In previous work, we presented the development of a piezoelectric switch for applications in ultra-low power wireless sensor nodes for monitoring the health condition of chickens. Using Pb(Zr0.52, Ti0.48)O3 (PZT) thin films, we have developed 'S'-shaped PZT cantilevers with proof masses. Since the resonant frequency of the PZT devices is around 24 Hz, we utilized superharmonic resonance to detect chicken movements as low as 5 to 15 Hz. However, the PZT devices broke when applied to other sensor nodes. 'S'-shaped PZT devices are adequate for low vibrations, but are beset by structural problems that cause fragmentation on impact. In order to address these problems, in this paper, we examine methods for utilizing PolyVinylideneDiFluoride (PVDF) films as piezoelectric switches. These are stronger and generate high piezoelectric output voltages under large stress. We suggest a structure in which the large load is applied to the PVDF films. One end of PVDF film is fixed on the case of the sensor node, and the he PVDF films are bonded on a part of the belts which are wound around a chicken's wing. Since the PVDF films are subjected to direct force generated by the chicken's motion, high output voltages are expected. Using the high output voltages, we are able to measure the chicken's activity levels. As a result, we were able to confirm circadian change of activity, and successfully fabricated tough wireless sensor nodes for chickens by utilizing the features of the PVDF films.