a bonobo humanity?

There are few simple pleasures to compare with watching birds of paradise display and perform, even if it’s only on video – and it would be pretty hard to see them otherwise. The forests of Papua are a wonderland for birds, and 39 of the 42 known species of birds of paradise are found only there. My attention was drawn to these very striking birds – in their very various ways – when I read Peter Raby’s biography of Alfred Russel Wallace several years ago, and I’ve associated them with exotic forest regions, miserable weather, malaria and an almost toxic other-worldliness ever since. A sort of anti-paradise doused with bewildering colour and cacophony.

The lineage of these birds has been hard to reconstruct, and apparent similarities to other birds, such as bower birds, have led ornithologists astray in the past. And to be scientific about it all, I’d have to master such concepts as order, family and clade, but I won’t go there in this post, except to say that the whole classification system looks a mess from the outside.. The most recent mitochondrial DNA research has set their ‘moment’ of emergence at about 24 million years ago. They’re quite close, genetically, to corvids, always a plus.

To an amateur, the most striking features of these birds are the plumage and displays of the males. And the females surely agree, even when they try to appear unimpressed. One immediately thinks of sexual selection – and Darwin. Here’s what Darwin had to say about the process, in The Origin of Species:

Sexual selection… depends, not on a struggle for existence, but on a struggle between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring.

…when the males and females of any animal have the same general habits… but differ in structure, colour or ornament, such differences have been mainly caused by sexual selection

On the origin of species, 1st edition, pp88,89

One has to wonder why it’s the males who grow their weird and wonderful plumage and create their elaborate dances to attract the females, and not the other way around. Generally the female coloration – and that of both sexes when young – has evolved so that they match and blend in with their surroundings. The males are taking serious risks in drawing attention to themselves in this way, which is why the differences appear late – as secondary sexual characteristics. In fact, males generally mature later than females, by quite a wide margin. But since they don’t bear the offspring the males are more dispensable. It’s interesting to note, in this light, that in polygamous species, birds are sexually dimorphic both in appearance and lifespan. That’s to say, monogamous birds tend to look alike and to have the same lifespans, whereas in polygamous species, the females live longer. In fact this is the case in all species, not just birds. The San Diego zoo, which specialises in this family, tells us that birds of paradise can live for some 30 years in captivity – but surely it would be tougher in the wild, especially for males.

Not all birds of paradise are polygamous though – they have a range of breeding systems, of which the most interesting is ‘lek-type polygamy’. Lek is a Swedish term which refers to fun activity bound by the loosest of rules. It was first used in a book about the avian life of that region back in the 1860s, and is now adopted worldwide, and applies to a bewildering variety of species, including birds, bees, butterflies and bats (and various species of reptiles, amphibians and fish). And not just because they all like to have fun; the term has been refined to refer to specific behaviours. Two general types of lekking are identified – classic and exploded. They refer essentially to the physical space occupied – the lek. In a classic lek (a more or less circular region), each of the males is within sight of at least some of the others, whereas in an exploded lek, this isn’t ‘necessary’, as long as they’re in earshot. In fact, with some booming birds, like the New Zealand kakapo, they can be kilometres apart. In these exploded leks, the variety of behaviours is greater, as if the woo-ers are less inhibited by their neighbours.

Of course the leks in thickly forested Papua would be very different from Sweden. Sometimes the males share and compete in a common ground such as a forest clearing, while in other species they display and dance in the trees, controlling their territory vocally. Displays involve spinning, charging, freezing, hopping and skipping, hanging upside down, making show of their most irridescent plumes, all the kind of stuff imitated by the Folies Bergère, but with males rather than females as the beauties.

Breeding behaviour, though, is very varied. Not all male species are brightly festooned, and male-female relations run from bim-bam-thanks-mam polygamy to the sharing of nest-building and child-rearing among monogamous species such as the manucodes (they don’t all bear the bird-of paradise name – apart from manucodes there are sicklebills, riflebirds, parodias, astrapias and others).

These birds are, unsurprisingly, and more than other types, very much tree-dwellers, preferring the high canopies and living largely off their fruits, so they need to have their forests protected. They’ve been hunted for centuries, and Wallace had no hesitation in killing as many as he could himself in the 1850s. Of course, being in straitened circs in those years, his income was largely dependent on producing exotic specimens for the home trade, and birds of paradise were like gold. But local tribesmen also valued the bright plumage as a status symbol. In recent times the popularity of the birds for twitchers has helped in their protection.

They’re a fairly raucous lot, and the striking, machine-like notes of riflebirds and sicklebills are very much worth listening to online. One might assume that in dense forest, loud calls to indicate location are a must.

In conclusion, I began writing this to find out more about a particular family of birds, but got sidetracked by a lot of fascinating stuff I’ve only touched upon here, such as sexual selection, sexual dimorphism and anisogamy. More about all that in later posts, I hope.