This study presents the in-flight radar cross-section (RCS) data of drones and birds at K-band and W-band obtained from extensive experimental trials. The focus of this study is to demonstrate the RCS characteristics of these targets in practical scenarios, hence experimental results are used exclusively. Owing to variations in orientation, aspect angle and target motion, the measured RCS values of these targets fluctuate significantly during their flight. Three very well-calibrated frequency modulated continuous wave radar systems, one operating at the K-band (24 GHz) and two at W-band (94 GHz), have been used to collect data for RCS analysis. Three drones of different sizes (DJI Phantom 3 Standard, DJI Inspire 1 and DJI S900 Hexacopter) and four birds of prey of different sizes (Northern Hawk Owl, Harris Hawk, Indian Eagle Owl and Tawny Eagle) have been used for data collection. The results demonstrate that the RCS scales broadly with the size of the target, consistent with the optical scattering regime and that the RCS values for each target are comparable at the K-band and the W-band. The statistical distribution of RCS for each target falls within a certain range which is useful for predicting the performance of a drone detection radar.