putting salt on its tail

Roald Dahlの短編小説 "Nunc Dimittis" からの引用です。
“Is it not possible,” I said, “that a man might be — how shall I put it? — extremely fond of a lady and at the same time have his own good reasons for not wishing her to know about it yet?”
“More than possible, Mr Lampson.” with a man has to stalk his quarry with great caution, waiting patiently for the right moment to reveal himself.”
“Precisely, Mr Lampson.”
“There are better ways of catching a bird than by chasing it through the woods.”
“Yes, indeed, Mr Lampson.”
“Putting salt on its tail, for instance.”
“Ha-ha?”
“All right, Mr Royden, I think you understand. Now—do you happen by any chance to know a lady called Janet de Pelagia?”
「鳥を捕らえる」と言うのは女性の心を捕らえることの比喩表現ですが、その鳥を捕らえる良い方法に "Putting salt on its tail" があると言っています。これは慣用句か何かでしょうか？

・Farlex Dictionary of Idioms: obsolete To try to capture or encapsulate someone or something. An allusion to the folk method of capturing birds by sprinkling salt on their tail feathers.: We spend so much time putting salt on the tail of an ideal version of life—more money, more property, better status—that we forget to enjoy our present circumstances.
"Putting salt on its tail" の説明を掲載しているのは上記の辞書だけでしたが、Web上には次の様な話が一杯ありました。

When I was little 5-6 my dad told me if I wanted to catch a bird all I need to do was put salt on its tail end and I would be able to catch it because then it could not fly.I kept trying this for a couple of years.lol