Progress 10/01/00 to 09/30/05

Outputs
We completed two of four winters of seed manipulation trials to examine the effects of seed size, diversity and nutrient content on site selection and diet of wintering sparrows. In the winter of 2003/2004, when avian diversity was low, we detected a significant treatment effect with the highest avian abundance on plots with 40 kg of sand dropseed whereas in 2004/2005, when avian diversity was higher, there was a significant treatment effect with the highest avian abundance on plots with 40 kg of the 5-seed mixture. Over both years, we observed the number of birds on plots increased over the winter period. In 2005 I initiated a study examining the effects grazing on seed production in dropseed grasslands. Dropseed grasslands were selected because in other studies, we found this seed type to be an important component of avian diets. This study is set up on the Fort Bliss Military Reservation, southeast of Las Cruces, NM. I selected 4 study areas based on grazing practices, accessibility and vegetation composition. Two grazing exclosures (625 m2) on each of the 4 sites have been installed. Each exclosure is paired with a grazed plot of similar size. A permanent automatic rain gauge has been installed in each of the 4 study areas. Transects measuring vegetation composition and structure were conducted in early August. Beginning in mid August, a 5x4 grid of seed traps was established in each plot to measure seed production. Seed traps are emptied every 2 weeks until the end of January and contents are stored in manila envelopes. Seeds will be sorted, identified and examined in relation to plant species composition, cover, and soil characteristics. We have completed two of five years of research examining the effects of desertification on nonbreeding grassland birds including minimum patch size requirements for site occupancy, effects of the surrounding landscape matrix on site occupancy, and within patch characteristics, including levels of shrub encroachment within 27 grassland patches (9 black grama, 9 dropseed and 9 tobosa) on the Jornada Long Term Ecological Research Site and Chihuahuan Desert Rangeland Research Center in southern NM. Preliminary results indicate that grassland species as a guild during migration and the winter were most consistently associated with a negative response to shrub encroachment. Responses to other variables, grass cover, grass height and patch size, were not consistent and depended on the season and dominant avian species. The shrub-adapted guild was strongly associated with shrub encroachment and the interaction between patch size and shrub encroachment. The influence of shrub encroachment on the shrub-adapted guild varied and depended on season and the dominant species, indicating that levels of shrub encroachment may surpass threshold levels preferred by even some shrub-adapted birds such as black throated (Amphispiza bilineata) and sage sparrows (Amphispiza belli). Other variables that influenced the shrub-adapted guild were patch size and grass cover. Additional years of data collection will be necessary to examine effects on individual species and identify thresholds for patch size and shrub encroachment.

Impacts
As a result of this project we will be better able to sustainably manage our native vertebrate fauna and desert grasslands. Data collected for this project can also help alleviate future entanglements related to the management needs and status of specific species. It will also contribute to enhanced wildlife viewing.

Publications

• Ginter, D. and M. J. Desmond. 2005. Site fidelity and movement patterns of wintering savannah sparrows on North Padre Island, Texas. Wilson Bulletin 117: 63-71.
• Haan, S. S. and M. J. Desmond. 2005. Effectiveness of 3 capture methods for a terrestrial salamander, Anedies hardii. Herpetological Review 36:143-145.
• Mason, L., M. J. Desmond and M. Agudelo. 2005. Influence of grassland type, nest type and shrub encroachment on predation of artificial nests in Chihuahuan Desert grasslands. Western North American Naturalist 65:196-201.
• Desmond, M. J., K. Young, B. Thompson, R. Valdez and A. Lafon Terrazas. 2005. Habitat associations and conservation of grassland birds in the Chihuahuan Desert Region: two case studies in Chihuahua Mexico. Chapter 22 in J.-L. E. Carton, G. Ceballos and R. S. Felger, eds. Biodiversity, Ecosystems and Conservation in Northern Mexico. Oxford University Press, New York.

Progress 01/01/04 to 12/31/04

Outputs
We sampled the diets of 610 sparrows of six species through stomach and crop regurgitation, and found approximately 80 seed species in their diets in southwestern New Mexico. Although these birds had diverse diets, 79% of their diet consisted of six seed species, Eragrostis cilianensis (stink grass), Panicum spp., Amaranthus palmeri (pigweed), Mollugo vesticilata (carpet weed), Chloris virgata (showy chloris), and Sporobolus cryptandrus (sand dropseed). We are currently in the process of separating seeds from soil samples to compare avian diet with seed availability in their foraging areas. We completed our first winter of seed manipulation trials and are in the process of collecting data for the second winter. We have established 30 plots with 4 treatments of seed manipulations and controls to examine the effects of seed size, diversity and nutrient content on site selection and diet of wintering sparrows. Complete sets of treatments are blocked according to within pasture variation in vegetation. Monsoonal summer precipitation in 2003 was well below normal resulting in little natural seed production and low avian abundance and diversity during the winter of 2003/2004. Unlike other winters, only one dominant species was present on plots that winter, horned larks (Eremophila alpestris). Birds responded well to our treatments. There was no detectable blocking effect however, we detected a significant treatment effect with the highest avian abundance on plots with 40 kg of sand dropseed (Repeated measures ANOVA: F = 3.254, df = 29, P = 0.041). Interestingly we observed the number of birds on plots increased over the winter period. Due to high summer monsoonal precipitation in 2004, we expect to have a more diverse avian community on our plots during the winter of 2004/2005. In 2003 we established 27 grassland plots (9 black grama, 9 dropseed and 9 tobosa) on the Jornada Long Term Ecological Research Site and Chihuahuan Desert Rangeland Research Center in southern New Mexico to examine minimum patch size requirements for site occupancy of grassland species, effects of the surrounding landscape matrix on site occupancy and within patch characteristics, including levels of shrub encroachment. This is a long-term study in its second year of data collection. Preliminary results indicate that grassland species as a guild during migration and the winter period respond negatively to shrub encroachment and positively to the amount of grass cover and the interaction between grass cover and grass height. As a guild, shrub-adapted birds responded positively to shrub encroachment, the percent grass cover and the variability in vegetative cover. This guild also responded positively to the interaction between grass cover and shrub cover and shrub cover and grassland type. Additional years of data collection will be necessary to examine effects on individual species and to identify thresholds for patch size and shrub encroachment.

Impacts
As a result of this project we will be better able to sustainably manage our native vertebrate fauna and desert grasslands. Data collected for this project can also help alleviate future entanglements related to the management needs and status of specific species. It will also contribute to enhanced wildlife viewing.

Publications

• Ginter, D, and M. J. Desmond. 2004. Avian mortality during fall migration at communication towers along the Rio Grande corridor in southern New Mexico. Southwestern Naturalist 49(3):414-417.
• Desmond, M. J. 2004. Habitat Associations and Co-occurrence of Chihuahuan Desert Hares: Lepus californicus and L. callotis in Chihuahua, Mexico. American Midland Naturalist. 151:414-419
• Desmond, M. J. 2004. Effects of grazing practices and fossorial rodents of a winter avian community in Chihuahua, Mexico. Biological Conservation 116 (2): 235-242.

Progress 01/01/03 to 12/31/03

Outputs
This research addresses the effects of desertification on wintering and migratory grassland birds in the Chihuahuan Desert. Grassland bird populations are declining throughout North America and many species winter in Chihuahuan Desert grasslands. Grasslands in the northern Chihuahuan Desert are being lost to desertification as shrubs (primarily mesquite) expand into areas of former grassland. This research examines how the desertification process has impacted the avian community. Many studies have examined the impact of habitat fragmentation on breeding grassland bird populations, but this issue has not been addressed on migration and wintering grounds. This research is also addressing how the seed crop, including abundance and diversity influences the winter avian community and is examining factors during the spring and summer that influence the seed crop and the nutrient content of seeds.

Impacts
We will have a better understanding of the distribution and ecology of vertebrate fauna native to this region, including permanent resident species and seasonal migrants, and an understanding of the effects of desertification on avian taxa particularly during the non-breeding period. As a result of this project we will be better able to sustainably manage our native vertebrate fauna. Data collected for this project can also help alleviate future entanglements related to the management needs and status of specific species.

Publications

• No publications reported this period

Progress 01/01/02 to 12/31/02

Outputs
This fall I brought three new graduate students into my research program. The projects that these students will focus on include (1) the spatial distribution of breeding burrowing owls in Janos, Chihuahua, Mexico, (2) the influence of habitat fragmentation on wintering grassland birds in southern New Mexico and (3) Effects of three different forest thinning practices on Sacramento Mountain Salamander populations. One Ph.D. project (Influence of resource manipulations on winter avian abundance, diversity and community dynamics in Chihuahuan Desert grasslands) is beginning its first field season in southwestern New Mexico. One of my students received his M.S. this past year and we have submitted two manuscripts from his research for publication (Influences of seed distribution on a wintering Chihuahuan Desert avifauna and Habitat associations of a winter Chihuahuan Desert avifauna: influence of vegetation structure and floristic composition). One other student will finish her M.S. during the spring of 2003 on burrowing owl nesting strategies in urban and grassland habitats in southern New Mexico. I have a book chapter in press (Avian diversity and conservation in Chihuahuan Desert grasslands of Northern Mexico: Case studies of passerine and raptor communities in Chihuahua), published one manuscript (The first nesting record of mountain plovers (Charadius montanus) in northeast Mexico) and submitted 2 manuscripts for journal review (Effects of grazing practices and fossorial rodents on the wintering avian community in Chihuahua, Mexico: implications for grazing management and conservation and Avian use of agricultural hedgerows during winter in northern Mexico).

Impacts
We will have a better understanding of the distribution and ecology of vertebrate fauna native to this region, including permanent resident species and seasonal migrants. As a result of this project we will be better able to sustainably manage our native vertebrate fauna. Data collected for this project can also help alleviate future entanglements related to the management needs and status of specific species. The potential economic impacts of this project are that state, federal and private land managers can benefit from the presence of sustainable wildlife populations through fee hunting and recreational wildlife viewing.

Publications

• Desmond, M.J. and F. Chavez-Ramirez. 2002. The first nesting record of mountain plovers (Charadius montanus) in northeast Mexico. Cotinga 17:17-19.

Progress 01/01/01 to 12/31/01

Outputs
Vegetation structure, composition and seed abundance, distribution, and diversity was significantly associated with wintering Chihuahuan Desert avian communities. Seed abundance influenced avian abundance and group composition. Abundance of mesquite had the strongest influence on bird community structure with a positive influence on shrub-adapted birds and a negative influence on grassland species. This has important implications as desert grasslands continue to be lost due to shrub encroachment in the Chihuahuan Desert. Seed type and abundance was associated with specific avian species indicating structuring of populations within the grassland and shrub systems. Urban nesting burrowing owls in Las Cruces, New Mexico were associated with rock squirrel burrows and human made cavities. Burrowing owls in grasslands were associated with reestablished black-tailed prairie dog colonies. No difference was found between reproductive success in urban and grassland habitats, however, different factors contributed to nesting success. Spacing between nests differed significantly between habitats with nests in prairie dog colonies significantly closer together and this negatively influenced reproduction. As these colonies expand, distance between nests should increase. Reproductive success in urban areas was positively related to the number of nesting pairs suggesting that owls benefit from the presence of other owls. Over this past year I have initiated 3 new projects related to winter and migratory ecology of grassland and shrubland birds. These projects include wintering grassland birds in coastal grasslands of southeast Texas and Tamualipas Mexico, migratory ecology of grassland and shrub-adapted birds in south central New Mexico and influence of fire and grazing on wintering grassland birds in southwest New Mexico and northern Mexico.

Impacts
We will have a better understanding of the distribution and ecology of vertebrate fauna (especially avifauna) native to this region, including permanent resident species and seasonal migrants. As a result of this project we will be better able to sustainably manage our native vertebrate fauna. Data collected for this project can also help alleviate future entanglements related to the management needs and status of specific species.

Publications

• Desmond, M. J., T. J. Parsons, T.O. Powers and J. A. Savidge. 2001. An initial examination of mitochondrial DNA structure in burrowing owl populations. Journal of Raptor Research 35(4)274-281.

Progress 01/01/00 to 12/31/00

Outputs
Chihuahuan desert grasslands are important habitat for a diversity of wildlife species, particularly grassland birds. In Chihuahua, Mexico, avian diversity was positively associated with grassland height, vegetative structure, black-tailed prairie dog density and shrub density and negatively associated with overgrazed sites. Avian abundance was highest in open grasslands that had large numbers of flocking species but negatively associated with overgrazed areas and banner-tailed kangaroo rats. Banner-tailed kangaroo rats may compete for seeds. Abundance of secretive species associated with open grasslands was positively associated with height and structure of the vegetation and negatively associated with shrub density. Unlike Chihuahua, Mexico avian abundance was positively related to the structural complexity of the vegetation. This difference may be related to the large numbers of flocking species found in Mexico and availability of suitable habitat. Similar to Mexico, avian richness in New Mexico was positively related to the structural characteristics of the vegetation. The most common species on the New Mexico sites were the Brewer's sparrow and the sage sparrow. None of the variables measured contributed to Brewer's sparrow abundance; however, sage sparrow abundance was strongly correlated with the height of the grass and the number of shrubs. Burrowing owls are a species of concern throughout much of the western United States. They nest in a variety of burrow types primarily in grasslands but are also associated with shrub habitats and disturbed areas. Urban populations in Las Cruces, New Mexico were associated with rock squirrel burrows and human-made cavities. Burrowing owls in grasslands were associated with recently established black-tailed prairie dog colonies. No difference was found between reproductive success in urban and grassland habitats; however, different factors affected reproductive success in the two habitats. Spacing between nests differed significantly between areas (urban = 155 m and grassland = 65 m). Nests in prairie dog colonies were significantly closer together and this negatively influenced reproduction. As these colonies expand, distance between nests should increase. Owls nesting in urban habitats exhibited spacing similar to the literature. Reproductive success in urban areas was positively related to the number of nesting pairs suggesting that owls benefit from the presence of other owls.

Impacts
Grassland condition (including grass height and vegetative structure) are important factors influencing the diversity and abundance of wintering grassland birds in the southwestern United States and Northern Mexico. Heavy overgrazing that influences the structural characteristics of grasslands will have a negative impact on avian species reducing both diversity and abundance. Maintaining sustainable populations of birds and other wildlife in these grassland habitats are valuable interms of fee hunting and recreational wildlife viewing.

Publications

• Desmond, M. J. and J. A. Savidge. 2000. Correlations between burrowing owl and black-tailed prairie dog declines: a 7-year analysis. Journal of Wildlife Management 64: 1067-1075.