“No longer needing to sing at high frequencies that could be heard over the highway’s rumble, the sparrows’ songs became more expansive, occupying more of the soundscape’s ‘acoustic bandwidth.’ Even those with quiet voices became audible; in those first months, ‘you could hear four times as many birds as you could before,’ says [Professor Elizabeth] Derryberry.”
“They also found that, in general, the size of the birds’ repertoire decreased as anthropogenic noise increased, especially when the birds were exposed to levels of anthropogenic noise that were above the usual noise to which they were accustomed.”
“[T]he fascination with humans and the failure to understand basic condor etiquette were signs of a more profound problem. Those first reintroduced birds were released too young, and had not had contact with adults who could teach them how a condor behaves.”
“Sometimes the birds would lose a tool, leaving it out of reach inside the cage. In that case, they’d reach for another tool but wouldn’t use it to retrieve the food—instead, they’d retrieve the first tool, then use that to get the food. One individual went three layers deep into this sort of recursion.”