= John Krebs
{c}
<John Krebs> investigated <animal behaviour> through experiments connecting signals with ecological outcomes. With <Ruth Ashcroft> and <Mike Webber>, he examined <birdsong> and <territory> maintenance in <great tits>. Their 1978 paper describes removing resident pairs and occupying the vacated areas with loudspeakers; new pairs settled faster in controls than in song-occupied areas.<Song repertoires and territory defence in the great tit by John Krebs and others>[Abstract; resident removal, playback and settlement comparison]{ref}
The experiment makes an invisible social boundary testable: physical space remains after the owners leave, while an acoustic cue can still influence newcomers. It supports a signalling role in territorial exclusion without requiring an observer to witness a fight at every boundary. The same paper tested the effectiveness of varied song repertoires, illustrating the use of controlled signal manipulation to study <animal communication>.
Institutional profile: https://www.biology.ox.ac.uk/people/john-krebs .
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