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Relations of aquatic bird species, irrigation systems, water reservoirs and natural areas in the Lower Rio Grande Basin: A spatial explicit simulation.

Weir, Dr. Enrique*,1, Wilkins, Dr. Neal1, Gil-Weir, MSc. Karine1, 1 Texas A&M University, 210 Nagle Hall, 2258 TAMU, College Station, Texas, USA

ABSTRACT- Alteration of water quantity and river flow regimes associated with water management has caused declines of aquatic birds. Habitat alteration has produced declines of many breeding birds in the LRGV of Texas during the 20th century. The dams and floods control projects, for example, have eliminated a significant source of fresh water input into the wetlands of the Rio Grande Delta and they have affected riparian plants and breeding bird community. The objective of this study is to evaluate several scenarios of water management in the LRGV irrigation system and wetlands areas on diving birds and shorebirds. We developed, in Visual Basic Net, a spatially explicit simulation model to describe temporal patterns in water use and aquatic bird over time. We used geo-referenced data on water bodies, refuges and canals from TNRIS (2002) and Flahive and Fipps (2002) in the simulation model. We also used in the model aquatic bird abundance data (diving piscivorous guild and shorebird guild) from the North American Breeding Bird Surveys (USGS, Patuxent Wildlife Research Center, 2003), Audubon Christmas Bird Counts (CBC, Audubon Society, 2004) and from Weinwright(1998). We spatially joined data bases in ArcGIS 9.0, generated maps overlaying diving bird and shorebirds abundance on the irrigation systems, resacas, and wetlands in the wildlife refuges in the LRGV. We then (non-spatially) correlated aquatic bird abundance with the area of irrigation canal, resacas and wetlands of wildlife refuges using the statistical program SPSS 11.0. The canal area was estimated through the product between the length of canals and the width of canal. Abundance of aquatic birds based on the NABBS transects and the CBC circles was correlated positively (p < 0.0005) with the area of canals, resacas, and wetlands. Abundance of diving bird species and shore bird species were correlated positively (p<0.007 and p<0.031, respectively) with the area of water bodies. The influence of wetland size on abundance of aquatic bird, diving birds and shore birds were reflected in a Linear Regression (Log-transformed). Results of this simulation indicate that reducing area of canals and water of resacas decreases the distribution and abundance of diving birds and shorebirds,and decreasing wetlands area decreases the abundance of diving birds and shorebirds associated.

Key words: Diving birds and shorebirds, Abundance, LRGV irrigation system, Water availability

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