Héctor Silva

Long-term changes in the bird community of Palenque, Chiapas, in response to rainforest loss

With increased human populations and subsequent pressure to develop or farm land, the rate of fragmentation of tropical rainforests has accelerated in the past several decades. How native organisms respond to such fragmentation has been the subject of intense study in temperate ecosystems and at several tropical sites in Central and South America, but there has been little study of this phenomenon in Mexico, the country bridging the Neotropics and temperate North America. A reason for this neglect is an apparent lack of long-term data; however, such data can be obtained from “non-traditional” sources, such as birders and tour leaders. We make innovative use of such data, combining them with more traditional data (e.g., museum specimens) to create a record of occurrence for Palenque, Mexico, from 1900 to 2009, including a near-continuous presence–absence record since 1970. We analyzed these data using logistic regression and, importantly, recent statistical advances expressly for sighting records. As recently as the 1960s Palenque’s forest was contiguous with that of Selva Lacandona to the east, but the protected area surrounding the famous ruins is now a forested island. As a result, various species formerly known from the site have disappeared, including species both large (Crax rubra, Penelope purpurascens, and Ara macao) and small (Notharchus hyperrhynchos, Malacoptila panamensis, Microrhopias quixensis, and Pachyramphus cinnamomeus). By contrast, several species of open areas or second growth have apparently colonized the area (e.g., Thryothorus modestus, Mimus gilvus, Euphonia affinis). Some species turnover has occurred within particular families, such as Columbidae, Trochilidae, and Troglodytidae. Losses and declines we documented at Palenque correspond with those reported from other sites in Mesoamerica, suggesting the soundness of our approach and the general vulnerability of certain species. Compilation and analysis of sighting record data holds great promise for tracking trends in many regions and across many taxa for which long-term census data are lacking.

Territoriality and Survivorship of the Sierra Madre Sparrow in La Cima, México

We studied the life-history of the Sierra Madre sparrow (Xenospiza baileyi) in a subalpine grassland-agriculture mosaic south of Mexico City. From March to early September 1999 we captured and color-banded 53 adults with mist-nets and mapped the breeding territories of 21 males. We again mapped territories in the same spot in April and May 2000. The number of breeding territories was found to be the same in the two consecutive years and interannual survivorship was found to be relatively high. Breeding territories were restricted to the bunchgrass-covered areas. We used the density of territories and the amount of remaining habitat to estimate a total population size of 5,380–6,150 adults for this species. Using this and other recent data, we recommend raising the Sierra Madre sparrow to the status of critically endangered using BirdLife International criteria.

Is the Taxonomic Composition of Landbird Communities in Mexico Predictable

Some bird families are more widespread than others both in geography and in habitat use (high-incidence fami- lies). The number of Mexican species in a bird family was found to be strongly correlated with the number of communi- ties that possess representatives of that family. This effect did not result from a higher probability of larger families hav- ing more widespread species or having species with broader diets or habitat preferences, nor from body size, abundance or clutch size, other factors which tend to correlate with the incidence of species. Instead, number of species per se (a trait of families) strongly influenced family incidence and thereby community composition. Therefore, community composition is influenced not only by ecological assembly rules at the species level, but also by the result of macroevolutionary proc- esses above the species level. This pattern may be related to species-area curves and provides an opportunity for coevolu- tion to occur even in situations in which species-specific coadaptation is not possible. This pattern increases the predict- ability of species composition of communities.