On a small island off the coast of Scotland, volunteers have counted seabirds every June since 1969. They walk the same cliff paths, look at the same ledges, and write numbers in a notebook. It is slow, repetitive work, and it has produced something no satellite could.
A single year of counting tells you almost nothing. Seabird numbers swing wildly with weather and food. One cold spring can halve a colony, and a good year can bring it back. Anyone who counted in 1991 and again in 1992 would have drawn a dramatic and completely wrong conclusion.
Fifty-seven years of counting is different. Across that span the noise averages out and a slope appears. For several species on that island the slope points down, steadily, in a way no single decade made obvious. Researchers were able to line the decline up with changes in the temperature of the surrounding water, and through that with the small fish the birds depend on.
None of this was planned as a climate study. It began because a few people liked birds and thought somebody should write the numbers down. The value came entirely from doing the same thing, the same way, for a very long time — which is also why such records are so easily lost. A gap of five years cannot be filled in afterwards. The data only exists if somebody walked the path that June.
Vocabulary in this text
- volunteer /ˌvɑlənˈtɪɹ/ — someone who works without being paid
- notebook /ˈnoʊtˌbʊk/ — a book of empty pages for writing
- satellite /ˈsætəˌlaɪt/ — an object sent into space to orbit the Earth
- span /ˈspæn/ — to extend across a period or distance
- average /ˈævɚɪdʒ/ — the result of adding values and dividing by their number
- appear /əˈpɪɹ/ — to become possible to see, or to seem
- species /ˈspiʃiz/ — a group of animals or plants of the same kind
- decade /dɛˈkeɪd/ — a period of ten years
- obvious /ˈɑbviəs/ — easy to see or understand
- temperature /ˈtɛmpɹətʃɚ/ — how hot or cold something is