Anything but Common: The Hidden Life of the American Crow

Erin asked: <

I imagine you have to use the gear that tree trimmers do to get to the tallest part of the tallest tree where the nest and babies are, and handle the babies and put tags and bands that are strange to them.    Why does that not spook the parents and make them leave the nest?  You always hear that birds and animals will abandon young ones if you scare them or make too much of a ruckus near their nests.>>

Erin, American Crows can be initially agitated when the tree climber is near the nest or young. However, the American Crows typically have too much invested in their 'kids' to abandon them or ignore their begging calls after they are returned to the nest.

Erin asked < < If humans need to use a blood test to tell the gender of the birds, how do the birds know who is male and female?  >>

There are some differences between male and female that a crow would be better able to access than a human or researcher. We are not aware of any studies that have been done to determine how the crows themselves know male vs. female.  The male does have a slightly lower voice than the female and while that is difficult for humans to easily use for "sexing" a bird the crows themselves might be better at using voice to tell male from female. There are probably other differences they pick up on such as slight differences in bill size or shape. Even trained researchers have a difficult time with any visual differences and that is why to be 100% sure researchers go by DNA tests. There are probably behavioral cues they could pick up on but without a proper study it is all speculation. Thanks for asking.

Can information regarding the baby’s health be detected by the colour of their tongue?

Dorothy, The color chart you noticed was used that year by a graduate student that was looking to see if inside mouth color variation was indicator of anything such as health, quality, or temperature. That student has not published study results so no updates or conclusions for us to post about.

The local researchers haven't noticed anything to indicate that the tags impede movement. The tags usually stay on for several years, but not as long as the leg bands. Crow "AP" the longest lived of the research crows still had remnants of his wing tag at age 17. When they first get the wing tags they fuss with them, investigating the new adornments. However after a day or so they seem oblivious to their presence. The antennas  haven't been put on very many crows thus far and don't stay on for very long. They usually fall off in less than 1 year.

When the males and females look the same they are called sexually monomorphic. The males are slightly larger than the females but not enough for humans to easily notice the difference without taking measurements and that is why DNA testing is the best way for humans to tell the sexes apart. Crows do have some courtship displays. However there is more that could be researched about the American Crow courtship process. The local researchers don't witness the meeting of a crow with a mate or potential mates and the courtship period is thought to happen quickly perhaps. They don't know if the males need to impress the females visually. It is difficult to make an assessment since the local researchers don't witness much if any of the courtship process.

@Eveline Hello Eveline, Corvids in general don't show a lot of display for courtship. With the American Crows they typically form a long term pair bond so they aren't having to do a lot of courtship displays and rituals every year for breeding season like some other types of birds might do. Once the bond is formed it can last for many years or until one dies so the odds of a researcher observing that first time period that a new couple is pairing up for the first time is slim. That coupled with the difficulty in humans differentiating individual crows which can't be reliably told apart from another crow without them being tagged and or color-banded.  If you are observing unmarked crows you don't necessarily know if you are observing a male or a female, parent, partner, child etc reliably. In the course there is an offer for course takers to get a discount on Birds of North America (BNA) subscriptions. BNA is  our more in depth online encyclopedia of North American Birds. Here is an excerpt from Birds of North America, American Crow : Pair Bond Courtship Displays and Mate-Guarding. Courtship display, if it exists, is rare, judging by the paucity of reports on the subject (Good 1952). Allopreening, often actively solicited by either mate, occurs regularly, but largely ceases during incubation (Kilham 1989). Billing, seen infrequently, involves a mated pair gently fencing with their bill tips, and bill-grasping (Kilham 1989, CC). Members of a breeding pair stay in close contact during egg-laying stage (Caffrey 1992). Breeding male guards mate during time of sexual receptiveness. At start of egg-laying in Florida, males stood generally on 1 of 2 or 3 favorite perches, on the ground below the nest, on a fence post, or in a tree as far as 150 m away, watching for periods of 30 min. Males hardly fed their incubating mates during mate-guarding period; helpers fed the females (Kilham 1989). In California and Oklahoma, guarding males sit for hours at a time, with only short breaks, in obvious high perches near incubating females (CC). Copulation; Pre- And Postcopulatory Displays Based on Black 1941 , Kilham 1989 . During precopulatory display, both sexes crouch, bodies horizontal, wings out and drooping, and tails vibrating up and down; females use same display posture during courtship begging (accompanied by nasal “ waahs ”; CC). Sometimes this same display occurs in other context; juveniles give it to older siblings and some-times to each other (CC). Begging nestlings and fledglings assume the same posture and produce nasal “ waahs ” as well (CC). Males sometimes pick up objects as part of copulatory behavior. During copulation, male settles on female, waving his outstretched wings; female stands and vibrates her tail up and down while the male works his tail under hers. Loud, hoarse calls by female, audible 250 m away, heard during 13 of 30 copulations seen. Copulations occur on the ground, in trees, and on nests; last from 4 to 12 s. Reverse mounting occurs (Kilham 1989 ).

For crows the eye color is a cue for the recognition of juvenile status. The blue eyes show that they are babies.  The blue eyes change to their adult color within a month or two after they fledge (leave the nest). The pink inside out the mouth is another visual cue for crows to recognize that the crow is a young crow. The pink inside of the mouth can last up to two years.

The size difference between male and female is so slight that even the crow experts don't always guess the sex correctly just by visual characteristics. Size can be deceptive and feathers can be fluffed up or smoothed down variably by a bird. So the only reliable way to sex crows is by DNA. Thanks for asking about this.