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Effects of captive rearing on vocal development of the Aga (Corvus kubaryi)

Andria Kroner Binghamton University

Effects of captive rearing on vocal development of the Aga

Åga vocalizing during a rare moment with a clear view through the canopy.

Two åga fledglings (siblings), showing a few of the vocalizations they are known to make.

Effects of captive rearing on vocal development of the Aga

Hiding the external microphone among the vines near a nest.

Effects of captive rearing on vocal development of the Aga

Spectrogram of a 4-hour-old åga hatchling at feeding time in captivity.

Effects of captive rearing on vocal development of the Aga

A 20-day-old captive-reared åga nestling, also at feeding time.

I arrived on the island of Rota in mid-August and the new equipment arrived in perfect condition. Some Åga (Mariana Crow) pairs have just begun nesting, and this breeding season is looking like it will be a good one.

This season my study will be comparing the vocalizations of captive-reared young to those of wild-reared young. While I wait for the San Diego Zoo Global team to collect the first eggs and chicks for the captive rear-and-release program (scheduled for early October), I am beginning to collect behavioral observations and recordings of wild Åga with my handheld microphone for later characterizing vocalizations.

I have also begun to test out Kaleidoscope's clustering analysis on recordings made in Åga territories last summer using SM3 and SM4 recorders. I am very pleased with how well Kaleidoscope is performing and is able to find Åga vocalizations even with other background noise in the recordings. It even found vocalizations that I missed when scanning through spectrograms visually!

Very soon I will be recording Åga at their nests with the new external microphones and extra long 50m cables I was awarded, resulting in thousands of hours of audio by the end of the season. Using Kaleidoscope's clustering analysis to find and identify Åga vocalizations recorded at these nests should allow me to analyze a substantially larger dataset compared to what might be possible using other available software. I can't wait till the first wild nest recordings start rolling in!

A lot has happened since my last update! Collections of wild åga eggs and chicks for the captive rear-and-release program (through San Diego Zoo Global) are now complete. The last of thirteen chicks have hatched, and I have been getting some quality recordings of them during their first months. We have found that the åga chicks make the tiniest begging "cheeps" even during their first feedings while only a few hours old!

In the wild, we have been steadily finding åga nests, and I have been getting out the ARUs to some of them. Working with a highly intelligent AND critically endangered species means that extra precautions must be taken when monitoring nests. This is where the external microphones and 50m long cables from my Wildlife Acoustics product grant come in. When we find a nest that I think will be good for recording, I hike in under the cover of darkness and set up the microphone in a tree near the nest, camouflage the cable with leaves and stretch the cable 30-50m away where I attach the ARU to another tree. I also camouflage the ARUs just in case. This is all to keep the åga from noticing the equipment and if they do see it then hopefully they won't associate it with humans. After this is all set up at night I can then check the batteries and SD cards weekly during the day with a much lower risk of disturbing the nesting pair.

The breeding season is now winding down and we're expecting to find only a few more nests between now and May. I am now focusing more on trying to get more observations and recordings of wild fledglings and adults as they move away from the nests to add to my library of vocalizations to characterize. I have already collected almost one and a half terabytes of audio so far this season! Very soon I will be putting Kaleidoscope to the full test as I begin analyzing this mountain of recordings I have accumulated.