Toad Research in Organ Pipe Cactus National Monument

In the Sonoran Desert, toads are a group of hardy desert animals that rely on the presence of seasonal water to live, breed, and lay eggs. The window to study the habits of these animals is rather short and sometimes unpredictable.

NPS photo/Sarah Feyers

Toad Research at Organ Pipe Cactus, 2023

For the past five years, researchers from Texas Tech University have spent their summers studying toads in the Sonoran Desert. Over the course of their research, the team has seen large monsoons, drought, and the Sonoran Desert’s impact on different species of toads. The aim of this research is to understand which species are present and where, as well as the geographical reach of the chytrid fungus, which causes infections, mortality, and mass die-offs in toads and other amphibians.

Eggs are a sign of toad activity within a body of water.

NPS photo

Background

Toads of the Sonoran Desert are reliant on water to breed and lay eggs, for those eggs to hatch, and for the tadpoles to successfully metamorphose into toads. The summer monsoon typically marks the start of the toad breeding season. Toads provide ecological services such as consuming insects and their larvae, and are in turn consumed by other charismatic animals, such as snakes and birds.

Chytrid fungus originated in Asia and can spread through human transfer. This may occur when mud on boots is tracked from an infected site to a chytrid-free site. Toads are susceptible to the fungus, which has led to massive die-offs of amphibians around the globe. Chytrid fungus typically infests amphibian populations in areas that are cool and damp — conditions that outside of the winter period are not typical of this region. Recently, this fungus has been found on toads in the area, prompting further research into its resilience in hot and dry conditions.

The researchers have no specific species focus and instead study all species of toad they encounter. Typical toads found and studied include the Sonoran Desert toad, red-spotted toad, Couch’s spadefoot, and occasionally the Great Plains toad.

There are many small ephemeral bodies of water that toads may make use of. For the sake of continuity and longevity of the study, study sites are tinajas that are usually named, managed, and reliably filled with water.

A red-spotted toad forgets that he is in a predicament and begins to sing. A researcher swabs the toad's skin to later test for the presence of chytrid fungus.

NPS photo/Sarah Feyers

Effort

Before the monsoon, researchers hike out to tinajas to collect water samples and assess the habitat. The researchers note the levels of ammonia, phosphate, and nitrate in the water, which can negatively impact tadpoles. The water is also tested for the DNA of the chytrid fungus. Once the monsoon arrives, the researchers pivot to a night schedule to collect data from toads.

During night surveys, the focus is placed on the physical presence of toads. The researchers start with a 20 minute visual and auditory survey of the area. They look and listen for signs of breeding, such as eggs and singing. A device placed at the site takes intermittent recordings throughout the night. This device allows the researchers to know who is singing after they leave the site.

Toads are then collected in zip-top bags. The researchers sex and measure the toads and check for deformities. The toads are then swabbed along their back, belly, and legs to later test for the presence of fungus.

Finally, the toads are marked to be identifiable if recaptured, and a genetic sample is taken.

The information about toads gathered from this observational study will be used to help determine which species is using a water site, and how often and in what density they frequent the site. The fungal samples will be used to help determine if certain waters foster fungal infections.

The researchers believe that the chytrid fungus relies on the toads’ bodies during the hottest and driest times of year. When the seasonal waters dry, and there is little sediment for the fungus to lie dormant in, it may sit on a toad’s skin until reemerging during the next rain event.