Tag Archives: Breeding

The birds and the bees

~This post describes sex in explicit terms ~

It’s springtime in Seattle which means the air is marked with the scent of warm, wet earth, the cherry trees are in full bloom, and our conversations of the goings on in the natural world are couched in the phrase “the birds and the bees”.  While its origin story is not completely clear, it’s very likely that this euphemism has been around for hundreds of years, dating back as early as 1644 in the Evelyn Diaries.  Despite the phrases’ ubiquity for discussing human sexuality, ironically very few people know much about the sex lives of the phrase’s subjects.  This is attributable largely to the fact that how these animals procreate is quite different from the mammalian systems we are familiar with.  So in the spirit of springtime let’s talk about the birds and the bees, the real story of the birds and the bees.

Birds
The most consequential departure by birds from mammalian systems is that most birds lack any kind of external sex organ. In contrast, most other kinds of animals have sex organs that are either maintained outside the body permanently, or can emerge temporarily as needed. Among birds, there are exceptions to this but fair warning you’ll probably never look at a duck in the same lighthearted way again if you pursue this line of knowledge. Which is to say of course that you absolutely should.

As far as crows and other songbirds are concerned though, sex must be conducted without penetration by a sex organ. So instead, these birds copulate by way of the “cloacal kiss”.  The cloaca is a bird’s single external vent and it’s used for both waste elimination and reproductive activities. During the breeding season, both the male and female’s vents swell.  To copulate, the male mounts the female and pushes her tail aside with his.  Once they make cloacal contact, the sperm that’s been stored in his cloaca is transferred.  It’s an awkward looking balancing act that lasts only a few seconds.  After the initial copulatory event the pair may mate again several times within minutes or over the course of weeks.

Whereas people need to consider timing, birds can successfully mate even in the absence of ovulation.  That’s because females have specialized sperm storage tubes inside their oviducts.  A female’s vagina is very picky, however, and only a very small number of the male’s sperm will reach this holding chamber.  Depending on the species, once there a female can store the living sperm for weeks or months. The exact mechanism of how the sperm are subsequently released is not entirely known, but possibilities include that it’s the mechanical pressure of the passing ovum (unfertilized eggs) that releases the sperm, or that it’s directed by hormonal changes during ovulation.1

One additional consequence of sperm storage is that it allows for different eggs within the same clutch to be sired by unique males.  In crows for example, about 80% of a nest has been sired by the female’s permanent partner.  It is unclear how many of these extra pair copulations are either solicited by or forced on the female.

Bees
While mid-air copulations have never been confirmed in birds, honey bees do in fact mate on the wing during what’s called the mating flight.  A newly minted, week old queen will take to their air followed by thousands of male drones.  She will only mate with about 10-20 of these individuals though.  To mate, the male inserts his endophallus (bee penis) into the queen’s sting chamber.  Once he has deposited his sperm, the male detaches.  Unfortunately for the male, however, he doesn’t do so with all the parts he arrived with.  His endophallus will rip off and remain inside the female, most often killing him.  As if that wasn’t brutal enough, the next male is required to remove the previous suitor’s leftovers before being granted the ability to seal his own fate.

By the end of the mating flight, the queen will be carrying hundreds of millions of sperm, most of which will be used immediately to begin fertilizing her eggs.  Like birds, the queen has a specialized storage chamber called a spermathecal where she keeps the unused sperm.  The stored sperm from her mating flight will last up to 4 years, after which the queen’s reign will come to an end, and the cycle begins anew.

Literature cited

  1. SASANAMI, T., MATSUZAKI, M., MIZUSHIMA, S., & HIYAMA, G. (2013). Sperm Storage in the Female Reproductive Tract in Birds. The Journal of Reproduction and Development, 59(4), 334–338. http://doi.org/10.1262/jrd.2013-038

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American crow nesting ecology 101

*This article was updated and renamed from Everything you want to know about crow nests on April 14th, 2020.

Spring marks one of my favorite times of year. Cherry blossoms abound, the rain smells sweet and the birds get busy putting their carpentry skills to good use. In fact for me, there’s nothing more iconically spring than watching the silhouettes of crows with bill loads of timber or soft material dot the skies as they shuttle back and forth to their nest trees. Like a townhouse development, these construction projects are over in the blink of an eye and soon, their bill loads of twigs will be replaced by food for their mate and, eventually, their insatiable young. Watching your local nest is both a great way to learn more about your neighborhood crow family, and avoid unpleasant conflicts with protective crow parents.  Whether you’re years into this tradition or just getting started, there’s always more to learn and enjoy!

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Nest site selection, construction, and reuse

Nest construction is initiated anytime from early February to late April, depending on the region.  In Washington, nest construction generally kicks of by the second week of March. Crows will nest in an astounding array of places, depending on where they live and what’s available.  In Seattle, I see them nest anywhere from the eaves of skyscrapers, to the crooks of well concealed tree limbs, to within reach in saplings that are struggling to support their weight. In areas where appropriate trees are unavailable they may even nest right on the ground!¹ How crows make their precise nest site selection is unknown, but most commonly in the PNW, nests are placed close to the trunk in a fork or on a horizontal branch in the top third of a conifer.

Both the male and female participate in building the nest. In areas where auxiliary helpers are present, helpers may also contribute to gathering nesting materials and may add these materials themselves, or leave for the female to work in.

If trees are abundant, the nest exterior is constructed mainly from twigs pulled from live trees.  In areas where such materials are in short supply, nests may be composed of as much as 50% grass and other plant stems.² After the bulk of construction is complete, they’ll line the cup of the nest with soft materials like grass, bark, moss, flowers, mud, cow dung, roots, paper, fabric, fur, etc. Fur may be found or collected from live animals, as this large-billed crow (Corvus macrorhynchos) demonstrated on a panda at the Beijing Zoo in 2015.  Contrary to the news anchor’s fears, this would not have been painful for the panda. 

It takes 1-2.5 weeks to finish a nest, though second attempts can take as little as 5 days in areas where helpers are present.  A new nest is usually about 1.5 ft across and 8-10 in deep. The life of a typical nest is only about 10 weeks (1-2.5 weeks of building, 6 days of laying, 20 days of incubating and 4 weeks of nestlings) though they are hardy structures and can remain intact for years. After the young fledge, the crows will not return to the nest. Generally speaking, crows will only use a nest once, though the occasional observation of a pair repairing and reusing an old nest have been reported across the country. More often it appears that if they are going to reuse a nest site, they will build on top of an old nest, particularly in areas where nest trees are especially sparse like downtown Seattle. This also appears to be more common in the Midwest.

Eggs and nestlings

Egg laying may begin immediately, or up to a week after the nest is complete.  Crows, like nearly all birds, have a single ovary and oviduct and can only lay one egg a day.  In some cases they may even skip a day or two between laying. Crows generally lay a clutch of 4-5 eggs, but nests with up to 9 eggs have been observed, though it’s possible this was the result of a second female laying in the same nest.³  Females will usually start incubating the nest once the third egg is laid. To aid with incubation, females develop a patch of featherless skin on their underside called a brood patch.  Brood patches are common in birds, and generally only occur on females but observations of male crows with brood patches have been reported. Only female crows incubate, though eggs may be briefly “incubated” by helpers.

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Common raven eggs left | American crow eggs right

For a couple of days before the full clutch is laid, the female will sit next to the nest and give begging calls.  This behavior continues even after she starts incubating, which in Seattle is most often the explanation for begging calls emanating from nests during April. Both her partner and helpers will bring her food, usually 2-4 times an hour. She may hop off the nest to help chase away threats, feed, preen, or stretch, but generally doesn’t leave for more than a few minutes.

The eggs will start hatching after about 15-20 days of incubation.  Since the female starts incubating before the full clutch is laid, crows exhibit asynchronous hatching, where not all the young hatch on the same day. In other species of birds like mallards, even though the eggs were laid days apart, the young all hatch within a few hours of each other because the female waited to start incubating until only after all the eggs were laid.

Like other songbirds, crow chicks are altricial and nidicolous, meaning they hatch blind and helpless, and will remain in the nest for many days after hatching.  Ducks, chickens, quails, etc. all produce precocial, nidifugous young which hatch sighted, covered in downy feathers, and ready to follow their parent(s) away from the nest within a few hours.

baby crow

Once the eggs start to hatch the female will continue to brood the nestlings continuously for the next couple of weeks.  Once the nestlings are more developed and covered in feathers, she will brood less and less often and transition mostly to food provisioning.  Nestlings appear to be fed primarily invertebrates, but their diets vary depending on local resources.  For the first couple of weeks after hatching, nestlings are fed about every 30min by parents and helpers, if they are present. After about 4 weeks the young will fledge (leave the nest permanently). Prior to fledging you may see the nestlings sitting on the rim of the nest and flapping around awkwardly.  Not all fledglings are flighted at the time of leaving the nest, so take care not to assume young have simply fallen out. After the chicks fledge, they remain in the care of their parents for the duration of summer, and will continue to be fed for about 4 months.

Differences among corvids

Crow, jay and raven nests are similar in shape and choice of materials and mostly differ in overall size. The main standout are magpies,  which build incredible domed-shaped nests the size of a large beach ball.  The nests require so much material that they can take as much as 40 days to build.  Japanese jungle crows are another species of note, as they have a (relatively) new and problematic habit of building nests out of wire hangers and causing massive blackouts.

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A Jungle crow nest in urban Japan. Photo: Götz

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

Avoiding conflicts

Most breeding related dive bombs occur as the result of a person being too close to a fledgling, but some crows get feisty around their nest too. Physical contact between birds and people during these altercations are rare, but can happen and might hurt. In areas where crows are less persecuted (like cities) they tend to be more aggressive than their rural counterparts. If you know where a nest is and can avoid it, do so and save everyone the aggravation. Otherwise a good strategy is to invest in an umbrella you don’t care about.  It’s a simple and inexpensive solution that protects both yourself and the legacy of recognizing that outdoor spaces are shared space between ourselves and wildlife.

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Crows build their worlds on our backs.  We might as well lean in and appreciate the joys of watching nesting birds!

Have more questions? Let me know in the comments!

 

  1. Gross, A. O. (1946b). “Eastern Crow.” In Life histories of North American jays, crows, and titmice., edited by A. C. Bent, 226-259. U.S. Natl. Mus. Bull. 191
  2. Good EE. (1952). The life history of the American Crow Corvus brachyrhynchos Brehm. Phd Thesis, Ohio State Univ., Columbus.
  3. Peck, G. K., and R. D. James (1987). Breeding Birds of Ontario: Nidiology and Distribution. Volume 2: Passerines. Miscellaneous Publications of the Royal Ontario Museum, Toronto, ON, Canada.

Most of the general information was sourced from:

  1. Verbeek, N. A. and C. Caffrey (2020). American Crow (Corvus brachyrhynchos), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi-org.offcampus.lib.washington.edu/10.2173/bow.amecro.01

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Filed under Birding, Breeding, Crow behavior, Crow life history, Crows and humans