Sentence:  The presence of suitable rodent prey introduced by people presumably at or near colonisation about 3000 years ago (Anderson and Clark, 1999; White et al. 2000) was probably the prerequisite that allowed barn owls, which are specialist predators of small mammals and specifically rodents, to <WSD>self-colonise</WSD>, presumably from the Solomon Islands. 
Meaning of the word marked with <WSD> tags:  To be introduced into an ecosystem via natural processes.