The top 50 centimeters of soil on Tiliga Island contain bones from the native birds eaten by the islanders since the first human immigration to the island 3, 000 years ago  A comparison of this top layer with the underlying 150 centimeters of soil -- accumulated over 80, 000 years -- reveals that before humans arrived on Tiliga, a much larger and more diverse population of birds lived there
Thus, the arrival of humans dramatically decreased the population and diversity of birds on Tiliga
The arrival of a species of microbe, carried by some birds but deadly to many others, immediately preceded the first human immigration to Tiliga.