Marckworth Forest and Pacific Tree Frogs with a Barred Owl

The Marckworth Forest is northeast of Carnation, Washington. The Department of Natural Resources manages these lands for timber. The state harvests trees to help support the school system. Yet, it has lots of natural habitats and can be an outstanding place to visit. The area is a few miles up the hill from Stillwater and accessible by a dirt road. Coniferous and deciduous trees grow throughout the area and it is home to many birds and Pacific tree frogs.

In early May, I went looking for natural wonders to ponder and also to stash several sound recording rigs in interesting places. Near a bend on Stossel Creek Road, I walked back along a deer trail until I found a small wetland. The stream was a tributary of Stossel Creek, not large, flowing softly, and in one place it spread into a wetland a dozen or more feet wide. A mixture of grasses, ferns, shrubs, and small open pools made an abundant habitat for species. I found a small sapling near the water’s edge and tied a stereo microphone to opposite sides of the trunk. The area looked suitable for birds and amphibians. What might I discover? One never knows what, if anything, will call, and it is always a fun mystery to open the recordings on my computer.

Several miles north of that point, a large pond sits northwest of the road where Stossel Creek opens into a vast body. On that morning, a pair of hooded mergansers lurked on the far side and several red-winged blackbirds called from the edge. Upstream of the pond lies a series of wet shrub thickets and small ponds, each with numerous water lilies. A clump of western hemlocks and red cedars grows on a small peninsula sticking into the marsh, forming like a small gazebo on a point. Several years ago, I’d stashed one of my recorders here and captured a wonderful sequence of a Barred Owl calling with its young begging in the distance. I found the same small vine maple where I’d put the microphones and set another drop rig up, thinking, who knows, maybe I’ll be lucky.

Two Days Later

I returned to retrieve the rigs. Each recorder is enclosed in a small dry bag to protect it from the weather, and a battery block is used to maintain power for longer periods than the internal batteries last. The recorders run continuously, creating a sequence of files, each with 2 hours of time. It is always a mystery to open the dry bag. Will the recorder still be running?

I must look crazy walking up to the setup, for I always say hi, then rattle off the time, date, where I’m located, weather, and other odds and ends before opening the dry bag. Each recorder has a unique ID, a name like B5, written on its bottom. I will then record the name of this particular recorder right into the sound file. This process allows me to have a second way, besides my notebook, of keeping track of the metadata for the recordings from a location.

Then, I head back to my house so I can transfer the files to my computer and see what might have called.

Small Wetland on the Tributary

Frogs, Pacific tree frogs (Pseudacris regilla), must have filled the wetland from one side to the other, and some had been right near the recorder. Their “rib-it” or “crek-ek” calls jumped out of my speakers like someone was playing a set of drums on both sides of my computer. It was gorgeous, and I leaned back to listen to their attempts to attract a female.

I could imagine their throat sacs bulging out, filled with air, forming a resonating chamber that the male then used to produce its call. The frogs sang on and off all night. One male would start chirping, and then they all must respond. At some points, the chorus would suddenly go silent for a few minutes before one couldn’t resist giving his call into the silence. The quiet periods were so complete that I checked the computer program to make sure it was still playing. The night had been calm, so there was very little rustling in the leaves.

I found a two-hour segment that started around 2 AM. It was free of human-made sounds, and I decided to study it more closely. In the first few minutes, a barred owl can be heard calling in the background. The bird calls, “Who cooks for you? Who cooks for you all?” Barred owls will eat these frogs, so these amphibians must pay attention to more than just attracting a female. It is a balancing act of survival and reproduction. The video here displays the frequency of individual notes between 20 hertz and 10,000 hertz. The height of the bars reflects the loudness of a note. It gives some animation to the 2-hour recording.

Pacific tree frogs are small. An adult might be about 2 inches long. To think that a little thing can belt out a tune with the intensity to carry across the marsh is awesome. They puff out their throat patch to make a resonating chamber, creating that wonderful “rib-it” or “crek-ek” call.

The Large Wetland

This recorder captured a sequence of files that covered day and night for two days straight. The Pacific Tree Frogs began to call as the sun started to set. In the night’s sequence I chose to examine, a red-winged blackbird gave a few last-minute announcements over the frogs before retiring for the night. It took an hour for the frogs to reach full chorus, after which they maintained high intensity for nearly 4 hours. A few times, they stopped briefly when a vehicle went by on the single-lane dirt road. After the intense period, the volume decreased as fewer males continued to display, and the concert continued for another 3 hours before the frogs stopped for the day.

The loudness of a male and the persistence of their singing are thought to be an indicator to females of each male’s fitness and, therefore, worthiness as a mate. I wondered whether the decrease in the second half of the night was due to many males having found a mate that evening, or whether it was just a matter of running out of steam. I’ve been to concerts where the performer sang or played for one hour and occasionally more, but never one where they sustained intense activity for four hours. Even if I could sing, there is no way I could perform for that length of time.

This recording goes for close to 8 hours. The white bar at the bottom displays frequency from 20 Hz to 10,000 Hz. The lines jumping up indicate the frequencies (pitch) heard at that time, and their heights indicate how loud those notes were.

Both recordings are stereo. You can fill your house with the sweet sounds of spring while you do other things. I sent it to my smart TV, so the chorus came over my stereo speakers. It made me think I was in the woods. Perfect music for a nap on the couch.

More Information on Pacific Tree Frogs:

https://wdfw.wa.gov/species-habitats/species/pseudacris-regilla#desc-range

https://en.wikipedia.org/wiki/Pacific_tree_frog

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