MEMS microphone nonlinearities are abused in dolphin ultrasonic attacks. The paper presents an analysis of problematic nonlinearities. To this end, two theoretical models were used. They allow to determine the frequency and amplitude of these distortions. The effectiveness of these models has been illustrated by computer simulations. Then acoustic tests were carried out using MEMS microphone. They were carried out in a quiet anechoic chamber. During testing, an additional reference microphone was used, which allowed to reduce non-linearity of non-MEMS elements of test setup. Tests illustrate the significant level of non-linearity of the MEMS microphone. Some convergence of theoretical models with the results of laboratory tests with potential development directions has been demonstrated as well.