Endangered and Threatened Species in the Rio Grande Basin
By Danielle Supercinski, Enrique Weir, and Karine Gil de Weir, October 2005
Contact: Neal Wilkins
Researchers in the Texas A&M Wildlife and Fisheries Sciences department have studied the habits of aquatic birds in an attempt to predict the changes in the abundance and richness of wildlife in the Rio Grande Basin, relative to water availability.
The abundance of aquatic birds has been decreasing in the Rio Grande Basin since 1969. Therefore, the need for an easily accessible reference to scientific information on aquatic birds and other wildlife in the Rio Grande Basin is important to keep track of such changes. A searchable database needed to be developed to help planners, students and researchers rapidly access and review scientific literature on ecology, management, conservation, and ecological models of species considered to be endangered and threatened.
In 2002 Associate Department Head Dr. Neal Wilkins and PhD candidate Karine Gil de Weir developed an Endangered and Threatened Species in the Rio Grande database CD providing a list and description of invertebrates, amphibians, reptiles, fish, birds, mammals and plants endemic to the Basin. A meticulous review was conducted of all species on the lists of endangered and threatened species for Texas, New Mexico and Colorado, and in some states in Mexico. Then, using the database and electronic journals at Texas A&M University, abstracts and references were found from 1972 to September 2002. The largest number of abstracts and references found were for aquatic birds. At present, 181 animal and plant species are represented in the database and more than 402 scientific publications annotated. This reference should provide a valuable resource for scientists working in the Rio Grande Basin.
Once the database was established it became clear that a simulation model was needed to assess how different actual or potential water availability scenarios might alter the distribution and abundance of aquatic birds in the Lower Rio Grande Valley. Dr. Enrique Weir, visiting scientist from Venezuela, was brought onto the project in 2003 to develop this simulation model, based on the bird community database.
Agriculture and urban development dominate land use in the Valley and their expansion has negatively affected native wildlife. Changes in irrigation water management are one possible cause of the decreasing abundance of aquatic birds. Canals support the aquatic bird community by providing large sources of water. However, to reduce leakage and evaporation from open canals, irrigation districts are installing pipelines. There is concern that changing from open canals to pipelines may restrict water available for aquatic birds.
The background data that was used for modeling the influence of various water management scenarios included aquatic bird surveys from the North American Breeding Bird Survey and a US Fish & Wildlife Service database.
The main research question is: If we change many of the canals to pipelines, what happens to the abundance and richness of species? Are aquatic birds affected by the reduction of water availability in open canals? If so, can we compensate by increasing water availability elsewhere, perhaps by constructing ponds, lagoons, reservoirs and/or resacas? Through this simulation model, we can estimate how many additional water sources would be needed to maintain, or even increase, the abundance and richness of the aquatic bird populations in the future.
Collected data was entered into the model creating several layers of information. Layers include canals, lagoons, wildlife refuges, vegetation areas, species locations and abundance, and other water bodies. For example, the canals layer and species abundance layer can be turned on to determine the abundance of aquatic birds around large canals versus small canals. The model can also represent all water available for wildlife in the area.
This model relates not only to water, but also to terrestrial conditions around canal areas. In the case of unlined canals, the vegetation around the canals can absorb and use the water leaking out, which limits the availability for wildlife. Many other features are available in this simulation model including estimating water availability, displaying canal and pipeline changes, and wildlife areas, to name a few.
Predicting scenario impacts is another major feature available through the simulation model. It represents changes in water availability in irrigation systems, resacas and reservoirs, as well as changes in lagoon areas in wildlife refuges, and changes in distribution, abundance and species richness of aquatic birds in Cameron, Willacy and Hidalgo Counties. For example, scenario impacts can estimate the effect of compensating for a reduction of canals per year with an increase in lagoon areas. Some scenarios to consider could be the effect of zero compensation (a scenario without lagoon compensation), an increase in lagoon areas per year plus the impact of habitat coverage for canals with minimum, mean, or maximum vegetative coverage.
The percentage of water available and the effects it has on the abundance of birds can be shown for years past and simulated for the future. It can predict what would happen to the abundance of birds if a large number of canals were converted to pipelines, based on past and present bird and wildlife abundance.
Weir uses a 2 percent increase rate to simulate the increase of lagoons needed to compensate for the amount of water being lost. If the simulation is extended, and more lagoons are created to compensate for water losses, then bird abundance may increase more over time. Unfortunately, there is not enough information to model the speed of change from canals to pipelines in the future, but the model will allow these changes when that factor is known.
Wildlife refuges now exist in lagoon areas and around other aquatic areas such as resacas and reservoirs. This leads to an increased concentration of bird abundance in lagoon areas than canals because there is more water available in the lagoons. If reservoirs are maintained and we focus on constructing more ponds and lagoons, then we could assure the maintenance of the bird species and wildlife in the area.
The next suggested step in this research area seems to lie in researching and cataloguing all the species of the Rio Grande Basin. Then a catalogue of biodiversity could be developed with information on the research found for each species. In the future, gathering and translating the research collected and developed by researchers in Mexico would be beneficial to add to the database as well.
Funding for this project was provided by the federally funded Rio Grande Basin Initiative, administered by the Texas Water Resources Institute of the Texas A&M University System.
