And to think that I saw it in a Mulberry tree

Ok, that’s a very poor use of a Dr. Seuss book title.  Well, maybe it’s not quite poor as just too simple.  The truth is, though, that I did see it in a Mulberry Tree.  No, I didn’t see a whole circus or anything, but it was a fair bit of activity, nonetheless.

So let me start at the beginning:  I was running down the greenway the other day.  As with many things, the beginnings aren’t always so exciting.  You don’t know that the cool stuff is there until it happens.  So…running down the greenway.  It was not too early, but the greenway was still mostly empty.  The sun was still coming up in the sky, though there was plenty of light.  It was one of those humid, heavy air mornings, too, so I was not having the most pleasant of runs.  As I ran the greenway along Little Sugar Creek from East Blvd towards the Carolina Medical Center, I could see a whole lot of bird activity in a tree.  From a distance, I could even tell that there were multiple species in the tree.  As I got closer, I could see dark fruits on the tree and I was starting to hear the birds, too:  the high ‘zzzzzee’ of Cedar Waxwings; the highly variable pattern of the Northern Mockingbird; and the weirdly irritating complex song of the European Starling.   When I was finally close enough to the tree, I could see that it was covered with ripe, dark fruits that looked like blackberries.  It also had a huge number of unripe white fruits growing on it.   It was a mulberry tree.  Ok, I didn’t quite realize that fact at that moment.  I had to come look it up.  Anyway, a mulberry!

And what did I see

While the waxwings went ‘ZZEEE’

In that mulberry tree?

I saw birds flying in and out of that tree eating fruit after fruit!  There was evidence of this process on the sidewalks around that stretch of greenway, too.  A great deal of the bird poop was stained purple- a clear sign that they’d been eating the mulberries.  Yes, I look at bird poop.

Now those fruits are not the most nutritious of food sources, as they’re low in protein.  They are, though, a very high energy reward for those quick-metabolismed-little birds.  They clearly took advantage of the mass fruiting in these trees.  And that brings up another thought.  I’ve spent a lot of time talking about communication in birds and the signals that they use.  Well, here’s a tree that’s also creating a signal.  Those fruits on the tree that change color are a huge advertisement to all the birds around the area (especially given that most of those song birds have very poor senses of smell).  If the fruits were green, they would blend in and be hard to see.  Brightly colored fruits are a signal that breakfast is ready!  For a mulberry tree, getting your fruits eaten by birds is very handy.  Those fruits contain seeds and the birds that eat the fruits fly off to poop, depositing those seeds somewhere else (another reason to look at poop).  The more birds that a tree can bring in, the more successful it is at getting its new kids (those seeds) sent off to other areas.

One way to draw in a bigger crowd is to put up a bigger sign, and that, apparently, is the strategy used by the mulberry tree.  Instead of just putting up one or two fruits at a time, it preps HUGE numbers of them, creating an enormous display of color that clearly draws in large numbers of birds.  People have modeled this sort of idea and feel that it’s not really the number of fruits on the tree that draws in the most birds, but the total amount of energy (which is a function of both the number of fruits and the size of the fruits) that draws in the birds.

Stapanian, M.A.  1982.  A model for fruiting display:  Seed dispersal by birds for mulberry trees.  Ecology 63:  1432-1443.

Since those variables are related to each other, though, we can still see how such an enormous signal by the tree functions to send a message to those birds: “Hey!  Look what I got here for you!”  Mulberries, by the way, have notoriously poor grammar.

So if you’re walking the greenway

keep your eyes up in the trees

if the fruits are brightly colored

you’ll never know what you’ll sees!


About thomasbiology

I'm an Associate Professor of Biology at Queens University of Charlotte with a background in animal behavior with an emphasis in bird song. I've got two secret goals with this blog (well, since I'm sharing them, they're not so secret): 1. To encourage people to look at the natural world around them- not just as a hiking destination, but to notice all the little things moving around them all the time; and 2. To show some of the science that relates to these little things moving around. There's some really fascinating research out there that so few people get to see.
This entry was posted in birds, communication, ecology, foraging, reproduction. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s