H I R U N D O. 



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at the extremity of our continents, we do not find such 

 an animal as a hare passing the winter in a dormant 

 state. On the other hand we find that, even in regions 

 near the equator, many of the reptiles which have a 

 cold system and a sluggish circulation remain dor- 

 mant tor part of the year. The necessity of feeding 

 and of breathing, and also the natural heat of many 

 animals, are in proportion to that animal's activity, for 

 the activity is part of the same system as the rest ; 

 and as birds feed more and breathe more than mam- 

 malia of the same size and weight, they are also more 

 warm in their temperament, and on that account both 

 less fitted for hybernation and less disposed to it. 



Flying is the most severe motion which any animal 

 has to perform, because the flying animal has both to 

 bear itself up in the air and to make progress, whereas, 

 in the case of a walking animal, the weight is borne 

 by the ground, and the moment that it ceases to have 

 progressive motion, it begins to be at rest, or in a 

 state of partial repose. But, even when a bird hovers 

 in the air without making any progression in distance, 

 it is not in a state of even partial repose, as it still 

 has to bear itself up in the air, which, in the case of 

 even the lightest bird, and the one whose plumage is 

 the most flocculent and takes the greatest hold on 

 the air, requires a considerable exertion of muscular 

 energy. 



The swallow tribe are more completely air birds, 

 and pass more of their time on the wing, than any 

 other birds which inhabit or visit the British islands. 

 Some of them, the swifts for instance, which are the 

 highest flyers, and which get their common- name 

 from the rapidity of their flight, are generally sixteen 

 or eighteen hours on the wing every day at that 

 time of the year when they have their broods. 

 During these hours, they cannot, on the average, 

 move over less space than a thousand or twelve 

 hundred miles ; and, if we consider the number of 

 loops and doublings which they make, the exertion, 

 upon one of their long days, must be as great as 

 would carry them at least two thousand miles in one 

 day, so that, at the rate of its ordinary motion in 

 hunting for its food in the sky, a swift could fly round 

 the equatorial circumference of the earth in less than 

 two weeks. 



This is a degree of exertion with which we have 

 nothing at all comparable in any animal that walks 

 or runs upon the ground. Some of the swiftest of 

 these can move at the rate of fifteen or perhaps 

 twenty miles in the hour ; but there is none that 

 could continue this for several hours, or even for 

 one hour, without being exhausted. There is no 

 miracle in the motion of a flying animal, any more 

 than there is in that of the slowest creature which 

 crawls upon the earth. The principle is the same 

 in them all, though differently modified and fur- 

 nished with different organisations. And this fact 

 of adaptation runs through the whole, that, in proper- 

 tion to the action must be the means of repairing the 

 waste occasioned by that action ; and among these 

 means respiration is one of the chief. When we make 

 an over-exertion in speed, the lungs are the first part 

 of the body upon which the effects of that over- 

 exertion is felt ; and we pant for breath long before 

 we feel any weariness of the limbs. _ The fatigue o' 

 moderate exertion long continued is of a different 

 character ; it is felt in the muscles of the parts exerted 

 while there is no uneasy sensation in the lungs ; anc 

 it is worthy of remark, that the pulse is rendered both 



larder and quicker, and therefore the circulation 

 ncreased, by that rapid exertion which fatigues the 

 ungs, while in the opposite case, if the pulse does not 

 )ecome slower it becomes more feeble, which equally 

 ndicates a diminished circulation. 



The motions of the swallow tribe are, as we have 

 said, and as any one may see, very constant and very 

 rapid ; and their quantity of respiration and need of 

 bod must, according to the general law of nature, 

 correspond. Their labour in flight is even greater in 

 )roportion to the rate of their going, than that of 

 nore slow-flighted birds. Feathers that take much 

 lold on the air would be the very worst adapted for 

 them, and accordingly all their feathers are firm and 

 smooth ; so that the keeping of themselves up is a 

 matter which requires constant exertion. The aux- 

 iliary breathing which they have in supplement to the 

 mere action of the lungs (see the article BIRD), no 

 doubt prevents the exhaustion of these organs ; but 

 still the action of the whole bird is not the less, 

 and the circulation must be in proportion, otherwise 

 the general law of nature would be at an end, and 

 the living world would become a mere mass of con- 

 fusion. 



All these circumstances show, in the clearest 

 manner, that swallows cannot possibly hybernate under 

 the water, or anywhere else. And why should they? 

 The very same powers which they exert every day 

 are competent to carry them from Britain to Africa 

 between sun and sun ; and, when they have this 

 power of shifting their place with the seasons, it would 

 be letting this run to waste to suppose that they 

 should in any manner hybernate. There is another 

 consideration, which, though very obvious to those 

 who attend to such matters, it may not be improper 

 to mention ; all the tribe are dark, approaching to 

 black ; of that very colour, in short, upon which va- 

 riations of temperature have the greatest effect ; and 

 this must co-operate with the falling off of their food, 

 in sending them from the northern countries when 

 the cold weather begins to set in. 



That the swallow tribe should appear over the 

 waters when they first arrive in our latitudes, and 

 resort to the same places before they take their 

 departure for the season, is also quite natural, and 

 what, from the circumstances of the case, we might be 

 prepared to expect. The whole race feed upon 

 winged insects, which they capture while on the 

 wing ; and the waters are the places over which 

 insects appear first in the spring, and linger longest 

 in the autumn. In the autumn, however, the insects 

 are not so directly over the water as they are in the 

 spring ; for by that time of the year the greater 

 number of those insects which commit their offspring 

 to the waters, have performed that, the final purpose 

 of their brief duration in the winged state, and have 

 ceased to exist. 



From their activity, their very general distribution, 

 and the rapidity with which they perform their migra- 

 tions from country to country, the swallows are a 

 most valuable race of animals ; and in all countries 

 they resort to the very places where their services are 

 most required, and perform them in a way which can 

 be followed by no others of the feathered race. The 

 common house-fly, which, though hardly known in 

 wild nature, follows man in all his migrations ; and 

 though it too has its use, its powers of multiplication 

 are so great, that if there were not some means of 

 keeping it within bounds, it would be an absolute 

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