30 Union Bay 



favored northern habitats cannot support them at that time 

 of year. They return when these places are again fruitful. 

 Light is thought to have an important part in stimulating 

 migration— the birds undergo physiological changes due to 

 the lengthening days and finally set off as a result of that 

 stimulus. But this theory does not explain why birds migrate 

 north from south of the equator when the days in that local- 

 ity are shortening and not lengthening. Elaborate experi- 

 ments continually test the validity of the different theories. 

 The exponents of the light hypothesis have shown that a bird 

 detained beyond its usual time of migration loses the desire 

 to migrate, and that by placing a bird in artificial light and 

 increasing the amount each day the date of migration can be 

 hastened. Someday more may be known about the nature of 

 the causes which produce these tremendous effects. 



In the fall and winter, the marsh register showed a con- 

 tinuous change in number and species of birds. The perma- 

 nent guests— a bittern or two, some Virginia rails, a few song 

 sparrows, some towhees, and usually a few pied-billed grebes 

 —were silent and unobtrusive, and only the gulls made their 

 presence known by crying loudly and fighting for the food 

 that one of them might discover. They spent much of their 

 time at the sanitary fill at the north end of the bay while the 

 other birds clung to the marsh margins where the lodged 

 cattails made pockets and tunnels which provided shelter. 



It was not the season for upland birds, and the transients, 

 shorebirds excepted, confined themselves to the open waters 

 of the bay and channels. Ordinarily, the different species did 

 not mix indiscriminately, although there were times when I 

 saw canvasbacks, pintails, mallards, scaups, and coots spotted 

 among the baldpates like black sheep in a flock. Incoming 

 birds came to that portion of the marsh which they liked and 

 there they stayed. If there were mergansers I usually saw 

 the larger species near the log rafts or on one of the logs 

 from which they would slip when disturbed so they could 



