Birds prove they are fly when it comes to moving with the times

John M. Marzluff

Yale University Press,£18.99

Everything John Marzluff has been taught as a biologist suggests that urban sprawl is terrible news for biodiversity. His academic colleagues regard cities as "unmitigated ecological disasters." Most of the time they are correct but there seems to be a cheering exception to the rule. Birds, or at least some of them, have learned to live and even thrive in the modern cityscape. Marzluff tells this tale of amazing avian adaptation and offers us some hints about how to make things better. In these gloomy ecological times there is considerable relief in picking up a natural history book with a potentially happy ending.

Marzluff has visited many cities and, wherever he travels, he notices the bewildering array of bird species. In Seattle, where he lives, there are bald eagles perching on street lamps and falcons nesting on skyscrapers. There are many less glamorous species in the suburbs, which appear to be the kindliest zones of all. The range of habitats, plants, and insects in "Subirdia" can be astonishing and, when things get tough, the man-made nesting-boxes and high-calorie bird food make life a little easier for our feathered friends. This, of course, is the least we can do. Humanity has not usually been kind to the birds and we have destroyed or transformed a staggering range of habitats - forests, prairies, shrublands and marshes. Thank goodness, then, that while "nature is fragile, it does not always break when bent."

It is important to note, of course, that almost all of the credit goes to the birds. Their ability to move with the times is astonishing. This can occur at two evolutionary levels. Within a few generations a species will adapt to its environment: the same kind of sparrow will be thinner in warmer climes and bulkier where the weather is less clement. Such genetic genius would "take even Darwin aback." "Cultural" adaptation is even more impressive. In order to "adjust to the hum of the city" birds learn, in no time at all, to sing louder, or in revised pitches and tempos. The humans build a golf course, a shopping centre, or an industrial estate and the birds exploit every possible opportunity. Sometimes, the most unlikely settings provide safe harbours. Who could have guessed that skylarks, linnets and partridges - three species in serious decline - would be so attracted to Dutch business sites?

This all sounds lovely but the lodestone of Marzluff's book is that the situation always remains precarious. Marzluff offers a few tips and I pick my favourites. Embrace a messy garden: less work for you, more food for the birds. Do everything you can to make your windows visible: who wants fledglings smashing into glass? Join every available campaign to keep night-time light pollution, which drives birds crazy, to a minimum.

Another of Marzluff's suggestions is more controversial. He tells us that cats kill as many as 3.7 billion birds in the USA every year and that the moggies in Bristol, UK, eat half the house sparrows. His solution is to keep all cats indoors. They'll likely live longer (no speeding cars or pesky parasites) and, needless to say, the birds will be delighted. This troubles me a little. I'm all for birds being birds, but a similar logic means that I also like the idea of cats being allowed to be cats.

This grumble aside (and I realise that it is likely to divide opinion), I have the greatest admiration for Marzluff's passionate book. He sets himself the task of distilling the latest specialist research for a wider audience and he succeeds triumphantly. There are many facts and figures here - concerning population numbers, infant mortality rates, life spans, and so forth - but they only enhance a clear, confident and convincing argument. Marzluff and his students have put in long hours of observation and they reveal a comforting fact: while we are busy ruining the planet, we have managed to create an unlikely web of natural coexistence in our backyards. More by accident than design, certainly, but it still counts.

The birds have been around for a very long time: 170 million years, give or take. They would doubtless have been happier if we had never built cities, but we did, and the birds have taken it in the avian equivalent of their stride. The results, for us, are spectacular. I have the humblest of suburban gardens but at least 30 bird species have paid a visit this year and there are few greater thrills than encountering something new. We are separated from nature, these days, and this can only be a source of cultural and spiritual impoverishment. The birds in our suburbs therefore take on extraordinary importance. Like anyone else, I can be annoyed when a magpie's early morning calls wake me up but I remind myself that the magpie would much rather be somewhere else: a tarmac-free landscape, for instance, where there would be no need to peck at discarded bags of chips in order to supplement the diet. We owe the birds countless favours, so do the decent thing: let your garden become a little scruffier and buy some dried meal worms once in while. Ecology begins at home. What you do with your cat is entirely up to you.