Hummingbirds

Female ruby-throated hummingbird (note white tips on tail)

Visiting purple loosestrife

What: The second half of the last post is a delightfully little bundle of energy! Ryan and I had headed down to the powerlines after Jon told us about how many hummingbirds there were. I have been waiting for the spotted jewelweed (Impatiens capensis) to blossom, as each summer around mid/late August we get a flush of ruby-throated hummingbirds (Archilochus colubris) feeding on the nectar.

Ecological notes: Any hummingbird gardening guide lists jewelweed as a must (apparently ruby throated hummingbirds prefer spotted jewelweed to yellow jewelweed, I. pallida). Bumblebees and some butterflies also visit jewelweed flowers, but they're not nearly as effective at pollinating the plant, indicating that an evolutionary relationship might exist between the morphology of the flower and the feeding behavior of hummingbirds. I found some interesting notes about the relationship between the two, with unsupported claims that the weak petiole of the flower allows the plant to bend away from the hummingbird's advances, thus protecting the plant's ovaries from the long sharp piercing bill of the bird. Problem is that the complex shape of the flower places the ovaries at the back of the flower, well out of reach of the bird.

Research out of UMass Amherst indicate another, more likely possibility. Jewelweed flowers have flexible pedicels (stems) that allow the flower to bend readily. When feeding, hummingbirds flick out their tongue to slurp out the nectar. Each time the bird does so the weak pedicel allows the flower to recoil back in response and before flapping back forward. As it springs forward the flower dusts its pollen across the upper bill of the bird. It all happens in a brief second, so it's difficult to observe, but the tight relationship is enough to ensure successful pollination. To test this relationship, the researchers immobilized some flowers by wrapping wire around their pedicels. The rigid flowers were far easier for the hummingbirds to suck nectar from (visits were 25% shorter to these flowers), but significantly decreased pollen transfer (by about 50%). They also found that the stems of the flower didn't move when visited by bees, indicating that this is indeed an adaptation specific to hummingbird foraging behavior.

According to the researchers, there may also be a link between the shape/size of the spur (the hook at the back of the flower) and which pollinators (bees vs. birds) go after the individual flower.

Where: Centennial Woods, powerline

Other notes: Summer is coming to an end - you can feel the first crisp coolness of the night air. Queen Anne's lace is going to seed, morning glories and bind weed flowers are out in full force, fruits are ripening (go harvest wild grapes!), Jerusalem artichoke is flowering, and the birds are getting antsy ready to head south.