How are humans killing animals?

Humans kill animals through hunting, slaughter for food and medical experiments. These are direct ways. 

Humans indirectly kill animals by destroying habitat including filling in wetlands, dredging rivers, mowing fields, and cutting down trees. Since 1970 about 60% of mammals, birds, fish  and reptiles have been wiped out by humans. Scientists are now of the opinion that the extinction of animal species is the gravest threat to human civilization at the time.

For more relevant articles refer to the links given below:

• UPSC Environment and Ecology Questions
• Conservation of Biodiversity
• UPSC Environment and Ecology