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VERNON Land managers on the Texas Rolling Plains should exercise care when applying prescribed burns to control mesquite if promoting wildlife is part of their overall management strategy.
That’s a preliminary conclusion from Dr. Dean Ransom, Texas Agricultural Experiment Station wildlife biologist and assistant professor of wildlife and fisheries sciences.
“We’ve been researching the effect of prescribed burning and herbicide application on bobwhite quail and songbird populations on the Rolling Plains,” Ransom said. “Other researchers here have been studying prescribed burning for mesquite control and management for many years, so we have a perfect natural laboratory in place for our wildlife studies.
“Our long-term goal is to help landowners develop management strategies that keep brush in check, enhance forage production for livestock, and promote sustainable wildlife habitats and populations.”
Rolling Plains landowners and managers typically use a combination of aerial herbicide application and prescribed burning to control honey mesquite. Does this combination pose a risk to fostering bobwhite quail populations?
“Other regions of Texas with stronger bobwhite populations contain more brush diversity than the Rolling Plains,” Ransom said. “Many of the 15 to 20 brush species common in other regions are preferred habitat for bobwhites species such as sand plum, spiny hackberry, some sumacs, lotebush and shinnery oak.
“But honey mesquite, our No. 1 brush species, is a not a great woody plant for bobwhites. When you manipulate honey mesquite by removing its top growth, its regrowth seems to become even more unsuitable for bobwhite quail.”
After several years of conducting plant surveys and documenting quail abundance, Ransom and his team have found more quail on unburned sites and fewer on burned sites.
“Some of our oldest fire treatment sites have the densest mesquite regrowth and hold the fewest quail,” Ransom said. “Statistically, however, bobwhite populations were not significantly different between sites treated with fire and pastures that had not been treated in 20 or more years. That was unexpected.”
This suggests at least two outcomes, he said.
“It’s possible that prescribed burning had no effect at all,” Ransom said. “Opening up dense mesquite canopies may not have increased useable space for bobwhites. If habitat conditions were poor to start with, fire may not have improved the situation.”
The other possibility is post-fire mesquite regrowth was rapid enough to swamp any short-term increase in bobwhite numbers.
“Large-scale burns may not be a viable strategy for improving bobwhite numbers in mesquite-dominated pastures,” Ransom said.
The study also looked at how bobwhites select small- and large-scale habitats. Ransom and his team fitted radiotelemetry collars to quail to track and record their movements.
“Quail have to be flexible enough to deal with environmental changes caused by land management,” he said. “We tracked bobwhites across untreated sites, those treated with fire and those treated with herbicides.
“Our data revealed that bobwhites prefer 30 percent shrub canopy cover that provides visual obstruction out to 4 meters (12 feet).”
A more important descriptor of preferred bobwhite sites was the “cone of vulnerability” a measurement developed by quail scientists in south Texas.
“The cone of vulnerability is the volume of airspace where quail are visible to avian predators such as hawks,” Ransom said. “Studies in other regions and habitats have shown that bobwhites select sites that minimize their exposure to predators.
“Our cone of vulnerability values were smaller and less variable, suggesting that overhead cover is especially important here…as protection from predators and as a source of shade.”
These findings suggest useable quail space in mesquite-dominated pastures is often minimal, and that large-scale application of fire and herbicides doesn’t appear to improve the situation.
“Our knowledge of how fire and herbicide treatments affect wildlife on native rangeland is very elementary,” Ransom said. “At field days, we often say that bobwhites need habitat that includes 5 to 20 percent brush cover. But these figures are more accommodative than empirical.
“Such figures provide a good rule of thumb, but we really don’t know what the upper and lower limits are. We need more data on how bobwhites are connected to the small ‘patch’ habitats they seem to prefer on the Rolling Plains. We have just started research to address these issues.”
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