Tuesday, August 23, 2011

Wildlife and the flood

Of all the possible responses to finding yourself trapped on a shrinking patch of dry ground during a flood, burying your head in the dirt seems the most ill-advised. Yet that is what Paul Hartfield, a biologist with the U.S. Fish and Wildlife Service, observed a pack of armadillos doing as the Mississippi River flooded the lowlands north of Vicksburg last spring.

“It was like the height of denial,” Hartfield said of the four armadillos’ behavior, which he observed while exploring the floodwaters by boat with his wife Libby, director of the Mississippi Museum of Natural Science, and Mississippi River guide John Ruskey. The armored rodents had dug a group hole, buried their heads, then clumsily attempted to cover the rest of their bodies with sticks and leaves.

Aside from being successful pioneers (they invaded the southern U.S. from South America), armadillos aren’t known for their intelligence. In fact, based on empirical road-kill evidence, it would be easy to conclude that they’re born dead on the side of the road. But their response to the threat of drowning seemed, well… downright stupid.

Armadillos are in fact able swimmers, capable of dog-paddling great distances, swimming for up to five minutes underwater, and even walking on the submerged bottoms of streams and ponds. Their behavior that day last spring seems to indicate that despite being able to do such things, sometimes they would just as soon not.

Though armadillos often bury their heads in response to a threat, it’s usually a defensive posture, not part of a long-term flood-survival plan. Hartfield said he expects the armadillos changed that plan once water began to fill their hole, that they were merely holding out until the last, and that, given their ability to swim, perhaps it wasn’t as dumb as it seemed.

Hartfield’s story raises an interesting question about wildlife during this year’s historic Mississippi River flood: How did they survive the inundation of millions of acres of land, from Illinois to the Gulf of Mexico, in many cases for months at a time?

Deciding whether to stay or go was on the minds of pretty much every animal in the Mississippi’s floodplain this spring, and unlike human residents, who made a run on every available U-Haul, farm trailer and hill-country storage building, wild animals had only their own legs, wings, fins or… wiggly muscles… to get them out of harm’s way. Making the wrong choice could mean death.

Seasonal fluctuations of water levels have been a part of life along the Mississippi River for millennia. Most of the region’s wildlife are hardwired to recognize the cues that the water is rising and move to higher ground, or, if necessary, swim or climb onto driftwood or into trees. Their responses to a major flood, such as occurred this year, are not unlike those of animals that have evolved within the context of wildfires in the American West, who typically graze as they move, unexcitedly, ahead of the advancing flames. That’s not to say animals don’t suffer, or, in some cases, die.

As Ruskey observed in his blog about a canoe trip he took from Memphis to Vicksburg at the height of the flood, the number of human evacuees along the river paled in comparison with the millions of wild animals that were either swept away or driven from its islands, sandbars and adjacent forests and fields. Still, Ruskey reported seeing only one dead deer during his entire trip.

As the flood retreats into history, biologists, hunters, fishermen and others have begun to assess how wildlife populations fared and how their habitats will be changed. Floods are integral to the ecosystems of the Mississippi River lowlands, but the 2011 event was unusually large in some areas, and a non-event in others, primarily as a result of manmade alterations that concentrate flows outside the protective levees. In many cases, those levees were the potential line of demarcation between life and death.

Ruskey, who operates a canoe guide service in Helena, Ark. and Clarksdale, Miss., noted that during his trip the flooded forests between the protective levees seemed eerily empty aside from an occasional, raucous flock of birds, and he predicted it will be “many seasons” before wildlife demographics return to normal. Along the way, Ruskey saw that one dead deer; another swimming in the surging river; a few snakes in trees; a black squirrel leaping through the forest canopy; and an armadillo, a raccoon and a wild boar that had taken refuge together on a small section of dry ground. Among the other species displaced by the flood were bear, fox, bobcats, coyotes, rabbits, opossums, raccoons, mink, bobcats, moles, beaver, wild turkey, turtles, frogs and skinks.

Given the general lack of wildlife that Ruskey and others observed in the flood zone, one might assume that there were widespread wildlife deaths, and that the ecological balance of the floodplain was significantly disrupted. Neither was likely the case, according to Hartfield, a recognized expert on the Mississippi River. He said that while some old, weak or very young animals no doubt died, most climbed into trees or onto driftwood, or walked, flew, slithered or swam to whatever higher ground they could find. The majority, he said, will eventually return to their home turf.

It comes as something of a surprise to learn that deer, with their spindly legs and small hooves, are actually remarkably strong swimmers, and can swim for miles, even in strong currents. Still, even they must eventually reach a resting spot, which posed a challenge during a flood that in some areas spread 30 miles wide.

For other species, such as wild turkeys, the challenge was to find a place to nest, because the flood coincided with their reproductive season. For still others, such as slow-moving, ground-dwelling moles, voles and earthworms, escape wasn’t really an option.

The danger of animals being forced into the open was primarily about human contact – encountering poachers, vehicles, dogs or manmade obstacles. Wild animals tend to become strangely tolerant of each other during floods, with mortal enemies sometimes congregating together, without controversy, of necessity.

As reports circulated about alligators basking on levees alongside animals that might otherwise have been their prey, I was reminded of something my grandparents told me about floods at their home along Steele Bayou, in the lower Mississippi Delta. The area was accessible only by boat during “high water,” as they referred to the seasonal inundations -- what we now routinely call a “flood.” A flood, in my grandparents’ view, was an unexpected, disastrous event, such as had occurred in 1927. This year’s event would have qualified as a flood, too, but most did not. In that sense, their vantage point was closer to that of the area’s wildlife than to typical contemporary human residents. When the water rose, a person either found a place to ride it out or migrated to higher ground. The biggest problem for my grandparents was the attractiveness of the doorsteps at their elevated house to rattlesnakes and water moccasins. When high water came, my grandparents entertained themselves by taking boat rides to various Indian mounds on which animals with conflicted histories had taken refuge, and where the consensus seemed to be: We’re in this together; let’s not have any trouble on the mound.

Such scenes were repeated during this year’s flood. For the most part, high ground meant the bluffs that abut the river in Memphis, Vicksburg, Natchez and Baton Rouge; the levees that in places run along both sides of the river; and scattered Indian mounds. In some cases the only refuge wasn’t ground at all: During the height of the flood, deer and other animals were frequently seen marooned on the roofs and porches of homes. In places such as tiny Rodney, Miss., which is unprotected by levees, the dispersal of wildlife added an unexpected edge to the flood, as alligators were seen swimming along submerged streets.

Hartfield said the flood likely dispersed a great many animals, and may have fragmented the small surviving populations of bear, though they are also accustomed to swimming and climbing trees.

As for the impact of the flood on lowland habitats, some riverbanks, sandbars and farm fields were scoured by the currents, and some trees were uprooted. But in most cases the flood will be a boon to wildlife because it will rejuvenate habitat and introduce new food sources. Some animals will feast on the occasional carcass or on sluggish fish trapped in shallow, diminishing pools.

“The floodplain is fertilized, and blooms following a flood,” Hartfield said. “Food is abundant, and wildlife populations rebound and prosper. Oxbow lakes are replenished, and fishing should actually improve.” He added that it is also worth remembering that floods are the reason those areas remain comparatively wild.

Photo courtesy John Ruskey

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