I am enclosing you a very rough water-colour sketch of a lovely little bird that I bought in Santa Cruz [Teneriffe], and whose proper name I do not know. Can you identify him for me? I have never seen him in England, which may be an oversight on my part. It is a finch from Caracas (South America) which is imported to Teneriffe, and mated with the Wild Canary, producing a mule-bird like a Wild Canary dipped in saffron.
Letter from the REVEREND HUBERT D. ASTLEY to R. PHILLIPPS (1902)
By the 1870s songbirds could be heard and seen in virtually every home in Europe. In Britain, Queen Victoria was still moping – despite the invention of the telephone and the best efforts of Gilbert and Sullivan – over the loss of her Albert, now ten years dead. At Down House Darwin was alternately busy and sick, pursuing the glory of his biological intuition. In France the Impressionists were using colour in ways never seen before and in Germany Otto von Bismarck presided over a newly unified country – the Second Reich.
The British National Cagebird Show of 1873 was held in Norwich at the Assembly Rooms. A popular event since its inception in the 1850s, this one attracted a huge crowd. The main hall was full of people squeezing and pushing between the long lines of trestle tables stacked with cages, desperate to catch a glimpse of the exhibited birds. Amazingly, despite the thick fog of cigar and pipe smoke that filled the hall, the voices of the birds rose cheerfully above the hubbub of the crowd. But the exhibition hall was buzzing with more than the sound of birds. The buzz was a human one and centred on a sensational set of Norwich canaries exhibited by a Mr Edward Bemrose from Derby.1 They were a bright, luminous orange and swept the boards, taking ‘Best in Show’. The Norwich canary – the Victorians’ favourite breed – was judged partly on its shape and posture but primarily on its colour. Rather than being a plain lemon or even gamboge, to win the Norwich had to be a rich yellow tending towards orange. Bemrose’s birds, the colour of marigolds, were more vivid than any previously shown and few in the Assembly Rooms on that day could quite believe their eyes. Rumours were rife. Had Bemrose fed his birds something exotic, or had he plunged them into dye to produce such a winning colour?
Orange canaries had been seen at shows in the previous two years, and one judge described them as ‘bursting upon the bird world like meteors’. Their owners claimed to have bred them rather than fed them, but many in the fancy were deeply sceptical – for two reasons. First, the men walking away with the prizes at these shows had produced entire broods of orange winners, whereas normally only one bird in a hundred ever made a champion. Second, fanciers who had bought these beautifully coloured birds – often for considerable sums – were later devastated to see them fade into jaundiced mediocrity after the autumn moult. At one show the judges broke all the rules by pulling a bird from its cage and attempting to rub off what they assumed to be applied colour. But all the rubbing did was to destroy the starlet’s tail feathers.
The first sign that things were starting to turn nasty occurred at the Crystal Palace show in February 1873, when Bemrose, described by W. A. Blakston, a top canary judge and author, as ‘one of the keenest fanciers of the day, and a man on whom no one could lay a finger of suspicion’, exhibited two wonderfully pigmented orange birds. Despite his impeccable credentials, Bemrose left the show under a cloud of suspicion and vowed defiantly that he would be back with even more winners. True to his word, at the new season in October the same year, Bemrose took every prize within reach at the great Norwich Show. His unsuccessful opponents, the Norwich canary breeders, were enraged and eventually rose up as a body to challenge him. Seven of Bemrose’s winning team suffered the indignity of having their orange feathers plucked and sent off for analysis, but the County Analyst’s Office found nothing irregular on the birds’ plumage. This was true, for the birds had certainly not been dyed – at least not externally. But by the end of the year Bemrose’s colourful secret had leaked out when one of his confidants foolishly sold the knowledge to another fancier for £50. Such behaviour could not be tolerated. Canary breeders were gentlemen and were expected to behave accordingly. Artificially colouring a canary was one thing but selling a secret for personal gain was a disgrace to the fancy. As soon as the society officials learned of this breach of etiquette they informed Bemrose, who then had little choice but to set the record straight by going public. He published his secret in the 11 December issue of the Cottage Gardener.2 The magic process that had so demoralised the rest of the canary fancy turned out to be utterly trivial: red peppers. Fed to them during their moult, red pepper pods transformed yellow canaries into bright-orange ones.
It was inevitable that if points were given for a canary’s colour, some men would stoop to devious means. Responding to the Bemrose scandal, George Barnesby,3 another well-known judge, pronounced, ‘The artificial colouring of birds, especially canaries, is a tricky artifice often practised by some, who much to their shame and disgrace, resort to the defacing of Nature’s works for the sake of gain.’ But they were all at it and prior to the discovery of red peppers fanciers had tried everything they could think of to enhance the intensity of their birds’ colour: marigolds, fuchsias, nasturtiums, port wine, beetroot, saffron, mustard seed and cochineal. It was only because their previous potions had produced little change that their use was never an issue. Red pepper was different: its effect was so dramatic that it took the breeders’ breath away.
Once the red pepper effect became public knowledge everyone started to use it and colour feeding, as it was called, became an accepted and legal part of the business of producing Norwich canaries. It had to: if Norwich fanciers were to compete on a level playing field, there was no other way. And they were optimistic. The future of the Norwich canary was bright and the future was orange. But not red. Feeding canaries peppers turned them the same hue as tangerines, peaches and marigolds, but however much red pepper fanciers forced their birds to eat, the canaries remained resolutely orange.
Reich must have told Duncker this story, which was a well-established part of canary folklore, during one of their many evening conversations. It probably made him laugh but it also did something else. It planted the seed of an idea in Duncker’s brain.
There was yet another example of men changing the colours of birds’ feathers that Reich probably knew about and related to Duncker. This was the trick of enhancing the colour of parrots by anointing them with frogs. The very notion sounds preposterous and it is easy to imagine Duncker dismissing Reich’s story as apocryphal. But Reich assured him that since no less an authority than Comte de Buffon had described it it must be true. Buffon’s description in his 1790s encyclopaedia of what he called ‘the artificial parrot’ probably came from ‘Dom’ Pernetty’s account of Louis-Antoine de Bougainville’s voyage of discovery to South America in the 1760s. Pernetty described one particular parrot thus:
All its plumage, especially the head, neck, back and belly is sprinkled with feathers, some of them yellow like daffodil, or yellow like lemon, some others carmine red or crimson red, mixed with feathers either more or less dark green, or bright blue especially around the ears. This type of plumage is due in part to nature and in part to the art. When the bird is very young, and has only got its feather-sheaths grown out after the down feathers, sheaths are plucked in several points, and instead is immediately inserted a sort of poison like liqueur. Feathers that grow after the sheaths then become yellow or red, instead of green as they should have been naturally.
Duncker and Reich almost certainly dismissed this as nonsense and of no possible relevance to their own work, but as unlikely as it seems, the change in colour in these parrots was not only genuine but genetic in nature. The ‘liqueur’ came from a frog – one of the colourful but highly toxic dart poison frogs, azure blue with gold stripes – aptly known as the dyeing frog Dendrobates tinctorius. Apart from transforming parrots, the most remarkable thing about this frog was something Duncker could hardly have anticipated: it could create genetic change in anything it came in contact with. The poisons in the frog’s skin are alkaloids, protecting the frog from bacterial and fungal infections. The ability to produce these toxins is determined partly by the frog’s genes and partly by what it eats. Frogs that in the wild could kill a man with one lick are rendered entirely harmless in captivity when deprived of their natural diet. With appropriate feeding, however, they rapidly regain their alkaloid secretions. Alkaloids are mutagenic – they cause genes to mutate. More familiar mutagens include X-rays, other kinds of radiation and ultraviolet light, but there are numerous chemical mutagens too, and many of them cause cancer. A growing feather is a mass of rapidly dividing cells and applying the frog’s alkaloids was like bombarding the feather genes with mutagenic missiles. The aim was to hit only those genes that control colour, but the technique was so crude that the mutagens usually struck many other genes and utterly disrupted the bird’s ability to produce proper feathers. Few birds survived the treatment. But in a handful of instances, just as Pernetty reports, the mutagens found their target – hitting only those genes controlling the biochemical pathways that determine the final colour of the feather and leaving everything else intact. These multicoloured parrots were much sought after and sold in the Paris bird markets for large sums.4
Buffon’s artificial parrot was in a sense genetically modified, but since its creators had no idea they were tinkering with genes and because the parrot was unable to transmit its new genes to its offspring, it hardly counts. Nonetheless, had Duncker known that the effect was genetic he would certainly have been intrigued.
Perhaps on that same evening, Reich also told Duncker about a well-to-do Bremen bird-fancier, Consul Carl Cremer, who was keen to meet him. Cremer was a successful budgerigar breeder, president of the Austauschzentrale der Vogelliebhaber und Züchter Deutschlands5 – the German bird-keeping society known as the AZ for short – and a member of the Bremen Natural History Society to which Duncker also belonged. Although Duncker knew him to nod to, they had never really spoken because thus far their interests in birds had been rather distinct. But following the publication of Duncker’s eight-part account in the popular cage bird paper Gefiederte Welt (Feathered World) in 1924, describing his successful unravelling of the canary’s tricky variegation helix, Cremer was anxious to talk to him. He wondered if Duncker’s genetic talents might help him breed better-coloured budgerigars.
Consul Carl Hubert Cremer was a tall, imposing businessman with a goatee and an obsession for foreign birds and budgerigars in particular. He had made his fortune as a merchant and a shipbuilder. Well-travelled, well-educated and extremely well-heeled, Cremer thought nothing of spending the equivalent of £500 on a single bird of a new colour.6 We don’t know for sure, but it seems likely that Cremer survived the early 1920s recession through his foreign investments, as other wealthy merchants had done.
The meeting took place at Cremer’s house in the autumn of 1925. Duncker made the short walk from his own home across town to where Cremer lived at No. 130 Am Dobben, an exclusive street not far from Reich’s hardware shop. Even before he rang the doorbell Duncker could see that, with its neoclassical façade and four floors, the house was the grandest of a magnificent row. A maid showed Duncker into the drawing room where Cremer came to greet him. Duncker was immediately impressed with Cremer’s friendly, forthright manner, by his dynamism and not least by his obvious prosperity. Duncker had never seen such affluence devoted to bird keeping. Cremer took Duncker on a guided tour of his aviaries. The first contained a dazzling collection of tropical jewels: orioles, tanagers, robins, thrushes and red siskins. In the next there were dozens of budgerigars, loud in voice and colour. Then on to Cremer’s breeding rooms to see the bloodstock. Here there were budgerigars of various shades of green, sky-blue, cobalt, mauve, yellow and white. Finding that Duncker knew nothing about budgerigars, Cremer explained how in 1840 the original pair had been sent to Europe from their native Australia by John Coxen, the brother-in-law of the famous naturalist John Gould. Like the canary, the original wild birds were green – albeit a much brighter green than the canary. The yellow mutation was the first to appear, Cremer continued, in 1870, and blue birds appeared just eight years later. The main English bird keepers’ handbook published in the 1870s had commented prophetically, ‘Without doubt another ten or twenty years will witness as great results of intelligent breeding of varieties of the Budgerigar as has been witnessed in the case of the Canary.’7
Cremer then showed Duncker his most prized possessions, his grey-winged budgerigars, one of the most recently established and most highly valued of all mutations. To Duncker these birds didn’t seem as attractive as the all-blue or all-yellow ones, but he knew from experience that beauty for a bird keeper was often in the eye of the beholder.
The two men retired to the palm-filled conservatory and continued to chat. From their comfortable cane chairs they looked out into the aviaries built on to the back of the house. Captivated, Duncker saw more than just birds; he also saw the enormous potential of Cremer’s facilities. The bird room in Reich’s home where they had done the variegation experiments had been adequate, but it was very modest by comparison. Duncker’s mind raced with the possibilities that Cremer’s aviaries offered.
Cremer started to tell Duncker about himself; how he was the eldest of seven children and how his two brothers and four sisters had teased him by nicknaming him ‘the principal’ because of his obvious enthusiasm for inheriting the family distillery business. He had been useless at school and bored by what he laughingly called the dried talk of petrified teachers. At sixteen he left school and started in his father’s business and at the same time began keeping and exhibiting budgerigars and canaries. He laughed again as his memory caught up with him: business and bird keeping kept him pretty busy, but not too busy, he said, to pursue the ladies. Seeing Duncker wince, Cremer quickly continued, describing how he had married the daughter of his father’s business partner. After his marriage he started to travel, setting up businesses wherever he went, in Antwerp, in Paris (where he had a wine business), in London and Oporto, eventually returning to Bremen where he met his future colleague Kühlke with whom he established an export company in 1892. This venture did well, and he then started his own ship-fitting organisation, which was also successful. During World War I he joined the diplomatic service in the Netherlands and was made Generalkonsul. Cremer stopped: this was his story, he said.
Cremer’s openness and enthusiasm encouraged Duncker to say what he had been thinking. Instead of simply keeping all these birds as decorations, why not use them to solve the great mystery of colour genetics – in budgerigars, canaries or, indeed, any species he wanted? Working as a team, Duncker said, they could do great things. Cremer beamed: he was hooked – it was the idea of budgerigar experiments that convinced him – and he happily agreed to provide whatever was needed. Better still, he told Duncker he was also happy to support his canary studies. But Cremer had another surprise in store. They wouldn’t conduct their proposed studies here in town, but instead would use his country house, Rosenau Villa at Vahr, two or three kilometres away on the east side of Bremen, where there was a bit more space.
A few days later, Cremer took Duncker to see for himself. Named for its rose gardens, Rosenau was huge: the gardens extended over six hectares and were bursting with exotic trees and shrubs. There were ponds with fountains, stables for the horses and in one corner a well-ordered vegetable garden. The house was typical of the mansions so loved by Bremen’s rich merchants: newly built of red brick, picked out with pale mortar and adorned with gracefully arched windows. In the grounds Cremer kept rare breeds of chickens, ducks and turkeys, and there were yet more aviaries full of exotic birds. Duncker laid it on the line to Cremer, saying that to understand the inheritance of colour, be it in budgerigars or canaries, it was absolutely essential to raise very large numbers of birds to obtain statistically valid estimates of the ratios of the different colour forms – just as Mendel had done with his peas. Cremer didn’t need much persuading: he threw money at the project, and within a few weeks of meeting Duncker he had workmen busy building new two-storey bird houses with aviaries inside and out, and hundreds of cages to hold all the birds they would need for their experiments. Duncker’s brain and Cremer’s cash created a unique synergism. Karl Reich wasn’t excluded; he was there to advise on the canary research. Almost overnight Rosenau metamorphosed into a research institute in which Duncker, Reich and Cremer would change the face of bird genetics for ever.
Inevitably, the initial thrust of the research was budgerigars. They started by trying to understand the genetic basis for Cremer’s grey-winged mutation. But Duncker’s real passion still lay with canaries and an idea that Reich had unwittingly planted in his brain. It was seeing the beautiful red siskins in Cremer’s aviary that had fertilised the latent red canary idea. Why not breed a red canary? For Reich, breeding was everything, just as it was with his nightingale-canaries – if an effect couldn’t be bred, it wasn’t worth having. For the higher echelons of German bird keepers nature was vastly superior to nurture in every respect. It was the challenge that mattered; any clown could feed a bird red peppers to turn it orange, but it took genuine skill to figure out how to breed an orange bird. Still more to breed a red one. Ever since that conversation, the idea of creating a red canary had worked away at Duncker’s neurones. The sight of the fiery red male siskin in Cremer’s aviaries caused it to flutter free and into the light. This was exactly the type of challenge Hans Duncker loved: it tested his ingenuity and pitted him against nature. Here was a small finch carrying vivid red genes and he was going to put them inside a canary.
Cremer told Duncker the story of how the red siskin had made its appearance in European aviculture.8 With its brilliant plumage and sparkling song the red siskin may have been kept as a cage bird in Venezuela even before the Spanish first appeared in 1530. With their long tradition of bird trapping and trading, the Spaniards appropriated the red siskin and transported it, along with dozens of other species, back home and to the Canary Islands. The two species crossed in the night as canaries were exported to South America and it was probably there that the first hybrids were created. For almost 300 years, however, the red siskin remained unknown to the rest of Europe – the Spanish at this time vigorously regulated the trade in wild canaries and kept a firm grip on their siskins too. It wasn’t until 1820 that the red siskin became known to science – centuries after most other known birds had been officially described. It was William Swainson, an avid English ornithologist and artist who spent much of his time in the Mediterranean, who first recognised the red siskin as something new. He came across a single male in the possession of an Englishman who told Swainson he had obtained it on the ‘Spanish Main’. In the following fifty years very few other red siskins were seen, until at the peak of the cage bird frenzy in the 1870s a few were imported into Continental Europe. August Wiener, co-author of one of the most magnificent English volumes on bird keeping, The Book of Canaries and Cage Birds, had acquired a single male in 1877, but didn’t think the species worth including in his book because it was so rare. Nor did the red siskin appear in Robson’s and Lewer’s follow-up volume, Canaries, Hybrids and British Birds in Cage and Aviary published in 1911, possibly because unlike its predecessor this volume was explicitly about British birds. Even so, the red siskin might have had a mention since by this time several people kept them. More significantly, several fanciers had successfully crossed them with canaries.
Hearing that bird keepers had already hybridised red siskins and canaries, Duncker needed no more encouragement. The logic was straightforward: in all other crosses between a finch and a canary – which breeders referred to as ‘mules’, to distinguish them from hybrids between two finch species – the cross-bred offspring almost always assumed the colour of their finch parent rather than the canary parent. Since the red siskin possessed red genes, it followed that a hybrid produced from a yellow canary would be red rather than yellow. Duncker’s mind raced ahead of itself: he and Reich would breed some red siskin mules; the following year they would breed the mules together and generate even redder offspring. By selecting only the reddest of their offspring for back-crossing with canaries, they would end up, in four or five years, with a pure red canary. It all seemed so simple, so straightforward and so exciting. Even Cremer was enthusiastic; budgies were one thing, but he readily acknowledged that a red canary would be utterly novel.
The term ‘mule’ originally referred exclusively to the cross-bred offspring of a donkey and a horse but has since been applied to hybrid plants, hybrid fish and in the bird-keeping fancy to the offspring of a canary and a finch. Textile workers, many of whom were also canary-mule breeders, even referred to one of their machines as a ‘mule’ because it comprised a mixture of Joseph Arkwright’s warp machine and Mrs Hargrave’s hand jenny. ‘Hybrid’ is similar to mule in that it, too, once had a very specific meaning, identifying the offspring of a female domestic pig and wild boar, but it now refers to the result of cross-breeding any two species of plant or animal. The term hybrid comes from hubris – insolence against the gods – reflecting the ancient view that there was something improper about inter-specific crosses. German bird keepers used the term ‘bastard’ to describe both mules and hybrids and it regularly appears in Duncker’s papers with reference to red siskin mules. Bastard was also used in Germany to describe people of mixed race.
Hans Duncker must have known that the terms ‘mule’ and ‘sterility’ invariably went hand in hand, and what was true for the mixed offspring of horses and donkeys was also true for other inter-specific crosses – including canaries and finches. Nonetheless, he hoped that they could somehow either leapfrog or ride roughshod over this general rule and generate fertile offspring from canaries crossed with red siskins. Duncker was confident that he could persuade red siskins to breed with his canaries and produce red mules. He had it on good authority that the Spaniards, both in South America and on the Canary Islands, had a long history of doing this. Indeed, ever since canaries had been bred in captivity, they had produced mules with other finches, mixtures that must have originally arisen by accident when female canaries and male finches were kept in the same aviary. One of the earliest examples was a beautiful goldfinch mule painted by Lazarus Röting in 1610. At that time only male finches were kept – for their song – and as the breeding season progressed these birds must have felt more and more like men in singles bars whose threshold for what is acceptable in a partner declines rapidly as closing time approaches. For a male finch, mating with a female canary was better than not mating at all.
When the breeders of mules and hybrids are successful they produce what are effectively new organisms. Some bird keepers find this prospect irresistible, not least because many crosses are stunningly beautiful in both feather and voice. As soon as it became widely known that creating mules was a possibility, bird keepers set about trying to breed them. By the time Hervieux wrote his book in the early 1700s, mule breeding was extremely popular:
It being natural for Man never to be satisfy’d with what he has, but to despise what is in his Power, and ardently to desire whatsoever is out of his Power; curious Persons at present act accordingly in respect of Canary-Birds. They are not satisfy’d with having an Abundance of Canary-Birds of the most beautiful sorts; but are for altering their Nature, and most of them take pains to make Canary-Birds couple with Birds of another sort, whose Young are call’d Mongrels.
Breeding mules has retained its hold over bird breeders since Hervieux’s day and it is now among the most status-driven part of the fancy. The lure is the ability, through a combination of skill and luck, to triumph over nature. Success is rewarded on the show bench and the more difficult two species are to breed together, the greater the achievement. Mules and hybrids often win ‘Best in Show’ at national competitions today merely on the basis of their implausibility.9
Although accidental matings between different species sometimes occur in captivity, breeding mules and hybrids to order is more difficult, and breeding birds that will win exhibitions even more so. In 1877 the cage bird judge George Barnesby wrote,10 ‘If anything in bird breeding tests the patience of a true fancier most, it is mule breeding’. It is precisely because of this challenge that bird keepers remain attracted to this branch of the hobby.
For the past 200 years mule and hybrid breeders have scored points over their fellow fanciers either by producing a hybrid from an unlikely combination of parent species, or by breeding a clear yellow mule – a cross between a canary and a finch with no dark feathers whatsoever, like Galloway’s famous mule of 1908. Duncker’s ambition was to achieve both these goals simultaneously, producing descendants of canary x red siskin mules with no dark feathers, but with the siskin’s red ground colour rather than the canary’s yellow.
Some mules are easy to produce. The goldfinch mule so lovingly illustrated by Lazarus Röting is a case in point: simply putting a male goldfinch into a cage with a female canary at the height of summer will invariably produce hybrid babies. The serin, the canary’s closest cousin, is the best of all muling finches and even produces completely fertile offspring. But this is like crossing wolves and dogs. They are effectively the same species. Easy mules and hybrids were of little interest to bird-fanciers – there’s precious little prestige in doing something simple.
Other mules are either too difficult or impossible. Johann Bechstein, the great German authority on cage birds, fantasised about a hybrid nightingale x canary; a bird, he said, that would be the ultimate songster. He and dozens of other fanciers in the 1700s and 1800s must have tried it, but with absolutely zero success.11 Canaries that sang nightingale songs were the closest they ever got.
In his bird-keeping book, Eleazar Albin included a colour illustration of an extraordinary-looking bird that he said was a hybrid between a cock swallow and a hen goldfinch. The bird is indeed like no other and its inclusion in the book was a clever sales ploy: such an unlikely hybrid must have fired the imagination of every bird-fancier who saw it. Were it produced now, it would probably score highly on the show bench for its sheer novelty, but in reality Albin’s extraordinary ‘hybrid’ was nothing more than an aberrant goldfinch whose striking blackness may have been either genetic or environmental in origin.12
Impossible hybrids were like fishermen’s stories of ones that got away: they conferred no kudos. What was needed was something unbelievably rare but not totally impossible, and when Bechstein wrote his monumental handbook on cage birds in the 1790s, he described a hybrid of exactly this type.13 It was a cross between a cock bullfinch and hen canary, bred by a fellow German. Mention of this extremely improbable hybrid (there was no picture of it) must have rattled the cages of bird keepers everywhere and spurred them to try to create one for themselves.
Who knows how many fanciers struggled, season after season, with a bullfinch cock and a canary hen to no avail? There may have been one or two false hopes – the occasional fertile egg and even the odd hatchling – but none of them survived. Eventually, a full century after Bechstein had first raised their hopes, a canary x bullfinch mule was reared to maturity – but contrary to the usual muling practice, this bird’s father was a canary and its mother a bullfinch. And what a bird it was – such as England had never seen before – one of the most lusciously coloured hybrids ever produced. At the Crystal Palace exhibition of 1898 its owner, John Williams of Liverpool, shot to stardom and took first prize – the highest accolade an exhibitor could hope for. But no sooner had he won than the floodgates of controversy burst. Suddenly there was concern whether the bird really was what Williams claimed it to be. The judge, Charles Houlton, was convinced, but much of the rest of the fancy remained aggressively sceptical. There is much at stake in such contests and bird breeders are deeply suspicious of extravagant claims, even from breeders like Williams, whose breeding skills had earned him the title of ‘Mule King’. Because a canary x bullfinch mule was so incredibly unlikely and because the bird’s parentage was so ambiguous, many felt it totally unacceptable to award Williams first prize. From the bird’s overall appearance one of its parents was clearly a bullfinch, but the other parent was far from obvious. The uncertainty was made worse because Williams had not bred the bird himself but had bought it from another fancier who, to confuse things further, swore that it was a cross between a linnet and a bullfinch. One of the most vociferous critics was Lambert Brown, whose greenfinch x canary mule had been placed second at the same show. Even after the National British Bird and Mule Club had agreed, following protracted discussion, that the bird really was a canary x bullfinch mule, Brown was still protesting. The issue of the mule’s authenticity rumbled on for years. So much so that when Charles Houlton came to write his book Cage Bird Hybrids years later he was still worked up about the bird that had caused him so much anguish.14 ‘To write about this wonderful cross . . . my pulse beats and my heart literally throbs with its earnestness and fullness, so that I am almost too full of the subject to know where . . . to start.’
Since then there have been several canary x bullfinch mules and they have all been produced using a male canary and hen bullfinch. Plenty of fanciers have tried with bullfinch cocks but with absolutely no success. What renders the male bullfinch such a useless hybridiser? The answer is that he is sexually dysfunctional – hopeless at sex. The mind is willing but the cells are weak. One could accept that bullfinch cocks might be hopeless hybridisers if they were particularly picky about who they copulated with but, as breeders are quick to point out, they aren’t. Rather, the reason lies in the fact that female bullfinches are incredibly faithful to their partners – unlike most other birds, whose promiscuity is notorious.15
The link between the female bullfinch’s sexual fidelity and a male bullfinch’s inability to sire hybrids is this. When females of a species routinely mate with several males (of their own species, of course), there is intense competition between the cocks to fertilise a female’s eggs. The cock with the most effective sperm passes on his successful genes to his sons. Having efficacious sperm depends to a large extent on overcoming the female’s reproductive defences in which she reduces the number of sperm from the millions the male gives her to the handful she actually needs to fertilise her eggs. When females are promiscuous the sperm numbers problem is intensified – especially since each male wants the female to retain his sperm at the expense of the other guys’. Males of those species with promiscuous females thus produce more sperm and, crucially, sperm that are much better at jumping over the female’s ticket barrier and getting to her eggs. The poor male bullfinch hasn’t got a chance. Aeons of female monogamy have blessed him with a derisory sperm count and a limp ejaculate. His sperm are sufficient for fertilising females of his own kind, but in the hostile and alien oviduct of another species they are utterly impotent.
Knowing the male bullfinch’s deficiencies, Duncker prayed that the red siskin might make a more tractable muling partner.
The other hybrid fanciers had always aimed for the completely yellow mule. Crossing a yellow canary with a wild finch in the hope of producing a canary-yellow mule is like the alchemists’ hope of mixing two base metals to yield gold. Unlike medieval magicians, bird breeders sometimes succeeded at this, but so rarely that these birds were actually worth many times their weight in gold. The goal of producing ‘clear’ or ‘light’ mules – brilliant-yellow birds with no dark feathers – is what drives many mule breeders. These are gorgeous birds to be sure, but their beauty lies partly in their scarcity. Rudolf Galloway, one of Davenport’s critics, reared hundreds of mules over his lifetime but only one completely clear bird.16
When Hans Duncker began the quest to breed a red canary in the 1920s a huge amount was known about hybrids.17 Bird-fanciers across Europe had been generating hybrids for more than 200 years and had written extensively about their obsession. Furthermore, biologists like Darwin and Mendel had also written many pages on the subject. Duncker was therefore well aware that to create his red canary he had to contend with three bits of biology. The first was probably a bonus, but the other two were serious obstacles. First, he knew that any mules he produced would be tough, long-lived birds – a phenomenon known as ‘hybrid vigour’ and well known to the Egyptians, who were the first to cross horses and donkeys. Second, as was common knowledge among bird breeders, mules are always more difficult to breed than canaries. The third and most significant hurdle was the fact that mules and hybrids are almost always sterile.
The true mule, the hybrid offspring of a horse and a donkey, is unbeatable as a beast of burden, combining the strength of a horse and the endurance and surefootedness of a donkey – unequivocal hybrid vigour. Bird breeders recognised the same phenomenon and in his forty-four-volume Histoire Naturelle, written in the mid-1700s, the great but eccentric Comte de Buffon reported that the offspring from the ‘cini [serin], siskin and goldfinch with the hen canary are stronger than canaries, sing longer, and their notes are fuller and more sonorous . . .’18 Even today breeders often comment on the longer lives of their mules compared with parent species.
Whatever bird breeders believe, the truth is that we do not really know whether hybrid finches are ‘better’ in any way than their parents for no one has bothered to conduct a proper test. Whether a hybrid is more vigorous than its parent species depends very much on the circumstances. When horticulturalists cross different strains of the same species, such as maize, the resulting offspring may indeed show increased vigour, but only because the parent strains were somewhat inbred. In this situation hybridisation restores any variation that was lost when the parental strains were inbred. On the other hand, hybridising very different species may have exactly the opposite effect, breaking up groups of genes that work particularly well together in their proper owners.
Strictly speaking, mule refers only to an animal whose father is a donkey and whose mother is a mare. When the parentage is the other way round – a more difficult feat – the offspring is a ‘hinny’. In the past some people claimed they could tell mules from hinnies because their front end resembled the sire and the back end the dam – reinforcing the already prevalent view of male superiority in reproduction.19 Some fanciers imagined they could see something similar in birds. Buffon related how hybrids assumed the father’s appearance in their head, legs and tail, and the mother’s in the middle. ‘It appears, therefore,’ he said, ‘that, in the mixture of the two seminal liquors, however intimate we suppose it to be, the organic molecules furnished by the female occupy the centre of that living sphere which increases in all dimensions, and that the molecules injected by the male surround and inclose these.’20
When bird keepers first produced mules from canaries and native finches, they invariably used a male finch and a female canary because, being domesticated, female canaries were more likely to reproduce in captivity than female finches. Hervieux, however, recommended the opposite: ‘For my part I am for the contrary . . . because the male communicates more of his kind to the breed than the female . . . and consequently the mongrels that come from a cock canary-bird will be more beautiful and sing better . . .’ This was simple canary sexism. Generations of experience subsequently gave no indication whatsoever that the appearance of mule offspring is affected by whether their father is a canary or a finch.
Another erroneous belief was something called ‘the effect of a previous sire’.21 The idea that a female’s very first sexual partner influenced all her subsequent offspring, regardless of later breeding partners, gained credence with the story of Lord Morton’s mare. Lord Morton’s aim in life was to save the quagga, a kind of zebra, from extinction, through a captive breeding programme. He failed before he had even started, for he only ever acquired a single quagga – a male. In desperation he allowed it to mate with a female horse, which in due course produced a nice hybrid offspring bearing on its back and legs the quagga’s stripes. When Lord Morton sold the mare and it was later mated to a black stallion, the offspring all bore the tell-tale quagga stripes, indicating – to Lord Morton at least – that the mare’s original partner, the quagga, had had an extremely long-lasting effect. Neither Lord Morton nor the Royal Society which published his account in 1820 seemed to have considered that the mare might have produced striped offspring regardless of whom she mated with.
Instead, the idea of previous sires took a firm hold on the imagination of animal breeders and so convinced were they that they even managed to confuse Darwin. He desperately wanted to believe his trustworthy informants who described instances of the effect-of-the-previous-sire, or ‘telegony’ as it was called – but his biological intuition told him it couldn’t be true. Not until the early 1900s, when Mendel’s laws of inheritance became common knowledge, was it generally appreciated that both parents contribute equally to the production of offspring, allowing biologists and animal breeders alike to stop worrying about telegony. Even so, as late as the 1920s racists hijacked the telegony idea for ideological purposes; in Germany some anti-Semites asserted that ‘a single act of intercourse between a Jew and an Aryan woman is sufficient to pollute her for ever. She can never give birth to pure-blooded Aryan children, even if she marries an Aryan.’22 The final bastion of telegony was among kennel clubs where, curiously impervious to biology, the idea lived on until the 1970s.
Darwin’s notebooks from the 1850s are full of anecdotes, snippets of information and curious facts about hybrids. He believed them to hold the secret to the origin of species.23 By looking at which species would hybridise and produce fertile offspring and which wouldn’t, Darwin thought he could establish boundaries between species. He knew, for example, that the more similar two species were, the more likely they were to hybridise, and that two finch species were more likely to breed together than a finch and crow. But there were so many exceptions to this pattern that by the time he put pen to paper twenty years later, Darwin was unable to infer very much at all about the origin of species from the study of hybrids. Normally a rapid writer, he took a full three months to write the difficult chapter on hybrids in the Origin, which he summed up by saying, ‘. . . crosses between forms sufficiently distinct to be ranked as species, and their hybrids, are very generally, but not universally, sterile. The sterility is of all degrees . . . and . . . does not strictly follow systematic affinity, but is governed by several curious and complex laws.’
Later, the evolutionary biologist Ernst Mayr confirmed that the only pattern is a rather messy one. First, it is true that the less related two species are the less likely it is that they will hybridise. On the other hand not all closely related species hybridise easily. Whether hybridisation is possible depends to some extent on whether the two species naturally occur in the same habitat. If they do then they may have evolved different courtship displays specifically to avoid hybridisation. Two closely related European warblers, the willow warbler and the chiffchaff, occur in the same areas of woodland and look very similar, but they have completely different songs, which enable them unambiguously to recognise each other and avoid mis-pairing. They are sexually isolated by song. Such differences evolve because hybrid offspring are generally less fertile than pure-bred offspring, so natural selection favours those individuals that breed with their own species.
Some species are in the strange position of being closely related yet not having encountered each other for millions of years, and this is precisely the situation of the red siskin and the canary. Both species evolved from a common ancestor but became separated millions of years ago when South America drifted away from Europe.24 Only when the Spaniards started taking red siskins to the Canary Islands were the two species united. As a result of their prolonged separation there were no major behavioural barriers to prevent them from hybridising.
It is curious that despite the difficulties of producing hybrids many people still believe that most domesticated animals originated from crosses between different species. This widespread conviction stems partly from the fact that generations of selection have rendered domesticated species so different from any wild species that it is often far from obvious what their ancestor was. Early ornithologists thought the canary was a combination of the true canary and the Elba citril finch; others considered canaries a mixture of one or more green European finches – the European siskin, serin or the citril finch. They probably did so for three reasons: they all look superficially rather similar; canaries hybridise easily with these species; their hybrid offspring often look very much like wild canaries. Florence Durham, one of the first scientists to use canaries to study inheritance, was absolutely convinced that the canary had a multi-species origin precisely because her imported wild canaries stubbornly refused to breed with each other, but, perversely, did so willingly with other finches.25 But canaries, like pigeons, domestic fowl and all domesticated animals, are derived from a single ancestral species. In some cases this has been verified by molecular analysis,26 but even without the insights of modern technology, the difficulty of producing hybrids and the fact that hybrids are usually sterile, tell us that it is extraordinarily unlikely that our ancestors would have struggled to produce domestic animals by cross-breeding them. Yet this is precisely what Duncker planned to do.
The more Duncker read, the more he was convinced that the widely held view that all hybrids are sterile was simply wrong. Hervieux, Buffon and Darwin all stated quite clearly that some hybrids – not very many, but some nonetheless – were fertile.27 He had also heard it said that the red siskin mules produced by Mexican and Cuban fanciers were fertile. Moreover, it was widely known that many plant hybrids were perfectly fertile, allowing nurserymen to produce new ‘species’ effectively in a single generation. Duncker went back and reread Hervieux: ‘The Young Ones that come from these mix’d Birds, often breed others the next Year, contrary to the Opinion of him that has writ the contrary . . .’ Duncker also looked again at what Darwin had said28 using information from the bird-fancier Bernard Brent, that the canary ‘has been crossed with nine or ten species of Fringillidae [finch], and some of the hybrids are almost completely fertile’. The important point for Darwin was that these cross-bred birds had not given rise to new species, but for Duncker it was enough that some hybrids were capable of reproducing.
Because hybrids are often sterile, the accepted wisdom is that hybridisation is rare in nature, but this too is a myth. Fully 40 per cent of all plant species are thought to have arisen naturally through hybridisation. For reasons we do not understand, plants interbreed much more readily than animals, a feature horticulturists have enthusiastically exploited. But hybridisation may have played a significant role in the origin of some wild animal species as well. The critically endangered red wolf of North America, it now transpires (on examination of its DNA), is nothing more than a hybrid between a grey wolf and coyote. Birds aren’t immune either and a recent survey revealed that 895 species – one-tenth of all known bird species – have been recorded breeding with another species in the wild to produce hybrid offspring.29 Among captive birds the figure is even greater – 1500 species have been recorded breeding with another species (incredibly, over fifty of these with canaries). A recent study on the Galapagos Islands showed that different species of Darwin’s finches sometimes hybridise and that their offspring often reproduce successfully with one or other of the parent species. Just as with plants, hybridisation may – occasionally at least – be a way of introducing new and beneficial genes into animal species, allowing very rapid evolution and the creation of new species, a result Hans Duncker would have found distinctly reassuring.
Some bird keepers disapprove of rearing mules, not because it goes against the will of God or nature, but because they see it as a dead-end exercise. In all other branches of the fancy, breeders select for better birds each generation, creating a sense of continuity and improvement – something completely lacking in mule and hybrid breeding. Undeterred by such views, breeders produce mules and hybrids either for exhibition or for song, but in both cases only males qualify. Females do not have enough colour to make them attractive as show birds and, of course, only the males sing. Most breeders therefore discard their cross-bred females at the earliest opportunity, unless they represent an extremely unusual hybrid. Through a strange quirk of genetics, however, male birds almost always greatly outnumber females among cross-bred offspring.
Buffon was among the first to comment on the unusual sex ratios among hybrids.30 When he was preparing the canary section of his enormous multi-volume natural history encyclopaedia his friend Père Ignace Bougot the local priest told him of a hen canary paired to a male goldfinch that had laid nineteen eggs giving rise to sixteen male and three female offspring. Buffon quipped that this was ‘a greater inequality than ever takes place in a pure breed’ – a pattern confirmed by subsequent breeders including the Scottish eye surgeon Rudolf Galloway whose records revealed that of 135 mules he produced between 1904 and 1908 and whose sex he established, no fewer than 110, or 81 per cent, were male.
Funny sex ratios had also been noticed in other hybrids. Among the mixed offspring of donkeys and horses there is always a preponderance of female foals – the opposite of what happens with birds. The brilliant evolutionary biologist J. B. S. Haldane was the first person to make sense of these unusual sex ratios. In 1922 he recognised that ‘when in the offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterogametic sex’, by which he meant the sex determining the gender of its offspring – an observation that has since become known as Haldane’s rule.
In humans and all other mammals, including horses and donkeys, males have two different sex chromosomes, an X and a Y, and when they make sperm, half of them carry an X and half a Y chromosome. Female mammals, on the other hand, have identical sex chromosomes – two Xs – and when they produce eggs, each egg has an X chromosome. When sperm and egg fuse at fertilisation, the resulting embryo always gets an X from its mother and either an X or a Y from its father. If an X sperm penetrates the egg the resulting embryo will be female (XX); if a Y sperm enters the egg, the offspring will be male (XY). So in mammals the male is the ‘heterogametic’ sex and determines the sex of the offspring. In birds and butterflies things are the other way round and females are the ones with the different sex chromosomes. It was Florence Durham, William Bateson’s research assistant, who discovered, during her studies of canaries in 1908 that in birds it was the female who called the shots regarding the sex of the offspring. Bateson was grappling with the same problem at the same time, using chickens, but canaries proved a more tractable system and Florence beat him to it.31 To his credit, Bateson, generally considered something of a bully and a sexist, allowed her to publish her findings without including him as an author – not something that would readily happen for such a momentous discovery in today’s ruthlessly competitive academic environment.
The crux of Haldane’s rule is that, among hybrids, if you are the sex with different sex chromosomes you are more likely to be sterile or dead, presumably because when the genomes of the two species fuse at fertilisation, the sex chromosomes prove unwilling partners.
Haldane’s rule has huge implications for the origin of species. Once two races or incipient species fail to produce viable offspring, or if their offspring are sterile, they are on their way to becoming separate species. His rule hinges entirely on the incompatibility of the sex chromosomes of different species, but despite eighty years of research, the way sterility or inviability is imposed on hybrid offspring remains a mystery. We do not know whether Duncker was aware of Haldane’s 1922 paper, but he certainly knew of Florence Durham’s findings, and he knew that among mules, males invariably outnumbered females. What is strange is that in compiling the evidence for his ‘rule’, Haldane seems to have been completely unaware of the extensive information available from bird keepers – even scientifically respectable ones like Galloway.32
The rumours that Duncker was hearing about the existence of red siskin x canary hybrids were true and they started to unfold at exactly the time he began his red canary project. Several fanciers had apparently reared red siskin mules and, just as the Spanish bird keepers had said, some of them were fertile when paired back to canaries. Even more encouraging, Duncker learned that two bird keepers, A. Dams and Bruno Matern in Prussia,33 had managed to produce ‘doppelbastards’, that is, double hybrids: offspring from breeding two red siskin mules together.
The success achieved by these amateur bird keepers made Duncker extremely optimistic about producing a red canary and in the late spring of 1926 he began his quest by pairing red siskins to ordinary yellow canaries. This first phase of the project was straightforward. Many of the eggs were fertile, and by the end of that season he and Reich had produced a respectable number of mules. Phase two, conducted the following year, involved pairing male and female mules together – just as Dams and Matern had apparently done. But this time there was no success. Only a few of the birds, mainly the males, showed any sign of breeding, and none of the very few eggs laid were fertile. It must have been a depressing time for Duncker and Reich. And they were puzzled. If others could get mules to breed together why, then, couldn’t they? It looked as though, despite all Cremer’s funding, they were going to fall at the first hurdle.
Fortunately they persisted.