536 DR. p. CHALMERS MITCHELL ON LONGEVITY AND 



low viability. It cannot be supposed that birds which are 

 resident in Europe, or in England, have a lower constitutional 

 viability than their congeners in more distant parts of the 

 world, and yet, if we were to form conclusions as to the via- 

 bility of such birds (or mammals) from the evidence given by 

 captive examples, we should have to assign to them a very low 

 position. So also insectivorous birds have usually a low via- 

 bility in captivity, but this may well be due to the difficulty of 

 providing them with suitable food. So also, if we were limited 

 to knowledge of parrots under the usual conditions of a Pari'ot- 

 house, we should have a very erroneous view of their poten- 

 tialities. 



Passerine birds are long-lived and hardy. Almost all of them 

 have a potential longevity probably well over 20 years, and some 

 of the larger forms may reach to over 60 years. The least hardy 

 in captivity are Warblers, Tits, Pipits, Wagtails, Bulbuls, Orioles, 

 Tanagers, and Larks. Tyrants, Bell-birds, aiid so forth, which are 

 generally regarded as a lower grade of Passerines, appear less 

 viable and shorter-lived. 



Of Picarian birds, Oolies, Hornbills, Motmots, Toucans, and 

 Barbets have potential longevities approaching those of Passerines, 

 but markedly lower, whilst their viabilities are relatively good ; 

 Woodpeckers, Kingfishers, Hoopoes, Bee- eaters. Rollers, Frog- 

 mouths, Cuckoos, and Touracous have much lower potential 

 longevities and are less hardy. Owls have a potential longevity 

 certainly extending to over 50 years, but their viability appears 

 to be constitutionally low, their short average durations in cap- 

 tivity not depending altogether on any specially unfavourable 

 conditions. 



Parrots have a high potential longevity, certainly ranging well 

 over 50 years. Their viability is almost certainly good, and 

 their low average durations must be assigned to unfavourable 

 conditions in captivity. 



Diurnal birds of prey have potential longevities probably 

 exceeding those of parrOt.s. Their viabilities are better than 

 those of Owls, the conditions in captivity being in neither case 

 satisfactory. 



Steganopodes Imve potential longevities ranging up to about 

 50 years, with very good viability ; there seems no constitutional 

 I'eason to assign a low viability to Gannets and Cormorants, 

 and their treatment in captivity does not difiei- much from that 

 of Pelicans. The actual figures show that they have had much 

 lower average and maximum durations than Pelicans, but this 

 most probably is to be associated with the failure in the case of 

 many other European birds. 



Herons, Storks, Spoonbills and Ibises appear to have a poten- 

 tial longevity of over 30 years, and a fairly good viability. 

 Ibises appear to have a better via.bility than the other members 

 of the group. 



