THE NATURALIST.

Otago Witness, Issue 1645, 2 June 1883, Page 27

THE NATURALIST.

A Wave of Life.

BY AN ARGENTINE NATCBAUST.

For many years, while liviug in my own home on the Pampas, 1 kept a journal in which all ray daily observations oq the habits of animals and kindred matters were carefully noted. Turning back to 1872-3, I find my jottings for that season contain a history of one of those waves of life — for I can think of no better name for the phenomenon in question — that are of such frequent occurrence in thinly-settled regions, though in countries like England seen very rarely, and on a very limited scale. An exceptionally bounteous season, the accidental lightening of a check, or other favourable circumstance, often causes an increase so sudden and inordinate of small prolific species, that when we actually witness it we are no longer surprised at the notion prevalent amongst the common people that mice, frogs, crickets, &c, are occasionally rained down from the clouds.

In the summer of 1572-3 we had plenty of sunshine with frequent showers ; so that the hot months brought no dearth of wild flowers, as in most years. The abundance of flowers resulted in a wonderful increase of humblebees. I have never known them so plentiful before ; in and about the plantation adjoining my house I found, during the season, no fewer than 17 nests.

The season was ateo favourable for mice; that is, of course, favourable for the time being, unfavourable in the long run, since the short-lived, undue preponderance of a species is invariably followed by a long period of undue depression. These prolific little creatures wero soon ;-o abundant that the dogs subsifeted almost exclusively on thorn ; the fowls alao, from incessantly pursuing and killing them, became quite rapacious iv their manner ; whilst the sulphur tyrant birds and the Guira cuckoos preyed on nothing but mice. The domestic cats, as they invariably do in such plentiful seasons, absented themselves from the house, assuming all the habita of their wild congeners, and slinking from the sight of man — even of a former fireside companion — with a shy secresy in their motions, an apparent affection of fear, almost ludicrous to see. Foxes, weazels, and opossums fared sumptuously. Even for the common armadillo (JDasypuß villosus) it was a season of affluence, for this creature is very adroit in capturing mice. This fact might seem surprising to anyone, considering the uncouth figure, toothless gums, and motions — anything but light and graceful — of the armadillo ; aud perhaps fancying that, to be a dexterous mouser, an animal should bear some resemblance in habits and structure to the Felidse. But animals, like men, are compelled to adapt themselves to their surroundings ; rew habits are acquired, and the exact co-relation between habit and structure is seldom maintained.

I kept an armadillo at this time, and good cheer and the sedentary life he led in captivity made him excessively fat ; but the mousing exploits of even this individual were most interesting. Occasionally I took him into the fields to give him a ,taste of liberty, though at such times I always took the precaution to keep hold of a cord fastened to one of his hind legs ; for as often as he came to a kennel of one of his wild fellows, he would attempt to escape into it. He invariably travelled with an ungainly trotting gait, carrying his nose, beaglelike, close to the ground. His sense of smell was exceedingly acute, and when near his prey he became agitated and quickened his motions, pausing frequently to sniff the earth, till, discovering the exact spot where the mouse lurked, he would stop and creep cautiously to it ; then, after slowly raising himself to a sitting posture, spring suddenly forwards, throwing his body like a trap over the moube, or ne»t of mice, concealed beneath tho grass.

In the autumn of the year countless numbers of storks (Cicouia tnaguari) and of short-eared owls (Otus brachyotus) made their appearance. They had also come to assist at the general feast.

Remembering tho opinion of Mr 18. Newman, quoted by Darwin, that two-thirds of the

humble-bees in England are annually destroyed by mice, I determined to continue observing these insects, in order to ascertain whether the same thing occurred on tho Pampas. I carefully revisited all the nests I had found, and was amazed at the r.apid disappearance of all the beos. I was quite convinced that the mice had devoured or driven them out, for the weather was still warm, and flowers and fruit on which humble-bees feed were very abundant.

After cold weather set in the storks went away, probably on account of the scarcity of water, for the owls remained. So numerous were they during the winter, that any evening after sunset I could count 40 or 50 individuals hovering over the trees about my house. Unfortunately they did not confine their attentions to the mice, but became destructive to the birds as well. I frequently watched thepa at dusk, beating about the trees and busheß in a systematic manner, often a dozen or mora of them wheeling about one treo like so many moths about a candle, and one occasionally dashing through tLa branches until a pigeon — usually the Zenaida maculosa — or other bird was scared from its perch. The instant the bird left the tree they would all give chase, disappearing in the darknes-s. I could not endure to see the havoc they were making amongst the oven-birds (Furnarius rufus— a species for which I have a regard and affection almost superstitious), so I began to shoot the marauders. Very soon, however, I found it was impossible to protect my little favourites. Night after night the owla mustered in their usual numbers, so rapidly were the gaps I made in their ranks refilled. I grew sick of the cruel war in which I had so hopelessly joined, and resolved, not without pain, to let things take their course. A singular circumstance was that the owls b^gan to breed in the middle of winter. The field labourers and boys found many nests with eggs and young birds in the neighbourhood. I saw one nest in July, our coldest month, with three half-grown young birds in it. They were excessively fat, and, though it was noonday, had their crops full. There were three mice and two young cavies (Oavia australis) lying untouched in the nest.

The short-eared o*vl is of a wandering disposition, and performs long jurneya at all seasons of the year in search of districts where food is abundant ; and perhaps these winterbreeders came from a region where scarcity of prey, or some such cause, had prevented them from nesting at their usual time in summer.

By August (1873) the owls had vanished, and they had, indeed, good cause for leaving. The winter had been one of continued drought ; the dry grass and herbage of tha preceding year had been consumed by tha cattle and wild animals, or had turned to dust, aud with the disappearance of their food and cover the mice had ceased to be. The faminestricken cats sneaked back to the house. Ifc was pitiful to see the little burrowing owls ; for these birds, not having the powerful wings and prescient instinct of the vagrant Otus bachyotus, are compelled to face the poverty from, which the others may escape. Just as abundance had before made the domestic cats wild, scarcity now made the burrowing owls tame and fearless of man. They were so reduced as scarcely to be able to fly, and hung about the houses all day long on the look-out for some stray morsel of food. I have frequently seen one alight and advance to within two or three yards of the doorstep, probably attacted by the smell of roasted meat. The weather continued dry uutil late in spring, so reducing tha sheep and cattle that incredible numbers perished during a month of cold and rainy weather that followed the drought. How clearly we can see in all this that the tendency to multiply rapidly, so advantageous in normal seasons, becomes almost fatal to a species in Beasons of exceptional abundance. Coyer and food without limit enabled the mice to increase at such an amazing rate that the lesser checks interposed by predatory species were for a while inappreciable. But as the mice increased, so did their enemies. Inseo tivorous and other species acquired the habits of owls and weazles, preying exclusively on them ; while to this innumerable army of residents was shortly added multitudes of wandering birds coming from distant regions. No sooner had the herbage perished, depriving the little victims of cover and food, than the effects of the war became apparent. In autumn the earth so teemed with them that one could scarcely walk anywhere without treading on mice ; while out of every hollow weed-stalk lying on the ground dozons could be shaken ; but so rapidly had they been devoured by the trained army of persecutors, that in spring it was hard to find a survivor, even in the barns and houses. The fact that Bpecies tend to increase in a geometrical ratio, makes these great and sudden changes frequent in many regions of the earth ; but it ia not often they present themselves so vividly as in tho foregoing instance, for here we see countless myriads of highly organised beings rising into existence only to perish almost immediately, scarcely a hard-pressed remnant remaining after the great reaccion to continue the species. — Field.