Here is a case study presenting the results of a study that was performed using a 3D cuckoo model created by the engineers at 3D Quick Printing using the material of choice ABS plastic. This is a clear example of the incredible possibilities of 3D printing. The result is a perfectly vivid model of a cuckoo which can be used to trick even these clever birds into thinking that there is a new member of the group.
To test if common cuckoos were attracted by the alarm calls and mobbing displays (i.e. perching on the top of the reed when alarming and jumping between reed stems) of their hosts, we elicited mobbing reactions from the great reed warblers at their nests, using playback recordings of conspecific alarm calls and a 3D printed cuckoo decoy. During the 51 experimental trials, we recorded 14 cases when a female cuckoo was present and 30 cases when at least one male cuckoo was present. Both male and female cuckoo responses were stronger during the 2 minutes of playback when the great reed warblers were alarming than in the 2-minute pre-alarming period. We note here that most cuckoos typically flew closer to the mobbing hosts and vocalised, while one male even hovered above the experimental setup for a prolonged period.
In this study we tested if brood parasites rely on the alarm calls produced by their hosts, rather than on visual nest searching when seeking for nests to lay their eggs in. We found that the nests of the great reed warbler, the host of the brood parasitic common cuckoo in our study area, are hardly visible in the dense reed bed from the nearest cuckoo perches and from mid-air. In contrary, the alarm calls uttered by the hosts are likely to be good nest location cues for the brood parasites, since both female and male common cuckoos exhibited interest towards alarming hosts and alarm call playbacks. Moreover, hosts that were more likely to alarm when approached by human observers during nest visits experienced a higher probability of parasitism.
Here is a video of the experiment.
The full article can be read here from nature.com: Host alarm calls attract the unwanted attention of the brood parasitic common cuckoo or read the PDF.