“It was about 9 am on 28th April 2011 when I heard an Oriental Magpie Robin (Copsychus saularis) singing in the Children’s Playground in my condo, one of it’s regular haunt. As I always enjoy listening to its songs, I immediately set my camera on video mode to record, while trying to locate the bird. Disappointingly, I was unable to do so.
“Subsequently, I extracted the audio and was surprised to hear calls similar to that of a juvenile Black-naped Oriole (Oriolus chinensis) (2 syllable cheep-cheep), always preceding the OMR’s songs: HERE – let’s name it the mimic call).
“The above picture shows the Audacity waveforms totalling 7 calls with noise filtered.
“Thinking of the possibility of either the OMR in a duet with a juvenile Black-naped Oriole, or the OMR mimicking the call of juvenile BNO and incorporating it into the former’s own song, I decided to investigate further.
“A comparison of the two respective waveforms is shown above.
“From the waveform picture, it can be seen that the second syllable of the juvenile’s call is slightly louder or has about the same loudness as the first syllable, whereas in the case of the OMR mimic call, the second syllable is visibly softer than the first. This is true in all the 7 calls.
“Using Sonogram to compare the two types of call, the first 2 syllables look similar. However, for the juvenile’s call, the frequency of its sound is about 3 Khz. As for the OMR mimic call, the frequency for the corresponding 2 syllables is higher at about 3.3Khz (below).
“I did the frequency check with another sample of the juvenile’s call and found that it was about 3.3Khz. So the frequency test was inconclusive.
“Nevertheless, there is another information favouring the mimic call conclusion. While there were a number of juvenile BNO around recently, they only vocalised the single syllable ‘cheep’ call at fairly close intervals. I have not heard them with the 2 syllable calls either before or after a few days of my recording the mimicking calls.
“All things considered, I am inclined to conclude that this is a case of OMR mimicking the call of juvenile BNO and blending it into its own song. However, as I did not see the OMR while it vocalised, I am not 100% sure.”
Sun Chong Hong
7th May 2011