CHAPTER V 



SEASONAL LIFE. RELATIONS TO MOISTURE, TEMPERATURE, 

 ETC., AND TO PERIODIC CHANGES IN THE COSMOSPHERE. 



The bleaching effect of light. Desert forms. The effects of a saturated 

 atmosphere. Arctic conditions. Size and latitude. Storms and drought. 



ALTHOUGH much valuable information has been ac- 

 cumulated as to the effect of light, moisture and 

 temperature on the lower invertebrate animals, but 

 little in the way of close observation or experiment has been 

 carried out with regard to the higher animals, and to birds in 

 particular. In the following short account an attempt is made 

 to bring together some of the more important facts which have 

 been collected on this subject. These do not refer, however, 

 to periodic,' seasonal, climatic conditions, which will be discussed 

 in another chapter. 



As to the direct effect of the action of light, and weathering, 

 on the feathers of living birds little seems to be known. It would 

 appear, however, to have a decidedly destructive influence, not 

 only destroying the colour, but also bringing about the dis- 

 integration of the horny tissue of the feather. This is well seen 

 in the large quill or flight feathers of birds, such as those of the 

 Plover tribe, which spend much time in exposed situations. 

 These feathers, in the first place, if examined just before the 

 annual moult takes place, will be found to have faded in just 

 those areas which are left uncovered when the wings are closed, 

 each feather, when the wing is extended, showing a silhouette 

 of the feather next above it, a dark area representing the portion 

 covered, and a distal light area representing the part subjected 

 to "weathering". Disintegration seems to accompany this 

 fading, and to take place most rapidly in those parts of the 

 feather which are unpigmented. Thus, in many waders, as in 

 the Curlew, where the darkly pigmented areas of the feathers 



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