One flew over the cuckoo´s nest

As a child, I was very upset when first learning about cuckoos and their brood parasitism. I considered cuckoos to be EVIL. Later, I was relieved to hear that all cuckoos aren't parasitic. At least the Cuculiformes as a whole weren't TAINTED. Naturally, I cheered inwardly when I read that Great Reed Warblers sometimes attack cuckoos, force them under water, and make them DROWN.

LOL!

OK, after this introduction, written just to get your attention, let's say something about the book...

Scientific works written for a narrow audience are often dry, technical and incomprehensible for out-siders (and sometimes you wonder whether even insiders understand them - J.F. Haldon's scholarly tomes on the Byzantine Empire comes to mind. Does *anyone* understand Haldon?). This book, while certainly not "popularized" in the traditional sense of the term, is one of the few exceptions. It's surprisingly easy to read, well-organized, comprehensive, and interesting. There's even something uncannily catchy about it. Had I read a book like this while in high school, I might have ended up as an ornithologist! Or at least a natural science writer for some magazine (my math grades were, well, bad).

"Cuckoos, Cowbirds and other cheats" by N.B. Davies is a comprehensive, scientific survey of brood parasitic birds, with emphasis on how co-evolution between parasites and hosts have shaped their respective behavioral patterns. Many other aspects of brood parasitism are covered as well. I found the historical overviews particularly fascinating. Did you know that the first known record of birds parasitizing other birds of the same species can be found in the Biblical prophecies of Jeremiah? Or that the first record of parasitic cuckoos comes from the Vedic scriptures of India? That the Common Cuckoo is a brood parasite was known by Aristotle, and modern biologists who want information on how fast cuckoos can change host species, might do well to study Chaucer and Shakespeare! Incidentally, it's obvious that Davies is British. Would American ornithologists feel at home in the world of British literature? I don't think so.

For those less literary inclined, the book contain informative and extensive chapters on the Common Cuckoo, Bronze-Cuckoos of Africa and Australia, the Great Spotted Cuckoo, honeyguides, cowbirds, parasitic finches, and conspecific brood parasitism. Thank god I didn't read this book as a kid: it seems everyone in the bird world parasitizes everyone else!

As already indicated, the main theme of the book are the evolutionary puzzles laid out by the phenomenon of brood parasitism. Many birds recognize their own eggs, and may therefore reject eggs laid by cuckoos or other brood parasites. To cope with this, cuckoos have evolved mimetic eggs, i.e. eggs that look like the eggs of their host species. However, very few birds seem to recognize their own chicks! Thus, cuckoo chicks usually don't have to mimick the young of their host species. This creates a rather uncanny situation: the host species may attack cuckoos flying across their territory, and evict cuckoo eggs that are markedly different from their own, but if they are fooled by a mimetic egg, they will uncritically accept the cuckoo chick, even when it's obviously different from their own chicks. How is it possible for birds to recognize obviously foreign eggs, but not obviously foreign chicks? This is one of the mysteries adressed by this book.

The plot thickens further, when we realize that there are cases where birds *can* tell the difference between their own chicks and foreign chicks. In South America, the Screaming Cowbird parasitizes the Baywinged Cowbird. Chicks of both species look identical, presumably an evolutionary response by the parasite to avoid being evicted by the host species. But the cowbirds are "stupid" small passerines. Why can a Baywinged Cowbird tell the difference between its own chicks and foreign chicks (unless the latter has evolved perfect mimicry), while the more intelligent corvids, parasitized by the Great Spotted Cuckoo, don't evict the parasite, although they look different from corvid chicks? Another mystery. One intriguing theory discussed by Davies is that the Great Spotted Cuckoo might use "Mafia tactics" to force Magpies into accepting their chicks. The Magpies do recognize the cuckoo chicks as foreign, but tolerate them anyway, since the adult cuckoo might otherwise attack and kill the Magpie chicks! (In contrast to the Common Cuckoo, the chick of the Great Spotted Cuckoo doesn't evict the chicks of the host species, but is raised together with them.)

To the American reader, perhaps the section on cowbirds is the most interesting (and disturbing). Above, I mentioned my childish teleological notions about cuckoos. It seems many adult Americans consider cowbirds to be even more evil than cuckoos! The Brown-Headed Cowbird is a small passerine that indiscriminately lay its eggs in the nests of over 100 other species of birds. Due to habitat change, the Brown-Headed Cowbird has become more and more abundant the last century or so, not giving its new hosts time to develop egg or chick discrimination. In some parts of the USA, cowbird parasitism have almost driven other passerines to extinction! The Kirtland's Warbler, endemic to a small part of Michigan, was almost exterminated by cowbird parasitism, until the proper authorities trapped and removed over 90,000 cowbirds (during a period of almost 20 years) from its breeding area. Other birds threatened by the Brown-Headed Cowbird include the Black-Capped Vireo, the Least Bell's Vireo, and the Southwestern Willow Flycatcher. A similar problem exists on Puerto Rico, where another parasitic passerine, the Shiny Cowbird, have established itself, threatening an endemic blackbird. Small wonder a certain US ornithologist recommend that any cowbird that reaches Europe should be immidiately shot on sight, no further questions asked!

But, as the author points out, the main culprit in the sad story of the cowbirds isn't the little bird itself, but humans. The Brown-Headed Cowbird was originally a bird of the great plains, where it followed the buffalo. With the near-extinction of the buffalo, the cowbirds switched to follow human-raised cattle, becoming even more abundant, and the turning of forests into farmland have exposed other passerines to cowbird parasitism, apart from the ususal problems associated with habitat destruction.

Perhaps inevitably, the most interesting chapter in the entire book is also one of the shortest: "Cheating on your own kind", about conspecific brood parasitism. The natural world is truly bizarre, filled with mysteries, wonders and plain absurdities, and some of these are recorded in this chapter. Snow Geese parasitize each other on a semi-regular basis. The parasitic female lays her egg on the ground, close to the nest of another female, and absconds. Then something spectacular happens: the nesting female accepts the foreign egg and gently rolls it into her own nest, despite the fact that she has seen the parasitic female laying it, and thus knows that the egg is foreign! The reason: a visible egg just outside a nest might help predators, such as skuas and gulls, to find the nest, attack it, and eat *all* the eggs. Thus, the only alternative open to the Snow Goose is to quickly accept the egg of the parasitic female, and treat it as one of her own. Even more sensational is the behavior of Ostriches. It seems that Ostriches voluntarily accept eggs of other, parasitic, Ostriches. The reason is selfish: if the Ostrich nest is attacked by predators, and contain both eggs of the resident female, and eggs of other females, there is a fifty-fifty chance that the predators eat the foreign eggs, thus saving at least some of the "native" eggs. To top it all off, there is even a bird, the White-winged Chough, that wants to have foreign fledglings, and actively tries to kidnap them from other families of the same species!

The final chapter of "Cuckoos, cowbirds and other cheats" discusses how and why brood parasitism might have evolved in the first place. The author takes issue with a British theologian, Charles Raven, who questioned whether brood parasitism could have evolved in a gradual, piecemeal fashion. Davies believes that this is perfectly feasible. He points out that many non-parasitic birds behave in a manner similar to parasitic birds.

For instance, young Kittiwakes, egrets, boobies and Cactus Wrens habitually evict their own siblings from the nest, often quite brutally. The chicks of the Blue-throated Bee-eater in Malaysia have hooks on their beaks, and if food is scarce, the older chicks attack and kill the younger ones. The same phenomenon can be observed among brood parasitic honeyguides and the Striped Cuckoo. There simply isn't any family harmony among the non-parasitic species, and plenty of behavioral patterns that natural selection can mould into all-out parasitism.

Another interesting observation in this regard concerns the cowbirds. The only non-parasitic cowbird, the Bay-wing, habitually attacks and takes over occupied nests of other species, while the parasitic Shiny Cowbird occasionally attempts to build nests, perhaps suggesting that parasitism have evolved from nest-building through an intermediary stage where the cowbirds nested, but in nests stolen from others. The parasitic finches in Africa are also closely related to species that take over nests of others, or species where only the males are involved in nest-building, with the females roaming at large. There are also many examples of nesting birds that occasionally parasitize other species to enhance their reproductive success, which could lead to all-out parasitism given enough time and selection pressure.

This book is WARMLY recommended.