Category Archives: Conservation

2018 research round up

As 2018 draws to a close, I want to dedicate a post to five of the most interesting and important publications about our favorite family of birds that came out this year. For the sake of a brevity, the reported studies are largely condensed with some tests/results omitted and little attention to normally key experimental elements like controls, statistical analyses, etc. Please click on the study title to be directed to the full publication.

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1. Townsed AK, Frett B, McGarvey A, and Taff CC. (2018). Where do winter crows go? Characterizing partial migration of American Crows with satellite telemetry, stable isotopes, and molecular markers.  The Auk 135: 964-974

Background: Depending on where you live, the answer to, “Do crows migrate?,” can be quite different.  For example, most Seattle residents would probably say no, since large numbers of crows can be seen here year round, while someone in say, a southern Canadian province, may notice a sharp decline in the number of crows during the winter.  That’s because crows are what’s know as “partial migrant species” meaning that within a population, some individuals may be migratory and others resident with more migratory strategies biasing in areas with harsh winters.  Despite the role of partial migration in how scientists currently explain the evolution of complete migration, little is known about the phenomenon.  Even elemental questions such as: is this behavior fixed or flexible within individuals, is it environmentally influenced, and how might species use it to adapt to changing conditions remain under-explored.

Methods: The study looked at two populations of overwintering crows: one in Ithaca, New York and a second in Davis, California.  They used a combination of intrinsic (meaning originating in the body) and extrinsic (meaning originating outside the body) markers to track the movement and origin of their 18 tagged subjects over 2-4 years.  The intrinsic makers included molecular and stable isotope data, and the extrinsic marker was a satellite tracking device that was attached to the bird via a light backpack.  I won’t go into the details of the molecular and stable isotope data, but suffice it to say that stable isotopes were used to identify the place of origin via the unique properties of the local food and water that embed into an individual’s tissue and the molecular data was used to sex individuals and establish relatedness.

Key findings: Of the 18 tagged crows across both east and west coast populations, they found that almost 78% were migratory.  This was a shock to me, TBH.  I had no idea just how many crow were making these annual trips.  The distance these birds traveled varied widely, with some going as “little” as 280 km (173 miles) and others as much as 1095 km (680 miles). Among resident birds, they found that individuals never ventured further than 25 km (15.5 miles) from the center of their breeding site.  For both resident and migratory individuals they found that birds were very loyal to their breeding sites; returning to the same territory year after year.  Given this finding, it should not be surprising to learn that individuals did not vary from year to year in whether they were migratory or not.  Together these results offer clues to how crows may respond to climate and urbanization induced changes in temperature to their local environments.

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2.  von Bayern AMP, Danel S, Auersperg AMI, Mioduszewska B, and Kacelnik A. (2018). Compound tool construction by New Caledonian crows. Nature Scientific Reports 8

Background: For decades people considered the use of tools to be a uniquely human feature.  Now we know that all sorts of animals, ranging from fish to monkeys, use tools and a handful of animals even create tools.  Among the small number of animals that create tools, we have only seen wild individuals modifying a single object.  For example, stripping a twig of small leaves or branches in order to probe small holes for insects.  Whether any wild animal is capable of making compound tools, those made by combining seperate non-functional parts, is unknown.  Even in captivity, this behavior only has limited observation in the great apes.  Understanding what animals are capable of this complex task and how they achieve it, might give us insight into the evolution of our own exective functions.

Methods: This study used eight wild caught captive New Caledonian crows.  Like many experiments involving novel objects, this one occurred over multiple different phases.  In phase I the birds were provided a long stick and a baited test box where food was within reach when using the stick, but not without it.  In phase II the birds were presented with the same baited test box, except that instead of a single long stick, they were given a hollow cylinder and a second, thinner cylinder that needed to be combined in order to generate a tool long enough to reach the food.  In phase III, the birds were given the same problem, only now with novel combinable items.  In phase IV, the researchers tested whether the birds were combining elements because they understood that they needed to, or if because they derived some other benefit from the process.  To do this, they presented birds with a bait box that had two tracks: one where the food was within reach of a single element and one where it required a compound element. In the final phase, birds were presented a bait box that required the combination of more than two elements.

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Image from von Bayern et al. 2018

Key findings: All birds passed the initial tool use phase handily.  Given that New Caledonian crows frequently use single element tools in the wild, this was not at all surprising. In the second phase, half of the subjects (four) were able to combine the two elements after no more than two failed attempts. These subjects were then able to transfer this knowledge when presented novel combinable objects. When given a bait box with food presented on the close and far tracks, birds most often only made compound tools when it was necessary, suggesting that they don’t do it just for fun.  In the final phase, only one bird succeeded in making a tool that required more than two elements.  These findings demonstrate that New Caledonian crows are not only on par with what’s know about compound tool use in the great apes, but actually exceed them.

Unfortunately what this study does not explicitly answer is whether the birds were able to create the needed tools as a result of mental mapping (i.e imagining the correct tool and how it might be assembled) or by happy accident.  Without this knowledge, what their ability to make compound tools suggests about the evolution of things like insight remains mysterious.  Given all the other remarkable ways New Caledonian crows show innovation when it comes to tool use, however, both myself and the authors of this study are hedging that it’s indeed cognition behind these behaviors rather than more simple mechanisms.

3. Boeckle M, Szipl G, and Bugnyar T. (2018). Raven food calls indicate sender’s age and sex. Frontiers in Zoology 15

Background:  One of the most frequent inquiries that come my way are requests to decipher various crow calls.  Given all we know about crows, this doesn’t seem like such an impossible request, but the reality is that crow communications remains one of the most impenetrable black boxes of crow behavior.  I’ll save more on this for a future post dedicated to an upcoming publication by my colleague Loma Pendergraft, who spent his MS learning this fact the hard way.  But suffice it to say that any progress on this front in the various Corvus species is groundbreaking news.  We do, however, know more about raven calls. For example long “haa” calls are thought to recruit other individuals to sources of food.  What was unknown at the start of this study was whether these calls encoded any class-specific information about the caller, such as their age or sex. Calls that impart class-level information about the caller have been previously demonstrated in some marmots and monkeys.

Methods: The researchers recorded hundreds of “haa” calls from wild ravens which had previously been color banded and whose age and sex were known.  Using acoustic software they analyzed the vocalizations for patterns in call elements like frequency and inflection rate.

Key findings: As the study’s title suggests, ravens appear to encode information about their age and sex in “haa” food calls.  For animals like ravens that live in “fission-fussion” social systems, meaning flexible social groups where individuals regularly reencounter familiar individuals, but also encounter unfamiliar ones, class-level information helps individuals quickly assess important aspects of a caller’s identity.  Such information may be key to helping individuals decide if they want to join a feeding event or not.  This decision is particularly important because aggression at feeding events can cause mortal injury, so grouping with a bad crowd can come at a high price.

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4. Kroner A, and Ha R. (2018). An update of the breeding population status of the critically endangered Mariana Crow (Corvus kubaryi) on Rota, Northern Mariana Islands 2013–2014. Bird Conservation International 28: 416-422 

Background: The Mariana crow or Aga is a native species to the islands of Guam and Rota.  After the introduction of the brown tree snake to Guam in the 1940’s, Guam’s entire population of Aga were wiped out leaving only those found on Rota to continue the species.  In 1982, the population hovered around 1,300 individuals but things were clearly in decline. In 1984 the Aga was officially listed as endangered and today is considered critically endangered by the IUCN.  Unlike on Guam, there is no clear reason why the Aga continues to decline on Rota, though habitat loss, persecution by humans, natural disasters and introduced predators like cats likely all work together.

Methods: During 2013-2014 researchers counted breeding pairs by surveying all known island territories.  During these counts (which took 845 hours of labor and traversed 1,485 hectares!) the researchers also documented any unpaired or subadult birds. Since the entire island could not be surveyed, to ultimately estimate the population size the researchers used models that accounted for missed detections.

Key findings: Spoiler alert: They are A BUMMER.  In all that searching only 46 breeding pairs were detected.  Accounting for unpaired birds and detection failures, the researchers estimate that the current population of Aga hovers around 178 individuals.  Obviously that number alone is a gut punch but it’s especially true when you consider that that’s a 10-23% decline since 2007 and a 46-53% decline since 1998.  Researchers estimate that at least 75 pairs are needed to maintain a viable population of Aga.  Without intensive predator management and community level advocacy for these birds, their future is sadly looking grimmer and grimmer.

5. Walker LE, Marzluff JM, Metz MC, Wirsing AJ, Moskal ML, Stahler DR, and Smith DW. (2018). Population responses of common ravens to reintroduced wolves. Ecology and Evolution 8: 11158-11168

Background: One of the most persistent myths about common ravens is that they have a symbiotic relationship with grey wolves; intentionally showing them carcasses they find and then sharing in the bounty together.  But while the case is actually that ravens are unwelcome dinner guests at the wolves’ table, there’s no question that the two species have profound effects on one another. The reintroduction of wolves to Yellowstone in 1995 therefore offers a valuable way to study how the presence of wolves affects the spatial distribution and feeding behaviors of park ravens.

Methods: This study was a collaborative effort between avian and spatial ecologists at the University of Washington and Yellowstone wolf biologists.  Using data from 2009-2017 on wolf abundance and prey kills, and raven surveys taken both within the interior of the park and at anthropogenic food sources in surrounding areas (ex: the Gardner town dump), the researchers were able to model raven abundance during both the study period and before the reintroduction of wolves.  I won’t go into the details of how these models are created, but suffice it to say that their purpose is to take the data you give them and find what predictors best explain your observed outcomes.  For example if, say, you have a bunch of data about where ravens were located at different times, and have data on different possible predictors, say, wolf abundance, weather, carcass abundance, carcass biomass, and distance to anthropogenic food, etc., the right model could help you identify that carcass biomass is the best predictor of raven abundance.

Key findings: Previous studies have demonstrated that wolves make more kills during severe winters with higher snowpack, because prey have a more difficult time evading them.  As a result, the researchers hypothesized that ravens would depend more heavily on wolf kills during severe winters,  but this is not what they found.  Instead, Yellowstone ravens seem to lean more on consistent, anthropogenic food sources during tough winters, but lean more on wolf provided carrion during more mild winters.  Still, the presence of wolves has increased and stabilized the number of ravens in the park, because they provide a second year-round source of food, in contrast to human hunter provided kills which are seasonally limited.  These findings are yet another demonstration of the value of top carnivores in stabilizing food webs and providing food for a cascade of creatures.

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6. And as a bonus let’s not forget the most important 2018 study of them all, “Occurrence and variability of tactile interactions between wild American crows and dead conspecifics,” which you can read all about here. 😉

leslie

 

 

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Filed under Conservation, Crow behavior, crow intelligence, New Research, Raven behavior, Ravens, Science

Denali Diaries Part II: The Wildlife

While Denali is worth visiting on the basis of its scenery alone, it’s the wildlife that will truly shape your experience.  In the summer, Denali is host to some eight species of medium to large sized mammals, including foxes, lynx, wolves, grizzly bears, black bears, caribou, Dall sheep and moose.  Among those, the moose, grizzly bear, caribou, wolf, and Dall sheep make up what’s known as the “Denali Big 5.”

Seeing wildlife in Denali is mostly about luck and timing, but the longer you’re in the park the more chances you have to view wildlife.  As I described in my earlier post, I scheduled and bus hopped my trips in such a way that I stayed in the park most of the day.  This is particularly important for moose, which are generally crepuscular, meaning they are more active in the morning and evening . Everything else is really just a gamble. Sometimes the odds are in your favor and sometimes they’re not. For what it’s worth, though, out of my four all-day trips into the park I got The Big 5 twice, both during the times I stayed primarily on the bus.

While I always left the park having experienced something new, there were definitely trips that were more memorable than others, and the range of experiences really made me appreciate the luxury of being able to go multiple times.  Whatever wildlife you do have the privilege of encountering is sure to fan the flames of your love affair with this park, but I imagine for many people that affair starts first and foremost with the most visible and charismatic of Denali’s wildlife: The grizzly bears.

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I took this photo in late August, just as the colors started to change.

By late July, bears across Alaska are gearing up for hibernation by entering a phase called hyperphagia, where they basically eat constantly and gain somewhere on the order of 400 pounds.  In the park, their diet consists mostly of blueberries, soapberries, and roots, but they will gladly eat whatever mammals they can catch, including small rodents, caribou, moose and even other bears.

A big highlight when bear watching is seeing sows out with spring cubs. Unlike mom, the young are generally a lot darker in color, prompting people to sometimes mistake them as black bears.  Observing cubs playing, foraging, and trying to keep up with mom is definitely the kind of experience that will make you wonder if you were somehow transported, Truman style, to some kind of nature documentary, but in the best kind of way.

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While I won’t pretend for a second that seeing bears ever gets old, they honestly weren’t the animal that I was most looking forward to encountering when I arrived in Denali.  Maybe it’s because I’d never seen one before, or because of some deep affection instilled by decades of Christmas marketing, but something about caribou utterly charms me.

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Unlike many of Alaska’s other herds, the Denali caribou do not undertake an immense seasonal migration, opting instead to remain almost exclusively within the bounds of the park year round. Unless you can travel into the interior of the park, however, you’ll have little luck seeing them in the winter.

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Denali used to play host to a herd that ranged in the tens of thousands, but after decades of over hunting followed by a mysterious period of low calf survival and harsh winters, Denali’s herd has dwindled to around 2,000 individuals.  Fortunately, things seem to have stabilized for the time being. I wish I had seen more before the end of the season, but I’ll never forget what it was like watching this small herd move through this painted hillside.

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The ungulates that seemed to most delight my fellow visitors, however, were the moose.  For all of Denali’s hooved animals fall is the rut, which means males have grown out their antlers or horns and are putting them to use in sparring (practice) matches, as they ready themselves for the violent matches to come.  I only saw such behavior between moose once.  They locked antlers for a few seconds and went back to grazing shortly thereafter.  Unfortunately it was too far away to bother with any photos.  I’ll admit, seeing a bull moose, particularly on foot, is a gripping experience.  However big you imagine them to be, they’re bigger in person.  The rack alone can be 40lbs.

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In Denali, the stakes of these fights are high, as the moose here operate in a polygynous system, where the victor will mate with and defend an entire heard of females.  In other places, moose form monogamous pairs for the breeding season.

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It was early morning still when we watched this cow move her two calves across the valley. They seemed pretty wary of our bus, though her biggest real threat is the park’s main carnivorous predator: The gray wolf.

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Even in Yellowstone I don’t get my hopes up about seeing wolves despite there being far more individuals there. Across the Denali’s 6 million acres, there are only 30 known packs comprising about 75 adults. You can imagine my delight then, when, as we were making our way out of the park at dusk on our first trip, we rounded a corner to see this rump trotting up ahead of us. As it happens, I had been walking the road on foot only minutes before. I probably wouldn’t have caught up with it had I not gotten on the bus, but it’s still pretty incredible to imagine that I more or less went hiking with a wolf. We must have followed this adult for about a mile. It stopped a few times, evening giving it’s signature mournful howl a before it disappeared off the side of the road. Honestly, that would have been enough for me, but our second to last trip had something really special in store.

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I had heard whispering about wolf pups back at our housing campus but I never thought much of it. I figured that was deep interior kind of stuff, the kind of trek our field schedule just wouldn’t permit. So while I figured it was something exciting when we arrived at a jam packed road, I just wasn’t picturing this…

Cue total F-ing meltdown on my part.

This pup was born sometime mid-may to the single male and female that comprise the Riley Creek West pack.  By around four months the pups start venturing away from their den site.  Lucky for us, for a few day stretch the area they were exploring was right near the road by Toklat.  After a few days, they moved away from the road, which was no doubt for the best.

The last animal I have the great pleasure to highlight is the most iconic of Denali’s wildlife.  In fact, it was this animal for whom the park was dedicated.  The endemic Dall sheep.

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In 1906, hunter and conservationist Charles Sheldon noticed a worrying decline in the Dall sheep favored by hunters.  He feared that without protection, they would be hunted to extinction. Now this is an all too familiar concept, but coming off the heels of the “era of abundance” this was actually a revolutionary way of thinking in western culture.  Until 1900, colonists/settlers in the United Stated hunted without regulation and, seemingly, without much thought or worry as to the integrity of ecosystems. As a frame of reference, the field of wildlife management wouldn’t come onto the scene for another two decades.

Sheldon, however, had the foresight to recognize that something must be done and set out to establish Denali as a national park.  It took 11 years, but in 1917 Woodrow Wilson signed the bill into law. Since that time Dall sheep populations rebounded and are currently considered healthy.

Despite their robust numbers, however, most of my experiences of seeing Dall sheep in the park were “technical”.  As in, “technically those white specks on the mountain side are Dall sheep”. So on our last day as we traveled out of the park, I couldn’t believe my eyes when a ewe and her lamb were jogging down a hillside close enough that you could judge their forms as Dall sheep even with your naked eye. For the minute or so that we were able to watch them, I felt myself overcome with equal parts joy and despair.  I was profoundly grateful for the gift of such beauty and yet so sad that once again its integrity is under such threat.

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Driving home one night, my fellow passengers and I shared our backgrounds and motivations for visiting the park.  Some came to experience mammals the size of which dwarfs anything in their native country, some were fulfilling missions to visit all the National Parks, while others had arrived with a spirit of adventure and little else.  Together, we marveled at the unforgettable things we had seen and shared our anxieties that future generations may not be so lucky.  We discussed our anger and disappointment (or among some of the foreign tourists utter bafflement) at the US government’s unwillingness to act more effectively on climate change.

One hundred years ago someone looked at this land, recognized that change must be implemented, and fought for over a decade to convince congress that in fact wild spaces and wildlife mattered enough to act.  As a result, my fellow passengers and I got to see and experience things that will bring us joy the rest of our lives.  The question now is whether we will wage our own fight for the future, or if we will watch from the sidelines as it turns to ash in our warming world.

***

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For information about climate change in the arctic please visit the following resources

NASA’s Arctic-Boreal Vulnerability Experiment

The National Snow and Ice Data Center

Chasing Ice

And remember…
~PLEASE VOTE ON NOV 6TH~

 

 

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Filed under Climate change, Conservation, Denali Diaries, Ecosystem, Photography, Wildlife

Saving the rarest crow

It can be hard to imagine crows as anything but ubiquitous.  During winter across the country, dusk marks the time where some cities see their skies turn black with thousands, even hundreds of thousands of American crows converging to roost.  These crows have taken nearly all that people have thrown at them: deforestation, mass waste, and the urban sprawl that simplifies previously complex ecosystems, and uses it to their advantage.  Not all species of crow have thrived in the Anthropocene, however.

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Thousands of gather accumulate in the skies above UW’s Bothell campus in the winter

Far from being icons of the ultimate adapters some species of crow represent some of the most endangered animals in the world.  Among those, the ‘Alalā or Hawaiian crow, is arguably one of the rarest birds on earth. Once locally abundant in the forests and woodlands of Hawaii’s Big Island, their decline began in the 1890’s following persecution by coffee and fruit farmers1.  Back in September, 2015 there remained only 114, all living  exclusively in captivity giving them the unenviable title of ‘extinct in the wild’.  How can one species thrive with such zeal while another holds on by a thread?

Island species are generally more specialized and therefore more sensitive to human induced changes.  In fact proportionally, islands host a higher number of endangered or extinct species than continental areas2.  In Hawaii alone, 77 different species of endemic birds have gone extinct since the arrival of the Polynesians 2,000 years ago4, all largely for similar reasons: habitat destruction and invasive species.

Unlike their generalist, continental counterparts, the ‘Alalā is more specialized to feed on understory fruits and nuts and in fact were key seed distributors for many of Hawaii’s native plants.  Island living also fostered a similar behavior seen in only one other species of crow: tool use.  Like the New Caledonian crow, the ‘Alalā is a dexterous tool user, though the two species are only distantly related.  Scientists believe this example of convergent evolution is fostered by aspects typical of islands, namely low predation and low competition for embedded food5.

Unfortunately, limited distributions and higher specialization also meant their population was more fragile than that of continental crows.  Logging, agricultural development, loss of native pollinators, and alterations by non-native ungulates challenged both food acquisition and breeding habitat.  Introduced diseases such as avian pox, malaria and the Toxoplasma gondii parasite carried by cats further weakened an already ailing population6,7. Invasive predators including rats, mongoose and cats consumed eggs, nestlings and fledglings.  Finally, humans continued their tradition of persecution, particularly feral pig hunters who would shoot the birds before they could alarm call and scare off their prey2.

Together, these threats set into motion a decline in population we failed to recover despite some increases in research and management starting in the 1970’s.  The last known wild egg was laid in 1996, and the last wild pair was seen in 20022,3.  Some people did recognize the urgency of their decline prior to 2002, however, and a captive breeding population was started successfully rearing over 90 birds8.  Although such a small number of breeders may raise red flags with respect to inbreeding and genetic depression, this is rarely as big of an issue as is commonly perceived.  Unfortunately, light management and depredation by the also endangered Hawaiian hawk (‘io), decimated the released population and reintroduction efforts were halted in 1999 until a larger captive population and better management strategy could be devised.

Since that time, the ‘Alalā Restoration Project (collaboration between the State of Hawaii, the U.S. Fish and Wildlife Service, and San Diego Zoo Global) has spearheaded captive breeding programs on Maui and the Big Island culminating in a population of over 100 birds.  An important part of these captive breeding programs is the use of puppets, which help prevent habituation to humans9.  In addition, intensive management operations have taken place to ready their prospective home at the Pu‘u Maka‘ala Natural Area Reserve including the removal of invasive/feral animals, erecting exclosure fencing, and constructing a sort of half-way house to help ease the birds into life in the wild.  These efforts have not been without setbacks, however.  Back in June, 2015 two miles of protective fencing was cut down by vandals, though their motivations remain unknown.

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A human dressed as an ‘Alala feeds captive reared nestlings. Photo c/o San Diego Zoo Global

Finally, after so much work, the end of 2016 marked the first time researchers and managers agreed the elements were in place for a reintroduction effort.  On December 14th, five male birds were released onto the reserve, marking the first time the ‘Alalā set claw into the wild since 2002.  Sadly, within weeks all but two had died. Two were killed by the native Hawaiian hawk or ‘lo, and the third was killed by “natural circumstances” which, I’m guessing, is related to a heavy storm that occurred shortly after their release.  As a protective measure, the remaining two were recaptured until the results from the necropsies are obtained.

While clearly disheartening, early hiccups in a release effort like this are not unusual and conservationists and biologists are not losing hope that success is still possible.  Part of ensuring such success, however, is undoubtedly public support particularly with respect to maintaining the strength of the Endangered Species Act and support of the ‘Alalā Restoration Project.  The perception that all crows are alike or that generous populations of American crows means protections for other corvus species is unwarranted or redundant will be a disaster for these rare birds.  So make your voice heard when funding for conversations efforts come under fire, and share your passion for endangered corvus species with friends and family.  The fate of the world’s rarest crow quite literally depends on it.

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Two newly released ‘Alalas peer around their new surrounding in the Pu’u Maka’ala Natural Area Reserve.  Photo c/o the San Diego Zoo Global 

Literature cited

  1. https://www.fws.gov/pacificislands/fauna/alala.html
  2. Faike, E. 2006. Wild voices in captivity: the date of the ‘Alala. Birding 38: 64-67.
  3. Banko, P. C.; Burgett, J.; Conry, P. J.; David, R.; Derrickson, S.; Fitzpatrick, J.;
  4. National Research Council (US) Committee on Scientific Issues in the Endangered Species Act. Science and the Endangered Species Act. Washington (DC): National Academies Press (US); 1995. 2, Species Extinctions. Available from: https://www.ncbi.nlm.nih.gov/books/NBK232371/
  5. Rutz C, Klump BC, Komarczyk L, Leighton R, Kramer J, Wischnewski S, Sugasawa S, Morrissey MB, James R, St Clair JJH, Switzer RA, and Masuda BM. (2016).

    Discovery of species-wide tool use in the Hawaiian crow.  Nature 537: 403-407 doi:10.1038/nature19103

  6. Maxfield, B. 1998. Wild ‘Alala population suffers major setback. ‘Elepaio 58: 51.
  7. Liebermann, A.; Nelson, J. T.; Simmons, P.; Unger, K.; Vitousek, P. M. 2003. Draft revised recovery plan for the Alala (Corvus Hawaiiensis. US Fish and Wildlife Service, Portland, OR, USA.
  8. Lieberman, A. C., Kuehler, C. M. 2009. Captive propagation. In: Pratt, T. K.; Atkinson, C. T.; Banko, P. C.; Jacobi, J. D.; Woodworth, B. L. (ed.), Conservation Biology of Hawaiian Forest Birds: Implications for Island Avifauna, pp. 448-469. Yale University Press, New Haven.
  9. Valutis LL, and Marzluff JM. (1999).  The appropriateness of puppet-rearing birds for reintroduction.  Conservation Biology 13: 584-591

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Filed under Conservation, Corvid diversity, Corvid health, crow conflicts, Crows and humans, Ecosystem