Few birds have such an ambivalent relationship with humans as the swifts. On the one hand, the ongoing destruction of habitats and food resources, the rampant and highly lucrative trade in “edible bird’s nests” – the nests that South-East Asian swiftlets build from their own saliva – and the use of insecticides and herbicides have become a serious threat to many swift species. On the other hand, many species benefit as synanthropes from an abundant supply of nesting sites on human buildings and in ornamental plantings, e.g. palms.
Of the roughly 94 species of the Apodidae, six have been placed on the Red List of the International Union for Conservation of Nature (IUCN), among them – tellingly – five swiftlets of the genus Collocalia. Overall, the proportion of threatened species within the family is therefore below the worldwide average of a good 10 % of threatened bird species (STATTERSFIELD and CAPPER, 2000).
The Common Swift is one of those bird species that, in historical times, spread very rapidly in the wake of human settlement, right up into northern latitudes (GLUTZ and BAUER, 1980). Originally breeding in the wild, where it used tree cavities and rock crevices as nesting sites, it found almost ideal breeding conditions in human cities: nesting places in the walls and gables of tall buildings, safe from predators and equally well insulated against cold and heat. In some regions of southern Europe, nesting sites were even created especially for it – though hardly out of altruism: towers with access to the nests, from which, towards the end of the nestling period, all but one of the young were taken, killed and eaten (BREHM, 1922). The original natural breeding sites lost almost all their importance for the Common Swift; today only a few tree-nesting colonies remain – in Germany, for example, in the Selke valley.
Yet this initially sensible “evolutionary opportunism” is now turning into a growing threat to the Common Swift. In its choice of nesting site, this species, which breeds exclusively in Europe, has become completely dependent on humans. During building renovations and roof work, however, more and more sites of long-established swift colonies are being destroyed and sealed up, partly deliberately, partly out of sheer ignorance. On the one hand, the trend towards the hostile, sterile big city is advancing rapidly, especially in Western Europe, and in renovations as well as in new buildings hardly any thought is given to providing opportunities for the animals that once shared our homes. On the other hand, the Common Swift finds it extremely hard to take up new breeding sites, returning instead undeterred, year after year, to its familiar nesting place.
There is therefore reason to fear that, without active conservation measures, these birds – still common today, and for centuries the enlivening presence in the summer evenings of our cities with their aerial displays and calls – will vanish from our towns and villages just as inexorably as they once conquered them.