36 BULLETIN 1328, U. S. DEPARTMENT OP AGRICULTURE 



tical application would perhaps be in a study of nectar secretion, as 

 it affords a measure of the variations in flight and in the duration 

 and number of trips which the bees make, as well as their average 

 daily load, facts which are to a large degree a reflection of the nectar 

 conditions in the field. 



This study demonstrates the feasibility of obtaining data on prob- 

 lems pertaining to the flight of bees by means of an automatic re- 

 cording mechanism. As far as can be ascertained, the mechanical 

 principles on which the design was made are in general correct. 

 Much work, however, on further details is desirable. 



Owing to factors incidental to any new and untried mechanism, 

 a variable experimental error was introduced which as far as can be 

 determined for any day varied from 0.08 per cent to as much as 27.81 

 per cent. The magnitude of this error, though prohibitive for cer- 

 tain phases of the study, was not entirely so for others, and by a 

 selection of those days on which it was obviously at a minimum, in- 

 formation may be obtained which is practically as valuable as if no 

 error were incurred. 



A survey of the total daily exits and returns for the period of the 

 observations shows that a factor or group of factors can reduce the 

 total number of possible exits by an amount varying from total pro- 

 hibition of flight to a fraction of 1 per cent. A threatening storm, 

 for instance, of but one hour's duration, reduced the possible flight 

 on one day in the honey flow by 7.41 to 9.67 per cent. 



Comparatively few data have been obtained on the effect of wind on 

 the flights. On one day, however, a wind velocity of 16 to 21 miles 

 per hour during the hours 9 a. m. to 6 p. m. reduced the possible 

 maximum flight by 28.53 per cent. 



Under a particular set of conditions the temperature at which the 

 day's flight commences is uniformly near a certain definite tempera- 

 ture, but this definite temperature is not always the same. In April 

 it was from 12° to 14° C. and in May from 16° to 18° C. On dull 

 days this temperature was usually 2° higher. The internal conditions 

 of the colony govern this temperature somewhat, a strong colony 

 commencing flight at a lower temperature than does a weak one. 



There is a considerable variation in the hour and temperature at 

 which the peak of the flight in the honey flow occurs. No conclusive 

 evidence has been obtained that under similar conditions a good 

 honey flow induces the bees to go out in large numbers at a lower 

 temperature than they would if no nectar were available. The tem- 

 perature at which the flights in the evening begin to slacken was 

 without exception higher by from 1° to 9° C. than the temperature at 

 which flight began in the morning. Days which appear to be simi- 

 lar in every respect but which show a variation of as much as from 10 

 to 25 per cent in their total flights are found to differ on account of 

 a lower temperature in the early part of the day. 



Under honey-flow conditions the total exits proved to be three to 

 four times as great as they were at any other time of the investiga- 

 tion. 



A typical flight, where all conditions are fairly uniform and fa- 

 vorable throughout the day, is a gradual to rapid increase in the 

 successive numbers of bees which set out from the hive, to be fol- 

 lowed by a condition of equilibrium in which the outgoing numbers 



