How Many Barn Owls Are There in the EAA?
Over the past 10-15 years, members of the EAA community have installed artificial nest boxes to increase the regional density of Barn Owls.
In spring 2005, there were 233 boxes in Palm Beach County. There were nests in 52% of these boxes, and the rest all showed signs of being used for roosting or nesting in the recent past.
In fall 2006, prior to hurricane Wilma, there were nests in 71% of the boxes; however, most nest boxes were destroyed by the storm. The boxes are quickly being replaced and are being re-colonized by the owls. As of spring 2006, 85 boxes have been repaired and there are nests in 78% of them.
Note: All boxes are on private property and are not accessible for public viewing.
What Types of Rodents Live in the EAA?
During fall 2005, just prior to the sugar cane harvest, live-trapping surveys were conducted along sixteen 250-m sections of field ditches located throughout the EAA to find out which rodent species were present. The resulting relative indices of abundance showed that cotton rats were the most common, but the actual number of individuals present varied. The three species listed on this chart, are of most concern regarding their potential to damage sugar cane crops.
Which Rodents are Responsible for Damaging the Sugarcane?
Individual rats of the three species of concern were placed in a cages for 24 hours with standardized sections of sugar cane stalk. The amount of cane eaten by the rats was then measured. All three species consumed sugar cane during the trials. Amazingly, some individuals ate more than 100% of their body weight in 24 hours! Because cotton rats are the most common species in the EAA, they collectively cause more damage than roof rats or rice rats.
Are Barn Owls Eating the Pest Rodents?
Barn Owls usually swallow their prey whole, and later regurgitate indigestible bones and fur in the form of a pellet. These pellets can then be examined to identify what the owls eat. Based on an analysis of 1107 of these pellets, cotton rats, roof rats, and rice rats comprise 56% of the diet of Barn Owls in the EAA.
So Are the Owls Making a Difference?
An experiment is currently underway to determine if rodent populations can be reduced by Barn Owl predation. Extremely high densities of owls are being established in several areas by installing dense clusters of nest boxes. The rodent populations in these areas are being tracked over time to see if they decline as the owls move in. Stay tuned!
Have You Seen This Owl?
Identification leg bands are being placed on Barn Owls to monitor their movements, nest box usage, and longevity. To date, 286 owls have been banded (89 adults, 197 nestlings). If you find one of these birds, please report the number on the metal band, the colors of the plastic bands, and the location and circumstances of your sighting to Jason Martin. Thank you!
Barn Owl Nest Monitoring
The nesting activities of the EAA Barn Owls are closely monitored to determine how many eggs are laid, the number of eggs that hatch, and the number of hatchlings that survive to leave the nest.
Young Barn Owls are banded and relocated after they leave the nest to determine how many survive and how far they travel. So far, 197 nestlings have been banded. 29 were found dead in or near their parents' nests, 2 were reported dead 4 km (2.5 miles) and 8 km (5 miles) from their birth sites, and 2 have established nests of their own at distances of 11 km (6.8 miles) and 16 km (9.9 miles) from their natal locations.
- Barn Owl (Tyto alba)
- Building a Barn Owl Nesting Box[173KB]
- Key to Rodent Skulls[181KB]
- Virtual Owl Pellet Dissection - KidWings
This barn owl has caught a
Checking a barn owl box.
Recording information about
a baby barn owl.