What were ernst mayr's main findings, publications?

He contributed to the conceptual revolution that led to the modern evolutionary synthesis of Mendelian genetics, systematics, and Darwinian evolution, and to the development of the biological species concept.

He published a book titled Systematics and the Origin of Species. Nobody really knew the explanation of evolution in his time but he came up with an explanation and is written in his book. He explained that a species can evolve by mating in their own species, by being isolated and over time different genes will form and start evolution with that species. That was his theory on how an animal can evolve from its same ancestors without mingling with other species. 

Ernst Walter Mayr, more commonly known as Ernst Mayr, was a German-born American who made decisive and groundbreaking contributions to avian taxonomy, evolution and population genetics. Widely credited as the world's greatest evolutionary biologist in history, Mayr was fondly called the “Darwin of the 20th century”.

I hope this answer is going to help you out.