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Downy Woodpecker

Goldenrod Ball Galls Provide Important Source of Winter Food for Downy Woodpeckers

12-11-15 goldenrod ball galls 058A number of insects cause goldenrod plants to form galls – abnormal growths that house and feed larval insects. The Goldenrod Ball Gall is caused by a fly, Eurosta solidaginis. The fly lays an egg on the stem of a Canada Goldenrod (Solidago canadensis) plant in early spring, the egg hatches and the larva burrows its way into the stem; the plant reacts by forming a gall around the larva. The larva overwinters inside the gall, pupates in late winter and emerges in early spring as an adult fly. Prior to pupating, the larva chews an exit tunnel to, but not through, the outermost layer of gall tissue. (As an adult fly it will not have chewing mouthparts so it is necessary to do this work while in the larval stage.)

Downy Woodpeckers (and Black-capped Chickadees) have discovered this abundant source of winter food, and dine on the larva after chiseling a hole into the gall. Downy Woodpeckers tend to make a tidy,narrow, conical hole by pecking, while Black-capped Chickadees tend to make a messy, large, irregular hole by grabbing bits of the gall with their bill and tugging them free. While woodpeckers prefer larger galls that are located high on goldenrod plants growing near wooded areas, these are not the only factors taken into consideration.

A woodpecker extracts the fly larva through the tunnel the larva excavates prior to pupating, as this facilitates rapid removal of the larva. Downy Woodpeckers can determine whether or not a gall has an exit tunnel, and if it doesn’t, they usually abandon the gall without drilling into it. The likelihood of smaller parasitic wasp larvae occupying the gall (and a plump fly larva not being present) is much greater if there is no exit tunnel, and these smaller prey apparently are not always worth the woodpecker’s time or energy.

NB: Correction: this week’s Mystery Photo was of a Gray Birch (Betula populifolia) bract, not a Paper, or White, Birch (Betula papyrifera) bract. While similar, there are differences between these two species of birch that I should have recognized (especially when looking at the leaf!). Thanks to Kathy, an alert blog reader, who caught this error.

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Red-osier & Silky Dogwood Fruits Ripening

10-6-15 silky dogwood 291Some of the most prolific flowering shrubs in the Northeast are dogwoods. In the spring, their flowers attract attention and at this time of year their colorful fruit stands out. There are many species of dogwood, two of which are Red-osier Dogwood (Cornus sericea) and Silky Dogwood (Cornus amomum). These two shrubs can be hard to tell apart, as they both have white flowers, red stems and similar foliage. In the fall, however, the color of their fruit differs, as does their pith, or central stem tissue. The mature berries of Red-osier Dogwood are dull white and its pith is also white. Silky Dogwood’s blue berries have white blotches, and its stem and branches have a salmon-colored pith.

The fruit of these dogwoods and others is an extremely important source of food for many migrating songbirds, as well as resident birds. Wood ducks, Northern Cardinals, Eastern Bluebirds, Gray Catbirds, Purple Finches, Evening Grosbeaks, American Robins, Yellow-bellied Sapsuckers, Wood and Hermit Thrushes, Red-eyed and Warbling Vireos, Cedar Waxwings and Downy Woodpeckers all consume dogwood berries.

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