Academic journal article The Geographical Review

Shifting Synanthropy of the Crow in Eastern North America

Academic journal article The Geographical Review

Shifting Synanthropy of the Crow in Eastern North America

Article excerpt

The extraordinary numbers and wide distribution of the American crow (Corvus brachyrhynchos) owe much to human interventions (Figure 1). Anthropogenic landscapes are congenial to crows for foraging and protection from predators. Several genetically transmitted attributes have allowed this species to capitalize on the human presence. An opportunistic feeder of the first order, crows eat seeds of wild and domesticated plants as well as insects, amphibians, eggs, fledglings, and small rodents, not to mention roadkill and garbage. Omnivory has enhanced their success, but so has their complex social life. Crows exhibit a large repertoire of vocalizations, communal roosting, and cooperative breeding behavior. Corvine ability to learn and adapt has brought humans into their design for survival. With a brain larger in proportion to its size than that of any other avian species, the crow's intelligence makes it much more than a creature of instinct. (1)


The American crow offers a prime example of synanthropy, defined as "a mutualistic relationship of an organism with humans." (2) Why, when, and where this species hitched its star to the walking and talking primate that has come to dominate life on the planet is a conundrum of time, space, and ecology. In North America crows have been around much longer than humans, which raises questions about the circumstances that brought man and bird together. The spaces that the crow occupies are best examined in multiscalar perspective. Its remarkable adaptability best explains the continental spread, whereas its intelligence is most evident in a farming neighborhood. The habitat requirements of the crow most clearly emerge at the level of the region. These spatial scales of the human-crow interface, when combined with time scales from the prehistoric to the observable present, unfold a particular perspective on an organism that is more holistically inclusive than the constraints of reductionist science. (3)


The continent-wide presence of the American crow places it as one of the most ubiquitous native avian species today (Figure 2). The same cannot be said for the past. The vegetation shifts that corresponded with the advance and retreat of the Pleistocene ice sheet affected crow distribution and numbers. Closed forest cover did not favor its spread, although lightning fires, blowdowns, beaver activity, and forest blight created local or regional openings that crows could have occupied until the canopy regenerated. Acorns, wild fruits and seeds, insects, eggs, and birds nourished prehuman crow populations. With the arrival of Homo sapiens on the North American continent the crow, preadapted to environmental change, benefited from the considerable power of paleotechnic humans to transform the surface of the earth. The open habitats that Paleo-Indian (10,000-8000 B.C.) hunters and gatherers with the use of fire facilitated hunting, but they also encouraged crows.

The appearance of agriculture in eastern North America during the late Archaic (3000-600 B.C.) further extended these landscape modifications. An early inventory of small-seeded, domesticated plants faded away with the diffusion of the much more productive and nutritional maize (Zea mays). By A.D. 200, the Middle Woodland Period, maize had spread east of the Mississippi River, and by A.D. 500 its cultivation had become established in the lower Great Lakes. By A.D. 1100 maize had become the basis of indigenous subsistence almost everywhere in eastern North America south of 46[degrees] N. (4) Adaptability to a range of climates had much to do with the substantial genetic plasticity of this crop. Crows relish maize and would have accompanied this crop's expansion over a millennium without responsibility for that spread. More generally, however, it was the creation of open land through burning and cultivation that favored crows (Maxwell 1910; G. …

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