B4

Elizabeth Walsh - Nature Notes

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The American crow is one of the most easily recognizable birds to all of us. Basically, if we see any black bird, we call it a crow. Unfortunately, many times we are mistakenly calling a common raven a crow. Although they are very similar in appearance, there are characteristics that can distinguish them apart.

The American crow is 40-53 cm in size with a wingspan stretching from 85-100 cm long. It is all black, with a square-shaped tail, black legs and bill, and a slim, sleek throat and head. Its feathers are completely black but pick up green and violet reflections from sunlight. The common raven is larger, has a more curved, longer, and heavier bill, has a shaggy throat, and a wedge shaped tail. While we know that the crow makes a sharp "caw" call and other rattles and coos, the raven has a much deeper and more guttural voice.

Crows are found throughout the southern zone of Canada. In the majority of Canada crows will migrate south in the winter. In our area, some crows are found all year round but some still migrate. In the wintertime, crows gather into large groups to sleep in communal roosts. The recorded sizes of these groups have varied greatly. They are often found roosting in groups of several hundred, but groups of several thousand to up to 2 million have also been observed. These winter roosts, once established, may stay in the same location for over 100 years.

American crows are monogamous, staying with the same mate for years. Crows are cooperative breeders and form into family groups of up to 15 individuals, where offspring from previous years stay with their parents to help look after the current year's young and to keep the territory free of predators.

Crows reach sexual maturity at two years of age, but individuals will often stay with their family for four or five years before they will venture out to start their own. Not all crows form into large family groups — some just stick with the breeding pair and raise young alone without the extra help. It is not certain why families stick together for years and why offspring will forego breeding to help their family when it has been shown that the large family units don't appear to be any more successful at raising young than the couple on their own.

Although the family unit is strong, individuals will leave their family to join other groups of crows congregating at feeding sites. The family also goes to the wintering roosts together, but once there they will split apart.

In North America, breeding can begin as early as February (in more southern areas) and will last until June. The nests are built by both mates in a tall, sturdy tree which can be either coniferous or hardwood. They construct a large cup-shaped nest from sticks and branches, lined with fur and soft plant material. The female lays four to five light green eggs with brown markings that she will incubate for 18 days. While she is on the nest, the male will bring her food.

The young are born entirely helpless and will be fed by both parents and older siblings. They will fledge from the nest at 35 days but will still require their family to feed and protect them for several weeks.