AVIAN MIGRATION AND REPRODUCTION 



687 



8 15 22 29 5 



MAR APR 



Fig. 1. Changes in body weight and fat deposition for the birds that 

 responded to treatment with a schedule of 5L-1D. Circles are used for 

 white-throated sparrows, triangles for the junco; scale for body weight 

 of the junco on right side of upper left graph. Fat deposition at each 

 point indicated as "follows: open symbol = no fat; line through sym- 

 bol = little fat; half of symbol filled in = medium fat; symbol filled 

 in completely = heavy fat. Experiment began on January 25. Each num- 

 ber and curve represents an individual bird. Note difi'erences in time and 

 extent of response. 



and fat deposition are shown in Fig. 1. The individual curves show 

 the variations in the amount and time of response. 



These results were interpreted as supporting the summation thesis 

 that the daily amount of light regulates the rate of response. However, 

 since the proportion of light to darkness per 24 hr and per cycle were 

 the same, there was the possibility that this proportion was the 

 effective stimulus and not the daily dose of light. The work of 

 Kirkpatrick and Leopold (1952) and Jenner and Engels (1952) 



