Category Archives: Corvid of the month

Corvid of the month: Rooks

In honor of last week’s #CrowOrNo photo, I wanted to spend some more time spotlighting a corvid perhaps less well known to my fellow North Americans, the rook (Corvus frugilegus).

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Photo c/o Pam P.

Among corvids, adult rooks might be one of the most unmistakable species. Their naked, chalk colored chin, lores, and bill base gives their face an appearance resembling no other bird.  The grey crow, or bare-faced crow (Corvus tristis), shares a similar facial pattern but is easily distinguished by its rather blushing appearance and blue eyes.  In addition, whereas the grey crow is known mainly to the peoples of Papua New Guinea, rooks have one of the widest distributions of any corvid species, breeding from Sweden all the way to China.

(Hover over tiled photos for captions)

Of course, what made last week’s #CrowOrNo submission such a challenge was that the photo was not of an adult, but rather a first year bird.  With their nasal hairs intact, first-year rooks look something like a crow/raven hybrid. Although bill shape is, I think, the best tell, one other field marker to look for are their notoriously shaggy “pants” (belly and leg feathers) in contrast to crows and ravens.

The transition to bare-faced adult occurs during the bird’s first complete body molt when they’re around 10-15 months old.  This process can take as little as 25 days but for most birds occurs over the course of several months1.  The evolutionary reason for this loss may have something to do with their foraging habits, which consists largely of probing for worms, though this remains unclear.

Unlike many Corvus species which are more general with respect to their diet, rooks are fairly specialized to feed on the small worms that live among the roots of plants.  One consequence of this diet is that there are distinct boom and bust seasons.  In April and November, wet conditions make worms plentiful, but in other times of years drier conditions drive worms deeper and out of reach.  Since access to food can be precarious, rooks have adopted a rather unusual incubation strategy compared to most birds.  Rather that commencing incubation when the entire clutch is laid, which promotes the same hatch date, rooks start incubating the first egg as soon as it is laid.  This chick is born earliest, giving it a clear advantage over its future siblings.  If food becomes sparse only this chick will survive. If food remains abundant, the parents can provision enough to supply the larger, more dominant chick, and its younger siblings.2

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Photo c/o Danny Chapman

Rooks are distinct from other corvids with respect to their behavior as well.  In contrast to crows or ravens, rooks are essentially non-territorial.  During the non-breeding season they are most commonly found in large foraging groups (much to the chagrin of local agricultural farmers, I imagine).  During the breeding season they nest in colonies, rather than individual territories, though they will defend the area around their nest and their mate as necessary.  A nest is often reused by the same pair year after year until it is razed by weather, or the pair is forced for some other reason to construct a new nest.  Like many other Corvus species, they maintain a socially monogamous life-long mate.3

Cognitively, rooks demonstrate many of the same skills that have brought some of their peers into the global spotlight. For example, when in the care of humans, rooks have demonstrated an astounding alacrity for tool use, though they are not known for manufacturing tools in the wild. For example, captive rooks have been shown to bend wire into hooks to extract food out of a tube like New Caledonian crows, or work together to solve problems like chimps (though unlike chimps, they do not appear to understand when cooperation is necessary or how it works).4,5

Taken together, these snippets of their biology and behavior demonstrate what unique members rooks are to the Corvus genus.  I envy my counterparts across the Atlantic and Pacific and encourage them to take a second look at the rook whenever opportunities present themselves.

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Photo c/o Paul Wilson

Literature cited

1.  Dunnet GM, Fordham RA, Patterson IJ. (1969).  Ecological studies of the rook (Corvus frugilegus) in North-East Scotland.  Proportion and distribution of young in the population.  British Ecological Society 6: 459-473

2.Green P. (1996). The communal crow.  BBC Wildlife 14: 30-34

3. Coombs CJF. (1960). Observations of the rook Corvus frugilegus in southwest Cornwall Ibis 102: 394-419

4. Bird CD, and Emery NJ. (2009).  Insightful problem solving and creative tool modification by captive nontool-using rooks.  PNAS 106: 10370-10375

5.  Bugnyar T. (2008).  Rooks team up to solve a problem.  Current Biology 18: R530–R532

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Filed under Birding, Corvid diversity, Corvid of the month, Diversity, Uncategorized

Corvid of the Month: How abundant food may be killing the Mariana crow

For most of us, it’s hard to imagine crows being anything but ubiquitous.  Here in Seattle, American crows can nest so densely, I once found myself within 50 m of three different active nests.  Such is the case for many other parts of the world too, where house crows, jungle crows, or hooded crows are an almost inescapable part of the landscape.  Given these species’ success, it might be tempting to assume that all crows welcome human presence and habitat modification.  Rules don’t exist without exceptions however, (especially in nature!) as our Corvid of the Month, the Mariana crow, tragically illustrates.

A female Aga and fledgling do some exploring. Photo: Matt Henschen

A female Aga and fledgling do some exploring. Photo: Matt Henschen

The Mariana crow, or Aga, is endemic to Guam and Rota and is the only corvid native to Micronesia1.  In appearance, they bear a striking resemblance to the American crow, only they’re 40% smaller (cue adoring sound effects).  Across their range they’re considered critically endangered and as of today, all of Guam’s birds have been extirpated by the invasive brown tree snake, and only about 46 breeding pairs remain on Rota.  If that wasn’t alarming enough, their numbers continue to dwindle and researchers at the University of Washington project they could be extinct within the next 75 years2.  Unlike Guam, however, there are no brown tree snakes on Rota.  So what is causing the drastic decline of this island crow?   As my colleague and Mariana crow researcher, Sarah Faegre, is beginning to tease out, the answer may lie in the delicate nature of island food webs, and the unanticipated butterfly effect that started with a few errant snails.

Like our American crows, Mariana crows are generalists and eat a wide variety of foods from insects, to geckos, to fruits and seeds.  But adult Mariana crows have one other food source they’ve come to specialize on: the humble hermit crab. Despite the presence of hermit crabs near other species of corvus, the Mariana crow’s frequent predation on them is unique, especially when you look at how they extract them.  Unlike most coastal or inland living crows that drop tough objects like clams or nuts onto hard surfaces to open them, the Mariana crow actually uses its bill to peck and break the shell at the seams to extract the vulnerable crab, a process that takes place entirely on the ground and is only shared by two other known bird species in the world (one of which is now extinct).  So what does this have to do with wanderlusting snails?  As it turns out, everything.

What's crackin' crabby? Photo: C. Brevimanus

What’s crackin’ crabby? Photo: Sarah Faegre

Rota is home to several species of native land and sea snail, though hermit crabs only utilize the larger shell of the sea snail.  Critically, these shells are extra hard and apparently impenetrable to even the most determined crow.  In the late 1930’s, however, humans introduced the Giant African Land snail which quickly invaded the island.  Two major differences between the native and invasive snails are 1) that the invasive snails have thinner shells, and 2) people were anxious to get rid of them.  So, naturally, we introduced  yet another invasive species (a predatory flatworm) and…it actually worked.  By the 1970’s the island was brimming with large, thin, empty shells, ready and waiting to be filled with hermit crabs.  Gradually, the crows learned that these shells were possible to peck open and now hermit crabs are an important staple for Rota’s crows.

Photo: Matt Henschen

Photo: Phil Hannon

On its surface, this seems like the making of an ecological disaster turned into a conservation blessing.  After all, we successfully controlled an invasive species while simultaneously creating a new food source for a threatened bird.  But in our tangled web of introduced species and ecological fallout we must considering the one remaining player: cats.  Although further study is needed, Sarah’s work3 suggests that all that extra time adult crows now spend on the ground cracking open hermit crabs may be making them more susceptible to predation by cats.

Couple the effect of cats with habitat destruction and persecution by people and the results project a bleak outlook for crow recovery.  But conservationists and researchers like Sarah are working tirelessly to better understand the threats facing this bird and how to solve them.  In fact Sarah and her husband, Phil Hannon, recently started a non-profit called Luta Bird Conservation to help raise awareness and conservation funds to better protect this unique crow.  At the top of their priorities is funding initiatives that would bring the science of crow conservation to the classrooms of local people, helping to raise both pride and awareness for the plight of this endemic species.

So the next time you look at a crow and experience a slight feeling of fatigue at such a ubiquitous bird remember; not all corvid species welcome the consequences of people and some have suffered greatly from them.  Aldo Leopold once said “to keep every cog and wheel is the first precaution of intelligent tinkering.” The lesson from Rota, and so many others, is that the same can be said of not adding any either.

If you wish to contribute directly to Mariana crow conservation, I encourage you to send Luta Bird Conservation Inc. a check at:

Luta Bird Conservation Inc. c/o Aron Faegre
520 SW Yamhill Street, Roofgarden 1
Portland, OR 97204
Sunny, Luta's educational Mariana crow captivates the students in a local school

Sunny the captive Aga on an ambassadorial trip to a local classroom with Luta Bird Conservation Inc.

Literature cited:

  1. http://www.fws.gov/pacificislands/fauna/marianacrow.html
  2. http://www.washington.edu/news/2010/12/20/without-intervention-mariana-crow-to-become-extinct-in-75-years-2/
  3. Faegre, S. (2014) Age-related differences in diet and foraging behavior of the critically endangered Mariana Crow (Corvus kubaryi) (Masters thesis; University of Washington).  https://digital.lib.washington.edu/researchworks/handle/1773/27571?show=full

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Filed under Corvid of the month, Crow behavior, crow conflicts, Crow life history, Crows and humans, Graduate Research, New Research, women in science

Corvid of the month: The jungle crow

If there’s one corvid that’s most notorious for getting into trouble, it’s probably the jungle crow (sp: Corvus levaillantii* genus: corvus).  A dubious reputation perhaps, but it’s one that’s been well earned through this corvid’s knack for exploiting humans and the opportunities we create.

Physical description: While jungle crows aren’t much bigger than an American crow, their square head and heavy bill gives them a more raven-like appearance.  To me, they look like what I might expect if a common raven tangoed with Rick Moranis’s contraption from Honey I Shrunk the Kids.

Range: They are found throughout the northeastern Asian seaboard to Afghanistan and eastern Iran in the west, through South and Southeast Asia, to the Lesser Sundas and Cambodia in the southeast.  Although in India the jungle crow and large-billed crow behave has two distinct species, in northern parts of Asia their distinction is less clear and colloquially the two are often analogous.

Conservation status: Given their large range, it may come as no surprise that their populations are abundant and are considered a species of least concern by the IUCN.  In fact, since the 1980’s the number of jungle crows in Tokyo has quadrupled1.

“Corvus macrohynchos map”. Licensed under CC BY-SA 3.0 via Wikimedia Commons

So what accounts for their bad reputation you ask?  Where to begin…how about vandalizing cemeteries1.  In Japan, food is left at the burial sites of loved ones as an offering.  Although in some cultures these offerings are meant to be eaten by animals, that is not the case here, and the crows’ stealing of food interrupts the intention of the ritual.  Historically, this probably wasn’t a conflict since jungle crow populations were much smaller than they are now.

As if that wasn’t enough to get people fired up, jungle crows also have a bad habit of, well, firing things up.  People were stumped how field fires near the Fushimi-Inari shrine in Kyoto were starting until someone thought to watch the crows.  There are 10,000 candle holders that line the walkways of the shrine and on busy days they may contain thousands of individual burning candles.  With some diligent watching, researchers discovered that crows were eating the melted candle wax (which is often made with tallow) and in some cases taking the burning candles out of the holders and flying off with them.  Although they never witnessed it, researchers suggested that crows’ attempts to cache burning candles may have been the cause of the mysterious fires2.

Photo: H. Higuchi

The crows appeared to show no fear of the flames according to the paper’s author. Photo: H. Higuchi

To top it all off, jungles crows seem to be just as good at turning out the lights as there are at lighting them up! Unlike American crows, which predominately use sticks to build their nests, jungle crows have developed a fascinating (and immensely frustrating for the Japanese government) habit of using clothes hangers to construct nests.  Mixing wire hangers with power lines is a recipe for disaster and in the summer time jungle crows are responsible for massive blackouts.  The Tokyo government spends millions of yen, and employs full time crews, to search for and destroy hanger nests in an effort to prevent such black-outs1.

Photo: Götz

Maybe Joan Crawford had just spent too much time around jungle crows…  Photo: Götz

It’s not all bad press for these resourceful crows, however.  One of the more spectacular things they are known for is using cars to crack open otherwise inaccessible nuts.  Not only that, but they also appear to be sensitive to crosswalk signals and know when it’s safe to collect the exposed nuts and when it’s not3.

So while the jungle crows make their fair share of trouble stealing food, candles and hangers, there are still plenty of people who adore these animals for their cleverness and ingenuity.  For those that don’t, well, some Japanese aren’t shy to take control measures into their own hands.  Or should I say mouths…

IMG_1922*The jungle crow was formally Corvus macrorhynchos, but the species was split into the large-billed crow Corvus macrorhynchos, the eastern jungle crow Corvus levaillantii, and the Indian jungle crow, Corvid culminatus.

Literature cited:

1Marzluff, J.M. & Angell, T.  2005 In the company of crows and ravens.  Yale University Press

2Higuchi, H. Crows causing fire. (2003). Manuscript from The University of Tokyo

3Marzluff J.M & Angell, T. 2012. Gifts of the crow.  Free Press

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Filed under Corvid of the month, Crow behavior, crow conflicts, crow intelligence, Crows and humans