beats, sounds like the rapid tick of a small watch*. All 

 these observations merely point to the exceedingly intense 

 metabolism and swiftness of physiologic processes in such 

 small birds, a combination of conditions that should produce 

 high body temperatures in small birds, and a brief study of 

 Table No. 6, shows clearly that the birds with highest tem- 

 peratures are, as a rule, the smallest of birds; moreover, it 

 is held by physiologists (151) that the power to produce heat 

 is proportionate to the activity or sluggishness of the animal 

 (not specifying class) . These facts again lead to a belief in 

 the general correctness of Sutherland's law as to low and 

 high temperatures in "low and high" birds. There are some 

 relatively small birds which have low temperatures, as, for 

 example, the apteryx. It seems to me that this is a good ex- 

 ample where it is not size but the primitive character of the 

 bird which determines the elevation of its temperature, but 

 this is not proven; it may be a true exception, or the low 

 record may be due to errors of observation. It is to be no- 

 ticed that one record of a pigeon, the speckled pigeon, shows 

 a very high temperature for a bird classed as relatively low ; 

 the whole of the facts in this, and similar cases, are not 

 known, and compel again one's suspending final judgment 

 pending further light. 



In further support of the relation between elevation of 

 temperature and taxonomic standing, it may be recalled that 

 as birds have grown up, and away, from their proto-avian, 

 or proto-reptilian ancestors, they have become better and 

 better feathered, and feathers are said to have made birds 

 what they are, the warmest-blooded creatures in existence, 

 whence it follows that the farther they have traveled (with- 

 out later recession) from their primitive ancestry, the more 

 elevated h-ave become their body temperatures. It seems to 

 me that weight of evidence supports Sutherland's hypoth- 

 esis, and for the purposes of this discussion it is held to be 

 true. 



Now, if one holds that birds' temperatures are more 

 and more elevated as the species is higher and higher in its 

 phylogeny, one may ask, does this condition have any influ- 

 ence on the length of incubation? It must here be remem- 

 bered that it is possible that "swiftness of life" may embrace 

 the embryonic period of birds as it seems to with mammals, 

 and that the specific temperature and the incubation length 

 are co-ordinate, assuming this to be true for the moment 



*Since the above was written I have learned that Buchanan (174) 

 has determined the heart rate in several bird species, using the electro- 

 cardiagram method for its detection. His results are almost incredible, 

 and show most strikingly the wonderful metabolic activity of birds, 

 especially the small species; Buchanan gives the heart rates as follows: 

 Gold-finch 900 to 925 per minute, green-finch 700 to 848, span'ow 745 to 

 850, pigeon 141 to 225, hen .304 to 345. 



61 



