Tag Archives: Crow breeding

Baby crow detective work

By now, most of us have come across these images of  “baby crows” so often it induces more of a yawn than a fit of aggravation.
Image-1If, somehow, these images are new to you feel free to check out my post fully debunking them, as I will not dedicate any further time to them here.   But there’s a new photo circulating social media, and it makes for a much more compelling crow doppelganger;

baby crow
You’ve got three, black, altricial baby birds in a nest and really, they’re not terribly un-crow like.   It doesn’t make you a complete crow rookie to make this mistake, but there are some key things wrong here.  And this is the moment where, as a scientist, these photos elevate from being simply another source of annoying misinformation (which, they are) to the kind detective work that childhood doctor visits fostered a deep love for.  Because, not unlike my favorite activity in the Highlights magazines I anxiously parsed through in those waiting rooms, there are 4 things that are different between these two photos and it’s up to you to find them.  So take a minute and see what jumps out at you….

Crows_v_no crows
Figured it out (or given up)?  The first thing to know is that all bird species are very specific in terms of both nest materials and nest construction.  Sure, some birds can happily use some ribbon in place of straw (like orioles) or build nests in old shoes just as easily as in gutters (like bewick’s wrens) but the basic style is always the same.  Robins will always use mud as a binder and bushtit nests will always look like cozy sleeping bags made of moss.  Knowing that, the material used in the nest on the right should jump out as a red flag.  Of course you’ll find crow nests with a bit of string, fabric or grass (especially for lining) but the bulk of the nest is always made of pinky-wide sticks.   Really, you need look no further at this point to know immediately that the photo on the right is an impostor but let’s keep going because it’s fun.

Next let’s look at the babies themselves, which is where the three remaining differences are.  Two of them are color-coded, did you catch them?  Ah yes, gape and eye color.  See that brightly colored area on the corner of the bird’s developing beak?  That’s called the gape, and the bright color that flashes when they open their mouths is a powerful signal that tells parents to “insert food here”.  Crows have bright pink gapes, whereas these other birds have yellow gapes.  Our other color coded giveaway is the eyes.  Granted the lighting is not great, but it’s clear that the crows on the left have light blue eyes whereas these other birds have dark eyes.  In some species of crow the babies are born with brown eyes that turn blue as they age, but such is not the case with our American crows and you can expect that nestlings will always have blue eyes.  The last clue, which takes more expert level knowledge to notice, is the bill shape.  The birds on the right have a slightly more embellished curve to the bill than a typical crow chick.

The final mystery, of course, is what the birds on the right actually are.  Unfortunately, I failed to track down the original poster, but as best I can tell they’re black drongo chicks.  Black drongos are members of the drongo family (Dicruridae) and are native to Southern and Eastern Asia.  Here’s another photo I found that looks consistent with the previous one.  If any drongo experts read this blog though and want to correct me, I’d love to hear from you!

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Filed under Birding, Crow life history

Help, I’ve found a baby crow!

You’re walking down the sidewalk when suddenly you notice a waddling little mass of black feathers trying awkwardly to hide under a bush or car.  When you begin to approach the young crow, it simply stares up at you or perhaps continues on its poorly planned waddle down the sidewalk or worse, into traffic. Clearly this baby crow cannot fly and has a habit of making bad decisions.  Your instinct (and perhaps the opportunity to interact with a baby animal) are tempting you to intervene and “save” this young crow who seems ill prepared to be out of the nest.  What should you do?

Does this baby scrub jay need to be taken to a rehab facility?

This baby scrub jay was found running around the grounds of an apartment complex.  Should it be taken to the rehab facility?

The answer, almost always, is to ignore your instincts and good intentions.  I’ve had many friends and colleagues who are either licensed wildlife rehabbers or who spent summers volunteering with their local rehab facilities, that can attest to the dozens of animals that get brought in during the spring and summer by well intentioned folks who assumed that simply finding such a vulnerable baby meant it needed help.  In many of these cases, these animals did not need help and now they’ve been separated from their parents or mother and stand a much lower chance of surviving once they’re released from the rehab facility.  So how do you avoid making the same error?

First, understand that corvid babies very often leave the nest before they are completely flighted (usually by about 7-10 days).   Evolution has taught them that it’s better to be flightless but still mobile on the ground than trapped in the nest where they stand no chance of escape, should they be located by a predator.  During this time they are still in the care of their parents who will continue to feed and defend them.  So finding a flightless baby crow or jay is totally normal between late May and July.  Perhaps it would be helpful to gently herd the fledgling away from traffic and under the safety of a bush but, outside of that, most baby corvids do not need your help and are better off (less stressed) if you give them a wide girth. The baby jay in the above picture was captured so it could be color-banded, and then was released under a bush where its parents quickly attended to it.

Simply knowing this piece of corvid biology will lay to rest the concerns for most situations you may find yourself in this summer.  For babies that are naked, are bleeding or have drooping wings, or are within reach of a dog or cat, etc., the following flow chart is excellent and will help navigate the situation (I’ve thrown in the mammal one too just for fun).

Help, I’ve found a baby bird
Help, I’ve found a baby mammal

The main thing to remember is; as long as the baby is mostly feathered and being attended by its parents, it’s just where it needs to be.  Only if it’s trapped in a storm drain, naked, injured, cornered by a cat, or after several hours has not been visited by its parents is it appropriate to intervene.  Even in most of those cases, simply creating a makeshift nest out of a basket and securing it to a tree, or placing the baby in a bush and leaving the area, is much better than taking it away to a facility.  So use your best judgment this summer and remember; if you feel your situation is unique and has not been addressed by the flow charts provided, give a rehab facility a call and let them help you decide if an animal needs to be removed before you make the mistake of taking babies away from their parents.

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A recently fledged juvenile waits for mom or dad to return with food.

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Filed under Crow behavior, Crow life history

Crow curiosities: who is begging in April?

Right now, in early spring, you may have noticed a crow or two fluttering their wings and making the classic “waaah, waaahhh” sound that roughly translates to “feed me, feed me”!  Although it’s tempting to think these are young crows, it’s far too early in the breeding season for fledglings to be on the loose.  So who are these juvie doppelgangers? Adult female crows.

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Begging juveniles like this one won’t be roaming around the PNW until mid June and later.

During the nest building stage you may hear females making these sounds just while on the ground foraging with their mate or while perched near the nest like this female was.  Why do they do it?  It’s essentially a way to prime the pump and remind their mate that they’re going to need to be fed once they’re saddled to the nest and can’t forage as much for themselves.  Once they are actively incubating, they’ll continue to beg only now it’s really a demand for the food they need and can’t get for themselves without risking their eggs getting too cool.  Although males will take a turn on the nest, they do not have a formal brood patch and can’t do much more than temporarily keep the eggs insulated.

Although it’s tempting, hopefully now you won’t be fooled by this April trick!

DSC_0084

A male returns to the nest with a bill-load of peanuts for his hungry mate.

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Filed under Crow behavior, Crow curiosities

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