were obtained (when available) from and tail length / wing length (TL/WL). Each ornithological gazetteers for each country (Rand of these shape variables has a potential func- & Paynter, 1981; Paynter, 1985, 1989, 1992; tional significance that may be as relevant to Paynter & Traylor, 1991) or from specimen la- fitness in different environments as size varia- bels. Each locality was plotted on a map. bles: BW/BL for manipulating food, and BL/WL, TS/WL and TL/WL as proportions of general size (Aldrich & James, 1991). Because Seasonal distribution ratios are nonlinear, often introducing spurious correlations (Atchley et al., 1976), they were An analysis of geographic variation would not subjected to statistical tests. be complicated by evidence for long-distance Because the untransformed data for the six migration. To examine seasonal distribution of morphometric variables met the assumptions E. platensis, the date of collection was obtained of parametric tests (normality and homogeneity from each specimen label and a bivariate plot of variances), two sample (Student’s) t tests of latitude and month of collection was made (Sokal & Rohlf, 1981) were used to compare for all specimens. An absence of specimens the means of each variable between the sexes from the southern latitudes and a concentration for both platensis and olivascens, and between of specimens at northern latitudes during the the two races for each sex. Because of the small austral winter (June-August) would provide sample sizes for gossei, I did not attempt to evidence for long-distance migration. statistically compare variables for gossei with those for platensis and olivascens. A principal components (PC) analysis (Sokal & Rohlf, Morphometric variation 1981) was computed using the correlation ma- trix of raw data for six morphometric variables Using digital calipers, I measured (nearest (BL, BW, WL, TS, TL and PB) to produce in- 0.1 mm) the following morphometric variables: dividual PC loadings for 326 specimens of E. bill length (BL), from depression between cra- platensis with data for each variable. PC1 and nium and maxilla to tip of maxilla; bill width PC2 were plotted to compare multivariate (BW), at widest (basal) part of bill; wing chord trends among E. platensis taxa.

Ardeola 50(2), 2003, 223-235 GEOGRAPHIC VARIATION IN THE GREAT PAMPA-FINCH EMBERNAGRA PLATENSIS COMPLEX 227

FIG.2.—Comparison of bill structure and colouration in Embernagra p. platensis and E. p. olivascens. The bill structure and colouration of E. p. gossei is indistinguishable from E. p. olivascens. The vertical line represents the measurement taken for the maximum height of pale bill colouration on the upper bill. [Comparación de la estructura del pico y su coloración entre Embernagra p. platensis y E. p. olivascens. La estructura y coloración de E. p. gossei es indistinguible de E. p. olivascens. Las líneas verticales representan la medida tomada como la máxima altura de la coloración pálida de la mandíbula superior del pico.]

Geographic variation 819286) taken in Department Beni in May and June 1965, appears to be disjunct, located far To assess geographic variation in morpho- from the nearest populations in central Para- metric traits, I computed Pearson correlation guay. coefficients (r; Sokal & Rohlf, 1981) for each Olivascens occurs in central and western morphometric variable with latitude, longitu- Bolivia and northwestern Argentina. In Bolivia de, and elevation. This was done for each sex its range approaches that of platensis, where of all E. platensis combined and separately for specimens (ANSP 790396, CM 81485) taken platensis and olivascens (data insufficient for in Incachaca, Department (hereafter Dept.) Co- gossei). Because temperature is correlated with chabamba (17°14′S, 65°49′W), were 265 km both latitude and elevation, a significantly po- from the nearest locality for platensis at Pam- sitive correlation between morphometric varia- pas del Río Imbare, Dept. Beni (15°10′ S, bles and either latitude or elevation would pro- 67°04′W; AMNH 792295, 792296). In wes- vide support for Bergmann’s rule. All statistical tern Paraguay, a subadult (AMNH 811534) analyses were computed with Statistix 7.0 soft- described by Short (1976) was taken in Lich- ware (Anonymous, 2000), with two-tailed pro- tenau, Dept. Presidente Hayes (22°50′ S, babilities and α = 0.05. 59°40′W), only 102 km from the nearest spe- cimens of platensis (AMNH 320997, 320998) at Makthlawaiya, Dept. Presidente Hayes RESULTS (23°20′S, 58°50′W). In Argentina, the ranges of examined speci- Geographic distribution mens of platensis and olivascens did not closely approach (Fig. 1). The locality of two old trade The specimens examined in this study and a specimens of olivascens (ANSP 78975, FMNH review of published specimen records within 307668) purportedly collected well within the potential zones of overlap reveal that the four range of platensis (La Plata, Argentina, in 1898) subspecies are parapatrically distributed (Fig. was assumed to be incorrect. However, speci- 1). Nominate platensis occurs from central Bo- mens of both races have been taken in Córdoba livia to central and eastern Paraguay, southern Prov., where their ranges nearly meet. Contreras Brazil, eastern Argentina and Uruguay. The po- (1980) reported a specimen of platensis in the pulation in Bolivia, represented by four speci- Museo Argentino de Ciencias Naturales mens (AMNH 792295, 792296, 819285, (MACN 41250), taken from Laguna del Monte

Ardeola 50(2), 2003, 223-235 228 HAYES, F. E. in extreme southeastern Córdoba Prov. Geographically restricted gossei occurs to (34°10′S, 62°50′N), about 313 km southeast the south of olivascens in west-central Argenti- from the closest specimen locality of olivascens na, where it is known only from the provinces (MACN 41248) at Yacanto, northwestern Cór- of San Juan, Mendoza and San Luis (Contreras, doba Prov. (32°03′S, 65°03′W; see Fig. 1). 1980; Nores & Yzurieta, 1986). It is not known Contreras (1980) reported that the fresh, un- to overlap with olivascens, but Contreras worn specimen from Laguna del Monte was (1980) reported two specimens (MACN 51487, ‘undoubtedly’ platensis but that its underpart 51488) of gossei, taken from Ullún, San Juan colouration resembled olivascens. He sugges- Prov. (not located), with ventral colouration in- ted that this specimen may represent a hybrid, termediate with olivascens. but also noted that another fresh specimen (MACN 49984) of platensis from farther sout- heast (Sierra de la Ventana, Buenos Aires Prov., Seasonal distribution 38°09′S, 61°48′W), taken well within the nor- mal range of platensis, possessed similar un- The occurrence of four specimens of platen- derpart colouration. Nores & Yzurieta (1979) sis at northerly latitudes in Bolivia in May and reported sight records of platensis from several June suggests that they may be long-distance localities in southeastern Córdoba Prov., inclu- migrants, but because the southernmost popu- ding Ucacha (33°02′S, 63°31′W), only 181 km lations of both platensis and olivascens remain from Yacanto. Olrog (1963: 331) reported both at southerly latitudes during the austral winter platensis and olivascens in Formosa Prov., the (Fig. 3), long-distance migration appears unli- former in ‘the east’ and the latter ‘except the ex- kely. However, post-breeding vagrancy may be treme east’, but did not state the sources of his expected. information or whether they represented sight or specimen records.

FIG.3.—Seasonal variation in the range of latitudinal distribution of Embernagra platensis specimens exa- mined in this study, with monthly sample sizes for E. p. platensis (above) and E. p. olivascens (below). Spe- cimens lacking adequate date or locality data are excluded. [Variación estacional en el rango de distribución latitudinal de los individuos de Embernagra platensis examinados para este estudio. Se incluyen los tamaños muestrales para E. p. platensis (arriba) y E. p. oli- vascens (abajo). Individuos sin datos de fecha o localidad se han excluido.]

Ardeola 50(2), 2003, 223-235 GEOGRAPHIC VARIATION IN THE GREAT PAMPA-FINCH EMBERNAGRA PLATENSIS COMPLEX 229

Morphometric variation nificantly larger; in olivascens, males were sig- nificantly larger than females for WL only (Ta- Although the sexes appeared to be monoch- ble 1). Within each race, bill size and shape romatic in plumage (not quantitatively asses- were remarkably similar between the sexes sed), they were morphometrically dimorphic in (Table 1). The extent of pale colouration on each race (data insufficient for statistical analy- the sides of the bill was significantly greater sis in gossei). In platensis, significant sexual for males of platensis, but not olivascens (Table dimorphism occurred in several size variables 1). Within each race, body shape ratios were (WL, TS, TL, MS), with males averaging sig- virtually identical between the sexes (Table 1).

TABLE 1

Descriptive measures of size and shape variables (BL = bill length; BW = bill width; WL = wing length; TS = tarsus length; TL = tail length; MS = mass; PC = principal component; PB = extent of pale colour on bill) for three races of E. platensis, with statistical comparisons between sexes and taxa for E. p. platensis and E. p. olivascens (data insufficient for E. p. gossei). [Variables descriptivas del tamaño y forma del pico (BL = longitud del pico; BW = ancho del pico; WL = longitud del ala; TS = longitud del tarso; TL = longitud de la cola; MS = peso; PC = Componentes Principales; PB = extensión del color pálido del pico) para las tres razas de E.platensis. Se incluyen las com- paraciones estadísticas entre sexos y taxa para E. p. platensis y E. p. olivascens (los datos para E. p. gossei son insuficientes para realizar los análisis).]

E. platensis platensis E. platensis olivascens E. platensis gossei Variable/Sex Mean±SD (min; max; n)Mean±SD (min; max; n)Mean±SD (min; max; n) [Variable/Sexo] [Media±DT (min; max; n)] [Media±DT (min; max; n)] [Media±DT (min; max; n)]

BL 17.81±0.96 (14.9; 21.9; 142) 18.04±1.00 (16.5; 21.5; 51) 18.13±0.31 (17.8; 18.4; 3) 17.67±0.99 (15.5; 20.2; 88) 17.89±0.83 (16.0; 19.5; 37) 19.07±0.74 (18.2; 20.0; 4) BW 8.96±0.44 (7.8; 10.1; 142) 9.10±0.48 (8.1; 10.2; 51)e 8.83±0.12 (8.7; 8.9; 3) 8.94±0.39 (8.0; 9.7; 90) 9.09±0.40 (8.3; 9.8; 37)e 9.28±0.68 (8.6; 10.0; 4) WL 90.29±3.07 (81.6; 98.0; 142) 94.98±4.48 (87.5; 106.4; 51)c 96.00±1.39 (95.1; 97.6; 3) 86.71±2.84 (80.4; 91.8; 91)a 91.95±4.87 (81.7; 103.0; 38)b, c 91.50±4.38 (86.6; 96.9; 4) TS 29.68±1.20 (25.8; 34.0; 142) 30.66±1.34 (27.4; 34.1; 51)c 31.37±1.10 (30.3; 32.5; 3) 29.15±1.07 (26.5; 32.5; 91)a 30.20±1.51 (26.6; 32.8; 38)c 31.00±1.23 (30.0; 32.8; 4) TL 93.50±5.83 (75.0; 109.0; 141) 101.90±5.50 (87.0; 118.0; 51)c 105.30±4.16 (102.0; 110.0; 3) 90.04±5.67 (77.0; 110.0; 89)a 99.97±4.69 (88.0; 111.0; 38)c 100.80±8.77 (91.0; 110.0; 4) MS 49.41±3.80 (42.6; 56.0; 13) 46.00±0.00 (46.0; 46.0; 2) — 44.66±3.42 (38.0; 49.8; 13)b 50.00 (1) — 44.6 (43.0; 49.6; 4)f 45.5 (45.0; 46.0; 3)f 44.4±2.05 (39.5; 48.5; 13)f C1 0.37±1.08 (–2.88; 3.15; 141) –2.04±1.13 (–5.69; 0.18; 51)c –2.44±0.27 (–2.65; –2.14; 3) 1.33±1.05 (–1.35; 3.73; 85)a –1.29±1.42 (–4.68; 1.51; 36)b, d –2.26±1.45 (–3.40; –0.63; 3) PC2 0.09±1.02 (–2.30; 2.50; 141) –0.42±1.17 (–2.75; 0.18; 51)c –0.92±0.34 (–1.12; –0.53; 3) 0.24±1.00 (–2.08; 2.45; 141) –0.27±0.91 (–2.21; 0.18; 36)d –0.11±1.22 (–1.45; –0.95; 3) PB 2.23±0.20 (1.8; 2.7; 142) 3.14±0.24 (2.7; 3.8; 51)c 3.03±0.35 (2.7; 3.4; 3) 2.15±0.19 (1.7; 2.6; 91)b 3.05±0.23 (2.6; 3.7; 36)c 3.07±0.32 (2.7; 3.3; 4) BW/BL % 0.50±0.03 (0.39; 0.60; 142) 0.51±0.04 (0.41; 0.59; 51) 0.49±0.01 (0.47; 0.50; 3) 0.51±0.03 (0.43; 0.57; 87) 0.51±0.03 (0.44; 0.55; 37) 0.49±0.02 (0.46; 0.51; 4) BL/BW % 0.20±0.01 (0.17; 0.24; 142) 0.19±0.01 (0.17; 0.21; 51) 0.19±0.01 (0.18; 0.19; 3) 0.20±0.01 (0.18; 0.23; 88) 0.20±0.01 (0.17; 0.21; 37) 0.21±0.02 (0.19; 0.23; 4) TS/WL % 0.33±0.01 (0.29; 0.38; 142) 0.32±0.02 (0.29; 0.36; 51) 0.33±0.01 (0.32; 0.34; 3) 0.34±0.01 (0.29; 0.37; 91) 0.33±0.02 (0.30; 0.36; 38) 0.34±0.01 (0.33; 0.35; 4) TL/WL % 1.04±0.05 (0.89; 1.17; 141) 1.07±0.06 (0.92; 1.20; 51) 1.10±0.03 (1.07; 1.13; 3) 1.03±0.05 (0.87; 1.21; 89) 1.09±0.05 (1.01; 1.17; 38) 1.10±0.05 (1.05; 1.14; 4) a differs from males of same race, P < 0.001; b differs from males of same race, P < 0.01; c differs from E. p. platensis of same sex, P < 0.001; d differs from E. p. platensis of same sex, P < 0.01; e differs from E. p. platensis of same sex, P < 0.05; f mass data from both sexes reported by Contreras (1980).

Ardeola 50(2), 2003, 223-235 230 HAYES, F. E.

Both sexes of olivascens averaged signifi- A bivariate plot of PC1 and PC2, which ac- cantly larger for each size variable (except BL counted for 63.2% of the variance (Table 2), and MS) than platensis (Table 1). Although the separated most specimens of platensis and oli- sample sizes of gossei were too few for statisti- vascens, but there was considerable overlap cal analysis, body size variables tended to ave- (Fig. 4). Specimens of gossei were distributed rage slightly larger than olivascens (Table 1). within the morphometric space of olivascens The body shape ratios were nearly identical bet- but a female overlapped with platensis (Fig. ween races; the only apparent difference was a 4). The three male Bolivian specimens of pla- relatively longer WL compared with TL in pla- tensis were within the range of overlap between tensis than in olivascens and gossei (Table 1). platensis and olivascens, but the female Boli- The bill structure differed distinctly between vian specimen was within the range of platensis platensis and olivascens, with the latter having only (Fig. 4). Both PC1 and PC2 were signifi- a more curved upper ridge (not quantitatively cantly greater for platensis than olivascens for assessed) on the upper bill (Fig. 2); although each sex (Table 1). In platensis, PC1 was sig- bill length did not differ significantly, the bill nificantly greater for females than males; the was wider in olivascens (Table 1). The bill co- sexes did not differ for PC2 in platensis or for louration also differed significantly. In olivas- either PC1 or PC2 in olivascens (Table 1). cens, the dusky colouration was restricted to the uppermost ridge of the culmen (Fig. 2), re- sulting in significantly more extensive pale co- Geographic variation louration (Table 1) on the sides of the bill that was deeper orange (not quantitatively asses- Significant geographic trends occurred for sed); in platensis, the dusky colouration exten- all morphometric variables; however, few data ded along the entire upper ridge of the culmen were available for MS in which significant co- from the nostril to the tip (Fig. 2). Although rrelations should be viewed with caution (Table there was slight overlap among taxa in the me- 3). Among all E. platensis specimens combi- asurements of PB (Table 1), all specimens (in- ned, latitude was negatively correlated with cluding those misidentified, misplaced with the each variable except MS (few data available), wrong taxon, or with questionable locality data) longitude was positively correlated with each were unambiguously diagnosed to taxon based variable (females only for MS) except BL and on the structure and pattern of colouration of BW, and elevation was positively correlated the bill (Fig. 2); no individual, including those with each variable (females only for BW) ex- in which measurements of PB overlapped, pos- cept MS (few data). sessed intermediate traits. In gossei, the bill Within platensis, latitude was negatively co- structure and colouration were indistinguisha- rrelated with BL, BW and TL (males only), but ble from olivascens. not with WL, TS, MS or PB. Longitude was

TABLE 2

Factor loadings for principal components analysis using the correlation matrix of raw data for six morpho- metric variables (BL, BW, WL, TS, TL and PB; see Table 1) of the Embernagra platensis complex. [Factores incluidos en el análisis de componentes principales usando la matriz de correlación de los datos de seis variables morfológicas (BL, BW, WL, TS, TL y PB; ver Tabla 1) del complejo Embernagra platensis.]

PC Axis Eigenvalue % of Variance Cumulative % of Variance [Autovalor] [% de la varianza] [% acumulado de la varianza]

PC1 2.70 45.0 45.0 PC2 1.09 18.2 63.2 PC3 0.87 14.4 77.6 PC4 0.67 11.1 88.7 PC5 0.43 7.2 95.9 PC6 0.25 4.1 100.0

Ardeola 50(2), 2003, 223-235 GEOGRAPHIC VARIATION IN THE GREAT PAMPA-FINCH EMBERNAGRA PLATENSIS COMPLEX 231

FIG. 4.—Principal components analysis of morphometric variables for Embernagra platensis specimens examined in this study. Bolivia specimens of E. p. platensis are indicated with an arrow. [Análisis de componentes principales de las variables morfológicas para los individuos de Embernagra platensis examinados es este estudio. Los individuos de E. p. platensis provenientes de Bolivia se han señalado con una flecha.] negatively correlated with BL (males only) and for males), BW (females only), WL and TS, BW, but not with WL, TS, TL or PB. Elevation but not with TL or PB. Longitude was positi- was positively correlated with BL, BW (males vely correlated with WL (females only) and only), WL (males only) and TL, but not with TL (females only), but not with BL, BW, TS TS, MS (few data) or PB. or PB. Elevation was positively correlated Within olivascens, latitude was negatively with BL, WL and TS, but not with BW, TL or correlated with BL (females only; P = 0.058 PB.

Ardeola 50(2), 2003, 223-235 232 HAYES, F. E.

TABLE 3

Geographic correlates (r) of body size and shape variables (see Table 1 for definitions) in Embernagra pla- tensis (all forms combined) and the subspecies E. p. platensis and E. p. olivascens (data insufficient for E. p. gossei). [Correlaciones (r) con variables geográficas del tamaño y formas corporales (ver Tabla 1 para las defini- ciones) de todas las formas combinadas de Embernagra platensis y sus subespecies E. p. platensis y E. p. oli- vascens (los datos para E. p. gossei son insuficientes para realizar los análisis).]

n Latitude Longitude n Elevation Variable Sex /Taxon [Variable] [Sexo/Taxón] [Latitud] [Longitud] [Altitud]

BL E. platensis 190 –0.32a –0.05 179 0.25a E. p. platensis 138 –0.35a –0.30a 126 0.31a E. p. olivascens 50 –0.27 0.05 51 0.29c E. platensis 124 –0.32a 0.12 121 0.31a E. p. platensis 85 –0.44a –0.12 81 0.45a E. p. olivascens 35 –0.44b 0.12 36 0.38c BW E. platensis 190 –0.29a 0.00 179 0.14 E. p. platensis 138 –0.41a –0.18c 126 0.20c E. p. olivascens 50 0.07 –0.17 51 –0.07 E. platensis 125 –0.31a 0.08 123 0.19c E. p. platensis 86 –0.29b –0.24c 83 0.09 E. p. olivascens 35 –0.34c –0.17 36 0.01 WL E. platensis 190 –0.47a 0.45a 179 0.59a E. p. platensis 138 –0.14 0.08 126 0.22c E. p. olivascens 50 –0.47a 0.02 51 0.49a E. platensis 127 –0.46a 0.54a 124 0.67a E. p. platensis 87 0.18 0.09 83 0.18 E. p. olivascens 36 –0.68a 0.47b 37 0.62a TS E. platensis 190 –0.36a 0.33a 179 0.44a E. p. platensis 138 –0.16 0.08 126 0.08 E. p. olivascens 50 –0.44a 0.09 51 0.51a E. platensis 127 –0.39a 0.32a 124 0.51a E. p. olivascens 87 –0.02 –0.09 83 0.14 E. p. platensis 36 –0.73a 0.17 37 0.56a TL E. platensis 189 –0.45a 0.50a 179 0.47a E. p. platensis 137 –0.32a 0.12 126 0.26b E. p. olivascens 50 0.09 0.14 51 –0.12 E. platensis 125 –0.45a 0.61a 122 0.59a E. p. platensis 85 –0.10 0.06 81 0.44a E. p. olivascens 36 –0.22 0.40c 37 0.23 MS E. platensis 15 0.49 –0.35 15 –0.09 E. p. platensis 13 0.46 –0.20 13 0.53 E. platensis 14 –0.05 0.72b 14 0.38 E. p. platensis 13 0.41 0.69b 13 –0.52 PB E. platensis 190 –0.48a 0.72a 179 0.66a E. p. platensis 138 0.04 0.03 126 –0.06 E. p. olivascens 50 0.22 0.20 51 –0.19 E. platensis 124 –0.54a 0.75a 121 0.70a E. p. platensis 87 0.00 –0.02 83 0.10 E. p. olivascens 34 –0.17 0.29 37 0.25 a P < 0.001; b P < 0.01; c P < 0.05.

Ardeola 50(2), 2003, 223-235 GEOGRAPHIC VARIATION IN THE GREAT PAMPA-FINCH EMBERNAGRA PLATENSIS COMPLEX 233

DISCUSSION failed to provide any evidence. On the basis of a fresh, unworn specimen of platensis with pale Although this study documents considerable underparts resembling olivascens, taken geographic variation in morphometric traits roughly 300 km from the nearest specimen lo- within E. platensis, it remains uncertain whet- cality of olivascens, Contreras (1980: 29) con- her such variation is attributable to natural se- cluded that ‘there are zones of secondary con- lection, environmental induction or stochasti- tact between both races in which some city. However, the geographic patterns of hybridisation is produced’. However, Contreras variability for temperature and humidity are (1980) examined only six specimens of platen- well known within the range of E. platensis sis in which another specimen well within the (e.g. Hoffman, 1975; Prohaska, 1976; Ratisbo- normal range of platensis possessed similar un- na, 1976), and an assessment of their potential derpart colouration. Hellmayr (1938: 636) si- effects on morphometric variation is warran- milarly described specimens of platensis from ted (Zink & Remsen, 1986). eastern Argentina, southern Brazil and Uru- Temperature is inversely correlated with both guay as being ‘nearly white along the abdomi- latitude and elevation. The negative correlations nal line’, which he attributed to their worn con- of most morphometric variables with latitude dition. Although Contreras (1980) regarded violate Bergmann’s rule; however, the positive plumage colouration as the primary distinction correlations of most morphometric variables among the races, some overlap occurs which is with elevation are consistent. The conflicting difficult to assess given the variability of wear evidence is puzzling, but a similar pattern of among specimens. variation occurs in the Suiriri Flycatcher (Suiri- I found the structure and colouration of the ri suiriri; Hayes, 2001), suggesting that a shared bill to be the most diagnostic traits distinguis- pattern may result from a common cause. Many hing olivascens, gossei and catamarcanus from North American birds do not conform to Berg- platensis, and failed to find any intermediate mann’s rule (Zink & Remsen, 1986). Because a specimens. Furthermore, the absence of clinal plethora of ecological variables (e.g. annual pro- variation in the extent of pale bill colouration ductivity, degree of seasonality, habitat quality, within each form demonstrates that intergrada- food availability, prey size, competition and pre- tion either does not occur or is potentially res- dation) potentially affect body size and presu- tricted to a narrow, still undiscovered contact mably covary with climate and topography (Ja- zone in central Bolivia, western Paraguay or mes, 1970; Cody, 1974; Case, 1978; Zink & north-central Argentina. Their apparent lack of Remsen, 1986; Hayes et al., 2004), seeking the sympatry could be attributable to competitive causes of geographic variation in body size is exclusion. exceedingly difficult. The consistent differences in size, plumage The western races of olivascens and gossei and soft part traits between two groups indicate occur in drier regions than platensis. Because that they meet the criteria of distinct species both the upperparts and underparts of these ra- according to the phylogenetic species concept ces are generally paler than platensis, E. pla- (McKitrick & Zink, 1988). The vocalisations of tensis appears to conform with Gloger’s rule, the two groups have not been compared, but which is well supported among North Ameri- published descriptions (Beton, 1985; Ridgely & can birds (Zink & Remsen, 1986). Tudor, 1989; Sick, 1993; Krabbe, 1990) sug- The suite of traits distinguishing olivascens, gest that the variability of their calls may com- gossei and catamarcanus from morphologically plicate such an analysis. Because similarly sub- distinct platensis, including larger body size, a tle differences in morphology and vocalisations more strongly curved, deeper orange beak with represent isolating mechanisms among sympa- less extensive dusky colouration on the upper tric congeners of seed-eating ‘finch-tanagers’ bill, reduced or absent streaking on the back, that rarely hybridise (e.g. Darwin’s finches; and a paler loral region and underparts, imply Grant, 1986), the distinctions between olivas- that substantial genetic differences may sepa- cens and platensis may be sufficient to preclude rate these two groups. The intergradation bet- or minimise hybridisation wherever the two ween platensis and olivascens in the east-cen- forms may meet, in which case they would be tral Chaco was assumed by Short (1975), who regarded as specifically distinct according to

Ardeola 50(2), 2003, 223-235 234 HAYES, F. E. the comprehensive biologic species concept BURNS, K. J. 1997. Molecular systematics of tanagers (Johnson et al., 1999). Helbig et al. (2002) re- (Thraupinae): evolution and biogeography of a di- commended that diagnosable, parapatrically verse radiation of Neotropical birds. Molecular distributed taxa within a superspecies complex Phylogenetics and Evolution, 8: 334-348. CASE, T. J. 1978. A general explanation for insular be regarded as distinct species. body size trends in terrestrial vertebrates. Eco- Ridgely & Tudor (1989) suggested that if logy, 59: 1-18. platensis and olivascens were demonstrated to CHESSER, R. T. 1994. Migration in South America: represent distinct species, the English name an overview of the austral system. Bird Conserva- Olive Pampa-Finch, presumably derived from tion International, 4: 91-107. Hellmayr’s (1938) ‘Olive Ground Finch’, CHUBB, C. 1918. Notes on Embernagra platensis should be applied to olivascens. I tentatively and its allies, with a description of a new species. propose the recognition of two species within Ibis, ser. X, VI: 1-10. the E. platensis complex: (1) the monotypic CODY, M. L. 1974. Competition and the Structure of Bird Communities. Princeton University Press. Great Pampa-Finch, E. platensis (Gmelin, New Jersey. 1789), and (2) the polytypic Olive Pampa- CONTRERAS, J. R. 1980. Avifauna Mendocina. II. Re- Finch, E. olivascens d’Orbigny, 1839, whose validación de Embernagra platensis gossei Chubb, recognised subspecies include nominate oli- 1918, y nuevos datos sobre las subespecies de Em- vascens, gossei and catamarcanus. Further stu- bernagra platensis (Passeriformes: Emberizidae). dies of morphometric variation, vocalisations, Boletín del Museo de Ciencias Naturales y An- behaviour and genetics are needed within the tropología Juan Cornelio Moyano, 1: 23-34. potential contact zone between the two forms to EISENMANN, E. & SHORT, L. L. 1982. Systematics of evaluate whether they ever meet and intergrade. the avian genus Emberizoides (Emberizidae). American Museum Novitates, 2740: 1-21. FJELDSA, J. & KRABBE, N. 1990. Birds of the High ACKNOWLEDGEMENTS.—This study was funded by Andes. Zoological Museum, University of Copen- grants from the American Museum of Natural His- hagen, and Apollo Books. Svendborg. tory (AMNH), Field Museum of Natural History GOULD, S. J. & JOHNSTON, R. F. 1972. Geographic (FMNH) and Loma Linda University. Assistance variation. Annual Review of Ecology and Syste- was provided by: M. LeCroy, L. Short and F. Vui- matics, 3: 457-498. lleumier at AMNH; D. Maurer, T. Schulenberg and GRANT, P. R. 1986. Ecology and Evolution of Dar- D. Willard at FMNH; K. Garrett at the Los Angeles win’s Finches. Princeton University Press. New County Museum; R. Browning and G. Graves at the Jersey. U. S. National Museum of Natural History; and P. HAYES, F. E. 2001. Geographic variation, hybridi- Chu, J. Hinshaw, R. Payne and R. Storer at the Uni- zation, and the leapfrog pattern of evolution in the versity of Michigan Museum of Zoology. I thank Suiriri Flycatcher (Suiriri suiriri) complex. Auk, the following individuals for the loan of specimens 118: 457-471. from their institutions: F. Gill of the Academy of HAYES, F. E., WHITE, S. A., FFRENCH, R. P. & BOD- Natural Sciences of Philadelphia; K. Parkes of the NAR, S. 2004. Geographic variation in body size Carnegie Museum; and R. Paynter of the Museum of of the Bananaquit (Coereba flaveola) in the Tri- Comparative Zoology. T. Schulenberg and B. Porte- nidad and Tobago archipelago. Journal of Carib- ous assisted with map measurements. bean Ornithology in press. HELBIG, A. J., KNOX, A. G., PARKIN, D. T., SANGS- TER, G. & COLLINSON, M. 2002. Guidelines for BIBLIOGRAPHY assigning species rank. Ibis 144: 518-525. HELLMAYR, C. E. 1938. Catalogue of birds of the ALDRICH, J. W. & JAMES, F. C. 1991. Ecogeographic Americas and the adjacent islands. Field Museum variation in the American Robin (Turdus migrato- of Natural History, Zoology Series, 13, pt. 11. rius). Auk, 108: 230-249. HOFFMAN, J. A. J. 1975. Climatic Atlas of South ANONYMOUS. 2000. Statistix 7 User’s Manual. America, Vol. 1. Maps of Mean Temperature and Analytical Software. Tallahassee, Florida. Precipitation. WMO (Geneva), UNESCO (Paris) ATCHLEY, W. R., GASKINS, C. T. & ANDERSON, D. & Cartographica. Budapest. 1978. Statistical properties of ratios. I. Empirical ISLER, M. L. & ISLER, P. R. 1987. The Tanagers: results. Systematic Zoology, 25: 137-148. Natural History, Distribution, and Identification. BELTON, W. 1985. Birds of Rio Grande do Sul, Bra- Smithsonian Institution Press. Washington, D.C. zil, part 2. Formicariidae through Corvidae. Bulle- JAMES, F. C. 1970. Geographic size variation in birds tin of the American Museum of Natural History, and its relationship to climate. Ecology, 51: 365- 180: 1-241. 390.

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