Birds and Vegetation Structure of Isolated Juniper and Oak Communities in the Trans-Pecos Chihuahuan Desert
Birds of the Trans-Pecos region are historically understudied, with most literature covering birds of desert grasslands and scrub in New Mexico and Northern Mexico. A multitude of vegetation communities within the Chihuahuan Desert have also been neglected due to this gap in the research, for reasons including lack of access to public or preserve land in West Texas, and rough terrain. Indio Mountains Research Station (IMRS), is located 42-km southwest of Van Horn, Texas and encompasses many different vegetation communities, including juniper-oak habitats of arroyo and canyon systems. The purpose of this study was to document the bird species utilizing these isolated areas, record mating and nesting in the summer, especially if using the oak or juniper as nest plants, get a snapshot of migrating, wintering, and summer breeding bird arrival and departure dates, and better characterize the vegetation communities. We hypothesized that habitats containing both juniper and oak species would contain more bird species richness and diversity than other oak, juniper or thorn-scrub communities. Plant surveys were conducted to calculate shrub and tree percent occurrences, and to document the presence-absence of flower-herbs, cacti, grasses, ferns, spike-mosses, agaves, and vines. Bird surveys were conducted from June 2016 to December 2017 in 4 randomly rotated sites containing these different vegetation communities from 0600-0900 for 30 minutes bi-weekly. Bird species, relative abundance, mating and nesting incidents, nest plants, photographs of nests were collected, and species richness data analyzed for differences in season and bird range category (summer breeding, migrating, wintering, year-round) between each site. Plant surveys indicated that the oak and juniper sites contained large percentages of Parthenium incanum, Viguiera stenoloba, Tequilia greggii or Acacia constricta shrubs, and large percentages of Quercus pungens, Juniperus coahuilensis, or small Forestiera pubescens trees. The data from the juniper and oak communities, including the flower/herb species found, indicated that these vegetation communities could be classified as Madrean Oriental Chaparral and Apacherian-Chihuahuan Mesquite Upland Scrub of the general shrubland ecosystem. We found 64 bird species total, and analysis indicated there were no significant differences in bird species richness by site overall (p > 0.50), in any season (p = 0.27), or by bird range category (p = 0.43), however, we did document several migrating, wintering, and summer breeding birds using the oak and juniper sites that were not documented using the desert thorn-scrub community. The juniper-oak community contained the most avian diversity and the thorn-scrub community had the least. We also documented Zenaida macroura using only Quercus pungens as a nest plant, with evidence of use in prior years, and Archilochus alexandri using Juniperus coahuilensis, both species not documented doing so in the past. Two winter range birds, Zonotrichia albicollis and Pipilo chlorurus, were found occupying the sites year-round, and Micrathene whitneyi was documented in pairs and groups of 3 using the juniper habitat in the summer and fall of 2016 and 2017, an owl that is not shown to have a range in far west Texas, but of which there is growing evidence for across all of the Trans-Pecos region. Chordeiles minor was also documented using an oak-juniper arroyo system, and no other habitat, in high relative abundance for one summer, an observation that warrants further research in habitat preference for mating and breeding in the Trans-Pecos region, and the trends in abiotic conditions determining these patterns of use. Comparison to the previous bird study on IMRS of the cattle tanks and permanent spring yielded many similarities in year-round birds, but major differences in species of more riparian oriented birds and rare migrants, as expected. This study provided a better understanding of the life history of several bird species, a clearer understanding of the plant species present in the habitats, potential updates to the range maps for particular birds, and an even better understanding of how birds use post-grazed ranchlands in the region.
Garza, Kayla Rochelle, "Birds and Vegetation Structure of Isolated Juniper and Oak Communities in the Trans-Pecos Chihuahuan Desert" (2018). ETD Collection for University of Texas, El Paso. AAI10815738.