Aitch wrote: ↑Sun Sep 12, 2021 6:12 am
Well...
Corvids are supposed to be among the most intelligent of birds, so no reason why they shouldn't learn to recognise the signs of a possible feast. And teach their offspring?
However, do they stay in family groups or do the generations spread out to their own territories? If the former, it would explain why the behaviour hasn't spread. And provide another nail in the coffin of morphic resonance?
Is this interesting enough for someone to do a PhD on it? Or failing that, for them there mods to split it off into it's own thread?
It's genuinely not a million miles from what I'm doing my PhD on
though I'm working with waterbirds rather than crows.
I think the way information spreads through natural populations is fascinating, and quite often overlooked. We often think about resources like prey or safe sites to shelter, but don't often think about how individuals get information about those resources. For populations that are depending on resources that are highly restricted in space and/or time, information could well be a limiting factor.
There is a period of a few weeks after fledging when corvids tend to stick with their parents and are deliberately "taught" about sites, dangers, prey etc. (At least, they accompany their parents while they deal with those things, and learn through observation.) During the winter, these species often form huge communal roosts with multiple species of corvids (
Crow County by Mark Cocker is a wonderful, wonder-filled exploration of the phenomenon). As well as the general safety-in-numbers aspect during the long nights, it's generally thought (though not well empirically confirmed yet) that these roosts serve as "information hubs", with birds able to share information about good places to forage etc.
For species that migrate, tracking studies are showing the importance of "horizontal" social learning for juvenile birds' survival (horizontal = learning from unrelated adults, rather than vertically from parents). One of the starkest demonstrations I've seen followed Lesser Spotted Eagles, comparing a native population with juveniles that were translocated as part of a reintroduction scheme. The native juveniles departed with adults, followed them by a more convoluted route, and arrived in Africa, whereas the translocated juveniles set off earlier, went in the wrong direction, and mostly
died in the Mediterranean.
There's two important take-homes from this:
1) animal behaviour is generally a mix of instinct and learned behaviour. For instance, those translocated eagles were setting off in a sensible compass direction to migrate from Latvia via the Suez Isthmus into Africa (as birds that glide on thermals, they're not good at crossing open water). But because they were starting off from Germany, they didn't run into any responsible adults to join up with. (In
Blackcaps this initial migratory orientation seems to be a single-locus mutation, so highly evolutionarily malleable).
2) learning doesn't have to be complex - it can be as simple as following a rule of "join with other members of the same species", and then at least you're in the right place. Loads of birds have a very strong instinct to join flocks, which hunters have exploited for millennia via building decoys for wildfowl or making imitative whistles.
Conservationists now consider these social phenomena carefully when planning reintroductions of migratory species/populations. For instance the project to reintroduce Whooping Cranes to North America included teaching them to migrate by getting them to follow an aircraft. They also found that unsupervised juveniles who joined up with adults chose more direct migratory pathways (
linkeroo). The
reintroduction of Black-tailed Godwits in East Anglia has found that the captive-reared birds soon join with wild individuals after release, and migrate with them to Africa and back.
In longer-lived, higher-intellect species, there's generally a process called "
canalization" - juveniles will try out all sorts of stuff, but increasingly specialise in a number of quite specific behaviours. If it ain't broke, don't fix it. This also has important conservation implications: once habitat is lost, individuals quite possibly won't find other suitable habitat even if it's close by. Furthermore, adaptation depends on a constant supply of new recruits, so if breeding success declines the population is really in trouble.
There's depressingly few good studies of this in an age of wholesale habitat loss, but at a local scale,
impounding some mudflats in Cardiff Bay caused Redshank survival to decline from 85% to 77% - birds observed to have moved to a new area (only 4km upstream!) had lower body condition, indicating that they struggled to find enough food in their new digs. At a much larger scale, the loss of most of the Yellow Sea in China - a key stopover site in the East Asia-Australasia flyway, is
associated with the decline of pretty much all populations that depended on it.
Waders tend to be highly site-faithful, though, whereas other species like corvids may be less so (I'm genuinely not at all sure, especially for US species). Where new opportunities become available, or old ones disappear, it would only take a few individuals to figure it out before the new information can spread through the population. For instance, in the early 20th century UK there was a well-documented phenomenon where Blue Tits (related to Chickadees in the US) learned how to open the foil tops of milk bottles left on people's doorsteps. The behaviour developed at multiple sites and spread through local populations.
Recent experimental work suggests that juvenile tits, especially females and subordinate males, are the quickest to learn stuff.
So yeah, despite the length of that post, I really want to conclude by saying that I think social learning is often quite a simple process ("join with others"), pretty ubiquitous (it clearly has a high survival value), and super cool. And on a personal note I always find reading these kinds of local natural history observations pretty stimulating, so thanks for sharing