“The idea of talking about vents and faeces may be gross or disgusting to some people. After thinking about it for quite some time, I decided to share my observations to add to the discussions about this topic.
“The Oriental Magpie Robin (Copsychus saularis) seemed to be breeding around my condo, as it can be seen once in a while in the playground area. On the morning of 19th May 2011, one suddenly appeared there in front of me and perched quietly in a matured Water Plum (Wrightia religiosa). It had its back facing me, in a not so nice position for bird photos. In the past I had many surprises from encounters which did not appear to have any significance. So I just move myself slightly to adjust for the back-lighting and recorded some videos in the hope of capturing something useful.
“On review of the videos through slow motion and screen by screen display subsequently, the bird was seen doing the usual thing of passing out faeces at one point. [The edited video above includes a replay at half speed.] Because of the position of the camera, the movements of the feathers covering the vent opening could be seen clearly during the brief interval. Altogether there were five cycles of contractions, including the first one which followed immediately after the discharge of the faeces.
“Attached are *13 consecutive screen shots showing part of the first and second cycles. As the feathers are splayed out, notice they are also curved outwards. I believe this is the result of natural evolution to prevent the soiling of vent feathers. [*The 13 screen shots are not included here as they do not show clearly the splayed feathers. These are easily seen in the attached video.]
“In an earlier post “Do Birds Fart” LINK, the image of a Common Myna (Acridotheres tristis) with the vent opened captured by Forest Ang prompted discussions on whether birds fart. As deduced from the video evidence I recorded, it is also possible that the Common Myna was photographed just after its faeces was discharged.”
Sun Chong Hong
3rd October 2011