Sierra Madre Sparrows (Xenospiza baileyi) are among the least known of all bird species in Mexico. Recent surveys have discovered previously unknown populations and the current known distribution of Sierra Madre Sparrows consists of two populations separated by >800 km. We used available distributional information to develop ecological niche models that (1) predict much of the distribution potential of the species, (2) establish that the broad disjunction separating the two populations has ecological correlates that appear to be important to the distributional of these sparrows, and (3) illustrate the extremely restricted ecological distribution of the species. We used two sets of climatic and topographic variables, with one including all 22 variables available and the second with only six variables that were positively related to quality of distributional models. Although indications of differences between the two sets of populations were found based on the full 22‐dimensional environmental dataset, such a highly dimensional analysis is vulnerable to over‐fitting; models based on the reduced dataset indicated that the two populations occur in areas with similar ecological conditions. Our models also suggest that southern population of Sierra Madre Sparrows covers most of their potential range in that region. The potential range of the northern population, however, extends beyond known points of occurrence. To clarify the distribution of Sierra Madre Sparrows and evaluate their status and conservation opportunities, detailed searches for additional populations in areas identified by the model are needed.

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The Sierra Madre Sparrow (Xenospiza baileyi) is a highly endangered and endemic species of the highlands of south-central Mexico, where it is resident in bunchgrass (Gramineae) and adjacent marshy habitats in the southern Sierra Madre Occidental (Jalisco and Durango states) and in the mountains around the Valley of Mexico (Distrito Federal and the states of Morelos and Mexico). This species was first collected in the southern part of this range on 23 April 1945 at La Cima, D.F., where its persistence has been documented essentially continuously since 1951. The first specimens of the taxon were collected in the Sierra de Bolaños of extreme northern Jalisco on 3–10 March 1889, including the type from which the genus and species were described in 1931. Two populations have been found in southern Durango: one 30 miles (48 km) south-west of the City of Durango on 22 March 1931, and the other 5 miles (8 km) west of El Salto on 16–17 June 1951. The Sierra Madre Sparrow has not been otherwise confirmed in the northern part of its range, which in July 2004 led us to conduct an extensive search for it in these areas of Durango and Jalisco as well as south-western Zacatecas. Here we present the findings from that search, during which several sites were intensively surveyed and a single population of this sparrow was located – a new one between the city of Durango and El Salto, Durango. This rediscovery increases possibilities for understanding the biogeography, ecology and basic requirements of the Sierra Madre Sparrow, information of fundamental importance for proposing measures that promote its conservation in any of its remaining populations.

Assessing patterns of genetic structure and diversity of threatened species has become an essential tool for determining conservation status and designing management strategies. We examine the genetic structure of the Sierra Madre sparrow (Xenospiza baileyi), a species restricted to fragmented patches of subalpine bunchgrass in three small isolated areas of northwestern and central Mexico. Coding and non-coding regions of mtDNA (1,878 bp) from individuals of the only three known populations revealed the existence of a single major lineage, with closely related haplotypes being shared between populations across the range. The sharing of haplotypes between the distant northwest and central populations (*800 km) suggests a recent fragmentation of a formerly contiguous population. Despite a lack of large-scale phylogeographic structure, haplotype frequencies at local scales revealed significant genetic differentiation and high F ST values between all three remaining populations, even between localities separated by less than 12 km. These results suggest restricted gene flow and limited dispersal, likely due to the species' inability to cross areas of unsuitable habitat. On the basis of genetic interchange and ecological equivalence criteria, we recommend that the species be managed as a single unit, permitting the strengthening of the small population in the northwest with individuals from central Mexico, and/or the translocation of individuals to new areas of suitable habitat.