Tag Archives: corvid

Of Jackdaws

[youtube http://www.youtube.com/watch?v=fYwRMEomJMM]

A juvenile western jackdaw (Corvus monedula spermologus) is served water by some nice humans in Supetar, Croatia.

While jackdaws are still listed as in the genus Corvus (with other crows) in most literature, many workers argue that the two species of jackdaw (western, C. monedula, and daurian, C. dauuricus) should be in their own genus Coloeus.  Indeed, they have long been listed in the ‘sub-genus’ Coloeus and a 2007 paper looking at the genetic diversity, using mitochondrial DNA of certain species of corvids, supports the assertion that jackdaws should be in their own genus.  In fact, the International Ornithological Union and Birds of South Asia: The Ripley Guide by Rasmussen and Anderton both list them as genus Coloeus.

Semantics aside, these small corvids have long been recognized as being morphologically distinct from the rest of the genus Corvus.  They are small (the smallest of genus Corvus) and very sociable; as evidenced by this video.  They are a common urban bird and thrive just as well in human dominated landscapes as they do in remote landscapes, like a number of other corvids.  However, jackdaws also differ from other crows in that they nest in crevices/holes, much to the distress of many a chimney-owner.

And while I’m on the topic of crows that are proposed as distinct from the others, another sub-genus, Corvultur, has been previously proposed for the fan-tailed raven (C. rhipidurus), white-necked raven (C. albicollis), and thick-billed raven (C. crassirostris) due to their close geographical relationship and unusually thick bills.  However, this division is not very robust, and a 2012 study placed white-necked and thick-billed ravens as closely related, but fan-taileds sorted out closer to pied crows (C. albus) and then common ravens (C. corax) and brown-necked ravens (C. ruficollis).  However, unlike the Corvultur, both jackdaw species still remained very distinct from the rest of genus Corvus, forming the most basal group.

All of that said…I hope you enjoy this video of a jackdaw getting a nice cool drink of water after coercing some primates into opening a bottle and pouring a cap-full for it.

(Preview image for this post by John Haslam from Dornoch, Scotland.)

Finally! A movie that’s fair to Corvids!

Finally!  A film (Maleficent) that portrays a raven accurately and fairly (though the CG flight animation could use some work).  Not to give too much away about the film, but this is the first movie where I’ve seen a raven portrayed as a “good guy”.  In fact, the raven, Diaval (renamed from Diablo in the animated movie), is the most morally consistent character in the film.

I can’t say more without giving away too many spoilers, but if you like corvids, especially the crows, see this movie.  I saw it on a whim and I was pleasantly surprised, not just by Diaval, but by the film as a whole.

This film gets The Corvid Blog’s endorsement!

(GIF from Cinemablend.)

Australian Crows – Guest Post by Matthew Brown!

This is a special guest post by fellow corvid researcher Matthew Brown. Matt is a PhD candidate at Griffith University’s Environmental Futures Research Institute in Brisbane, Queensland and studies Torresian crows (Corvus orru).  I asked him to write about Australian crows and his research for this blog and he was kind enough to do so.  Enjoy!!
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For the past three years I have been studying one of the most common birds on the Australian continent, the Torresian crow. Crows have become extremely common in Australia over the past two decades, nowhere moreso than in the Queensland capital city of Brisbane. A subtropical city of two million people, Brisbane provides enough lawns and rubbish to support enormous populations of crows and other scavengers. Such is the abundance of crows and their interaction with humans so common that the Queensland Government Department of Environment and Heritage Protection has a “Living with Crows” page on its website.

A Torresian crow caught at Griffith University’s Nathan Campus in Brisbane. The crow, 40cm long and approximately 750g, was banded for identification and released.

Five species of corvid exist in Australia, including three sedentary species: the Torresian crow (Corvus orru), Australian raven (C. coronoides) and Forest raven (C. tasmanicus), and two smaller nomadic species, the Little crow (C. bennetti) and Little raven (C. mellori). Only the Torresian crow exists in Brisbane.

Despite having the names crows and ravens, these five species are a monophyletic clade, which means they all come from the same ancestor. So an Australian raven is more closely related to the Torresian crow than to, say the common raven (C. corax) from the Northern Hemisphere. The exception to this being that the Torresian crow also exists in Papua New Guinea, as a separate subspecies.

The five species are best identified by their geographic location, but also their calls. Each species have very distinct, though extremely complex and variable, calls which can’t really be mistaken for each other (with the possible exception of the Australian raven and little raven).

The current theory about how, after crossing over from PNG, the corvids split into five species across Australia is explained in-depth in the late Ian Rowley’s paper “Why five species?

Torresian crows, while territorial, spend the night in permanent communal roosts scattered throughout Brisbane. These vary widely in size, and can contain anything from a few dozen to 200 birds. The roosts are often also shared with rainbow lorikeets and ibis.

All Australian corvids hatch with blue eyes as chicks, then change to the juvenile brown, then the adolescent hazel before finally becoming the adult white with a blue inner ring at about 2 years old. The process is the same for all 5 species, though the exact time of each stage varies. This is the easiest method to tell the juveniles apart from the adults. Early European scientists used to consider them separate species (the brown-eyed crow and the white-eyed crow) before they finally figured it out.

Juvenile crows stay with their parents for approximately six months, though this appears to be highly variable. After leaving, they join what are known as ‘juvenile gangs’, which often congregate around shopping centres or parks, areas with a large amount of human scraps. One of the largest of these gangs permanently live in the South Bank Parklands. The Queensland Government estimates that crows have a 95% infant mortality rate, though those surviving to adulthood (2 years old) can live up to 30 years.

One of the largest permanent juvenile gang sites is the popular South Bank Parklands, likely due to the abundance of human food available.

Compared to the extensive research conducted on New Caledonian crows, American crows, common ravens etc, very little is known about the Torresian crow. Because of this, my studies are focussing predominantly on replicating Northern Hemisphere studies on this species. These include:

In addition, I have already undertaken a study comparing neophobia (a fear of novel objects) in Torresian crows with other non-corvid corvines including butcherbirds, currawongs and Australian magpies. The extreme neophobia present in crows has made working with wild birds very difficult, requiring an extensive familiarisation process. My study of the Torresian crow’s vocalisation system also revealed not only extraordinary diversity in calls, but suggested the presence of a nested hierarchy similar to that deemed present in American crows by researchers in the United States. Professor John Marzluff described crows as likely possessing a basic form of language, and on the surface at least it appears that Torresian crows can match or even surpass their American cousins in this regard.

Torresian crows have already shown some of the remarkable qualities expressed in their overseas cousins. The invasion of North-Eastern Australia by cane toads has been disastrous for all native fauna, except the crow. Crows in Eastern Queensland were first recorded to be flipping toads onto their backs, allowing them to peck at their bellies and avoid the poisonous glands on their backs. Very soon after, much sooner than one would expect, crows as far as Darwin were performing the same behaviour. How the information spread so far so quickly is unknown. Crows have also been reported unzipping school bags and stealing food from children’s lunchboxes, and working as a team to move large carrion off of rural roads, while one acts as a sentry warning of oncoming traffic.

My own observations have confirmed that Torresian crows can recognise friendly or unfriendly human faces and act accordingly, though are extremely wary of all humans that pay them any attention. The infamous crow funerals appear to be present in Brisbane as well, though crows being hit by a car or electrocuted is quite rare.

Crows are a joy to study anywhere in the world, but in Australia there is a level of mystery that makes it all the more rewarding. So little is known about the crow that everything is a new discovery, and provides an intriguing comparison with better-known species from the Northern Hemisphere and in New Caledonia.

Two crows, one banded, participating in the familiarisation process of an experiment at Griffith University’s Nathan Campus.

 

Winter Crow Invasion!

Do you have a metric tonne of crows flooding into your neighborhood/town/city each night?  Do you feel like the crow population is getting out of control?  Are you worried that Alfred Hitchcock’s “The Birds” is about to be a reality?  Do not fear!  What you are experiencing is perfectly normal winter behavior for crows!  In this post we will discuss ROOSTS!

Thousands of crows coming in to roost for the night.

What is a roost?

A roost is a place where birds sleep.  In the context of crows, a roost usually consists of many birds gathering in one location, at dusk, to sleep for the night.  In the winter American crows (Corvus brachyrhynchos) in particular gather in the hundreds to thousands to even millions, in some exceptional cases, each evening.  It’s quite a sight to see and might be a bit disturbing for anyone unfamiliar with this winter behavior!  However, the behavior is just that, a winter one and is therefore temporary.  Crows form massive roosts from November (at the earliest) to about March, when they go back to their home territories to start the nest-building and breeding process.

Why do they gather in such large roosts?

We don’t know for sure, but it’s something American crows have done forever.   One hypothesis as to why they gather like this in winter, is for safety.  One of the main predators for American crows is the great-horned owl.  With longer nights in the winter, having a large group to sleep with after dark might help your chances of not being attacked by an owl.  Having so many other birds means there’s a greater chance it will be a different individual that gets attacked, and also means you have more birds that can detect a predator and send up the alarm to everyone else.  Other hypotheses involve possible information exchange, about foraging sites, but it hasn’t been studied in crows, and many crows just return to their home territories during the day.  It could be that visiting crows (that may have migrated from the north, for the winter) might find out about good foraging sites, but it’s probably not a large contributing factor to roosting behavior.  Finally, roost sites may be conveniently close to good foraging sites, and therefore a good place to sleep.

Crows coming in over an industrial area.

Why do they gather in my town/city?  And not the woods?

I’m sure there are roosts in the woods that people don’t know about, but the biggest conflict with roosts and people are in towns and cities.  Ever parked your car under some trees filled with thousands of birds?  Ever walked under thousands of birds?  Neither the car, nor yourself, likely come out without a fair deal of poop covering you.  Roosts are also quite noisy before the birds all settle down to sleep.  And even then, if they get disturbed in the night, they all sound the alarm, which is quite loud coming from thousands of already-noisy birds!

There are no studies saying exactly why the roosts tend to be in towns, but one hypothesis is that the crows like the light.  Crows see about as well as us humans at night, and the added light might help them spot and evade the dreaded great-horned owl a bit easier.  Great-horned owls are also less abundant in towns.  Urban areas are slightly warmer than rural areas as well, which is an added bonus in the cold winter.  Thirdly, most urban areas prohibit the discharge of firearms, which protects crows from being shot.  Urban areas may also provide better actual sleeping sites, such as taller or specific kinds of trees.

In some cases a roost may have been near a town before the town was even built up, and then the town itself became suitable for roosting (due to the reasons I just gave).  In the case of one roost the Crow Research Group studies, the roost has been documented in the same rough location for over 100 years.  It used to be three miles south of the town, but is now in the middle of downtown, and it likely moved due to the reasons I stated above.

Crows gathered in a group of tall trees.

Doesn’t a roost of so many birds indicate that crows are overpopulated?

No, and there are a couple of reasons why.  Remember that I said crows have been doing this forever?  Well, even if there were only 10 crows in a 100-mile radius, they would come together in the winter to roost.  Additionally, some crows migrate.  In the winter here in New York we tend to get migrant birds down from Canada that join our roosts and communal foraging sites.  So the number of crows in a roost is NOT indicative of the population in a particular area.  The roost contains birds from many miles around and possible migrants.  In the case of roosts further north, they may see fewer crows, as many of theirs have taken off to warmer climes for the winter.

There’s a roost in my town or nearby, what should I do??

Go watch them an enjoy yourself!  Seeing such large aggregations of birds is thrilling and you get to see all sorts of great flights, behaviors, and hear a variety of sounds.  It’s quite comical watching crows vie for space on a branch in a particularly over-loaded tree.

I say bring revenue into the town by having a crow festival in the winter!  Do crow-themed foods, crafts, attractions, competitions, etc.!  Make an eco-tourism site and bring in the money as well as educate people about crows and how wonderful they are!

Is there current research on roosts?

Glad you asked!  The Crow Research Group is trying to get some funding via Experiment.com (crowd-sourcing) to do some movement and roost research!  My colleague, Ben Eisenkop, is interested in how these large roosts affect nitrogen cycling in local environments (since crow poop is chock full of nitrogen).  If you would like to contribute, please click the following link! (The fund raising is over, but please still visit the link to learn more about crow roost research!)

What are the patterns and effects of American crow movements?