He speculates that the robins have discovered that traffic drives away their predators, and this is why they choose the lesser of two evils, putting up with the pollution in exchange for the traffic's protection.
「黃鼠狼、猛禽、星鴉等大型生物，對車輛更敏感，更容易受人煙喧嘩驚嚇，」羅柳墀猜測，栗背林鴝是「兩害相權取其輕」，牠們發現車輛可以趕走天敵，因此選擇忍受「公害」，以換得車輛的「護衛」。