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Wednesday, April 19, 2006
BILLS AND BEAKS
Birds' amazing 'tweezers'
By MARK BRAZIL
The chances are that you are reading this while holding The Japan Times in one or both hands. Alternatively you may be reading online after having tapped on various keys with your fingers to make images appear before your eyes. Either way, manual dexterity will have enabled you to access your daily read, while perhaps also holding a cup of tea or a slice of morning toast.
From washing to eating, grooming to studying and working, the odds are that you use your hands to effect most of those tasks. Imagine then, if you can, belonging to a species that also needs to do those things, but which has had to "hand over" (pun intended) those abilities because of a prior call on its forelimbs.
Birds are in exactly that position; a high price for flight comes at the expense of forelimbs totally committed to aerial locomotion. As a consequence, it falls to their beaks, or bills, to assume the roles that our forelimbs fulfill -- holding, carrying, probing, picking, scratching and fighting. For birds, it's rather like us attempting to do everything while wearing a two-fingered glove ending in a pair of tweezers.
Armed only with that metaphorical pair of tweezers, birds somehow manage it all. So closely adapted are their bills to the food they eat, and to their foraging tactics, that we birdwatchers can tell a great deal about a bird's habitat, habits and food merely by glancing at the bill.
There are birds, such as the hawfinch, with short, massive, conical bills like stub-nosed pliers capable of cracking or crushing seeds. Other species, including warblers and flycatchers, have short delicate beaks that are all the better for snapping at passing insects. There are long, broad-beaked birds such as spoonbills that use their specialized feature for filtering water; the oddly beaked flamingos do much the same, but from a very different angle.
A sharp, hooked tip is a typical indicator of something predatory, whether of fish, fowl or game, and these range in size from tiny hooks to massive cleavers. Then there are the consummate chiselers and hackers -- woodpeckers with their blunt chisel-like beaks, and fine-beaked probers, such as treecreepers, able to search tiny crevices in tree bark for insect prey.
A whole group of birds, shorebirds -- or waders -- has specialized in feeding on the ground, particularly from wet or mud surfaces, although some find food in more arid settings.
This group is especially fascinating because many of them are long-distance migrants, their annual journeys taking them not merely from country to country, but on continent-spanning odysseys during which they traverse both the northern and the southern hemispheres.
Specialization among this group of enthralling, intrepid travelers is more than enough for a lifetime's study.
There are plovers, which, with their short, blunt-tipped bills, run and pause, stare with a large beady eye, then lean and pick from dry surfaces. There are sandpipers, stints, peeps, shanks, snipe, dowitchers, godwits, stilts and curlews, all of which may leave you wondering (among other things) why so many bird groups' names start with "s."
Some names, though, give hints about those bearing them, such as oystercatcher and turnstone. The latter is a brightly patterned bird of rocky or shingly shores that probes between stones and flips them over in search of invertebrate prey. The oystercatcher -- though it goes by a slight misnomer, it does eat shellfish -- commonly hammers away at mussels with its long bright-orange chisel of a beak, or probes into somewhat sandy substrates for cockles or mud-worms. Some oystercatchers actually specialize, typically eating mostly either shellfish or mud-worms; as a result, their bill shapes actually differ subtly.
Those other groups mentioned are all adapted to a remarkable suite of habitats -- the rich margins of wetlands.
Plovers typically pick food from rather dry surfaces, while sandpipers, peeps and stints have finer, short bills, with which they pick minute invertebrates from the wet surface along the tide line or water's edge. Shanks (redshanks, greenshanks, yellowlegs and so on) wade into deeper water, picking delicately, and though the snipe and dowitchers sometimes also wade, they are probers, not pickers -- pushing their long, slightly bulbous-tipped beaks deep into soft mud to extract their food. Godwits and curlews have the longest beaks of all, some straight, some slightly upturned, others deeply down-curved, but each serving a slightly different though related purpose, reaching deeper than the next species.
To see a mixed flock of shorebirds foraging across an open wetland is to witness one of nature's miracles of adaptation, specialization and co-existence. If they all had similar bills, their numbers would quickly exhaust the reachable food supply, while leaving other prey species untouched. As it is, the various bill lengths of the different species enable them to co-exist in the same habitat by targeting a slightly different foraging niche in search of different prey.
Some of these wading bird species favor inland wetlands, marshes, bogs and swamps, others prefer coastal tidal estuaries, mudflats, sandy beaches or rocky flats and shallow lagoons -- so you can tell already that they are at home in both salt and freshwater.
Many species inhabit the vast northern tundra during the brief Arctic summer, dividing it up territorially based on various microhabitats, and take advantage of the plethora of insect larvae during that brief season. When those latitudes turn frigid, they head for warmer climes for the winter to find food -- and it is during these immense, long-distance migrations that they typically turn to very different wetlands, biologically highly productive coastal wetlands , which they use as stopover sites to rest and restock on calories -- in our terms, highway service areas. Thereby hangs a tale, but more of that in my next column.
I have been fortunate enough to watch a tremendous diversity of shorebirds at innumerable sites around the world, yet my most recent encounter was certainly one of the most impressive.
While sitting peacefully by a shallow coastal lagoon beside the Firth of Thames at Miranda in North Island, New Zealand, just a few weeks ago, a great flurry of wings engulfed me. I felt like I was sitting beneath a living umbrella of feathered creatures, as they wheeled in a dome above my head: red knots, godwits and wrybills were making a deep noise like the rushing of wind through an immense feathered fan. They swept back and forth above me, then -- as if on cue -- settled down, like a huge feather blanket wafting down over the ponds right in front of me, offering me close-up views in the near silence that followed.
What a marvelous, moving experience! Here they were, hundreds of them, whichever way I looked. And all were dependent on wetlands and the freedom to forage from them.
Mark Brazil is professor of biodiversity and conservation at Rakuno Gakuen University in Hokkaido. He welcomes readers' contact by e-mail at firstname.lastname@example.org
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