Some Crows and Ravens I have known—
Wednesday, July 27, 2016 1:53 PM
After years of watching and photographing them, I decided to create a slide presentation all about corvids. Corvids are members of the crow-like family of birds that we all encounter in our daily lives. With 120 corvid species worldwide, Maine has five representatives: Common Raven, American Crow, Fish Crow, Blue Jay and Canada Jay. Not all corvids have black feathers, but members do share common traits such as a powerful bill, assertive harsh voice and a relatively aggressive approach to life management. Corvids are definitely some of our most intelligent and resourceful of birds, with a brain-to-body mass ratio that is equal to that of the great apes and cetaceans.
Common Raven (Photos by Don Reimer)
What’s in my slide presentation? Several flight photos demonstrating the size and shape differences between ravens (heavy, bulky bill and head; long, fluid wings; and wedge-shaped tail) and crows (smaller bodies and bills, with compact, broad wings and a fan-shaped tail). If you happen to see the two species flying closely together or during aerial disputes, the crow’s choppy, flapping manner of flight becomes apparent.
I included shots of ravens and crows being hotly pursued by various songbirds after the corvids had robbed a nest egg or two. In one sequence a male Red-Winged Blackbird grabs and rides the tail section of a fleeing raven. In turn, corvids routinely mob large predators such as hawks and owls that could pose bodily threats. This is a particular concern for crows that face occasional nighttime owl raids at communal roosting sites.
Crows and ravens differ in their basic family structure, as the far more plentiful crows occupy and defend tighter territories. Highly communal in their social family ties, crows frequently dwell in inter-family groups where several generations of relatives may serve as helpers at the nest, delivering food and support to nestling crows. During the first season of life, young crows must choose whether to remain in proximity to family’s home range where life conditions are more predictable or depart and join wandering squads of unsettled birds.
Winter roosts containing hundreds or thousands of individuals are formed to increase the safety odds against predators. Huddled collectively together in groves of trees, some shared thermal advantage is also achieved on frigid winter nights.
One downside to living in such densely packed conditions is the possible spread of disease. This became evident in the Midwest two decades ago when contagious West Nile virus rampaged through crow populations, significantly reducing populations there for a period of years.
My slides show bold techniques that ravens use to hoard and protect valuable winter food resources, as when a male raven in my backyard attacked and routed an adult Red-Tailed Hawk that had attempted to steal his cache. Days later, that same raven settled stoically atop the cache, shielding it from view of a roving hungry gull. The slides also highlight playful instances of dynamic soaring, rolling and aerial dropping maneuvers where raven instantly tuck their wings on windy days and plummet sharply for hundreds of feet.
Ravens do not migrate. They occupy larger territories than crows and are less likely to tolerate nesting intrusions nearby. Hence, raven numbers are lower. Immature and sub-adult ravens wander in prenuptial “dating” pairs or loose groups for several years before reaching breeding age. Groups of these sub-adult birds assemble at major carcass sites to overcome the powerful resistance of possessive territorial pairs.
I conclude my presentation with a few jay photos. Pro or con, most folks seem to hold definite opinions on this active, vocal species. We can discuss the jays more fully when you hear my presentation at some future local venue.