Changing Colours
After the instinct for survival, the most powerful force in nature is propagation of the species. Living beings are, by and large, programmed to breed and create offspring. They expend considerable energy and ingenuity on this task. Birds are no exception to this rule.
The feathers of many bird species change when they are ready to mate. Usually the colours become brighter and change hue. Sometimes additional luxuriant feathers grow. For some species this change happens in males and females, but in many species only the male changes. This new appearance of feathers is called breeding plumage.
A simple yet striking example I have seen is the babui (baya weaver.) Normally males and females look nearly identical – an unremarkable tan colour. But at breeding time, the male grows a bright yellow crown over its head. It is unmistakable and can be seen from far away. That crown clearly sends a message.
Another commonly seen bird with breeding plumage is the kani boga (Indian pond heron.) Its normal dark-brown head changes to a yellowish-buff colour and its light-brown back takes on a maroon hue. It grows white neck plumes, looking very graceful. This happens to males and females.
The bok (egret) also changes plumage during breeding season. Long graceful feathers appear in its breast, base of upper neck and back. The head of the go-bok (cattle egret) turns orange during breeding.
What really happens? Birds displaying breeding plumage actually shed their feathers before the breeding season starts and grow a new set of feathers of breeding colours. Then the breeding and mating takes place. After breeding, some species – including the male bon morog (red jungle fowl) and several types of ducks - shed the breeding plumage and grow unusually drab looking feathers. This is called eclipse plumage.
There are so many ways that feather colours change that it can be confusing. The notion of changing plumage is generalised in a method called the Humphrey-Parkes system. According to this nomenclature, the plumage covering the bird most of the year is called the basic plumage. When the feathers change, they are called the alternate plumage.
For the birder, breeding plumage can often create confusion. Fortunately most of our common birds such as fingey (drongo), doel (oriental magpie robin), machranga (kingfishers), bulbuls, choroi (sparrow) and myna (common myna) do not change plumage during breeding season. However, most ducks and waterbirds exhibit breeding plumage.
Of course breeding plumage is only one of the methods that birds employ to find mates. Some birds such as the red-crowned cranes of Hokkaido, Japan, perform an elaborate mating dance. Others such as ospreys “show off” by hovering in the air with food or nesting material. The Bengal bushlark shoots straight up into the air, singing a loud song, and then drops to the ground like a stone. The harrier throws food to the female. The babui, as we saw last week, builds a strong home.
It is all for one overarching purpose: so the parent can find the best possible partner for creating offspring and propagating the species.
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