By Becky Schneider and Erin Ragheb
The unique Florida dry prairie, a habitat type that has been substantially encroached upon by development, is where the endemic Florida grasshopper sparrow (Ammodramus savannarum floridanus) calls home. Named for both their diet and buzzy insect-like vocalizations, grasshopper sparrows are intensely secretive songbirds that prefer walking over flying and build their nests directly on the ground. The federally-endangered Florida subspecies is one of the rarest birds in North America, and population numbers are dwindling at alarming rates. If this downward population trend continues, the Florida grasshopper sparrow may become extinct within the next decade. Starting in 2013, we initiated an intensive demographic research project on the largest remaining population of Florida grasshopper sparrows, located at Three Lakes Wildlife Management Area, in attempt to identify and alleviate the causes of decline.
Beginning in 2015, we placed nest cameras in front of Florida grasshopper sparrow nests to document specific causes of nest failure. We recorded previously unconfirmed nest predators including Eastern spotted skunks, Southern black racers, and red cornsnakes. After identifying these key predators, we set out to develop a technique to effectively exclude hungry mammals and snakes from Florida grasshopper sparrow nests. In the subsequent field seasons, we designed and constructed predator fences and installed them around Florida grasshopper sparrow nests. These 10-ft wide exclosures are inconspicuous enough that the incubating female can return to her nest naturally but robust enough to keep predators at bay. The fences have proven to be highly effective at reducing nest predation, and a fenced nest is up to five times more likely to successfully fledge young than an unprotected nest.
Still, predation is not the only factor contributing to low nest success, and our predator fences are not effective at eliminating other sources of nest mortality such as flooding. To reduce the risk of nest loss by flooding, we developed a successful method for elevating nests prior to severe rain events. These intensive management actions have been effective at increasing annual fledgling production and will buy time to develop landscape-level conservation strategies.
Our color banding and resighting data demonstrate that low adult survival rates are another worrying cause of population decline. Apparent survival rates for adult males have decreased dramatically from 75% in 2014 to 36% in 2017. We have also observed recent declines in adult female survival and an increasingly male-biased sex ratio. Our next important step in this study is to determine the causes of reduced adult survival and explore management actions in response. We are now partnering with the University of Florida to screen wild birds for a suite of potential pathogens to identify if disease is contributing to reduced adult survival.
Stalling, stopping, and reversing the perilous decline of the Florida grasshopper sparrow is indeed a daunting task, but with a team of dedicated researchers and strong public support we expect to conserve this charismatic songbird and increase our knowledge and understanding of Florida’s unique grassland prairie habitat.