Wednesday, March 30, 2011

Surveying for Oregon Spotted Frogs in Western Washington

Love is in the air this time of year for many species of frogs around western Washington. With cool spring rain, male frogs find suitable areas for attracting a female mate, then use a unique call to attract females to the area. Many species of frogs will return to the water body where they were born to find a suitable mate.

Here in western Washington, several different kinds of frogs are found, including Pacific tree frogs and red-legged frogs. One species of special concern to U.S. Fish and Wildlife Service (USFWS) biologists is the Oregon spotted frog. Once widespread, this frog species may have been lost from at least 90 percent of its former range. Causes for the decline in frog populations include loss of habitat, non-native plant invasions, and the introduction of exotic predators such as bullfrogs.

Oregon spotted frog eggs
Around this time each year, USFWS biologists travel to the three areas in western Washington where Oregon spotted frogs are still known to persist. A survey of the area is performed to count the number of frog egg masses. When an egg mass is found, it is marked and monitored as it develops. Eggs typically hatch in 3 weeks and, once hatched, the young tadpoles graze on bacteria, algae, and plant tissue in the water.  By monitoring the egg masses, biologists can keep a close eye on the status of these populations.

Females deposit egg masses in shallow, often temporary, pools no more than 6 inches deep. Sometimes, though, the frogs choose areas where the water level drops, leaving the eggs high and dry. As you can see from the picture below, several Oregon spotted frog pairs chose the same area to lay their eggs. This large mass, which contained 16 individual egg masses, was found in an area where the water level had dropped. With careful and gentle hands, the eggs were moved by one of our biologists into an area that contained a bit more water. There the eggs will be able to develop and, in a couple of weeks, little tadpoles will hatch out and begin to feed.

Large egg mass before move to wetter habitat

Biologist's coat being used to move egg masses

Gently placing frog eggs in new home
With some habitat protection, population monitoring, and a little assistance from their two-footed friends, these Oregon spotted frogs will hopefully continue this cycle for many years to come in western Washington.