Loud townsfolk, quiet country bumpkins
City air is said to speed up the rhythm of life, making everyday urban life more hectic and sometimes less talkative. Even European great tits cannot escape this trend compared to their rural cousins.
What an idyll – somewhere in the country, far away from the next main road or the next provincial airport, no farmer works, no forest worker lets the chainsaw howl, and no notoriously loud hiking club outing disturbs the silence. In the distance you can hear the hammering of a woodpecker, bees are humming, now and then a cuckoo lives up to its name, blackbirds, thrushes, finches and titmice are chirping in the treetops or from the forest floor. Life progresses rather leisurely here.
The city is completely different: cars rush by, jackhammers rip the asph alt like an eardrum, occasionally a techno parade passes by, alcohol-intoxicated pub-goers at night use verbal insults or romantic booze to tell plagued residents that they are the innkeeper and despise his curfew or adore certain ladies or football clubs. In short, in addition to many conveniences, urban life certainly has an increased noise level that strains the nerves, damages he alth in excess and sometimes disrupts communication. After all, it's hard to yell at yourself against the noise.
This also applies to birds, which rely heavily on verbal exchanges to attract females, mark out territory or warn of the neighbor's kitty lying in wait. How do the Piepmätze remedy this? Do they flee the noise? Or do they adapt to the background noise? Questions that the Dutchmen Hans Slabbekoorn and Ardie den Boer-Visser from the University of Leiden have been investigating in great tits (Parus major) for some time.
These songbirds are among the most assertive urbanists, they flutter through every city park and don't shy away from the busiest pedestrian zones as long as there is a little puny roadside greenery. Slabbekoorn and den Boer-Vissen have now evidently decoded one of their secrets of success in a comparison of ten metropolitan and adjacent forest populations of the species from all over Europe: the animals whistle appropriately for their urban or rural environment. Whether in Berlin, Prague, London or Amsterdam - great tits, which are confronted with a lot of dull background noise, intoned their songs everywhere in higher frequencies than their relatives in the much quieter surrounding regions and avoided low tones that could be swallowed up by the hum of traffic, for example.
The high-pitched pitches clearly set them apart from the city's low-frequency background noise, but that wasn't the only innovation the researchers noticed. In this way, the birds also adapt to the urban hustle and bustle by singing shorter and faster, while the rural conspecifics take more time to modulate and develop their performances. The townsfolk simply shorten the intervals between each repetition. On the other hand, the frequently made statement that agglomerations such as Brussels or Paris are the source of inspiration and epicenters for innovations was confirmed: the town tits less frequently intoned the songs with two to four notes that were generally typical of the species, at least in the past, and instead used unusual song lines more frequently, which sometimes consisted of only one note, sometimes five notes. In Rotterdam, the two biologists even discovered a specimen that performed a 16-note piece and incorporated elements from the blue tit (Parus caeruleus).
But the urbanized great tits are not alone in their art. Nightingales (Luscinia megarhynchos), for example, also turn up the heat the louder the traffic noise. After all, as Slabbekoorn and Boer-Visser point out, it still saves energy for the birds to sing louder than to get caught up in exhausting territorial battles just because the rival didn't hear the demarcation song for lack of tonal assertiveness. Not to mention the lack of offspring if the female doesn't find one just because it starts making soft sounds. And corvids that are capable of learning, such as jackdaws and magpies or starlings, imitate the noises of their surroundings in a variety of ways, such as cell phone ringtones or squeaky swings, as ornithologists repeatedly report from German and British cities. The tone sequence must not be too complicated. However, some species also use higher pitched sounds when there is a lot of ambient noise in natural background noises: chaffinches (Fringilla coelebs), which live near roaring waterfalls or rapids, rely on this stylistic device to draw attention to themselves.
It is possible that this adaptability - or a possible lack of it - is also a reason for the different successes of individual bird species in urbanized regions, as the two Dutchmen add. Because species whose song originally covers a wide frequency range and who can adapt it flexibly to their environment have a clear advantage over representatives who are determined to pitch and variability at an early stage. In the case of zebra finches (Taeniopygia guttata), which are popular in behavioral research, the melodies are already established in the first few months of life and later it is probably difficult to adapt to new life situations. The song could also be one of the reasons why the same, rather loud species live in European cities, while quieter representatives disappear.
But whether the urban and rural great tits can no longer communicate with each other and are therefore already on the way to becoming independent species is very questionable. Eventually, their ranges overlap in the suburbs, where they continue to mate happily. A study by the British nature conservation organization Royal Society for the Protections of Birds showed years ago that city life is not always fruitful, even for noisy birds. Traffic noise on streets with up to 60,000 cars a day disturbed the behavior of the birds within a radius of about three kilometers, that of quieter traffic axes with 10,000 cars still within a radius of one and a half kilometers. The result: they had fewer offspring.
