The Golden-cheeked Warbler (Dendroica chrysoparia) is a federally endangered migratory passerine that has its breeding range contained within the range of Ashe juniper (Juniperus Ashei) on the Edward’s Plateau of central Texas. Its listing as endangered in 1991 was a result of the rapid degradation and increasing fragmentation of habitat, causing a decline in their population (Benson 1990). Pulich (1976) estimated the breeding population to be approximately 14,950 birds. Wahl, Diamond, and Shaw (1990) believed that their estimation of 4,822 to 16,016 breeding pairs was “unrealistically” high. As of 1995, the species was believed to breed in at least 24 central Texas counties, a reduction of 23% since 1976 (31 counties; Pulich 1976; U.S. Fish and Wildlife Service [USFWS] 1996).
The species is entirely dependent upon the mature Ashe juniper forests of central Texas for its nesting and foraging substrates. The species builds its nests almost entirely from shredded juniper bark at a height of 4 to 5 meters, most commonly in Ashe juniper and occasionally in hardwoods common to the region (e.g., live oak, Texas oak; Pulich 1976). Only mature Ashe juniper trees shred their bark, limiting the Golden-cheeked Warbler to forests with a high proportion of juniper trees older than 40 to 50 years (Pulich 1976). Warblers, however, rarely exist in stands of pure juniper, as they also require hardwoods for foraging substrate. Early in the season, they forage most frequently in deciduous hardwood trees, primarily oaks, then switch to juniper as a principal foraging substrate later in the season (Beardmore 1994). For a more detailed description of the Golden-cheeked Warbler and its habitat, see Pulich (1976).
Fort Hood, Texas is located partially in both Bell and Coryell counties in east central Texas. Vegetative cover on the installation varies with slope, aspect, moisture, and previous use (e.g., cattle grazing and military activities), and consists of grassland, open savannah, hardwood thickets, and dense juniper-oak stands. For a more detailed habitat description of Fort Hood, see Tazik and Cornelius, 1993. Within its 87,890 hectares (ha) is approximately 16,000 ha of Golden-cheeked Warbler habitat.
The Golden-cheeked Warbler was listed as endangered in 1991 under the Endangered Species Act (ESA) of 1973, as amended. To assist in conservation and recovery of the Golden-cheeked Warbler and comply with the ESA, environmental managers need information on the demographic parameters of the population on Fort Hood. In 1991, these demographics were not available.
Quality and amount of warbler habitat appeared stable on Fort Hood between 1991 and 1995 (Figure 1). However, in February of 1996, a large wildfire destroyed approximately 4,300 ha (25%) of warbler habitat, mostly in the northern and northeastern sections of Fort Hood (Figure 2). A separate study was initiated to investigate the effects of this fire on warbler return rates and dispersal distance; males affected by the fire were not reported in this paper, and their numbers were not used in analyses of return rate or dispersal distance.
Figure 1. Map of Fort Hood, TX, showing approximate extent of Golden-cheeked Warbler habitat, including areas burned in February 1996. (1 cm ~ 2,900 meters.)
Figure 2. Map of Fort Hood, TX, showing approximate locations of intensive study area (ISA) and areas burned in February 1996 fire. (1 cm ~ 3,100 m.)
The objectives of this work were to determine and document (1) demographic parameters (return rates, dispersal distances, productivity, and mated status) affecting population status and (2) occurrence of the Golden-cheeked Warbler on Fort Hood, Texas.
Research on the Golden-cheeked Warblers was conducted on Fort Hood, Texas between 1991 and 1996. Landsat MSS data were integrated with a Geographic Information System (GIS) application, Geographic Resources Analysis Support System (GRASS), to suggest potential warbler habitat. Researchers then surveyed these areas, documenting the presence or absence of habitat, and numbers of birds seen or heard. Researchers also established an intensive study area in 1991, banding Golden-cheeked Warblers, and determining territory, mated status, and productivity. The research work consisted of systematically surveying possible Golden-cheeked Warbler habitat, color-banding adults, and monitoring an intensive study area to determine species productivity. Data from these studies were compiled and analyzed, and recommendations were made regarding the monitoring and management of the Golden-cheeked Warbler population on Fort Hood, Texas. Study methods are described in Chapter 2 of this report and in Hayden, JettJ, and Weinberg (in prep.).
This research contributes to a fundamental understanding of the ecology of the endangered Golden-cheeked Warbler, and serves as an example of a proactive approach to endangered species management on Army lands. This and other related reports are being transmitted to military, land, and wildlife managers at Fort Hood, TX; Headquarters, U.S. Army Forces Command (HQ FORSCOM); and the Department of the Army for use in ESA compliance efforts.