Audubon's Dr. Paul Gray reports on the recent (rare) occurrence of the planet Venus passing between the earth and the Sun twice in eight years. Why is this important for birds? Learn more below! Enjoy:

On June 5 and 6 of this year, the planet Venus passed directly between the earth and Sun for the second time in 8 years, leaving its shadow during the passage.  The paired transits occur about once every 120 years, and the pair of transits in 1761 and 1769 helped increase the number of bird species known in the world.

The 1769 transit was not visible from Europe, thus a series of expeditions were timed to carry astronomers to Siberia, Madagascar, New Guinea, the Pacific, and Norway to study the event (measurements allowed a more precise calculation of the distance of the earth from the Sun, and confirmation that Venus had an atmosphere).  In addition to astronomers, the expeditions carried naturalists who found myriad new bird species[1].

The late 1700s was a time of accelerating interest in birds and natural history, especially new birds from new lands. It was customary for the seafaring European countries to place scientists on these voyages, so they could describe the geography, geology, and natural resources that might be profitable for that nation to exploit. Scientists of the age were versed in many disciplines, as was the case for Charles Darwin on his famous voyage on the Beagle (after these transit expeditions); he was primarily a geologist by training.

One transit voyage was a land journey to Siberia from Russia, carrying the German scientist Peter Pallus (1741-1811; Pallus’s Gull and 12 other old world birds), where his journals reported six new species of birds, and myriad plants and animals.  The English Captain James Cook was making one of his round-the-world voyages during the transit, arriving in Tahiti in 1769, and bringing back collections of 28,000 mostly-new specimens. French King Louis XV sent Louis Antoine de Bougainville in a circumnavigation with only one naturalist on board, Philibert Commerson.  Commerson was primarily a botanist but has a patronym for Commerson’s Scops Owl (now extinct) and discovered a vine we love and hate in Florida, the bougainvillea, named for his Captain.

Many of the specimens collected during these early voyages have been lost to mishaps through time, and if not lost, bird skins decomposed (arsenic use was not widespread by this time). All of Cook’s birds are gone. Many of the descriptions were qualitative and the identity of some of the birds have never been verified.

Interesting to me, is some of the best records extant from the period were from artists, whose illustrations still clearly show the bird in question.