CONTENTS 



Paee 



Method of observation 355 



Tower locations 357 



Background panels 358 



Turbulence reducers 358 



Count ing aids 359 



Estimation of the runs 360 



Method of sampling 360 



Method of calculation 361 



Results 361 



Factors influencing visual counts 362 



Errors introduced by individual counters 362 



Errors associated with migration intensity 362 



Effect of weather conditions 363 



Effect of disrupted migration pattern 364 



Accuracy of estimates 364 



Effect of interruptions in the counts 364 



Population fluctuations 365 



Confidence limits of the 1959 escapement 366 



Effect of changing the sampling design 367 



Summary 368 



Literature cited 369 



HI 



