Study

Birds sing at a higher pitch in urban noise

Slabbekoorn, Hans; Peet, Margriet

Nature, 2003

Peer-reviewedfield observationwild

What they did

Great tit song was recorded across territories in a city spanning a wide range of background noise levels, and the minimum frequency of song was compared against the measured ambient noise at each territory.

Studied in: Parus major
Sample size: great tit territories across an urban noise gradient in Leiden

What they found

Birds in noisier territories sang with a higher minimum frequency, with the relationship holding across the gradient within a single city.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Great tits adjust song frequency upward in noisy environments, plausibly reducing masking by low-frequency traffic noise.

How NatureHQ reads it

The origin of one of the most repeated claims in urban ecology, and the gap between what it shows and what gets said is instructive. It is a correlation across territories within one city in one species — a real, well-measured correlation, and not a demonstration that noise causes the shift, that individual birds adjust, or that the shift helps. The claim as it circulates ("city birds sing higher because of traffic") asserts all three. The later amplitude work below is what complicates it most.

Limitations

Observational: noisy territories differ from quiet ones in vegetation, building density and disturbance as well as in noise.
A between-territory comparison cannot distinguish individual adjustment from birds with higher songs settling in noisier places.
One species in one city; the effect is inconsistent across species and cities in later work.