科学美国人60秒:Hawaiian Crows Ready for the Call of the Wild

Once upon a time, on the big island of Hawaii, it would not have been unusual to hear: 

[wild Hawaiian crow call]

That’s the call of the Hawaiian crow. It’s is a critically endangered species, now extinct in the wild after decades of habitat loss, persecution by farmers, and invasive diseases. In the mid-1990s, wildlife biologists rounded up the few surviving crows and put them into a captive breeding program. Today, Hawaiians can once again hear the calls of more than one hundred Hawaiian crows – or 'alalā, as it is called there – but only in aviaries.

[aviary crow call]

Researchers once focused their efforts primarily on breeding and husbandry. But now they need to know more. 

"And now that they are doing so well, and it's at the point where they could be in the wild again, now we can look at their vocalizations and their behaviors and things like that." 

University of Hawaii bioacoustics researcher Ann Tanimoto. Those other aspects—culture, if you will—are critical for a species as socially complex as the 'alalā.

Tanimoto and her team made recordings of captive-bred 'alalā pairs at the Keauhou Bird Conservation Center in Volcano, Hawaii, and compared them to recordings made in the early 1990s by Fish and Wildlife service biologists of the last few wild pairs.

"The wild have more, almost double the number of alarm calls, than the aviary 'alalā do. And they also have these really cool territorial broadcast calls they do in the wild 

[Wild territorial call]

that weren't found in captivity."

The absence of the territorial call in captivity makes good sense, because captive birds have different territory demands that wild ones. It also makes sense that they would have fewer alarm calls, because captive birds don't experience the threat of predation. The study was published in the journal Animal Behaviour. [Ann M. Tanimoto et al.. Changes in vocal repertoire of the Hawaiian crow, Corvus hawaiiensis, from past wild to current captive populations.]

"So we think that their vocalizations that are similar, aviary and wild, are more innate, so basically naturally inside of them. And those that differ are socially learned by being passed on generation to generation."

So what happens when the captive-bred birds are released? They won't have the luxury of learning these calls from their ancestors.

"It will definitely be interesting to determine if they will begin vocalizing something similar to those that they used in the wild before, or if they will begin vocalizing call types that are completely different than those that were in the wild previously."

In Hawaiian mythology, the 'alalā are thought to lead souls to their final resting place near the Ka Lae volcano. With luck, scientists can help the rare species avoid their own journey to Ka Lae.

—Jason G. Goldman