Charlene Yeong, Conservation and Research Officer of the Singapore Zoological Gardens, sent in a series of images showing the nesting progress of a pair of Olive-winged Bulbul (Pycnonotus plumosus). The nest was built at the top of a potted dracaena plant next to her work desk.
The first time she noticed the nesting birds with an egg was on 14th July 2008. Two days later there was another egg. The first egg hatched on the 28th July while the second the next day (below).
“Most of the time, I only saw one adult at the nest. Sometimes both were at the nest, but only very briefly. Those times, either one or both would fly away. At night, I saw only one at or near the nest.”
To summarise: The incubation period for the first egg was 14 days and the second, 13 days. The eggs hatched one day after the other. The chicks were born naked and with eyes closed i.e. the young is altricial. This means that it is totally dependent on the parents. This is contrasted to precocial young where they are born with their eyes open, covered with down and are able to move about soon after.
In the image below (top row, left), an adult brought what looks like a praying mantis for the chick. The right image shows the older of the two chicks gaping widely, begging to be fed as soon as an adult appeared. Note the prominent reddish inner lining of the gape, the prominent yellowish oral flanges and the apparently bottomless pit of the throat. Such signs deliver a clear message to the adults that the chick needs to be fed. Note also that although parts of the body are feathered, the chicks are mostly naked.
In the image above (bottom row, left), the body of the chicks are covered with pin feathers and the feather vanes have yet to emerge from the sheaths, seen as whitish pencil-like structures. The older is 8 days old while the younger 7 days. In the right image, with the chicks one day older, the back of the older chick is almost fully covered with feathers, with the head still with pin feathers. The pin feathers of the younger chick have yet to emerge from their sheaths.
One chick fledged on the 7th August, 10 days after hatching (above left). It left the nest and landed on the pot below. Note the prominent oral flange. The younger chick remained in the nest with an adult (above right). The next day the other chick fledged (left). For the next week or two, both chicks will be fed by the adults until they have fully master flight and capable of foraging for themselves. Until then they will constantly beg for food.
“Around 4th September, two Olive-winged Bulbuls flew into the balcony. They were around the old nest for less than a minute, before they flew off. They have not been seen since.”
Input and images by Charlene Yeong and Lucia Meijer