A crow's life
The Torresian crow begins life as a hatchling accompanied by one or two siblings, in a large, bowl-shaped nest of twigs in a tree often 10m or more above the ground.
Both parents provide food in a shuttle service that starts after dawn and continues till just before dusk. Adult crows also defend their breeding ground and regularly confirm their whereabouts with the familiar harsh caw, as well as a much softer ‘snoring’ caw, which most people tend not to notice.
Calling between adults in a breeding territory is relatively low key and rarely attracts the sort of attention that large aggregations of unattached, non-breeding crows do.
At about six weeks, young crows graduate from test flight flapping to fully competent aerial manoeuvres, although they still depend on their parents for food. A few months later, they are evicted from the family territory. Survival is difficult with some estimates suggesting only about one in twenty crows make it through the first year of independence. Those that survive to their second year may go on to live for up to 30 years.
Appearance
You can tell juvenile from adult crows by the colour of their eyes. In immature crows, the iris is chestnut brown, while in adults they are pure white. Nestlings have blue eyes (and shorter wings and tail).
There are rarely many brown-eyed crows in a flock, indicating this age group has a very low survival rate.
Crows are not simply black. In bright sunlight, the reflective qualities of corvid feathers produce a surprisingly brilliant array of deep metallic blues and greens.
Flocks and roosts
Crows usually form flocks made up of mostly young unpaired birds and share a common roost site; usually a cluster of large gum trees. The combined calls of a flock of crows can make a roost site a very noisy place.
Roost sizes can change seasonally, as new juveniles join and older birds pair up and leave. Roosts are largest in autumn and smallest in spring. Roosts also change in size as birds find new food sources and move closer to the food supply. Major roost sites will always have some birds throughout the year.
Sometimes a large tree will suddenly become a temporary roosting site for 20 or 30 crows, probably indicating a temporary supply of food is nearby. When this runs out, so do the crows.
More about corvids
Crows are members of the genus Corvus and the family Corvidae (‘cor-vid-day’), which contains most crows, ravens and rooks. These birds are generally called corvids and are found across much of the world. In terms of evolution and survival fitness, corvids are very successful.
Native crows
In Australia, there are five native crow species:
- Australian raven Corvus coronoides
- little raven C. mellori
- forest raven C. tasmanicus
- little crow C. bennetti
- Torresian crow C. orru
As well as these natives, the house crow C. splendens from the near north Asian region has made regular appearances as a ship-assisted vagrant. To date, this exotic crow has not become established in Australia.
Crows versus ravens
The question often arises: what is a ‘crow’ and what is a ‘raven’? The terms ‘crow’ and ‘raven’ are originally British names. Traditionally, a corvid with feathers forming prominent throat hackles, especially noticeable when the bird is calling, were known as ravens, and birds without these features were known as crows. Australian species are more difficult to group this way, but generally if a corvid has white bases to the feathers on its neck and shoulders it’s a crow (this can only be seen when the feathers are ruffled or the bird is moulting); and if they’re totally black it’s a raven.