Naturespeak A naturalist's view of the world

November 14, 2007

One Day at the Mudflat

Filed under: Uncategorized — wykes @ 6:09 pm

 The water has not returned to this portion of the coastal marsh since it blew out in early October. Exposed mudflats, edged by a cat-tail border, mark the previous location of the liquid element.  The pasty black basement of the marsh is pockmarked with small pools and ribbons of water in the low spots. Millions of stranded duckweeds pepper the surface with flecks of green. Like the alligator swim holes in the droughty Florida everglades, only the muskrat canals retain any significant water. These channels mark the habitual travel routes of the ‘rats as they traverse the marsh on their daily rounds. They are not deliberately excavated but are created through constant use – worn trails marking the outlines of a wet pasture. Most canal systems originate from the cat-tail edge and fan out dendritically into the open water portions, but are invisible when coated over with a liquid veneer.  The exposed canals are outlined clearly against the muck background and stand as evidence that the ‘rats claim nearly every portion of the marsh.

  Such a mudflat scene normally lasts only a day or two and is typically the result of a temporary phenomenon known as a sieche. When prolonged stiff westerly winds push the near shore contents of Lake Erie towards Buffalo, New York, the resulting wind tide drains the precious shallow water from the shoreline marshes on the Michigan end. Life waits in suspended animation until the winds play themselves out and the waters inevitably return. The lake level here always drops during the fall and sieches are frequent events, but this year the levels have been extremely low.  It seems that the winds have carried the water away for good and will not return it before the freeze-up. 

  This morning, four Common Snipes took advantage of the situation and were busily probing the wetter portions for aquatic insects. These brown and cream streaked birds are secretive by nature and rarely venture out into the open like their gregarious cousins the sandpipers, dowitchers, and yellowlegs.   Today, the prospect of easy hunting overcame their reclusive tendencies. The birds pushed their long bills into the mucky water to pluck out insects and mechanically probed in and out as they walked.  One bird, standing off from the others, added a rhythmic bob to his gait as if portraying Popeye in one of those shaky early cartoons. He was timed to a beat that the others did not perceive (in the world of the snipe he may be the “special one” – who knows).

  There is one small corner of the marsh, ¼ mile distant from the lake, which retains a large murky pool of water. The Snipe avoided it because the water is too deep for their short little legs, but four mallard ducks have found it much to their liking. It contains just enough water to provide three green-headed drakes and a single brown hen with a secure swimming space. Since the advent of duck season, this corner also provides an additional benefit as a refuge tucked away from the hunted portions of the lakeshore.  Perhaps most importantly, these muddy shallows are a fertile ground for dabbling.

  Mallards are classified as dabbling ducks which means they feed on plants and invertebrates found within neck-reach in shallow water.   When swimming, they typically tip their rump into the air and dip their heads below the surface to muddle through the debris with their beaks.  When presented with mud flat shallows they resort to walking with their necks extended down and forward while noisily dabbling the mud as they go. They systematically sweep the area before them as if metal detecting.  The constant pitter patter of shutting beaks generates the sound of a gentle rain.

   The top and bottom bills of the mallard are edged with tooth-like structures called lamellae.  These act as sieve plates when the beak is partially closed.  The birds scoop up mouthfuls of mucky water and force the water out through the lamellae with a push of the tongue – in the manner that whales use their baleen plates. Bits of plants, tiny snails and other edible fare are separated out and duly ingested.

  As the herds of dabbling mallards worked the far edge, a pair of muskrats busily foraged at the deeper end.  This pair of ‘rats wisely chose to construct their winter lodge along the deeper part of the marsh.  Working primarily at night, the two have piled up a mass of bottom debris and cat-tail stalks towering three feet over the water level. The afternoon found them attending to some light lodge duties as well. The primary entrance to the structure is an underwater tunnel accessible from the deeper east side.  The back side of the lodge sits at the edge of the pool where it approaches zero depth. They have built another house across the pool close to where the mallards were now operating, but haven’t spent much time there today.

  In between diving trips to gather up tender cat-tail rhizomes followed by periods of contented feeding, at least one ‘rat appeared distracted by the activity of the ducks.  On occasion this one would float stiffly at the surface and scan the birds with an unblinking stare, before resuming his feeding.  While the other ‘rat was satisfied where he was and with what he was doing, the staring ‘rat couldn’t let the thing be.  To say that he looked irritated, while anthropomorphic, certainly fits his demeanor.

  Eventually he ventured out closer to the ducks while in the process of gathering in a mouthful of bottom detritus and water plants.  He lingered a moment in their vicinity, but turned and took the bundle back to the lodge and dove under.  A few moments later he came out and nervously cut away a dead cat-tail leaf while continuing to eye up the feathered intruders.  This leaf he also took into the lodge for necessary interior adjustments.

  The next time out, he worked his way immediately over to the dabblers but clung to the shallows on the lodge side of the pool. Although appearing to gather material, he didn’t actually pick anything up.  Alligator-like he slid over towards a drake that was preening atop a mound of mud.  Suddenly the determined ‘rat exploded out of the water and leapt directly at the bird. His attack propelled him into an airborne arc and he landed exactly at the spot that the surprised Mallard quickly vacated.

  The muskrat bounded off the hummock and continued his pursuit of the drake by hurtling back into the water.  The duck swam rapidly ahead of his pursuer but even his swimming ability was taxed as the angry ‘rat pulsed forward with powerful tail thrusts that lifted his forequarters out of the water. They two zigged and zagged about for a while as the other ducks scattered. The gator-rat stuck to the path of his chosen victim and ignored those about him.

 For a moment the natural order of things was rendered katty-whampus. Should the muskrat capture his chosen prey what would he do with it? Would bland plant material ever satisfy his calm vegetarian needs again? But as quickly as the situation presented itself, it ended. The muskrat broke off the pursuit and the flustered drake slowly regained his composure.  The ‘rat had made his point and confidently swam into the seclusion of a dense cat-tail stand to revel in his victorious statement of territoriality.

  The late afternoon sun was casting long shadows over the battlefield by this time and heralded the return of the natural order. The piddling ducks resumed their activities and the other muskrat calmly remained in his part of the mudflat pool.

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