The California clapper rail (Rallus longirostris obsoletus) is a highly endangered subspecies of the clapper rail that is found exclusively in the San Francisco Bay Area. As of 2021, there were an estimated 1,500 California clapper rails left in the wild. This bird faces numerous threats to its survival, including predation from a variety of animals.
Mammals
Several mammalian predators prey on the California clapper rail. Some of the main ones are:
- Red fox – An invasive species that was introduced to California in the 1900s, red foxes are prolific predators of clapper rails, especially eggs and chicks.
- Raccoon – These opportunistic omnivores readily eat eggs and chicks. Raccoon predation accounts for up to 60% of clapper rail egg mortality in some areas.
- Norway rat – An invasive rodent, Norway rats consume both eggs and chicks.
- Feral cat – Feral and free-ranging domestic cats kill both adult rails and chicks.
- Coyote – As habitat generalists, coyotes may prey on rails when the opportunity arises.
Mammalian predation takes a heavy toll on clapper rail populations by reducing reproductive success. Predators target eggs and chicks, decreasing the number of juveniles that survive to adulthood.
Birds
Avian predators also pose a major threat. Birds that prey on California clapper rails include:
- Northern harrier – Harriers are raptors that hunt over marshland, preying on both adult and young rails.
- White-tailed kite – A raptor that hunts from hover position, diving down onto rail prey.
- Peregrine falcon – The fastest animal on earth, peregrines readily catch clapper rails in flight.
- Bald eagle – Opportunistic predators, bald eagles have been documented preying on rails.
- Barn owl – An adept nocturnal hunter, barn owls prey on adult rails at night.
- American crow – Crows will eat eggs and chicks.
- Common raven – A corvid species that takes eggs and chicks.
Bird predation reduces rail numbers through direct mortality of adults and juveniles. Raptors such as harriers, kites, falcons, and eagles prey on adults, while avian egg predators reduce reproductive success.
Reptiles
Reptilian predators are less significant overall, but still pose a localized threat:
- Northern Pacific rattlesnake – An ambush predator, rattlesnakes take ground-nesting eggs and chicks.
- Gopher snake – Prey on eggs.
- Racer – Will eat eggs and take small chicks.
Crustaceans
Crabs are major nest predators of clapper rails. Two species are particularly problematic:
- Red swamp crayfish – An invasive species from the Southeast, these crayfish consume rail eggs. They can destroy up to 47% of nests.
- Yellow shore crab – A small native crab, these readily eat clapper rail eggs.
By depredating nests, crabs reduce reproductive success and decrease the number of juveniles hatched each year.
Other Invertebrates
Some insects act as specialized egg predators:
- Marsh earwig – Preys on eggs at night.
- Solitary wasps – Parasitize eggs by laying their own eggs in rail eggs.
Though less significant than crabs overall, these invertebrates contribute to loss of eggs and lower hatching success.
Humans
Historically, humans have also posed threats to California clapper rails:
- Hunting – Rails were hunted for food and sport in the 1800s-early 1900s. Bag limits of 25/day decimated populations.
- Habitat loss – 90% of the Bay’s marshes were lost to development, removing rail habitat.
- Disturbance – Human activities near rail nesting areas can lead to nest abandonment.
Though no longer hunted, population recovery efforts are limited by the extensive habitat loss. Ongoing impacts include disturbances from shoreline development and recreation.
Predator Control Efforts
Several predator management actions aim to improve California clapper rail breeding success:
- Exclusion cages – Wire cages placed around nests keep out crabs, raccoons, and other egg predators.
- Predator trapping – Trapping targets species like red foxes, rats, and feral cats in rail habitat.
- Vegetation control – Removing vegetation along levees eliminates predator hiding spots.
- Site monitoring – Wildlife cameras help identify problem predator species.
Despite these efforts, predation remains a major obstacle to rail recovery. Further habitat restoration and management will be necessary to reduce predator pressures.
Summary
The endangered California clapper rail faces predation pressures from a diverse array of species:
- Mammals such as foxes, raccoons, and feral cats prey heavily on eggs, chicks, and adult rails.
- Birds, including raptors, corvids, and owls, reduce reproductive success and kill adults.
- Reptiles like rattlesnakes consume eggs and small chicks.
- Crabs are major nest predators, with two invasive species being especially problematic.
- Insects and other invertebrates also damage eggs.
- Historically, human hunting and habitat loss decimated rail populations.
Despite predator management efforts, ongoing threats from multiple predator species limit rail population growth and recovery. Further habitat restoration and protection will be needed to reduce predation rates on this rare species.
