Prof. Heinrich Mendelssohn was a young student of medicine and zoology in Berlin, where he was born in 1910. When the Nazis came to power, he immigrated to Israel with his family, completed his studies at the Hebrew University in Jerusalem, where he also wrote his doctoral thesis in zoology. Mendelssohn invested great efforts to expand zoological knowledge in Israel, and later became the director of the Zoological Institute, one of the cornerstones of Tel Aviv University. He served as vice president of the university and dean of the Faculty of Natural Sciences. His extensive research earned him the title of "the father of zoology" in Israel and one of the founding fathers of the field of nature conservation. From the beginning of his studies at the Hebrew University of Jerusalem, Mendelssohn kept a journal in which he recorded his observations of flora and fauna throughout the country and neighboring countries. The Journal was recorded in many notebooks from the year of his immigration, 1933, until 1958. He made many drawings of birds and other animals. In his wonderful drawings, he "captured" the character of the subjects and their behavior in a unique way. Many of them accompany the pages of this book. The journals are a document of enormous importance for the study of nature in our country, a basis and source of information that provides contemporary researchers with the possibility of understanding and researching many processes that have occurred since then and to the present day. Those who peruse the book will learn a lot about Mendelssohn's path and will be able to learn firsthand about the character of our rich animal world in the first half of the twentieth century.