Transcription: During the breeding season, male birds find a territory that will provide food and shelter for their young. In this example, nine male Eurasian robins have claimed a territory. The boundaries are invisible to us, but not to the robins. Some follow natural barriers, but others cut right across roads and gardens. One year later, there are just eight territories to be defended against rivals. This is because robins have a short lifespan and many die each winter. After a severe winter, even fewer male robins survive and each survivor is able to claim a larger territory. On this piece of ground, th ...
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