Friday, April 29, 2011

Bird brained?

A story on the BBC site this week reports that birds with bigger brains are better able to adapt to city living.  In a paper published in Biology Letters, researchers describe their study of 82 species of birds from 22 families, in which they conclude that birds that have large brains compared to their bodies are more adaptable to living in urban areas.  Their motivation was that since the earth is becoming more and more urbanized, it's the species that are better able to adapt to city life that will succeed in the long term. They say in the paper:
These data support findings linking relative brain size with the ability to persist in novel and changing environments in vertebrate populations, and have important implications for our understanding of recent trends in biodiversity.
Harpy eagle and chick
Although they don't explain the correlation, they do say that brain size has been "repeatedly linked to the ability of animals to adapt to novel or changing environmental conditions, as well as to innovative behavior".  This is brain size, not relative brain size, or the brain/body ratio, so it's hard to know what to make of this study.  Is it that birds with bigger brains are more adaptive?  In which case why don't harpy eagles, with their 6 foot wing spans and legs the size of a toddler's arm, live in cities, and why do hummingbirds come to urban feeders?

And it's never been clear what brain size in itself is all about.  Male and female brains vary by a clear (average) amount -- roughly 10% in humans but varying among species with their sexual dimorphism.  But the intelligence of males and females is comparable.  And one can argue about whether urban or rural environments, with their different threats and opportunities, vagaries and resources, are more demanding of 'intelligence'.  Does being fed by old folks in the park take more intelligence than finding food while worrying about hawks?

Or is it the brain/body ratio that's important, in which case, do crows and tits and wrens in the countryside have the same size brains as their city-dwelling cousins?  And what is it about bigger brains relative to body size that would make an animal more adaptable?  And is adaptability really correlated with intelligence?  Amoeba adapt to changing environments, after all.

But whichever it is, if the underlying assumption is that adapting to city living is the ultimate in adaptability, this suggests that other birds are somehow less adapted or adaptable, but all birds are adapted by definition, and given that environments change all the time, they've all managed to adapt to change.  And, there's probably an ascertainment bias here anyway -- a lot more observations have been made on urban birds than non-urban birds, so that we have a lot more evidence of this presumed superior adaptability in these birds than we do on birds that we don't see nearly as much. 

A few more things are worth considering here.  One is that if this result is indeed correct, this would reflect organismal selection rather than Darwnian natural selection: birds who like the urban environment go there, birds who find it unpleasant or confusing don't.  Genes related to environmental response could be partitioned in this way, but there need not be any differential reproductive success.

Of course lifestyles in cities and country, including diet, amount and nature of exercise, and who knows what else may differ during the growth and development of the birds.  This would not pertain if the country relatives of the urban species the authors studied are also bigger-brained, but then it would imply that country life was originally responsible.

The authors also found small-brained birds in the urban areas but (clinging to their hypothesis) tried to explain that away by invoking ad hoc (or post hoc) special explanations.  That means that the rule, if true, is only a sometime-thing.

In any case, the study (if it can be confirmed in a systematic way, and if what it actually means about brain size can be clarified) is interesting.

And whatever the reason, crows have certainly adapted to city dwelling.  But then, crows are in a class of their own.

17 comments:

Anne Buchanan said...

While I love this video, I've been thinking about the assumption that city living is the hardest thing a bird is called upon to adapt to. What about flying half way across the globe two times a year, including all the calorie loading they do in preparation, and then the flying thousands of miles with no food, often with no rest, and then adapting to the new environment, new predators and so forth? Mortality is very high during every migration. If this urban living study means anything at all, shouldn't we expect a correlation between the distance birds migrate and brain/body size ratio? Though, I'm not sure whether flying the furthest would require the most or the least intelligence...

occamseraser said...

Absolute brain size does apparently matter (a lot)-- in primates too. Marino's comment in PNAS (2006) on "Absolute brain size: Did we throw the baby out with the bathwater" is provocative, and Deaner et al's (2007) paper in Brain Behavior and Evolution ("Overall brain size, not encephalization quotient, best predicts cognitive ability across nonhuman primates) is also worth a read. That's not to say that this new report on bird brains doesn't have some problems, per your comments. Any brain data out there on wildebeasts compared to their nonmigratory relatives?

Anne Buchanan said...

And Canada Geese that migrate, and don't migrate, and live in urban and non-urban areas should have the biggest brains of all birds.

But, I do get the premise about brain size, Occam. My basic problem with this study is that it's based on what I think are rather unfounded assumptions -- what is it about brain size (or brain/body ratio, whichever they actually think is important) that matters, and is urban living really the ultimate challenge to a bird's intelligence?

Ken Weiss said...

The question of brain size, as sexual dimorphism indicates, is not simple. If women are as intelligent (or more?) than men, but brain size differences only reflect body size, then how can size be related to intelligence? This is a legitimate question about mechanism.

If the general idea is that brain size has to do with communication with the body (muscle control, for example), then the brain-body size correlation makes plausible sense. Or, if it were just allometric, one might expect larger to be smarter because there'd be more in the 'thinking' parts in larger animals.

Anyway, while nobody can dismiss the legitimacy of the question, many answers can have comparable plausibility.

And, I think, this is not helpful to judging whether the post-hoc 'explanation' that urban life must be more challenging to the IQ has any particular plausibility. We suggested some other explanations and issues.

So we're just raising our usual skepticism about too-easily-invoked specific adaptive explanations, not saying that the issue doesn't belong on the agenda of science!

Ken Weiss said...

Hey, and as I write this, the Royal wedding has just been consummated (well, the ceremonial part has, at least). Now, they live in a very complex environment and have garnered inordinate resources. What would one expect intelligence or craniometric studies to show? I'll leave that one to historians or others....

Holly Dunsworth said...

I didn't read the study, but what if living in the urban environment is simply building slightly bigger brains in the urban birds? Wondering about mice, rats, squirrels, coyotes...

Anne Buchanan said...

Yeah, a possibility that would need to be ruled out. Are the brains of city birds bigger than those of birds of the same species in the country?

Holly Dunsworth said...

(because the squirrels I've become familiar with since moving to Chicago have quite a diverse, protein rich diet compared to the squirrels I know back in Happy Valley)

Anne Buchanan said...

Clearly someone needs to measure their brains here and there!

Holly Dunsworth said...

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0017514

Holly Dunsworth said...

I'm not kidding, I'll get on it this Fall.

Anne Buchanan said...

Ok, so the idea is that the abundant urban diet could be the sole reason for increased brain sizes of urban animals. Ok, yes, sounds reasonable. I look forward to your results!

Holly Dunsworth said...

Show me how to kill a bunch of squirrels first.

Holly Dunsworth said...

;)

Anne Buchanan said...

Road kill? Though that could be a problem, if the probability of getting killed by a car happened to be correlated with intelligence...

Ken Weiss said...

How about this analogy to humans: urban environments select for bigger bellies?

The answer is because of McFood and McCouchPotatoes.

One could go on, and once again (as almost always) it is the problem about weeding out the facile from the substantial.

Holly Dunsworth said...

Anne, you read my mind. I have two roadkill squirrels (skeletonized now, thanks to help from a student) and almost quipped the same thing about intelligence ;).

Ken, I just saw a squirrel eating a Big Mac yesterday.