|Winterberry berries stay until robins or cedar waxwings|
show up. Click on photos to enlarge.
Japanese barberry is an invasive, naturalized from ornamental plantings. Sales now banned in Massachusetts. In wooded areas, barberry is a low, thorny shrub festooned with oval, red berries. It displaces native shrubs. Deer avoid eating it because of the thorns. Burning bush, also an escaped ornamental, is also banned in MA. It forms dense thickets three to nine feet tall, with small, rust-hued berries. Multiflora rose has modest white flowers in spring, branch-ending clusters of small, dark-red berries in fall. Together, these three can dominate a forest understory.
|Winterberries covered with ice|
Last/worst is Oriental bittersweet, a woody-stemmed, vining invasive that can blanket treetops with a haze of red/orange berries. It is a tree-killer. If there is any on your property, cut the stems as close to the ground as possible. While many bird species will consume multiflora rose and burning bush berries, winterberry and bittersweet are left for the robins (and the occasional flock of cedar waxwings). Examples of all five can be seen along the Assabet River Walk trail, which has signed entrances at Colbert Avenue and Concord Street. As a bonus, there is a decorated spruce tree 1/3 mile in from the Colbert Avenue end.
Back to birds. The addition of these invasive plants provides enough forage that some robins choose to not migrate south. Males especially, will remain here, to be closer to territory they intend to claim in the spring. These are not the plump and placid birds of summer. Rather, they move about in jittery flocks of 15 to 30 birds descending on winterberry like raucous starlings. Cardinals do not migrate and do not winter-flock, but they do eat other types of red berries and incorporate the color compounds into feathers (males more than females).
|Robins do not always migrate, instead staying north as long as|
there is food. This photo taken in 2011, winterberry bush.
From the plants’ perspective, birds eating berries is a means to making more plants. This explains why fruits and berries undergo veraison (turning color) when they do. Once the seeds are ready, the pulp becomes sweeter and the skin colorful, as a ‘please eat me’ signal. It is the reds, yellows and oranges of these skins – courtesy of compounds called carotenoids – that robins, cardinals, orioles, basically any bird of reddish feather, incorporate into feather color. Goldfinches get their yellow the same way. Insectivores such as red-headed woodpeckers get their share from plant compounds those insects ate.
Color matters only if an animal (or its predator) can see color. Insects, fish, amphibians, reptiles and birds see color, perhaps better than we do, including ultraviolet hues we cannot see at all. Birds are caught in a dilemma – be a brightly colored male to secure a mate, but then be at more risk of being seen by a predating bird or snake. Females, meanwhile, evolved more toward camouflage colorations that allow them to stay on the nest without being detected. Some species, such as mallard ducks, molt twice a year, the males brightening up for mating season, then going drab for the rest of the year.
|Male Mallard duck in courting/mating colors.|
Oh, and yes, a “dishonest signal” is lying, to either dissuade predators or fool potential mates. The tasty butterfly that has evolved a wing pattern and coloration similar to a different species that is distasteful is an example of Batesian mimicry. People who color their grey hair are just hoping for the best.
The genesis of this column was a 2009 observation that robins were no longer migrating south for the winter, to then become harbingers of spring