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The behavior observed in the North Tower following the loss of an egg in the second nesting attempt is puzzling. Although the crippled male was at a disadvantage, nest construction, mating, brooding and the first few days of care for the single hatchling seemed more than adequate.
With the exception of the Prism, all nests lost at least one egg in 1999 - some to infertility, others to being lost "over the edge". Several of our Research Associates also reported fallen eggs. With the precarious nature of swifts' nests, it is surprising that more eggs are not lost in this manner. However, we do suspect foul play by our clandestine resident Canyon Wren in the egg piercing in the South Tower.
Chimney Swifts normally begin continuous brooding when the next to the last egg is laid. The reluctance of the South Tower parents to brood until 72 hours after the last egg was laid is remarkably inconsistent with known behavior.
It has been published and we have confirmed with our own observations that Chimney Swifts exhibit strong nest site fidelity. We found it unusual to have only one return breeding bird to the Twin Towers. We speculate that swift was the only survivor of the 2 pairs that occupied the Twin Towers in 1998. Several of our Research Associates reported a complete lack of swift activity in sites which were occupied in 1998. We cannot help but wonder if Hurricane Mitch was a factor. The human toll of this devastating storm was well documented by the media, but the impact on migrating birds must have also been catastrophic. We received a second hand report of a storm-destroyed building in Central America which contained thousands of dead swifts which had apparently sought refuge from the weather.
Chimney Swifts fledge from the nest chamber at 28 to 30 days of age. It is not unusual for them to return frequently for a few days afterward. Fledglings will also be fed by their obliging parents for those few days before the young are completely independent. However, once a bird becomes independent it no long makes the unmistakable begging call. When the begging calls were heard in the Castle 20 days after the young had fledged and again 12 days later, we were at a loss to understand what was happening. We know that fledgling swifts "practice" flying within their nest structures for at least a week before they actually leave the safety of the site. It is possible (although not probable) that birds that are flushed from a chimney by intolerant homeowners might be able to reach another structure at this age. Younger birds would undoubtedly perish. We believe that on both occasions when we heard the begging call, nearby families of swifts were displaced from their chimneys and managed to find their way to the Castle. In fact, we did discover that a traditionally successful nest chimney had been capped on a nearby house that had just been sold.
We were determined to construct 2 new towers in 1999. Unforeseen circumstances delayed the start of construction until early May. We are always hopeful that swifts will accept a new structure, but we were unprepared for the tenacity of the pair claiming the North Pool Tower. Construction could not be delayed once the birds began nest building because it was unsafe for them in the current state. Completion require additional cinder block stacking and mortaring, capping the blocks, installing a sun baffle, sealing the inside of the tower to stabilize the surface of the cinder block so it would allow the saliva in the nest to hold to the wall, put a smooth stucco on the outside so predators could not climb the towers, and install a door on the clean out to prevent unwanted visitors from entering through the bottom. The swifts were just as determined in their construction. Fortunately, we were all able to coordinate our activities and 4 healthy fledglings were the happy result.
In spite of the small diameter of the Pool Towers, the thermal mass of the cinder blocks prevented the overheating problems we have experienced with wooden towers of the same size. This obvious benefit, along with the permanent nature of concrete, make cinder block construction ideal for Chimney Swift towers. The only drawbacks are that the inside of the tower must be sealed with a concrete sealer and that masonry work requires an expertise that most homeowners may not have.
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