Four grassland types on Holloman Air Force Base (HAFB), New Mexico were studied from September 2007 to October 2008 and from May 2009 to September 2010 to assess the avian population status and the importance of the habitat for neotropical migrant bird species. These grasslands included Alkaline Sacaton, Four-wing Saltbush Alkaline Sacaton, Four-wing Saltbush Gyp Dropseed, and Gyp Dropseed Gyp Grama.
Because this study involved multiple bird groups, a multi-method approach was designed to respond to the information needs. The surveys included 0.5 kilometer randomized line transects, driven routes, and mist net stations. The line transects and driven routes were implemented monthly, and the mist netting was conducted during the spring and fall migration months of April, May, September, and October.
During 2009/2010, seventy one species were detected during transect surveys. An additional 17 species were recorded during driven routes, and 23 additional species were recorded during the mist netting operation. The 2009/2010 bird inventory list was therefore 111 species. Including the 2007/2008 surveys, the total bird inventory was 118 bird species occurring in the HAFB grasslands.
All of the collected information was organized in a database of bird species per grassland type. Each habitat type was associated with a detailed bird list and relative bird abundance index per square hectare per season of the year. Density and diversity indexes were produced per species and by season for each grassland habitat to be used as indices of species richness, habitat associations, and to estimate population size. A total of 10 species of Falconiformes and 49 species of Passeriformes were analyzed because of their relevance to the HAFB grasslands, high density, and seasonal occurrence.
The 2009/2010 data showed birds preference for the Four-wing Saltbush Alkaline Sacaton grassland. The migration seasons were the most diverse in all four grasslands on HAFB. Bird density during the winter was highest in the Four-wing Saltbush Gyp Dropseed grassland. During the spring, bird density was highest in the Alkaline Sacaton grassland. During both the summer and the fall, bird density was highest in the Four-wing Saltbush Alkaline Sacaton grassland.
Mist net stations were also utilized to collect additional information on the physical condition of birds and to evaluate the grassland habitat. Body fat measurements and migration cues were analyzed. During the 2007/2008 study period, a total of 208 birds were captured during the spring (n=61) and during the fall (n=147) migration periods of 35 different species. During the 2009/2010 study period, a total of 1236 birds of 68 different species were captured during the fall 2009 (n=910), spring 2010 (n=133), and fall 2010 (n=193) migration periods.
Thank you to Bob Basile for the wonderful photos!