Since 1928, thousands of chimney swifts have roosted at Fleming
Hall, a university building in Kingston, Ontario. For decades,
they fed on local insects, and excreted the remains down one of
the building’s chimneys. Around 2 centimetres of droppings, or
‘guano’, built up every year until the chimney was finally
capped in 1992. To this date, Fleming Hall contains a hardened
guano tower, two metres tall and 64 years in the making, which
preserves a layered record of the swifts’ meals. Now, a team of
scientists, led by Joseph Nocera, have used this archive of
historical poo to explain why the swift populations have fallen
by 90 per cent since their heyday. The guano tower was
discovered by Chris Grooms from the Kingston Field Naturalists,
who brought it to the team’s attention. They reached it via a
2-foot-wide square door at the bottom of the chimney, and found
a two-metre-tall column. “One has to be somewhat of a
contortionist to get in,” says Nocera. “The guano is compacted
and very dry, like a popcorn-cake.