These are a couple of photos I took of an American crow (Corvus brachyrhynchos) roost this month. Have a similar gathering of crows where you live? Learn more about crow roosts in this post, “Winter Crow Invasion!”
These are a couple of photos I took of an American crow (Corvus brachyrhynchos) roost this month. Have a similar gathering of crows where you live? Learn more about crow roosts in this post, “Winter Crow Invasion!”
I’ve mentioned in previous posts that some crows are among the most endangered birds on the planet, such as the ʻAlalā, or Hawaiian Crow (Corvus hawaiiensis) and the Mariana crow, or Aga (Corvus kubaryi). A colleague and friend, Sarah Faegre was kind enough to send me information on the new non-profit she and Phil Hannon have created for the conservation of Mariana crows. I asked Sarah to please send me information so I could spread the word, especially since they are doing incredible work with the local community to spread the message of conservation and coexistence. Here is what Sarah had to say:
Luta Bird Conservation Inc. (LBC) is a 501(c)3 nonprofit, created by Sarah Faegre and Phil Hannon to raise funds to conserve endangered birds and their habitats by working with the human communities surrounding them. LBC’s first project is the conservation of the Aga (Mariana Crow, Corvus kubaryi) on Rota, Commonwealth of the Mariana Islands (CNMI). Specifically, LBC’s aim is to use education and community outreach to involve local people directly in research and management of the Aga on Rota. The Aga is the only crow species in Micronesia and is endemic Rota and Guam, to the two southernmost islands of the Mariana Islands archipelago. Once common on both Guam and Rota, the Aga was extirpated from Guam by the Brown Tree Snake (Boiga irregularis). The Aga now exists on only Rota, an 86-square-kilometer island. Rota does not have snakes, but other problems, such as feral cats, human persecution and habitat changes (among other possible causes) have caused a steep decline on Rota as well. As of 2014, an estimated 130 individuals remain on this small island (and in the world) and the population is still declining.
The majority of the funding for Aga conservation comes from the US Fish and Wildlife Service and the CNMI Department of Lands and Natural Resources. However these funds are limited and, in particular, education and community involvement has been underutilized. Community outreach and education are extremely important; without the support of the local people the Aga is unlikely to survive. Currently, a high percentage of the local population has a negative view of the Aga, due to land-use conflicts and due to conflicts between federal and state-run governmental programs. LBC’s goals include working in the schools to help kids understand the value of the Aga and to encourage them to take pride in their native animals by working with biologists and educating their peers.
Many mainland residents may think that crows are everywhere and shouldn’t need much extra help to survive alongside people. In fact, these beliefs are also common among the local population on Rota, due to the lack of education about the uniqueness of Rota’s Aga. The the appearance may be similar to the casual observer, the Aga is quite different from the crows of the mainland US. Aga do not gather in large groups, but stick to their family unit and small home range area in the jungle. They have unique foraging abilities, such as opening hard-shelled hermit crabs with their beak. Since Aga evolved without predators for thousands of years, they lost their vigilance behaviors and are now unable to protect themselves from introduced predators.
LBC’s recent activities include raising funds for Aga T-shirts that kids and adults can wear, in hopes that we can spread knowledge and pride about this unique crow species. The painting used for the T-shirt was created by artist, biologist and Corvid expert Jennifer Campbell-Smith. The painting depicts an adult Aga (foreground) and fledgling Aga (background). The adult is cracking open a hermit crab while the fledgling observes. The design surrounding the painting depicts some of the Aga’s common food items and also the Brown Tree Snake, the invasive species that resulted in the extirpation of the Aga (and other native birds) from Guam. Luckily the Brown Tree Snake is not present on Rota and with the help of the local community, we still have time to save the species. The Chamorro phrase at the top of the T-shirts translates to: “Make Rota Beautiful”, which a common motto of Rota island.
I tend to leave incidental posts, responses to Tumblr posts, and Tumblr replies to the Tumblr incarnation of this blog, trying to keep this official Coyot.es space more for original content and longer posts. However, this reply was lengthy enough and contained enough original material beyond the initial reply that I thought it would be good to post it here.
I appreciate you pointing out this distinction, though manufacture versus use is sort of a continuum, depending on how we are defining “manufacture”. It is true that New Caledonian crows are amazing tool makers (something I give lectures about on a nearly annual basis when I talk about animal culture), but more than three species make tools. Chimpanzees, of course, are tool makers, along with documentation of manufacture in orangutans, mandrills, and Asian elephants. This is leaving out animals that develop tools or can be taught to develop tools in captivity (ex. bonobos, hyacinth macaws, and a Goffin’s cockatoo, just to name a few). Also depending on how complex the manufacture, gorillas have been observed breaking off large sticks for stabilization, woodpecker finches have to break off cactus spines to use them (and more recently they are modifying non-native blackberry spines), and bottle-nosed dolphins have to select and break sponges off their substrate to use them. I still assert that we will probably find a lot more tool use and manufacture in the wild, the more chances we get to observe different species in the wild. There are certainly many anecdotal and incidental observations of many more species creating and using tools. However, what you have to keep in mind is that if an animal gets along fine without making and using tools, then there’s not point in them doing so. Tool manufacture and modification, while really cool to us, isn’t always necessary for other animals. In chimpanzees and humans, for example, tool use is integral in how we forage and exist in the world, but for other species tool manufacture and use may only be needed on occasion, when a situation calls for it.
In the case of New Caledonian crows, they, like woodpecker finches, live in places that lack woodpeckers. This is significant because it leaves open the niche that specializes in locating, removing, and eating wood boring insects. Rather than spending the time to evolve physical adaptations to do this (like woodpeckers have) these two species use tools to the same ends. Arguably, there is a distinction between woodpecker finches (which are actually most likely in the tanager family, despite the common name) and New Caledonian crows when it comes to the cognitive department.
What happens when nature takes a bird, already a part of a large-brained, cognitively complex genus of birds (Corvus) and puts it on an island that has a goldmine of a niche to fill? You get the incredible New Caledonian crow (Corvus moneduloides).
Drs. Russell Gray and Gavin Hunt observed these birds in the wild manufacturing and using tools. The earliest documented account of tool us in NC crows was by an explorer who reported the use of anvil sites to crack open nuts and snails in 1882. In 1909 Le Goupils observed NC crows probing a dead log with a stick-tool (reported in 1928) and Orenstein gave a more detailed report on crow tool-use in 1972, but it was Hunt (his first study published in 1996) and Gray who brought attention to these incredible corvids and who still do work on them today. In 2000, birds were taken from New Caledonia and sent to England to be studied by Alex Kacelnik‘s Behavioral Ecology Research Group (BERG) at the University of Oxford. Two of these birds were Betty and Abel. Betty blew the minds of the world when she spontaneously bent a metal wire into a hook to retrieve food after Abel made off with the hooked tool.
Part of the reason the NC crows were brought into captivity by Kacelnik was to see if the tool behaviors were innate or due to complex cognition and problem solving, or even if they were cultural as Gray and Hunt suggested. The BERG found that young NC crows, with no training or example, had a proclivity for tearing materials and probing holes with other objects.
So if the birds could manufacture and use tools completely on their own, what makes them more noteworthy than woodpecker finches or other animals that innately use tools? What makes them rival and often exceed chimps in the cognitive department? Tradition, the understanding of the functional properties of their tools, innovative use of tools, and cumulative tool evolution all combine to make NC crows stars in the world of animal cognition.
Gray and Hunt found that different tool types were being used by NC crows in different regions of New Caledonia. These tool types were not reproduced by Kacelnik’s captive crows, which lends more support to those tools’ forms being based on a tradition, or culture, rather than just a genetic ability to make them (after all, humans babble as a precursor to language). NC crows also understand the functional properties of the tools they use and make. They use a range of materials and techniques for making tools, demonstrating that it’s the crow that decides on the tool, not the material. Understanding of the functional properties of their tool was also demonstrated by Betty bending the wire, and again in further experiments. One experiment even showed that the crows could determine the rigidity of tools that would be appropriate for a task. Finally, NC crows show cumulative tool evolution, something we humans still clung to as unique to us. Cumulative tool evolution is the ability to take a tool and modify it to a different or better function and build on previous technology. The tools that were created by precisely snipping and tearing Pandanus spp. tree leaves (the form of which were not replicated by Kacelnik’s captive birds) showed strong evidence of enhancement over time. Hunt and Gray found and compared tool types and their functions from all over the island, including historical records of negatives left in leaves up to four years old. Their findings suggest that the Pandanus tools have had significant improvement on their shape and function. If this doesn’t blow your mind, I don’t know what will!!
Researchers have since found evidence of cumulative tool evolution in chimpanzees as well. And thus, the battle for most cognitively complex non-human tool user rages on between chimpanzees and NC crows. In recent years, the ability to use tools to get tools (or meta-tool use) has been a focus of attention, with several studies demonstrating that NC crows can figure out what tool they need for a task, and use other tools to get the appropriate tool (here’s a video). There have also been studies into the brains of New Caledonian crows, among other cognitive work that shows that these birds are truly complex animals that blur the line between human and non-human intelligence and understanding of the world around them. Click here for The University of Auckland’s page on NC Crow research still run by Gray and Hunt, and here for a list of their publications which go well beyond what I’ve related to you here. Both researchers at The University of Auckland and The University of Oxford are continuing work on these birds, so you should keep an eye out for their continued publications and findings.
I’m a huge fan of NC crows, if it wasn’t apparent. One of my most treasured possessions is a genuine Pandanus tool made by a New Caledonian crow. I even had one of Hunt and Gray’s papers signed (how big of a nerd can I be?), but that was sadly destroyed in a flood. It is a life goal to make it to New Caledonia and observe these birds in the wild. Thank you Pamela Turner for giving me an excuse to blather about NC crows and I hope all of you who read this now appreciate them as much as I do!
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:
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!)