24 BULLETIN 1328, U. S. DEPARTMENT OF AGRICULTURE 



numbers of outgoing bees decrease, followed later by a corresponding 

 decrease in the number of returns until flight ceases for the day. 



The characteristic differences typical of the flights during a honey 

 flow and dearth are respectively : 



1. During the honey flow, as on May 20 (fig. 8), there is a very 

 steep ascent of the outgoing curve on the advent of the optimum 

 conditions for flight, with a corresponding abrupt descent in the 

 curve on the approach of sundown. In a dearth, as on May 19 

 (fig. 6) or July 12 (fig. 10), these ascents are more gradual. Instead 

 of the peak of the flight being reached within three-quarters of an 

 hour or an hour after the main flight to the field begins, as in the 

 honey flow, it is not attained until about four or even five hours later. 



2. In the honey flow the portion of the curve lying between the 

 morning peak and the time when, at the close of flight, the number 

 of exits begins to drop, approximates a horizontal straight line, 

 showing that the rate of flight is fairly constant, there being almost 

 as many bees departing as arriving. In the dearth, on the other 

 hand, as on July 12 (fig. 10) , this portion of the curve is not horizon- 

 tal but tapers away gradually to zero, indicating that on the dis- 

 covery of the dearth the bees conserve their energies by reduced 

 activity. 



3. The horizontal distance (indicating length of flight) between the 

 curves representing the outgoing and incoming bees in a heavy honey 

 flow is always shorter and sometimes very much shorter than it is 

 in a dearth. This is specially apparent when in the morning the 

 flights are on the increase and again in the evening when they are 

 on the decrease. This distance, which is indicative of the average 

 duration of each voyage, can not be followed precisely on a curve 

 plotted in this manner. This will be dealt with separately in a dis- 

 cussion of the average duration of the trips (p. 26). 



4. A study of the changes in weight of the hive, indicated in 

 Figures 4 to 10, shows that as the successive number of departing 

 bees increases the weight correspondingly decreases; then, again, 

 as the number of nectar-laden returning bees increases the hive be- 

 gins to regain its early morning weight. During the first days of 

 the honey flow the time at which this regaining of the original weight 

 occurs is well on in the afternoon or even at the end of the day. As 

 nectar conditions improve, the time at which the original weight is 

 regained comes earlier in the day. Then, as the honey flow wanes, 

 this time again occurs toward the latter part of the day. In the 

 dearth proper the drop in weight of the hive is considerable. This 

 is due more to the long trips, with the majority of the flying force 

 absent from the hive at one time, than to the small loads that they 

 bring back. Since little or no nectar comes in, the morning weight 

 is frequently never regained, a loss in weight being continually re- 

 corded for the entire day. This loss indicates the amount of stores 

 consumed to maintain this flight activity in a main search for nectar, 

 and to maintain other colony activity. 



The amount of nectar gathered on any particular day depends 

 not only upon the factors governing nectar secretion, but also on the 

 factors governing the flights for that day. The secretion may be 

 equally good on two selected days, but on account of a relatively ad- 

 verse condition for flight of shorter or longer duration on one of these 



