FEATURE A bronze Martha attracts visitors to her memorial aviary and reminds people of the scale of the loss (Mark Avery)
On 1 September 1914, when a Passenger Pigeon named Martha died in Cincinnati Zoo, Ohio, the world lost its most abundant bird species for ever. The Passenger Pigeon’s Ectopistes migratorius extinction was about the 100th avian extinction since 1500 (and there have been c.30 since) but its loss represented the passing of more individual birds than all those other 129 avian extinctions put together. Martha lived and died in captivity, but only 60 years earlier the skies over the forests of eastern North America would darken as flocks of Passenger Pigeons numbering billions passed overhead. The descriptions of immense flocks of Passenger Pigeons by the likes of John James Audubon and Alexander
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Wilson from the early decades of the 1800s strain our imaginations to grasp the numbers of birds involved. The accounts of these two famous “American” ornithologists (the first a Frenchman and the second a Scot—but both doing their ornithological work in the USA) give numbers of a billion and two billion respectively and are sufficiently detailed that we can check their maths, if not the observations on which they were based. A later, less well-known account of a flock of Passenger Pigeons, by an English soldier stationed on the Canadian side of the Niagara River, came from the mid-1800s; it appeared to involve a spring flock of around three billion birds. Many other accounts describe the sky darkening as the flocks
passed by, stretching from one horizon to the other for hours or days at a time. Unless the witnessed flocks included all the world’s Passenger Pigeons in one place, at the same time, then we simply do not know what proportion of the total population was involved. The Passenger Pigeon was a nomadic species because of its dependence on the acorns, beech mast and chestnuts of the eastern North American forests from southern Canada down to Florida and Texas. The almost extinct American Chestnut (wiped out by a fungal disease imported to the USA in 1904 but formerly abundant and widespread) produced its seed in fairly regular quantities each year, but the oaks and American Beech produce their acorns and beech mast
periodically in abundance, depending on weather conditions around flowering time. Tree mast production is synchronised over large areas of hundreds of square kilometres, but the locations of plentiful acorns and beech mast vary from year to year. Passenger Pigeons scoured the forests to search for those rich areas of food; they then nested in enormous colonies where food was abundant. The main breeding range stretched from southern Canada to Kentucky and Virginia, bordered by the Atlantic Ocean on the east and, roughly speaking, the Mississippi River to the west. In winter, the pigeon flocks moved south to forests where the absence of snowfall allowed the ground to be cleared of
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tree mast. Passenger Pigeons probably laid only one egg, perhaps sometimes two eggs, but this almost certainly meant that they had to nest successfully a little more often than once a year on average. Much of their breeding biology seems to have been adapted to a quick nesting attempt, to allow a further attempt to be made later in the season, and perhaps further north as the snow melt uncovered more and more tree mast on the ground. In his book on the Passenger Pigeon (published in 1955), William Schorger estimated the Passenger Pigeon population at 3–5 billion birds at the time of the European colonisation of the continent and commented that this would mean that about one in three birds of North America
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at that time was a Passenger Pigeon. I wonder whether the population was even higher, up to 10 billion, but in the absence of survey data we just can’t really know. But we do know that the Passenger Pigeon was numbered in billions. That makes it even more numerous than the Red-billed Quelea Quelea quelea which, since the Passenger Pigeon’s extinction, has taken on the mantle of the world’s commonest bird (at a population of perhaps a billion pairs or so, give or take a few hundred million either way!). Although the extinction of the Passenger Pigeon is in no doubt (it is as dead as a Dodo – or as passed as a Passenger Pigeon), and although the timing of its final demise is known to within half an hour (between midday and 1pm on 1 September 1914), the reason for its extinction is still a matter of some doubt. However, I think it is foolish to look for “the” reason for an extinction as if there is only one cause. To some extent, the Passenger Pigeon became extinct through “old age”, when Martha died in her cage in Cincinnati Zoo a century ago. But that last death was not representative of earlier losses, and they may not have shared a cause with later ones. There are two factors which were certainly important in the species’ extinction, and another which may have played a part, but we are still left with a bit of a biological conundrum. The most obvious factor which reduced Passenger Pigeon numbers was that we killed millions of them. Native Americans harvested the fatrich Passenger Pigeon chicks (squabs) from their nests for centuries. They scouted for colonies each spring and moved their dwellings to be close to a colony if one were available. But the plundering of the vast nesting colonies by Europeans was a different matter, entirely and occurred on a different scale. Particularly after 1860, improved firearms, a more
ABOVE Pair of Passenger Pigeons by Louis Agassiz Fuertes. Frontispiece from a volume of articles, The Passenger Pigeon, 1907, The caption reads: “PASSENGER PIGEON (Columba Migratoria) Upper bird, male; lower, female” BELOW Shows the scale of the nets to catch birds – “Passenger Pigeon Net, St. Anne’s, Lower Canada” watercolour by James Pattison Cockburn, 1829
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A message from Martha
Albert Cooper, a trapper who used decoy pigeons to trap hundreds of wild birds (c.1870)
extensive railroad system and the invention of the telegraph meant that trainloads of hundreds of armed men could hear about a Passenger Pigeon colony and arrive to exploit it within days. Those same trains would then transport millions of Passenger Pigeons, dead in barrels, or sometimes still alive, back east to the city restaurants of New York and Philadelphia. Pigeon pie was no longer a meal whose availability was restricted to a very local market; improved communications opened it up to a market of millions of people. That market grew as the US population’s birth rate expanded and immigration from Europe continued. The plundering of nesting colonies exemplifies the antithesis of sustainable harvesting. The slaughter was almost entirely unregulated; attempts at regulation generally failed to be implemented on the ground. Adults were shot or trapped, leaving their squabs to die in the nest; trees were felled to get at squabs in the nest (a single tree might contain over 100 nests); and sulphur and fires were used to frighten the squabs into leaving their nests. It was carnage; the impacts went well beyond
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the millions that were killed directly: as David Blockstein and Harrison Torduff pointed out, the continual disturbance of these colonies must have added immensely to the death toll of birds and the reduction in productivity. Passenger Pigeons were also trapped alive, to be used in shooting contests, because their rapid flight ( an alternative name was the ‘Blue Meteor’) made them attractive living targets. It’s for this reason that we now have ‘clay pigeons’ for such contests rather than ‘clay pheasants’ or ‘clay grouse’. The revulsion against using living birds, trapped in their nesting sites, for shooting competitions grew as the pigeon population decreased; but we should regard this, in numerical terms, as a sideshow rather than an important factor. The Passenger Pigeon was a forest pigeon: it nested in trees, roosted in trees and fed on the fruits of the forest produced largely by trees. But by 1872, the forest cover of the USA had been reduced to less than half of its extent when the Pilgrims arrived at Plymouth Rock 250 years earlier. We should expect that halving the forest cover should have halved the Passenger Pigeon population, but there are reasons to think that the impact would have been even greater. Even where forest cover remained, the likelihood is that older trees, that produce the most mast, would have been selectively felled. The fragmentation of the forest would have made life more difficult for the breeding birds, increasing the time spent on foraging trips. Any new plantings of trees during this period would have been useless to Passenger Pigeons until the trees reached mast-producing maturity after 30–50 years. Thus, the recovery in forest area after 1872 was of little benefit to Passenger Pigeons. Moreover, the remaining forests were increasingly filled with free ranging, semidomesticated pigs (hogs)
that also fed on tree mast. Pig farmers complained that the arrival of a vast flock of Passenger Pigeons could clean out an area of forest of its tree mast, causing their pigs to starve. Yet, presumably, the pigs’ depletion of the same resource also affected the pigeons. Cincinnati was nicknamed “Porkopolis” during this period as it was the centre of the pork packing industry. Perhaps introduced diseases played a part; it would be very difficult to tell in retrospect (and quite difficult at the time). Wouldn’t it be ironic if the introduction of the House Sparrow Passer domesticus into North America from 1851 introduced diseases that affected the Passenger Pigeon? The role of introduced competitors or diseases is probably not a large one in this story; but then again, would we really know at this distance in time?
All of these factors, deforestation, trapping for sport, shooting for food, competition with pigs and even the possible (but totally unproven) role of exotic diseases were part and parcel of what we call “progress”. They accompanied an increasing human population and an increasing standard of living. It was the trappings of “progress” that drove the Passenger Pigeon extinct: better technology, better transport links, better communications and a larger, richer population. Surely, this should make us query our definition of “progress”? Moreover, the Passenger Pigeon was not the only victim of “progress” at this time. In the USA, the Carolina Parakeet Conuropsis carolinensis lived on only a few years after the Passenger Pigeon’s demise; remarkably, the last individual, this one named Incas, a male, died in the very same cage
A nesting captive Passenger Pigeon photographed in 1896
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in Cincinnati Zoo where Martha perished; the Eskimo Curlew Numenius borealis, or “prairie pigeon”, was brought to the brink of extinction; the Ivory-billed Woodpecker Campephilus principalis suffered from forest clearance; the Rocky Mountain Locust Melanoplus spretus was driven extinct; the Bison Bison bison was reduced from 30 million individuals to fewer than 1000 in the same period; and Beavers Castor canadensis, Sea Otters Enhydra lutris, Great Auks Pinguinus impennis, Pronghorns Antilocapra americana and many other species suffered as the forests were cleared, the prairies fenced and ploughed and the seas pillaged. European colonists desecrated North America’s ecology in a few brief centuries, with much of the impact coming in the 50 years after the American Civil war (1862–65) and up until the time of Martha’s death. This was when the American frontier was closed; when the West was “won”, the Wild was lost. Europeans had a similar impact on our own fauna, but our methods were more gradual and more distant. When Europeans arrived in the New World, they marvelled at the richness of the fauna, having destroyed much of their own. It seemed as if the Passenger Pigeons and the Bison, the forests and the prairies, were inexhaustible resources. But we did exhaust them. It was such a short time ago: my grandparents were born before the Passenger Pigeon went extinct in the wild (around 1900); they could have visited Martha if they had lived nearby. Have we learned since then? After all this time, does it matter that the skies no longer darken as a billion Passenger Pigeons fill them? I’m sometimes asked if we would be better off if we had saved the Passenger Pigeon. I think the honest answer is “no”, in economic terms. Yet, the
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world would be a better place if we had saved this species: it would have retained more of its natural beauty, the thing that makes Earth special. Would we be richer, economically? No, I don’t think so, but I also think that is irrelevant, because neither would we be economically any poorer! In the big scheme of things, saving a few more species, conserving the forests and grasslands where they lived, would not have prevented the USA from being the superpower it is today. The USA would still have played its part in World War II, 30 years after Martha died; it would still have put a man on the Moon a little over 50 years after she died. US standards of living would not be lower now if Passenger Pigeons still flew over the Potomac on their migration south each autumn (or fall!). Silicon Valley would still be there and the NASDAQ Stock Exchange index would be at the same level. No, we wouldn’t be economically richer or poorer; but the world would be a better place, and we could hold up our heads higher, if we stopped driving species extinct. Just in passing, it’s worth noting that the extinction of the commonest bird in the world has not had huge ecological impacts either, at least as best we know. Once, it was thought that two species of feather louse went extinct with the Passenger Pigeon: now we know that one of them lives on in other pigeons; the other had probably hopped across a museum cabinet from another species of pigeon anyway. But dare we even say that the loss of two feather louse might not count as a huge ecological impact? The forests of eastern North America are subtly different: there is a different balance of oak species, now that the Passenger Pigeon is gone. It has been suggested that Lyme Disease may be more prevalent, if rodents that eat tree mast have benefitted from the Passenger Pigeon’s demise. But in these days, when
ecosystem services are a trendy subject, it is worth noting that the removal of about a third of the birds from North America had rather little impact on the world; except it was a world more damaged and of reduced beauty. So, is there a message from Martha? We could, perhaps, excuse ourselves for the ecological damage wrought on the USA by “progress”. We could say that we didn’t realise what we were doing. We can just about get away with that. But that excuse has run out. Now we know exactly what we are doing and the nature of our impacts on the planet’s other species. We now know enough. But do we care enough?
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by Mark Avery
Mark Avery worked for the UK BirdLife Partner, the RSPB, for 25 years (12 of them as Conservation Director) until he left to go freelance in 2011. His book, A Message from Martha: the extinction of the Passenger Pigeon and its relevance today is published by Bloomsbury in the UK and USA.
A stuffed Passenger Pigeon displayed at Royal Ontario Museum, Toronto
Preventing Extinctions
The BirdLife Preventing Extinctions Programme is counteracting an increasingly diverse array of threats to birds by delivering conservation action—underpinned by science—where it is most needed to prevent what happened to the Passenger Pigeon happening to other species. The programme is implemented by the BirdLife Partnership working with whoever is best placed to help a particular species. The development of two communities plays a central part in the programme: BirdLife Species Guardians—experts who take the lead in conserving threatened species in their country; and BirdLife Species Champions— organisations or individuals who raise awareness of and fund the vital conservation that is so urgently required. Find out more at http://bit.ly/1oo6hxQ
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