224 



NATURE 



[May 23, 1918 



not looking for food or anything else, and did literally 

 appear to be 'scared stiff,' as one might say. If it 

 was mobbing, it was very different from such active 

 mobbing as I have seen — one might call it ' passive 

 mobbing,' for there was no attempt at offence either 

 by word or deed. The feeble chirps sounded more like 

 a faint protest than anything else." 



It must be remembered, as Mr. S. A. Neave has 

 pointed out to me, that in such cases the presence of 

 numbers is in itself disconcerting, however feeble may 

 be the powers of the mobbers. Capt. Carpenter's 

 description suggests that the snake was disturbed and 

 harassed. 



I was mistaken in supposing that Mr. F. Muir's 

 observation (quoted in Nature of January 17, p. 385) 

 was made in East Africa. He informs me that it was 

 in Amboyna in the latter f^art of 1907 or early in 1908. 

 Mr. Muir writes :— 



"Is it not -possible that birds are paralysed with 

 fear rather than ' fascinated ' in such cases ?' I had a 

 parrot in Africa (now living at Brockenhurst with 

 Dr. Sharp's family) which would fall off her perch 

 if a dead or living snake was brought near to her ; 

 even a piece of rope suddenly brought into view would 

 produce a fright which would paralyse her and pre- 

 verrt her even from screaming." 



I have just received the following interesting record 

 of observations by Mr. C. F. M. Swynnerton, writing 

 from Chirinda, South-East Rhodesia : — 



" March 29, 1918. 



"For more than a year past I have lived in a house 

 in an open space, but our old house was closely 

 surrounded by trees, and, in the breeding season par- 

 ticularly, the mobbing of tree-snakes by birds was 

 often, for a week or ten days together, a daily occur- 

 rence. 



"Birds probably mob tree-snakes whenever they 

 detect them, for I have seen such mobbings both 

 out of the breeding season and when I was unable 

 by a careful search to find a nest; but in most cases 

 where a nest was concerned the birds — most com- 

 monly 'bulbuls in my observations — that were the. 

 parents of tht fledglings were the first to detect the 

 snake's approach to the nest and to start the hue and 

 cry. Shrikes, sunbirds, flycatchers, warblers- in fact, 

 any bird that happened to be near — would quicklv 

 join in and mob the snake, scolding all round it and 

 occasionally darting in at it in the very manner in 

 which they mob an owl. The mobbers remain, for 

 the most part, out of striking distance of the snake, 

 but some— and this applies especially, in my observa- 

 tions, to the ' puff-back shrike ' {Dryoscopiis cubla) — 

 are very bold, both in the matter of darting in and 

 in staying near the snake. A bird perched in front of 

 the snake, as I have sometimes seen it, with its 

 wings drooping and quivering with excitement, might 

 well be taken by an ignorant person, who did not 

 follow his observations up, to be fascinated by it; 

 whereas it is, in reality, busy hurling at the snake 

 every unpleasant name it can lay its tongue to. The 

 mobbing sometimes continues for half an hour, some- 

 times for much longer, though the individual mobbers 

 do not always — with the exception of the owners of the 

 threatened nest— remain the same. Some" tire and go 

 off^ — anyway, temporarily — and their places are taken 

 by others. The snake in general appears to take little 

 notice of the birds, though it will commonly face a 

 specially bold one; and I have seen it lunge some- 

 tirhes, but unsuccessfully. Were it to succeed, I 

 suppose the believer in fascination would be con- 

 firmed in his belief. Probably, too, even when ap- 

 parently indifferent, it is sometimes embarrassed and 

 delayed, for it will sometimes stay quite still for long 

 together-^except for the Constant flickering of the 

 NO. 2534, VOL. lOl] 



tongue. When it reaches the nest there is a great, 

 scene on the part of the parents, and they lose any 

 fear of the snake they may have had before in their: 

 attempts to save their young. The latter, if nearfjrji 

 fledged, generally take fright as the result of ^ei: 

 parents' actions, . and not (as I have proved experi 

 mentally) from afty instinctive fear of the snake, and, 

 flutter down. 1 Have seen little bulbuls come dowa 

 thus unharmed from a nest 50 ft. up. Mostly I havi 

 shot the snakes before they have reached the nest» 

 but I have seen young birds taken, and I have also-] 

 taken them from inside snakes that had left a nes 

 or were coiled about it. The snake in nearly ever 

 case has been Disphoridus typus , I believe, for I 

 do not remember if I have actually taken it to Mr. 

 Boulenger. 



" For two or three seasons I watched all the mob- 

 bings I could, as I had noticed in the case of birds 

 of which I knew the courting display that this 

 tended to be repeated under the excitement of mob- 

 bing, and I felt that the converse would also be true. 

 So I watched in order to get the displays of the 

 different species. I obtained in this way a certain 

 number of notes, but these do not bear on your ques- 

 tion, referring, I believe, solely to this matter of dis- 

 play. The watching of these mobbings of snakes — 

 which I supposed were well known — long ago con- 

 vinced me that there was nothing at all in the 

 ' fascination ' idea. The birds show great daring and 

 insolence, and it is hatred and indignation, and per- 

 haps partly the desire to assist, and not ' fascination, *■ 

 that draws them to the snake. It is the same, I 

 believe, in the case of hawks and owls — for the bitds 

 will certainly recognise the latter as an enemy, apart 

 from its rough resemblance to a hawk. I have taken 

 a freshly eaten bird from an owl's stomach {Syrnitm 

 woodfordi) when it was barely twilight and sma' 

 birds were still active." Edward B. Poulton. 



Oxford. May 6. 



As I was correcting the proofs of the above, the 

 following letter from Capt. Carpenter reached me. 

 The behaviour observed by him is, I believe, to be 

 interpreted as due to the interplay between two oppos- 

 ing impulses, both beneficial — one based on the fear of 

 snakes, the other on social stimuli which incite tCK 

 combination for the purpose of harassing an enemy. 

 It is only to be expected that such interplay will lead 

 to different behaviour with different species of 

 bird, and perhaps with the same species in the 

 presence of different types of snake. Differences are, 

 above all, caused, as Mr. Swynnerton shows, by the 

 behaviour of the snake, which, when it attacks the- 

 nest, brings in a third impulse — the defence of off- 

 spring — and leads the parent birds to act as though 

 they were altogether without fear. E. B. P. 



May 13. 



" I have only recently received the copy of Nature 

 for November 29, 1917, in which you printed Prof. 

 Poulton 's letter commenting on an observation of mine 

 on the subject of ' fascination ' of birds by snakes. 

 Prof. Poulton suggested that this was a case . of 

 ' mobbing,' and has just sent me a proof of his second 

 communication on this subject, giving instances of. 

 ' mobbing ' noted by field naturalists. 



" I wish to direct attention to the following point :— . 

 The mobbing of a snake or a bird of prey is most 

 definitely a voluntary act on the part of the small 

 birds. 



" In the Case which I described, however, the be- 

 haviour of the little finches strongly suggested that they 

 were there against their will, or perhaps one should 

 say their better judgment. 



"The 'faint chirps' which I described were not the 



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