What is so advantageous to crows in taking care of their parents?
Why does natural selection favour such filial acts?
Wouldn’t doing this take resourses that could otherwise be used to creating more young?
Thx in advance
This is one of the many things that come as news to me. Where can we find confirmation that they do this?
This is another of the many things that come as news to me. Have you got a site confirming that crows do this?
Much to my disapointment i couldn’t get website confirmation that crows do this but i do remember from my textbooks that crows do care for their parents.
Not much of a prove but assuming it is true, why would it happen?
I don’t recall hearing about crows specifically, but it is documented that this behavior occurs in several species of birds, for a variety of reasons.
If new territories are scare, young adults may stay to help the parents raise new offspring.
If the environment is particularly harsh, young adults may spend a year assisting their parents in raising the next offspring.
Both the above strategies can arise because although they individual is not directly reproducing, they are supporting the reproduction of relatives, and thus the genes that can lead to this sort of behavior.
Birds that need to learn to obtain food - hunters, or possibly omnivorous scavengers, might take a year of assisting mom and dad while refining their own hunting/scavenging skills. Thus, when junior and juniorette move off to start their own families their skills will be up to feeding the young’uns
All of the above, by the way, are not limited to birds but have also been observed in mammals as well.
This sounds like the sort of thing that Game Theory has revealed about evolution.
Decades ago, nearly everyone assumed that competition and pure selfishness was the optimum behavior for organisms. Life was a “zero-sum game” with each winner creating losers. Cooperation between organisms would be foolish (and hence theories like Margulis’ cellular endosymbiosis were dismissed.) Natural selection should guarantee that there should be no altruists in the animal world. This attitude changed partly because of John “a beautiful mind” Nash, and his idea that multiplayer games could have equilibrium points where many players simultaneously become winners.
Pure competition precludes the cooperation necessary to form social patterns among unrelated organisms. But, as is demonstrated by the Iterated Prisoners’ Dilemma, sometimes a community of “cooperators” makes larger gains than a bunch of competing individuals. In other words, sometimes the best “self-interested” decision involves acting far less self-interested. The Reciprocal Altruists can sometimes out-survive the purely selfish individuals. (Note that this is all about behavior, and has little to do with group selection and genetic relatives.)
Search on keywords:
evolution of altruism
prisoner’s dilemma
reciprocal altruism
non-zero-sum games
The greatest instinct in animals is survival of the species, not self-preservation, so this “game theory,” altho a good argument, is not the real reason, IMHO. The Reciprocal Altruist may out-survive the purely selfish animal, but even if he or she doesn’t, his or her actions will contribute to the survival of the species more than the purely selfish animal.
brachyrynchos could probably tell you if you can find her. If memory serves, she’s a bit of a bird person.
Oh, goody, my favorite topic. Yes, I am a bit of a bird person (:)) and corvids (crows, magpies, jays and ravens) are my speciality.
But the person who should be answering this question is Carolee Caffrey. She studied American Crows (Corvus brachyrhynchos) in southern California at the right time and with the right methods. By this, I mean techniques to easily identify genetic relatedness were available, and she did also individually marked crows. She could follow their behavior and then see if there were any correlates to their relatedness. Very cool, but not done very often because it’s a lot of work (and with monomorphic species, there is no other was way).
Anyway, she found that siblings from previous years do stay home and help with their younger sibs. Not all stay home. Not all help. But this was previously undescribed behavior in crows. During the past few decades, we’ve been seeing cooperative breeding behavior in more and more species (we look, we find it). Most types of cooperative breeding that involve offspring contributions are where males stay home (as with the Florida Scrub jay (Aphelocoma coerulescens). In another corvid that does NOT show signs of cooperative breeding, the American Magpie (Pica hudsonia), young of the year males disperse inversely to their size (and presumed dominance): the smaller you are the farther you go. It’s not a difficult step to go one further and stay at home. There are benefits to accrue (the strength and safety of family, knowledge of a home territory, indirect increase in fitness if your sibs live). But you do delay breeding.
What Caffrey also found that was highly unusual was that female crows would stay home. I can’t think of a study that shows the female avian offspring remaining to help at the nest (Colibri?, anyone else?). Female sibs would on occasion sit on the nest to incubate (although mom will chase them off, and they won’t take food while on the nest like mom will). I don’t remember exactly what they did contribute - I don’t have the paper in front of me, but I do remember that their overall contribution was also less than expected.
Why would any offspring delay breeding? For one thing, passerine nesting success is notoriously low, and crows are no different. Kevin McGowan at Cornell has been following his birds for many years, and generally sees about a 50% nesting success rate, which is really quite high in comparision with some other species and crows in other areas. Others have reported lower rates. So, perhaps a cooperative breeding strategy will increase success rates. Caffrey found that it does, but not quite as much as was expected. So, the effect is there, but perhaps something else is going on to maintain the system.
Caffrey’s work can be found at:
Caffrey, C. 1991. Breeding group structure and the effects of helpers in cooperatively breeding Western American Crows. Ph.D. dissertation, Univ. California-Los Angeles, Los Angeles.
Caffrey, C. 1992. Female-biased delayed dispersal and helping in American Crows. Auk 109: 609-619.
Caffrey, C. 1999. Feeding rates and individual contributions to feeding at nests in cooperatively breeding Western American Crows. Auk 116: 836-841.