SCIENCE-GOSSIP. 



295 



CHANGING HABITS OF ANIMALS. 



By J. Beecham Mayor, L.R.C.P., M.R.C.S. 



THE relation of environment, that is, of the 

 conditions of life, to variation is very interest- 

 ing. From different causes old characters become 

 of slight value, and so are discarded in favour of 

 new ones, which, proving useful in the " struggle 

 for existence," are preserved and transmitted to 

 the offspring. These new qualities gradually 

 produce in time a change in the animal's structure, 

 or its habits. Thus, a sea-gull, a fish-eating bird 

 whose stomach naturally has thin muscular walls, 

 when fed for a whole year upon barley was found 

 to have its stomach-walls increased in thickness, 

 and pertaining more to those of a grain-feeding 

 bird. Again, the increase of the European rabbit, 

 due to its enormous fecundity, is kept within 

 reasonable bounds in its native habitat by weasels, 

 birds of prey and other destructive animals. The 

 boldness of the weasel in pursuit of its prey was 

 forcibly brought to my notice last summer while 

 rambling across the braes above Callander, in 

 Scotland. Walking along the path which crosses 

 the open ground to the falls of Bracklin, in the 

 middle of the day, and with several people in 

 view, I saw two weasels chasing a young rabbit. 

 Though I was only a few yards away, and 

 accompanied by my brother, they caught it close 

 to the path, and would not leave their victim until 

 we came close up to them. The poor rabbit lay 

 there on its side unable to move, giving a few 

 convulsive kicks and soon expired. Now when 

 man, regardless of such provisions of nature, 

 introduced this prolific herbivorous animal into 

 Australia he forgot that its natural enemies, the 

 birds of prey and the smaller carnivora, were 

 unrepresented on that continent. Consequently, 

 though only a few pairs were let loose in Victoria 

 in i860, it has already overrun the greater part of 

 the colony, and is spreading into other districts, 

 bidding defiance to all means of repression. 

 After a time it was found that wire-netting placed 

 round the pastures and gardens, and sunk a few 

 feet into the ground, entirely prevented the rabbits 

 from burrowing under it. But now the rabbit, 

 nothing daunted, is showing a facility for climbing 

 over the netting, by the development of a modified 

 hooked nail which enables it to hook its claws on to 

 the wire strands and thus sustain its weight. By 

 the same means it is also able to ascend the trunks 

 of trees in its search after bark. The offspring of 

 those rabbits possessing this structural modification 

 are thus placed in a better position for survival 

 over the ordinary form, and so will increase in 

 numbers. From a similar alteration in environ- 

 ment, we see a variation in habit of the common 



English fox, which, introduced into Australia to 

 keep down the rabbits and for sport, has taken to 

 feeding upon the young lambs, and is proving very 

 destructive Another well-known extraordinary 

 change or variation in habits, has occurred in the 

 Kea, a parrot found in the mountains of New 

 Zealand. The natural diet of this bird is fruit 

 and berries, but since England has occupied the 

 country and introduced sheep-farming, it has 

 gradually become carnivorous. At first it picked 

 off the fragments of flesh on the sheep-shins hung 

 up to dry ; then it was attracted to the meat which 

 was curing in the open air, and finally, about 

 thirty years ago it attacked living sheep, alighting 

 upon their backs and eating its way down to the 

 kidneys, which are its special delicacy. 



Lately, another instance of this variation in habit 

 has been noticed in the case of the mongoose, an 

 animal about the size of a weasel, which was 

 introduced into Jamaica twenty years ago to 

 destroy the rats which were very destructive to the 

 sugar-canes. The natural food of the mongoose 

 becoming scarce, and being also very prolific, 

 they began to prey upon young pigs, kids, lambs, 

 newly-dropped calves, young rabbits, game-birds 

 and certain fruits, vegetables, and even the edible 

 black-crab which has thus almost been exterminated 

 in the island. The few rats remaining upon the 

 island have also undergone a change of habit, in 

 in order to escape this new enemy, and so now 

 instead of making their nests upon the ground, 

 build them high up in the banana and cocoa-nut trees. 

 The alteration in the mode of living due to 

 change in the conditions of life, has been well 

 shown in the beaver, Those specimens still 

 surviving in Europe, though undoubtedly descend- 

 ants of social, hut-building animals, being relent- 

 lessly pursued by man, have given up their colonising 

 habits with the prominent domed huts and dams, 

 and have taken to constructing solitary deep bur- 

 rows in the margins of the streams they frequent. 



A beautiful adaptation to environment is to be 

 noted in a Brazilian frog, Hyla faber, in its efforts 

 to protect its offspring from the destroyer. The 

 female, instead of acting like the common frog and 

 leaving the young tadpoles to the mercy of the 

 first-comer, scoops out the mud on the bottom of 

 the pond, thus making a little hollow, round which, 

 by means of her hands used as trowels, she builds 

 up walls. Inside these small shelters or nurseries, 

 the eggs are deposited and the young tadpoles are 

 confined therein until of sufficient strength to fight 

 their own battles. 



2, St. Alban's Villas, Hcaton Chapel, near Manchester 



