“Atypical flowers can be as profitable as typical hummingbird flowers”

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Nickolas M. Waser, Paul J. CaraDonna, and Mary V. Price (Nov 2018)

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Don’t ignore the unexpected! Our example: visits to “atypical” flowers can be surprisingly profitable for hummingbirds

A fledgling Broad-tailed Hummingbird (Selasphorus platycercus) feeding systematically from the tiny flowers of pinedrops (Pterospora andromedea). This parasitic plant is in the same family (Ericaceae) as manzanita (Arctostaphylos spp., see main text for details), and the flowers are similar in size and shape.
(© Audrey Boag, used with permission)

What is a hummingbird flower? It may not be what you expect! Nick Waser and Mary Price began to learn this lesson while camping as graduate students in the 1970s. They were repeatedly surprised to see hummingbirds systematically visiting flowers that lacked the characteristic features of “typical” hummingbird flowers. Curious about whether the birds were being “duped” by these flowers, they began to measure foraging rates of the birds and the energy content of nectar provided by a variety of atypical and typical flowers and to compare that with what was known about the birds’ energetic needs. They continued their observations opportunistically over the next four decades at various locations throughout the southwestern USA, eventually enlisting help from younger colleague Paul CaraDonna. The three ecologists discovered that the birds are making no mistake in their behavior—the atypical flowers often are just as energetically profitable as typical red, tubular hummingbird flowers. In fact, the nectar rewards of atypical flowers in some cases appear to be adequate by themselves to support the high metabolic needs of hummingbirds throughout a 24-hour period. What these observations tell us is that atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly scarce in suitable resources. They also emphasize what can be gained by attending to the unexpected.


Abstract

In western North America, hummingbirds can be observed systematically visiting flowers that lack the typical reddish color, tubular morphology, and dilute nectar of “hummingbird flowers”. Curious about this behavior, we asked whether these atypical flowers are energetically profitable for hummingbirds. Our field measurements of nectar content and hummingbird foraging speeds, taken over four decades at multiple localities, show that atypical flowers can be as profitable as typical ones and suggest that the profit can support 24-hr metabolic requirements of the birds. Thus, atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly depauperate in suitable resources. These results illustrate what can be gained by attending to the unexpected.