MISCELLANEOUS NOTES. 365 



I have so far absolutely no proof that any one species does make these 

 holes or that any other does not. The bird however that 1 have seen most 

 frequently in areas where the trees are much attacked is Ib/iwpicus hypery- 

 thrus the Rufous-bellied Pied Wood-pecker, and this bird I have also 

 watched systematically visiting the olcl lines of holes, thrusting his bill 

 quickly two or three times into each cavity and working sometimes up, some- 

 times down the trunk. It is in fact my belief that Hijpopicics hyperythrui^ 

 is one, if not the only, perpetrator of these attacks though I admit 

 that there is also much in favour of Uendrocopus Mvialayensis the Western 

 Himalayan Pied Wood-pecker, and there is nothing to prove that the other 

 three species do not assist. 



To return now to the reason for these attacks. Why does the wood- 

 pecker originally make these holes ? Why does he make them almost invari- 

 ably in such neat horizontal lines ? and why does he visit them again as he 

 most certainly does ? These are some of the questions to be answered. It 

 would be most natural to suppose that the holes are made in order t<:i 

 permit the bird to reach some insect, probably some noxious beetle attack- 

 ing the cambium layer. This theory is, however, easily disposed of by a 

 careful examination of a number of attacks on different species of trees. 1 

 have made many such examinations, but 1 have never once discovered any 

 insect in the cavities, nor have I found anything to indicate that an insect 

 had previously been living there beneath the bark. In fact I have found 

 that the trees attacked are usually in perfect health and not the subjects of 

 insect attack. It is necessary here to distinguish between the holes made 

 in rows as described above and holes made haphazard all over the surface 

 of the stem. In the latter case it will almost invariably be found that the 

 tree is the subject of some insect attack or else that the stem is unsound. 



The only other theory that has suggested itself to me is that the bird 

 either sucks in the sap or actually eats the softer layers of the inner cortex 

 and cambium. This theory is, I believe, the true one. It is however a 

 theory which is obviously difficult to prove. One argument in its favour is 

 the absence of any better theory. That the wood-pecker drinks the sap is 

 not as improbable as it might at first appear. On one occasion I watfhed a 

 female yEthopyya sp. repeatedly visit an old wound in an oak tree from 

 which a sappy fluid was exuding. I was only a few yards distant and I 

 could be quite certain she was drinking the sap. On another occasion I 

 watched a male yEthopyf/a horsjieldi visiting again and again some rows of 

 wood-pecker holes in a Karshu tree [Quercus semecarpifolia) . The bird kept 

 returning to this tree and I was able to watch it through my glasses from 

 no great distance. It certainly appeared to me to be extracting sap from 

 the bases of the cavities. So if sunbirds visit these holes to drink the sap 

 they contain, there is no reason why wood -peckers should not do so. At the 

 same time I think the wood-pecker probably also eats the inner soft layers 

 of tissue, especially perhaps the secondary growth tissue which forms at the 

 bases of old cavities. In confirmation of this, when examining an old 

 attack on a Karshu tree at 10,000' elevation where the bark had swollen up 

 and cracked across the original line of holes, I found the crack contained 

 soft new tissue in process of formation and a wood-pecker (or what I presume 

 to have been a wood-pecker) had fairly recently attacked this in order 

 apparently to eat it. 



The reason why these holes are made in such neat rows is also difficult to 

 understand. It seems possible that they are made in this manner merely 

 because the bird finds it simplest to work round the stem in a horizontal 

 line having once made a start at any point. The question, however, re- 

 quires further investigation. I have never yet been fortunate enough 

 to watch the process whereby the holes are originally made. 



