{"id":123,"date":"2015-11-03T21:53:01","date_gmt":"2015-11-03T21:53:01","guid":{"rendered":"http:\/\/studentblogs.viu.ca\/danagullison\/?p=9"},"modified":"2017-08-23T17:31:19","modified_gmt":"2017-08-23T17:31:19","slug":"as-the-northwestern-crow-flies","status":"publish","type":"post","link":"https:\/\/wordpress.viu.ca\/biol325\/2015\/11\/03\/as-the-northwestern-crow-flies\/","title":{"rendered":"AS THE NORTHWESTERN CROW FLIES"},"content":{"rendered":"

 <\/p>\n

\"Stiver,<\/a><\/p>\n

A murder in the \u2018hood!<\/p>\n

You may not have heard about the events in my neighbourhood on Vancouver Island last night or on every autumn evening preceding it. I\u2019m referring to the fall and winter pre-dusk flocking behaviour of crows, specifically \u00a0Northwestern Crows\u00a0(Corvus caurinus).\u00a0<\/em>\u00a0<\/em>Like all species of crows they are in the Corvidae family with jays, magpies and ravens and are easy to differentiate from most other birds because they are social and relatively large with shiny black plumage and familiar loud calls.\u00a0Among the world\u2019s most intelligent creatures Northwestern Crows and\u00a0crows in general, have complex cognition comparable with chimpanzees\u00a0(Emery and Clayton, 2014)<\/a>.<\/span>\u00a0\u00a0<\/span><\/p>\n

Ubiquitous within their range, the crows live in both rugged, remote habitats and highly urbanized environments\u00a0(http:\/\/www.birdvancouver.com\/b_northwestern_crow.html<\/a>).\u00a0<\/span><\/span>During the evening, the crows of my neighbourhood fly from their daytime foraging spots on beaches, backyards and street corners to a few Douglas Fir trees on my street above the harbour. From these treetops they can, with their excellent vision, no doubt observe a \u00a0spectacular and expansive portion of the species\u2019 range extending along the Pacific coast from Puget Sound in northwestern Washington, north up the entire shoreline and coastal mountains of British Columbia all the way to Kodiak Island in western Alaska\u00a0(Brewer, et al., 2006)<\/a>.<\/p>\n

\"Screen<\/a><\/p>\n

A keen eye, ear and sense of geography is needed to accurately differentiate the Northwestern Crow. It has a lower call, smaller size (380gm), slightly\u00a0shorter body length (40cm), and purely coastal range in comparison with the similar, closely related American Crow (Corvus brachyrhynchos<\/em>)\u00a0(Sibley, 2003).\u00a0<\/span><\/span>\u00a0Additionally, the species hybridize\u00a0(Tweit, 2015)<\/a>\u00a0and both exhibit monomorphism meaning there is no difference in size or appearance between the sexes. \u00a0Genetic testing is underway to help resolve whether they are \u00a0actually separate species\u00a0or whether the Northwestern is simply a subspecies of the American genus\u00a0(Tweit, 2015)<\/a>.\u00a0Many people also confuse coastal crows with the Common Raven, a larger corvid with a more robust bill, a wedge-shaped tail, shaggier feathers on the neck and legs and a deep \u2018croaking\u2019 call\u00a0(Brewer, et al., 2006)<\/a>\u00a0(Link, 2005)<\/a><\/span>.<\/p>\n

\"stanley<\/a><\/p>\n

The Pacific coastal habitat provides rich feeding opportunities for the birds. Along the shore they forage on sandy beaches and rocky outcrops eating mussels and clams, or searching in tide pools for other marine invertebrates and picking at animal carcasses. They will prey on small mammals and in the summer their predatory instincts result in stealing seabird eggs and juveniles from nests\u00a0(Cornell University, 2015)<\/a>.\u00a0In fact, they have adapted so well to every type of coastal environment that their omnivorous diet leads to a combination of natural foods and, though usually indirectly, human supplied food that they supplement their diet with\u00a0(Marzluff and Angell, 2008)<\/a>.\u00a0<\/span>A frequent visitor to dumpsters in my community, crows have learned that a brown bag dropped on the street likely contains a source of fast food<\/span>\u00a0(Marzluff and Angell, 2008)<\/a>.<\/span><\/span><\/p>\n

\n

\"Piper's<\/a><\/p>\n

Crow carrying vole meal<\/p>\n<\/div>\n

I miss the crepuscular gatherings between April and August\u00a0when<\/span>\u00a0the birds are active locating nesting territory,<\/span>\u00a0building or repairing nests, incubating eggs and feeding juveniles\u00a0(http:\/\/www.ec.gc.ca\/aobc-cabb\/index.aspx?lang=En&nav=bird_oiseaux&aou=489<\/a>)<\/span>. \u00a0Northwestern Crows\u00a0are monogamous and together pairs choose a discrete nesting location that they may perennially return to \u00a0on rocky islets, high up in a crook of tree lining city streets, or in dense brush (Ehrlich et al., 1988).\u00a0<\/span><\/p>\n

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\"20151028_162931<\/a><\/p>\n

Northwestern Crow Nest<\/p>\n<\/div>\n

Tree nests are made of long sticks with a soft grass and hair lined cup-shaped interior and ground nests are a smaller more loosely amalgamated version (Ehrlich et al., 1988).\u00a0<\/span>The male assists the female in nest building\u00a0and then the female lays 4 or 5 bluish-green coloured eggs with brown speckles that incubate in 17-20 days\u00a0(Cornell University, 2015)<\/a>.\u00a0The birds are born altricial meaning they are helpless at birth unlike a precocial duckling which can swim and walk almost immediately after hatching\u00a0(Cornell University, 2015)<\/a>.\u00a0 Juveniles remain in the nest 29-35 days\u00a0(Cornell University, 2015)<\/a>\u00a0during which time the parents may be assisted by a young offspring from a previous season that guards the nest or helps supply food\u00a0(Link, 2005)<\/a>.\u00a0Through this cooperative behaviour adults pass on information to the next generation and there is the added benefit of reduced incidence of nestling mortality (Ehrlich et al.,1988).\u00a0<\/span>Crows that have left the nest and are finished feeding may leave or stay with the parents to assist in the following year\u2019s breeding activity and then will annually gather again in fall and winter to roost over their decade long lifespan<\/span>\u00a0(Link, 2005)<\/a><\/span>.<\/p>\n

As the seasons change to fall, high in the crown of my neighbourhood trees crows perch for a brief time to stage and announce their presence with a distinct loud:\u00a0\u2018kaah kaah\u2019<\/a>\u00a0(Gullison, 2015)<\/span>. As more crows locate them and their numbers increase they continue on their way to their nocturnal roosting territory. Roosting activity is\u00a0considered a form of security and information exchange aiding in food and mate finding and is an important way for young individuals to learn from older ones\u00a0(Link, 2005)<\/a>.\u00a0 My local twilight gatherings involve only a few dozen individuals and are modest in contrast to some flocks.<\/p>\n