Life History of the Common Raven

Common Raven by John James Audubon.

The common raven is a large, completely black passerine (perching bird) that can be found across most of the northern hemisphere. They can be found in a wide variety of habitats, including forests, tundras, mountains, fields, and urban areas (Campbell et al. 1997). Ravens are classified as a species of least concern and their population numbers have been growing significantly over the past forty years (IUCN, 2014). Ravens are similar in appearance to the Northwestern and American Crow but they can be identified by certain distinguishing features such as their shaggy neck feathers, larger size, longer wings, stronger beak, and wedge-shaped tail. Ravens also have a deep, throaty call while crows have a more high pitched ‘cawing’ call.

Comparison of a crow (left) and a raven (right) by Tom Grey.
Comparison of a crow (left) and a raven (right) by Tom Grey.

A comparison of crow and raven calls from the Cornell Lab of Ornithology.

Ravens are opportunistic omnivores who will eat almost anything they can get their beaks on including carrion, small animals, bird eggs and hatchlings, insects, berries, and human food found in landfills or garbage bins (Cornell Lab of Ornithology, 2015). Landfills have even become a major food source for ravens living in harsh environments like the snowy B.C. interior (Campbell et al. 1997). Ravens have also been observed scanning highways for roadkill to eat and following wolf packs to pick at the scraps of prey they leave behind (Campbell et al. 1997).

A raven sitting on a deer carcass by Bob Armstrong.

Young ravens without mates will form large groups that roost together at night and cooperate to find carcasses in harsh winters. The individuals in these groups change constantly and are formed of random birds with no familial ties. When a young raven locates a carcass, it will return to its roost that night and communicate the location to the other ravens in its group. When the juveniles return to the carcass they will fight off any resident adults that may have claimed it for their own. A lone juvenile would have no chance of chasing off a breeding pair of adults but a group could force them out in order to eat the carcass. Cooperating in this way ensures the young ravens will have a better chance of finding food and that they will be able to keep control of their food sources. (Heinrich & Marzluff, 1995 & Marzluff et al. 1996)

A group of ravens squabble over a beaver carcass by Michael S. Quinton.

Common ravens usually don’t breed until they are two to four years old. They are monogamous and form life-long bonds with their mates. The pair will stay together year round and roost near one another at night. Ravens will build their nests by weaving sticks and other materials together to form a basket in a tree, cliff, or man made structure. A cup is made in the basket and can be lined with fur, grass, or other detritus found by the birds. Nests are mostly made by the female and may be reused in following years by the ravens or other bird species. The female lays between three to seven eggs and incubates them for around twenty days. The young will leave the nest after four to seven weeks, staying close for the first week or so. The male raven assists in feeding the young and also brings food to the female while she is incubating the eggs. (Cornell Lab of Ornithology, 2015 & Seattle Audubon Society)

Raven eggs in the nest by Mike Jones.
A raven feeding their young by Jack A. Bailey.

Ravens have become well known for their impressive intellect and ability to solve complex problems that many other animals can’t. One such problem that was posed to a group of ravens by Bernd Heinrich involved a piece of dried meat on a string hanging off of a perch. In order to get the meat, the ravens had to pull the string up and then hold it with their foot while pulling up more of the string. Eventually they would be able to grab the meat after repeating these steps. Many of the ravens couldn’t solve the problem right away but once they figured out the solution they remembered it without fail in their future attempts (Heinrich, 1995). Many other studies on raven intelligence have been conducted and will be discussed in a future blog post.

Another endearing trait of ravens is the playful behaviour they exhibit with fellow ravens and even when they are alone. Playing begins in the nest when feathers first form on the newly hatched ravens. They will stand at the edge of their nest, facing inwards, and vigorously flap their wings. This may help to develop their flight muscles for when they’re ready to fledge. After fledging, ravens will engage in play flights with each other where they will chase one another and perform aerial acrobatics. These displays get more complex as they age and play an important role in how a raven chooses its mate. Paired adults will also engage in aerial acrobatics with each other to strengthen their bond before the breeding season. Young ravens have been observed caching inedible items such as sticks to play with later and playing tug of war with other ravens. They’ve also been seen bathing together, rolling in the dirt, hanging upside down from branches, and vocalizing in ways not seen in adult ravens. Perhaps the most dramatic display of play behaviour occurs when ravens are seen sliding down snowy inclines. Sometimes they’ll use a tool to slide down the hill, such as a can lid, or even go down on their backs! This doesn’t seem to serve any function other than calling attention to themselves, but maybe they just enjoy playing in the snow the way humans do. (Heinrich & Smolker, 1998)

A raven playing in the snow from Nature on PBS.

Ravens are fascinating birds who have captivated humans for centuries. They’re present in the myths and legends of many cultures and continue to be a symbolic figure in modern popular culture. Their intelligence, opportunistic feeding style, and ability to adapt ensure they’ll be living among us for many years to come.

References

Campbell R. W. , Dawe N. K. & McTaggart-Cowan I. 1997. Common Raven. In: Birds of British Columbia, Volume 3: Passerines: Flycatchers through Vireos. Vancouver, BC: UBC Press. [accessed October 30, 2015]. ProQuest Ebrary

Corvus corax. 2014. The IUCN Red List of Threatened Species; [accessed 2015 Oct 30]. http://www.iucnredlist.org/details/22706068/0

Common Raven. 2015. The Cornell Lab of Ornithology; [accessed 2015 Oct 30]. http://www.allaboutbirds.org/guide/Common_Raven/id

Heinrich, B. & Marzluff, J. 1995. Why Ravens Share. American Scientist [accessed 2015 Oct 30]; 83 (4): 342–349. http://www.jstor.org.ezproxy.viu.ca/stable/29775481

Marzluff, J. M., Heinrich, B. & Marzluff, C. S. 1996. Raven roosts are mobile information centres. Animal Behaviour [accessed 2015 Oct 30]; 51: 89–103. http://sefs.washington.edu/research.acl/Crows_and_Other_Corvids/roosts_anbehav1996.pdf

Common Raven. Seattle Audubon Society; [accessed 2015 Oct 30]. http://www.birdweb.org/birdweb/bird/common_raven

Heinrich, B. 1995. An Experimental Investigation of Insight in Common Ravens (Corvus corax). The Auk [accessed 2015 Oct 30]; 122 (4): 994–1003. http://www.jstor.org/stable/4089030

Heinrich, B. & Smolker, R. 1998. Play in common ravens (Corvus corax). In: Byers J. A. Animal Play: Evolutionary, Comparative and Ecological Perspectives. Cambridge, UK: Cambridge University Press. [accessed October 30, 2015]. https://books.google.ca/books?id=jkiTQ8dIIHsC&lpg=PA27&ots=07ziZX3u4r&dq=corvus%20corax%20intelligence&lr&pg=PA27#v=onepage&q=corvus%20corax%20intelligence&f=false

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VIU BIOL 325 – Ornithology Blog Project

Students in the ornithology course were asked to put together two blog posts for a local bird species of their choice.  The first post introduces the species and the second post highlights an area of recent research featuring the bird species.  This page provides a portal to the class’ blogs.  Enjoy and provide feedback!

Band-tailed Pigeon by Alexandra Lamberton

Barn Owl by Maggie Dietterle

Canada Goose by Stew Pierce

Chestnut-backed Chickadee by Stephanie Wetten

Common Raven by Paris Musto

Gray Jay by William Francis

Marbled Murrelet by Krystal Bachen

Northern saw-whet Owl by Caitlin Smith

Northern Shrike by Raquel Greiter

Northwestern Crow by Dana Gullison

Red-breasted Nuthatch by Michael Lester

Red-tailed Hawk by Eric Friesen

Rufous Hummingbird by Sarah Chalmers

Western Bluebird by Deanna Leung

Western Meadowlark by Sharlene James

 

 

 

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AS THE NORTHWESTERN CROW FLIES

 

Stiver, 2015 (fig.1)

A murder in the ‘hood!

You may not have heard about the events in my neighbourhood on Vancouver Island last night or on every autumn evening preceding it. I’m referring to the fall and winter pre-dusk flocking behaviour of crows, specifically  Northwestern Crows (Corvus caurinus).  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. Among the world’s most intelligent creatures Northwestern Crows and crows in general, have complex cognition comparable with chimpanzees (Emery and Clayton, 2014).  

Ubiquitous within their range, the crows live in both rugged, remote habitats and highly urbanized environments (http://www.birdvancouver.com/b_northwestern_crow.html). 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  spectacular and expansive portion of the species’ 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 (Brewer, et al., 2006).

Screen Shot 2015-11-01 at 9.00.06 AM

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 shorter body length (40cm), and purely coastal range in comparison with the similar, closely related American Crow (Corvus brachyrhynchos(Sibley, 2003).  Additionally, the species hybridize (Tweit, 2015) and both exhibit monomorphism meaning there is no difference in size or appearance between the sexes.  Genetic testing is underway to help resolve whether they are  actually separate species or whether the Northwestern is simply a subspecies of the American genus (Tweit, 2015). Many 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 ‘croaking’ call (Brewer, et al., 2006) (Link, 2005).

stanley park - northwestern crow

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 (Cornell University, 2015). In 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 (Marzluff and Angell, 2008). 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 (Marzluff and Angell, 2008).

Piper's Lagoon Nanaimo BC

Crow carrying vole meal

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

20151028_162931 nanaimo bc Dana Gullison

Northwestern Crow Nest

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). The male assists the female in nest building and then the female lays 4 or 5 bluish-green coloured eggs with brown speckles that incubate in 17-20 days (Cornell University, 2015). The birds are born altricial meaning they are helpless at birth unlike a precocial duckling which can swim and walk almost immediately after hatching (Cornell University, 2015).  Juveniles remain in the nest 29-35 days (Cornell University, 2015) during which time the parents may be assisted by a young offspring from a previous season that guards the nest or helps supply food (Link, 2005). Through 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). Crows that have left the nest and are finished feeding may leave or stay with the parents to assist in the following year’s breeding activity and then will annually gather again in fall and winter to roost over their decade long lifespan (Link, 2005).

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: ‘kaah kaah’ (Gullison, 2015). As more crows locate them and their numbers increase they continue on their way to their nocturnal roosting territory. Roosting activity is considered 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 (Link, 2005).  My local twilight gatherings involve only a few dozen individuals and are modest in contrast to some flocks.

(Ward, 2013)

In BC, where the majority of the global population resides (Campbell et al., 1997) a decline in the species’ population has occurred over the past twenty years. However, due to  a longer term increase they are considered secure in province (BC Conservation Data Centre, 2005).  A successful synanthropic adaptation (living among humans),  has led to a population increase in urban areas (Marzluff et al., 2001) and with that come challenges that frequently occur when any abundant population lives in close proximity with humans. There is the threat of West Nile Virus as corvids are highly susceptible, the fear of health risks associated with feces and feathers at large roost sites, the threat of attack during nest protection behaviour and those that simply perceive them as a pest (Link, 2005). Consequently, throughout the three larger jurisdictions they inhabit, Alaska, BC and Washington,  Northwestern Crows can be hunted, with a few restrictions, and with a licence  (Alaska Department of Fish and Wildlife, 2015) (BC Ministry of Environment, 2015) (Link, 2005).

I’m rather fond of crows and have no plans whatsoever to shoot them, however, I’m looking forward to the next murder…

 

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INCREASING OCCURRENCES OF BEAK DEFORMITIES EMERGING IN NORTHWESTERN CROWS

Fig13_NOCR_maxilla by leaningcedarstudio (broken link)

As I mentioned in my previous post, Northwestern Crow populations have shown a strong overall increase over the past half century, despite a 4%  (BC Conservation Data Centre, 2015) decline in BC and Alaskan records over the past 2 decades . The crow populations appear superficially healthy, however there may be an emerging reason for concern. In Alaska, and further south, beak deformity has been recorded at rates significantly (Van Hemert and Handel, 2010) higher than ever previously observed in a wild bird population (Van Hemert and Handel, 2010). This suggests a possible epizootic, equivalent to an epidemic in humans This epizootic of beak deformities may be a warning that this seemingly robust bird may be more vulnerable in its environment than it’s adaptive behaviour might suggest, or there has been a marked change in the ecosystem (Handel et al., 2010).

NOCR_flyer

 

In Alaska, government scientists have been studying native bird populations to learn more about the beak deformities. Normally bill deformities are not prevalent within populations (Van Hemert and Handel, 2010).  High incidents of beak deformity in wild bird populations can point to environmental problems (Handel et al., 2010)  (Van Hemert and Handel, 2010). Through her research on Black-capped Chickadees, Alaskan scientist Colleen Handel was alerted to a few birds with deformed bills showing up at bird feeders in the late 1990’s. Handel requested public help in documenting occurrences of beak deformities in chickadees at bird feeders and received numerous accounts about other birds, including a considerable number of Northwestern Crows with beak deformities, many of them south of Alaska.  Beak elongation affected either the top and bottom beak or both beaks at the same time and frequently resulted in the bird having difficulty feeding (Kay, 2014) The abnormalities of the two avian species was found to be a result of avian keratin disorder, a condition that occurs when the outer keratinized layer on the beak becomes grossly overgrown (Van Hemert et al., 2012). The parallel condition led to a study on the prevalence and morphological extent of beak deformities in crows and the geographic range of occurrences (Van Hemert and Handel, 2010).

NWCrow with deformed beak eating

Handel and her research partner Caroline Van Hemert  sampled crow populations at six coastal sites in Alaska for 1 year between 2007 and 2008. Each site was near a human settlement and provided a mixture of natural and human generated food available to the crows (Van Hemert and Handel, 2010). They measured 186 crows and found 19 adults with beaks classified as deformed and no juveniles with the deformity. The overall level of deformities exceeded their expectations by over 30 times. The prevalence of beak deformity in the crows was as much as 17%, much higher than the 6.5% found in the chickadees (Van Hemert and Handel, 2010). At two of the sites with greater occurrences of deformities, eight other species of birds displayed beak deformities. These two locations were also in close proximity to where the highest occurrences of beak deformity were noted in chickadees. Through a review of literature and observations compiled since 1980, 148 crows were  found  to have beak deformities, most of them since 1997. Sixty-four reports came from BC and Washington of crows with abnormal beaks. Only five observations were recorded from the rest of North America. This clear prevalence of occurrences since 1997 is equivalent to that of Black-capped Chickadees (Van Hemert and Handel, 2010).

images

Distribution Map of NOCR with deformed beaks

While no conclusions have yet been drawn, the authors have suspected both viruses and environmental contaminants and point out possible clues and directions for future research. They suggest the deformities are unlikely to be caused by parasites or infectious disease, because these localized avian populations are not exposed to transient agents.  They suggest that because of the overwhelming similarity of characteristics there is some factor ‘unique to the region’ causing the same disorder in crows as in all the birds studied. If it is an environmental factor or contamination then it would be diffuse because of the large geographic range of occurrences and more specific testing is necessary.  Further studies of crows living away from human habitation would provide useful comparison.  Further research into the pathology of avian keratin disorder may also be helpful in isolating the cause.

References for blog posts 1 & 2:

Emery N.J, Clayton N.S. 2004 The Mentality of Crows: Convergent Evolution of Intelligence in Corvids and Apes Science V.302, pp.1903-1907   http://www.sciencemag.org/content/306/5703/1903.abstract?sid=e39eb11f-f3eb-47ff-80f3-0a2ada1b9c4b

Vancouver Avian Research Centre, Species: Northwestern Crow Corvus caurinus http://www.birdvancouver.com/b_northwestern_crow.html  (Oct. 27 2015)

Brewer et al., Canadian Atlas of Bird Banding,  2006, Volume 1: Doves, Cuckoos, and Hummingbirds through Passerines 2nd edition, 1921–1995 http://www.ec.gc.ca/aobc-cabb/index.aspx?lang=En&nav=bird_oiseaux&aou=489

Sibley A.S., 2003, The Sibley Field Guide To Birds of Western North America, A.A Knopf, New York, p.308

Tweit B. 2015, E-Bird Northwest News and Features, Northwestern Crows, Genetics, and eBird: New Science for an Old Problem http://ebird.org/content/nw/news/northwestern-crows-genetics-and-ebird-new-science-for-an-old-problem/ (Oct. 27 2015)

Cornell University, 2015, All About Birds-Bird Guide Northwestern Crow, Life History, http://www.allaboutbirds.org/guide/Northwestern_Crow/lifehistory (Oct. 31, 2015)

Marzluff J.M., Angell T.,2008, In the Company of Crows and Ravens, Yale University Press, p. unavailable https://books.google.ca/books?id=Bc5YO5PnPmMC&pg=PT244&lpg=PT244&dq=In+the+company+of+crows+and+ravens+mcdonalds&source=bl&ots=ONLek6aA6o&sig=Jf20d0ckm-XyxKE51omzjtfy0VI&hl=en&sa=X&ved=0CDAQ6AEwAWoVChMIne61wJHyyAIVxDKICh2VWwo2#v=onepage&q=In%20the%20company%20of%20crows%20and%20ravens%20mcdonalds&f=false

Link R., 2005, Washington Department of Fish and Wildlife, Living With Wildlife, Crows,  http://wdfw.wa.gov/living/crows.html (Oct.31, 2015)

Ehrlich P.R., Dobkin D.S., Wheye D., 1988, The Birder’s Handbook, A Field Guide to the Natural History of North American Birds, Simon and Schuster, New York, p.416.

Gullison, D. 2015, Northwestern Crow Call, (sound recording), Nanaimo, Canada.

Ward M., 2013, Crows Over Commercial Drive, Vancouver (video)  https://www.youtube.com/watch?v=sgmdW_Uut1U (Oct. 27, 2015)

Campbell W., Smith G.E.J., McNall M.C.E., Kaiser G.W., Cooper J.M., McTaggart-Cowan I., Dawe N.K., 1997, Birds of British Columbia, Volume 3 Passerines – Flycatchers through Vireos, UBC Press, Vancouver, p.11. https://books.google.ca/books?id=xynPkpa6vToC&pg=PA11&lpg=PA11&dq=campbell+northwestern+crow+population&source=bl&ots=xGLv4onQpm&sig=D6ERfD2KLeho_HtrFQdw2XQf1vw&hl=en&sa=X&ved=0CCYQ6AEwAmoVChMI7rvCp53yyAIVUKWICh3H8QII#v=onepage&q=campbell%20northwestern%20crow%20population&f=false

B.C. Conservation Data Centre. 2015. Conservation Status Report: Corvus caurinus. B.C. Minist. of Environment. http://a100.gov.bc.ca/pub/eswp/esr.do;jsessionid=5pCQSVnfh3vwyxBLPbzWntmyq8KvDqhnpNV04xrGpywP3nmyprbm!1298844341?id=18443 (Oct. 30, 2015)

B.C. Ministry of Environment, 2015, Human/Wildlife Interactions, Nuisance Fauna, Birds http://www.env.gov.bc.ca/cos/info/wildlife_human_interaction/docs/nuisance_fauna.html#birds (Oct. 31, 2015)

Alaska Department of Fish and Wildlife, 2015, Small Game Hunting in Alaska, Regulations http://www.adfg.alaska.gov/index.cfm?adfg=smallgamehunting.regulations (Oct. 31, 2015)

Van Hemert C., Handel C.M. and O’Hara T.M.,  Evidence of accelerated beak growth associated with avian keratin disorder in black-capped chickadees (Poecile atricapillus), Journal of Wildlife Diseases, vol.48, p.686 http://www.ncbi.nlm.nih.gov/pubmed/22740534

Colleen M.H,  Pajot L.M., Matsuoka S.M., Van Hemert C.,  Terenzi J., Talbot S.L.,  Mulcay D.M., Meteyer C.U. and Trust D.A., 2010, Epizootic of beak deformities among wild birds in Alaska: an emerging disease in North America?,  The Auk, v. 127 pp. 882-898  http://alaska.usgs.gov/science/biology/landbirds/beak_deformity/pdfs/Auk_Handel_beak_deformities2.pdf

Marzluff J.M., McGowan K.J., Donnelly R. and Knight R.L., 2001, Causes and consequences of expanding American Crow populations, Avian Ecology and Conservation in an Urbanizing World,  Kluwer Academic Press, Norwell, MA. p.331 http://www.birds.cornell.edu/crows/Marzluff%20et%20al%202001%20Avian%20Urb%20Ecol.pdf

J. Kay, Environmental Health News, Winged Warnings, Twisted beaks: Scientists exploring mysterious deformities focus on new virus http://www.environmentalhealthnews.org/ehs/news/2014/aug/wingedwarnings6deformed-chickadees  (Nov. 2 2015)

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Current Research on Western Meadowlarks

WEME, non-breeding plumage, October2015, Nanaimo River Estuary.

WEME, non-breeding plumage, October2015, Nanaimo River Estuary.

Birds are what us science people call a model species – they have been studied for a long time and continue to be studied because there are lots of them and they are relatively easy to study. This amount of research and data collected allows for increased improvement in conservation efforts. However, more research is continuously required due to the massive number of bird species. I would like to share with all of you some of the current research that has been done on Western Meadowlarks (WEME); where “current” in biology means within the last ten years!

As previously mentioned it is recognized that yellow-breasted meadowlarks consist of two species – Western and Eastern. It is the suggestion of Barker et. al. that the Southwestern population of Eastern Meadowlarks, known as Lilian’s Meadowlarks (S. linanae), should be separated and recognized as its own species (2008). This segmenting into three species was proposed after research into mitochondrial and sex-linked genes resulted in historically isolated lineages (Barker et. al. 2008). In biology, the segmentation of species can be evolution in the works; however this reduction in genetic variation can end up being detrimental to the species, in some cases.

WEME, non-breeding plumage, October2015, Nanaimo River Estuary.

WEME, non-breeding plumage, October2015, Nanaimo River Estuary.

A study by Giovanni et. al. in 2011 looked at the effectiveness in detecting Western Meadowlark nests as a way of estimating nest density. They observed adults attending nests and also looked for adults in flight as a result of being flushed from a nest in response to a rope-drag method disturbance (commonly used for grassland bird nests) (Giovanni et. al. 2011). They found that the probability of adults attending nests was 0.46, while the probability of rope dragging provoking a flight response from the adults was 0.19 (Giovanni et. al. 2011). This demonstrated that nest density is subject to detection error and lead to the recommendation for sampling and modeling (computers and math!) to be combined for grassland nest detectability and nest density research (Giovanni et. al. 2011).

With grassland bird populations continuing to decline across North America, Giovanni et. al.  looked at Western Meadowlark fledgling preference and survival relative to age and ambient temperature in an effort to enhance conservation efforts (2015). They found that at high ambient temperatures fledglings preferred locations that had deeper litter with shorter vegetation, whereas younger, nearly flightless, fledglings preferred locations with shallow litter and high vegetation (Giovanni et. al. 2015). Fledgling survival was shown to increase with the ambient temperature and chick age, but decrease as litter depth increased (Giovanni et. al. 2015). Of the 46 fledglings they radio-tracked in 2006/2007, 23 died – 8 from predators (largely by snakes), 2 from haying operations, and 13 from unknown causes (Giovanni et. al. 2015). Although controlled burning would both reduce litter and snake populations – awesome!, it is not a viable conservation strategy in the location of this study – :(  (the meadows of the Nebraska Sandhills) (Giovanni et. al. 2015). Thus, they recommend late summer harvests to allow time for chicks to fledge (Giovanni et. al. 2015). I agree this strategy should be put forth, although I don’t think it is enough to save our grassland bird species. Yet another reason for more research!

Western Meadowlark, non-breeding plumage, singing in a tree, fall 2015.

Western Meadowlark, non-breeding plumage, singing in a tree, fall 2015.

Another study in 2014 looked at the nesting ecology of multiple species, including Western Meadowlark (Ludlow et. al.). It found that predation was the primary cause of nest failure and accounted for 75% of all nest losses (Ludlow et. al. 2014), whereas it accounted for only 35% of fledglings that died in the previously mentioned study (Giovanni et. al. 2015). The study showed that of all species looked at, only Sprague’s Pipit was not parasitized by cowbirds, however few WEME nests were parasitized and of them an average of zero cowbirds fledged (Ludlow et. al. 2014). For those of you whom do not already know about cowbirds, yet another species of blackbird, they don’t fledge their own young. Cowbirds will lay their egg in the nest of another species to be fed and raised until fledging, costly to the host species and nest but very beneficial to the cowbirds – brood parasitism. How awesome are blackbirds?!

Research was done in 2012 on grassland birds in their breeding season during the second and third year after large wildfires (Roberts et. al.). This study was done because fires are a key aspect in maintaining a healthy grassland ecosystem, and was able to vocalize that controlled burns have similar effects on the avian community as the wildfires (Roberts et. al. 2012). It showed that while wildfires were beneficial to some species, for species like WEME that prefer dense vegetation, wildfires have a negative impact on their breeding (Roberts et. al. 2012). However all bird populations seemed to return to pre-burn levels after only three years (Roberts et. al. 2012).

I hope this brief look into how complex ornithology research can be, has been not only informational but enjoyable! And, that I have brought you to the dark side and you have an immense appreciation for blackbirds!

WEMEbannerinfield

 

References:

Barker, K.F., A.J. Vandergon, and S.M. Lanyon. 2008. Assessment of species limits among yellow-breasted meadowlarks (Sturnella spp.) using mitochondrial and sex-linked markers. The Auk 125(4); 869-879.

Giovanni, M.D., M.P. Van Der Burg, L.C. Anderson, L.A. Powell, W.H. Schacht, and A.J. Tyre. 2011. Estimating nest density when detectability is incomplete: variation in nest attendance and response to disturbance by western meadowlarks. The Condor 113(1): 223-232.

Giovanni, M.D., L.A. Powell, and W.H. Schacht. 2015. Habitat preference and survival for western meadowlark (Sturnella Neglecta) fledglings in a contiguous prairie system. The Wilson Journal of Ornithology 127(2): 200-211.

Ludlow, S.M., R.M. Brigham, and S.K. Davis. 2014. Nesting ecology of grassland songbirds; effects of predation, parasitism and weather. The Wilson Journal of Ornithology 126(4): 686-699.

Roberts, A.J., C.W. Boal, D.B. Wester, S. Rideout-Hanzak, and H.A. Whitlaw. 2012. Grassland bird community response to large wildfires. The Wilson Journal of Ornithology 124(1):24-30.

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All About Western Meadowlarks

Western Meadowlark, non-breeding plumage, singing in a tree, fall 2015.

Western Meadowlark, non-breeding plumage, singing in a tree, fall 2015.

Western Meadowlarks, Sturnella neglecta, are a type of blackbird, this alone expresses their awesomeness; however I shall continue this post to make sure you receive the full package of why they are amazing. They are members of the Icteridae family, a group of medium/large songbirds that mostly have long pointed bills and long tails (Sibley 2003). Western Meadowlarks, WEME, are distinguishable by their notorious yellow belly and throat, studdly black breast-band, and teasing white outer tail feathers observable as they fly away.

Notorious outer white tail feathers as it flies.

Notorious outer white tail feathers as it flies.

As you may have guessed by now, there is both Eastern and Western Meadowlarks and the two species look nearly identical – here in British Columbia we only have the Western species. Hybrids of these two species usually only occur along the ranges edges, although captive breeding experiments have shown that the hybrids are fertile, their hatched clutch sizes are reduced (Cornell University 2015). WEME are observable at the Nanaimo River Estuary, and although their range map shows an extremely large range and that they are in our area year round, they can typically be found at the estuary from October to April (Cornell University 2015, eBird Canada 2015).

Western Meadowlark, non-breeding plumage, October 2015, Nanaimo River Estuary.

Western Meadowlark, non-breeding plumage, October 2015, Nanaimo River Estuary.

© Cornell University, 2015.

© Cornell University, 2015.

Eastern Meadowlark, breeding plumage, June 2015, Belize.

Eastern Meadowlark, breeding plumage, June 2015, Belize.

 

WEME are commonly found in grasslands, they are ground foragers known to feed on seeds, insects, and worms. Like other blackbirds WEME use a feeding behavior called “gaping”, this is the process of inserting their bill into a substrate, and then forcing it open with their unusually strong muscles (Cornell University 2015). This method creates a hole in which the meadowlark can then access a food source usually unavailable (Cornell University 2015) – their own niche!

Dandelion or Bird?!?

Dandelion or Bird?!?

Due to their habitat choice they can be hard for people to spot – you basically want to look for a small spot that pops up in the grass, if you’re lucky your eyes may catch some yellow or black – you are much more likely to hear them singing. Males will develop an arsenal of up to a dozen buoyant songs made up of whistles and warbles which he uses to defend his nesting territory (Cornell University 2015).

Male Western Meadowlarks usually have two mates simultaneously – polygyny (Cornell University 2015). The females are responsible for majority of the raising and feeding of their chicks (Cornell University 2015). They have ground nests that can be open in the grassland or completely covered with an entrance tunnel (Cornell University 2015). They will lay about 3-7 eggs, the nestlings will leave the nest at about 12 days, and are continued to be tended to for about 2 more weeks as they cannot fly yet – the process of fledging (Audubon 2015).

Conservation Status

© BirdLife International, 2012.

© BirdLife International, 2012.

Under the IUCN (International Union for Conservation of Nature) Red List Western Meadowlarks, Sturnella neglecta, are listed as least concern – as of 2012 (BirdLife International).  For those of you who do not already know, the IUCN is a comprehensive collection of conservation status’ of biological organisms – more inclusive than COSEWIC, the Canadian version which does not even have a status recorded for WEME at this time (COSEWIC 2015).  The species is shown to be decreasing – classified as lower risk/least concern in 1988, 1994 and 2000, and then upgraded to least concern in 2004 and for assessments in 2008 and 2009 (BirdLife International 2012).

 

References:

Audubon. 2015. Guide to North America Birds: Western Meadowlark Sturnella neglecta.Retrieved October 31, 2015, from https://www.audubon.org/field-guide/bird/western-meadowlark.

BirdLife International. 2012. Sturnella neglecta. The IUCN Red List of Threatened Species 2012: e. T22724256A39917671. Retrieved November 1, 2015, from http://www.iucnredlist.org/details/ 22724256/0.

Cornell University. 2015. All About Birds: Western Meadowlark. Ithaca, NY. Retrieved October 31, 2015, from http://www.allaboutbirds.org/guide/Western_Meadowlark/id.

Cosewic. 2015. Wildlife species search: Western Meadowlark. Retrieved November 1, 2015, from http://www.cosewic.gc.ca/eng/sct1/SearchResult_e.cfmcommonName=western+meadowlark&scienceName=&Submit=Submit.

eBird Canada. 2015. Western Meadowlark Hotspot: Nanaimo River Estuary. Retrieved November 1, 2015, from http://ebird.org/ebird/canada/map/wesmeaneg=true&env.minX=&env.minY=&env.maxX=&env.maxY=&zh=false&gp=false&ev=Z&mr=1-12&bmo=1&emo=12&yr=all&byr=1900&eyr=2015.

Sibley, D.A. 2003. The Sibley Field Guide to Birds of Western North America. Alfred A. Knopf Publisher, New York. p. 434, 438, 439.

Zip, J. 2012. Western Meadowlark singing on territory in Wyoming. Wild Bird Video Productions. Retrieved November 1, 2015, from https://youtu.be/Sk4S2spFdcs.

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The Magnificent Western Bluebird

Male Western Bluebird with its characteristic blue body and orange chest Photo credits: http://www.mangoverde.com/wbg/picpages/pic138-63-2.html

The Western Bluebird, one of three species of bluebirds in North America, is commonly located in the western part of Canada and southwestern part of the USA and is often seen within open coniferous or deciduous woodlands¹.

Geographic range of Western Bluebirds showing where they can be found during the different seasons.  Photo credit: http://identify.whatbird.com/obj/150/overview/Western_Bluebird.aspx

Like all bluebirds, males sport the bright blue plumage with a bright orange breast, while females are considerably duller in colour – only having some blue within their wings and having a pale orange breast. Because of the plumage seen in males, they can be confused for the Eastern Bluebird (Sialia sialis) but key differences between the two species come down to the colour on the throat and the belly. The Western Bluebird maintains the blue colouring on their throat and belly while the Eastern Bluebird has an orange throat and lacks any colour on their belly¹. If plumage colour doesn’t help with the identification, know that where they can be found does not overlap with each other.

Female Western Bluebird distinguished by its duller colours in comparison to its male counterpart Photo credit: http://tgreybirds.com/Pages/WesternBluebirdp.html

Bluebirds are social creatures and the Western Bluebird is no exception. They can be seen forming flocks with each other and with other birds to feed¹. They will typically feed on insects, leaping down from their perch in order to catch them, as well as berries. Western Bluebirds are birds that nest within holes in trees or in nest boxes. They are not equipped to form their own holes which cause them to rely on woodpeckers to create appropriate nesting areas for them. Within these cavities, females with form their nests and lay their eggs. Western Bluebirds are generally monogamous, with each pair of bluebirds raising their young together. But they are also known to have helper birds that will help them raise their young¹.

Western Bluebird returning to its nestbox with food Photo credit: http://www.examiner.com/article/the-western-bluebird-san-diego

You would be hard pressed to see a Western Bluebird in open woodlands. While according to the IUCN Red List, Western Bluebirds are in no risk, sightings of these birds are hard to come by. The biggest reason is due to loss of habitat which leads to loss of appropriate nesting areas for these birds. Logging, competition for space, and limited nesting areas have all contributed to seeing fewer birds. Western Bluebirds are threatened by increased competition for nesting cavities from other cavity nesters, especially from invasive species, such as the European Starling and the House Sparrow².

There are several conservation efforts to re-establish breeding populations on Vancouver Island, with the most well known project from the Garry Oak Ecosystems Recovery Team (GOERT), Bring Back the Bluebirds, leading the way. By providing new nestboxes and with the use of translocations, the project hopes to release 90 adult bluebirds back into the Cowichan Valley³.

However, there are some ways YOU can help increase the chances the seeing Western Bluebirds, even possibly seeing one in your own backyard. You can help the bluebirds by putting up a nestbox, monitoring activity, and reporting bluebird sightings.

¹ Western Bluebird. Cornell Lab of Ornithology. [accessed 2015 Oct 20]. http://www.allaboutbirds.org/

² Western Bluebird. March 19, 2015. Nature Conservancy Canada. [accessed 2015 Oct 20]. http://www.natureconservancy.ca

³ Goert.ca,. ‘GOERT : Our Activities : Bring Back The Bluebirds Project’. N.p., 2015. Web. 2 Nov. 2015.

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Plumage Colour and Assortative Mating

A male and female Western Bluebird pair Photo credit: http://www.sfgate.com/homeandgarden/thedirt/article/Western-bluebirds-offer-pest-control-on-the-fly-2446193.php

The bright blue plumage of the Western Bluebird is a key identifying characteristic for these birds. This plumage also helps the males to find their female partner. One study, performed by Anne Jacobs, Jeanne Fair, and Marlene Zuk, looked at the effect of this colouration on mate selection.  They tested whether birds with brightly coloured feathers would mate with partners of similar appearance (assortative mating), along with determining if colouration is involved in the formation of extra-pair partners – an individual outside of the original pair bond.

Through their experiment, they observed that pair bonded birds mated assortatively according to plumage colouring as they had brightly coloured males mate with brightly coloured females but this colouring was limited to the bright blue feathers, as they noticed that no assortative mating occurred with a brightly coloured breast. With the formation of extra-pair bonds, they observed that plumage had no effect on the assortative mating between a female and her extra mate and a male and his extra mate. It seemed that the only thing that had any effect on assortative mating was the age of the male; it seemed that older males in extra-pair pairings had success in rearing offspring in comparison to their younger counterpart.

The end result was they concluded that in the formation of pair bonds, colouration played a role while there was no observable effect on the formation of extra-pair pairings.

Read the original paper here.

References
Jacobs, A.C., Fair, J.M., and Zuk, M. 2015. Coloration, Paternity, and Assortative    Mating in Western Bluebirds. International Journal of Behavioural Biology. 121(2): 176-186

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Barn Owl (Tyto alba)

Description

The Barn Owl is unmistakable in the field. It’s ghostly appearance and distinctive heart shaped facial disc differentiates it from the other owls occurring in BC (Cornell University, 2015). It is a medium sized owl ranging from 30-37 cm with a wingspan of about 104-120 cm (Zevit, 2010). Barn Owl’s have a white or tan underbelly with black specks.The males are generally whiter and smaller than    

females and have fewer black spots (Figure 1) (Martin, 2009). They have a screeching call that is easily distinguished without seeing the owl.

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Figure 1:Female (left) and male (right) Barn Owls (Tyto alba) resting. Female is noticeably larger and darker than male. (Photograph Tambako Jaguar).

 

Distribution & Habitat

The Barn Owl is globally distributed, absent only from parts of the West Indies, New Zealand and Indonesia. They seldom occur in high Northern latitude and have limited range in British Columbia (Martin, 2009). Within BC, the Barn Owl occurs at the lowest elevations available in southern BC (Zevit, 2010). During the daytime, they nest in the hollows of trees or more commonly in human infrastructures where there is little human activity. These nests will likely be located near or on the floor of a building or tree. (Martin, 2009). Barn Owl’s are strictly nocturnal and inhabit grasslands, open fields and agricultural areas where they feed on rodent species, especially voles (Taylor, 1994).

 

Hunting & Diet

Barn Owls have excellent sight and hearing. Their low-light visibility and the use of their facial disc for funneling sound is responsible for their hunting success. These features allow barn owls to find their prey even when they are hidden from view (i.e. buried in snow or in burrow) (Martin, 2009). In North America and Europe, Barn Owls primarily feed on Townsend’s Vole (Zevit, 2010). Non-mammalian prey, such as birds, reptiles and frogs are occasionally consumed when voles and other rodent species are unavailable. Prey is generally consumed whole. (Taylor, 1994).

 

Behaviour

As mentioned before Barn Owls are nocturnal animals. During the day you will find them ‘roosting’ or resting in quiet areas that are well protected (Figure 2). Barn Owls are commonly found resting in pairs and more than one pair of owls may inhabit in close proximity if food is abundant in the area (Martin, 2009). These owls are unlikely to defend their hunting territories from other owls, but they will defend territory that is in close proximity to their nesting sites (Martin, 2009). When defense is needed Barn Owls have a variety of maneuvers to wean off predators: hissing and bill snapping are common, as well as opening wings in order to look bigger is used along with shaking their head back and forth (View Link Below) (Bunn, 1982).

roosting

Figure 2: Barn Owl roosting in a hole of a tree, a common place to spot a barn owl during the day. (Photograph: Brendan McGarry).

 

 

Mating & Reproduction

Barn Owls are known to be monogamous and may stick with the same partner for several breeding seasons or for their entire life. Males attract females many ways, one way is by performing a ‘moth flight’ which is where they hover in front of the female for several seconds (oolala). Once chosen the male will bring prey to his partner and often it is more than she could consume prior to their breeding time (Cornell, 2015). Breeding season usually occurs between February and June. Breeding occurs in February in warmer climates such as Florida and later in spring for more temperate areas such as BC.

 

Threats, Conservation & Management

Population decrease coincides with industrialization of farmland habitats necessary for Barn Owl hunting and feeding. This development leads to the inevitable decrease of British Columbia’s Barn Owl population. Not only are Barn Owls susceptible to these habitat changes but so istheir prey, Townsend’s Vole. Car accidents and pesticide use are also killers of Barn Owls (Zevit 2010). Public knowledge and ability to identify Barn Owls is a necessity for keeping track of Barn Owl populations. In “BC’s Coast Region: Species & Ecosystems of Conservation Concern” objectives for Barn Owl management hopes to protect large tracts of habitat from development. Timing crop harvesting, protecting known nest sites and encouraging landowners to conserve and protect nesting habitats suitable for Barn Owl nesting are all factors that could help protect the Barn Owl. The Barn Owl is protected by the British Columbia Wildlife Act and the federal Species at Risk Act (SARA).

 

 

 

 

References

  1. Zevit, Pamela. 2010. BC’s Coast Region: Species & Conservation Concern – Barn Owl (Tyto alba). Consultants of South Coast Conservation Program. Web. 25 Sept. 2015.
  2. Martin, J.M., Raid, R.N. & Branch, L.C. 2009. Barn Owl (Tyto alba). University of Florida, IFAS. Web. 17 Oct. 2015.
  3. Barn Owl. 2015. All About Birds. Cornell Lab of Ornithology. Web. 17 Oct. 2015.
  4. Jaguar, Tambako. 2014. AWWDUCATIONAL. Awwducational. Web. 26 Oct. 2015.
  5. Taylor, Iain. 1994. Barn Owls- Predator-Prey Relationships and Conservation. University of Edinburgh. Web. 22 Oct. 2015.
  6. Bunn, D.S., Warburton, A.B., & Wilson, R.D.S.The Barn Owl. Soho Square, London: A&C Black Publishers Ltd, 1982. Print.

 

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Catching Prey in the Dark

Scientist Masakazu Konishi evaluates how barn owls catch their prey in complete darkness. By testing their auditory localization skills in a variety of tests the Barn Owls accurate localization becomes better understood.

   The ability to hunt in complete darkness is an incredible feat that requires excellent hearing and motor senses. This nocturnal behaviour is rare among birds. This habit is seen in less than 250 species and within those species some may only be considered crepuscular (active at dawn and/or dusk) (Martin, 1985). This point alone makes the study of nocturnal behaviour fascinating for any bird fanatics. Payne and Drury were the first to demonstrate the acoustic hearing abilities of Barn Owls in 1958 (Konishi, 1973). Masakazu Konishi revisited their observations in his own study in order to gain further information.

 

Barn Owl (Tyto alba) taking a Field Mouse: sequence showing owl launching itself from a fence post.

Sequence showing a Barn Owl launching itself from a fencepost to catch a field mouse. (Photograph Warren Photographic).

    There are two important points in Konishi’s experiment. First is that the Barn Owl does not depend on scent or body heat to track prey and that an owl will not strike prey whose sounds are unfamiliar. The first point was determined by attaching a piece of crumpled paper behind a mouse. When the lights were turned off and the owl was cued to attack, it striked the paper instead of the mouse. This indicates that the mouse body heat and scent was not a determinant for mouse location by the Barn Owl. The second point was determined by noticing that new sounds that did not ensure an award, were ignored. In order to move forward in experiments of the auditory capability, the frequency threshold of the Barn Owl needed to be determined. Three owls were used for this experiment: the owls were trained to leave their perch when they heard certain cues for a reward. In the end it was found that the Barn Owl could hear in a range of 500 Hz to 10 kHz. This range is much larger when compared to other birds. In addition the Barn Owl has specializations that help in its localization of prey by acoustic cues alone which other birds and even other owls do not possess (Dyson, 1998).

Reaching out for its prey: the Barn Owl tilts back wings and opens talons to prepare for its catch. (Photograph: John Waters).

     Three experiments were created to further test the Barn Owls ability of sound localization: locating artificial sounds, locating pure tones and locating noises. To determine accuracy of location of artificial sounds (electronically developed sounds), a ‘chess-board’ set up was created consisting 10cm x 10 cm squares and 20 cm x 20 cm squares making up 100 squares. Loud speakers were set up under certain squares. When the owl heard the sound cue it would land on the square and the accuracy of measurement was determined by sensory pads in the squares. It was determined that the midpoint between the owl’s feet was always near the centre of the plate square, indicating almost perfect accuracy throughout trials. In locating pure tones barn owls seemed less able to accurately track sounds at low and high frequency tones, such as 3 kHz and 10 kHz whereas intermediate tones were more easily detected (6-9 kHz). For locating noise sounds with varying bandwidths were played, the sound would last from the time the owl left the perch until it landed on the ground. It was determined that the owls tracked best when provided sounds with frequencies ranging 5.5-9.5 kHz and a frequency range of 4-7.5 kHz was sufficient for accurate location. In short, the Barn Owl is able to locate a mouse based on a small section of the frequency spectrum. Since mice make a variety of frequency noises while moving through their habitat, owls are able to be very successful nocturnal hunters (Konishi, 1973).

The ability of the Barn Owl to locate sound is complex. Accurate localization depends on a variety of spatial cues or spatial information which is reliant on the right size and shape of the owl’s head and ears (Knudsen, 1985). It was also proven relevant that prey continues to move after the owl takes off for accurate localization. In Konishi’s experiment the prey was missed 69 times out of 86 when a spatial cue did not persist from the time of leaving the perch to landing. Whereas the same bird hit the target 46 times of 58 trials when the cues persisted through takeoff to landing (Konishi, 1973). Finally, a well known factor of sounds localization is the use of the facial shaped disk of the Barn Owl. This facial disk helps in funneling sound into the ear holes and helping with sound localization (Martin, 2005).

Many birds make use of perch- and flight hunting techniques besides the Barn Owl (i.e. Kestrels). However the grace and beauty of the Barn Owls soundless and seemingly weightless flight is unmatched by many birds (Taylor, 1994). There is a vast amount of research on different aspects of auditory localizations in bird species and the Barn Owl specifically. The Barn Owls ability to hunt successfully in complete darkness is remarkably unique among bird species and deserves attention among ornithology researchers.

 

   

    References

  1. Konishi, Masakazu. How the Owl Tracks its Prey: Experiments with trained barn owls reveals how their acute sense of hearing enables them to catch prey in the dark. American Scientist, 61.4 (1973): 414-424. Print.
  2. Martin, G.R. Sensory capacities and the nocturnal habit of owls (Strigiformes).Ibis, 128.2 (2008): 266-277. Print.
  3. Dyson, M.L., Klump, G.M. & Gauger, B. Absolute hearing thresholds and critical masking ratios in the European barn owl: a comparison with other owls. J Comp Physiol A, 182 (1998): 695-702. Print.
  4. Taylor, Iain. 1994. Barn Owls- Predator-Prey Relationships and Conservation. University of Edinburgh. Web. 22 Oct. 2015.
  5. Knudson, E.I. & Knudsen, P.F. Vision Guides the Adjustment of Auditory Localization in Young Barn Owls. Science, 230.4725 (1985): 545-548. Print.
  6. Martin, J.M., Raid, R.N. & Branch, L.C. 2009. Barn Owl (Tyto alba). University of Florida, IFAS. Web. 17 Oct. 2015.
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