Biology Reference
In-Depth Information
south that runs the length of New Guinea were able to colonize the newly rising Foja Moun-
tains and other isolated ranges. Once settled on this recently uplifted chain, these populations
of plants and animals were slowly carried upward into the mists as the mountains inched
higher year by year. In isolation from others of their species and through the process of evol-
ution by natural selection, these populations evolved unique traits.
This uplift created the series of mountain islands where species evolved, resulting in
changes in some aspect of their appearance from the first arrivals. The geologic account rein-
forces a near-immutable law of rarity: the isolation of tropical mountain ranges leads eventu-
ally to the creation of new species and, in turn, drives patterns of rarity. This is because—by
definition—when one species diverges from another in an isolated habitat, it often starts out
as rare in terms of its narrow range. In some cases, a collision of continental plates may cause
uplift that separates one widespread, abundant species into two populations, which may di-
verge. In general, however, many species on tropical mountains lack the dispersal capability
to rejoin their former populations. Even tropical birds that could fly over the mountains tend
to avoid such flights if it means leaving the altitudinal belt in which they are most accustomed
to live.
Bruce's field journal included a most-wanted list. Truth be told, the expedition was for him
an intensely personal pursuit of a quest species, the golden-fronted bowerbird, endemic to the
Fojas. It was a dream shared by many. This species had not even been described until 1895,
when Lord Walter Rothschild identified it from trade skins collected by locals from some-
where in western New Guinea. The discovery inspired many naturalists to search for the bird,
but over the following eighty-two years all returned from their expeditions without success.
Consider this entry by Michael Everett in his topic
The Birds of Paradise and Bowerbirds
,
published more than three decades ago: “Nothing is known of the Golden-fronted Bowerbird,
except for what can be learned from only four known museum skins, all males . . . it has nev-
er been found in the wild . . . and among bowerbirds or birds of paradise is unique in this
respect. It may be either a very rare bird or one which is virtually extinct—but it is certainly
one which has a very restricted range.”
The bowerbirds must have been eavesdropping. The next day, the team found several dis-
play bowers of this elusive species close to camp. According to the
OxfordEnglishDiction-
ary
, a bower is “a pleasant shady place under trees or climbing plants in a garden or wood.”
The bowers these birds construct are remarkable, fashioned from moss and sticks and decor-
ated with blue and yellow fruit. The males spend hours each day vocalizing from perches in
the saplings beside their bowers, often imitating the songs of other birds as well as other nat-
ural sounds. At the sight of the bowers, Bruce felt elated at the prospect that his quest might
soon be realized. Now if they could just see the bird!
The next day, while marking survey trail routes through the forest with colored flagging
tape, Bruce stumbled upon a male in attendance at a bower. The first encounter took his
