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Five pair of Swifts fledged 18 offspring in 2000. The South Tower mates showed an inclination toward a second nesting attempt. Their four fledglings caused considerable damage to the front edge of the nest during their in tower flight training. Although we did observe the adults return with nest sticks and attempt to fasten them to the edge, no repair was evident.
The discovery of dead hatchlings in the West Field Tower was disturbing. The adults had abandoned the site within a week of laying the eggs. Incubation normally requires 21 days of brooding by alternating adults. We assumed that the embryos would fail to develop without parental care. Apparently the exceptional central Texas summer heat provided the warmth needed for development and the hatchlings entered a parentless world.
Additional data will be required to answer many of our questions concerning temperature variations within our test towers. However, at this time we are definitely recommending that all wooden structures incorporate insulation as opposed to an air space between the inside and outside surfaces. A moderation of only a degree or two during daytime high temperatures can render the success or failure of a nesting attempt.
For many years we have wondered what happens in a Chimney Swift roost at night. In 2000, Mel Rinn designed and built an infrared light source for us to use in the towers. Our unaided human eyes could not detect the light source, but the black and white cameras that we use could "see" the light. We were able to observe and record images on the TV monitor that were illuminated by the infrared source. However, we had no idea if the swifts would be able to see the light, and we felt considerable trepidation about using the device for the first time. Fortunately, the swifts were apparently unable to detect the infrared and we were able to observe them without disturbing them. We should be able to add considerably to our knowledge about nocturnal Chimney Swift behavior with this important new tool.
At the Driftwood Bird Banding Station, Chimney Swift towers have been constructed on all four corners of a large pole barn that serves as a rainwater collection system and pavilion where groups are assembled to observe the bird banding. In all the years the barn had been there, no swifts had ever been observed flying under the structure -- although it is quite tall and completely open on all sides. This changed one year when we captured a swift from one of the towers before dawn for Rick and Nora Bowers to photograph. Their technique is to place a bird in a 2' x 2' x 2' box with appropriate habitat. In this set up they can control the lighting and take some remarkable photographs of birds. While the swift was being photographed, it made no sounds that we could hear. However, other swifts made several passes under the roof where the photography was taking place. We wondered if it was more than coincidence and that perhaps the swift in the box was emitting some sound we were unable to detect. Since bats use sounds in frequency ranges that are beyond our audible range, we conveyed this observation to Mark Kiser of Bat Conservation International. Mark graciously agreed to bring his "bat detector" out to the Twin Towers for a listen. What he found was that in addition to the audible sounds that the Chimney Swifts made as they prepared to go to roost, they were also emitting sounds that were out of our human range of hearing. He suggested that we repeat the experiment at a later date with more sensitive equipment and even conduct a computer analysis. We look forward to their assistance with this interesting project in 2001.
Chimney Swifts were on or over the station for 216 days in 2000.
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