Use of Broad-scale data to assess changes of scaled quail populations in Texas

Date

2000-08

Journal Title

Journal ISSN

Volume Title

Publisher

Texas Tech University

Abstract

Scaled quail {Callipepla squamata) is an upland species that has declined in areas of historical distribution in Texas. Potential causes for the present decline have been attributed to precipitation and changes in landscape characteristics. The effects of long-term landscape modification, precipitation variation, and scaled quail populations were evaluated using a Geographic Information System (GIS). Three databases were included in the construction of the GIS. The first database included records for precipitation for the state of Texas from 1968 through 1997. The second database consisted of Multispectral Scanner (MSS) satellite images for the state of Texas obtained during 1973, 1986, and 1991 to determine land use and land cover changes. Finally, the third database consisted of annual records for scaled quail population in Texas from 1968 through 1997. The objective of this project was to evaluate the use of broad-scale data to describe local reduction of scaled quail densities in Texas due to (1) changes in suitable habitat; (2) temporal precipitation variation; and (3) the combined effect of long-term habitat modifications and temporal climatic variation.

The temporal distribution of precipitation was studied for two main rainy seasons, corresponding to the months of April-June (first rainy season) and July-September (second rainy season). Temporal precipitation variability and scaled quail population trends were analyzed using cross-spectral analysis for time series to determine whether or not these series were correlated. Scaled quail data were obtained from Breeding Bird Survey records for the 1968-1997 period. Long-linear models were used to determine scaled quail population trends at individual Breeding Bird Survey routes, ecoregions, and the area of scaled quail distribution in Texas. Two ecoregions were not included in the analysis due to the lack of data. A landscape gradient including rangelands, cultivated lands, water bodies, and urban areas was created to determine changes in suitable habitat during 1973, 1986, and 1991. Scaled quail population densities were compared at state, ecoregion, and Breeding Bird Survey route.

Analysis of the temporal distribution of climatic parameters suggested the presence of annual trends plus lag-times that varied from 2 to 11 years; however, most sites presented periods ranging between 2 to 3 years. The use of cross-spectral analysis suggested that scaled quail populations in the Basin and Range and the Rolling Plains ecoregions were cross-correlated with precipitation. The Rio Grande Plain and the Texas High Plains ecoregions did not present strong correlations between scaled quail and either rainy season.

Multiple regression indicated that changes in precipitation explained changes in scaled quail for ecoregions were the species is distributed; however, only the Basin and Range ecoregion presented statistically significant slopes. The combined effect of precipitation and vegetation did not explain changes in scaled quail populations in the Texas High Plains ecoregion. The combination of vegetation and precipitation influenced scaled quail only in the Rolling Plains but the slopes were not statistically significant.

The lack of complete scaled quail records presented a big problem in the analysis of the population trends for the complete distributional range of the species. However, it provided a potential tool to determine changes at the ecoregion level. To develop state- wide management plans for scaled quail populations in Texas, the first step was to develop complete data sets.

Scaled quail populations generally have declined in the past 3 decades. This negative trend may have been influenced by the combination of the temporal and spatial distribution of climatic parameters and habitat modification, however the lack of a strong data set may weaken results making them inconclusive and contradictory. The methodology used in this research provided alternatives to handle missing values and the presence of potential lag-effects in the data. These techniques in combination with more complete databases may provide, in the future better estimations of the relationships between scaled quail and long-term habitat modifications at different scales. Also the use of GIS allowed the integration of large databases to aid in the analysis of potential causes for scaled quail decline in the state of Texas. This approach may also provide the tools for management of other species.

Description

Keywords

Habitat (Ecology), Quails, Animal populations, Biogeography, Wildlife monitoring -- Texas

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