Popular Science Monthly/Volume 48/February 1896/The Effect of Prolonged Drought on Animal Life
|THE EFFECT OF PROLONGED DROUGHT UPON ANIMAL LIFE.|
FROM July 6 to October 31, 1895, both inclusive, a period of one hundred and eighteen days, there were but seven days when brief showers occurred, no one exceeding one tenth of an inch of rain; and there were four days when prolonged, heavy showers occurred, no one exceeding seven tenths of an inch of rain; and three days, or parts of twenty-four hours, when the fog condensed and for a brief time a drizzle or "Scotch mist" prevailed.
The more prolonged rains occurring September 26th and October 13th caused little brooks, that had been dry for several weeks, to "run" for forty-eight hours, but there was no freshening of the weeds or grass on either upland or meadow. About our dooryards and along the headlands, even where shaded by rank weed growths and the fences, the ordinary grass was brittle, brown, and resting flat upon the earth. Before the beginning of September the landscape had a scorched appearance, this applying also to the foliage of several species of deciduous trees. By this time, too, the last trace of surface moisture had disappeared from the ordinarily wet or "mucky" meadows.
During this time, even at its close, I did not notice any appreciable diminution of the volume of water flowing from the hillside and meadow-surface spring.*, although I learned that many wells had partly or wholly failed. But, in all cases save one that I examined, the water did not pass over its usual course and join ordinarily permanent brooks, and through them reach the river. The extremely dry ground immediately about the springs absorbed the entire outflow at greater or less distances from their sources. Of course, near the springs there was the usual luxuriance of aquatic and semi-aquatic vegetation, and, what is of interest to the zoölogist, an abnormal abundance or overcrowding of animal life in these oasitic areas.
The continued presence of animal life depends upon the food supply. It is equally evident that no form of animal life can survive for any protracted period an absence of moisture. During the prevalence of the drought heavy dews doubtless afforded a sufficiently copious morning draught to slake the thirst for a period of twenty-four hours, and so met the needs of small mammals, as mice and shrews, and birds, like sparrows, but ordinarily these same creatures drink much oftener than once a day. But this briefly moist condition of the dawn and early morning hours was not of itself sufficient to keep the wide range of animal life in health or comfort, and the result was a migratory movement from the drier uplands to the moister meadows; a noticeable depletion of the fields and overcrowding of the marshes. This was not suddenly brought about, but rather gradual, and would not probably have been noticed except by one daily upon the scene. The parched vegetation had, of course, its effect upon seed-eating birds, but probably a more marked one upon insect life. Certainly the insect-eating birds left their old haunts to a great extent and were found in unusual abundance along the two creeks that divide the meadows into three great tracts; and it was noticeable during the evening that bats and night hawks were more abundant over the meadows than the fields. Mice and hares certainly were unusually scarce in the uplands. Here, it should be remembered, no observations were practicable that gave positive results. No census could be taken of the life in the two localities, and every statement is one of general impressions gained by almost daily visits to the more important points. One unquestionable fact was ascertained: there was an unusual abundance of life of every kind in the lowlands, and a quiet, desolate condition of the fields above, wholly different from what obtains in ordinary summers. As the weeks rolled by, the smaller meadow streams failed entirely, and hundreds of acres of land, usually more or less wet the year through, became as dry, parched, and desert-like as the sandiest field in the higher ground. Aquatic and semi-aquatic plants withered and died. The rose mallow failed to bloom, arrow-leaf wilted, and the pickerel weeds were soon as brown as sedges. This condition necessitated a second migratory movement of many forms of life, but was fatal to others. Such creatures as took refuge in pools found when too late their means of escape cut off and perished. Small minnows, young salamanders, and even aquatic insects gradually succumbed, and their dried remains were found resting upon the parched mud which became quite hard, sustaining an ordinary foot-press without retaining any mark thereof. Lifting the mummified remains from their resting place, there were found impressions of each, distinct in almost every feature. It was instructive as showing how fossils are formed, and further so, in indicating how animals not associated in life become accumulated in small areas. In one such dried-up pool I found a mouse, a star-nosed mole, and remains of many earthworms, as well as fish, batrachians, and insects. Just why the mouse and mole should have remained there and died can only be surmised. But, to return to the uplands: a more striking instance of the effects of the drought was to be seen in a small stream known as Pond Run. This is fed by scattered springs; is a stream of perhaps an average depth of six inches and a width of two or three feet. Sudden dashes of rain swell the volume of waters, but this accession is as rapidly run off. In ordinary summers the volume is reduced to considerably below the estimated average measurements, but the stream has not before been known to be absolutely dry throughout its course. For a period of five weeks the water from the springs along its valley were insufficient to give it running water, and in many cases there was no perceptible moisture at the fountain heads. As the water gradually disappeared, that portion of the stream's fauna dependent wholly upon moisture, as fish, turtles, and batrachians, collected in the pools, particularly those beneath bridges, and there by overcrowding soon poisoned the water to which no fresh supply was being added. It might be asked why these animals, except the fish, did not seek other and healthier localities, but the reason is plain. Everywhere about them was an arid region exposed to a tropical temperature into which they did not dare to venture. Again, while lingering in the pest holes into which they had gathered, they had gradually undermined their strength and were too weak to travel when, if ever, it occurred to them to do so.
And now back to the meadows. The last general migratory movement was to the tide-water flats, and here, of course, the moisture and vegetation were unaffected, and I have never seen so crowded a condition as that in which were many of the streams that were never quite dry at even the lowest stage of the tide. The carnivorous fishes waxed fat, for there was an available minnow ever in front of every pike, perch, and bass; and the grasshoppers driven to the creek banks, where alone there was green herbage, were continually leaping into the stream, and were snapped up before they could reach the opposite shore. There was here, however, not such an accession of batrachian life, frogs in particular, as might have been expected, and I failed to notice any undue number of the mud minnow (Umbra limi). This fact led me to make a few examinations of the parched or semi-desiccated areas. I found in two locations, that I had never before known to become dry, that frogs, of three species, and the mud minnow had buried themselves where there still remained moisture, but with a crust of dry earth above it. These frogs and fish were like hibernating animals when exhumed—i. e., soundly asleep, rather than dead, and all slowly revived when placed in clear, cool water. I estimated that they had been in their cramped quarters for at least three weeks. Two weeks later, I hunted for others but failed to find them; but the day after the first prolonged rain I found the mud minnows in their usual abundance in this same brook, which now had about one half its ordinary flow of water, and the frogs were dozing on the banks and leaping into the stream as unconcernedly as if nothing unusual had occurred.
Possibly the above simple narration of certain facts may seem to be of no special interest or importance, but there were two features of it that do not appear to have been treated of in general natural histories: the self-inhumation of the fish and frogs, and the wonderful promptness of the return of life to the temporarily depopulated areas. It does not seem unreasonable to suggest that as long as these inhumed animals could retain their moisture they could preserve their lives. Both the frogs and this one fish can withstand prolonged deprivation of food. I have tried the cruel experiment in one instance, and a mud minnow had no food for seven weeks, and had only lost two fifths of its weight when it died. As this is a period longer than the duration of any drought on record, when fish-sustaining streams were actually dry, it goes to show that this species is better prepared than any other to accommodate itself to certain geological changes when they come about. Curiously enough, the mud minnow looks more like a fossil than an ordinary brook minnow, is the sole representative of its genus, and is the only species of fresh-water fish found in both Europe and America.
While the drought destroyed much life, it more largely deported it, and I have, in many years of wandering about my home, seen nothing more positively wonderful than the promptness with which every nook and corner was repopulated when the autumn rains came. Vegetal as well as animal life responded at once. The fish were promptly in the brooks, the aquatic salamanders under the flat stones, and the frogs in their places, and on many an afternoon of sunny October days I heard their croaking, as if thankful for the return of the old-time conditions.
- This article treats of an area of about two thousand acres of upland and meadow in the Delaware River Valley, lying between Trenton and Bordentown, Mercer County, New Jersey.