Drama of sunbird and bulbul nesting together in the Curry Leaf Tree

posted in: Interspecific, Nesting | 0

Fred and Jasmine Tan had the privilege of observing the complete nesting cycle and behaviors of two bird species on the same tree in their own backyard. The two bird species, Olive-backed Sunbird (Cinnyris jugularis) and Red-whiskered bulbul (Pycnonotus jocosus) had a hostile relationship while nesting close to each other on the Curry Leaf tree (Murraya koenigii).

“The table below shows chronologically the full nesting cycle.
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Nest building
“Fred and Jasmine Tan noticed some commotion in their backyard in early February 2017. The adult bulbuls were chasing the adult sunbirds frequently throughout the day. They noticed both species were building their nests on the same tree. The sunbirds were chased away by the bulbuls every time the sunbirds flew close to the bulbuls’ nest. If both bulbuls were away from their nest, the sunbirds will fly directly to theirs while carrying nesting materials. If the sunbirds were chased, they would take an alternative route to their nest. The sunbird and bulbul nests were completed on 6 and 10 February respectively.

“During the nest building stage, Jasmine noticed an interesting behavior. When the sunbird accidentally dropped nesting material such as a feather while being chased by the bulbul, the bulbul will salvage it by catching the feather in mid-air and used it for its own nest. It was interesting to note that both species chose to build their nests on the same tree, close to each other, less than a metre away. This close proximity is definitely too close for comfort for any bird species.

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“It was also interesting to observe that both species chose to build their nests near the ground (above) which seems more vulnerable for predator attacks, instead of higher up the tall tree (below). The sunbird nest was less than a metre above the backyard floor and the bulbul nest was slightly over a metre above the floor. During a heavy downpour one day, Jasmine noticed the branches supporting the bulbul nest was blown down and came very close to the ground.

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“It was interesting to note how greatly diverse the design of the nests were from each other. The sunbird nest was constructed below a clump of leaves which seem to provide shade and good camouflage for the long hanging nest (below).

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“The entrance to the sunbird nest was partially covered by the clump of leaves which makes observation difficult. The sunbird nest was the first nest to be completed as it was started earlier. The bulbul nest was constructed above a clump of leaves and exposing its open-top round nest. The bulbul nest was first constructed with a few strands of twigs (below)…

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“…and progressively became a neat and almost perfectly circular nest, lined with broad dried leaves at the base (below).

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Incubation behaviours
“The female sunbird and female bulbul each laid two eggs on 12 and 15 February respectively. There are no photos of the sunbird eggs. The bulbul eggs were white with speckled mauve spots on them (below).

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“It was easier to observe the bulbul nest as it was closer to the kitchen window. An adult bulbul can be frequently seen sitting on the eggs during incubation (below). Occasionally the adult bulbuls will leave their nest leaving the eggs exposed for some time. At this incubation stage, the adult bulbuls were frequently seen chasing the sunbirds away, forcing the sunbirds to take alternative routes to their nest.

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Feeding behaviours
“The sunbird eggs were hatched on 22 February, ten days after incubation. The bulbul eggs were hatched on 25 February, ten days after incubation.

“The sunbirds behaved differently at this stage. Each of them with food in their beaks, would perch a distance away from the nests for a minute before flying to their nests. It seems they were surveying the backyard by perching on either the wired fence or cement walls to ensure no predators were around. They would behave this way throughout the rest of the feeding period. The adult sunbirds would each hunt at the same time, leaving their nest alone most of the time. The sunbirds frequency of obtaining food for their chicks seems much higher than that of the bulbuls. At this stage too, the adult bulbuls were observed chasing the adult sunbirds whenever they were close to each other. Again the sunbirds would take an alternative route to their nest. The sunbirds were observed carrying small insects and spiders (below) in their beaks to feed their young.

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“The hunting behavior of the bulbul seems different. One adult would sit or guard the chicks while the other would hunt for food. Occasionally, the adult bulbul guarding the nest would fly off too leaving the chicks exposed (below).

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“The adult bulbul with food in their beaks would fly directly to their nest unless they detected the presence of humans and they would hesitate for a minute or so before flying to their nests. Some of the food source the bulbuls were seen carrying in their beaks were mainly insects (below-top) and fruits (below-bottom).

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“The ripe fruits came mainly from a palm tree (below) located in the same backyard. The adult bulbuls will cleverly remove the seed of the palm fruit before flying to their nest.

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“The adult birds besides harvesting the palm fruits, would also feed from this palm tree (below).

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“It was easier to monitor the development of the bulbul chicks. The bulbul chicks were blind and naked after hatching as shown in the picture when the chicks were two days old (below).

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“It was interesting to note that the egg shells were also removed from the nest, keeping the nest clean and tidy. When the chicks were five days old, feather shafts were observed on the chicks’ wings and neck (below).

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“When the chicks were nine days old, a bigger area of the body were covered with feathers but some fleshy skin can still be seen (below).

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“The chicks’ eyes were closed when they were at rest. When the chicks were eleven days old, most of the head feathers had grown and covered the whole head (below). Traces of the white cheek feathers were also developing. The yellow gape was still evident.

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“When the bulbuls were eleven days old, it was observed that the chicks after swallowing the food, would immediately eject their fecal sac by raising their backs for the adult bird to collect the faecal sac with its beak – LINK. The adult bird would then swallow the faecal sac. On 8 March, I observed an adult bulbul swallowing some of the faecal sac that had dropped onto the backyard floor some time ago. The droppings had dried up (below) and ants were surrounding the area.

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Fledgling behaviours
“The sunbird chicks fledged on 5 Mar 17, eleven days after hatching. The first chick flew and perched on the fence. The second chick flew unsteadily and landed on the floor of the backyard (below). After some attempts and encouragement from the adult sunbird, it managed to fly back to its nest. By the next day, both chicks were not seen in the nest nor in the backyard.

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“The two bulbul chicks fledged on 10 March, thirteen days after hatching, the first one in the morning and the second one in the later part of afternoon. The first chick flew to the fence and perched there (below). In this photo, it was interesting to observe that the chick had some resemblance with the adult. The chick had developed straight crest feathers at its forehead, similar to the adult bird. The white cheek feathers had developed and looked similar to the adult. However, the gape at the mouth had not disappeared yet. Little white tail feathers had also developed.

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“The adult bird was frantically flapping its wings to force the chick to fly back to its nest. After perching on the fence for some time (below).

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“On 10 March, Jasmine observed a bizarre behaviour by one of the adult bulbul birds. One of the fledgling bulbul chicks had landed on the backyard floor. To distract Jasmine, the adult bird flew down, sat on the floor on its vent with both feet raised above the floor but moving in circular motion. It then used its wings to waddle forward for a short distance, about half a metre before it stopped and flew off.

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“A photo of both chicks taken on 11 March (above) clearly showed the development of their pale orange vent that would eventually turn bright reddish orange when they become an adult. On 13 March, both bulbul chicks were still in the backyard, perching on the branches close to the canopy of the Curry Leaf tree. The adult bulbuls were still bringing food to feed them. Jasmine observed on one occasion, the family of four bulbuls flying to the Palm tree to feed but immediately flew back to the Curry Leaf tree when a Pink-necked pigeon (Treron vernans) flew into the Palm tree to feed on the fruits.

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“On 17 March when the bulbul chicks were 20 days old, Fred photographed an adult and a chick at the canopy of the Curry Leaf tree (above). He was able to capture a wonderful close-up shot of the 20-day old chick which showed greater development of its crowned feathers, traces of the red whiskers, white cheek and pale orange vent feathers (below).

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“In conclusion, it was a wonderful opportunity to observe the successful nesting cycles and behaviours of two different bird species on the same tree at the same time. This is how Jasmine summarized her experience, ‘Fred and I felt doubly blessed to have such an awesome encounter with God’s wonderful creation. It is an amazing wonder to see how two bulbul birds can create a near perfectly symmetrical nest in the shape of a hollow hemisphere. The opening of the bulbul nest was almost a perfect circle. And also how two sunbirds can build a little pear shape nest with a little side opening and hanging from a branch yet strong enough to bear the weight of parent birds and two chicks. Watching these two different species surveying a nesting place, diligently and painstakingly collecting materials piece by piece to build such intricate and yet strong nests; in such a short time (about three days) tells me how much hard work, planning, creativity and thought must have been put in by these amazing creatures. Watching them feeding and protecting their chicks reminds me of the human maternal instincts. I stand amazed with wonder of God’s creation. A great lesson for Fred and me'”.

Thong Chow Ngian & Fred and Jasmine Tan
Singapore
15th March 2017

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