28 DISEASE IN WILD MAMMALS AND BIRDS 
life rises. Carnivora have a reasonably good vitality, 
their potential periods varying from ten years in the 
foxes to thirty-three years in bears. Insect eating 
animals are short lived, three years being a maximum. 
The Bat family shows great variations, the greatest Ufe 
being not over seventeen years. The Rodentia have long 
lives compared to their sizes — twenty years in porcupines, 
fifteen years in squirrels, thirteen in marmots, nine in 
agoutis and capybaras, and three in dormice (which is 
also about the maximum for the rat). Hyraces live four 
years on the average. Proboscidea, although reputed to 
live to great age, probably rarely live a half century and 
may be said to have an expectancy of twenty to thirty 
years. Perissodactyla (horses, tapirs and rhinoceroses) 
while they may live half a century, have an average life 
of between fifteen and thirty years. The closely related 
Artiodactyla fall into two groups, a first comprising 
antelopes, sheep, goats and deer which rarely exceed 
seventeen years, and a second consisting of cattle, camels 
and giraffes, which vary in expectancy from eighteen to 
thirty years. The smaller members of the Ungulata have 
in relation to size a relatively greater viability, the 
ruminants, however, having on the whole a low viability. 
Marsupials vary from a maximum of seven years in the 
opossum to eighteen in the wombats, but none of this 
group has a good viability. The Aves as a class or if 
compared according to dietary requirements, have longer 
potential ages and better viability than mammals. Pas- 
serine birds average twenty years and many live to sixty, 
while the Picariae approach the former figure but do not 
have such good ^dability. Psittaci and Striges may live a 
half century but the resistance of the latter is much 
reduced by any unfavorable surroundings. The rapta- 
tory birds live fifty years, but their viability is variable. 
Herodiones have a maximum expectancy of thirty years 
and good resistance, while their relatives, Steganopodes, 
may live fifty years, and Odontoglossae have a good 
