May, 1905. 



KNOWLEDGE & SCIENTIFIC NEWS. 



105 



MoLmmals that Carry 

 Their Young. 



By R. LVDEKKER. 



" While taking bats one day in December, I captured 

 a female of our common Buenos Ayrean species 

 (Molnssus bonariensis), with her two young attached to 

 her, so large that it seemed incredible she should be 

 able to fly and take insects with such a weight to drag 

 her down. The young were about a third less in size 

 than the mother, so that she had to carry a weight 

 greatly exceeding that of her own body. They were 

 fastened to her breast and belly, one on each side, as 

 when first born; and possibly the young bat does not 

 change its position, or move, like the young developed 

 opossum, to other parts of the body, until mature 

 enough to begin an independent life. On forcibly 

 separating them from their parent, I found that they 

 were not yet able to fly, but when set free fluttered 

 feebly to the ground. This bat certainly appeared 

 more burdened with its young than any animal I had 

 ever observed. " 



Thus wrote Mr. W. H. Hudson in that delightful 

 book, " The Naturalist in La Plata," rather more than 

 a dozen years ago. The passage appears, . however, 

 to have been generally overlooked by later naturalists 

 (the present writer among the number), for in 1902 the 

 fact that certain female North American bats habitu- 

 ally carry about with them more than a single offspring 

 clinging to their own bodies was brought to notice as 

 an entirely new discovery. So utterly incredible, in- 

 deed, did it appear to naturalists of an earlier date, 

 that a bat should be able to fly with a couple of young 

 ones clinging to her breast, that in 1878 the late Dr. 

 G. E. Dobson expressed the opinion that, in the case of 

 twins, one of the pair might be transferred to the male 

 parent, and carried about by him. Not only, how- 

 ever, has no instance of such a transference ever been 

 observed, but the discovery that female bats are cap- 

 able of carrying not only two but actually four offspring 

 about with them indicates that, in the great majority 

 of species, it never occurs at all. 



The case of the above-mentioned North American 

 bat (Lasiurus borealis), of which a full description wull 

 be found in " Knowledge " of November, 1903, alto- 

 gether eclipses the instance quoted by Mr. Hudson, for 

 two specimens of this species have been brought to 

 notice with four young ones clinging to their nipples. 

 And although no one has hitherto taken a female thus 

 loaded in actual flight, from the fact that bats of the 

 genera Lasiurus and Dasyptcrus are furnished with two 

 pairs of nipples, it appears probable that a quartette of 

 young ones is commonly carried by the female parent 

 during her aerial wanderings. On the other hand, as 

 European bats have but a single pair of nipples, it may 

 be inferred that the females never carry more than two 

 young, although an instance of even this does not ever 

 appear to have been observed. 



As already mentioned, the weight of the twins 

 actually seen to have been carried by the South Ameri- 

 can species is reported to have greatly exceeded that 

 of her own body. In the case of one of the North 

 American specimens, the weight of the quartette was 

 12.7 grammes; while that of the mother was only 11 

 grammes. The offspring in this instance were, how- 

 ever, much younger than in the case recorded by Mr. 

 Hudson, so that it is a fair inference in the instance of 



the North American species that the weight of the off- 

 spring would have eventually doubled that of the 

 parent before the burden was finally discarded. How 

 such a sorely over-burdened mother could have 

 managed to fly at all is little short of a miracle. 



From their peculiar mode of life it is, of course, 

 evident that bats of all kinds must habitually carry 

 their young about with them; and in the case of the 

 large fruit-bats, or flying-foxes, which can be easily 

 kept in captivity, it has been observed that in repose 

 the young cling head-downwards to the under surface 

 of the body of the female parent (Fig. i). In the re- 

 markable naked bat (Chirnmchs torquata), of the Malay 

 countries, the absence of fur would, however, effectually 

 prevent the young being carried about in the ordinary 

 way; and we accordingly find the nipples enclosed in 

 large pouches of skin, which doubtless form receptacles 

 for the young bats. From the fact that these pouches 

 are present in both sexes, it has been suggested that, 

 in the case of twins, the care of one of the pair is 

 undertaken by the male parent. Even, however, if 

 twins are ever produced by this species, the case of 

 the above-mentioned American bats suggests that no 

 such transference of a share of the burden is essential. 



^ 



Fijf. 1. -Female Fox=Bat with young 



1__^^ ..J 



, (From Sclaler, Pruc. Zvol. Soc. 



Next to these sorely-tried American bats, the most 

 overburdened animals would appear to be the females 

 of the American opossums, some of which are in the 

 habit of carrying their numerous progeny about with 

 them on their backs, as many of the young as can find 

 room securing a firm hold by twisting the tips of their 

 own prehensile tails around the tail of their parent, 

 which, in some instances, at any rate, appears to be 

 bent forward over her back for this special purpose. _ In 

 the case of one of the larger South American species, 

 which is considerably inferior in size to an average 

 cat, Mr. Hudson tells us that he has seen as many as 

 eleven young ones, each as large as a full-sized rat, 

 carried about on the parental back. In this instance 

 the burden must be proportionately greater than in the 

 case of a terrestrial animal, for these opossums when 

 thus loaded follow their usual practice of climbing 

 swiftly and with the greatest agility among the higher 

 branches of trees. Indeed, it would seem that the 

 creature must capture its prey while thus burdened 

 for the members of the family, like Sinbad's old man of 

 the sea, seem never to voluntarily relinquish their 

 equestrian position until old enough to shift for them- 

 selves. 



