Monthly Archives: March 2015

Yellowstone field experience

Last week I had the great pleasure of spending a week in Yellowstone National Park with both corvid expert, John Marzluff and predator-prey dynamic expert, Aaron Wirsing.  In addition to spending an entire week with these two, I also had meetings and saw presentations from folks like the golden eagle team of Al Harmata and Marco Restani, the head researcher of the wolf project, Doug Smith, Bison expert Rick Wallen, and wolf and cougar kill expert Dan Stahler.  It was an amazing week of breath taking wildlife and in depth expertise on what’s going on in the park.  This week, I thought it would fun to take a little break from corvids and just share some of the photos I took along with the stories and biological details that go with them.

Birds
Ungulates
Predators
Miscellaneous

Birds

To kick the trip off we headed outside of Bozeman, Montana to meet up with eagle researchers Dr. Al Harmata and Dr. Marco Restani.  They’ve been doing research on eagles for more than 30 years and know more about these birds than maybe anybody.  Right now, they’re conducting an ongoing study to look at the effects of lead poisoning on  eagles.  Although lead shots have been banned in waterfowl hunting and in some states like California, in most other places lead bullets are still used for other kinds of game.  The lead fragments end up in the gut piles hunters leave behind, or in the prairie dogs or other carnivores that their shooters had no intention of taking home.  Eagles scavenge these remains and can wind up with deadly levels of lead in their bloodstreams.  Elimination of lead from bullets will likely be a necessary step to protect eagles, though I expect a robust fight from the NRA and some hunting communities.

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For corvids, spring time means nesting time and the magpies were busy at work.  Unlike crows and ravens which build more traditional looking nests, magpies make nests with roofs, further protecting them from predators.  If that’s not cool enough, magpies are known to build several of these dome nests and have been observed moving both eggs and chicks between them.

The magpie's nest is the big clump in the middle of the tree

The magpie’s nest is the big clump in the middle of the tree

A bill-load of mud to finish off lining the nest

A bill-load of mud to finish off lining the nest

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Seeing peregrine falcons perched along the 520 bridge on my way to school is always a treat, but there’s something about seeing them in this setting that’s all the more spectacular.

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At lunch time we were greeted by John’s special raven friend, Big Guy, which has been visiting him in the park for the last 15 years.  He and his mate were also busy nest building though we were unable to locate it.

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Mountain bluebirds were such a spectacular addition of color to the park, and I was super lucky to be in the right place at the right time to snap this photo.

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Ungulates

When we first arrived to the park, we were surprised to be greeted by pronghorn.  John has been leading classes to Yellowstone for 15 years and had never seen them as far into the park as we did.  Pronghorn aren’t adapted to run very well in deep snow, so they generally avoid the higher elevations in the park until later in the year. The snow melt came incredibly early this year, however, allowing them to penetrate further into the interior of the park than usual.  While the level of early snow melt we experienced isn’t unheard of, it was unusual and fit the models that predict increased drought in this area as a result of climate change.

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Bighorn sheep were prolific across the park.  In the winter and spring, male bighorns form large groups while the ewes and lambs heard up to do their own thing. I never got tired of seeing those big curls!

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Bison are truly the iconic ungulate in the park.  Theirs is a story of an amazing comeback, and one that’s really not so different from wolves.  As of 1902 there remained only 23 bison left in the park, and but thanks to ranchers and the US Army administrators of YNP, new animals were brought in and over the next 50 years that small population grew to over a 1000 animals.  Now, the park supports about 4000 animals, and is considered the only place in the country that has both maintained bison since prehistoric times, and supports non-cattle hybridized bison.

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Right now, bison regulation within the park is subject to much debate due to the presence of brucellosis.  Brucellosis is a bacterial infection that was brought when settlers first introduced cattle to the west.  It results in the abortion of calves in animals like bison, elk and livestock.  It’s transmitted by contact with an infected mucous membrane, which generally happens when curious animals touch and smell the aborted calves.  Although it’s not fatal to the mothers, the aborting of calves represents a potential economic threat to ranchers.  Although elk are also important vectors of this disease, a rancher we spoke with echoed the opinion of the ranching community at large in saying that bison are the main problems and their departure from the park needs to be controlled.  As of 2002, the Sate and Federal government developed an inter-agency management plan to control bison and the spread of the disease, which basically means that many (think in the thousands) of animals are killed once they cross the boarder.  Lead park bison biologist Rick Wallen described to us the controversial nature of this tactic which results in, one the one hand, folks from the ranching community saying there isn’t enough being done, while on the other, members of the public decrying the park for killing such an iconic species.  Despite these culls, however, the park maintains a stable population of bison, which other than run-ins with lakes and geothermal features, are basically free from predation apart from one particular wolf pack which occasionally manages to take one down.

One of my colleagues illustrating the difference between cow (left) and bull (right) bison horns.  She also sports a radio transmitter used to track an individual bison across the park.

One of my colleagues illustrating the difference between cow (left) and bull (right) bison horns. She also sports a radio transmitter used to track an individual bison across the park.

A couple of bison playfully testing each other

A couple of bison playfully testing each other

One of the most interesting insights from Rick was the observation that bison both engage in what looks like altruistic behavior, like the time he witnessed a heard protect an injured female from wolves, to completely brutal behavior like the scene my classmates and I had the serendipitous opportunity to witness.

We happened upon this scene when checking the area for signs of a bear we had heard was scavenging some bison carcasses. Although we didn’t see the bear, we quickly noticed that there was a bison calf trapped in the water, and not too far from drowning by the sounds of its breathing. The banks of these lakes are incredibly slick, and it can be impossible for an animal to get out. We watched with bated breath, conflicted between rooting for the bison to make its escape and for it to drown, as that would mean an almost guaranteed bear and wolf sightings the following days. Finally after about 10 minutes the calf managed to pull itself from the water. While all this was going on, its heard had been nearby and quickly after the calf escaped began to approach it. We were all expecting a Disney style reunion but to our shock the entire heard proceeded to haze the calf! They pushed it about 100 m down the valley before finally relaxing their assault and letting the calf rest and start to graze. Since we didn’t see bears the next day, our best guess is the calf managed to regain its strength and make it through the night.

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A tree shows some ears after being used as a scratching post for a bison.

A tree shows some wear after being used as a scratching post for a bison.

Although much of our time in the park was dedicated to simply looking for, and observing wildlife, we also collected a couple of different kinds of data while we were there.  For the last 7 years this class has been conducting “elk follows” which means that we select an individual elk in the different parts of the park and record its activities for 15 min.  Later, we will use this data and match it up with data from the Wolf Project to ask questions about elk behavior, condition, and spatial use in light of the presence of wolves.  This big bull was taking a little rest and is a great illustration of the hardship of winter.  You can clearly see the low fat reserves on its rump, as evidenced by the outline of its spine and pelvic bones.

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This bull is a good example of one that’s already lost its antlers, and it’s probably feeling a little lighter than its 5-point companion, since elk antlers can weigh up to 40lbs!  Antlers are the fastest growing tissue and in the height of spring and early summer they can grow up to an inch a day.  One of our faculty members, Aaron Wiring, told us an incredible story of seeing a big 6 point bull being chased by wolves in an earlier trip, only to loose one antler during the chase. A little lopsided, the bull managed to fend them off until it was finally cornered against a tree when, you guessed it, the second antler fell off.  It was all over soon after that. Talk about bad timing!

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Predators

A coyote makes off with the leftovers of a bison carcass.  Coyotes are often killed by wolves, and they need to be extra mindful when in open spaces near kills sites like this.  Why wolves are so predatory towards coyotes and not foxes is something of a mystery.

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One of my favorite experiences while in the park was seeing the wolves.  There’s just something about seeing such an iconic animal that lifts your spirit.  The reintroduction of wolves was, and still is, incredibly controversial.  There’s no doubt that their presence on the landscape is a threat to ranchers and pet owners alike, but I was inspired by our talk with Hannibal, a rancher who lives adjacent to the park boundary.  Despite loosing three dogs and many sheep and calves to wolves, he maintains his position that they are a necessary part of the Western landscape and deserve a place along side he and his family.  After his daughter, Hilary Zaranek, started range riding (rounding up and sleeping with the heard at night) predation by wolves dropped to nearly zero and their three current dogs seemed very happy to me.  By shifting the ranching paradigm to one where multiple ranchers join herds and share space, range riders become a sustainable and economical option for ranchers.  Hannibal and Hilary are the forefront of this shift and their dedication to the presence of wolves was awe inspiring.

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While we were in the park we were privy to some pretty special changes going on within the packs. Inside the park, wolves are killed almost exclusively by other wolves.   Recently, the alpha male of the Lamar Valley pack was killed by members of the competing Prospect pack after he confronted them.  His death put the alpha female in an incredibly precarious position since she will be unable to hunt after she gives birth to her dead mate’s pups and in a few weeks.  Although her 6 current pups are nearly a year old they are still too young to provide for her during this time.  As a result, she is attempting to court 4 of the male members of the Prospect pack in an effort to gain a new alpha male that will help raise her pups.  Unlike lions which will kill the cubs of a competing male, wolves will help raise the former dad’s pups after they take over.  Some readers may even be familiar with the famous story of 8, the hero ‘little wolf” who did just this.  While we were in the park the female appeared to be courting a spectacular grey male, but shorty before we left we learned that he fell out of contention.  Who the next alpha male is is up to the alpha female, and only time will tell who she chooses.

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The effects of wolves in the park have been profound and their necessity to maintain a balanced and healthy ecosystem is unquestionable.  For more information on the wolves’ effects on the Yellowstone ecosystem check out this Ted talk.

One of the most interesting things we did was meet up with wolf expert Dr. Dan Stahler.  He and fellow carcass expert, Kai, lead us to a recent cougar kill and described how to identify kills as either wolf or cougar and showed us the kinds of data they collect off such kills.  Key signs off cougar kills are puncture marks around the throat, neat, cleanly picked bones, and characteristic caching (or covering and hiding) of the carcass.  Wolf kills, on the other hand, are not hidden, show signs of hemorrhaging around the animal’s back legs, and the carcasses are found dismembered.  This particular cow elk was killed and partially eaten by a cougar before being discovered by wolves and other scavengers.

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Miscellaneous

A badger skull found while hiking the bighorn lambing grounds on the edge of the park boundary.

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On our last day I spotted a couple of yellow-bellied marmots, marking the fist time John has seen them inside the park during this trip.  I’ve never gotten such a good look at these little animals and I must say they’re very pretty!

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Antler drops are an important source of calcium for many animals in the park, and this particular one shows its age with a beautiful patina of lichen.

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A bison carcass lays peacefully in its resting place of Lamar Valley.

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Filed under Being a scientist, Birding, Field work

Crow curiosities: Do crows play and why?

A few years ago, on a mildly windy day, I watched a group of crows line up on the top of a building and then take turns flying off into the draft before letting it gently return them back to the rooftop to do it all over again.  This continued for at least ten minutes before I had to bid my feathered friends adieu and go to work.  Last summer, I watched two juveniles perch on a cable wire that ran from the power lines down to the ground at a steep incline.  While one of the kids was minding its own business the other snuck up and pecked and pulled its sibling’s tail until the sibling lost its balance on the crooked wire and was forced to fly to a higher perch.  Then the mischievous, ah hem, ‘pecker’ followed its sibling to the higher perch and started again. And every winter without fail, at least one person will send me the video of the snowboarding Russian hooded crow or the barrel rolling crow or the crows having a snowball fight.  Ok, so that last one isn’t real, but with all the other videos of crows at play it certainly seems like it’s only a matter of time before they start hocking little crow-sized snowballs at each other.  With all these videos and stories comes the inevitable question: Are corvids having as much fun as it looks like and, if not, what are they doing?

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For scientists, this question is inherently difficult to answer.  There’s the obvious part where it still remains impossible to ask animals how they feel about their activities, but at an even more fundamental level is the question of:  how do we define play?  Play, as all things in science do, requires a very specific definition that may or may not depart from how we use the word in everyday language.  The most widely referred to definition is the following very dry and jargony sentence:  ‘…all motor activity performed postnatally that appears purposeless, in which motor patterns from other contexts may often be used in modified forms or altered sequencing’1.  And with that, what I can only imagine must be one of the most fun things on the planet to study suddenly becomes sleep-inducingly boring and the humor of the picture below is no longer confined to biologists.

wildlife bioFor now, let’s just focus on the part that said “…activities that appear purposeless.”  That leaves scientists with a different problem; how do we define ‘purposeless’ (i.e do you mean right now, or indefinitely? What if it has a purpose but I just don’t know what it is?), and therefore, how do we even identify when animals are playing and when they’re not.  Can you see the big circular rabbit hole we’ve gotten ourselves into?  Since I think most people use the catch-all definition from Potter Stewart and simply say that you know it when you see it, it can be difficult to empathize with why play has been such a difficult behavior for scientists to say a whole lot about.  Now that I hope I’ve given you some insight into why this is a difficult subject to study and thus, in many ways remains mysterious, let’s get to the fun part of talking about what we do know.

So far, observations of play in birds is limited to corvids, parrots, hornbills and babblers, reaching a grand total of about 25 species2.  To put that in perspective, there are ~10,500 species of birds in the world, making it an incredibly rare behavior among birds, and emphasizing the awesomeness of getting to observe it in our own backyards here in the PNW.

Although the snowboarding crow is probably the instance of crow play that gets the most attention, there’s actually 7 kinds of play that researchers have documented3.  Maybe I’ll try and publish my observation of the bickering crow kids, but for now, irritating-your-siblings-play is not one of them.  Here are the big 7:

  • Object play (manipulating things for no reason)
  • Play caching (hiding inedible objects)
  • Flight play (random aerial acrobatics)
  • Bath play (more activity in water than necessary to get clean)
  • Sliding down inclines (snowboarding, sledding, body sliding)
  • Hanging (hanging off branches but not to obtain food)
  • Vocal play (you know how kids go through that phase when they talk to themselves a lot? The crow version of that.)
A crow just hanging out

A crow just hanging out

So what are we to make of seeing ravens hanging, apparently joyfully, from the ends of buoyant branches in our yards or magpies playing tug of war with an otherwise ordinary twig or crows doing elaborate aerial maneuvers for no obvious reason?

Young crows playing tug of war. Photo c/o Bob Armstrong

Young crows playing tug of war. Photo c/o Bob Armstrong. (The white eye of the bird on the left is not from disease or injury, but is the protective nicitating membrane that many animals have, in case you were wondering.)

Let’s start with the conventional wisdom that everyone grows up hearing: Animals play to practice skills they need to be successful later in life.  Cats play with strings to hone attack skills, dogs wrestle to practice fighting skills their wolf ancestors would have needed as adults, etc.  The problem with this wisdom is that despite all the intuitive sense it makes it turns out it’s not very…true. In mammals, it has been shown over and over again to be unsupported.  In birds it hasn’t been looked at as extensively, and there’s at least one exception I know of that showed  ravens play cache (hide things) to evaluate competitors so that they know who is most likely to steal their cache once the stakes are raised and they’re actually hiding food4.

Other then that, the vast majority of data across both birds and mammals have shown that animals who play most often or most fiercely are no better hunters or fighters later in life than their peers.  Same goes for the studies that have compared animals that are allowed to play with those who were not5.  No difference.  So is it as easy as saying crows play just because it’s fun?  Well the problem with that is that play can be risky. Playful, distracted kids are often snatched up by predators or accidentally killed by a miscalculation of their environment.  With the level of risk that’s involved it seems unlikely it’s not doing anything for them. To make matters more complicated, although animals don’t seem to be better at the skills they appeared to be practicing, some studies show that they do seem to be better off overall.  In mammals we’ve seen that they’re more successful parents and have longer life expectancies6.  So what might be the adaptive value of fun?

Although there’s still much to be learned as far as testing play in corvids, right now I’m inclined to agree with play researcher Lynda Sharpe, who wrote a piece on this topic for Scientific American which I encourage everyone to check out.  Stress is in no way unique to humans, and it can be as debilitating and deadly for animals as it is to us.  Play is a great way for animals to hone their stress response so they’re less high strung as adults7.  Not to mention the complex, stimulating nature of play helps the brain grow8.  So why do crows play?  Learning about their peers, gaining new experiences in a low risk way, honing their stress response, and growing their big brains all seem like a good excuse to have a bit of fun to me.

Literature cited

1. Bekoff, M. and Byers, J.A. (1981) A critical reanalysis of the ontogeny of mammalian social and locomotor play.  An ethological hornet’s nest.  Behavioral Development, The Bielefeld Interdisciplinary Project.  pp296-337.  Cambridge University Press.

2. Diamond, J, and Bond, A.B. (2003) A comparative analysis of social play in birds.  Behaviour 140: 1091-1115

3. Heinrich, B. and Smolker, R. Play in common raves.  In: Animal Play: Evolutionary, Comparative and Ecological Perspectives.  Ed: Bekoff, M and Byers, J.A. Cambridge University Press

4.  Bugnyar, T., Schwab, C., Schloegl, C., Kortschal, K., and Heinrich, B.  (2007).  Ravens judge competitors through experience with play caching.  Current Biology 17: 1804-1808.

5. Thomas, E. & Schaller, F. 1954. Das Spiel der optisch isolierten Kasper-Hauser-Katze. Naturwissenschaften, 41, 557-558. Reprinted and translated in: Evolution of play behaviour. 1978. (Ed. by D. Muller-Schwarze.) Stroudsburg, PA: Dowden, Hutchinson & Ross.

6. Cameron, E.Z., Linklater, W.L., Stafford, K.J. & Minot, E.O. 2008. Maternal investment results in better foal condition through increased play behaviour in horses. Animal Behaviour, 76, 1511-1518.

7. Meaney, M.J., Mitchell, J.B., Aitken, D.H. & Bhatnagar, S. 1991. The effects of neonatal handling on the development of the adrenocortical response to stress: implications for neuropathology and cognitive deficits in later life. Psychoneuroendocrinology, 16, 85-103.

8. Ferchmin, P. A. & Eterovic, V. A. 1982. Play stimulated by environmental complexity alters the brain and improves learning abilities in rodents, primates and possibly humans. Behavioral and Brain Sciences, 5, 164-165.

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Filed under Being a scientist, Crow behavior, Crow curiosities

A scientist’s thoughts on The Crow Box

The first time I watched the writer and hacker Josua Klein’s crow vending machine TED talk as a college undergrad, I was floored.  It was my first exposure to Betty, to the tool making capabilities of some crow species, and to the idea you could potentially train wild crows.  The purported success of the vending machine filled me with ideas.  I used clips from the talk for a variety of public outreach presentations and they were always met with the same kind of GTFO amazement that I love watching people experience as they learn about crows.

Betty just doing her normal New Caledonian crow thing of making hooks out of wire to pull up buckets of food.  No big deal.  :)

Betty just doing her normal New Caledonian crow thing of making hooks out of wire to pull up buckets of food. No big deal. 🙂

As I moved on to graduate school, however, and was fully immersed in the scientific community of crow nerds, I started to hear rumblings that gave me pause.  Rumblings that suggested the vending machine wasn’t all that it was cracked up to be and, in fact, had not worked as it was implied in that TED talk.  Since I’ve never worked personally with Klein, I’ll let my fellow crow scientists speak for themselves on the issue.  You can find one of the graduate students he worked with relating her experience during a reddit AMA here, and as well as the correction that the New York Times Magazine was forced to run after publishing an article on Klein’s effort with the vending machine.  If you don’t want to read them, suffice it to say the main point is that Klein gave people the impression that it had been tested (successfully even) on zoo and wild crows when it hadn’t.

The Crow Box

The Crow Box

Leading the public to believe that we’ve arrived at conclusions when we haven’t is the stuff of stress dreams for scientists, and it’s why the peer review process is the foundation of good scientific practice.  By taking “results” that were only in the early stages of being tested and bringing them to the attention of the public without permission or support from the scientists he was working with, Klein burned his bridge to the folks who had offered to help him test the idea, and any other crow scientist he might approach next.  Which brings me to the recent article I read titled “This Machine Teaches Wild Crows to Bring You Coins for Peanuts.”  

No, it doesn’t.  It might, but probably not.  No one has been able to train wild crows to bring specific items in exchange for food, the website selling the machine even points this outGabi Mann did not intentionally train her crows to bring her things.  They did this of their own volition which is why her collection is as diverse, unique, and beautiful as it is.

Gabbi showing me a sampling of her favorite gifts from the crows

Gabbi showing me a sampling of her favorite gifts from the crows

The suggestion that this machine could train crows to bring you quarters holds about as much water for me as saying you could use a dog whistle to train wild wolves to roll over on command.  The reason that the machine worked on captive birds in the Brooklyn apartment where it was originally tested is that, in captivity, you have a certain amount of leverage over an animal.  You can motivate it with food or treats or affection.  The chances that a wild crow would go to the effort of looking for coins when it could simply skip that step and look for other food seems insurmountable.

All that being said should you turn your nose up at The Crow Box if the idea intrigues you? No, go for it! Maybe yours will be the mind to figure out how to motive wild birds to participate. Or, perhaps you don’t care if it works or not, you’re just in it for a new experience or the joy of trying.  Trying and failing is part of discovery and I see no reason people should wash their hands of it if it sounds like fun.  Plus, even if it doesn’t work, you may end up learning different, but just as amazing things about these birds.  Just don’t hold it against the crows if they decide it’s simply not worth the trouble and leave it to you to go collect the quarters you lost buying The Crow Box.

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Filed under Being a scientist, Crow behavior, crow intelligence, Crows and humans

All in the (crow) family

With the breeding season fast approaching, I thought it would be fun to write a post dedicated to some of the finer details of growing up in a crow family.  From territory selection to the function of helper birds I hope this post illuminates some of the less familiar aspects of what goes on between crow parents and kids.

Mate/Territory selection
Crows reach sexual maturity between 2-4 years, with females generally maturing faster.  Once they’ve bonded with a mate it’s time to secure a territory.  After they’ve settled on a territory they’ll hold on to it for years, if not the rest of their lives, providing a great opportunity for some in depth crow watching!  With few exceptions, crows generally nest in areas similar to where they were raised1.  Meaning, rural crows settle down in rural areas, suburban crows in suburban areas and so on and so forth.  Dispersal distance ranges (generally) from 0-60 km, and some birds will settle down right next door to their natal territory.

Monogamy
As far as mating goes, we refer to crows as being socially monogamous but genetically promiscuous.  This means mated pairs will typically stay together for life, but extra pair copulations are not unusual.  On average, the breeding male sires 82% of his offspring, with the rest of the clutch resulting from extra pair matings 2.  Whether females are soliciting these extra pair matings is unclear, but most data suggest that females do not have complete control over their extrapair partners 2.  Loss of paternity increases dramatically if the male has been non-fatally injured.  Although his partner won’t leave him altogether, he is generally at risk for smaller brood sizes and paternity loss jumps to about 48%, likely due to more difficultly mating and guarding his mate, as well as lower sperm counts as a result of stress3.  In these cases, females may be more willing to accept fertilization from extrapair males,  though this is poorly supported.

The mechanics of mating
lovers
For those that want the biological details on crow sex, male crows, like the majority of birds, do not have an external penis.  So mating is generally preceded by solicitation from the female, followed by the male mounting and rubbing his cloaca against hers, which transfers the sperm.  This is known as the cloacal kiss (which, bleh, saying reminds me of Tina Fey in 30 Rock talking about the word ‘lovers’).  The whole process takes a couple of seconds.

Nesting

A typical looking crow nest with a water bottle for scale.

A typical looking crow nest with a water bottle for scale.

Crows start to nest in mid to late march with both males and females participating in nest building.  Nests are constructed from sticks and lined with grass, fur, feathers or other soft materials.  The building process is pretty conspicuous if you know what you’re looking for (and very fun to observe) but be warned; I have little doubt that crows will build fake out nests if they believe they are being watched by someone they don’t know or trust.   Females lay a clutch of usually 3-4 blue and brown speckled eggs.  Although males will occasionally (rarely) sit on the nest while the female is away they can’t really incubate because they lack the necessary brood patch to transfer heat.  Chicks hatch after about 19 days of incubation followed by another 30-45 days in the nest before fledging.   Once they fledge they spend 1.5-2 months dependent on their parents before they’re ready to strike it out on their own.

Helpers
I dedicated another post to talking about the behavior and survival rates of hatch-year offspring which you can find here.  Let me use this space to pick up where that post left off addressing helpers.  Crows, like a number of other birds including nuthatches and kingfishers, engage in cooperative breeding, though they are not obligate cooperative breeders meaning they can successfully fledge young without helpers.  Cooperative breeding is defined as when more than two individuals contribute to the care of young in a single brood.  For crows this means that, in addition to the mated pair, there can be up to 10 additional birds helping to raise this year’s brood1.  Generally, these are young males that are related to the male breeder2. The motive behind cooperative breeding is somewhat mysterious since there are costs to both breeders and helpers.  Costs to parents including diversion of food provisioning towards helpers and, for males, threat of paternity loss to helpers.   Costs to helpers are more straight forward; they’re delaying their own breeding efforts to rear offspring which only share some of their genetic identity.  So why do crows bother?
Let me preface this by saying that quantifying the helpfulness of helpers is surprisingly difficult.  A central roadblock has been; how do you tease out the effects of helpers, vs the underlying quality of parents that produce lots of helpers?  This chicken and egg problem has confounded getting to the bottom of this question, but here are the best answers that we have so far.

Why parents keep them around:

Helping behavior in carrion crows.  Photo c/o V. Baglione

Helping behavior in carrion crows. Photo c/o V. Baglione

One insight comes from studies done on carrion crows (a species native to Western Europe and Asia).   In these birds, differences in helper helpfulness are so obvious that some individuals are scientifically referred to as “lazy” group members.  Amazingly, however, if one of the parents is injured it’s these lazy group members that pick up the most slack to compensate for the reduction in effort by another group member4.  So they’re kinda like your State Farm policy.  Most of the time they feel like an annoying burden that will never come in handy, until that one time they do.  Alternatively, in other birds, it’s been shown that although helpers don’t make much of a difference as far as each individual breeding attempt goes, they do increase the breeding female’s overall life expectancy and therefore pay off in the long run5.

Why helpers help:

Now the connection between HBO's Game of Thrones and corvids takes on yet another meaning...

Now the connection between HBO’s Game of Thrones and corvids takes on yet another meaning…

For the helpers themselves, there are more potential benefits.  Whether it’s by choice or force,  helper males sire about 7% of offspring, so breeding is in fact not out of the question3.  Although it’s a small number, some of that percent is even from mother/son relationships, though this isn’t consistent among corvids and some species do a better job avoiding incest than others. Even if they don’t breed with the female, they’re still helping to raise siblings that share some of their genetic material so it’s not a complete loss from the standpoint of their DNA (something known as inclusive fitness).  They also stand to inherit the territory, should something befall the territorial pair.  Finally, though this has been especially difficult to quantify, it’s possible that sticking around and observing a breeding attempt offers valuable insights that helper birds will go one to use when they raise their own brood.

How did such a behavior evolve?
That really is the million dollar question.  It may have to do with delayed dispersal, which is basically a fancy way of saying there wasn’t always places for these young juveniles to go so they just stuck around at home (ah ha! See, millennial are just doing what comes naturally).  It’s notable that the majority of birds that partake in cooperative breeding do so in kin based groups, which seems to suggest that perhaps this is a product of the fact that kin tend to settle down close to each other and as time went on a more loose, flexible system of helping became the more formal cooperative system we see today.

This is one of my favorite nesting locations I've discovered so far.  Rather than being deterred by the bird spikes, they've essentially used it as rebar!

This is one of my favorite nesting locations I’ve discovered so far. Rather than being deterred by the bird spikes, they’ve essentially used it as rebar!

Literature cited

1McGowen, K. 2001.  Avian ecology and conservation in an urbanizing world.  Kluwer Academic Press, Norwell, MA.  p 365-381

2Townsend, A.K., Clark, A.B., McGowen, K.J., and Lovette, I.J. 2009.  Reproductive partitioning and the assumptions of reproductive skew models in the cooperatively breeidng American crow,  Animal Behavior 77(2)

3Townsend, A.K., Clark, A.B., and McGowen, K.J. 2011.  Injury and paternity loss in cooperatively breeding American crows.  J. Field Ornithology 82(4): 415-421

4Baglione, V., Canestrari, D., Chiarati, E., Vera, R., and Marcos, J.M. 2010.  Lazy group members are substitute helpers in carrion crows. The R. Soc. Proc. B.  282(1804)

5Wright, J., amd Russell, A.F., How helpers help: Disentangling ecological confounds from the benefits of cooperative breeding.  British Ecological Society 77(3): 427-429

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Filed under Crow behavior, Crow life history