Our largest preserve, Baker Sanctuary, is 715 acres of ashe-juniper woodland, prime habitat for the endangered Golden-cheeked Warbler and many other species. We manage this land, but we also monitor it to see how bird populations are doing, and elucidate which conservation techniques could lead to better outcomes for species in need.
Below is a summary of the results from two surveys conducted at Baker Sanctuary in 2025: the Sanctuary-wide Breeding Bird Survey and the Golden-cheeked Warbler Survey.
We will continue to conduct both surveys in the years to come. You can support that work by making a donation.
Sanctuary-wide Breeding Bird Survey
Survey period: 5/20 – 6/02
Station count: 38
Survey site: Entire sanctuary
In late spring, our land manager at Baker Sanctuary completed the fifteenth-annual sanctuary-wide Breeding Bird Survey. For two weeks, Chris visited 38 stations across the preserve and did a 10-minute count, looking and listening for birds at each stop; a majority of the IDs were from calls heard by ear. This survey gives us a sense of how bird populations are trending at the preserve.
Not surprisingly, the most abundant species at Baker Sanctuary this year was the Northern Cardinal. The Painted Bunting, Lesser Goldfinch, and Mourning Dove all tied as the second-most abundant species, edging out the Black-crested Titmouse, which was the third-most abundant species.
Linear regression tests were performed on the accumulated 15 years of data in an attempt to detect significant population trends amongst the species over time. Species found to exhibit a significantly negative population trend were the Black-and-white Warbler (BAWW), Great-tailed Grackle, Northern Bobwhite, Northern Mockingbird (NOMO), and Turkey Vulture. Grackles and Bobwhite have never been common at Baker, so that trend is not a surprise, and Turkey Vultures are abundant but tend to be missed in early morning point counts. A bit more worrisome are the trends for BAWW and NOMO.
Chimney Swift, Great Crested Flycatcher, Lesser Goldfinch, Northern Cardinal, Painted Bunting, Red-eyed Vireo, Summer Tanager, White-eyed Vireo, and Yellow-billed Cuckoo exhibited significant positive population trends. The trend for the Golden-cheeked Warbler population was essentially flat. Golden-cheeked Warblers were detected at 21% of the stations.
Any number of things could be contributing to the observed bird declines: loss of wintering habitat, natural population fluctuation, decline in resource quality or quantity, etc. We will carry out this survey again next year and continue to follow land-management best practices that promote biodiversity.
Golden-cheeked Warbler Survey
Survey period: 03/15 – 06/15
Survey site: 97 acres in southwest section of sanctuary
Baker Sanctuary is home to the endangered Golden-cheeked Warbler (GCWA), so we carry out an additional survey for that species every year. This survey was conducted between March and June across a 97-acre plot in the southwest section of the sanctuary. Next year will wrap up the three-year study of this plot and we will move on to another plot in the sanctuary in 2027. A team of seven volunteers and staff completed the survey, using a combination of mist-netting and visual and audio tracking to identify birds. Each year, our land manager Chris attempts to mist-net and color-band all the males on the survey plot so we can delineate their territories and determine how productive their breeding season was.
They recorded 364 GCWA observations, about the same as previous years, indicating that the habitat is as occupied as it typically is. Surveyors identified 15 full territories in the study plot and tracked the number of females and fledglings in each territory to calculate the birds’ breeding success.
The pairing success rate in the Southwest plot was 80% (females were observed in 12 of the 15 full territories). The breeding success was estimated at 33% with five of the 15 full territories producing fledglings. The estimated brood size was 1.8 fledglings. Overall productivity was estimated at 0.6 fledglings per territory based on the total of nine fledglings observed in five of the 15 full territories.
While the 100-acre survey has been performed at Baker since 1999, intensity and methodology have varied enough to make significant comparisons between years problematic. With the onset of color-banding and adoption of a standardized survey protocol beginning in the 2011 season, the results of the subsequent seasonal surveys can cautiously be compared. The comparison is worthwhile to begin to ascertain if certain areas of the sanctuary are more productive than others and, if so, what the possible causes of such a difference could be. Ultimately, the goal is to elucidate management techniques which would increase productivity in areas where it is comparatively lower, if possible.
Results from the 2025 Southwest survey appear to be consistent with results from surveys spanning 2014 – 2024 in most measured parameters, the exception being territory density, breeding success and overall productivity. Territory density in prior surveys has ranged from 0.09 – 0.14 territories/acre (Southwest = 0.16), pairing success 67% – 100% (Southwest = 80%), breeding success 44% – 100% (Southwest = 33%), estimated brood size 1.50 – 3.70 (Southwest = 1.80), and overall productivity 1.00 – 2.80 (Southwest = 0.6).
With a territory density of 0.16 territories/acre, the Southwest plot has demonstrated the highest measured territory density at Baker since surveys were initiated. Further surveys will determine if the result is an outlier or more indicative of the typical density for that area. Even more interesting is the distribution of the territories. While the western half of the plot was saturated with territories, the eastern half of the plot had large swaths of similar habitat in which GCWA were not detected. This distribution could simply be observer bias, or it may indicate a significant difference in habitat quality. One possible explanation, at least for the eastern edge of the plot, is the presence of a swath of degraded habitat which experienced a large degree of tree mortality in the summer of 2011. While the bulk of the degraded habitat is adjacent to the study plot, a tendril does extend well within the plot’s boundary. It is conceivable that the presence of the degraded habitat, the tendril and the bulk to the east, confers a less appealing nature to the adjacent, non-affected habitat for GCWA. Surveys over the next several seasons should offer some illumination to this question.
The measures for breeding success and overall productivity for the 2025 Southwest plot survey were the lowest recorded since the surveys were initiated in 2014. While the cause of these observations is not readily apparent, a contributing factor may have been the unusually hot and dry temperatures witnessed for the months of March and April (combined average for March and April 2025 = 80? F, 2.0 inches; 13-year combined average for March and April = 74? F, 2.75 inches). These conditions may have contributed to a decreased availability of food resources later in the breeding season, potentially causing nests to fail at a higher rate than typical.
On an anecdotal note, throughout the entire breeding season, it seemed the adult GCWA males were singing less frequently and less robustly. While singing usually tapers off in May, for the 2025 season it was not uncommon to hear very few birds singing at any time, including from March through April when typically, they are more vocal.
Findings from the survey will be included in the annual Balcones Canyonlands Preserve report.
Banner photo: Golden-cheeked Warbler by Rich Kostecke
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