The burrowing owl (Athene cunicularia) is a small, long-legged owl found throughout open landscapes of North and South America. In Florida, burrowing owls were once a common sight in grasslands, pastures, and disturbed areas across the state. However, in recent decades, the burrowing owl population in Florida has declined dramatically. This article will examine what has happened to the burrowing owls in Florida and discuss the major threats contributing to their disappearance.
What are burrowing owls?
Burrowing owls are small owls, measuring about 7 to 10 inches in length with a wingspan of 20 to 24 inches. They have long legs, yellow eyes, and whitish spots on their brown feathers that help camouflage them against the landscapes they inhabit.
Unlike most other owls, burrowing owls do not live in trees and do not make their own nesting cavities. Instead, they rely on underground burrows made by mammals like prairie dogs, ground squirrels, and tortoises for roosting and nesting. In Florida, burrowing owls typically utilize burrows created by gopher tortoises. The owls line the burrows with materials like grass, feathers, and dung, and often decorate the entrance with animal dung and other objects. Adult pairs will remain together year-round and aggressively defend their burrow and the surrounding area.
Historic range and population in Florida
Burrowing owls historically inhabited dry, open prairies and grasslands throughout the state of Florida. Some estimates suggest there may have been close to 10,000 breeding pairs in Florida before European settlement. Their numbers started to decline around the early 1900s as development increased and natural habitats were altered.
The species was evidently common throughout central and southern Florida through the 1930s. By the 1970s, there were estimated to be 1,500 to 3,000 nesting pairs left in the state. The statewide population continued to drop in following decades. Surveys in 1999-2000 estimated there were only 600 to 1,500 breeding pairs remaining.
Major threats and declines
Habitat loss
The major contributor to burrowing owl declines in Florida is the extensive loss and fragmentation of habitat. Native grasslands and prairies have been converted for agricultural and urban uses across much of the owl’s former range. As natural burrow availability decreased with prairie dog eradication and lands were tilled for farming, burrowing owls became dependent on burrows created by gopher tortoises in remnant grassland patches and pastures. However, tortoise populations have also declined significantly due to habitat loss and overharvesting.
Remaining grasslands face ongoing threats from expanding urbanization and conversion to improved pastures or groves. A 2004 study found that breeding sites in central Florida were surrounded by lands that were changing rapidly, resulting in increased habitat fragmentation and isolation of owl populations. Loss of habitat and natural burrow availability likely led to localized extinctions of burrowing owls in parts of their historic range.
Increased predation and competition
Habitat fragmentation increases risks to burrowing owl populations from predation and competition. Main predators of eggs, young, and adult burrowing owls include snakes, feral cats and dogs, foxes, raccoons, and falcons. As natural habitats are altered and fragmented, these predators may have increased access to remnant owl populations.
Competing species including armadillos, opossums, and gopher tortoises can take over burrows, evicting owls from nesting sites. Fire ants have also expanded their range in Florida over the past century, and have been observed preying on young burrowing owls and causing nest abandonment. Limited availability of usable burrows makes owl populations more vulnerable to effects of predation and competition.
Vehicle collisions
A significant source of mortality for burrowing owls in Florida is vehicle collisions. Owls that nest and forage in proximity to roads are susceptible to being hit by passing cars and trucks. Vehicle strikes have accounted for around one-third to one-half of burrowing owl deaths in parts of central and south Florida. Roads fragment habitat and act as population barriers when roads bisect owl territories. Mitigation approaches like wildlife crossings, exclusion fencing, and signage warning drivers are needed to reduce road mortality.
Impacts of pesticide use
Exposure to pesticides and other environmental contaminants poses risks to burrowing owls in agricultural areas. Insecticides applied to crops and grasslands can accumulate in tissues of owls or their prey, causing acute or chronic toxicity. A Florida study found burrowing owls had modestly elevated levels of DDE (a breakdown product of DDT). Further research is needed, but pesticide exposure may have subtle negative effects on burrowing owl physiology and reproduction. Restricting pesticide usage in key habitats could benefit owl populations.
Climate change
Climate change may worsen existing threats to burrowing owls. Rising sea levels are projected to inundate coastal breeding sites in places like Cape Coral. Increased drought, heat waves, and wildfires could further alter natural grassland habitats. However, limited data is available on climate change impacts specific to Florida’s burrowing owls. Tracking population trends under climate change scenarios would elucidate this emerging threat.
Lack of genetic diversity
Florida’s remaining burrowing owls likely suffer from depressed genetic diversity due to small, declining population sizes and isolation. This can increase inbreeding depression and reduce fitness over generations. Augmenting in situ populations with birds from other states or provinces may improve genetic diversity and viability. But more genetic research is needed to support active manipulation of owl populations.
Conservation actions taken
Various steps have been taken to try to halt the decline of Florida’s burrowing owls, though most actions have not been enough to reverse statewide population trends. Some key conservation and management actions include:
- Listing burrowing owls as a State Threatened species in Florida in 1979, providing legal protections.
- Initiating the Florida Burrowing Owl Project in 1979 to monitor populations and promote voluntary habitat management on private lands.
- Using artificial burrows and nest boxes to provide additional nesting sites and attract owls to protected habitats.
- Installing perch poles, protective fencing, and signage to reduce vehicle collisions in high-risk areas.
- Purchasing conservation lands containing burrowing owl populations, like Kissimmee Prairie Preserve State Park.
- Controlling invasive vegetation and conducting prescribed burns to maintain open nesting habitat.
- Establishing Burrowing Owl Mitigation Banks where developers can offset impacts by enhancing owl habitat.
- Promoting landowner incentives and best management practices to benefit burrowing owls on agricultural lands.
- Raising public awareness and support for burrowing owl conservation through education programs.
While meaningful, most recovery actions have been small-scale or inconsistent across the owl’s Florida range. Broader habitat protection and restoration work is still urgently needed. Ongoing monitoring and adaptive management will also be key to ensure existing and future conservation actions have their intended benefits.
Current status and future outlook
Burrowing owls remain listed as a State Threatened species in Florida, though their population likely continues to decline. The Florida Fish and Wildlife Conservation Commission’s most recent burrowing owl status update report was published in 2012. They cited an estimate of only 4,400 to 7,200 breeding burrowing owls statewide based on data from the early 2000s. However, high-quality statewide surveys have not been conducted since the late 1990s, so up-to-date abundance data is lacking.
Localized ornithological observations suggest burrowing owls now appear rare or absent across much of their former range in Florida. For example, burrowing owls were described as an uncommon species and “declining dramatically” in central Florida between the 1980s and early 2000s. The Cape Coral area contained hundreds of nesting pairs in the 1990s, but only 9 pairs were found in 2015. Without heightened conservation efforts, biologists believe burrowing owls could potentially face extirpation in Florida in coming decades.
Though the overall situation seems dire, some reasons for hope remain. A core population of several hundred breeding pairs persists on lands like Avon Park Air Force Range and Kissimmee Prairie Preserve State Park. Ongoing management activities on public and private conservation lands, if sufficiently supported over time, may slow or halt declines in focal areas. Targeted habitat restoration and expansion of mitigation programs could stabilize populations in other regions. And public involvement in owl monitoring and conservation is increasing, which may translate to greater commitment to protect Florida’s remaining burrowing owls. But the window of opportunity for conserving the species in Florida appears to be closing, making robust and coordinated actions a clear priority.
Conclusion
In conclusion, burrowing owl populations have declined precipitously in Florida over the past century due to widespread habitat loss compounded by vehicle strikes, predation, pesticide effects, and lack of genetic diversity. Conservation measures like habitat management, nest box programs, and land acquisition have failed to reverse ongoing statewide declines thus far. While future research and monitoring are still important, the focus for sustaining viable burrowing owl numbers in Florida should be enacting habitat protection and restoration at larger scales without delay, before it is too late. With adequate resources and political will, it may still be possible to conserve these charismatic grassland owls for future generations.
Time Period | Estimated Breeding Pairs in Florida |
---|---|
Pre-1900s | ~10,000 |
1930s | Common |
1970s | 1,500 – 3,000 |
1999-2000 | 600 – 1,500 |
Early 2000s | 4,400 – 7,200 |
2015 (Cape Coral only) | 9 pairs |
References
Millsap, B.A. and Bear, C., 1990. Double-brooding by Florida burrowing owls. The Wilson Bulletin, pp.313-317.
Millsap, B.A., 1996. Florida burrowing owl. In Rare and endangered biota of Florida (pp. 368-378). University Press of Florida.
Bowen, P., 2000. Demographic, distribution, and metapopulation analyses of the burrowing owl (Athene cunicularia) in Florida (Doctoral dissertation, University of Central Florida Orlando, Florida).
Florida Fish and Wildlife Conservation Commission, 2012. A species action plan for the burrowing owl. Tallahassee, FL.
Courser, W.D. 1979. Continued breeding range expansion of the burrowing owl in Florida. American Birds 33: 143-144.
Mrykalo, R.J., 2005. Florida burrowing owl mitigation: a management experiment. Transactions of the Western Section of the Wildlife Society 41, pp.76-82.