Today, I began reading Stephan Jay Gould's collection of essays on natural history, Ever Since Darwin, and came across this passage in the book's fourth essay, "Darwin's Untimely Burial":

One might think that the first chapter of such a revolutionary book as Origin of Species would deal with cosmic questions. It doesn't. It deals with pigeons.

• Zero One

To their surprise, Penzias and Wilson found in the spring of 1964 that they were receiving a sizeable amount of micro-wave noise at 7.35 centimetres that was independent of direction. They also found that this 'static' did not vary with the time of day or, as the year went on, with the season.

Clearly it was necessary to reconsider whether the antenna itself might be producing more electrical noise than expected. In particular, it was known that a pair of pigeons had been roosting in the antenna throat. The pigeons were caught; mailed to the Bell Laboratories Whippany site; released; found back in the antenna at Holmdel a few days later; caught again; and finally discouraged by more decisive means.

However, in the course of their tenancy, the pigeons had coated the antenna throat with what Penzias delicately calls 'a white dielectric material', and this material might at room temperature be a source of electrical noise. In early 1965 it became possible to dismantle the antenna throat and clean out the mess, but this, and all other efforts, produced only a very small decrease in the observed noise level. The mystery remained: where was the microwave noise coming from?