Egg-dumping is the term used by birders to refer to nest parasitism. This is where a bird lays its eggs in the nest of other birds. It can be a bird of the same species (intraspecific parasitism) or of another species (interspecific parasitism). The former is fairly widespread but seldom noticed. However, this can be detected when there are two eggs seen in a day as few birds lay more than one a day. The latter is seen in the Asian Koel (Eudynamys scolopacea) where the koel lays its eggs in the nests of other birds. This is because the koel never builds its own nest.

In Singapore these koels parasitise the nests of House Crows (Corvus splendens) mainly. We had a number of earlier postings by Angie Ng (1, 2, 3, 4, 5) and by Hung Bun Tang (1, 2, 3). Below are some engaging discussions on the subject.

Ong Kiem Sian reported that she saw a cuckoo nesting in a fantail nest. The female cuckoo pecked the egg of the fantail and immediately deposited her egg in the nest. This was completed within a few seconds when the host was not around. She wondered if the cuckoos were desperate and cannot find a host nest, would they then become aggressive, like the koels reported in the postings? She added: “And if the female bird still cannot find and cannot tahan (ie desperate to lay her egg), maybe she will drop her egg on to the ground.”

Yap Kim Fatt countered: “I would have thought the koel chabohs (Hokkien for females) would deposit their eggs in the crow’s nest by stealth rather than by the gangster-ish method as witnessed by Angie Ng (see links above). I would expect a sort of a hit-and-run ova-parturition when the adult crows are not around the nests.”

Jeremy Lee is of the opinion that “If they are nest parasites, I believe they would have to evolve a quick hit-and-run method of depositing the egg in the nest. I have seen documentaries on TV showing cuckoos caught in the act. And it is surprisingly quick to drop the eggs in the nest.”

At the talk in the National Library by Prof NS Sodhi and Ilsa Sharp to launch their book, Winged Invaders – Pest Birds of the Asian Pacific (Singapore: SNP References, 2006) on 10th March 2006, I nearly got my answer to the above. It would appear that the male Asian Koel will seek out an active House Crow’s nest after which he will call out for his mate. Once the female koel appears, the male will approach the crow’s nest whereby the incubating crow will immediately chase it away. At that split second, the female koel will sneak into the nest and lay her egg. The female will then call to signal to her mate that the mission has been accomplished.

But I was unable to elicit a direct response from Prof Sodhi on whether the female koel will drop her egg on the ground if she is not able to immediately find a nest to lay her egg. He believes that in all probability the crow will leave its nest to chase off the male koel, giving the female an opportunity to lay her egg.

Geoffrey Davison has this to say about fertilisation and egg laying: “I had a look at what few books I have at home, but didn’t find anything specific on the time taken from fertilisation of the ovum to laying of the egg by birds. But for all birds, fertilisation has to take place at the top end of the oviduct, before the fertilised ovum is surrounded by albumen, two membranes, and the shell. Since eggs of poultry and many other birds are laid at about one-day intervals, this implies about 24 hours for the egg to proceed down the oviduct.

“Smaller birds lay eggs at shorter intervals, but seldom less than 15 hours or so, and big birds like ostriches would lay eggs at intervals of several days - again, that implies several days for each egg to travel down the oviduct being wrapped in albumen, membranes and shell after fertilisation.

“…It’s also possible that copulation is performed shortly before the laying of an egg that was fertilised by an earlier copulation.”

Input by Ong Kiem Sian, Yap Kim Fatt, Jeremy Lee, Prof NS Sodhi and YC; additional comment by Geoffrey Davison; and images of a female Asian Koel sneaking into the nest of the House Crow by YC

After only three days trying to incubate their eggs, the House Crows (Corvus splendens) gave up on the morning of 28th December 2005. Thereafter, it was open house for the Asian Koels (Eudynamys scolopacea)! They were increasingly daring, stealing into the nest throughout the day, but the height of activity was always in the mornings and late afternoons, and one female even stayed in the nest for more than 10 minutes. There were two occasions when the male koel took an interest, hopped into nest, looked around before hopping off again.

Although the crows seem to have abandoned their nest, they are not averse to visiting it every day, and sometimes twice or three times a day - to check on the contents? Once I saw presumably the female pecking, pushing and pulling some of the twigs. It seemed to be tidying the nest or doing some house-keeping! However, on another day one crow actually took away some fine twigs from the nest!

I would know they were visiting because often they would caw but other times I just happened to look up and there they were! The crows would still chase away the female koels if they chance to see them approaching the nest, but I think they are losing interest. They behave as though they have another nest somewhere else. Lately, they sometimes fly overhead by-passing our tree. Female koels still visit the nest, though not as frequently.

And throughout the days I was home, a lone male koel would spend long periods sitting on the lower branch mournfully calling ‘koe-ell koe-ell’ its pitch gradually rising in desperation.

The nest looks a little thread-bare/twig-bare this morning.

If each time a female koel visits and lays an egg, we’d have more then two dozens eggs in nest. But do they necessarily lay eggs at each visit?

This is the end of koel-crow watching, I hope. Maybe I will still watch to see when the nest will drop its load of eggs!

Postscript:
Just after writing the above and when I was sweeping the floor, four crows flew up to branches near the nest. One had some food (?) in its beak, flew into the nest, moved around and came out before another crow went in. This crow cawed and fussed around, unsure whether to sit in or leave. While the other three crows left, this crow hopped to an adjacent branch, sharpened its beak, looked around, spied a female koel hiding in the far end of tree and chased it all the way to Lewis Road.

Who are these four crows? Obviously two couples. Is one pair the owners of the nest?

Contributed by Angie Ng, 14th January 2006; image by YC.

January 7th 2006 was 15 days since I first saw the three eggs in the nest. When I went out to buy groceries at around noon, I went up to my usual place to take a look at the crows’ nest. The first chick had hatched! I was excited and was wondering when the next two eggs would hatch.

I returned home at 2 pm. Quickly I took out my camera and went straight to the next block. From afar, I saw the two House Crows (Corvus splendens) hopping among the branches of their nesting tree. This looked strange. As I got closer, I was shocked to see that the whole nest had disappeared. Could it be an attack by the Asian Koels (Eudynamys scolopacea)? From the 4th level of the block, I could not see any traces or remnants of the nest. The pair of crows was calling desperately from the top of a nearby lamp-post. I decided to go down to the ground level to inspect the area beneath the tree. Yes, there was the chick, dead, of course, and a cracked egg. I didn’t see any trace of the third egg.

I started to reason. It couldn’t be the work of the koels. They couldn’t possibly remove the whole nest. It must be people. As I looked up to the nest site, a small girl and her maid were looking out of their window on the second level, talking to each other and pointing to where the nest was. They told me it was two workers and their boss who removed the nest with a long stick with a knife attached at its end. The whole nest fell to the ground and the workers took the nest away. The maid and the small girl were also sad about this.

Well, crows are pests. What can I say?

In 1995 when we were staying in Yishun, the Town Council sent a team of workers to our estate to conduct a massive felling of rows of lovely trees, some reaching 20 m in height. The whole operation lasted one week. The Town Council explained that these trees attracted many birds (Barn Swallows, Hirundo rustica) to perch in. I moved house the next year.

Text and images by Hung Bun Tang

I have given an earlier account of the series of attacks on the House Crows’ nest (Corvus splendens) by Asian Koels (Eudynamys scolopacea). Well, on Wednesday 28th Dec 2005, the tenth day after they began building their nest, the crows were again seen. That morning at 8.20 am two crows stood on the branch beside their nest, cawed several times and flew off. Soon after a koel called and two females hopped cautiously from the lower branches right up to the nest. They took turns to climb in and stayed a few seconds each time before flying off.

One crow returned at 9.30 am, stood at the edge of the nest, made a 3-sec inspection and flew away. Soon after, a single female koel sneaked up to the nest, climbed in and out, and in again.

I saw a crow again at 2.10 pm when it hopped out of its nest, cawed and flew away. As the nest was unattended, two females and a male koel flew from a nearby bauhinia tree (Bauhinia sp.). A female climbed into the nest, came out and the male climbed in as if to inspect the eggs. The other female tried to get into the nest but the male charged at her while making that loud koel call. This loud call brought back a crow that chased them all away. But the crow also stayed away.

At 4.15 pm the male koel was inside the nest again for about 5 seconds before flying off. A while later a female flew up and hopped in and out of the nest several times.

At 6 pm, three koels were seen on the tree. A female’s ‘kuacking’ brought a black bird flying in towards the tree but it was intercepted by another black bird, both flew away from the tree. Meanwhile the female koels took turns to hop in and out of the nest. The first female made one of the loudest ‘kuack-kuack’ sound when she hopped out of the nest (like a hen cackling after it has laid its egg). When the two black birds returned, the females flew off. One of the black birds landed on a branch near the nest, peered in and flew off again into the dark.

At 6.15 pm a broken egg shell, still moist with albumin was on the ground below the angsana tree (Pterocarpus indicus). Shell was blue-greenish with dark speckles.

The next day (eleventh day) saw batches of koels boldly, and taking their own time, hopping in and out of the unattended nest. The male koel made two visits to inspect the nest.

Are there more than a dozen koel eggs in there? If the blue-green eggs were crow eggs, then the crow had laid only 2 eggs!

The crows have since abandoned their nest! After the dramatic night raid of 27th December, no crow was seen incubating.

Everything quiet this morning, with no activities. Is this the end of the koel-crow saga? Are crows smarter than what we think? Will they not play surrogate parents anymore?

Contributed by Angie Ng, 30th December 2005
Image also by Angie.

The three eggs in the crows’ nest as seen in Tang’s earlier image, also shown here, show similarity in colour and pattern. However, one of the eggs is of slightly different shape than the other two and smaller. And according to the literature, the Asian Koel’s (Eudynamys scolopacea) egg is smaller than that of the House Crow’s (Corvus splendens). Can the smaller egg then be that of the koel’s? We need to monitor the situation and wait for the hatching. The nestling of the koel can easily be differentiated from that of the crow once feathers develop (see image of koel nestling, bottomj).

Angie found bluish shells with dark speckles as well as light cream ones at the base of the tree where the crows’ nest was the day after koels attacked the nest (see image on left as well as earlier posting. Is it possible that either the crow or the koel laid eggs of two different colours? After all, as Lin Yang Chen pointed out, there are reports of egg dimorphism among certain species of birds. Unfortunately bird watchers have yet to pay much attention to such details.

Input by Hung Bun Tang, Angie Ng and Lin Yang Chen
Images (top to bottom) by HBT, Angie and YC