A Commemorative Issue All About Birds $2.50

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A Commemorative Issue All About Birds $2.50

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NATURAL HISTORY

American Museum oj Natural History Robert G. Coelet, President

Thomas D. Nicholson, Director

Vol. 92, No. 9. September 1983

Alan Ternei. Editor

Managing Editor: Erik Eckholm

¡Judith Friedman, on k'avfj Thomas Page, Deaigner Board of Editors: Carol Brestin, Sally Undsay. Viltorio Mae.<itro, Rebecca U. Finnell, Daxid Weinberg Florence C Edelstein, Copy Chief Rita Canipon, Copy Editor E. Kay Danzig. Art Asst.

Kay Zakaria.sen, Picture Editor Kelly L Matthews, Editorial Asst.

Lillian Berger

L Thomas Kelly. Publisher

Ruth D. McCrea, Jr, Bu.iiness Manager Ernestine Weindorf, .4í,t(. to the Publisher Cary Castle, Circulation Manager Jeff Pieper. A.isoc. Circulation Mgr Ramon E. Alvarez. As.it. Circulation Mgr.

Frank Slevera, As.U. Fulfillment Mgr Frederick F. Grossman. Production Manager Sherry Krukwer Sundel, Production Asst.

Elaine M. Caltender. Advtg. Production Mgr, Douglas J. Preston, FublicatioiLi Manager Carol A. Midkiff

NuTiiRAi HiiioKV {ISSN I)<}2H-07I2) is puhli.<ihed monthly fiy ¡he American Museum iif Natural History, Central Park West at JVth Street, New York. i\.Y. 10024.

Subscripliom: SIS.OO a year In Canada and alt other countries: S2J.0O a war. Seionä-class postage paid at Nev York, N. Y. and at ' additional offu-es. Copyright © I9S3 by

/American Museum of Natural History. All rights reserved. No part of this pt'riodtcat may frf reproduced without wrimii toiLtenI o/N;itural Hislor>'. The opinions e.\pre.ised by authors do not netrssarily reflect the policy of the American Museum. Naturjl History Is inde.\ed in Reader's Guide lu í^:rjüdica] \.\\CTí\\Ií\C

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The Joy of Birds

From Ernst Muyr's introduction on the inside cover to Ray Sokotov's scrambled eggs on the last page, this entire issue is dedicated to the science, the art, and the pleasure of birds.

It commemorates the centennial meetlngofthe American Orniihologist.i' Union this month at the American Museum of Natural History, where the AOÜ held its founding meeting. The articles that follow show that ornithology•one of the oldest sciences and one particularly open to amateurs as well as professionals•is as vital and fascinating as ever. This special issue was edited by senior editor Rebecca B. Finnell.

4 Authors

10 At the American Museum The AOU's Fledgling Years

14 This View of Dfe Stephen Jay Gould Darwin at Sea

22 A Migratory Bird's Baedeker Kenneth R Able 30 Fligiitless Birds Helen F, James and Starrs L. Olson 42 Marsh Wrenditions Donald E. Kroodsma

48 The Bowerbird's LalMir of Loie Melinda Pruett-Jones and Stephen Pruett-Jones 56 Night Owls Are Good Listeners Masakazu Konlshi

60 Remembrance of Seeds Stashed Stephen Vander Wall and Russell P. Balda 66 Bird Art Roger Tory Peterson

76 The Origin of a Species Peter R. Grant and Nicola Grant 82 Gone with the Trees David S. Wllcove and Robert F. Whitcomb 94 Boolis in Review Michael Harwood

A Birder's Library

9$ Additional Reading

102 A Matter of Taste Aajti/Moni/5o/co/ov About Eggs

Cover: Armed with asymmetrical ears, a face that functions as a sound collector, and a mental map, the nocturnal barn owl uses .wund to lixate Its prey. Photograph by Rick Mclntyre: Tom Stack. Story on page 56.

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Authors

A bird watcher since childhood, Ken- neth P. Abie was impressed early on by the dramatic migration of birds in north- ern latitudes every spring and fall. As his studies of birds became more formul, he learned that just how birds lind their way during these migrations is far from completely understood. Since that rev- elation, his research has centered on ori- entation and navigation mechanisms in animals, especially those of migratory birds. Able is associate professor of biology at the Albany campus of îhe Slate University of New York.

Convinced that much remains to be learned about bird song by looking at species with complex song systems, Don- ald E. Kroodsma examined different populations of one of North America's most voluble songsters•the mar.sh wren. Associate professor of zoology at the University of Massachusetts in Am- herst, Kroodsma is currently focusing on species of warblers that use different songs in different contexts. He hopes to determine to what extent the birds learn, rather than know innately, which .songs are appropriate for which situations.

clearly demonstrated thai bird fossils, often thought to be too scarce or frag- mentary to be of much scientific use, can contribute significantly to our understanding of avian evolution. In addition to her work on Hawaiian fossils, James plans to study 5-mi I lion-year-old bones of cormorants and parrots from South Africa. Olson's projects include bird fossils from Bermuda, the North Atlantic, and North America.

Both Helen F. James and Storrs L. Ol- son work in the Division of Birds of the Smithsonian Institution's National Mu- seum of Natural History, James as a research assistant and Olson as curator.

An interest in paleontology and the evolution of birds has taken them several times to the Hawaiian Islands, where a number of exciting bird fossil finds have been made in the last decade. Their research in the Pacific and elsewhere has

When Melinda Pruett-Jones arrived in Papua New Guinea in 1980 with her husband and coauthor, Stephen, she found Macgregor's bowerbirds in the forest near the Wau Ecology Institute where they planned to work. "There was no doubt in my mind what I was going to study," she says. Ever since she was an undergraduate at the University of Washington, she has been aware of the unique behavior of bowerbirds, which build and decorate terrestrial display sites for courtship, Melinda had come to New Guinea to conduct research for her M.S. degree at Brigham Young Univer-

sity; Stephen to initiate his Ph.D. research in association with the University of California at Berkeley. His disserta- tion will focus on the evolution of social behavior in Lawes's six-wired bird of paradise. The couple work on indepen- dent projects, but the underlying questions in their studies are the same and they collaborate in much of their work.

Their scholarly interests are evolutionary biology and promiscuous mating patterns in birds. When not in the field, they enjoy sailing, the ballet, good Italian res- taurants, and gourmet ice cream•none of which can be found in Wau.

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Flightiess Birds

Recení fossil finds in Hawaii suggest that in prehistoric times, islands in the Pacific supported a rich assortment of flightless birds

by Helen F. James and Storrs L. Olson

Hundreds of years ago, a group of hard- pressed, sun-baked navigators sailed a double canoe through unfamiliar waters for day after weary day, until the sudden appearance of a string of majestic moun- tains, rising out of the middle of the Pa- cific Ocean, revived their withered spirits.

With fearful anticipation, they paddled ashore and became the first human beings ever privileged to walk on a Hawaiian beach. This is a scene that we have played over and over again in our minds with un- suppressed envy in recent years. Our research on fossil bird bones of the Hawai- ian Islands has given us a special insight into what these Polynesian discoverers must have found, and we now know that it was very different from what anyone had previously imagined.

We had long known that the islands were once clothed in virgin forests com- posed mostly of plants found nowhere else in the world, but only in the last twelve years have we begun to realiz.c the extent to which the forests were home to a remarkable variety of endemic species of birds, most of them doomed to rapid extinction at the hands of humans. More than half of Hawaii's endemic species of land birds would never be seen by western- ers. Forty-five or more species•including ibises, geese, rails, owls, a hawk, an eagle, ravens, and a plethora of songbirds•^vanished in the prehistoric Polynesian period.

Curiously, a large number of these birds, no fewer than seventeen, were incapable of flight. The existence of these unusual birds was Hawaii's best kept secret up to the last decade.

Partly because of two unsubstantiated bi!t prevalent bits of wisdom- -that volca- nic islands are unlikely spots for fossil col- lecting and that fossils of birds are rare in any case•no paleontologist or biologist seriously considered looking for fos.sil birds in the Hawaiian Islands until 1971.

in that year, Joan Aidem, an ardent natu-

ralist from Molokai Island, managed to ig- nite some interest with her discovery of the complete skeleton of an extraordinary flightless goose weathering out of a wind- blown sand dune on Molokai. Since then, fossil sites have been discovered on five of Hawaii's eight main islands, in settings as diverse as limestone sinkholes, a sea clifl", collapsed lava tubes (tunnellike caves formed after rivers of molten lava drain away), and a flooded cavern where skeletons were found under fifteen feet of fresh water.

Archeological sites containing the remains of prehistoric meals have proved to be another good source of bones of extinct birds. These are doubly interesting because, in combination with stratigraphie and radiometric dating studies, they con- firm that many extinct species siill survived when the Polynesians first arrived, about 1,500 years ago.

The fossils from all these sources, now gathered at the Smith.sonian's National Museum of Natural History, number in the tens of thousands. The tasks of identi- fying and cataloging the bones, isolating new species, writing scientific descriptions of ihem, and tracing the evolutionary rela- tionships among them arc complex and time con-suming. The work is sometimes tedious, bul it is amply rewarded by occa- sional breakthroughs, each augmenting our knowledge of evolution on islands.

The flightless species of the Hawaiian Islands were not representatives of some obscure, long-extinct lineage but were descendants of such familiar kinds of birds as ducks, geese, rails, and ibises. Their ancestors had to have been excellent fliers;

otherwise they never could have crossed the more than two thousand miles of ocean between the Hawaiian Islands and the nearest significant land mass. Once arrived in the Islands, many species of birds responded to the changed conditions of life by losing the ability to fly. Evolution- 30 NATURAL HISTORY 9/83

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ariiy speaking, the process may have hap- pened fairly rapidly: the oldest of the main islands, Kauai, is a mere six million years old, and the youngest, the island of Ha- waii, may be less than a million years old.

Less time than this was available for the evolution of flight lessness because the ancestors of the flightless birds could not colonize a particular island until after enough soil had formed and plants arrived to cre- ate an environment suitable for terrestrial birds.

The genetic mechanism for the evolution of a flightlcs,s bird from a llying one is actually quite simple. All birds are flightless when they are small chicks, and the young of flying birds have the same features that characterize the adults of flightless birds•proportionately large legs, reduced wings, and a small or no keel on the sternum, or breastbone, (¡n flying birds, the bony keel is where ihe large flight muscles are attached.) Merely by retaining the skeletomuscular structure of in- fancy into adulthood•probably by the alteration of a few regulatory genes•almost any bird species could become flightless. This process of retention of juvenile characters, known as neotcny, is a fairly common evolutionary phenomenon.

But why become flightless? To must people, birds symbolize flight, and most of the evolutionarj- history of the class Aves has indeed revolved around the opportuni- ties created by flight, on the one hand, and the physical constraints of flight, on the other. Yet the Hawaiian Islands are not unique; flightless birds occur on islands throughout the world's oceans. What great selective pressure spurs the develop- ment of flightlessness on islands?

Beginning with Darwin, some scientists suggested that flying organisms on islands might be blown away by winds and perish, thus leading to the evolution of flightlessness. Many flightless birds, however, are found on New Zealand and other large is-

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Flyingbirds. like this modern goose, have well-developed scapulae and coracoids, which mee! at a fairly sharp angle and help to brace the wing bones. They also have a sizable keel, for the attachment of flight muscles.

Douglas Cranner

Flying Goose

Coracoid

lands, where there is ample protection from winds. Moreover, tiny islands•Lay- san and Nihoa in Hawaii, for example•

are home lo small birds that retain the ability to fly. The wind theory therefore is not a satisfactory one.

The real evolutionary advantage of flightlessness on islands may revolve around more ellicient use of energy.

Mainly because of the difficulty terrestrial mammais have crossing large bodies of water, predators•other than birds of prey•are relatively scarce on oceanic islands. When neither escape from predators nor seasonal migration is necessary, individual birds with a reduced ability to fly could have an important advantage.

With no large wings or massive flight muscles to support, they would need less food to survive and reproduce. Loss of the ability to fly would not be an advantage for all types of birds, however. Species that must

fly lo obtain food, such as birds of prey and small arboreal species that forage in treetops, do not become flightless, while those that feed on or near the ground fre- quently do.

Among the most con.spicuous species that must have greeted the first Hawai- ians were large, ungainly gooselike crea- tures. Flightlessness in these birds had proceeded to the extreme stage in which the sternum no longer bore any îrace of a keel. The rest of the skeleton had taken on a somewhat comical aspect, with tiny, dis- torted, and useless wings contrasting with a massive pelvic girdle and large, stout leg bones. These were not fieet-footed birds.

The early Hawaüans doubtless had little trouble catching them for dinner.

The evolutionary process had so pro- foundly altered the skeleton of these Ha- waiian geese that for years we despaired of ever being able to pinpoint their closest 32 NATURAL HISTORY 9/83

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relatives. Then in 1982, an ¡mportanl cäue turned up in the form of a fossil trachea!

bulla ttiat we received in a collection of goose bones found by naturalist Michael Severns in a lava tube on Maui. The tra- chéal bulla is a hollow, bony expansion of the windpipe thaï occurs in males of most groupsofducksbut not in true geese (gen- era Anser and Brama) or swans, which can therefore be eliminated as possible ancestors of the odd Hawaiian birds. Further osteological comparisons have narrowed the field to sheldrakes and the typical ducks, such as mallards.

Many different species of these geese have been found in fossil deposits on various Hawaiian islands. They probably evolved in response to the absence of na- tive herbivorous mammals in the islands.

Several species belong in the peculiar genus Thambetochen, meaning "astonishing goose," and arc characterized by bony, toothlike projections on the jaws. These birds may have fed by browsing or grazing on coarse vegetation. Another genus had a very broad, flat lower jaw, almost like that of a turtle, and an extremely heavy upper jaw higher than it was long, giving it a most unusual appearance. This bill form may also have been an adaptation for browsing or grazing.

Intriguing as these goosclikc birds are, they had diverged so much from the an- cestral species that they are of little use in our efforts to track down the very t>egin- nings of flightlessness. Hawaii does boast one true goose, however, which may prove helpful in this respect. The living nene, or Hawaiian goose {Bratita sandvicensis), is the only endemic Hawaiian goose to survive into historical times, probably because it is perfectly able to fly. whereas the other species of geese were not.

Threatened with extinction during this century, the species was rescued by a captive breeding program and survives in the upland regions of Hawaii and Maui.

Unlike the big, flightless forms of Thambetochen, the nene still closely re- sembles its nearest continental relative, the Canada goose (B. canadensis). In addition, fossil finds have turned up some interesting relatives of the nene. Remains have been found on many Hawaiian is-

34 NATURAL HISTORY 9/83

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lands, including ones where no nene has ever been recorded alive. Some of the fossil skeletons resemble those of typical modern nenes; others belonged to bigger- bodied birds with shorter wings, birds that were barely capable of night, if at all. We hope thai comparisons of the various fossils will elucidate patterns of speciation during the early stages in the evolution of flightiessness.

Among the other flightless birds found on the islands of Hawaii are rails and ibises, the latter being familiar to most people as long-legged water birds with long, curved, curlewlike bills and excellent powers of flight. Before the discovery on Molokai and Maui of the remains of twoorthreespcciesofibisesthat were ab- solutely unable to fly, no one had given the first thought to the possibility that a flightless ibis might have existed. Yet within a year after the first Hawaiian ibises had been described, bones of another, even stranger, flightless ibis from Jamaica were found in the American Museum of Natu- ral History's Department of Mammalogy, scattered among drawers of fossil mam- mal scraps.

The leg bones of our Hawaiian ibises are much shorter and stoutcr.ihan those of typical ibises, so much so that we were not confident they belonged to an ibis until most of an associated skeleton was found in a lava tube on Maui. With such short legs, these ibises were certainly no longer water birds but had shifted to foraging on land. They must have made their living fossicking about in litter much like the New Zealand kiwis.

If there is one group of birds that paleontologists can almost always expect to find represented by flightless species on unexplored islands, it is the rails (family Rallidae). Rails are well known for their ability to colonize distant islands, and on many of these islands, flightless species have evolved. Most flightless rails are extinct, but at one lime they wcrea common feature on oceanic islands. At ¡east two species survived into modern times in the Hawaiian Islands: one on the island of Ha- waii and one on the tiny northwest atoll of Laysan. Both are now extinct. The fossil record shows that there was an additional

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Compared with a flying goose, the extinct ftighüess Thambetochen. below, had stout hind ¡imbs and a massive pelvis, small and unscuiptured wing bones, anda small sternum with no keel. The angle between the coracoid and scapula is wide, a trait common amongflightless birds but never found in adullßying birds.

Some of the siieletalfeatures of adult flightless birds result from the retention of juvenile characters.or neoteny. This hatchling of a flying goose, bottom, is too young to fly. Notice the open angle between coracoid and scapula, reduced wings, and absence of a keel.

OOU^S CrHTWF

Extinct Flightless Thambetochen

Scapula

Coracoid

Hind Limb

Hatctiiing of /"""^

Ftying Goose f ^

species on Hawaii, and at least one fiight- less rail on Kauai, two on Oahu, three on Maui, and one on Molokai, a species that was smaller than any other rail ever found.

Why so many species? Archipelagoes have certain characteristics that promote speciation. A colonizing species that in- vades an archipelago usually spreads to most or all of the islands present. Each population may become sedentary, mini- mizing gene flow between islands and al- lowing the various island populations to drift apart genetically, which may lead to speciation.

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The South American rhea belongs to an assortment of flightless birds, known as ratites, thai are distinguished by peculiarities of the palate and often considered to be an ancient group descended from a common ancestor.

The new fossil evidence from Hawaii, however, suggests that many of the ratites may have evolved independently of one another.

In time, flying birds in an archipelago can recolonize neighboring islands, so that a single island could eventually be host to numerous species, all evolved From the original colonizers. In contrast, populations that become flightless are efí'ectively held captive on their home island. The only easy way for them to spread to nearby islands is via land bridges, which rarely form between oceanic islands. In the Ha- waiian Islands, such bridges did occur between the islands of Maui, Molokai, and Lanai during the last ice age. At that time, so much water from the world's oceans was frozen in glaciers and the polar icecaps that sea levels worldwide were about three hundred feet lower than they are today. The shallow channels that now separate Matii from Lanai and Lanai from Molokai were then exposed as dry land, forming a single large island called

Maui Nui (Big Maui) and permitting overland dispersal among three formerly separate islands. While there can be little doubt that such dispersal occurred, estab- lishing precisely how the joining and sub- sequent fractionation of Maui Nui has in- fluenced the distribution of a particular species or group of species remains frus- tratingty out of our reach.

Since land bridges are rare, mcst flightless species never had the opportunity to colonize a neighboring island. This means, significantly, that flightlessness has arisen independently again and again in the Ha- waiian islands and an untold number of times on oceanic islands the world over. It is a common evolutionary response to the conditions of life on oceanic islands of all sorts, from tiny atolis to huge, mountain- ous land masses. This repeated evolution of flightlessness is a testimony to the tre- 38 NATURAL HISTORY 9/83

(11)

mendous potential of organisms to independently evolve convergent or parallel adaptations in response to similar selective pressures.

Flightless birds are extremely vulner- able to introduced predators and other human disturbances, and an untold number of ihem must have vanished as humans discovered and settled islands everywhere.

Why, with ail the islands in the tropical Pacific, some of them larger and older than the Hawaiian Islands, have truly bi- zarre flightless birds been found only in Hawaii, New Zealand, and New Caledo- nia (home of the kagu)? In our minds, the

lack of examples reflects, not reality, but our ignorance. Without doubt, flightless birds did exist on most major islands in the Pacific. The early Hawaiians, through habitat destruction, prédation, and the introduction of foreign plants and animals, drove at least seventeen species of flightless birds, and no fewer than twenty-eight flying species, to extinction. There is no reason to believe that prehistoric human settlement did not also bring about great changes in the avifauna of other Pacific islands. The coming years may prove to be a golden age for paleontologists exploring the Pacific for bird bones.

From our studies, we can envision the Hawaiian Islands at a time in the past, when eagles soared over unbroken forests that swarmed with an undreamed-of variety of small birds, when troops of ungainly, waddling flightless geese grazed on plants no botanist has ever seen, and when flightless ibises probed among litter for insect species that never felt the thrust of an entomologist's pin. The material evidence for this former glory now consists mainly of tray upon tray of bare bones.

But we are the lucky ones. The botanists and entomologists will unfortunately never know what they are missing, D

The flightless birds of Hawaii, particularly the geese and ibises, raise some per- plexing questions about the evolution of another assortment of flightless birds, the so-called ratitcs. These include running birds, such as ostriches, rhca.i, and emus;

the giant, lumbering extinct moas of New Zealand; and the little, long-billed kiwis of shoe polish fame. Many scientists con- sider ratites to be an ancient group, descended from a single common ancestor, that is separable from all other birds by the palcognathous palate, a peculiar con- figuration of the bones in the roof of the mouth. The Hyvi-aiian fassils, however, seem to suggest that at least some of the ratites may have originated more recently from more typical flying birds.

The term raiite, from the Latin ralis for raft, was originally applied to these birds because their sternum lacks a keel.

But [he keel may also be greatly reduced or even absent in flightless birds that are clearly not ratites. in some of the Hawai- ian geese, the sternum has no trace of a keel and has lost all resemblance to the sternum in typical ducks and geese; in- stead, it is rounded and bowllike, more like the sternum of an ostrich or an emu.

In some of the ratites•moas, for example•the bones in the leg are relatively shorter and much stouter than in running ratites. Again, wcsec very similar adaptations in the flightless birds of Hawaii.

Some of the geese had ponderous legs that contrasted greatly with their little wings.

The fiightlc.ss Hawaiian ibises had leg bones,so much stockier than those of their long-legged wading ancestors that they

Lessons from a Flightless Ibis

are remarkably similar in proportion to those in the New Zealand kiwis.

We find that almost all the features in the body plan of ratites have evolved re- peatedly in a variety of nonratites through the retention of juvenile traits (neoteny).

Might the paleognathous palate likewise be a result of neoteny, and consequently something that could theoretically develop in many kinds of birds? Thi.s is the subject of current investigation, for if all of the characteristics of the paleognathous palate are present in the embryonic condition, as some of them are known to be, the various kinds of ratites might have evolved independently of one another by retaining such a palate into adulthood.

With this possibility in mind, the strik- ing parallels between the flightless birds of the Hawaiian Islands and those of New Zealand become of even greater interest.

Hawaii had an extensive radiation of gooselike birds, derived from at least two dilfcrcnt ancestors, that were flightless

Great spotted kiwi of New Zealand

Brian Ëntinç. pnotc fíoi^stctvrí

and had widely divergent bill shapes, evi- dently for feeding on diJTerent kinds of vegetation. Similarly, in New Zealand, the moas were large, flightless, herbivorous birds with a variety of bill shapes.

Taxonomists have at times divided the moas into two different families that might actually represent separate coloni- zations of New Zealand by flying ancestors. The resemblance between living kiwis and the extinct Hawaiian ibises are not restricted to leg bones; both also have long, probing bills quite unlike those of geese or moas.

The flightless birds in the main Hawai- ian Islands lost the ability to fly in con- siderably less than 6 million years. The flightless ibises, for example, which were restricted to {^e islands of Maui Nui, could not have colonized those islands more than 1.8 million years ago, the age oí the oldest rocks found on Motokai, the oldest of the Maui Nui group. But New Zealand has been available for coloniza- tion by vagrant birds for tens of millions of years. If an ¡bis could become almost un- recognizable in less than 1.8 million years, what would it look like if it had continued to evolve for another 10 or 20 million years? Are the moas and kiwis of New Zealand merely the descendants of geese, ducks, and ibi.ses that had much more time to diverge? Such intriguing questions would probably never have been raised had the Hawaiian fossils gone un- discovered. Perhaps more work with fossil birds from other Pacific islands will help us find the answers.

Storrs L. Olson