Monsoon Rearrangements

The monsoon season in southeastern Arizona extends from early July to late September, and usually means hot and humid weather with frequent thunderstorms.   The thunderstorms seem to be the definition of chaotic systems, so you never quite know where they will appear or how much rain they will produce.

This rainy season, an extension of the Mexican monsoon, is one of the factors accounting for the tremendous biological diversity of southeastern Arizona.  Hot rainy weather is a boon for plant life, which in turn supports diverse communities of insects, birds, and mammals.  A large number of Mexican species reach their northern limits here.  In addition, a number of bird species that migrate further north to breed will stop here on their migration south, to take advantage of the rich food supply to regenerate their feathers during their molts.

Much of the monsoon season was a bust this year over many parts of southeastern Arizona, while other areas received massive amounts of rain.  The east side of Tucson was one of the dry areas, as was the Cienega Creek drainage all of the way to Sonoita.  Most of the rain occurred during heavy downpours in early July and early September, with little in between.

In mid-August, I went down to Las Cienegas National Conservation Area south of Tucson to do some tracking and recording.   I hiked in to Mattie Spring, which is a lovely perennial water source that supports a lot of wildlife.  The spring is located not far from the confluence with Cienega Creek, although the drainage, as a usually dry wash, extends east into the Whetstone Mountains.

The Whetstones were hit with some very big thunderstorms in early July, which sent a massive wall of water down Mattie Wash.  The impact on the drainage, especially downstream from the spring was profound.

The normally sleepy little stream had raged and thundered, ripping up trees and gouging large holes in the stream bed.  Most surprising, though, is that the stream was now mostly dry, with a few scour pools and only short stretches where it still ran as a small stream.  But there were large stretches of dry stream bed.  Previously, it had run almost the entire 2-3 miles to the confluence with Cienega Creek.

Yet in spite of all the rearrangements at ground level, the bird and bug activity in the tree canopy was alive and well.   Just past the start of the spring, a large cut bank, part of an old oxbow, creates a natural amphitheater.  Combined with the cottonwood canopy , this creates a lovely acoustic ambiance.  I often come here to just listen.  Each time it is a little different, with a different cast of avian and insect singers, depending upon the season.  An ever-changing whisper in the cottonwood canopy.   And the stream never sounds quite the same either.  On this particular day, the stream was flowing so slowly that I couldn’t detect any sound from it.

I set up the microphone and headed downstream to see what kinds of wildlife sign I could find.  Shadow and I meandered across the stream bed and climbed over flood debris, encountering tracks of opossum, squirrels, bobcats, deer, raccoons, turtles, frogs, and black bear.  The bear tracks looked pretty fresh, and sure enough, a few hundred yards from where we first saw the tracks, I saw Shadow stop and cautiously look around.  He quickly ran back to me, his demeanor indicating something scary was up ahead.  As he usually does this when there is a bear around, I stopped and listened.  I could hear something large moving through the leaf litter up ahead.  I climbed up the bank a bit, and glimpsed a large red bear that faded into the vegetation before I could get a photo.   Not wanting to stress the bear or the dog, I took this as a cue to head home.

References: 
Pyle, P. et al. 2009. Temporal, spatial, and annual variation in the occurrence of molt-migrant passerines in the Mexican monsoon region. Condor 111: 583-590.

Recording notes:  Recorded with Sony PCM-M10 with Audio-Technica AT2022 mic with Felmicamps SK3.5 pre-amp.