Hybrid flying squirrels are not science fiction...

Recently the PhD candidate in my lab, Colin Garroway, along with our supervisor and other collaborators published a paper "Climate change induced hybridization in flying squirrels" in the journal Global Change Biology (see abstract/PDF here).

This is big news for climate change proponents... two species of flying squirrel at their respective northern and southern range boundaries have been shown to be hybridizing. The range boundary of southerns has been moving north with climate change, and therefore has increased the contact between the two species. This could in effect reduce biodiversity as two species merge to become one.

Anecdotely, I had southern and northern flying squirrels using the same nest tree at the same time, though I could never find the cavity and therefore I could not confirm if they were using the same cavity or not.

But more importantly, this story is not restricted to the academic journal. It has been featured on the Trent University website.

It is slated to appear in the Globe and Mail, and they have been in contact with science television programmers. This is great! Getting the story out to the public, those who influence change (since climate change is a policitically controlled issue) is critical. I'm glad the that the communications offices at Trent and MNR understand this and make an effort to publish these stories!

Where flying squirrels go to count sheep...

I tracked squirrels to find their nest cavities, which I then measured (eg. volume, the direction the opening faces, opening area). Flying squirrels are secondary cavity nesters, which means they use cavities excavated by another species, such as a woodpecker.

A regular cavity looks like the one on the right. If you're lucky, once you track a squirrel to its tree you can hit the tree with a stick and a squirrel will either stick its head out of the cavity or actually run out and up the tree. If you're REALLY lucky, you may even get a glide right out of the cavity to another tree. That's always fun to see :) If you look really closely, you can see the nose of a squirrel towards the bottom of the cavity circle.

But then sometimes northerns shrug convention and do this to me. It's not new news that flying squirrels build leaf nests. It was just a little unexpected given the cold winter temperatures. Southerns do not even build leaf nests this far north. So when I stumbled upon my first nest, I thought it would likely be an outlier. But then I found more and more leaf nests...

So that brings us to this winter. This winter I collected several known leaf nests from last winter and deployed them with temperature loggers to look at the difference between outside (ambient) temperature and temperature inside the nests.

So far analysis of that temperature information shows that leaf nests are likely equivalent to tree cavities for buffering capacity. Stay tuned for more rigorous comparisons soon.

How to find the needle in the haystack, that is if you've deployed it with a radio collar

I've always wanted to radio-track an animal, ever since seeing it on National Geographic or some other Discovery Channel program when I was a kid. We've all seen it, a scientist holding a huge antenna (or maybe it's mounted on the back of a truck), tracking tigers or mountain lions or bears - something big and ferocious (and far-ranging).

So when I took on my project, I was really excited to track my first flying squirrel. Luckily, the antennas are much smaller (because squirrels don't move nearly as far as larger mammals) and the larger the antenna, the further away it can detect a signal. Especially since we don't drive around in a truck, we hike through the forest to find the squirrel's tree.

Since I was interested in squirrel nest trees (and more specifically, the cavities they used), I would trap squirrels at night, attach a radio collar and let them go. Flying squirrels are nocturnal, which means they are active at night, so we would leave and come back in the day when they were asleep in their nests. That way I could find the cavities they used.

To find them, you just follow the beep. Whichever direction is the strongest sounding beep on your received is the direction they are in. Every now and then a rock face or hill can throw you off, but you soon discover your error as soon as you get to the top, and the reception is clearer. The trickiest part is when you get down to two or three trees that are close together. Squirrels tend to nest high in the trees, so it's not as simple as pointing the antenna at the tree at face height. You have to angle and twist and turn to make sure you have the right tree.

Looking for cavities always helps... if there are two trees, and one has several obvious cavities and the other has none, they are more likely in the one with the cavities. You still need to double check though. My favorite way is to hit the tree with a stick - if the cavity isn't really deep, a squirrel will poke its face out of the cavity to see what's hitting its tree (which doesn't seem like a great survival strategy I know). Years ago this was actually how biologists caught flying squirrels, by netting them out of their cavity holes (it seems like such a cowboy tactic - squirrel wrangling).

All in all, it's like playing hide and seek with such an advantage that the seeker always wins. And finding a squirrel's cavity is very satisfying (especially if you can get an impromptu glide out of a squirrel by banging on the tree)!

Trapping is an art best left for tall men

To trap flying squirrels, I mount brackets on trees and place tomahawk traps on top of the bracket. The higher the trap is on a tree, the more capture success it will have. Now picture your 6' co-worker setting traps as high as he can reach, and then sending me (5'4) to set them.

See the problem? I spent half of my winter trying to scramble up trees with traps totally out of my reach. And to put the bait in the trap (peanut butter on the little peddle that shuts the door once its stepped on), I need to be "face and eyes" into the trap.

After about the 6th time climbing a pine's dead lower branches and then sliding down the tree, getting stabbed by the nub left by the branch when it broke off on the way down, I decided I needed a step of some sort - and I choose a milk crate for that purpose, because it was light and sturdy. The milk crate was my sidekick all winter, giving me the extra height needed to set traps with ease.

My Project (the dry stuff)

First things first, what do I research?

I'm looking at two species of flying squirrels (Glaucomys) in Ontario. Southern flying squirrels (G. volans) are moving north with climate change, and that could have impacts on the populations of northern flying squirrels (G. sabrinus) that live further north.

What are my objectives?

I'm interested in the possibility that these two species could be competing for nest trees (cavities) when they live in the same area. As well, southern flying squirrels could be passing a parasite to northern flying squirrels that northerns are not adapted to. Both of these interactions could put negative pressure on northern flying squirrels.

How will I test my objectives?

Nest cavities would be most critical in winter, when temperatures are low. I will record tree cavity temperatures during that time, and model which cavities are warmest using measurements from inside the cavities.

I want to know if southern flying squirrels are nesting in the warmest cavities, so I will also measure known flying squirrels nest cavities to see where they fit in the model. I think that in sites where they are only one species, both northerns and southerns would use the warmest cavities. In areas where there are both species, I think that southerns would use the warmest cavities (they have been shown to be more aggresive than northerns in defending nest boxes).

I will also test both species for the parasite Strongyloides robustus. It lives in the intestine and has no measureable effect on southerns, but causes harm to northerns. To test for the parasite, I will collect scat samples on a north-south gradient in Ontario, to see if it is moving north with southerns.

So that's the gist of it - my Coles Notes version :) Now onto the interesting part, field work - the good, the bad, and the ugly... stay tuned