Answer:
Overexploitation
Explanation:
Gradual declination of certain species of organisms in an ecosystem, which leads to their extinction occurs from time to time. This is referred to as the loss of biodiversity or simply biodiversity loss. Many factors contribute to the loss of biodiversity in an ecosystem, they include: habitat loss, invasive species, overexploitation etc.
Based on the description of the cause in this question, the biodiversity loss is as a result of OVEREXPLOITATION. Overexploitation is when certain animals are utilized more than the surviving ones can reproduce to cover the loss.
In this case, the sailors overexploited the dodo birds in their island habitat by feeding on them excessively because they were a easy catch.