Barn Owl Extension
WANTED ... ALIVE! Natural Born Killer
The Barn Owl (aka Tyto alba), a skilled rodent predator, is wanted for providing sustainable control of rats and mice in south Florida's Everglades Agricultural Area (EAA). Rodents are responsible for millions of dollars in damage to crops and farm equipment each year. Over the past decade, members of the EAA community have installed barn owl boxes throughout Palm Beach County to increase the abundance of these owls. It is hoped that they will impact the regional rodent population and reduce the need for chemical rodenticides. All boxes are used by owls for either nesting or roosting, and research is currently underway at the EREC to determine if this artificially inflated population is capable of reducing rodent abundance.
Barn Owls also provide a unique opportunity for local students to learn about the ecology of the EAA in a hands-on manner. The owls typically devour their prey whole, and later regurgitate the indigestible fur and bones in the form of a pellet. In educational programs conducted by EREC personnel, students dissect these pellets and exam their contents to determine what the owls have been eating. Students also have built many of the barn owl nest boxes, and thus have gained an appreciation for ecologically friendly agricultural practices.
Barn Owls usually swallow their prey whole, and their food passes into their gizzard. The gizzard is an organ that uses digestive fluid and bits of sand and gravel to grind and dissolve digestible material. Soft tissue, such as muscle, fat, and internal organs are easily processed, but the digestive acids of owls are too weak to dissolve tougher material, such as bones, fur, feathers, teeth, and claws. The gizzard compacts these leftovers into a tight pellet that the owl regurgitates.
YUCK, THAT'S GROSS! I'M NOT TOUCHING THAT!!
Believe it or not, barn owl pellets are an exceptionally popular educational tool. School kids across the country, including those here in Palm Beach County, FL, routinely dissect pellets and examine their contents. Initial squeamishness is soon replaced by scientific curiosity and excitement. This activity often is incorporated into units on owl ecology, predator/prey relationships, and anatomy.
CSI: BARN OWL
Because Barn Owls swallow their prey whole, the entire skeletons of last night's dinner often can be recovered from pellets and then reassembled.
Specific prey items can be identified by examining the shape and form of the bones. By identifying the contents of many pellets, the general dietary preferences of barn owls can be determined.
- Key to Rodent Skulls[181KB]
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.
Rodents of the EAA
- Cotton Rat (Sigmodon hispidus)
- House Mouse (Mus musculus)
- Rice Rat (Oryzomys palustris)
- Roof Rat (Rattus rattus)
- Round-Tailed Muskrat (Neofiber alleni)
OTHER SMALL MAMMALS
- Eastern Cottontail (Sylvilagus floridanus)
- Marsh Rabbit (Sylvilagus palustris)
- Southern Short-Tailed Shrew (Blarina carolinensis)
Head & Body: 5-8 in (127-203 mm)
Tail: 3-6 in (81-152 mm)
Weight: 4-7 oz (113-198 g)
2-12/litter; up to 9 litters/yr; gestation about 27 days; leave nest at 4-7 days; age of reproduction: 40 days
Feeds primarily on green vegetation. Nests on surface or in burrows. Makes surface runways through vegetation.
Head & Body: 3-4 in (81-86 mm)
Tail: 2-3 in (71-81 mm)
Weight: 2/5-4/5 oz (11-22 g)
3-11/litter; several litters/yr; gestation 18-21 days; age of reproduction: 6 weeks; breeds year round
Occasionally found if fields, but usually in or near buildings. Eats anything edible. Not native to U.S.
Head & body: 4-5 in (121-132 mm)
Tail: 4-7 in (110-183 mm)
Weight: 1-3 oz (40-80 g)
1-7/litter; several litters/yr; gestation about 25 days; age of reproduction: 50 days; breeds year round
Found in wet parts of grassy fields. Feeds on green vegetation and seeds. Makes surface runways. Nests above ground.
Head & body: 7-8 in (178-203 mm)
Tail: 8-10 in (214-253 mm)
Weight: 5-10 oz (142-283 g)
4-10/litter; up to 12 litters/yr; gestation 21-22 days; age of reproduction: 3 months
Found near buildings and in fields. Feeds on vegetation and grains. Nests on surface or in burrows. Not native to U.S.
Head & body: 7-8 in (20-22 cm)
Tail: 4-6 in (11-17 cm)
Weight: 5-11 oz (156-330 g)
1-3/litter; probably breeds year round
Found in bogs, marshes, weedy boards of lakes and wet fields. Feeds on water plants and crayfish.
OTHER SMALL MAMMALS
Head & body: 14-17 in (35-43 cm)
Tail: 2-3 in (64-76 mm)
Weight: 2-4 lb (1.1-1.8 kg)
3-4/litter; breeds March-September; gestation 26-30 days
Found in brush, weedy patches and field edges. Feeds on vegetation. Fur grayish or brownish. Cottony-white tail.
Head & body: 14-16 in (35-41 cm)
Tail: 2-3 in (64-76 mm)
Weight: 2-3 lb (1.1-1.6 kg)
2-5/litter; breeds February-September
Found in marshes and other wet areas. Feeds on vegetation. Fur is reddish-brown. Feet relatively small. Tail inconspicuous
Head & body: 3-4 in (76-102 mm)
Tail: 3/4-1 in (19-30 mm)
Weight: 2/5-4/5 oz (11-22 g)
2-6/litter; 2-3 litters/yr; gestation 21-30 days; breeds February-November
Found in wooded and brushy areas. Lives in underground burrows. Feeds on insects, worms, and other invertebrates. Saliva is poisonous.
- Web Cam Highlights