There are 18 Chimney Swift towers on the Chaetura Canyon Sanctuary. Most are monitored only periodically and then nesting success is evaluated after the swifts have departed for South America in the fall. However, three of the towers are equipped with audio and visual equipment and are monitored throughout the nesting season: the cinder block castle and the two 24-feet tall wooden towers on the residence (“North” and “South”).
We focus this tale on the South Tower. This year there was additional monitoring equipment installed by Dr. Carlos Rodrigues with the University of Texas to hopefully capture the ontogeny of the swifts and be able to study their vocalizations within the nesting structure – something which to date has never been done. It was a year like no other.
Swifts in the South Tower built their nest and laid two eggs in May. But each time an additional egg was laid, a third swift entered, and the territorial scuffle ended with the egg knocked out of the nest and broken on the bottom of the tower. By the end of the month, the pair was still in the South Tower and still working on the nest, but there were no eggs.
On June 22nd, a couple of weeks after the last egg was lost, the pair once again began to mate and continued to work on expanding the nest. Shortly thereafter, a new egg was laid. The parents returned frequently to check on and cuddle the egg. That evening a bird entered the tower and obviously, purposely ejected the egg from the nest using its mouth. In more than 30 years of observation, we have never before witnessed this behavior and pondered the situation.
So, what happened? Did an adult return without a mate, take another mate and the original mate showed up later? Swallows often toss out the eggs of rival mates, but to our knowledge this has never been documented with Chimney Swifts.
When we contacted Dr. Charlie Collins, co-author of the species account for Chimney Swifts in Birds of the World, he concurred. Charlie suggested that competing females were perhaps tossing out a rival’s egg. If this was the case, as soon as two eggs were laid the activity would cease – since they could no longer distinguish their own egg from that of their rival. Turns out, he was correct.
We lined the bottom of the tower with soft material so that if the activity continued, we could hopefully retrieve and replace an unbroken egg. Fortunately, that did not happen and egg laying resumed. However, there were still several scuffles.
On June 26th, there were two new eggs in the South Tower nest – which was now much larger due to ongoing construction. Because a new egg is laid every other day, we expected a third on the 28th. But by mid-morning on the 28th there were four eggs…what? A female Chimney Swift is not expected to be able to produce enough calcium to lay an egg except every other day – their diet is calcium-poor. Had another female entered and laid her egg in a surrogate nest? On June 30th, a fifth egg was laid.
On July 1st, there were six eggs in the nest – again too soon for the same female to lay another egg, and two more were laid by July 4th for a total of eight. The most we have ever documented is seven, and never in such rapid, daily succession. Clearly two females were laying eggs in the same nest.
By July 20th, seven of the eight eggs had hatched. The nestlings grew rapidly, and we often observed three adults feeding them.
On July 31st, the nestlings’ feathers were covering their previously naked, pink bodies, their eyes were beginning to open, and they completely obscured the nest where they clung steadily. Normal development continued over the next few weeks, and by the end of August “The Magnificent Seven” had successfully fledged.
Meanwhile, to our delight, in the North Tower a sizable roost formed. It fluctuated nightly from 150 to 318 individuals. But the South Tower family preferred to remain in their own tower at night – often joined by half a dozen or so others who perhaps did not enjoy the rowdy crowd in The North.
We have been studying, watching and wondering at the Chimney Swifts of Chaetura Canyon since we built our first tower in 1989. And every year they still teach us some new.
The relatively mild summer was kind to the vegetation, and with 6.54 inches of rain August was out wettest month of the year to date. This fall promises to be very colorful with great stands of Prairie Agalinis and a ridiculous amount of Plateau Goldeneye – the latter of which has been over-performing. Although the local pollinators would likely disagree.
We have worked on our own for months to clear the trails following the ice and snow damage from the February storm, but there is still much residual damage and a large quantity of slash to be hauled out and chipped. We are hopeful that once the weather cools, we will be able to host a few Stewardship Days. But with the Delta surge, we will have to wait and see…
Georgean and Paul Kyle