Bird Sense (20 page)

These studies confirmed that, despite their relatively small number of taste buds, birds respond to the same taste categories – salt, sour, bitter and sweet – as we do. (It is not known whether they respond to the most recently discovered taste category, umami – savouriness.) We also know that hummingbirds can taste differences in the amount of sugar in nectar, that fruit-eating birds can distinguish between ripe and unripe fruit – on the basis of its sugar content – and that wading birds such as sandpipers can taste the presence of worms in wet sand.
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On the other hand, birds and humans are known to respond very differently to certain tastes. Birds seem to be indifferent to capsaicin, the substance that for us makes chilli peppers hot; indeed, in the late
1800
s bird breeders fed red peppers to their canaries to turn their plumage red, and the birds ate them with no evidence of discomfort.
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Despite this, a major article on taste in birds published in
1986
concluded: ‘Research on taste in birds has been handicapped by the general assumption that they live in the human sensory world.’
16

In
1989
, Jack Dumbacher, a PhD student at the University of Chicago, made a remarkable discovery: he found the world’s first distasteful bird. Jack was studying Raggiana birds of paradise in Varirata National Park, Papua New Guinea. He and his fellow students set nets to catch their birds of paradise, but, as often happens, they caught other species as well. One of the commonest bi-catch species was the hooded pitohui (phonetically: pit-oh-wheez), a bird with striking orange and black plumage. The pitohui were a nuisance, not least because they smelled and were always feisty on being removed from the net. On one occasion a bird scratched Dumbacher as he was handling it, breaking the skin. Not long after, while sucking the wound, Dumbacher became aware that his mouth had become numb. At the time he thought little of it, but when another student reported the same thing some time later he began to wonder if there was something special about the pitohui. There wasn’t time that season to check, but the following year Jack took a single feather from a pitohui he had just caught and tasted it. The effect was electric. There was something extraordinarily unpleasant on the feathers.

When Bruce Beehler, Dumbacher’s PhD supervisor, visited a few months later, Dumbacher told him what he had found, wondering modestly whether it might make an interesting note for a local bird journal. Beehler erupted: ‘Are you telling me you’ve found a poisonous bird? . . . This should be on the cover of
Science
! Turn the car around! We’re going back to town to get permission to study this bird!’

Bruce Beehler probably knows more about New Guinea birds than almost anyone else – he wrote the definitive
Birds of New Guinea
– and he recognised immediately that Dumbacher had made an extraordinary discovery. He was amazed that no one had previously commented on the hooded pitohui’s toxic feathers – the species had been known to science since the mid-
1800
s, it was common locally and there were dozens of skins in museums across the world.

In fact the local people
did
know all about the hooded pitohui – they called it the
wobob
, which literally means ‘the bird whose bitter skin puckers the mouth’. It was one of Dumbacher’s colleagues who told him that the pitohui’s unpleasant taste had previously been described in ‘an old book’ written by a New Zealand anthropologist, Ralph Bulmer, with a local man, Ian Seam Majnep. Old? When I checked, I discovered that the book had been published as recently as
1977
. When Dumbacher checked, he was surprised to learn that, in addition to the
wobob
, local people knew of yet another distasteful New Guinea bird, this one from the highlands: the blue-capped ifrita (a species that behaves like a nuthatch),  known locally as
slek-yakt
, meaning ‘bitter bird’.
17

Dumbacher wondered what the toxin on the feathers of these birds was and, by an extraordinary stroke of luck, was directed to the only person in the world who could help him find out. John Daly, a pharmacologist at the National Institute for Health, had spent years studying the toxins (so-called batrachotoxins) produced by South American dart poison frogs. As Dumbacher told me:

I was also incredibly lucky to have teamed up with the one chemist in the world who could have isolated and identified batrachotoxins easily in the lab. We were so skeptical about our initial findings (partly because . . . it seemed so unlikely that these toxins would turn up in a New Guinea bird) that we repeated the extractions on several birds before believing the results. But there they were, and after much collecting and work, we even described several new batrachotoxin compounds [from the birds] that had not previously been recovered from the frogs.
18

The toxins in the feathers and skin of the pitohui are derived from its diet (as they are in other toxic animals), in this case from melyrid beetles. The new batrachotoxin is more toxic than strychnine. Indeed, when extracts from pitohui feathers were injected into mice, they had convulsions and died – fairly convincing evidence for toxicity.

Ongoing research by Dumbacher and colleagues revealed a total of five toxic birds in New Guinea (so far): the hooded, rusty, black and variable pitohuis and the blue-headed ifrita, all with the same toxins and all often emitting a powerful, acrid odour. The toxins may have evolved initially as a way to keep feather-eating lice at bay, and only later developed to deter larger predators. Jack Dumbacher has never seen a bird of prey attempt to catch or kill one of his distasteful birds to observe its reaction, so we don’t know whether they would find it unpalatable. He has, however, conducted experiments with snakes and told me: ‘Brown tree snakes and the green tree python both react strongly to the toxins and appear distressed and generally irritated by it, but we were not able to do sufficient experiments to confirm (or refute) that these snakes learn to avoid the toxins.’ He also said: ‘I personally suspect that the greatest benefits of the toxins accrue during nesting, and help protect the otherwise defenceless nests (eggs and young) or roosting birds from predators. An earlier description of a single hooded pitohui nest suggests that downy chicks are brightly colored, and I have always wanted to find an active nest to test for toxins, but I have never been so lucky.’ Dumbacher’s idea is that the substances from the adults’ feathers rub off on to the eggs during incubation and help deter egg predators such as snakes.
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Dumbacher and Beehler duly published their paper in
Science
in October
1992
– with a cover photograph – alerting the scientific world to the presence of distasteful, poisonous birds.
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It prompted researchers to tell them about other birds that appeared to be toxic. These included the story of John James Audubon, who boiled up the carcasses of ten Carolina parakeets he had shot (the bird is now extinct) for his cat, specifically to see if they were poisonous. He doesn’t say, but the cat disappeared, and he commented on the fact that seven cats had died the previous summer from eating ‘parokeets’. The birds fed on cocklebur seeds – known to contain a toxin – so they probably were poisonous.
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Another intriguing example is the suitably conspicuous red warbler of Mexico, described in the Florentine Codex – the pre-Columbian account of Aztec flora and fauna – as inedible. Prompted by Dumbacher’s discovery, researchers revealed that the feathers of the red warbler contain alkaloids, which, when injected into mice, caused ‘unusual behaviour’.
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This particular study is tantalisingly incomplete: a wonderful opportunity for a Mexican ornithologist and biochemist to collaborate.

Because no one has so far witnessed a predatory bird catching a pitohui or an ifrata, we simply do not know how it would respond. Would it react like Jack Dumbacher or the snakes he tested – with disgust and rejection? My guess is that it would.

New Guinea’s distasteful but brightly coloured birds were similar to Darwin’s and Wallace’s caterpillars in which bright colours serve as a warning:
Don’t eat me, I’m distasteful
. Neither Darwin nor Wallace ever imagined this might also be true of birds, mainly because so many birds – duck, woodcock, even larks and thrushes – are to us extremely tasty.

Jack Dumbacher’s discovery showed convincingly that birds could be distasteful and that distastefulness was linked to bright plumage. Yet this was not without precedent, for fifty years earlier this had been a hot topic of research.

In October
1941
Cambridge zoologist Hugh Cott (
1900
–
87
) was serving with the British Armed Forces in Egypt. He was on a week’s leave and was skinning some birds he had shot and preparing them as museum specimens. As did so, he noticed something unusual. Beneath the table at which he worked lay the carcasses of a palm dove and a pied kingfisher. Hornets were feasting on the palm dove, but ignored the pied kingfisher lying alongside it. The dove was cryptically coloured, the kingfisher a striking black and white. This set Cott thinking. He was already fascinated by the colour of animals and his book
Animal Colouration
, now a classic, had been published the previous year.
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As Cott later said, his hornet encounter was ‘a good example of the way in which a chance and quite unexpected observation may suggest and lead to a fruitful and little explored line of enquiry’.
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At this time the idea that the bright plumage of birds might serve to protect them from potential predators was entirely novel, and over the next twenty years Cott pursued it relentlessly. Using hornets, cats and people as his ‘tasters’, together with accounts from fellow bird-eaters, Cott assessed the palatability of species as diverse as hoatzins, hawfinches, hoopoes and house sparrows. He concluded that the really palatable birds, like woodcock, grouse and pigeons, are dull- or cryptically coloured, whereas distasteful species are more colourful – warning colouration. His discovery led to a paper in
Nature
in
1945
.
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Cott’s study, however, is full of holes. Part of the problem, it would be fair to say, is that the nature of scientific investigation has changed enormously since the
1940
s, and Cott’s methods, which at best seem merely quaint, are by today’s standards simply inappropriate. In scoring the plumage brightness of birds, for example, Cott used only females, ignoring the (inconvenient?) fact that males and females are often strikingly different. He assumed (but never checked) that males and females tasted the same. Cott also tasted only the flesh, and cooked flesh at that, unlike Dumbacher, who (albeit accidentally) tasted the pitohui’s feathers – which, after all, is what predators would encounter first. As we have seen, human senses do not necessarily provide a good measure of avian senses, so what tastes bad to us may not taste bad to a raptor or a snake. We also know that some of Cott’s informants were unreliable – to say the least.
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It is unlikely that anyone will ever redo Cott’s study using more rigorous methodology, but, as far as I am concerned, the question of association between plumage brightness and palatability across birds
in general
remains open. Since there is good evidence that plumage brightness plays an important role in avian mate choice, any reappraisal of colour and distastefulness would need to take this into account, too. On the other hand, we now know that some birds at least have a well-developed sense of taste and learn to reject certain insects on the basis of this. In principle it would not be that difficult to undertake some simple behavioural tests to discover if certain birds are distasteful to their predators. One could, for example, give some captive New Guinea raptors a piece of meat (just enough to test their reaction without putting them at risk . . .) wrapped in pitohui feathers, to see how they respond.

We can end this chapter by confirming that birds do indeed have a sense of taste. It isn’t staring us in the face, so it has been underresearched, but it is there. Our knowledge of which birds have this ability is still limited and it would be wonderful if someone were to undertake a really comprehensive survey, perhaps using brain-scanning technology as a rapid way of screening a large number of species. I recognise that to some readers our lack of knowledge about what birds can or cannot taste may seem frustrating, but, as a researcher, I look on this as an opportunity. The field is wide open, with fabulous opportunities for discovery!