Asian Koel

Some time back, a pair of Asian Koel was sighted on the tree outside my office. Big and long-tailed, the male is glossy black all over with red eye and pale heavy bill. Female similar in shape but dark brown with bold spots and bars all over.  Calls unmistakable, often starting before dawn: ten or more increasingly loud glissading notes, koel!

A remarkable case of rapid spread: in ten years koels have colonised the whole peninsula of Malaysia, as nest parasites of crows and mynas. Like many species of cuckoos, Asian Koel practices brood paratism, which is defined as a bird laying its eggs in the nest of another bird (either another species or another individual of the same species) so that the young will be raised by the host parents.

NUS Kent Ridge

My search on the internet reveals that cuckoos have evolved various strategies for getting their egg into a host nest, depending on the host defensive strategies.

Egg-laying strategy: Female cuckoos have evolved secretive and fast laying behaviors, and in some cases, males have been seenn to lure host adults away from their nests so that the female can lay her eggs in their nest in the first place. It is also noted that the shells of the eggs of brood-parasites is usually thick - they have two distinct layers with an outer chalky layer that is believed to provide resistance to cracking when the eggs are dropped in the host nest. 

Egg-mimicry strategy: Some host birds are able to distinguish cuckoo eggs from their own, leading to those eggs least like the host's being thrown out of the nest. In such setting, female parasitic cuckoos lay eggs that closely resemble the eggs of their chosen host. Parasitic cuckoos that show the highest levels of egg mimicry are those who hosts exhibit high levels of egg rejection behaviour. Some hosts do not exhibit egg rejection behavior and in these cases, the cuckoo eggs look very dissimilar from the host eggs.  

Egg-camouflage strategy: Other species of cuckoo lay "cryptic" eggs, which are dark in color when their hosts' eggs are light in color. This is a trick to hide the egg from the host, and has evolved in cuckoos that parasitize hosts with dark, domed nests.

Big-bully strategy: Some parasitic cuckoos have also exhibit "mafia-like" enforcement, in which adult cuckoos will completely destry the host's clutch if they reject the cuckoo egg. In this case, raising the cuckoos chick is less of a cost than the alternative - total clutch destruction!

It's in the genes: The cuckoo egg hatches earlier thatn the host's, and the cuckoo chick grows faster; in most cases the chick evicts the eggs or young of the host species. Since the chick has no time to learn this behavior, it must be an instinct passed on genetically.

  

source: Davidson & Chew (2008); wikipedia.