Monday, January 21, 2013

Bowerbirds: Nature’s Artists?

 
Animal Architects, Building and the Evolution of Intelligence, 2007, published by Basic Books, is a book by James R. Gould and Carol Grant Gould (they are married), which explores the building methods of insects, spiders, and birds.  It is a fascinating read albeit a bit clipped in its writing style in order to make is accessible to scientific layman.  Getting past the classroom presentation, there are many insights into the way that such small creatures can produce such profound structures and how this reveals tiers of interaction and cognizance of the world around them and also the purposes in which they construct and build.  The methods in which the creatures discussed procure and produce is impressive to understand and daunting in its scale and intricacy.  There is one particular animal of focus in this book that is thought shifting though and that is the Bowerbird whose constructions possibly thwart the idea that we humans are the only species with a knack and an impulse to make ‘art’ or have aesthetic impulse.

Many animals have various ways to show off their genetic dominance and this is used to seduce a mate and hence continue their genetic linage and ensure the species best overall survival.  This can be done with displays of strength, plumage, song, and various other feats. Almost always this is the task of the males as females have the biologically arduous and energy-depleting task of birthing and also many times rearing offspring on ones own.  This of course has variances.  In the case of the bowerbird, the male is also the displayer but the operations and processes are different then anything else seen in the animal kingdom, excluding our own.

Bowerbirds are found in Australia and in isolated New Guinea.  There are varieties of sub-species within this group whose habitats range from dry open bush to dense forests.  Their topographic location as well as their degree of evolution determines the complexity of their building structure.  The structures they create is called a bower or a maypole.  These structures are unique in that it has no other function other then to be a display as the female bowerbird makes their own nest for egg laying elsewhere and will rear the offspring alone.  The fact that the bowerbird’s habitats allow them to have long mating periods, little competition for food and not many predators are reasons why these birds can make these elaborate displays. 

The most simple bower structure is a platform at the base which is sometimes raised slightly off the ground.  The male bird constructs what is called an alleyway with sticks intricately positioned to make an open doorframe.  They will also clear out a circular area at the base of this, removing all debris and many times meticulously lining it with leaves or moss.  The Satin Bower makes this sort of structure in its simplest form.  What is interesting is that once the main construction of the bower is built the bird will then decorate.  They will ‘paint’ it with the juices of crushed berries with its beak and will ornament it with very particular selections of shells, flowers, and other pleasing elements, many times shiny.  What is interesting is that the Satin Bower seems to have a bias towards dark blue and purple flowers, which are the rarest colors in nature.  This may reflect some sort of selective process but what is fascinating is that they will also very rarely include red, pink or orange blossoms, which are very hard to find in this area as well.  In contradiction, they will insert the occasional yellow or white blossom which are much more common.  Why they are hyper selective on some counts but not on others is interesting and will be further investigated into thinking about motives of this decorative display. 

During the building process some bowers are so entranced and focused on their construction that if a female happens to be in the area to check out what is going on they will actually chase it away!  Another revealing aspect is that in some bower species rampant theft and vandalism will occur between males and the ability to maintain the structure and ornamentation is rigorously upkept. 

With all this effort one would think that the male bower with the most impressive structure would be victor to the most mates.  This does happen, to a degree, but the dominance of a male plays no direct role in the selection process of the female.  The females survey each structure and tend to select those with the most impressive and fortified structures but it’s a process that is not one to one and in the end it is the female’s choice that has final say. 

There are other species of bowers and their levels of construction and decoration vary in great degrees.  The Spotted Bowerbird makes their avenue structure out of pebbles and snail shells along with twigs and also up to thousands of sun-bleached rabbit bones as they live in the bush.   The Great-Grey Bower also uses bone but in its case sun-bleached kangaroo bones and white and green ornaments and berries and flowers.  What is interesting with them, and some other species, is that their collections are “zoned” meaning that they will pile and display objects in like groupings of color.  One of the most impressive bowers, the Lauterbach, makes two avenues, one smaller inside a larger one that is constructed of stones and sticks and can weigh up to 16 pounds, an immense feat for a 6 ounce bird. 

The maypole is another structure made by some bowers that has the bird creating a platform surrounding a vertical bower, whence he will clear out, decorate and assemble a vertical structure with twigs and sticks and a variety of other decorative elements. Some will have walls reaching 18 inches high with vines and courtyard like the Archibold bower while others will be hyper selective in the moss they use for the platform like the MacGregor, who will only use moss from upper parts of trees versus the more plentiful and easily accessible floor moss.

One of the most impressive structures is by the Vogelkop Bower who inhabits New Guinea and they create a thatched arena with two internal bower supports and then plinthed bowers on top that create a hatch.  These can measure to 16 feet in diameter and 18 to 30 inches tall.  Unlike some bowers, its collection of decorations is not at the base of the structure but in discreet piles outside of the doorway. 

Now up to this point, this seems like just another exercise in male display to lure as many females as possible right?  Well yes, to a degree, but what thwarts this is all is of the variances.  The male bowers, within each sub-specie, do have programmed construction methods and preference but within each there is such a variety that it is not consistent with what is generally practiced by animals, which usually is: the best = the best.  In the case of each, it is the discretion, nay preference, of the males to select which type of flower, berry, beetle wing, etcetera, or not.  Some Vogelkop’s will have a pile of one thing while its neighbor will not.  Some will select rare things like shimmery snail shells while also just as heartily selecting very plentiful things like acorns.  This degree of arbitrariness is not normal to the formula of display shown by other animals. 

Another fascinating thing is that there seems to be fads within the male bowers selection of ornamentation.  Some years they will have a preference for only things white, another they will have no white things and gather say only blue and black things and when something white is presented close at hand or placed near their structure they will immediately discard it.  Their seems to be an impulse for novelty, to find something new, even if it is not scarce, to one-up or to match the competition.  Bowers are also fastidious in upkeep, they will replace and rearrange their displays with fresh flowers, berries, leaves, etcetera and perfectly rearrange piles if disturbed.  And although this impulse is the same in all bowers, what is selected for display and how it is arranged varies with each showing and even with the same bird through the years. 

A most compelling idea is that the bower, in that all its fussing, may reflect the bird’s advanced social intelligence.  This is ranged in science in tiers, 0 being, “Social Isolation: conspecifics are either ignored or attacked” to tier 3 which is, “Attribution and intention: animal has an ability to understand the cognitive processing in the brain of a conspecific, and can alter its behavior to exploit that knowledge.”  Bowers may be considered to be acting in a tier 3 mode of social intelligence.  In this case the knowledge it wants to exploit is that of the female bower whose pickiness and non-formulaic decision process results in the male bower to use such a degree of variety in its construction and decoration process.  This may be a leap, but it is an interesting thing to think over.  Moreover, this behavior produces a positive-feedback loop which is unique to the bowerbird in that: greater cognitive potential allows for more elaborate bowers which makes possible to greater reproduction success and selects for greater cognitive potential, and lopping back again through the generations. 

The male bowers on creating their displays seem to have an affixed ‘vision’ on how it will be constructed and the elements that will be selected.  They will go to Herculean efforts to carry this out and to maintain it.  The isolation and the variances produced by this isolation is also an interested thing to think about in relation to human forms of expression and variety.  In the end the bowerbird is creating something with the end goal of securing mates and of ensuring its genetic line but in this process it shows a complexity of thought, selection and possibly even specific aesthetic choice that is impressive at any degree or in any species.