Marinus Adrianus Koekkoek, usually called Marinus Adrianus II for the sake of clarity, belongs to the fourth generation of the Koekkoek painting family. He was born in Amsterdam and traditionally learned the tricks of the trade from his father Willem. At a young age, however, he preferred painting landscapes, while he also spent many hours observing and drawing the animals in the Amsterdam zoo. Inflamed by the 'biological revival' that under the influence of the teachers E. Heimans and Jac. P. Thijsse in the capital, he developed into a lover of the 'small' nature, of the small animals in their natural environment on the forest floor and in the low bushes. The happy combination of artistic talent and precise observation ability led to assignments for illustrating scientific publications at home and abroad. The most important of these is the standard work 'Ornithologia Neerlandica' (1929-1939), better known as 'The Birds of the Netherlands' by Prof. E.D. van Oort, for which the painter made all 407 illustrations between 1922 and 1935. In addition, from 1918 he worked for twenty years as a scientific draftsman at the Natural History Museum in Leiden. The bird plates for the above publication are now stored there, in addition to a series of plates of Dutch mammals that Koekkoek made for a later, never published publication by Van Oort. As a free artist, he painted impressionistic, not exceptionally artistic landscapes with poultry and birds, in which his meticulous treatment of songbirds in particular immediately catches the eye.