88 FLORIDA BIRD-LIFE 



and only 1,500 nests were built. This would imply a breed- 

 ing colony of only 3,000 birds, but what became of the 

 remaining 4,000 birds is a mystery. 



Possibly this variation in nesting date was occasioned by 

 the exceptional climatic conditions which prevailed in Flor- 

 ida during the preceding year, when for a period of seven 

 months no rain fell. 



Whatever may be the cause or causes for this variability 

 in the date of the Pelicans' migration — for it is true migra- 

 tion — it is evident that they act upon all the birds uniformly. 



The island colony is not formed gradually, virtually all 

 the birds come at once, moved by a common impulse. What 

 is it? It is not a question of food, for the birds rarely feed 

 near their nestinsr place. It is not a question of climate, for 

 they do not sco far enough from their breeding resort to 

 experience climatic change when returning to it. The imme- 

 diate cause of the .iourney is doubtless physiological and the 

 promptina: comes from within. With birds the season of re- 

 production is periodic, and with migratory species, whether 

 the journey be to a near-by island or to another zone, 

 the return to the breeding ground is only one phenomenon in 

 a cycle of events which includes, in regular order, migration, 

 courtshi]^, egg-laying, incubation, the care of the young, the 

 molt, and the retreat to winter quarters. 



Newly awakening sexual activities now stimulate the 

 flocking impulse and the birds doubtless gather in small 

 companies later to be merged in one great flock as they are 

 brought together by the instinct which leads them to the 

 place of their birth. The actual return to the island is ap- 

 parently not made until the last comers have arrived, and 

 we have here a partial parallel to the roosting of Crows 

 which, assembling in some near-by field, do not enter the 

 roost until apparently the last bird has come, when they 

 arise to seek their resting-places for the night. 



It is a reniMi-kjiMc ?:u-\ fli;it while the Policnns of the east 

 f^oast of Florirln bpi2:in io l;iv in "NTovember, those of the west 



