Jill M. Mateo


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Horse Corral, Field Season 2009
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This year's field assistants during the mating period: Karen Fowler, Andy Dosmann (now a second year graduate student; see 2007's season), Kevin Bender and Tamara Rocabado. This photo was taken on the LAST day of mating, after several days with no evidence of females in estrus or signs of copulations. It was a long season, lasting almost a month. The day ended with ominous, dark, swirling clouds, which suddenly opened up, drowning us in rain and hail. Note the wet clothes and Karen's poncho. Not a nice way to end the mating period!

A low snowfall year in the area, like last year. Unlike the rest of the eastern Sierra (such as Mammoth Ski Area), Rock Creek Canyon received only 30% of its 'normal' snowpack. So when we arrived many spots had already melted out. This made it easy to follow the squirrels - no snowshoes required!! But, the low water content can spell disaster later in the season, when the food disappears before juveniles have deposited enough body fat to survive the winter.

We often see pine martins early in the season, waiting to snatch an unsuspecting ground squirrel. Kind of hard to see here, but it's sitting up in the tree. And it did get a squirrel later that day.

Our Super Stud from previous summers (see pages from other years), "Beard" is still alive! I was a bit worried, because normally he's the first squirrel we trap, at his hibernaculum in one corner of the meadow. When we arrived, there was no snow hole there. And no sign of him anywhere. But after several days of trapping he was caught in a different area. He's eight years old now. He was a stud in the past, as I noted, but not so much last year. And as it turned out, not so much this year either. He sure played the game, though. He cruised around, got into fights, and was near estrous females each day. As you can tell, he got beat up. A lot. The wounds on his back took weeks to heal. I was worried they would not, but he's still with us. Over the whole mating period, he had only one copulation. Is this because he is related to most of the females and there was mutual avoidance? Because he's old and in poor condition and the females rejected him? Both?

How do males get these injuries? From fighting for females. It is a bit hard to tell from this photo, but here are two males engaged in a ball fight. The squirrel on the right has his mouth open (the pink area) as he bites the squirrel on the left. Not quite sure where Beard, the guy on the left, is biting his opponent....
Beard wasn't the only male to suffer injuries during mating. This is 'Arrow', one of our studs (also wearing a radio collar; see previous years for how we track males), sporting several serious wounds.
Heart, a returning stud from last year, did much better this year. He really hit it off with the ladies! Despite his face busted up....
For years we've been measuring hormones in both blood and feces (see other pages on the site), but this year we experimented with salivary hormones, another non-invasive way to measure hormones. We put cotton swabs in the mouths of squirrels for five minutes or so (such as while we were dye-marking them). Some squirrels were very cooperative, and helped out by holding the swabs!
Another cooperative squirrel. Unfortunately, we found that after spinning the swab in a centrifuge to collect the saliva, we simply had too little 'spit' to work with. Bummer...
I think this is really cool! We found this mummified squirrel after the snow melted. It's curled up in a sleeping/hibernating position. It was found aboveground, but I'm not sure where it died. It is SO intact, I love it! Just skin and bones - no other tissue. The ear tags were still attached, so we could identify it. You can even see its 'fingers' curled up.
The underside. The only hair left on it was on the tip of the tail. I wonder what happened to this poor guy. Did he not put on enough body fat, and died during hibernation?
Now the females are either gestating or lactating. Females stock their 'natal burrows', where their babies are, with lots and lots of dried grass. This female made about 30 trips one morning stocking her burrow.
A female's burrow system consists of multiple tunnels and burrow entrances, including a toilet chamber. As she prepares to give birth, she will dig a new chamber for her babies - the natal burrow. Then she'll block belowground access to the burrow, plugging it from the rest of her system. That means the only way to get in is from above. The entrance is somewhat cryptic compared to other burrow entrances, having no dirt around it. In fact, some moms pull grass over it, or even dirt, to conceal it. They want to hide it from terrestrial predators, such as snakes or weasels, and infanticidal squirrels.
Here is the entrance to a natal burrow.
So if mom digs a new chamber, what does she do with all that dirt? She pulls it all out, scraping the soil under her belly with her front legs, and kicking it behind her with her rear legs. She'll do this all the way through the burrow system, up to 10 meters. And then kick it all out above ground, as seen here. That's a lot of work for a small squirrel! Their long nails, which grow constantly, help them with this.

One of our first litters of the season! Checking out the new, scary world aboveground.