Wild Basin Nature Preserve is host to several research projects this summer. I had the opportunity to interview one of the researchers and accompany him on a hike. Darrell Hutchinson, is a biologist working for the City of Austin to map the demographics of the Golden-cheeked Warbler at Wild Basin as well as the rest of the Balcones Canyonland Preserve (BCP). The main point of this research is to find out just how many nests there were this year versus the previous seasons. Wild Basin is one of few protected areas for the Golden-cheeked Warbler (GCWA) and part of Darrell’s research is to determine how sustainable the Golden-cheek population is on the BCP. Some of the questions that Darrell and the other biologists ask are: How many Golden-Cheek Warblers do we have? How successful are they at breeding? How many nests are there and how many young do they produce? How many are coming back?
Darrell told me that the main purpose of this research is to inform management decisions on what is happening to the GCWAs in this area. “The issue is that if we don’t have enough land we need to make sure we are doing the best we can.” We need data to ensure that the GCWAs are being taken care of as they should. We want to know all that we can. The study plots that the biologists use include parts of Wild Basin and the nearby Vireo Preserve, as well as other preserves within the larger 30,000 acres of the BCP. This covers a huge area and quite a bit of it is not accessible to the public, either because it is too dangerous or because these areas are privately owned. GCWAs like lower areas, the drainages and valleys as opposed to higher up areas near the tops of the hills. Because of this it is more difficult to find the GCWA and their potential nests without trekking down into the wilderness.
Another aspect of working as a biologist on the survey is identifying and banding individual males. If an un-banded male establishes a territory in the plot, Darrell assists the other researchers in setting up a mist net. Once the net is in place, the researchers play tape recordings of a male GCWA singing in order to lure the target male into the net. Once captured, they place a unique combination of color bands on its legs. After banding it, they watch the newly banded male find a female and observe them nesting to find out the fate of nest. There are a lot of colored bands that can be combined to identify different birds. A male could have red, mauve and silver bands, and would therefore be able to be seen as different from a male that had blue, orange and pink bands. The researchers input this information into a database so that they can keep track of which male is where, if he comes back year after year, where he might come back to, and how many fledglings the male produced year, etc.
The male GCWA arrive before the females in March. Dominant males defend their females against other males. By following the male you can find the nest. The nest can then be monitored to see the females and to find out fate of the nest. The fate of the nest is either failed or successful. If it successfully fledges, Darrell and the other researchers count the number of fledglings to quantify the reproductive rate. Sometimes nests can be abandoned while the birds are building it and other times they are left after having been predated by a predator. The most common predators of GCWA in this area are Rat snakes and jays. Rat snakes use taste, or chemo receptors, to find the nest, go up the tree and eat the eggs or young nestlings. Jays are known to patrol and predate other birds’ nests.
Darrell found one nest during incubation and said that most times you “Have to be fortunate and lucky to find it.” The nestling period is generally 10 – 12 days and it is important to get the young out of nest and learn to fly. When they fledge (come out of the nest) Darrell and the other biologists monitor the fledglings and the parents. GCWA never reuse a nest but they might steal material from the previous year’s nest. Fledglings grow quickly from one or two days to a month and change drastically in appearance. They are still with parents and, because they are fairly conspicuous, it is easy to use fledglings to determine if a nest was successful. Darrell also does a vegetation survey around the tree, the canopy and undergrowth to find out trends regarding the nests/areas that are successful and areas that are not.
This season, Darrell only found one nest at Wild Basin but another researcher found a second nest on the border of the Vireo preserve. Last year there were also two nests found. The number of mating pairs is about the same as last year – four or five pairs at Wild Basin, however, only two of them were successful this season:
-The first male that Darrell watched is nicknamed “Woody” because his territory is near the Woodland Trail in Wild Basin. Woody had a nest with three nestlings this season. This shows that the fate of the nest was successful.
-Another male that Darrell watched is called “Candy” because of his mauve, silver, and white bands. His nest was never found but he had four fledglings and is therefore determined successful.
Woody and Candy were both banded in 2011 and they both came back to the same territory, this is known as site fidelity. There are no bands on females as they are harder to catch. Also the females switch mates sometimes and they don’t always come back to the same place or the same male, whereas these three males all came back to their same territories. All of this data plays into the return rates. From the 2011-12 seasons there were more returns at Wild Basin, but from the 2012-13 seasons there were less. What this shows is kind of a prediction. How successful is this regional population? Is it increasing or decreasing? How vulnerable are they? What is the rate of reproduction? We don’t know what happens to fledglings after they leave with their parents, they are too young to be banded until their first year back. Darrell says that, based off the data he and the other biologists have, “We think that birds in Wild Basin are subject to strong predation pressures.”
Wild Basin may have a higher rate of failed and unsuccessful nests compared to other areas within the BCP, but this data is still incomplete. Land management on all the tracts of the BCP will be made aware of this data and may include planting more juniper or oak trees or reducing predators. Two of the main predators of GCWA are blue Jays and scrub jays. Blue jays are an eastern species and have recently been expanding in great numbers into the Central Texas area due to rapid development in West Lake Hills. This influx of new homes provides more bird feeders for the jays to feed from. If the data can prove that Jays, along with other creatures, are preying upon the GCWA nests, then land management can think of ways to deter the predators.
It is important to understand how endangered the GCWA are and why this area of the world is pertinent to their continued existence. They are endemic to this region and nest nowhere else in the world. They are dependent on Central Texas because of the juniper-oak woodlands which they use to build their nests and get insects from to feed their young. Hopefully, the data that Darrell and the other biologists have collected will prove helpful for the small population of GCWA in the Central Texas area. Perhaps we may even see a rise in the amount of mating pairs and nests in Wild Basin within the next couple of years.
-Anna Hall, Intern at Wild Basin Creative Research Center
English Writing and Rhetoric, Class of 2014
The Write Way TX 