With a high-temperature scanning tunneling microscope, we study several kinds of point defects at Si(111)-7x7 surfaces. A special type of defect, which we call pseudo-vacancy, appears dark in both tunneling polarities. They are not real vacancies, and they are neither caused by reaction of silicon surface atoms with residual gases, nor due to dopants coming from the Si substrates. On Si(111)-7x7, we can create single vacancies or vacancy clusters at elevated temperatures, which are found to be filled up after a period of time. In addition, we study defects caused by adsorption of O-2, CH4, C2H4 and H on clean Si(111)-7x7 surfaces from room temperature to some elevated temperatures. The species produced for adsorption at elevated temperatures are often different from those for adsorption at room temperature. Also, we can observe interesting dynamic behavior, such as site hopping and desorption, at high temperatures. In this work, we find that different surface defects exhibit very different dynamic behavior, which can be used to distinguish between defects.