Wednesday, October 13, 2010

Birds and memory

I was amazed to learn the other day that some birds grow new brain cells in the autumn-- all in the aid of boosting their memories.

As I've mentioned before, over the summer, I really got into birding. One of the unexpected pleasures of that was discovering the joys of birding gossip. I can't begin to guess how many birders haunt Seattle's Union Bay Fill, which contains, among other things, the wetland reclamation area I've talked about in past posts, but there must be dozens, if not hundreds (easily identifiable by binoculars, or high-powered cameras or even telescopes, and sometimes even folding stools) regularly visiting the site. I've been reading birding books and have become more attentive and focused, and so I'm seeing a lot that I'm sure I previously missed. But even before I got serious about this new pursuit, I had already begun engaging in one of the pleasures intrinsic to birding: making narratives out of the "dramas" going on in the bird world that I've been visiting. Now that I, too, walk around with a pair of binoculars slung around my neck, other birders frequently ask me if I've seen anything interesting. That question is usually the prelude to a gossip fest about certain of the on-going or recent-past bird dramas. For instance, a couple of weeks ago when I mentioned the osprey that I've seen around the Cove since early September and remarked on its ineptness fishing-- diving down to the surface of the water only to ascend empty-beaked-- my interlocutor said yes, she was sure that osprey was a juvenile and that just the other day she saw it successfully catch a fish, which she was delighted to see-- only to have one of the resident bald eagles swoop past it and steal the fish right out of its beak. And then there's the gossip about the three young Cooper's hawks who seem unable to catch anything and will they starve to death if they don't soon figure things out?

And of course there was that pied-billed grebe who laid three eggs in August (see the photo)-- and sat on it for weeks, until finally it abandoned the nest when she figured out the eggs weren't viable, and the next day, the eggs [three of them, but I'm afraid you probably can't make them out in the small version of the photo to the right) were gone. And so on.

I've always been interested in the birds in my own yard, but since I grew up in the midwest, my ability to identify them (beyond crows, robins, sparrows, and starlings) was pathetic. I've always liked to listen to them in the early morning, but again mostly couldn't tell which birds I was hearing. But now I know, for instance, that black-capped chickadees and Steller's jays are habitues. I have actually frequently noticed a couple of Steller's jays hanging out here over the last couple of years. (They like to forage on the ground, which makes them easily visible.) I've only seen black-capped chickadees at the Fill-- but I hear them all the time in my yard. (Their song as well as their other sounds are highly distinctive.) But then it's difficult for me to see anything in the huge old cherry tree that a lot of birds like to perch in, because the leaf cover is thick.

The other day I decided to learn more about them than I could find in my birding books. And this is when I discovered that they are among the birds that discard some brain cells in their hippocampus in the spring and grow new ones-- causing their hippocampus to expand by about 30%-- in the fall. The reason for this? They cache food all over the place and need to be able to remember where they put it. Here's an excerpt from an abstract for a paper by David F. Sherry and Jennifer S. Hoshooley, Seasonal hippocampal plasticity in food-storing birds:
Both food-storing behaviour and the hippocampus change annually in food-storing birds. Food storing increases substantially in autumn and winter in chickadees and tits, jays and nutcrackers and nuthatches. The total size of the chickadee hippocampus increases in autumn and winter as does the rate of hippocampal neurogenesis. [...] The peak in recruitment of new neurons into the hippocampus occurs before birds have completed food storing and cache retrieval for the year and may therefore be associated with spacing caches, encoding the spatial locations of caches, or creating a neuronal architecture involved in the recollection of cache sites.[...] Available evidence suggests that changes in hippocampal size and neurogenesis may be a consequence of the behavioural and cognitive involvement of the hippocampus in storing and retrieving food.

Since the discovery in the 1990s that black-capped chickadees grow new brain cells every year, researchers are exploring the phenomena, some of them interested in finding appplications for humans who are inacapable of growing new neurons to replace the ones they are constantly losing. Kurt Pfitzer reports, for instance:
Songbirds are the first species of vertebrate in which brain growth during adulthood has been found to occur, Saldanha says. By studying neurogenesis in the black-capped chickadee, Saldanha hopes to learn how hormones help guide the brain’s development and reorganization. He is particularly interested in the role played by the hormone estrogen in the growth of the hippocampus. Songbirds (like most vertebrates) make estrogen in their ovaries; scientists have determined that their brains also express aromatase, the enzyme that makes estrogen. Perhaps not surprisingly, the area of the songbird brain with the highest estrogen-making capability is the hippocampus.

"We know hormones affect the reorganization of the brain in ovo, in utero and during the early physical development of most vertebrates," Saldanha says. "We are trying to figure out whether the ability to make estrogen in the hippocampus is helping the dramatic reorganization of the [adult] brain."

[Colin] Saldanha [assistant professor of biological sciences at Lehigh University] uses transmission electron microscopy (TEM) to examine neurons (nerve cells) and synapses (connections between nerve cells, where scientists think learning occurs) from the brain of the black-capped chickadee. His goal is to determine whether estrogen is being made in the cellular body or in the synapse, and whether the location of this estrogen-making ability changes seasonally.

"We’re looking at the ability of nerve cells and connections to make estrogen in the brain and asking if this ability is involved in brain reorganization," he says.

"We are the first lab, I think, to look at estrogen-synthesizing neurons in the songbird hippocampus at the electron-microscope level. We may, in fact, be the only lab using this technology to investigate songbird spatial memory."
This is fascinating research. But I have to say the chickadees can't be too thrilled by it themselves. For them, Saldanha must just be another predator-- only one they don't instinctively recognize.

ETA: Wouldn't you know it-- shortly after posting the above, I was out in the yard and saw two black-capped chickadees in flight. 

1 comment:

Vandana Singh said...

This is really interesting, Timmi! Thanks for posting.

It occurs to me that if we knew more about our fellow inhabitants there would be so many stories we could eavesdrop on. today I saw masses of starlings on powerlines, jabbering away. Would have loved to know what they were talking about...