Cotinga 14 W estern Mexico: a significant centre of avian endem ism and challenge for conservation action A. Townsend Peterson and Adolfo G. Navarro-Sigüenza Cotinga 14 (2000): 42–46 El endemismo de aves en México está concentrado en el oeste del país, pues entre el 40 al 47% de las aves endémicas de México están totalmente restringidas a la región. Presentamos un compendio de estos taxones, tanto siguiendo el concepto biológico de especie como el concepto filogenético de especie, documentando la región como un importante centro de endemismo. Discutimos estrategias de conservación en la región, especialmente la idea de ligar reservas para preservar transectos altitudinales de hábitats continuos, desde las tierras bajas hasta las mayores altitudes, en áreas críticas. Introduction and Transvolcanic Belt of central and western Mexico has been identified as a megadiverse coun­ Mexico were identified as major concentrations of try, with impressive diversity in many taxonomic endemic species. This non-coincidence of diversity groups20. Efforts to document the country’s biologi­ and endemism in Mexican biodiversity has since cal diversity are at varying stages of development been documented on different spatial scales13,17 and in different taxa17,19,20 but avian studies have ben­ in additional taxonomic groups17. efited from extensive data already accumulated18 In prior examinations, however, western Mexico and have been able to advance to more detailed lev­ (herein defined as the region from Sonora and Chi­ els of analysis6,12,17. huahua south to Oaxaca, including the coastal In the only recent countrywide survey of avian lowlands, the Sierra Madre Occidental and Sierra diversity and endemism6, the south-east lowlands Madre del Sur, and Pacific-draining interior basins were identified as important foci of avian species such as the Balsas Basin) has not been appreciated richness. In contrast, the Sierra Madre Occidental sufficiently as a centre of endemism. Our ongoing Figure 1. Map of Mexico, showing the region here treated as western Mexico, with elevations marked as increasingly darker shades of grey by 1000s of metres of elevation. The three reserve systems discussed in the text are indicated with squares, triangles and circles. 42 Cotinga 14 Western Mexico: a significant centre of avian endemism systematic studies of Mexican birds3,5,9,14–16, as well endemic to Mexico, 99 of which are endemic to west­ as our re-examination of Mexican bird taxonomy ern Mexico — 29 in montane regions, 55 in the from alternative viewpoints10, have led us to appre­ lowlands, and 15 in the interior. Twenty-two ciate western Mexico as the primary focus of avian phylogenetic species are restricted to north-west endemism in Mesoamerica. Although the region has Mexico, whereas 42 are restricted to south-west been mentioned as important by previous authors4,7, Mexico. the purpose of the present contribution is to em­ Overall, western Mexico supports a substantial phasise the biological uniqueness of the region and portion of Mexican bird diversity. In all, 45% of the to explore the implications of this for conservation 100 endemic biological species and 40% of the 250 strategies. endemic phylogenetic species in the country are found only in the west of the country. Indeed, three Endemism in biological and phylogenetic genera —Euptilotis , Deltarhynchus, and Philortyx — species are endemic to the region, as well as two others The dominant taxonomic viewpoint for birds has sometimes considered separate genera (Neochloe = long been the Biological Species Concept8, as exem­ Vireo, Aechmolophus = Xenotriccus). Other regions, plified in North America by the American such as the Sierra Madre Oriental, the Yucatán Ornithologists’ Union’s check-list series2, and has Peninsula, and the southern tip of Baja California11, been the basis for previous examinations of Mexi­ hold smaller concentrations of endemic species. can bird endemism6. Under this concept, 101 species Patterns of endemism in other taxonomic groups are endemic to Mexico, 46 of which are restricted to generally appear to parallel those of birds2,3, sug­ western Mexico — 13 in montane regions, 20 in the gesting that the patterns outlined herein may be lowlands, and 13 in the interior of southern Mexico quite general for Mexican biodiversity. (Table 1). Eleven of these species are restricted to north-west Mexico (south to Jalisco), whereas 20 Conservation challenges occur only in south-west Mexico (Jalisco south to The enormous concentration of endemic birds in Oaxaca). western Mexico represents both a challenge and an Alternative taxonomic viewpoints, such as the opportunity for conservation efforts in Mexico. The Phylogenetic Species Concept and the Evolution­ challenge results from the paucity of reserves es­ ary Species Concept21, are beginning to acquire tablished in the region. Presently, the only greater significance in ornithology. These concepts large-scale, effective reserves in western Mexico, emphasise monophyly as a base criterion for iden­ north to south, are El Carricito del Huichol (moun­ tifying potential species taxa. The Phylogenetic tains of northern Jalisco), Chamela/Cuixmala Species Concept then focuses on diagnosability — (coastal lowlands of Jalisco) and the Sierra de distinct populations that are essentially 100% Manantlán (mountains of western Jalisco)1. Large identifiable and distinguishable from other groups. areas of important habitat rich in endemic species The Evolutionary Species Concept refers to the idea both north and south of this limited zone remain of identifying populations that have taken independ­ either unprotected or poorly protected. ent evolutionary trajectories as species; we have The western Mexican centre of endemism also implemented this concept in similar manner as the represents an opportunity. If biologically unique Phylogenetic Species Concept — evolutionary inde­ elements were scattered randomly, without geo­ pendence is signalled by the fixation of distinct graphic foci, development of cost-effective character states. Hence, we applied the two alter­ conservation strategies would be extremely diffi­ native concepts under a single decision rule: we cult13. Rather, given clear concentrations, those same sought sets of populations that exhibit unique areas can represent priority areas for conservation phenotypic character suites that distinguish them attention. from other populations. We detected potential al­ In the present case, we recommend three lati- ternative species units via the scientific literature tudinally separated sets of reserves linked to cross and via inspection of specimens, and checked our altitudinal gradients in western Mexico. In the hypotheses in at least one additional scientific col­ north, perhaps in Nayarit and northern Jalisco, link­ lection based on an independent series of specimens. age of El Carricito del Huichol with coastal slope Although these approaches have been applied sites and coastal sites (e.g. Marismas Nacionales in to several avian clades, they have not yet been ap­ coastal Sinaloa and Nayarit) would be an ideal start­ plied to an entire region; we are presently preparing ing point. A nearby, but more southerly reserve a revision under these concepts for Mexican birds10. assemblage could link Sierra de Manantlán with Based on this information, we have been able to the coastal Chamela/Cuixmala complex. The com­ assess levels of endemism across the country11, and bination of these two mega-reserves would summarise species endemic to western Mexico (Ta­ effectively protect habitat appropriate for almost ble 1). Under this view, c. 250 bird species are all of the ‘northern’ species endemic to the region, 43 Cotinga 14 Western Mexico: a significant centre of avian endemism T a b l e 1 . Summary of distributions of 99 bird species spadiceus), W hite-bellied Becard Pachyramphus albiventris endemic to western Mexico, divided by geography. For (Pachyramphus aglaiae), S inaloa B ecard Pachyramphus uropygialis names representing recognisable phylogenetic species, (Pachyramphus major), W e s te rn T ity ra Tityra griseiceps ( Tityra names of associated biological species taxa recognised by semifasciata), San Blas Jay Cyanocorax sanblasianus, W e ste rn A O U 2 are given in parentheses. Com m on names are G re e n Jay Cyanocorax speciosa (Cyanocorax yncas), Happy W ren prelim inary in nature. Thryothorus felix, Sinaloa W ren Thryothorus sinaloa, Rufous-backed R obin Turdus rufopalliatus (Turdus rufopalliatus), G o ld e n V ireo Vireo hypochryseus, W estern Parula Parula pulchra (Parula pitiayumi), Red-breasted Chat Granatellus venustus, Pale-vented Euphonia S p e c ie s Euphonia godmani (Euphonia affinis), W estern Ant-Tanager Habia affinis (Habia rubica), M exican T h ru s h Ta n a g e r Rhodinocichla Northern Mountains: schistacea (Rhodinocichla rosea), W estern Saltator Saltator vigorsii Thick-billed Parrot Rhynchopsitta pachyrhyncha, M exican (Saltator coerulescens), Yellow Grosbeak Pheucticus chrysopeplus, W o o d n y m p h Thalurania ridgwayi ( Thalurania colombica), E ared Pacific Bunting Cyanocompsa indigotica (Cyanocompsa parellina), Q u e tz a l Euptilotis neoxenus, Arizona W oodpecker Picoides Orange-breasted Bunting Passerina leclancherii, W estern Olive arizonae (Picoides stricklandii), Imperial W oodpecker Campephilus Sp a rro w Arremonops sumichrasti (Arremonops rufivirgatus), imperialis†, Sinaloa Martin Progne sinaloae, Tufted Jay Cyanocorax Rusty-crowned Ground-sparrow Melozone kieneri, Cinnamon-