Friday, June 8, 2012

Tanagers, Cowbirds and Questionmark Butterflies

The Male Scarlet Tanager
Last week, I observed 2 of our Male Scarlet Tanagers dueling over territory. Decidedly, it was a low intensity conflict; they were essentially waging battle with their songs. One bird would issue its song on top of a tall Hemlock tree and the other would immediately respond with a nearly identical song from a neighboring Beech Tree. After every 5th (or so) round of songs, one tanager would invade the other’s tree and a low speed pursuit would begin. However, nothing would come of it and both males would then return to their prospective posts with all feathers intact. 
The male oversees his territory

It’s likely that one if not both of these males is already breeding. Back in mid-May, in this same section of the woods, I watched a courtship ritual taking place between a male and female tanager. This consisted of the male arching his back and drooping his wings while the female, in a gesture that mimics a begging fledgling, bowed her head and quivered her wings. Luckily for me, this behavior took place only about 10 feet off the ground, so it was very visible.

The female tanager with a beak-full of food for its young

Last year 2 Pairs of Scarlet Tanagers nested in approximately this same area, though I never did locate the actual nests. The species tends to place its nest fairly high in the forest canopy, where their domestic activities are well shrouded by foliage. Last year, one of the female tanagers was seen feeding a recently fledged cowbird chick. We can assume that the tanager’s own eggs or nestlings were destroyed by the female cowbird before she laid her egg(s) into the “foster” family’s nest. The tanagers, like scores of other songbirds, are very susceptible to brood parasitism as practiced by the Brown-headed Cowbird.
A newly fledged cowbird waits to be fed by its tanager foster mother

Some of the forest that the tanagers nest in is part of a recent acquisition of our nature preserve. Before it was ours the property had been selectively logged twice in the past 12 years. The forest gaps created by the loss of large trees have helped to facilitate the cowbird’s penetration deeper into the forest; the result of this is that fewer woodland songbirds successfully raise their own young. Now that we control more of the forest, we can expect that over time, the forest gaps will fill in, mature forest will recover and less brood parasitism should take place.

No, he's not tearing out his own red feathers, that's a berry in his bill!
Last year, while one of tanager pairs was diligently raising a cowbird, another nearby pair was actually raising their own fledgling. An immature tanager looks much like the adult female, with yellow body plumage and with black wings and tail feathers. The youngster called to its parents with a weak whistled call, very different from the male tanager’s song or its “chip-bur” alarm calls. When the fledgling begs, it quivers its wings and opens its beak –doing its best to encourage its parent to put something tasty into it.

Later in the summer, before the tanagers begin their journey to Central America for the winter, the male will start to molt out of his scarlet breeding plumage. For a while his feathers will look very blotchy, with lingering patches of scarlet on top of irrupting yellow contour feathers.
The Questionmark Butterfly
The Questionmark Butterfly has become exceptionally common in recent weeks. Not as ubiquitous as the Red Admiral became earlier this spring, but still impressively common. Always one of my favorite butterflies, these medium sized orange, black, and brown butterflies often allow a close approach, so one can really get a good look at its detail. The Questionmark is an anglewing butterfly and a pretty decent dead leaf mimic, so when their wings are closed, depending on the background, you might not notice one so easily. On the underside of their wing, there is a small silvered mark in the shape of a question mark; this is how the species earned their common name.
Note the small silver questionmark on the wing

This time of year, I enjoy watching female butterflies lay their eggs and I’m particularly curious about what species of plant they will select to lay their eggs on. The other day I saw a Questionmark lay a single egg on Narrow Vetch. Interestingly, this is not one of the acknowledged food plants for the Questionmark’s caterpillars.
The egg of the Questionmark Butterfly on Narrow Vetch

A few days later, I checked on the tiny egg and to my surprise I found that 2 more Questionmark eggs had been laid on the same vetch plant. About a foot away from the vetch is a small American Elm seedling; the elm is a known foodplant for the questionmark, so it’s possible that the elm was the targeted food all along. Hopefully, we’ll find out what happens when the butterfly’s eggs hatch.

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