Since very little data has been collected on California American Kestrel populations, the goal of my project is primarily to look at nesting success and nest box occupancy on different agricultural properties in the Central Valley. I am also curious as to whether American Kestrels provided natural pest control services on farms. I began the 2018 breeding season not knowing what to expect in terms of my first season of data collection. After a few setbacks, I was able to install 50 American Kestrel nest boxes on four different properties and started monitoring the boxes for occupancy and nesting status in March. In total, six nest boxes were occupied by American Kestrels, fledging a total of 19 successful kestrels! In addition, one box was occupied by a Western Screech-owl and another by an Ash-throated Flycatcher.
Top: An adult female kestrel with 5 eggs. Bottom: A Western Screech-owl adult with three nestlings.
Interested in documenting prey delivered to nestlings, I stationed myself and volunteers in range of the nest boxes with binoculars where we attempted to identify prey being delivered and monitoring provisioning rates. That proved to be difficult, as most prey items were so small it was almost impossible to identify them, and the kestrels moved faster than we had expected making it difficult to focus on the prey items. That’s when I knew it was time to go back to the drawing board. I installed a motion-activated camera for my last nest box to document prey items as the adults brought back prey to the nest boxes and this proved to be the solution I was looking for! Even though I installed the camera in the middle of the nesting cycle at only one nest box, I documented the prey deliveries to the young from 15 days old to fledging.
An adult female kestrel delivering a Western Fence Lizard to her young.
Unfortunately, that was also the same time the County wildfire decided to hit, and the property hosting the nest box was evacuated. I was unable to access the camera and nest box for a couple weeks due to the smoke. Luckily, the fire was finally controlled, and I was able to get in to assess the damage. All nestlings had survived but were slightly underdeveloped likely due to a decrease in prey delivery during the fire. Amazingly, the camera batteries hadn’t died, and I captured the smoke of the fire descending on the nest box. I was also able to see that the parents were still delivering to the young and were, hopefully, making up for the period of slower deliveries.
The visible layer of smoke and glowing sun visible from the nest box camera on the second day of the County Fire.
After a week more of development, three of the young successfully fledged, which was captured on camera. After the successful implementation of the motion-activated camera on one nest box, next season I will be installing cameras on all of the occupied nest boxes in order to document prey items delivered to the nestlings and capture any other interesting behavior.
A “leap of faith” as one of the nestlings leaves the nest box for the first time.