Of the currently recognized 253 bird families, species in 75 have been observed and reported visiting flowers to consume nectar, pollen, and/or petals—some 1,390 species. The actual number is likely to be higher, given that many tropical forest trees with flowers in canopy foliage are challenging to study and in regions thus far little visited by either botanists or ornithologists focused on this intriguing phenomenon. What’s known from combining the 2 disciplines is that 6% of flowering plants are pollinated, at least in part, by birds—approximately 18,900 plant species. The relationship is old: avian fossils of likely pollinators have been found in Europe from 40 million years ago, when the area was covered in tropical forest, and fossils of 3 hummingbirds, once inhabitants of that continent, are dated to 30 million years ago.
For birds with a taste for sugars, the benefits of extracting nectar from flowers are obvious. Some...