Imagens das páginas

upon the theory of natural selection, inasmuch as it could contribute in no way to the advantage of the animal; that it seemed to him quite clear that it was rather calculated to hinder than to help the creature in the race of life by warning its prey of its presence." But he intimates that he is now ready to say, that this appendage can be explained upon the theory of natural selection. He considers the idea that it might be used as a sexual call as untenable, but that the whirring sound of the rattles closely imitates the sound made by the Cicada and for this reason is used as a call-note, as a hunter uses his bone-turkey-caller, to induce the bird to come within the range of his weapon. Now the first question which naturally arises is this: Does the snake sound its rattles when seeking to capture its prey? I have always understood that it is only when it throws itself upon the defensive and prepares for battle that the rattles are sounded; that it is an alarm note, a war-cry, and not a gentle, deceptive invitation to the victim. I have never seen a rattlesnake, and know of course nothing personally of its habits. But if this use is not made of the rattles as suggested by Prof. Shaler, and the sound only serves to call the attention of its enemies and thus invite destruction, then indeed is the theory of natural selection nonplussed. But as I view the matter, instead of inviting his destruction by sounding the rattles, it is one of the most effective means of self protection and is as useful to it in the race for life as is the growl of the tiger when threatened with danger. The snake does not sound its rattles until it considers itself discovered, and not then unless it apprehends danger. It throws itself in position to strike and says in unmistakable language, "Look out, I am ready for you!" If pushed upon, it makes its leap at its antagonist, and again throws itself in position to renew the conflict, and again sounds the note of defiance; a note calculated to alarm and, like the war-whoop of the Indian, strike terror to the heart of the assailant; but it maybe said that the Indian only utters his yells when rushing on his enemy, or when actually engaged in the conflict, and the sounding of the rattles upon the first approach of danger is a disadvantage. Now it seems to me, if this were true and if it be a piece of rashness upon the part of the snake thus early to exhibit his combatativcness, that natural selection would cure the matter by selecting and preserving the more timid, and that, eventually, rattlesnakes would only sound their tail-bells when it would best promote their interests.

"We are not to judge of the advantage or disadvantage of the rattles by their effect upon the nerves of man alone, though no doubt many a man has turned his back and been deterred from making an attack by the sound of these rattles and the defiant attitude of their possessor.

The ability of the snake to defend itself does not consist in its strength or size, or in its power of overcoming its adversary by a prolonged conflict, for most of its enemies are its superior in size and strength. Nor does its deadly poison act quickly enough to secure its own safety when it is attacked, but, in most cases, the victim, after the deadly stroke is given may still revenge itself by the destruction of the snake. But the certainty of the effect of the poison serves as a warning and is advantageous, not in defense after the attack is made, but in preventing an attack from being made. If, then, the color of the rattlesnake were different from all harmless snakes, so much so as to render it conspicuous, this would be beneficial to it, by the readiness with which all animals would recognize it, and thus protect the snnke by this notice of the deadly character of its weapons. If then a conspicuous color would lie of advantage, it seems to me that an}' other means which it may be able to use in making known its character to any animal that may come near it, would be advantageous, and would be increased and preserved by natural selection, and that the whirring noise which it produces, in this view of the matter, admirably serves its purpose. In effect it amounts to this, and by experience its enemies learn to understand its language, "I am a rattlesnake, armed with what will be death to you if you come too near; give me a wide berth!"

Prof. Shaler remarks that it is a fact well known doubtless to those who have observed serpents, that many when in a state of excitement vibrate the end of their tail just as the rattlesnake does. This statement reminded me^of a South American species described by Darwin in his "Voyage of a Naturalist" (vol. i, p. 123, Harper's ed.), where he says : —

'• Of reptiles there are many kinds: one snake (a Trigonocephaly, or Cophias), from the size of the poison channel in its fangs, must be very deadly. Cuvier, in opposition to some other naturalists, makes this a sub-genus of the rattlesnake, and intermediate between it and the viper. In conformation of this opinion I observed a fact, which appears to me very curious and instructive, as showing how every character, even though it may be in some degree independent of structure, has a tendency to vary by slow degrees. The extremity of the tail of this snake is terminated by a point, which is very slightly enlarged; and as the animal glides along, it constantly vibrates the last inch; and this part striking against the dry grass and brushwood, produces a rattling noise, which can be distinctly heard at the distance of six feet. As often as the animal was irritated or surprised, its tail was shaken; and the vibrations were extremely rapid. Even as long as the body retained its irritability, a tendency to this habitual movement was evident. Tins Trigonocephalus has, therefore, in some respects, the structure of a viper, with the habits of a rattlesnake; the noise, however, being produced by a simpler device."

It was these remarks of Darwin that first suggested the problem of the rattlesnake's tail to my mind, and, as I had thought considably about the matter, of course I was deeply interested in the paper by Prof. Shaler; but I must acknowledge that, while many of his suggestions are correct and highly valuable, I was disappointed to find that the only advantageous use, in his estimation, of this tail appendage of the rattlesnake, is an imitative call-note to allure birds within its reach, and that, otherwise, it is rather a disadvantage than an advantage to be preserved and perfected by natural selection. If it is useful for both purposes, then there is a double reason for the action of natural selection. If it is not used as an imitative call-note, but is useful in the manner I have pointed out, then I have shown that it is explained by natural selection.




In the spring of 1871 an expedition to the Plains and the Rocky Mountains was sent out by the Museum of Comparative Zoology, under the charge of the writer. During the nine months spent in the field by the party in question, the department of ornithology received a large share of attention. In the following pages it is proposed to give a hasty resume of such observations as may be supposed to interest the ornithological readers of the Naturalist, reserving a more detailed and formal report for publication elsewhere.*

Leavenworth, Kansas, was the point at which we commenced our labors. During the ten days spent at this locality we collected or observed nearly one hundred species of birds. Although we arrived here May 2d, the country wore the aspect of a New England June. The prairies were already green with waving grass and the forests were nearly in full leaf. The apple trees were some days out of bloom, and the young cherries were as large as very large peas; the vegetation being fully a month in advance of its usual stage in Southern New England at the same date. Comparatively few of the birds, however, were nesting; some had not arrived from the South, and others whose breeding stations were more to the northward still lingered.

"We found in the vicinity of Leavenworth a collector's paradise, the forests of the Missouri bottom-lands literally swarming with birds, many of which none of the party had before seen in life, the general aspect of the ornithological fauna being strikingly diverse from that of the northeastern states. The red-headed and red-bellied woodpeckers (Melanerpes erythroceplialus and Centurus Carolinus) revelled among the grand old elms and cottonwoods of the bottom-lands, some of which tower to the height of one hundred to one hundred and fifty feet. The golden-shafted flicker (Colaptes auratus) was almost equally abundant, and showed its close affinity with its red-shafted brother of the mountains and the Pacific Slope (C. Mexicanus) by already frequently presenting touches of red in its black check patches. Although the hairy and downy woodpeckers (Picas villosus and P. pubescens) were both observed, they seemed by no means common. The crested titmouse (Lophoj)hanes bicolor) and the merry cardinal (Cardinalis Viryinianus) vied with each other in their noisy demonstrations, both being exceedingly abundant and garrulous. Their vocabulary seemed inexhaustible, as they every day astonished us with new sounds, which we often at first supposed to proceed from some bird hitherto unknown to us. The blue jay (Cyanura cristatd) was equally at home, and as vivacious and even more gayly colored than at the north. While he seemed to have forgotten none of the droll notes and fantastic ways one always expects from him, he has here added to his manners the familiarity that usually characterizes him in the more newly settled parts of the country, and anon surprised us with some new expression of his feelings or sentiments,—some unexpected eccentricity in his varied note*, perhaps developed by his more southern surroundings. The yellowbreasted chat (Icteria virens) disported himself among the tangled underbrush, and seemed highly to enjoy the discomfiture to which he often put us, through his well-known ventriloquial accomplishments, in our search for his exact whereabouts. The Carolina wren (Thryotliorns Litdovicianus) was more or less common, and already had young full-fledged on our arrival, while the only other birds then found breeding were the cardinal, the towhe and the brown thrush. Most of these, however, were still pairing and nestbuilding. The common chickadee (Parus atricapillus) and the house wren (Troglodytes aedon) were both common, but were far less numerous and much more retiring than their more demonstrative southern relatives already mentioned.

*Thls report will embrace annotated fauna] lists for eight localities, with a general summary list for the whole. Mr. C. W. Bennett accompanied the expedition as taxidermist, and Mr. Richard Miss as ichthyologist, both of whom, especially the former, greatly aided in the ornithological work.

Among the warblers three southern forms were the most common, their bright colors often attracting the eye as they flitted through the openings among the trees. These were the Kentucky (Oporornis formosus), the hooded (Wilsonia mitrata Bon.) and the blue-winged yellow (Helm inthophaga piims). They seemed aware that they were especial objects of attention to the collector, and took good care not to exhibit themselves unnecessarily. The golden-crowned warbler (Helminthophaga celata) was also one of the most numerous of the Sylvicolidce. The Nashville (77. rubricapilla), the blue yellow-backed (Panda Americana) and the black and white creeper (Mniotilta varia) were likewise moderately frequent. The beautiful caerulean warbler (Dendrmca cairidea) was met with a few times, the Blackburnian (D. Blackburnim) once or twice, and the yellow rumped (D. coronaU.i) but once, though the latter was doubtless common somewhat earlier in the season. The yellow warbler (D. mstiva) was more or less common along the outskirts of the forests; the chestnut-sided (D. Pennsylvania) was by no means rare; redstarts (Setophaga ruticilla) were seen but a few times, and the Maryland yellow-throat (Geothlypis trichas) was far from numerous.

« AnteriorContinuar »