CYCLES OF REPRODUCTION 



II 



passing from south to north, the southern water birds 

 breeding on the equator at about the same time as the 

 northern hawks. Again it is rare for any species to breed 



80'/V 



60"N 



WN 



2a'N 



0* 



20''S 



40'S 



60'5 



XII 



IV V VI VII VIII IX X XI XII 



XII 



III IV 



VI VII VIII IX 



XI XII 



Fig. 2. — Diagram showing the variation with latitude in 

 the start of the egg-laying seasons of hawks and of water 

 birds (after Baker). Also shown are the seasonal changes 

 in the position of the overhead sun. The months are in- 

 dicated by Roman numerals. 



more than once a year, but an example may be provided 

 by the sooty tern of the Ascension Islands which is said 

 to breed with both the northward and the southward 

 swing of the sun. 



Of course neither the breeding habits of the northern 



