Wintering Grassland Birds as Bio-Indicators in the Rio Grande Drainage Basin

Several species of grassland birds migrate every year from the northern United States and Canada to spend the winter in the grasslands of the Chihuahuan Desert, a portion of which is located in the Rio Grande Basin.  Native grasslands are a limited and important environmental resource in the Rio Grande drainage basin and are both economically and biologically significant.  We conducted winter bird and vegetation surveys in the states of Texas in the US and Chihuahua in Mexico to determine which birds may be used as indicators of grassland quality, or to describe certain grassland attributes in the region. 

Birds are excellent indicators of the biological integrity of ecological systems and are useful for monitoring changes in these systems because they are directly affected by factors such as ecosystem productivity, vegetation structure and composition, water quality, and landscape integrity. We conducted bird counts along a line transect to obtain bird data, and made a visual estimation of the vegetation every 100 meters of the line transect.  A total of 67 species of birds were recorded and the locations of the birds were compared to the vegetation data to determine the habitat attributes that related positively or negatively to each species of bird.  We also identified the locations that seem to be critical for migratory birds in the region. 

An important species that was considered an indicator of tall grasses and high grass cover was the grasshopper sparrow. The vesper sparrow was also a significant indicator of tall grasses.

The chestnut-collared longspur was an indicator of low shrub cover and high shrub cover were indicated by the Black-throated Sparrow and Pyrrhuloxia.  Lastly, the white horned lark was an indicator of bare ground and short grasses.  The La Perla grasslands in Chihuahua and Marfa grasslands in west Texas were identified as two important areas for wintering grassland birds in the Rio Grande Basin area, and the conservation of these two areas is crucial to keep a natural corridor for migratory grassland birds and other species of wildlife.  The information collected over the course of this study will be helpful in developing land and avian conservation strategies.

groundcover

Visual estimations of groundcover and grass height were recorded to be compared to the presence of certain bird species in each area.

 

aplomado falcon

After a significant decline in the mid 1900’s, Aplomado Falcons have started to make a comeback in the Marfa grasslands and surrounding regions due to re-introduction efforts.  Aplomado falcons rely on open grassland, where they mainly prey on birds and insects.