Signals of Need in Parent-Offspring Communication and their exploitation by the common cuckoo. Part III

3) What, exactly, did the researchers find (i.e., what were their data)?

In regards to the call experiment noted above, the researchers observed that there was a linear correlation between brood size and call frequency. They then created several regression equations in an attempt to quantify the impact of each factor.  After manipulating the call rates of clutches they determined that the regression equation derived is: feeds delivered per hour = 2:28 (maximum number of gapes displayed) + 2.30 (maximum number of chicks calling) + 8.23. This equation was exclusive to 6-7 day old chicks so they manipulated the factors so that they could apply this to chicks of any age. The resulting regression equation thus derived was: feeds delivered per hour =0:0162 (gape area displayed (in mm2 )) + 0.178 (calls per 6 s) + 8.2. When analyzing the cuckoo chicks they determined that 1. A cuckoo chick intakes the amount that 4 warblers would normally require to survive and that a Cuckoo that is 6-8 days old has a call frequency that matches that of 4 warbler chicks. 2. This increased intake is not related to size,  as black birds and song thrushes, even with augmented warbler calls, did not receive the same amount of food. However, in the presence of a cuckoo call they did receive more food. They then used the equation 0162 (gape area displayed (in mm2 )) + 0.178 (calls per 6 s) + 8.23, to determine if the cuckoo’s reduced gape area would in turn increase their call frequency in a predictable fashion.