May, 1917 



WILD DUCKS IX A CITY PARK 



87 



foreground. The flock resting upon the water is composed mainly of Canvas- 

 backs (Marila valisineria) , a deep water species that feeds but little upon Land. 



These birds arrive about October of each year. After the dose of the shoot- 

 ing season they begin to scatter, for, with general protection elsewhere there is 

 no longer need of congregation within this sanctuary; so that the ducks cease to 

 be a conspicuous feature of Lake Merritt some time before their departure for 

 distant breeding grounds. 



Oakland. California. February 11. 1917. 



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Fig. 35. Same flock as in figs. 33 and 34. There is a limit to tiie trustful- 

 ness OF EVEN VERY TAME WILD DUCKS AND PHLEGMATIC MUDHENS. 



SOME FACTORS INVOLVED IN THE NESTING HABIT OF BIRDS 



By CLARENCE HAMILTON KENNEDY 

 WITH TWELVE DRAWINGS BY THE AUTHOR 



ONE OF the most interesting series of problems in ornithology is that con- 

 nected with the high development of the nesting habit in birds. But little 

 has been done to correlate bird anatomy and nesting habits, or even to fig- 

 ure out the causes leading to the great diversity of nests which birds build, for 

 when the present writer wished to look up some obscure points on the nesting 

 habits in this group, great was his surprise that in a group so thoroughly worked, 

 so little had been done in the study of nidification other than the mere collection 

 of data on the nesting habits of individual species. No group in the animal king- 

 dom has been so thoroughly worked as that of the birds, yet the attempts to fig- 



