tree frogs
...that tree frogs have been used as barometers because they respond to approaching rain by croaking?
...that <b id="mwAkE"><a href="./European_tree_frog" id="mwAkI" rel="mw:WikiLink" title="European tree frog">tree frogs</a></b> have been used as <a href="./Barometer" id="mwAkM" rel="mw:WikiLink" title="Barometer">barometers</a> because they respond to approaching <a href="./Rain" id="mwAkQ" rel="mw:WikiLink" title="Rain">rain</a> by croaking?