Jasmine
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I knew that males do not participate in raising young. The degree of sexual dimorphism and "flashiness" of the males is often indicative of this parental arrangement, e.g. grouse, ducks, and birds of paradise males also display little/no participation in raising young. Often, when both parents participate, the degree of sexual dimorphism is less, sometimes to the point where both species look the same (monomorphism), e.g. Canada goose, crows, and sparrows. Note in these cases, the plumage is more muted or camouflaged, to protect the bird(s) sitting on the nest (like most female hummingbirds!). So, I was quite surprised to learn that there are SOME species of hummingbirds that do NOT display sexual dimorphism...and in some photos that were shown, the females were very flashy!! I am wondering what the purpose of that iridescent plumage would be for females - is there female competition? It certainly would not be beneficial as the sole nest incubator, vulnerable to predation.
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Extra-pair fertilization is a useful strategy for both parties (ie. the breeding female and extra-pair male) to have greater reproductive success, as they aren't putting all of their eggs in one basket, so to speak. The extra-pair male gets to sire extra offspring without spending any energy needing to raise them. The female gets more genetically diverse offspring which should statistically increase their chances of survival - e.g. if the extra offspring have some extra good trait(s) - assuming there is enough food to go around. The only "loser" here is the breeding paired male, who spends time and energy raising young that are not genetically related to him. However, given that crows breed cooperatively, there is still an advantage to this as the extra-pair offspring will help him the future.
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The fact that many birds have to wait several years before breeding (graph seen earlier in the course), and that some crows have to settle for shared parentage or joining unrelated groups, makes me think it is more difficult for crows to become full breeders. I suspect this is generally the case in cooperative breeding systems, which is why they have evolved: it is better to play some role in helping raise related birds (kin selection) than to not have the opportunity to breed at all. I think the points that everyone has spoken to such as a greater selection of breeding strategies, crows being generalists, and crows living in community would lead to greater reproductive success.
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I was walking home one afternoon when I noticed a crow sitting on a lamp post. As I approached, the crow intentionally dropped a nut in front of my path (a walnut, if I recall correctly). I had seen a documentary about crows and learned that they would drop nuts in front of cars so the vehicles would crack the shells and the crows could retrieve the nuts. I stomped on the walnut, cracking it, and kept walking. A little while I later I looked back and sure enough, the crow flew down to retrieve the nut. What a creative bird.
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Recently, I travelled to coastal Washington and BC for a birding trip, and I was amazed at the sheer numbers of birds flocking in certain bays, presumably good feeding spots. I saw hundreds of dunlin, Western sandpipers, and thousands of American wigeon - I would guess 3000-5000 in places.
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My friend, who admittedly was one of the crow-haters, nevertheless recognized how smart and sociable they were. She told me a story that she once observed a crow that had died, and a number of other crows, presumably family, congregated around it in a circle as they just stared at the dead crow in silence. She figured it was a crow funeral. Has anyone heard of such a thing with birds?
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3. I live in British Columbia where there are both. I find sound to be the best indicator; tail shape when flying or bill shape and size if perched closer. The differences in large "fingers" in the wings from the lesson is good to know (ravens - 4; crows - 5). Ravens tend to soar more, while crows don't. In general, I would say you find ravens more often in higher-elevation habitats and forest, whereas crows are more urban (though certainly, both can be found in places - like the dump!).
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I used to live in Burnaby. Every morning the crows would take a noisy neighbourhood census, and I was upset when they would decide to do that outside my window. Every evening, I would see them flying over in the tens or hundreds to roost - I think they were travelling to Deer Lake or possibly Burnaby Lake.
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It was alluded to in the lessons that several other birds cough up pellets, and I believe hawks and eagles (i.e. other birds of prey) are amongst those that do.
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With birds that use this strategy (asynchronous hatching), juveniles that hatch later are usually at a disadvantage to their older and bigger, stronger, noisier siblings who can out-compete them for food. In years where food is scarce, younger and smaller hatchlings may die if they are under-fed. It actually functions to give the parents the best reproductive success, as rather than distributing scarce food amongst all their offspring, which may mean that none are particularly well nourished, this strategy ensures that the strongest and most viable chicks get the best nutrition possible, increasing their chances of survival.
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I had a majestic experience with a great grey owl in April 2022, British Columbia, Canada. My friend and I found one at the edge of the forest. The bird flew in close and landed not 10 metres from us on a fence post, surveying the grass, then diving to catch a rodent. It obligingly posed on the post with the rodent in its beak, then soared silently right over my head; I could feel a breeze from its wings. It flew away deep into the forest, probably bringing that rodent to its nest. Magical! My friend got spectacular pictures.
Viewing 11 posts - 1 through 11 (of 11 total)