SCCF wildlife biologists are asking for your help in continuing to investigate the presence of pig frogs on Sanibel.

The pig frog (Lithobates grylio) has been a popular topic of conversation over the last year. First, it was suspected that it may have been lost due to Hurricane Ian’s storm surge. Then, 2-3 individuals were discovered during frog call surveys on the west end of Sanibel in the fall of 2023.

That verification was followed by the lack of detection of pig frogs during frog call surveys earlier this month when every other species on the island was heard.

“There is still concern about the continued existence of this species on Sanibel,” said Wildlife & Habitat Management Director Chris Lechowicz. “We would really appreciate the help of islanders and visitors with keen ears to let us know if they hear them — we want to know where they are, but we can’t be everywhere at once.”

How to Identify its Call
Many people who grew up or vacation here frequently during the rainy season consider the grunt of the pig frogs to be a staple sound of the summer months. Their call or grunt is usually repeated two or three times, reminiscent of a pig, which is how it received its name.

FUN FACT: Many people hear this sound and mistakenly think it’s an American alligator.

Click below to listen to a recording to help you verify the call.

If you hear the grunts of a pig frog, please email clechowicz@sccf.org to let him know the location. If you are able to record the sound with your smartphone, please send that as well.

The History of Pig Frogs on Sanibel

The history of this species on Sanibel is interesting, as it was not known to occur on Sanibel until 1952. Even though this is a native frog found throughout most of Florida, including Fort Myers, it was never documented on the island.

The pig frog is a true frog (Family: Ranidae), meaning it is a resident of permanent freshwater bodies, which Sanibel was lacking historically.

“Before the Sanibel Slough was altered by the Mosquito Control District in the 1950s to control the saltwater mosquito populations, the island was a relatively dry place over the winter months,” said Lechowicz.

Most years, very little freshwater remained in most areas as wildlife such as American alligators (Alligator mississippiensis) and various aquatic turtles would congregate in the low muddy areas of the slough — known as alligator holes — to wait out the remainder of the dry season.

During extreme tropical storms or heavy rain events over the summer back then, excess freshwater would exit the island, naturally, in three main areas.

“Following the alteration, or ditching, of the slough and the creation of the Tarpon Bay Weir, freshwater has been artificially held on the island to reduce the breeding of the saltwater mosquito,” he explained. “This benefitted many forms of wildlife such as alligators, freshwater turtles, freshwater game fish that were released in 1961, freshwater macroinvertebrates, and especially pig frogs.”

How Pig Frogs Ended Up on the Island

In 1952, J.N. “Ding” Darling National Wildlife Refuge Manager Tommy Wood caught 49 pig frogs at Loxahatchee National Wildlife Refuge and released them on Sanibel at the Bailey Tract and Stewart Pond near the Chateau Sur Mer development.

“From there, the pig frog established across the island, especially with the increase of freshwater habitat across the island in the late 1950s. It has been considered a common frog species on Sanibel ever since,” said Lechowicz.

Native wildlife, such as alligators, and raptors certainly benefitted from having a larger aquatic prey source on the island. Some residents back then also learned to catch and eat them with a technique called “gigging” as they are known as a great source for frog legs.

Impacts of Hurricane Ian

The inundation of the freshwater bodies by saltwater from Hurricane Ian wiped out pig frogs in many areas, among other species.

Pig frogs do not have a high salt tolerance, especially the aquatic tadpoles that take a long time to metamorphize into frogs. Prior to Ian, many impounded lakes throughout the residential areas had large populations of these frogs and most, if not all of these, became too salty for amphibians and other forms of wildlife following the intense storm surge.

“We were lucky enough to hear them on the far west end last fall, which is the oldest and highest part of the island that had the least number of effects of the storm,” he said. “We were surprised to not hear them during our survey earlier this month that occurred at the optimum time for frog breeding — heavy rains after a long drought.”

The wildlife teams hope to document the iconic call of the pig frog during upcoming surveys this summer.

In the meantime, if you hear the grunts of a pig frog, please email clechowicz@sccf.org to let him know the location.