A surprise furry visitor to the contact station bird feeder! It’s a Brush Rabbit. We haven’t seen it since the grass was mowed around us, but there is a good chance it will come back. Maybe it is a night visitor. Although, with the Great Horned Owl often sitting in the breezeway between the two bathrooms at night, maybe that is not a good idea.
And speaking of the feeder station, a big thank you goes to Rietdyk’s Milling Co. here in Ridgefield. They supply pet, horse and livestock needs (and birdseed) in the area and have generously agreed to contribute seed to our contact station bird feeder, which is maintained by the Friends and volunteers. More on recent activities at the bird feeder in next month’s e-news.
A couple weeks ago I went down to the Refuge to do a very early morning round on the River S. It was a pleasant morning as I started the leg to the hunt gate. As I moved westward, I saw these odd patches of what looked like a foamy white circle of goo on the slough. Geez I thought, do we have sewer sludge? I noted the Mexican waterfern, that tight mass of green, was expanding across the slough and the heads of a couple frogs could be seen. Moving on, I spent some time on the second leg driving toward the blind as I listened to bird songs and tried to identify all I was hearing. Then I got smart and pulled out my Merlin App to help me sort through the songs – Swainson’s Thrush and Robins, Yellowthroat and Yellow Warblers, then Willow Flycatcher and Black-capped Chickadee. Merlin kept identifying Cedar Waxwings which I can’t quite hear so well anymore given their high pitch, but I started looking and finally spotted one. My trip around proceeded until I was stopped by a cacophony at the pond to the right just before Number 11. First one, then another, then the chorus took voice. It was bull frogs…… everywhere.
American Bullfrogs, Lithobates catesbeianus, is an invasive species in the Pacific Northwest. They are classified as a Prohibited Aquatic Animal Species in Washington, meaning they may not be possessed, purchased, sold, propagated, transported, or released into state waters. Yet they are here. According to the Washington State Invasive Species Council, they are found throughout the lowlands of Washington. And they entered the state through the aquarium and pet trades, and possibly via release after being used in science classes. Although, in the sciences classes I took long ago, none of the frogs lived to see another pond again, sadly for them.
For those who like slightly more exotic food, Bullfrogs are a choice item. The only parts normally eaten are the rear legs, which resemble small chicken drumsticks, with a similar texture and flavor (isn’t everything exotic like chicken?). I recall, quite vividly, sitting across from my great Uncle Victor consuming frogs’ legs at a popular fish restaurant on Fisherman’s Wharf in San Francisco when I was maybe eight. The idea hasn’t grown on me. But their presence as a nutritious food source has led to Bullfrogs being distributed around the world outside of their native range of the Eastern US.
Bullfrogs compete with, and prey on, a wide range of native species, and can significantly affect native ecosystems such as wetlands. Bullfrogs are predators that eat practically anything they can catch. They can swallow tree frogs, other amphibians, and reptiles such as the western pond turtle, minnows, small birds, bats, and young snakes. Introduced Bullfrogs have been blamed for native species declines in much of North America. One of the big projects on the Refuge complex is providing optimum habitat for Pond Turtles on the Pierce Refuge. Bullfrogs are a big threat to the Pond Turtles and lot of time and effort is required to mitigate that threat.
Why are the Bullfrogs so prolific? Lots of reasons. They are built for eating, no, devouring food with their big mouths, sticky quick tongues and strong hind legs that propel them forward, mouth open to ambush prey. They can grow as much as eight inches from their snout to vent and weigh about a pound, some reaching a pound and a half. They live seven to nine years in the wild, so that is a lot of protein consumption over those years. And the female can produce thousands of eggs in a season.
Bullfrogs are among the most wide-ranging of all North American amphibians, found in freshwater ponds, lakes, and marshes from Nova Scotia, Canada, throughout the continental United States. Once established, being very skittish, they are difficult to capture and control. We have an ideal habitat for them on the Refuge.
What was I witnessing as I drove around the refuge mid-June? Here is a little bit about Bullfrog romance that is enlightening. Males and females are dimorphic, they can be told apart. The top of the bullfrog has an olive-green base color, either plain or motley grayish brown. The underside is off-white blotched with yellow or gray. There is a contrast in color between the green upper lip and the pale lower lip. The males are generally bigger than females and have yellow throats compared to the female’s white throat. Behind the eyes is the round eardrum, the male eardrum is larger than their eyes, whereas that of the female is about the same size as the eyes. Sometimes the head is all you can see as they sit in the water, but that is enough to tell the sexes apart.
The Bullfrog breeding season typically lasts two to three months, usually around May to July. Territorial males will occupy an appropriate site spacing about 10 to 20 feet apart. This has been compared to a lek; like the breeding ground for prairie chickens. The males congregate, and the
females arrive to the site to mate. Males call loudly to attract females to the breeding pond. Only the male has a call. Three different types of calls have been noted in male Bullfrogs. These distinctive calls include territorial calls made as threats to other males, calls made to attract females, and encounter calls which precede male combat. The males continuously engage in sexual activity throughout the season, with multiple matings.
Choruses, another name for the gathering of males, are dynamic, forming and remaining associated for a few days, breaking down temporarily, and then forming again in a new area with a different group of males. This is what I witnessed at the pool at #11 on the tour. The males were well separated and once one started calling, they all chimed in. To demonstrate their dominance, the males will lift higher in the water by filling its lungs with air, showing most of its body and the bright yellow gular. Occasionally, they will approach a competitor to move it out of their chosen territory.
Low posture with only the head exposed above the water surface is typical of subordinate, or non-territorial males, and females. I saw all this behavior play out as I watched the pond.
Females move in and out of the breeding pond, selecting a male associated with a prime territory. During mating, the male rides on top of the female, grasping her just behind her fore limbs. The female chooses a site in shallow water among vegetation,
and lays a batch of up to 20,000 eggs, and the male simultaneously releases sperm, resulting in external fertilization. That white foamy goo I saw in the slough along the road to the hunt gate, it was Bullfrog eggs! The embryos develop best with water temperatures between 75 and 86 °F and will hatch in three to five days. Given our mid-June storms and temperatures, it is hard to say if the embryos made it or not. But meanwhile, habitat volunteer Tom was out there scooping up the masses with a long pole net to help control our Bullfrog population. Much easier to catch the egg masses than trying to catch the adult frogs.
Emerging tadpoles will move to shallow water where they feed by filtering small particles through their gills, trapping bacteria, single-celled algae, protozoans, and pollen grains. As they grow, they move into deeper water and consume larger particles. Time to metamorphosis depends on water temperature and ranges from a few months in the southern part of their range to three years in the north, where the colder water slows development.
Bullfrogs are an important item of prey to birds like our Great Blue Herons. I saw a heron consume an entire Bullfrog in one gulp last month. It took a bit of work on the heron’s part, but multiple stabs from the big bill assured a nice snack for the heron. The eggs and larvae are unpalatable to most fish and salamanders. Our River Otters will also consume Bullfrogs, but we don’t have the allegators, copperheads and cottonmouths of the southern states to help control their populations. We must rely on the big birds, the herons and even Belted Kingfishers, when they find the right sized Bullfrog, will take them. Meanwhile, the Refuge staff has been issued permits to use efficient methods to suppress the population, like air guns.
The state allows taking of Bullfrogs by angling, hand dip netting, spearing (gigging), or with bow and arrow. It is always open season and requires no permit. And they are not easy to catch that way. Just as a reminder, nothing can be harvested or taken from the Refuge at any time. So, if you have a craving for Bullfrog, you must collect them somewhere else. But feel free.
Some fun facts: The baritone call of the Bullfrog is deep and resonant; it resembles the mooing of a cow. That’s how the Bullfrog got its name. How far can a Bullfrog jump? Up to ten times its body length!
Summer suggestion: Now that the Kiwa Trail is reopened, take some time to watch the Black Phoebe family at the entry where the trail crosses the slough. This parent was seen feeding the new fledgling mid-June. See the February 2023 Friends e-news for more information on the expanding population of Black Phoebe on the Refuge.
-Susan Setterberg, Contact Station Volunteer
images by Susan Setterberg unless otherwise noted
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