He is internationally recognized for his work with carnivore conservation, and in particular the endangered Ethiopian wolf (Canis simensis).
His work includes the conservation of endangered species, protected areas management, and wildlife surveys for 35 years spanning four continents.
In 1998 he received the Whitley Award for Animal Conservation from the Royal Geographical Society for his work in Ethiopia.
Becoming increasingly involved in the relationships between protected areas and their surrounding rural communities, he is now working with biodiversity conservation policies and practices, particularly in South America, India and Ethiopia.
Prof Sillero is frequently a keynote speaker at the annual Wildlife Conservation Network expo.