'Neighborhood Watch' Protects Against Notorious Nest Thiefs

Reed warblers have set up a "neighborhood watch" to protect their nests from invasive cuckoos, who lay their eggs in local nests for others to raise. When reed warblers spot a cuckoo, they mob it and emit alarm calls that alert neighbors a cuckoo is at large and they should monitor their eggs closely. This has greatly benefited warblers, but cuckoo populations appear to be suffering.