F O R experiments in the value of tits as controls for insect pests in woods I have put up some 500 nest boxes in 20 sites round Perth. Some of these sites are as much as 40 nv'les to the north of Perth, others in Tentsmuir about 20 miles to the east. In the course of my visits to these boxes in 1948 I suspected t h a t nestling mortality was rather higher at Tentsmuir than elsewhere, but did not c...

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