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!!
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.
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.
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:
- Testing for mirror self-recognition.
- Testing the insight hypothesis through string-pulling experiments.
- Testing quantity discrimination and symbol recognition.
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.
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!
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.
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.
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!)
On Monday, January 27th, 2014, myself and three other crow researchers will be doing an IAmA day on Reddit!! For those of you who don’t know what an “IAmA” is, it’s basically a day-long question and answer session with an individual or a group of interest. Get those crow questions you have always wanted to ask answered by experts!!
Here is a link to where the Crow Research Group IAmA will be taking place: http://www.reddit.com/r/iama
Please share this advertisement and pass it on to any of your friends and family that you think will be interested.
I got this question from csmithstudio on Tumblr:
Hi Jenn! A friend told me about your blog and I’m delighted and grateful to you for taking the time to post this! I am an artist focusing almost entirely on birds and I would like to do a painting of crows including the treasures they commonly collect. I’ve tried to research what they might be attracted to but so far have only found golf balls and angry golfers! Do they stash their hoard in a nest or somewhere else? Thank you! Christina
I’m super glad you asked me this! I’ve been meaning to post about this topic. The reason you can’t find anything is because crows don’t collect shiny things. This is an extremely common myth, but it’s just that, a myth. (And I’ve seen way too many “official” websites state this myth like it’s fact, so don’t feel bad for believing it!) The thing is, stories about crows collecting shiny things are anecdotal, and not observed by people who watch crows constantly and study them.
There’s a couple of reasons why people might think crows like and collect shiny objects and continue to pass along the myth. First, young crows are very curious about everything. They play with all sorts of objects they find in nature, and chances are if something is glinting they may me more likely to explore that object (just like how you might notice something glinting in the grass and investigate it), than something that blends in to the background. As I talked about in a previous post, juvenile crows are the same size and, to the untrained eye, look just like adult crows, therefore people may be attributing a juvenile play behavior to all age groups, accidentally. Are they particularly attracted to shiny objects, or obsessed with them? Highly unlikely, they may just be more likely to find them because they are easier to see/attract attention easier (welcome to why advertisers use shiny and bright things on other humans to attract their attention). Honestly, adult crows are more likely to be terrified of brightly colored or shiny objects unless heavily associated with food on multiple occasions.
Second, a lot of observations about crows playing with shiny objects come from people who have had pet crows. A hand-raised crow is going to have a lot of exposure to human objects, and will therefore play with those objects. They may be attracted to what their “parents” (the humans) are attracted to, and therefore be more interested in rings, watches, silverware, etc. for the reason that they are of high value to their “family” not because they are shiny objects.
Third, it is likely that the shiny or bright objects simply remind the crows of food, or the crows are investigating them for potential food opportunities. The going theory for why crows and ravens are so attracted to golf balls, as Christina mentioned in her note, is that they look an awful lot like delicious eggs. I have personally watched crows play with and steal golf balls off a golf course (which was hilarious). However, they lose interest pretty fast after, presumably, realizing the objects aren’t food (though I swear some of the crows just had a blast chasing those golf balls around).
There are a number of reasons why crows may be attracted to shiny or bright objects and trinkets, but no more so than you or I or most animals would be attracted to them. In other words, their interest in shiny objects does not appear to be inordinate.
So, do crows hoard the objects they find? No.
Crows don’t hoard anything. If a crow takes off with your keys, it was likely that the bird wasn’t done exploring them for any food opportunities and took off with them to finish it’s inquiry in safety (and probably dropped them somewhere when it realized it had no use for the keys). Crows, and other corvids, do cache items, which means that they store them for later (see my post about Nutcrackers for the most incredible cachers), but wild crows only store food items (I say “wild” because captive birds may cache non-food items, which would be expressing an instinctual behavior, using non-typical items found in the captive habitat). Furthermore, they don’t cache all of the food items in the same location (larder). Crows (and most corvids) are scatter cachers and leave bits of food all over the place within their territory (I once watched a crow pull half a ham sandwich out of the branches of a spruce tree…I still have NO idea where he was keeping it in there, but it was pretty hilarious to watch). So there is no secret hoard full of shiny objects to find in a crow territory.
What about the nests? Well, crows don’t use nests for anything but raising babies. The nests are built just before egg-laying at the beginning of the breeding season, are lined with soft grass and moss, and are immediately abandoned once all the kids fledge. Crows don’t store objects in a nest or sleep in a nest (unless you are a baby or the bird on incubation duty during the breeding season). Although crows have been reported to use wire hangers and other urban metal materials to build the structure of their nests, this is more likely due to the utility and availability of these objects as construction material, not because they are shiny. You may wonder if crows might put shiny objects in the nest to attract attention from potential mates, but crows have selected mates far before nest building begins. If you find a crow nest in the wild, you won’t find wondrous treasures, you are likely to find a pile of sticks, grass, and poop….and sometimes a sleeping raccoon (true story).
So in conclusion, Christina, I would love to see you possibly illustrate caching behaviors of food, since those are the most valued treasures for crows. In urban/suburban environments I’ve seen them cache everything from seeds and dead animals/insects, to ham sandwiches, pizza, and french fries. It might be more fun (and accurate) for you to explore the wide and variable diets of these birds. Feel free to contact me for more details if you are interested! 🙂
You have also given me the chance to review a game a friend bought for me recently, Crows by Valley Games, Inc. I brought this game to a lab meeting and as a crow research group we played. While thoroughly not impressed by the premise of attracting crows with shiny objects and trinkets, it was still quite fun! We highly recommend it with the caveat that you replace “shiny objects and trinkets” with “peanuts and road kill.” They certainly hit the mark with the trash tiles though.