Yellow-Eared Spiderhunter

A pair of Yellow-eared Spiderhunter with a somewhat strange behavior. Wonder what they were up to? This was recorded near the office of the Rainforest Discovery Centre in Sepilok, Sabah, Malaysia.

Update (08 July 2013) : I met a couple of birders at the recent Borneo Bird Festival in Sepilok and mentioned this behavior to them. They said that some male birds who suspect that a rival male could have mated with its female mate would sometimes try to remove the sperm of the rival this way. 

I read further that this 'cloaca pecking' behavior is also seen in dunnocks in what is termed as a 'sperm competition'. It is believed that male birds peck at the cloaca to get the female to eject sperm that could be stored internally in tubules. In doing so, the male bird would likely increase its chances of parenting its own chicks and not of its rival.